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  • Articles  (1,947)
  • Springer  (1,946)
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  • 1995-1999  (1,947)
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  • Process Engineering, Biotechnology, Nutrition Technology  (1,947)
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  • Articles  (1,947)
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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature biotechnology 14 (1996), S. 1257-1263 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] We report the generation of superactive analogues of human glycoprotein hormones, with potential applications in thyroid and reproductive disorders. Current biological and structural data were used to rationalize mutagenesis. The 11–20 region in the α-subunit with a cluster of lysine ...
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  • 2
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    Adsorption 2 (1996), S. 5-7 
    ISSN: 1572-8757
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
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  • 3
    ISSN: 1572-8757
    Keywords: binary adsorption ; micropores ; nanopores ; molecular simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Monte Carlo and molecular dynamics simulations are performed to study fluid adsorption of a two component fluid in slit pores of nanoscopic dimensions. The slit pores are immersed in a binary fluid bath, which is comprised of spherical molecules having a size ratio of 1.43, at constant temperature and composition. Pore width is varied to determine how the heat capacity and self-diffusion coefficient are linked to the composition and structure of the adsorbed fluid. In pores where the fluid structure is most pronounced, we observe: perfect (or near perfect) exclusion of one component by the other component, a heat capacity that rapidly oscillates and is of greater magnitude than in the fluid bath, and self-diffusion coefficients on the order of 10−8 cm2/s. The behavior of the heat capacity and diffusion coefficients appears to arise from a near solid-like layering of OMCTS that occurs at certain favorable pore widths.
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  • 4
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    Adsorption 2 (1996), S. 9-21 
    ISSN: 1572-8757
    Keywords: nanopores ; zeolites ; Monte Carlo simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A Grand Canonical Monte Carlo simulation method is used to determine the adsorption isotherms, interaction energies, entropies, and density distribution of a Lennard-Jones fluid adsorbed in smooth-walled nanopores of varying size and shape. We specifically include very crowded pores, where packing effects are important. Differences in the isotherms of slit, cylindrical, and spherical nanopores of varying sizes can be explained in terms of the adsorbate-adsorbate interaction energy, the adsorbate-pore interaction energy, and the density profiles, which influence the balance between the former and the latter energy contributions. The expectation from low loading studies that the most energetically favorable adsorbate-pore interactions maximize adsorption is not borne out at intermediate and higher loadings. Instead, the relationships between adsorbed amounts and pore size and shape are found to be strong functions of the depth and steepness of the external potential, the extent to which adsorbate-adsorbate repulsion establishes short range fluid order, and the accessible pore volume. This study has implications for high pore density processes in nanoporous materials, such as zeolite catalysis, separations, and templating in zeolite synthesis.
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  • 5
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    Adsorption 2 (1996), S. 23-32 
    ISSN: 1572-8757
    Keywords: GCMC ; DFT ; adsorption ; MCM-41 ; buckytube ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract MCM-41 and buckytubes are novel porous materials with controllable pore sizes and narrow pore size distributions. Buckytubes are carbon tubes with internal diameters in the range 1–5 urn. The structure of each tube is thought to be similar to one or more graphite sheets rolled up in a helical manner. MCM-41 is one member of a new family of highly uniform mesoporous silicate materials produced by Mobil, whose pore size can be accurately controlled in the range 1.5–10 nm. We present grand canonical Monte Carlo (GCMC) simulations of single fluid and binary mixture adsorption in a model buckytube, and nonlocal density functional theory (DFT) calculations of trace pollutant separation in a range of buckytubes and MCM-41 pores. Three adsorbed fluids are considered; methane, nitrogen and propane. The GCMC studies show that the more strongly adsorbed pure fluid is adsorbed preferentially from an equimolar binary mixture. Ideal adsorbed solution theory (IAST) is shown to give good qualitative agreement with GCMC when predicting binary mixture separations. The DFT results demonstrate the very large increases in trace pollutant separation that can be achieved by tuning the pore size, structure, temperature and pressure of the MCM-41 and buckytube adsorbent systems to their optimal values.
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  • 6
    ISSN: 1572-8757
    Keywords: Monte Carlo simulation ; Gibbs-Duhem integration ; adsorption ; liquid mixtures ; faujasite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Grand canonical Monte Carlo simulations of adsorption of N2 and O2 and their mixtures in a model zeolitic cavity 14 Å in diameter were performed at 77.5 K for pressures ranging from zero up to saturation, where the adsorbed phase is in equilibrium with coexisting vapor and liquid phases. The same intermolecular potential functions were employed for gas-gas interactions in the vapor, liquid, and adsorbed phases. The gas-solid interaction potential includes dispersion-repulsion energy, induced electrostatic energy, and an ion-quadrupole term to model the interaction of the electric field in zeolites like NaX with polar molecules like N2. The simulation of the coexisting vapor and liquid phases reproduces the saturation properties of pure liquid oxygen and nitrogen at 77.5 K. Activity coefficients in the adsorbed phase derived from simulations as a function of cavity filling and composition show negative deviations from Raoult's law, even though the non-idealities in the bulk liquid phase have the opposite sign. The simulation of the surface excess isotherm for adsorption from liquid mixtures exhibits preferential adsorption of N2 and has the commonly-observed quadratic shape skewed toward the more strongly adsorbed component. Micropore condensation is observed for oxygen but not for nitrogen. The condensation of oxygen is similar to a first order phase transition but because of the small number of molecules that can fit into a micropore, coexistence of the two phases is replaced by oscillations between gas- and liquid-like densities.
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  • 7
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    Adsorption 2 (1996), S. 51-58 
    ISSN: 1572-8757
    Keywords: adsorption in pores ; computer simulation ; wetting ; heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Calculations are presented to illustrate the dependence of capillary adsorption upon the interactions present in model pores. The sequence of phase transitions at zero temperature is determined for a Lennard-Jones lattice gas in a pore consisting of 4 × 4 × ∞ sites. The dependence of the specific filling sequence upon the comparative strength of the gas-pore wall and the gas-gas interaction well-depths is determined. Grand canonical Monte Carlo simulations of sorption at finite temperature in the continuum version of the same model pore are also reported. Both the theory and the simulations were performed with variable gas-solid and gas-gas energy well-depths. At a temperature of 90 K, the gas-solid heterogeneity associated with atoms adsorbed in the corners, on the walls and in the interior pore volume gives rise to sequential adsorption similar to that observed in the lattice gas calculation at 0 K. A gradual approach to non-wetting behavior is observed as the gas-solid well-depth decreases. Values of the gas-solid well-depth needed to produce pore filling at saturation (i.e., “pore-wetting”) are discussed.
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  • 8
    ISSN: 1572-8757
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This work describes the adsorption behavior of associating and non-associating chains and their mixtures in pores with activated surfaces. The systems are studied using Gibbs ensemble Monte Carlo molecular simulations. Fluid molecules are modeled as freely jointed Lennard-Jones chains. Associating chains have, additionally, an associating square-well site placed in an end sphere. The pores are modeled as regular slit pores via an integrated Lennard-Jones potential (10-4-3); activation is achieved by placing specific association sites protruding from the surface. Two different solid-fluid interaction parameters are used, one of which corresponds roughly to alkanes on graphite, the other being a much weaker interaction. Adsorption isotherms are presented for several different cases: associating and non-associating chains confined within both neutral and activated walls. Mixtures of associating and non-associating chains are also considered. The effects of pore size, temperature and chain length are quantified. Selectivities obtained are in the range of those seen in adsorption experiments of alkane-alkanol mixtures.
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  • 9
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    Adsorption 2 (1996), S. 69-76 
    ISSN: 1572-8757
    Keywords: ultra thin films ; molecular dynamics ; n-alkanes and phase transitions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In this paper we present the findings of our investigations using molecular dynamics, on molecularly thin films of n-octane confined between topographically smooth solid surfaces. We focus on the effect of increasing solid surface-methylene unit energetic affinity and the effect of increasing pressure (normal load) of the film in inducing liquid-solid phase transitions. We observed an abrupt transition in the structural features of the film at a critical value of the characteristic energy that quantified the affinity between solid surfaces and methylene units. This energetically driven transition was evident from the discontinuous increase of intermolecular order, a precipitous extension of the octane molecules and freezing of molecular migration and rotation. Increasing pressure had a similar effect in inducing a liquid-solid phase transition. The characteristics of the transition showed that it is a mild first order transition from a highly ordered liquid to a poorly organized solid. These findings demonstrate that the solidification of nanoscopically thin films of linear alkanes is a general phenomenon (driven either energetically or by increasing pressure), and does not require the aid of commensurate surface topography.
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  • 10
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    Adsorption 2 (1996), S. 77-87 
    ISSN: 1572-8757
    Keywords: diffusion ; molecular-dynamics simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In this paper, we review our recent theoretical and simulation studies of the surface diffusion of n-alkanes, ranging in size from ethane to hexadecane, physically adsorbed on Pt(111). The model system exhibits many features seen experimentally. Through both animation of the molecular trajectories and determination of the minimum-energy path for nearest-neighbor hopping, we find that the shorter molecules (ethane through octane) all have similar diffusion mechanisms, involving coupled translation and rigid rod-like rotation in the surface plane. In addition, the diffusion energy barriers for these molecules increase nearly linearly with chain length in both the static and dynamic calculations. The diffusion of decane and hexadecane does not adhere to the trends for the shorter molecules and a decrease can be observed in the dynamical diffusion energies for these molecules. The diffusion of the longer molecules involves hops, with unique mechanisms, to second and third neighbor sites. Our static analysis has indicated, for decane, that the diffusion-energy barrier for third-neighbor hopping is lower than that for nearest-neighbor hopping and is in agreement with the trend seen in the dynamical diffusion barriers. Even though there is agreement between theoretical and simulated diffusion energy barriers for many of the molecules, the motion observed in the MD simulations does not agree with the assumptions of the hopping model. A model that can incorporate the influence of long flights would provide a more realistic description of the motion.
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  • 11
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    Adsorption 2 (1996), S. 89-94 
    ISSN: 1572-8757
    Keywords: protein adsorption ; desorption ; memory function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A formalism for the adsorption kinetics of systems where the desorption rate is a function of the residence time of the adsorbed particle is presented. The adsorbed density at time t is expressed simply as a convolution of a memory kernel, Q(t), and the available surface function, φ(t). For completely irreversible adsorption, Q(t) = 1, while for a system which approaches an equilibrium state, Q tends to zero at sufficiently large times. When the desorption rate, k d , is constant, Q(t) = exp(−k d t). Two models for the memory kernel are considered. In the first, the molecule is assumed to interact with the surface via two ligands which bind and debind at rates λ and µ respectively. In the second model, the adsorption is assumed to be partially reversible: molecules transform to a permanently bound state at a rate λ and desorb at a rate µ. In both models, the adsorption kinetics and memory kernels are found analytically. Strategies for determining the memory function from experimental data are discussed.
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  • 12
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    Adsorption 2 (1996), S. 95-101 
    ISSN: 1572-8757
    Keywords: osmosis ; reverse osmosis ; adsorption ; diffusion ; molecular dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Computer simulation studies using the method of molecular dynamics have been carried out to investigate osmosis and reverse osmosis in solutions separated by semi-permeable membranes. The method has been used to study the dynamic approach to equilibrium in such systems from their initial nonequilibrium state. In addition density profiles of both the solute and solvent molecules have been investigated, especially near the walls for adsorption effects. Finally the diffusion coefficients and osmotic pressure have also been measured. Our results show both osmosis and reverse osmosis, as well as a smooth transition between the two when either the solution concentration is changed, or the density (pressure) difference between the solvent and solution compartments is varied. We believe this new method can be used to improve our understanding of these two important phenomena at the molecular level.
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  • 13
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    Adsorption 2 (1996), S. 111-119 
    ISSN: 1572-8757
    Keywords: pressure swing adsorption ; bulk separation ; experiments ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The piston-driven ultra rapid pressure swing adsorption (URPSA) equipment was developed and oxygen enrichment from air was examined as an example. The adsorbent bed is directly connected to the cylinder where a piston moves at high frequency. Thus pressurization and depressurization in the bed are driven by mechanical piston motion, which can achieve far more rapid cycles compared with the conventional pressure swing operation using valves. The cycle time is usually on the order of seconds or sub seconds. Oxygen enrichment from air up to about 60% or higher of oxygen concentration was achieved by small-scale equipment using zeolite 5A with a oxygen production capacity of 100 Nm3-product gas/m3-zeolite/hr, which is about ten times larger than those of commercialized PSAs for this purpose. A simplified numerical model describing the mass transfer taking place in URPSA was developed. The model could simulate fairly well the air separation characteristics in terms of oxygen concentration, oxygen production capacity and oxygen yield. The proposed model helps in the understanding of the basic nature of URPSA and possible applications. This novel PSA is promising as a compact yet high-capacity PSA to be utilized in a wide variety of applications.
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  • 14
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    Adsorption 2 (1996), S. 133-143 
    ISSN: 1572-8757
    Keywords: diffusion ; sorption kinetics ; ZLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The theoretical model and underlying assumptions used in the analysis of ZLC (zero length column) desorption curves are examined in detail. It is shown that the long time analysis generally yields reliable diffusivity values although, if the initial equilibrium condition is not properly established there will be significant error in the apparent equilibrium constant. The short time analysis is much more sensitive to such errors and a modified way of data analysis is suggested to overcome this problem. Varying the initial equilibration time provides an alternative ZLC experiment that can be used to establish the nature of the rate controlling mass transfer resistance. The utility of this approach is illustrated experimentally for the system C3H8-13X zeolite.
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  • 15
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    Adsorption 2 (1996), S. 121-132 
    ISSN: 1572-8757
    Keywords: adsorption heat pump ; experimental kinetic data ; heat and mass transfer ; simulation ; zeolite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Heat and mass transfer during the adsorption of water on zeolite has been studied both theoretically and experimentally. A dynamic simulation model of a zeolite layer has been developed to estimate the predominant transport resistances and calculations were carried out to assist the simultaneous experimental investigations. On one hand, a metallic matrix was added to the compact zeolite layer to improve the heat transfer. On the other hand, pore-forming materials such as melamine or tartaric acid were used. These organic components are removed during drying of the zeolite so that the mass transfer inside the zeolite is significantly enhanced compared to a granulated zeolite bed. The experimental investigations show that the theoretically deduced possibilities of improving the adsorption process can be realized in the manufactured zeolites. The investigations described here are of interest for the development of adsorption heat pumps. Due to the thermodynamic characteristics the adsorption system zeolite-water is a promising working pair for this application. The investigations show that the main shortcoming of these machines, the thermal output, can be increased significantly.
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  • 16
    ISSN: 1572-8757
    Keywords: equilibrium - experimental data ; liquid phase ; measurement ; techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Equilibrium constants (K) and free energies (— ΔG) of adsorption of amino acids, short linear peptides and cyclic dipeptides (2,5-piperazinediones) on silica from neutral aqueous solutions were calculated from the retention values measured by means of high-performance liquid chromatography on a silica gel column. For most amino acids and linear peptides — ΔG values were negative and K 〈 1, thus showing very weak adsorption. 2,5-Piperazinediones exhibited higher adsorbability (for most of them, — ΔG 〉 0 and K 〉 1) as compared to related dipeptides. Influence of the structure of a-substituent on the adsorbability is analyzed. A linear dependence of — ΔG on the number of aliphatic carbon atoms in a sorbate molecule was found for the series of aliphatic bifunctional amino acids, related dipeptides and 2,5-piperazinediones, as well as for the group from glycine to triglycyl glycine.
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  • 17
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    Adsorption 2 (1996), S. 153-156 
    ISSN: 1572-8757
    Keywords: fullerene ; micropore filling ; N2 adsorption ; point defect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Defective state of C60 crystals was controlled by the recrystallization and annealing. The defective structure was examined by the X-ray diffraction and N2 adsorption at 77 K. Recrystallized C60 crystals without annealing showed broad diffraction peaks and the N2 adsorption isotherm had marked low pressure uptake and a hysteresis in the high pressure region, indicating presence of both micropores and mesopores. The average micropore width was 8 Å which is closed to the C60 molecular size, while the average mesopore one was 50 Å. The mesopores disappeared by annealing up to 393 K. On the other hand micropores of 8 Å remained even by heating up to 673 K.
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  • 18
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    Adsorption 2 (1996), S. 181-182 
    ISSN: 1572-8757
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
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  • 19
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    Adsorption 2 (1996), S. 185-186 
    ISSN: 1572-8757
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
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  • 20
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    Adsorption 2 (1996), S. 157-178 
    ISSN: 1572-8757
    Keywords: applications ; bibliography ; processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper provides a review of the 1994 journal literature and complete bibliography concerned with adsorptive separations. The references are taken from the 45 most important chemical engineering journals. This paper provides an update to the literature as provided in previous bibliographic papers (Ray 1990; 1991; 1995). References for membranes and membrane-type separations (for 1992–1993) were the subject of a separate bibliographic paper (Ray 1994), due to the number of papers now published on this topic each year. A review and bibliography paper covering 1994 for membranes has been submitted for publication. Bibliographic papers covering traditional unit operations (Ray 1992; 1993; 1994; 1994) and supercritical extraction (Ray 1994) have been published. A bibliography of the chemical engineering journal literature from 1967–1988 has been published by the author (Ray 1990), and can provide access to a wider range of topics. A complete bibliographic listing of the chemical engineering journal literature from 1989 to 1994 (with subsequent six-monthly updates) is available on a CD-ROM database (Published by Royal Melbourne Institute of Technology) and full details can be obtained from the author.
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  • 21
    ISSN: 1572-8757
    Keywords: diffusion ; kinetic measurements ; NaX zeolite ; water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The thermal frequency response and pulsed field gradient NMR methods are applied in a comparative study of water diffusion in zeolite NaX under non-equilibrium and equilibrium conditions. The obtained results are found to be in satisfactory agreement with each other, indicating that by applying the thermal frequency response method, complications due to uncontrolled water adsorption at the chamber walls inherent in conventional frequency response measurements may be circumvented.
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  • 22
    ISSN: 1572-8757
    Keywords: mixture adsorption ; cabon dioxide ; methane ; carbon pores ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We have used the grand canonical Monte Carlo method to study the adsorption and selectivity of mixtures of carbon dioxide with methane and nitrogen at high (i.e., ambient) temperatures in model slit pores with graphitic surfaces. Experimental data, including new high pressure measurements for carbon dioxide and methane on a non-porous graphitic standard, were used to test the potential models. The mixture simulations predict that carbon dioxide is preferentially adsorbed in both systems. The results are discussed in terms of competing energetic and entropic effects and the underlying molecular mechanisms.
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  • 23
    ISSN: 1572-8757
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The role of concentration-dependent surface diffusion in the adsorption kinetics of a multicomponent system is investigated in this paper. Ethane, propane and n-butane are selected as the model adsorbates and Ajax activated carbon as the model adsorbent. Adsorption equilibrium isotherm and dynamic parameters extracted from single-component systems are used to predict the ternary adsorption equilibria and kinetics. The effect of concentration-dependent surface diffusion on the adsorption kinetics predictions is studied by comparing the results of two mathematical models with the experimental data. Three diffusion mechanisms, macropore, surface and micropore diffusions are incorporated in both models. The distinction between these two models is the use of the chemical potential gradient as the driving force for the diffusion of the adsorbed species in one model and the concentration gradient in the other. It was found that the model using the chemical potential gradient provides a better prediction of the ternary adsorption kinetics data, suggesting the importance of the concentration dependency of the surface diffusion, which is implicitly reflected in the chemical potential gradient. The kinetic model predictions are also affected by the way how single-component adsorption equilibrium isotherm data are fitted.
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  • 24
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    Adsorption 2 (1996), S. 227-235 
    ISSN: 1572-8757
    Keywords: pillared clays ; heavy metal ions ; adsorption ; cation exchange capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The effect of base treatment on the cation exchange capacity (CEC) of pillared clays and their adsorption isotherms for Cu2+, Cr3+ and Pb2+ have been investigated. Results indicate that although the CEC of pillared clays are only about 15% of that of the parent clays, a large fraction of the native clays CEC may be recovered by treatment with base. The fraction of the CEC recovered depends upon the base strength, its concentration, and the temperature. Contrary to previous suggestions the mechanism of recovery is related to the destruction of pillars which is accompanied by the loss of surface area. It is possible under conditions specified to prepare these base treated pillared clays as a new class of useful, regenerable adsorbent for heavy metal adsorption from aqueous solution.
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  • 25
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    Adsorption 2 (1996), S. 237-243 
    ISSN: 1572-8757
    Keywords: gold adsorption from dilute cyanide liquor ; chelating hollow fibers ; chemical modification of sulfochlorinated polyethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In a resin-in-pulp process for the recovery of gold cyanide from a very dilute solution it is desirable that the resin should exhibit the ability to load gold at the natural pH of the leach liquor and be stripped by an aqueous alkali. The present work describes the results of gold cyanide adsorption by new ion-exchange hollow fibers prepared by the amination of sulfochlorinated polyethylene. The fibers, chopped into suitably sized pieces, showed very fast adsorption and desorption of gold from mixed cyanide solutions.
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  • 26
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    Adsorption 2 (1996), S. 245-255 
    ISSN: 1572-8757
    Keywords: oxide/electrolyte interface ; ion adsorption ; energetic heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract It has been shown that the adsorption of ions at oxide/electrolyte interface should be treated in terms of adsorption on a heterogeneous solid surface. This is because the adsorption runs via formation of complexes with surface oxygen atoms. Because of the small degree of oxide surface organization, different surface oxygens may have different status with respect to electrostatic interactions and the strength of the chemical bonds formed between the surface oxygens and the adsorbed protons or metal ions. We have shown that the equations describing the equilibria of formation of surface complexes can be transformed to Langmuir-like equations for multicomponent adsorption. One can apply, therefore, for these systems theoretical methods used to describe mixed-gas adsorption on heterogeneous solid surfaces.
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  • 27
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    Adsorption 2 (1996), S. 265-277 
    ISSN: 1572-8757
    Keywords: frequency response ; diffusion cell ; kinetics ; diffusion ; heat effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper deals with frequency response (FR) analysis of a closed diffusion cell system with two resonators, that is both the LHS and RHS volumes are modulated. The analysis is made for a homogeneous particle described by a single effective diffusivity as well as a biporous pellet described by macropore and micropore diffusions. It is shown that if the perturbation of the volume of the reservoir #2 is lagged behind that of the reservoir #1 by 3π/2, the pressure response in reservoir #1 is significantly enhanced with larger amplitude as well as phase angle. When the perturbations of the two reservoirs are out of phase, the heat effect is reduced and can become insignificant when the two perturbations are completely out of phase (ψ = π). Under such a condition, the pressure difference between the two reservoirs could be doubled. In the case of biporous pellets, it is shown that the FR behaviours obtained for micropore diffusion control and macropore diffusion control are well distinguished. In the former case, the FR system reduces to a traditional batch adsorber one while in the latter case, the FR behaviour is the same as for a two resonator system with homogeneous particles. This difference can be used for the discrimination of micropore and macropore diffusion processes.
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  • 28
    ISSN: 1572-8757
    Keywords: micropore analysis ; nitrogen adsorption ; activated carbon fiber surface fluorination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Nitrogen adsorption isotherms for fluorinated activated carbon fiber (F-ACF) and fluorinated carbon black (F-CB) were measured at 77 K. Surface structures of F-ACF and F-CB were examined by α s -plot analysis using the adsorption data on the nonporous carbon black (CB) and F-CB. The surface energy of F-ACF was lower than that of ACF. The micropore structure of ACF was preserved even after fluorination, although the limiting adsorption amount and the micropore width decreased with fluorination.
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  • 29
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    Adsorption 2 (1996), S. 287-292 
    ISSN: 1572-8757
    Keywords: silica ; alumina ; composite ; nitrogen sorption ; porosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The effect of modification of porous silica and alumina with a copolymer of styrene and vinylsilane on the porosity of oxides have been investigated by means of low temperature nitrogen sorption. Only small changes of the specific surface area and of the specific pore volume were observed on modification of oxides with non-cross-linked copolymer. The specific surface area significantly increased after the cross-linking of the deposited polymeric layer while the specific pore volume remains almost unaffected. A broad hysteresis loop appears in the nitrogen sorption isotherm for the alumina modified with the cross-linked polymer. The porosity of oxides modified by chemisorption method differed strongly from that observed for composites modified by physisorption of polymer.
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  • 30
    ISSN: 1572-8757
    Keywords: mathematical models ; experimental data ; measurement method ; thermal desorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This work describes a novel method that enables the calculation of a series of adsorption isotherms basically from a single Temperature-Programmed Desorption (TPD) experiment. The basic idea is to saturate an adsorbent packed in a fixed bed at a certain feed concentration and temperature and to subsequently increase its temperature linearly with time, while maintaining a constant feed concentration. We measured TPD response curves for carbon dioxide on activated carbon at different heating rates for various combinations of feed concentration, molar flow rate and particle size. Response curves from an axially dispersed plug flow model were fitted to experimental data by adjustment of the Langmuir parameters. Adsorption isotherms calculated with these fitted parameters are in good agreement with adsorption data obtained by other methods over the full temperature range. The influence of heating rate on intraparticle mass transfer resistance is discussed.
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  • 31
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    Adsorption 2 (1996), S. 323-326 
    ISSN: 1572-8757
    Keywords: pressure swing adsorption ; air separation ; zeolite ; rapid cycle ; heat integration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The capital and energy costs of production of oxygen enriched air by a rapid pressure swing adsorption (RPSA) process can be reduced by decoupling the air drying and the air separation duties of the process. Integration of the oxygen-RPSA process with an enhanced combustion application system allows thermal swing adsorption drying of air feed to the RPSA process. The air separation process then can be run using an ad(de)sorption pressure envelope of 2:1 atmospheres, which significantly reduces the cost and energy of operation of the air compressor.
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  • 32
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    Adsorption 2 (1996), S. 299-309 
    ISSN: 1572-8757
    Keywords: intraparticle convection ; intraparticle diffusion ; pressure swing adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The importance of intraparticle convection during and after the pressurization step of a pressure swing adsorption process is assessed by considering a single, cylindrical, closed-end pore with adsorptive walls exposed to a binary mixture of an adsorbable component and an inert gas. Gas-phase mass transfer is comprised of pore diffusion and convection, and surface diffusion occurs in the adsorbed phase. Concentration, velocity, and flux profiles are obtained inside the pore both during and after pressurization. Solutions are obtained analytically for the limiting cases of no adsorption, no diffusion, and no inert gas. Complete solutions of the material balance equations are obtained by orthogonal collocation. The pressurization rate, the adsorptive capacity of the pore wall, and the gas-phase mole fraction are varied over a wide range to study the relative importance of convection and diffusion under different conditions. Results show that convection makes a large contribution to transport in the pore except when the adsorbable component has a small mole fraction.
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  • 33
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    Adsorption 2 (1996), S. 317-321 
    ISSN: 1572-8757
    Keywords: activated carbon ; characterization of properties ; regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Repeatedly passing current of high intensity (2 A) in the pulsing mode through a granular bed of activated carbon was accompanied by changes of bed resistance. These changes did not diminish when the current stopped but proceeded during 2 to 10 days of exposure. X-ray lattice parameters of the carbon before and after it was subjected to numerous current pulses have been measured. The second sample differed considerably because it was more amorphous. Nitrogen and water adsorption isotherms on these samples have been measured. They showed a reduction of specific surface area (volume of micropores) and probably an increase of the average diameter of mesopores. The observed significant changes of carbon texture and structure are explained by inductive electromechanical interactions between planar layers of carbon atoms in microcrystallites of activated carbon during pulses of passing current.
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  • 34
    ISSN: 1572-8757
    Keywords: heat pipe ; heat pump ; carbon fibre ; ammonia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The key elements of solid sorption machines are the chemical compressors-adsorbers. Two categories of the solid sorption system are analyzed: adsorbents NaX zeolite, carbon fibre “Busofit” with NH3, and complex combinations that undergo chemical reaction and physical adsorption (CaCl2 + carbon fibre “Busofit” with NH3). Two phase ammonia motion inside the adsorbent bed was checked. That accompanied NH3/CaCl2 solution redistribution between the cold and hot surfaces of the sorbent bed, resulting in a rich CaCl2 concentration at the boundaries. Solid sorption heat pump and refrigerator technology utilizing heat pipe heat recovery with a condensing/evaporating refrigerant holds considerable promise for bivariant (space and domestic) applications due to the variable temperature and variable load capabilities of such machines.
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  • 35
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    Adsorption 2 (1996), S. 327-330 
    ISSN: 1572-8757
    Keywords: equilibrium ; multicomponent equilibrium ; theory
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    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
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    Adsorption 2 (1996), S. iii 
    ISSN: 1572-8757
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  • 37
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    Adsorption 2 (1996), S. v 
    ISSN: 1572-8757
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  • 38
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    Adsorption 3 (1996), S. 107-115 
    ISSN: 1572-8757
    Keywords: adsorption ; molecular simulation ; isosteric heat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Experimental measurements of adsorption yield the surface excess. The Gibbs surface excess is the actual or absolute amount of gas contained in the pores less the amount of gas that would be present in the pores in the absence of gas-solid intermolecular forces. Molecular simulation of adsorption yields the absolute amount adsorbed. Comparison of simulated adsorption isotherms and heats of adsorption with experiment requires a conversion from absolute to excess variables. Molecular simulations of adsorption of methane in slit pores at room temperature show large differences between absolute and excess adsorption. The difference between absolute and excess adsorption may be ignored when the pore volume of the adsorbent is negligible compared to the adsorption second virial coefficient (V≪B 1s ).
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  • 39
    ISSN: 1572-8757
    Keywords: methane adsorption ; on-board storage ; mathematical modeling ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The charge of natural gas adsorption storage systems is studied numerically, With emphasis given to the impact on its dynamics of intraparticle diffusional resistances to mass transport. Besides adsorption kinetics and thermal effects, the simulation model takes into account both mass transport inside the adsorbent and hydrodynamics of flow through the packed bed. Numerical results are presented for change with methane of a 50 liter cylindrical reservoir, filled with hypothetical adsorbents with diffusional time constants in the range 10−3 s1 D/R p 2 ≤ ∞. and with the adsorption equilibrium curve of a commercially available activated carbon with a good adsorptive storage capacity. An attempt is made to assemble the charge histories for different values ofD/R p 2 , in a single cure by using a modilied time scale.
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  • 40
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    Adsorption 3 (1996), S. 137-149 
    ISSN: 1572-8757
    Keywords: column dynamics ; liquid adsorption ; multicomponent ; algorithms
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    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract New and efficient numerical algorithms were developed for simulating column dynamics of multicomponent liquid phase adsorption. Simple and realistic models are used for the simulation. Langmuir form of isotherm and linear driving force rate expressions are employed in the model equations. Algorithms were formulated for three different rate control mechanisms, namely, film diffusion control, particle diffusion control and combined film and particle diffusion control. The algorithms derived are explicit with the exception of the requirement of solving a nonlinear equation in one single variable which is the concentration of a reference species. Thus the tedious iterative calculation procedure for solving simultaneous nonlinear equations in a multicomponent fixed bed system is avoided. Example calculations indicated very good numerical accuracy as verified from an independent check by means of an overall mass balance.
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    Adsorption 3 (1996), S. 127-136 
    ISSN: 1572-8757
    Keywords: intraparticle convection ; intraparticle mass transfer ; pressure swing adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The importance of adsorption induced convection in the macropores of a bidisperse adsorbent particle is studied for a step change in mole fraction or total pressure at the surface of the particle. Material balance equations for a binary gas mixture are written for both the macropores and the macropores with allowance for convection in the macropores, which is described by Darcy's law. The coupled set o1' partial differential equations is solved by orthogonal collocation. The enhancement in mass transfer as a result of convection is assessed by comparing the fractional uptake curves obtained with and without allowance for convection. Both equilibrium-based and kinetic-based separation processes are considered. The effect of the presence of convection in determining the controlling diffusional resistance (macropore or micropore) is also examined. Due to inclusion of convection no single non-dimensional group alone can determine the relative importance of macropore and micropore resistances. Results show that convection can significantly affect the performance of an equilibrium-based macropore diffusion controlled process and that the enhancement in mass transfer is more for a particle with a high value of Darcy permeability.
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    Adsorption 3 (1996), S. 165-171 
    ISSN: 1572-8757
    Keywords: mordenite membrane ; deformed pore structure ; adsorption properties ; membrane synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Nitrogen adsorption at 77 K was measured for a self-supporting mordenite membrane synthesized on and detached from, a polytetrafluoroethylene (PTFE) substrate, and for a simultaneously formed powder. The adsorption by the membrane saturated an amount which was about half that found for adsorption by the powder. To examine this difference in adsorption characteristics, both of powder and membrane were measured for adsorption for water, methanol,n-hexane andtert-butyl alcohol. For methanol,n-hexane andtert-butyl alcohol, the powder and membrane both showed the same adsorption behavior as for nitrogen. When water molecules were adsorbed, however, there was no difference in saturated adsorption amount between powder and membrane, suggesting the presence of “deformed pores” in the rectangular crystal layer of the mordenite membrane. The deformed pores are assumed to occur as gaps among crystallites which displaced along theab planes of the rectangular crystals, forming the rectangular crystal layer. The channel bonding sites resulting from such displacement were found to serve as pore walls against adsorbable molecules which have a cross-sectional area greater than that of the water molecule. and so to hinder their entrance into the deformed pores. X-ray diffraction analysis revealed that the rectangular crystals have no periodic, continuous structure along thec-axis; they show a slight distortion of the crystallite shift from the plane perpendicular to thec-axis.
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    Adsorption 3 (1996), S. 151-163 
    ISSN: 1572-8757
    Keywords: pressure swing adsorption ; environmental ; activated carbon ; simulation ; factorial design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A two-level fractional factorial study was performed by computer simulation on the periodic state process performance of a pressure swing adsorption-solvent vapor recovery process (PSA-SVR). The goal was to investigate factor (parameter) interaction effects on the process performance, i.e., interaction effects that cannot be ascertained from the conventional “one-at-a-time” approach. Effects of seven factors, i.e., the purge to feed ratio, pressure level, pressure ratio, heat transfer coefficient, feed concentration, feed volumetric flow rate and bed length to diameter ratio, on the process performance were investigated. The results were judged in terms of the light product purity, heavy product enrichment (and relative enrichment) and recovery, and bed capacity factor. Only the purge to feed ratio, pressure ratio, and feed concentration had significant effects on the benzene vapor enrichment (and relative enrichment); and no two-factor and higher interactions were observed. The light product purity was affected by all seven factors; and the relative importance of the effect of each factor depended on the levels of the other factors, i.e., significant two-factor interaction effects existed. Two-factor interaction effects also existed on the benzene vapor recovery, although the effects of all seven factors and their interactions were relatively small. The bed capacity factor was affected mainly by the purge to feed ratio, the heat transfer coefficient and the feed concentration; two factor and higher order interaction effects were insignificant. Overall, this study demonstrated the utility of fractional factorial design for revealing factor interactions and their effects on the performance of a PSA-SVR process.
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  • 44
    ISSN: 1572-8757
    Keywords: electronic spectra ; adsorption of liquid ; zeolites ; p-nitrotoluene ; high pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The behavior ofp-nitrotoluene adsorbed at zeolite/n-heptane interface has been investigated by the electronic spectroscopy under pressure up to 300 MPa. The uv-vis absorption bands of adsorbedp-nitrotoluene were deconvoluted into ones for the species adsorbed on the cation sites, and one for that on the pore wall of zeolite. The peak of adsorbed species on the cation site red-shifted by 20–80 nm from the position of the same species in the liquid phase, and their magnitudes of shift depended on the strength of electric field generated by the cation in zeolites. The peak intensities of adsorbed species on the cation site were enhanced but these or the pore wall site were reduced with the increase in pressure, suggesting that a part ofp-nitroluene molecules on the pore wall site desorbed and the adsorption on the cation site was enhanced by compression. The pressure dependence of peak intensity indicated that the behavior of this adsorption system was strongly governed by the solvation structure of the adsorbate in the zeolite pore. In particular, it was found that the adsorption of solvent molecules on the cation site strongly affected the volume change of the adsorption system.
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  • 45
    ISSN: 1572-882X
    Keywords: metal chelates ; hydroxyethyl cellulose complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Reactions of hydroxyethyl cellulose (HEC) with Cr III, NiII, CoII, or CuII chlorides in aqueous medium yielded complexes with formulae [M(HEC)Cl m .n H 2O], wherem =1 or 2 and n=2 or 3. HEC acted as a uninegatively charged bidentate ligand in the case of CrIII and NiII, and as a neutral ligand in the case of CoII and CuII complexes. The spectra showed that the binding sites in CrIII and NiII complexes were the ether oxygen between two ethoxyl groups and the oxygen of the hydroxyl group; while in the CoII and CuII complexes the binding sites were the oxygen of ethoxyl groups and the primary alcoholic O atom of glucopyranose rings. These complexes would most likely exhibit octahedral geometry with CrIII, NiII, and CoII, but square planar configuration in the case of the CuII complex. The ligand parameters of the CrIII, NiII, and CoII metal chelates were calculated in different solvents and at different temperatures. The thermal stability of the above complexes was investigated and the overall thermodynamics functions ΔG0, ΔH0, and ΔS0, associated with complex formation, were estimated.
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  • 46
    ISSN: 1572-882X
    Keywords: regio-selectively substituted cellulose hetero-esters ; X-ray fibre diagram ; electron diffraction diagrams ; conformational analysis, packing analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The molecular and crystal structure of cellulose propanoate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propanoyl cellulose) has been determined through combined X-ray fibre diagrams and electron diffraction patterns of single crystal analysis, aided by stereochemical restraints by using a constrained linked-atom least-squares refinement. The unit cell of CPDA is orthorhombic with space group P2 12121 and parameters:a =1.239 nm,b =2.498 nm and c (fibre axis)=1.044 nm. Based on these data, coupled with the observed density of the crystals, there are four chains per unit cell, distributed in two antiparallel pairs of parallel chains, and the independent repeat is the disaccharide unit in each chain. A preliminary CPDA disaccharide unit was derived based on the centre residue of cellotriose undeca-acetate, and this model was refined through a conformational analysis. The best model obtained by combining the stereochemical refinement with the diffraction intensities gave R=0.272 (R″=0.259) for the three-dimensional information from the X-ray fibre diagram and R=0.248 (R″=0.246) for the base plane data resulting from electron diffraction analysis.
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  • 47
    ISSN: 1572-882X
    Keywords: cellulases ; dissolving pulp ; Trichoderma reesei ; cellulose hydrolysis ; alkaline solubility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Hardwood dissolving pulp was treated with purified Trichoderma reesei endoglucanases and cellobiohydrolases. Endoglucanases were more efficient in hydrolysing pulp carbohydrates than were the cellobiohydrolases at the same protein dosage. Endoglucanases also lowered the viscosity and improved the alkaline solubility more dramatically. There was a clear correlation between the alkaline solubility and viscosity, and therefore the solubility could only be improved by lowering the viscosity of the pulp. At the same degree of cellulose degradation, endoglucanase II was found to be most effective in reducing the viscosity and thus improving the solubility. Cellobiohydrolases had a less pronounced effect on the viscosity or solubility.
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  • 48
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    Cellulose 3 (1996), S. 189-202 
    ISSN: 1572-882X
    Keywords: water-fibre interactions ; hornification ; drying ; water retention value ; differential scanning calorimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The state of water in wet pulps was studied over a wide moisture range, reflecting the conditions on the paper machine from the press section to the reel. Two methods were used: water retention value (WRV) and differential scanning calorimetry (DSC). To increase the measuring accuracy, a modification to the WRV procedure was introduced. The results were directly compared by plotting the values over the observed moisture range. Different types of water were defined from DSC data: free water, freezing bound and non-freezing bound water. The water types were plotted in water distribution charts against the solids content. These charts were compared with the WRV data. For all pulps, the three water fractions were found to be interdependent while the free water removal rate decreased. Water removal did not take place as an independent water fraction removal sequence. The presence of fines and pulp recycling were found to influence the amount of freezing bound water, but not non-freezing bound water. The results showed an irreversible decrease in WRV (hornification) for all investigated pulps in the range of 20–75% solids content. This pattern corresponded to the relative amount of free water present. Freezing bound water disappeared at a solids content of over 80–85%. With the absence of free water, no further hornification occurred. It was concluded that the WRV appears to be reduced by a closure of large voids by adhesion of the cellulosic pore walls. The softening effect of water is required to cause ‘wet hornification’ of the structure.
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    Cellulose 3 (1996), S. 21-44 
    ISSN: 1572-882X
    Keywords: paper tear strength ; chemical pulps ; organosolv pulps ; surface analysis ; cellulose structure ; cation content ; fiber surface properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Research has intensified in recent years on organic solvent pulping processes to supplement or replace conventional pulping processes. One of the main problems with organosolv pulps is the inferior tear strength compared to kraft pulps. An investigation of the properties of two acidic (acetic acid organosolv and acid sulfite) and one basic white spruce pulp (kraft) was carried out to determine factors affecting differences in tear strength. Properties evaluated were lignin and sugar content, mineral composition, ESCA oxygen-to-carbon ratios, acid-base characteristics, water wettabilities, degree of polymerization and crystallinity of cellulose, fiber length and coarseness, and physical properties of the various pulps. Differences in tear strength have been attributed to degradation and changes in the cellulose structure, the hemicellulose-lignin matrix in which the degree of polymerization of hemicelluloses plays the most important role in low yield pulps, and finally, the bonding capacity of the fiber surfaces.
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  • 50
    ISSN: 1572-882X
    Keywords: regio-selectively substituted cellulose hetero-esters ; X-ray fibre diagram ; electron diffraction diagrams ; conformational analysis ; packing analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The molecular and crystal structure of cellulose acetate dipropanoate (CADP, 6-O-acetyl-2,3-di O-propanoyl cellulose) has been determined by using a constrained linked-atom least-squares refinement method, combined with X-ray and electron diffractograms and stereochemical refinement. The diffraction analysis indicated that CADP crystallized in a P2 1 monoclinic space group with unit cell parameters:a =1.088 nm,b (unique axis)=1.593 nm,c (fibre axis)=1.509 nm and β =94.1°. The best model derived from combining the stereochemical refinement with the diffraction intensities gave R=0.217 (R″=0.195) for the three-dimensional information from the X-ray fibre diagram and R=0.198 for the base plane data resulting from electron diffraction analysis. In the model, the crystal structure of CADP consisted of a system of right-handed threefold helices packed in an antiparallel fashion, with two molecules passing through the unit cell.
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    Cellulose 3 (1996), S. 183-188 
    ISSN: 1572-882X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
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    Cellulose 3 (1996), S. 281-284 
    ISSN: 1572-882X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
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  • 53
    ISSN: 1572-882X
    Keywords: bacterial cellulose ; Acetobactor xylinum ; cellulose crystals ; CPMAS13C NMR ; FT-IR ; xyloglucan ; carboxymethyl cellulose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Effects of polymeric additives with different degrees of polymerization (DP) or substitution (DS) on the crystallization of celluloses Iα and Iβ have been examined at an early stage of the incubation of Acetobactor xylinum by using newly developed FT-IR spectroscopy. It was found that the mass fraction of cellulose Iα is greatly decreased with increasing concentrations of carboxymethyl cellulose sodium salt (CMC) or xyloglucan (XG) in the incubation medium. Such a decrease in the mass fraction of cellulose Iα, which corresponds to the enhanced crystallization of cellulose Iβ, is more prominent for CMC or XG with lower DPs, but the additives with too low DPs are not so effective probably due to higher solubility and the lower adhesion on the surface of microfibrils. Moreover, the mass fractions of celluloses Iα and Iβ are highly correlated with the crystallite size of microfibrils, indicating that Iα is crystallized in larger-size microfibrils while Iβ is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses Iα and Iβ is discussed in the Acetobactor xylinum system.
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  • 54
    ISSN: 1572-882X
    Keywords: accelerated tests ; aging tests ; cellulose degradation ; durability ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Accelerated aging tests are credible and useful to predict paper permanence only if such tests can be shown to correlate with natural aging. In the first part of this study, a kinetic model was developed based on the accelerated aging results. In this report, we have shown that this kinetic model can indeed predict the natural aging results of lignin-free sheets with a statistical confidence. This is the first quantitative comparison of accelerated aging with natural aging.
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  • 55
    ISSN: 1572-882X
    Keywords: solid-state NMR ; cellulose degradation ; magic-angle spinning ; power transformers ; insulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A series of laboratory-aged transformer insulating papers were investigated using solid-state NMR spectroscopy. Carbon-13 CPMAS, and proton MAS experiments were carried out along with static proton relaxation (T1, and T1ρ) and free induction decay (FID) measurements. Some proton CRAMPS and proton-carbon-13 correlation (WISE) experiments were also undertaken. A change in the proton T1 and FID with ageing was detected. No detectable change was found in the proton T1ρ. Some amorphous cellulose was detected in the carbon-13 spectrum. There was, however, no evidence for a substantial change in the nature of the cellulose with ageing. The carbon-13 spectra from some aged samples showed signals not present in the spectrum from an unaged sample. This was taken to be evidence of chemical degradation. Proton MAS and the WISE exeriment gave some information about the nature of the water in the sample.
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  • 56
    ISSN: 1572-882X
    Keywords: cellulose ; hydroxyethyl cellulose ; methylation analysis ; substituent distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Monomer compositional data of a series of hydroxyethyl celluloses (HECs) with molar substitutions (MS) ranging from 0.2 to 2.4 were used to analyse the substituents in the samples. The data reveal that the reactivity of the pendant hydroxyl groups in the substituents decreases in progressed states of derivatization, and that the reactivity of the 6-O-positions is only large compared to the 2-O-positions in non-derivatized glucosyl residues. These two processes are not taken into account in any of the statistical models for the description of the substituent distribution in HECs, which shows that the assumption that the relative reaction constants of the various hydroxyl groups in HECs remain constant throughout the whole reaction is false. The occurrence of maxima in the mole fractions of the monomers was examined as a function of the MS of the samples by principal component analysis of the monomer compositional data. The results show that in the beginning phase of the derivatization mainly monosubstituted monomers are formed and that chain propagation of these substituents takes place, whereas in the progressed states of conversion mainly di- and trisubstituted moieties are formed. The changes in the reactivity of the various hydroxyl groups during the conversion of cellulose to HECs can be described by a model wherein the interactions of both NaOH and the diluents with the cellulosics are taken into account.
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  • 57
    ISSN: 1572-882X
    Keywords: cellulose dissolution ; dissolution mechanism ; morphology ; electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The influence of different solvents on the morphology of cellulose during the dissolution process was studied. Spruce sulfite pulp, cotton linters and hydrolysed cotton linters were treated for a short time with lithium chloride: N,N-dimethylacetamide (LiCl:DMAc) and an alkaline solution of iron sodium tartrate (EWNN), respectively. The changes occurring at the fibre surfaces and within the cell walls were observed by scanning as well as by transmission electron microscopy. The cellulose fibres show significant differences in the dissolution behaviour when comparing the reaction of the two solvents. Using LiCl:DMAc, the cotton linters fibres become lamellar separated and within the spruce sulfite pulp fibres solvent channels appear in the first step with the fibrils becoming separated. In contrast, EWNN has a swelling effect on the surface of the cellulose fibres. Both solvent systems predominantly affect the ends of the fibres and places where the wall structure has been damaged.
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  • 58
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    Cellulose 3 (1996), S. 165-181 
    ISSN: 1572-882X
    Keywords: mercerization ; Direct Blue 1 ; dyeing ; surface area ; accessibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The accessibility of cotton cellulose was determined after it had been mercerized both in the slack and tension states. Mercerized samples were either dried or retained in the undried state before dyeing to determine their accessibilities by the adsorption of Direct Blue 1. Samples were characterized also by techniques such as moisture adsorption, water retention value (WRV) and X-ray analysis. It appeared that the crystallinity of cotton mercerized under tension was slightly increased during dyeing. Dye adsorption increased in the order nonmercerized 〈tension-mercerized 〈slack-mercerized. Products mercerized and not dried adsorbed more dye than counterparts given the same swelling treatment but dried after mercerization. The presence of dye in a sample mercerized and undried before dyeing did not affect its crystallinity. From both the dye adsorption and WRV data it was concluded that structural collapse of the fibre is greater for the slack-mercerized product than its tension-mercerized counterpart after it is dried. It was also concluded from dye adsorption and water adsorption data that about 34% of the internal surface of cotton and mercerized cotton, available for water adsorption, is inaccessible to Direct Blue 1.
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  • 59
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    Cellulose 3 (1996), S. 243-267 
    ISSN: 1572-882X
    Keywords: aging tests ; cellulose degradation ; durability ; kinetics ; paper properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The validity of accelerated aging tests to predict and rank papers on their permanence has been under question, preventing the development of performance-based standards for permanent paper. We conducted a general kinetic analysis to investigate the aging process of paper. A general kinetic model is proposed to describe the depolymerization of cellulose. Experimentally it was shown that in the case of aging, cellulose degradation follows classic first-order kinetics as a special case of our general kinetic model. The Arrhenius equation was critically re-examined for the case of a multiple reaction system. It was shown analytically that the Arrhenius equation is still applicable when certain conditions are met. This was convincingly supported by experimental results. We also analysed the dependence of the degradation rate on the moisture content and hydrogen ion concentration. By conducting systematic experiments on these two factors, a general and quantitative relationship was established to explain the contribution of each factor and their interactions. Finally, based on this kinetic analysis, the effects of storage conditions on the life expectancy of paper were estimated.
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  • 60
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    Cellulose 3 (1996), S. 125-125 
    ISSN: 1572-882X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
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  • 61
    ISSN: 1572-882X
    Keywords: cellulose I ; cellulose II ; disordered cellulose ; hydration ; principal component analysis ; ball milling ; NMR-spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by13C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the ‘amorphous region’ between 79 and 86 ppm in the13C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing ‘amorphous’ cellulose mainly as surface layers and induced reversible lattice distortions.
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  • 62
    ISSN: 1572-882X
    Keywords: cellulose ; diffuse reflectance FT-IR spectroscopy ; fluorescence spectroscopy ; ozonation ; photochromism ; UV-visible reflectance spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Samples of ozonated pure cotton cellulose have been subjected to three extended periods of irradiation with monochromatic light at 350 nm, with intervening dark periods. The changes during the treatments were monitored using fluorescence spectroscopy. Photochromic behaviour, comprising a fairly rapid emission intensity decrease during irradiation and a slower recovery of the emission intensity in the dark at ambient temperature, was observed. Starting from the completion of the first irradiation/dark treatment the intervening dark reaction almost completely restored the situation prevailing before irradiation. The photochromism observed for a reference sample of cellulose not pretreated with ozone and for microcrystalline cellulose was similar but differed both in amplitude and in fluorescence recovery during the dark periods. The ozonated sample was also irradiated with the entire spectrum of a medium pressure Hg lamp. This treatment caused a strong increase in the emission intensity and a red-shift of the emission maximum. The changes caused by ozonation and irradiation were also studied by diffuse reflectance FT-IR and UV-visible reflectance spectroscopy.
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  • 63
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    Cellulose 3 (1996), S. 217-228 
    ISSN: 1572-882X
    Keywords: microcrystalline cellulose ; nitric acid ; addition compound ; amorphization ; sorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract For preparation of various modified forms of microcrystalline cellulose, an optional combination is proposed of hydrolytic activity with other properties of nitric acid such as, adduct forming ability (manifested as Knecht compound formation), oxidizing, bleaching and nitrating. The manifestation of a chosen acid function is reached by variation of the reaction conditions: concentration, temperature, time, etc. The sole-reagent continuous procedure involving several operations made in a predetermined sequence allows the use of a more simple technological scheme and saves energy, time and materials. The features of transformation of fibrous and microcrystalline forms of native cellulose into cellulose-II through the Knecht compound are discussed. Purely acidic transformation schemes of native cellulose into microcrystalline cellulose hydrate and amorphous low-nitrate powder cellulose according to the above scheme are considered. Morphological features as well as distinguishing properties — enhanced hydrophilicity, sorption activity and degree of whiteness — of the prepared materials are pointed out. The possibility of obtaining uniformly oxidized forms of powder cellulose according to this scheme and the outlook for the use of nitrogen(IV) oxide as a multifunctional reagent are discussed.
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  • 64
    ISSN: 1572-882X
    Keywords: crack propagation ; simulation ; films ; compacts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A model originally developed to simulate crack propagation in viscoplastic materials, where the micromechanism consists of void growth, has been evaluated for both pigmented films and porous compacts of cellulose derivatives. The program allows both visualization of crack growth and the calculation of crack velocity. The program is easy to use, enabling many simulations to be performed with minimum effort. The agreement with experimental observation both qualitatively and quantitatively is very good.
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  • 65
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    Cellulose 3 (1996), S. 63-75 
    ISSN: 1572-882X
    Keywords: antibodies ; cellulose synthase ; Acetobacter xylinum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An immunochemical method was used to analyse the 83 and 93 Kd polypeptides of cellulose synthase from Acetobacter xylinum.Polyclonal antibodies were raised against the LDS-PAGE-fractionated 83 and 93 Kd polypeptides isolated from A. xylinum.Using these antibodies, the 83 and 93 Kd polypeptides were localized in the different fractions during purification of cellulose synthase, and the ratio of these two polypeptides was determined to be 1∶1. A differential solubilization of the 83 and 93 Kd polypeptides from the cell strongly suggested that the mechanism by which these two polypeptides originate from a single acsAB gene product (Saxena et al.,1994) must be via a post-translational cleavage. The results of trypsin treatment of the membrane fraction used in the purification of cellulose synthase were analysed to determine the fate of these two polypeptides and their relationship to the enzyme activity.
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  • 66
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    Applied microbiology and biotechnology 44 (1996), S. 582-588 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Xanthobacter Py2 grows on propene as sole carbon source, converting propene to propene oxide (epoxypropane) using an alkene-specific monooxygenase, as the first step in catabolism. Four mutants, NZ1–4, with a propene− propene oxide+ phenotype were isolated by 1-methyl-3-nitro-1-nitrosoguanidine mutagenesis or by enrichment with the suicide substrate vinylidene chloride, and were shown to have lost the ability to convert alkenes to epoxides. All four mutants were complemented by a number of clones of Xanthobacter Py2 chromosomal DNA in the broad-host-range cosmid pLAFR5, some of which appeared to be non-overlapping. Representatives of the different clones obtained were transferred into Xanthobacter autotrophicus JW33 and one, pNY2, the most frequently isolated clone, was shown to express an inducible, fully functional propene monooxygenase. Subcloning revealed that all four mutants were complemented by a 2.4-kb EcoRI-PstI fragment situated at one end of the cosmid insert. However, activity in X. autotrophicus JW33 could only be expressed from pNY2, containing the complete insert (25 kb), suggesting a large operon or some form of long-range control. pNY2 failed to express in E. coli. In X. autotrophicus JW33 [pNY2] at least three new polypeptides were evident after induction with propene compared with a control carrying only the cosmid pLAFR5.
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  • 67
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The organization of the genes of the penicillin cluster has been studied in three different mutants of P. chrysogenum impaired in penicillin biosynthesis. The three blocked mutants (derived from the parental strain P. chrysogenum Bb-1) lacked the genes pcbAB, pcbC and penDE of the penicillin biosynthetic pathway and were unable to form isopenicillin N synthase and isopenicillin N acyltransferase. All strains were identified as P. chrysogenum derivatives by fingerprinting analysis with (GTG)n as a probe. The borders of the deleted region were cloned and sequenced, showing the same junction point in the three mutants. The deleted DNA region was found to be identical to that described in P. chrysogenum npe10. The frequent deletion of the pen gene cluster at this point may indicate that this cluster is located in an unstable genetic region, flanked by hot spots of recombination, that is easily lost by mutagen-induced recombination.
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  • 68
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    Applied microbiology and biotechnology 44 (1996), S. 620-623 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A large cassette, 4.6 × 103 bases (4.6 kb) in length, containing an inducible expression system (the yeast CUP1 promoter fused to the Escherichia coli lacZ structural gene) and a bacterial neomycin-resistance gene (neo) has been cloned into the noncoding region of a GAL1-regulated Ty1 retrotransposon. Galactose was used to induce retrotransposition in Saccharomyces cerevisiae, and cells containing integrations were selected by resistance to the aminoglycoside G418. Integrations of neo and CUP1p-lacZ were verified, and β-galactosidase activity was confirmed. Analysis via Southern blots demonstrated integrations at various chromosomal locations, and the number of insertions obtained ranged from one to five after three rounds of induction. Therefore, the packaging limit of Ty1 virus-like particles for RNA is at least 10.3 kb and Ty1 can transpose foreign genes as large as 4.6 kb, demonstrating the practical application of Ty1 for the insertion of large regulated expression cassettes.
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  • 69
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We have sequenced the gene encoding Bacillus stearothermophilus ATCC12016 α-glucosidase (α-d-glucoside glucohydrolase, EC 3.2.1.20) specific for non-reducing terminal α-1,4 bonds of maltosaccharides and α-glucans. The amino acid sequence of the enzyme deduced from the nucleotide sequence of the gene (1665 base pairs) consisted of 555 residues with a molecular mass of 65233. The enzyme showed 40%–57% sequence similarities to α-d-glucohydrolases with very different substrate specificity, such as Bacillus cereus ATCC7064 oligo-1,6-glucosidase, Bacillus thermoglucosidasius KP1006 oligo-1,6-glucosidase, Saccharomyces carlsbergensis CB11 α-glucosidase, Bacillus sp. F5 α-glucosidase, Streptococcus mutans (Ingbritt strain) dextran glucosidase, Bacillus sp. SAM1606 α-glucosidase and Escherichia coli ECL116 trehalose-6-phosphate hydrolase. All these enzymes had sequences equivalent to secondary elements revealed in B. cereus oligo-1,6-glucosidase by X-ray crystallography. We have suggested that the B.stearothermophilus enzyme adopts the same polypeptide folding, i.e. an (α/β)8-barrel in the N-terminal active-site domain, as the B.cereus enzyme and other α-glucohydrolases.
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  • 70
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The influence of two phytogenic surfactants on the elimination of polycyclic aromatic hydrocarbons (PAH) was studied in shaken-batch cultures of three soil bacteria under axenic conditions. At sufficiently high concentrations, quillaya saponin and soybean lecithin solubilized phenanthrene or fluoranthene efficiently. However, complete solubilization of the PAH by lecithin only doubled the maximal rate of elimination of the two PAH compounds by Pseudomonas 0259, strain MKm (Rhizomonas ?) and Mycobacterium EMI 2. By contrast, quillaya saponin did not improve PAH bioavailability, and in strain MKm it caused significant growth lags above 2.5 g/l. Simultaneously with the elimination of the PAH the bacteria utilized the surfactants as substrates for growth. Intermediate formation of PAH metabolites was noted. The results suggest that some phytogenic surfactants might improve PAH bioavailability in rhizospheres.
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  • 71
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    Applied microbiology and biotechnology 44 (1996), S. 676-682 
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A kinetic model of continuous treatment of waste water by Rhodopseudomonas palustris Y6 immobilized on soft fibre in a columnar bioreaction system was established. Good agreement was found between the model prediction and the experimental data from continuous operation [initial chemical oxygen demand (COD) concentration = 29.700 g/l] of the system. The optimum operational conditions for the maximum COD reduction capacity were investigated from the model prediction and the experimental data. The waste water treatment process may significantly increase the waste reduction capacity because a large amount of active biomass for COD reduction is immobilized in the system, resulting in operation stability. The results presented here provide a useful basis for further scaling up and efficient operation of waste water treatment processes.
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  • 72
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    Applied microbiology and biotechnology 44 (1996), S. 553-556 
    ISSN: 1432-0614
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    Notes: Abstract  Solvent-producing cultures of Clostridium beijerinckii NCIMB 8052 can reduce a variety of aldehydes and ketones to the corresponding alcohols, but the enzymes that catalyse these biotransformations have not been identified. The possibility that butanol dehydrogenases were involved was tested by comparing the ability of solvent- and acid-producing pH-auxostat cultures to reduce representative biotransformation substrates. The ability of the cultures to produce solvents was manipulated by controlling the biomass concentration, and this was achieved by varying the glucose concentration in the inflowing medium. The solvent-producing culture could reduce cyclohexanone and benzaldehyde. In contrast, very little reduction of these substrates occurred in the acid-producing culture. This suggested that one or more butanol dehydrogenases did indeed catalyse these biotransformations.
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  • 73
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    Applied microbiology and biotechnology 44 (1996), S. 589-596 
    ISSN: 1432-0614
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    Notes: Abstract Determination of the nucleotide sequence downstream from the Lysobacter lactamgenus pcbC gene encoding isopenicillin N synthase revealed that five open-reading frames (ORF) including the pcbC gene were tightly linked in the same orientation. Each ORF has the remarkable feature of the protein-coding frame in the DNA sequence with a high G + C content. Expression in Escherichia coli and a comparison of the deduced amino acid sequences with published sequences showed that the gene cluster contained a deacetoxycephalosporin C synthetase (DAOCS) gene (cefE), an ORF having homology with the Cephalosporium acremonium DAOCS/deacetylcephalosporin C synthetase gene (cefEF), an isopenicillin N epimerase gene(cefD), and a β-lactamase gene. The gene order was pcbC-cefE-ORF3-cefD-β-lactamase.
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  • 74
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The glucoamylase gene of the yeast Arxula adeninivorans Ls3 has been cloned from a genomic library and sequenced. The gene could be localized on chromosome 2 from A. adeninivorans and comprises 1875 bp. The first 16 N-terminal amino acids represent the signal sequence for entering the endomembrane system. Comparing the amino acid sequence from this glucoamylase with those of other fungal glucoamylases shows that the glucoamylase of strain Ls3 has a homology to the glucoamylases from Rhizopus oryzae (32.6%), Saccharomycopsis fibuligera (23.1%), Aspergillus niger (22.1%), and Saccharomyces diastaticus (15.4%). No homology could be detected to the glucoamylase of Schwanniomyces occidentalis. By using the GAL1 promoter from Saccharomyces cerevisiae within an autonomously replicating plasmid it was possible to express the isolated Arxula glucoamylase gene in Saccharomyces cerevisiae. The transformants secreted 95% of the enzyme into the culture medium. The N termini of glucoamylases synthesized in A. adeninivorans and S. cerevisiae transformants are identical, which means that the signal sequences were cleaved at the same positions during maturation of the proteins. The highest glucoamylase activities were reached in the culture medium of S. cerevisiae transformants after 36 h of fermentation. Northern hybridization showed that the glucoamylase transcripts were formed continuously for up to 70 h. These results reveal that the glucoamylase is expressed and secreted more rapidly in the S. cerevisiae transformants than in A. adeninivorans Ls3.
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  • 75
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Changes in intracellular composition after hyperosmotic shock were studied in the lysine-producing mutant Brevibacterium lactofermentum NRRL B-11470 and the wild-type Corynebacterium glutamicum ATCC 13032. Both strains accumulated betaine, proline, glutamic acid, glutamine and trehalose in response to stress. The accumulated amino acids were synthesized by the cells, while betaine and trehalose were taken up from the medium. The contribution of synthesized osmoregulators was highest in C. glutamicum. In a sucrose-limited continuous culture, the increased outer osmotic pressure was balanced within 15 min for C. glutamicum and somewhat later in B. lactofermentum. The rapid regulation was due to both accumulation of osmoregulators, and shrinkage of cell and cytoplasmic volume. Immediately after shock, glutamine and glutamic acid were the dominating osmolytes. During the adaptation process, glutamine was replaced by the better osmoprotectant proline. In betaine-enriched cultures, betaine accumulation increased at the expense of glutamic acid, glutamine and trehalose. The total intracellular concentration of osmolytes increased linearly with increasing stress for all stress factors.
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  • 76
    ISSN: 1432-0614
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    Notes: Abstract A bacterial strain was isolated from a sample of contaminated heating oil and identified as a strain of Acinetobacter calcoaceticus, named MM5. The bacterial isolate was able to grow on petroleum derivatives and brought about an emulsification of those compounds. A bioemulsifier was extracted from the culture medium of MM5 strain and partially characterized. This compound was able to emulsify petroleum fuels and both aliphatic and aromatic pure hydrocarbons and was stable over a wide range of temperatures. Studies developed by light, scanning electron and transmission electron microscopy showed that, during the growth on petroleum derivatives, the microorganisms were orientated on the surface of drops enclosed in a skin or membranous polymer produced by the bacteria. These droplets may represent the hydrocarbon/water emulsion of the liquid culture. The growth of A. calcoaceticus MM5 on media containing both hydrocarbon and water-soluble substrates as carbon sources also results in the formation of a film, consisting of amorphous and membranous layers. The bacteria were connected to the biofilm and showed intercellular contacts through cell-surface appendages, forming a complex network. The importance of the biofilms for bacterial adhesion to oil droplets and for its nourishment is discussed.
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  • 77
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    Applied microbiology and biotechnology 44 (1996), S. 690-692 
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  • 78
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  The glucoamylase gene of the yeast Arxula adeninivorans Ls3 has been cloned from a genomic library and sequenced. The gene could be localized on chromosome 2 from A. adeninivorans and comprises 1875 bp. The first 16 N-terminal amino acids represent the signal sequence for entering the endomembrane system. Comparing the amino acid sequence from this glucoamylase with those of other fungal glucoamylases shows that the glucoamylase of strain Ls3 has a homology to the glucoamylases from Rhizopus oryzae (32.6%), Saccharomycopsis fibuligera (23.1%), Aspergillus niger (22.1%), and Saccharomyces diastaticus (15.4%). No homology could be detected to the glucoamylase of Schwanniomyces occidentalis. By using the GAL1 promoter from Saccharomyces cerevisiae within an autonomously replicating plasmid it was possible to express the isolated Arxula glucoamylase gene in Saccharomyces cerevisiae. The transformants secreted 95% of the enzyme into the culture medium. The N termini of glucoamylases synthesized in A. adeninivorans and S. cerevisiae transformants are identical, which means that the signal sequences were cleaved at the same positions during maturation of the proteins. The highest glucoamylase activities were reached in the culture medium of S. cerevisiae transformants after 36 h of fermentation. Northern hybridization showed that the glucoamylase transcripts were formed continuously for up to 70 h. These results reveal that the glucoamylase is expressed and secreted more rapidly in the S. cerevisiae transformants than in A. adeninivorans Ls3.
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  • 79
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Changes in intracellular composition after hyperosmotic shock were studied in the lysine-producing mutant Brevibacterium lactofermentum NRRL B-11470 and the wild-type Corynebacterium glutamicum ATCC 13032. Both strains accumulated betaine, proline, glutamic acid, glutamine and trehalose in response to stress. The accumulated amino acids were synthesized by the cells, while betaine and trehalose were taken up from the medium. The contribution of synthesized osmoregulators was highest in C. glutamicum. In a sucrose-limited continuous culture, the increased outer osmotic pressure was balanced within 15 min for C. glutamicum and somewhat later in B. lactofermentum. The rapid regulation was due to both accumulation of osmoregulators, and shrinkage of cell and cytoplasmic volume. Immediately after shock, glutamine and glutamic acid were the dominating osmolytes. During the adaptation process, glutamine was replaced by the better osmoprotectant proline. In betaine-enriched cultures, betaine accumulation increased at the expense of glutamic acid, glutamine and trehalose. The total intracellular concentration of osmolytes increased linearly with increasing stress for all stress factors.
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  • 80
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    Applied microbiology and biotechnology 44 (1996), S. 676-682 
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  A kinetic model of continuous treatment of waste water by Rhodopseudomonas palustris Y6 immobilized on soft fibre in a columnar bioreaction system was established. Good agreement was found between the model prediction and the experimental data from continuous operation [initial chemical oxygen demand (COD) concentration=29.700 g/l] of the system. The optimum operational conditions for the maximum COD reduction capacity were investigated from the model prediction and the experimental data. The waste water treatment process may significantly increase the waste reduction capacity because a large amount of active biomass for COD reduction is immobilized in the system, resulting in operation stability. The results presented here provide a useful basis for further scaling up and efficient operation of waste water treatment processes.
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  • 81
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    Applied microbiology and biotechnology 44 (1996), S. 576-581 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A bacterium, Azotobacter chroococcum 4A1M, isolated from a soil sample, produced an alginate-decomposing enzyme in the culture broth. The enzyme was purified to an electrophoretically homogeneous state. The purified enzyme showed maximum activity at pH 6.0 and 60°C;it was stable up to 60°C at pH 6.0 and activated by Ca2+ and inhibited strongly by Hg2+. The molecular mass of the enzyme was estimated to be 23 kDa by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and 24 kDa by gel filtration. Therefore, the enzyme was considered to be monomeric. The NH2-terminal amino acid sequence was determined to be H2N-Ala-Ser-Ile-Ala-Ile-Thr-Asn-Pro-Gly-Phe. The enzyme reacted only on the polymannuronate block of alginic acid, and two main reaction products were obtained when short-chain polymannuronate was used as a substrate. The degrees of polymerization of the two products were three and two respectively.
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  • 82
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    Applied microbiology and biotechnology 44 (1996), S. 731-735 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  The microbial oxidation of ebastine to carebastine was investigated. Among the 15 micro-organisms examined, only the Cunninghamella strains showed the desired biotransformation. Cunninghamella blakesleeana oxidised the substrate within 7 days, via the intermediates alcohol and aldehyde, mainly to carebastine, the corresponding carboxylic acid. Optimisation of the culture conditions increased the yield from initially 10% up to a reproducible 40%. For the synthesis of carebastine a substrate concentration of 200 mg/l, a starting pH of 5.0 and the addition of 1% poly(vinyl alcohol) is favourable. The results achieved in experiments with shaking flasks are transferable to the fermentation scale and yielded 270 mg carebastine in a 3-l fermentation of 600 mg ebastine. The progress of the reaction was detected by TLC and HPLC, the products were identified by mass spectrometry and NMR.
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  • 83
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  A bacterial strain was isolated from a sample of contaminated heating oil and identified as a strain of Acinetobacter calcoaceticus, named MM5. The bacterial isolate was able to grow on petroleum derivatives and brought about an emulsification of those compounds. A bioemulsifier was extracted from the culture medium of MM5 strain and partially characterized. This compound was able to emulsify petroleum fuels and both aliphatic and aromatic pure hydrocarbons and was stable over a wide range of temperatures. Studies developed by light, scanning electron and transmission electron microscopy showed that, during the growth on petroleum derivatives, the microorganisms were orientated on the surface of drops enclosed in a skin or membranous polymer produced by the bacteria. These droplets may represent the hydrocarbon/water emulsion of the liquid culture. The growth of A. calcoaceticus MM5 on media containing both hydrocarbon and water-soluble substrates as carbon sources also results in the formation of a film, consisting of amorphous and membranous layers. The bacteria were connected to the biofilm and showed intercellular contacts through cell-surface appendages, forming a complex network. The importance of the biofilms for bacterial adhesion to oil droplets and for its nourishment is discussed.
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  • 84
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    Applied microbiology and biotechnology 44 (1996), S. 553-556 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Solvent-producing cultures of Clostridium beijerinckii NCIMB 8052 can reduce a variety of aldehydes and ketones to the corresponding alcohols, but the enzymes that catalyse these biotransformations have not been identified. The possibility that butanol dehydrogenases were involved was tested by comparing the ability of solvent- and acid-producing pH-auxostat cultures to reduce representative biotransformation substrates. The ability of the cultures to produce solvents was manipulated by controlling the biomass concentration, and this was achieved by varying the glucose concentration in the inflowing medium. The solvent-producing culture could reduce cyclohexanone and benzaldehyde. In contrast, very little reduction of these substrates occured in the acid-producing culture. This suggested that one or more butanol dehydrogenases did indeed catalyse these biotransformations.
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  • 85
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    Applied microbiology and biotechnology 44 (1996), S. 557-562 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Partial hydrolysis of triacylglycerols of high-erucic-acid seed oils from white mustard (Sinapis alba), oriental mustard (Brassica juncea) and honesty (Lunaria annua), catalysed by lipases from Candida cylindracea and Geotrichum candidum, leads to enrichment of erucic acid and other very-long-chain mono-unsaturated fatty acids (VLCMFA) in the acylglycerols (mono-, di- and triacylglycerol) while the C18 fatty acids (oleic, linoleic and linolenic) are enriched in the fatty acid fraction. Partial hydrolysis of the high-erucic-acid triacylglycerols, catalysed by lipases from porcine pancreas, Chromobacterium viscosum, Rhizopus arrhizus and Rhizomucor miehei yields fatty acids with substantially higher levels of VLCMFA, as compared to the starting material, while the C18 fatty acids are enriched in the acylglycerol fraction. Lipases from Penicillium sp. and Candida antarctica are ineffective for the fractionation of either group of fatty acids. Transesterification of the high-erucic-acid triacylglycerols with ethyl, propyl or butyl acetate or with n-butanol, catalysed by the lipase from R. miehei, leads to enrichment of VLCMFA in the alkyl (ethyl, propyl or butyl) esters, whereas the C18 fatty acids are enriched in the acetylacylglycerols and acylglycerols.
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  • 86
    ISSN: 1432-0614
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    Notes: Abstract Physostigmine is a plant alkaloid of great interest as a therapeutic candidate for the treatment of Alzheimer's disease. Fortunately, this compound is also produced by Streptomyces griseofuscus NRRL 5324 during submerged cultivation. A fermentation process that used chemically defined medium was therefore developed for its production. By means of statistical experimentation, the physostigmine titer was quickly increased from 20 mg/l to 520 mg/l with a culture growth of 19 gl dry cell weight on the shake-flask scale. Further medium optimization resulted in a yield of 790 mg/l in a 23-l bioreactor using a batch process. A titer of 880 mg/l was attained during scale-up in a 800-l fermentor by employing a nutrient-feeding strategy. This production represents a 44-fold increase over the yield from the initial process in shake-flasks. The defined-medium fermentation broth was very amenable to downstream processing.
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  • 87
    ISSN: 1432-0614
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    Notes: Abstract  Manganese peroxidases were overproduced by Phanerochaete chrysosporium I-1512 immobilized on nylon net in a bubble-column reactor. This study investigates a new design of bioreactor, a compromise between a pneumatic reactor and an immobilized biofilm reactor. The carrier, a sheet of nylon net, was maintained by a cylindrical stainless-steel frame installed vertically. It was characterized by its hydrophilic nature, its surface morphology and its surface roughness. P. chrysosporium adhesion was highly efficient; mycelial hyphae invaded the tridimensional structure and strengthened the bonding to the network, as shown by electron scanning microscopy. High levels of Mn peroxidases were produced by strain I-1512 under conditions of glycerol and nitrogen sufficiency when the medium was supplemented with phospholipid and veratryl alcohol. Yields of 3600 U/l Mn peroxidase were produced after 95 h of incubation, indicating significant productivity for industrial purposes (900 U day-1 l-1).
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  • 88
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    Applied microbiology and biotechnology 44 (1996), S. 724-730 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Overproduction of proteinase A by recombinant Saccharomyces cerevisiae was investigated by cultivations in a cell-recycling bioreactor. Membrane filtration was used to separate cells from the broth. Recycling ratios and dilution rates were varied and the effect on enzyme production was studied both experimentally and by computer simulations. Experiments and simulations showed that cell mass and product concentration were enhanced by high ratios of recycling. Additional simulations showed that the proteinase A concentration decreased drastically at high dilution rates and the optimal volumetric productivities were at high dilution rates just below washout and at high ratios of recycling. Cell-recycling fermentation gave much higher volumetric productivities and stable product concentrations in contrast to simple continuous fermentation.
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  • 89
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Alginate polymer was evaluated as a carrier for seed inoculation with a genetically modified strain Pseudomonas fluorescens F113LacZY, which protects sugar-beet against Pythium-mediated damping-off. F113LacZY survived in alginate beads at 5 log10 CFU/ bead or higher counts for 8 weeks of storage, regardless of the conditions of incubation. In plant inoculation experiments, colonisation of the growing area of the root by F113LacZY, derived from alginate beads placed in the soil next to the seed or from an alginate coating around the seeds, was improved compared with application of just free cells of the strain. F113LacZY trapped in alginate beads was an effective producer of antifungal phloroglucinols as indicated by direct HPLC quantification of phloroglucinols and in vitro inhibition of both the indicator bacterium Bacillus subtilis A1 and the pathogenic fungus Pythium ultimum. Alginate polymer represents a promising carrier for the delivery of biocontrol inoculants for root colonisation and production of antifungal metabolites.
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  • 90
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Yeasts were isolated from exudates of algarrobo trees from nine sites in northwest Argentina, three in the Chaco region, from pods of algarrobo and acacia, collected in the Quebrada de Cafayate, and from rot pockets in decaying columnar cacti at Cachi (Parc Nacional des Cardons), and at Las Ruinas de Quilmes. Most of the yeasts isolated from exudates of algarrobo were identified asBullera variabilis, Candida famata, Cryptococcus albidus and otherCryptococcus species,Debaryomyces hansenii, Pichia angusta (Hansenula polymorpha),Pichia ciferrii, Pichia farinosa andTorulaspora delbrueckii. OtherCandida, Kluyveromyces andPichia species were found. Most species were osmotolerant. The high sugar content of the exudates influenced the nature of the yeast species present. The pods containedCryptococcus spp.,Candida famata andCandida ciferrii spp. Half the species isolated from rotting cactus wereCryptococcus species.Pichia membranaefaciens andTorulaspora delbrueckii were also isolated. Of 553 cultures investigated, 49 utilized methanol.
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  • 91
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    Applied microbiology and biotechnology 44 (1996), S. 753-758 
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The streptavidin gene fromStreptomyces avidinii was expressed inE. coli as a non-fusion protein and as a glutathioneS-transferase fusion protein. The streptavidin protein accumulated primarily in the inclusion bodies and did not alter cell growth. In contrast, the glutathione-S-transferase-streptavidin fusion protein was soluble. Nondenaturing polyacrylamide gel electrophoresis indicated that the chimeric glutathione-S-transferase-streptavidin protein was present mostly as a monomer, with some detectable polymeric forms. Cells grown in the presence of [3H]-biotin had label specifically associated with the expressed glutathione-S-transferase-streptavidin fusion protein, indicating this protein bound biotin in vivo. The mojority of the radiolabeled biotin was associated with polymetric forms of the gluthione-S-transferase-streptavin protein. The growth rates of biotin auxotrophs ofE. coli growing in biotin-deficient media were substantially decreased by the expression of the glutathione-S-transferase-streptavidin gene. The decreased growth rate correlated with a decrease in acetyl-CoA carboxylase activity.
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  • 92
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Lactobacillus helveticus CNRZ32 possesses and Xaa-prolyldipeptidyl aminopeptidase (PepX), which releases amino-terminal dipeptides from peptides containing proline residues in the penultimate position. The PepX gene, designatedpepX, fromLb. helveticus CNRZ32 was sequenced. Analysis of the sequence identified a putative 2379-bppepX open-reading frame, which encodes a polypeptide of 793 amino acid residues with a deduced molecular mass of 88 111 Da, The gene shows significant sequence identity with sequencedpepX genes from lactic acid bacteria. The product of the gene contains a motif that is almost identical with the active-site motif of the serine-dependent PepX from lactococci. The introduction ofpepX intoLactococcus lactis LM0230 on either pGK12 (a low-copy-number plasmid vector) did not result in a significant increase in PepX activity, while the introduction ofpepX into CNRZ32 on pGK12 resulted in a four-fold increase in PepX activity. Southern hybridization experiments revealed that thepepX gene from CNRZ32 is well conserved in lactobacilli, pediococci and streptococci. The physiological role of PepX during growth in lactobacillus MRS (a rich medium containing protein hydrolysates along with other ingredients) and milk was examined by comparing growth of CNRZ32 and a CNRZ32 PepX-negative derivative in MRS. However, the CRNZ32 PepX-negative derivative grew in milk at a reduced specific growth rate when compared to wild-type CNRZ32. Introduction of the cloned PepX determinant into the CNRZ32 PepX-negative derivative resulted in a construct with a specific growth rate similar to that of wild-type CNRZ32.
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  • 93
    ISSN: 1432-0614
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    Notes: Abstract Two composting systems were compared on a laboratory scale as a bioredediation technology for degradation or immobilization of 2,4,6-trinitrotoluene (TNT) in contaminated soils. The first compost was aerated from the beginning whereas the second compost was only aerated after an anaerobic prephase of 65 days. In the first compost system the TNT concentration declined rapidly by 92% but, at the end, TNT could be partially recovered. During the anaerobic prephase of the second compost system, TNT was almost completely converted to aminodinitrotoluenes, which during the subsequent aeration almost entirely disappeared. In addition, the second compost generated less toxic material than the first one as confirmed by inhibition of bioluminescence ofVibrio fischeri. These data show that microbiological TNT-degradation systems can be successfully designed which are prerequisite for an efficient bioremediation of contaminated soils.
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  • 94
    ISSN: 1432-0614
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    Notes: Abstract Anaerobic granules developed for the treatment of pentachlorophenol (PCP) completely minearilized14C-labeled PCP to14CH4 and14CO2. Release of chloride ions from PCP was performed by live cells in the granules under anaerobic conditions. No chloride ions were released under aerobic conditions or by autoclaved cells. Addition of sulfate enhanced the initial chloride release rate and accelerated the process of mineralization of14C-labeled PCP. Addition of molybdate (10 mM) inhibited the chloride release rate and severely inhibited PCP mineralization. This suggests involvement of sulfate-reducing bacteria in PCP dechlorination and mineralization. Addition of 2-bromoethane sulfonate slightly decreased the chloride release rate and completely stopped production of14CH4 and14CO2 from [14C]PCP. 2,4,6-trichlorophenol was observed as an intermediate during PCP dechlorination. On the basis of experimental results, dechlorination of 2,4,6-trichlorophanol by the granules was conducted through 2,4-dichlorophenol, 4-chlorophenol or 2-chlorophenol to phenol at pH 7.0–7.2.
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  • 95
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    Applied microbiology and biotechnology 44 (1996), S. 724-730 
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Overproduction of proteinase A by recombinantSaccharomyces cerevisiae was investigated by cultivations in a cell-recycling bioreactor. Memebrane filtration was used to separate cells from the broth. Recycling ratios and dilution rates were varied and the effect on enzyme production was studied both experimentally and by computer simulations. Experiments and simulations showed that cell mass and product concentration were enhanced by high ratios of recycling. Additional simulations showed that the proteinase A concentration decreased drastically at high dilution rates and the optimal volumetric productivities were at high dilution rates just below washout and at high ratios of recycling. Cell-recycling fermentation gave much higher volumetric productivities and stable product concentrations in contrast to simple continuous fermentation.
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  • 96
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Alginate polymer was evaluated as a carrier for seed inoculation with a genetically modified strainPseudomonas fluorescens F113LacZY, which protects sugar-beet againstPythium-mediated damping-off. F113LacZY survived in alginate beads at 5 log10 CFU/ bead or higher counts for 8 weeks of storage, regardless of the conditions of incubation. In plant inoculation experiments, colonisation of the growing area of the root by F113LacZY, derived from alginate beads placed in the soil next to the seed or from an alginate coating around the seeds, was improved compared with application of just free cells of the strain. F113LacZY trapped in alginate beads was an effective producer of antifungal phloroglucinols as indicated by direct HPLC quantification of phloroglucinols and in vitro inhibition of both the indicator bacteriumBacillus subtilis A1 and the pathogenic fungusPythium ultimum. Alginate polymer represents a promising carrier for the delivery of biocontrol inoculants for root colonisation and production of antifungal metabolites.
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  • 97
    ISSN: 1432-0614
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We have found that the upstream region of the isocitrate lyase gene (UPR-ICL) from then-alkane-utilizing yeastCandida tropicalis was functional inSaccharomyces cerevisiae as a novel promoter with non-fermentable carbon sources, such as oleic acid, acetate, ethanol, and glycerol/lactate. The expression of two foreign genes coding for β-galactosidase fromEscherichia coli (LacZ) and glutamate decarboxylase from rat brain was carried out under the control of UPR-ICL. Expression ofLacZ was repressed by glucose and enhanced over 300-fold by acetate. When an expression vector pW13 containing multicloning sites between UPR-ICL and the transcriptional terminator of the isocitrate lyase gene (TERM-ICL) was used, the smaller isoform of glutamate decarboxylase (GAD65) was highly produced in a soluble and active form. These results demonstrate that the novel expression system using UPR-ICL and TERM-ICL fromC. tropicalis is useful for the production of heterologous proteins inS. cerevisiae.
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  • 98
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    Applied microbiology and biotechnology 44 (1996), S. 778-784 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Previous research indicated that the production of peroxidases inBjerkandera sp. strain BOS55 increased under N-sufficient conditions. In this study different organic N sources (amino acids, peptides, proteins) were tested as N supplements. Most N sources significantly enhanced the titres of peroxidases, which increased in parallel with growth. While peroxidase production byBjerkandera sp. strain BOS55 was not repressed by the addition of sufficient or excess nitrogen, the occurrence of ligninolytic activity was a secondary metabolic event triggered by the cessation of growth. Among the factors studied (O2, macronutrients, micronutrients, and vitamins), only those supplements with additional carbon or carbon and nitrogen increased the growth, indicating that the secondary metabolism was triggered by carbon limitation.
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  • 99
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    Applied microbiology and biotechnology 45 (1996), S. 158-161 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Fourteen strains of yeast from genera Kluyveromyces, Candida, Debaryomyces and Schizosaccharomyces were investigated for inulinase production. In the first stage, the microtitre reader system SLT was used for the determination of enzyme activity and the evaluation of cellular growth. Different culture conditions were tested and four strains of Kluyveromyces were selected on the basis of enzyme activity and growth capacity at low pH and high temperature: K. marxianus CBS 6397, DSM 70792, ATCC 36907 and IZ 619. These strains were tested in greater volume using pH 4.0, 45°C and inulin (10 g/l) as selection conditions. On the basis of results obtained, the strain K. marxianus ATCC 36907 was selected for inulinase production. Enzyme stability at low pH (4.0) as well as high temperature (50°C) for 10, 30 and 60 min was also evaluated, but no significant difference in enzyme activity was observed. It could be demonstrated that the microtitre reader system is an excellent method for the screening of microorganisms.
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  • 100
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    Applied microbiology and biotechnology 45 (1996), S. 162-168 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  A glycolipid-producing bacterium, Pseudomonas aeruginosa GL1, was isolated from the soil contaminated with polycyclic aromatic hydrocarbons (PAH) from a manufactured gas plant. The glycolipid produced was characterized in detail by chromatographic procedures as a mixture of four rhamnolipids, consisting of different associations of rhamnose and hydroxy fatty acids: the main component was monorhamnosyl di-3-hydroxydecanoic acid. The rhamnolipid composition presented marked analogies with a defined part of P. aeruginosa outer membrane lipopolysaccharides (lipopolysaccharide band A). Rhamnolipid production was stimulated under conditions of nitrogen limitation. Glycerol yielded higher productions than did hydrophobic carbon sources. Cell hydrophobicity decreased during growth on glycerol and on n-hexadecane whereas glycolipid production increased. P. aeruginosa GL1 was found to be unable to grow on a variety of 2, 3 and 4 cycle PAH. However, it was shown to persist after at least 12 subcultures in a bacterial population growing on a mixture of pure PAH, suggesting a physiological role for rhamnolipid as a means to enhance PAH availability in a mutualistic PAH-degrading bacterial community.
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