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  • Organic Chemistry  (824)
  • Chemical Engineering  (418)
  • 1995-1999  (1,242)
  • 1980-1984
  • 1970-1974
  • 1997  (1,242)
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  • 1995-1999  (1,242)
  • 1980-1984
  • 1970-1974
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 16 (1997), S. 231-236 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A numerical simulation of the convection process in a thermally unstable solid storage container has been carried out. The obtained results show that natural convection shifts the thermal ignition to higher induction times. Beyond a critical Rayleigh number, natural convection can prevent the system against thermal ignition. Temperature and velocity fields are calculated. The influence of the dependence of Biot numbers on temperature and the radius/height ratios on the induction times for thermal ignition has been also examined.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 339 (1997), S. 758-762 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 339 (1997), S. 534-540 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two pyruvated galactosyl donors, 2,3-di-O-benzoyl-4,6-O-[1-(R)-methoxycarbonyl(ethylidene)]-α-D-galactopyranosyl chloride (6) and trichloroacetimidate 13, were coupled to position 3 of suitably protected mono and disaccharide benzyl glucoside acceptors. For both donors, an unusual high content of the α-(1 → 3)-linked products was obtained. The corresponding β-(1 → 3)-linked di- and trisaccharides are related to exopolysaccharides of Rhizobium leguminosarum.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-, 13C-, and 17O-NMR spectra for the 2-substituted enaminones MeC(O)C(Me)=CHNH(t-Bu) (1), EtC(O)C(Me)=CHNH(t-Bu) (2), PhC(O)C(Me)=CHNH(t-Bu) (3), and MeC(O)C(Me)=CHNH(t-Bu) (4) are reported. These data show that 3 exists mainly in the (E)-form, 4 in (Z)-form, and 1 and 2 as mixtures of both forms. Polar solvents favour the (E)-form. The (Z)- and (E)-forms exist in the 1,2-syn,3,N-anti and 1,2-anti,1,N-anti conformations A and B, respectively. The structures of the (E)- and (Z)-form are confirmed by X-ray crystal-structure determinations of 3 and 4. The shielding of the carbonyl O-atom in the 17O-NMR spectrum by intramolecular H-bonding (ΔλHB) ranging from -28 to -41 ppm, depends on the substituents at C(l) and C(2). Crystals of 3 at 90 K are monoclinic. with a = 9.618(2) Å, b = 15.792(3) Å, c = 16.705(3) Å, and β = 94.44(3)°, and the space group is P21/c with Z = 8 (refinement to R = 0.0701 on 3387 independent reflections). Crystals of 4 at 101 K are monoclinic, with a = 16.625(8) Å, b = 8.637(6) Å, c = 11.024(7) Å, and β = 101.60(5)°, and the space group is Cc with Z = 4 (refinement to R = 0.0595 on 2106 independent reflections).
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 475-485 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Strong intraparticle diffusion resistance was observed and the apparent effectiveness factors were measured for the hydrogenation of 3-hydroxypropanal (HPA) to 1,3-propanediol (PD) over Ni/SiO2/Al2O3 catalyst pellets at 45 to 80°C and 2.60 to 5.15 MPa in a stirred reactor with a spinning basket. A mathematical model was proposed to describe the intraparticle diffusion and to estimate the effective diffusion coefficients of HPA, PD and hydrogen under reaction conditions by a maximum likelihood function of the apparent effectiveness factors of HPA and PD. The calculated concentration distributions of HPA, PD and hydrogen in catalyst particles reveal an excess of hydrogen at 80°C and higher temperatures, but an excess of HPA at 45°C. It results in a weak dependence of the consumption formation rate of HPA and PD on the partial pressure of hydrogen at high temperature.
    Additional Material: 9 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2657-2664 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Silica and stannic (tin) oxide powders were synthesized by oxidation of their respective chlorides in single and double (inverse) diffusion flame reactors. The effect of reac-tant gas mixing on the characteristics of these powders (size and morphology) was investigated by altering the position of the fuel (CH4) and oxidant (air or O2) streams in the burner. Reactant gas mixing plays a key role in controlling particle size since it affects the temperature history, residence time, and initial particle concentration in the flame, thus, yielding a simple technique for particle-size control over a wide size range in flame reactors. The different material properties (such as sintering) of silica and stannic oxide result in particles of different size and morphology, although they were made at nearly identical flame conditions. Moreover, the oxidant composition affects significantly the properties of silica particles.
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2960-2969 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The algebraic solution for linear, ideal simulated moving-bed (SMB) chromatography derived previously revealed important new properties of the SMB process. This solution was validated by comparing with experimental data and with the results of numerical solutions of the equilibrium-dispersive and the lumped kinetic model. This earlier solution, however, was limited to the simple case in which the safety factor was assumed to be the same for the flow rates in all four sections. An extension of this solution to the case in which the safety factors differ and allow an independent selection of the four different flow rates (within limits) is derived. This solution accounts well for most practical situations. It permits the discussion of the influence of different flow rates on the performance of an SMB unit, an issue of critical importance for the optimization of the design and operation of these separators.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1265-1277 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A compartmental model is used to study imperfect mixing and its effects on polymer properties. Examples of imperfect feed mixing caused by a rapidly decomposing initiator are shown for styrene polymerization, high-pressure ethylene polymerization, and vinyl acetate/methyl methacrylate solution copolymerization. Continuation analysis indicates mixing can change reactor steady states and stability. A composite approach is proposed to construct full molecular weight distribution (MWD) under imperfect mixing. In linear polymerization imperfect mixing broadens MWD; however, in nonlinear polymerization mixing can cause either broader or narrower MWD. By changing the dominant chaintermination mechanism to chain transfer, the influence of imperfect mixing on the MWD can be reduced. Depending on reactivity ratio and monomer composition, mixing also affects copolymer composition and chain sequence length.
    Additional Material: 18 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2793-2801 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Hexagonally-packed mesoporous Nb-doped silica molecular sieves were hydrothermally synthesized with various siliceous sources and dopant concentration levels. The microstructure of mesoporous materials was characterized by a variety of physico-chemical methods. The pore packing order of the Nb-doped material depended strongly on the synthesis conditions such as aging temperature, pH of reaction mixture, surfactantto-Si ratio, and dopant concentration. Different silica precursors gave rise to different reactivity with the Nb dopants and interactions with the surfactants. The pore size and surface area of the materials can be systematically varied. The chemical environment of the Nb dopants in the silica framework was studied by XPS, EPR, PA-FTIR, UV-Vis, and 29Si MAS NMR. The results indicated that the Nb5+ ions were well dispersed in the framework of the mesoporous silica. The diffuse-reflectance UV-Vis spectrum of the mesoporous Nb-doped silica is red-shifted with respect to pure mesoporous silica. The 29Si MAS NMR spectrum contained a broad component at about -105 ppm, which may have been attributed to the presence of Nb-O-Si bonding in the mesostructure.
    Additional Material: 13 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1871-1876 
    ISSN: 0947-3440
    Keywords: Phenylsulfinyl glycosides ; Nephritogenoside ; Oligosaccharides ; Glycopeptides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new strategy for the construction of the O-glycoside bond in the nephritogenoside unit using the phenylsulfenyl method is reported. The readily accessible phenylsulfinyl glycoside proved to be an excellent glycosyl donor, leading to high yields and good selectivity. The extremely mild conditions utilized in glycosylation reactions allow trityl and other sensitive protecting groups to be used for temporary protection. The fact that phenyl thioglycosides function as glycosyl acceptors during the coupling reaction and can easily be transformed into glycosyl donors by conversion to phenylsulfinyl glycosides, enables complex oligosaccharides to be prepared in a highly convenient manner.
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