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  • Chemical Engineering  (3,294)
  • 1990-1994  (3,294)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 7-7 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 2
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 9-9 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 3
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 8-8 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 4
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 128-138 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper addresses a number of accident case histories in pressurized ethylene systems comprising heaters, driers, purifiers and High Pressure Polyethylene product receivers. Also covered are compression-heating accidents in pipelines and compressors, and decomposition via external fire exposure of piping.Several companies contributed accounts; few of these have been reported in the open literature. The probable event scenarios are discussed with reference to safety information that in many cases postdates the contemporary loss reports. While there may be room for some debate over probable causes, insight can be gained simply by reading the accounts.The objective is to provide real examples of design and operational oversights contributing to preventable losses. As usual in Loss Prevention case histories, an important lesson is that years of uneventful operation often pass before a problem is recognized, and that subsequent investigation often uncovers the potential for other failure routes and possibly worse outcomes.
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  • 5
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 146-152 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The design of high integrity interlock systems involves more than the simple specification of high-quality components. Redundancy of components is often used as a strategy to improve the reliability of an interlock system. This paper uses quantitative reliability engineering methods to explore the relationships of component reliability, time between proof tests, redundancy and common cause failures to overall system performance. The paper demonstrates that addition to redundancy often, but not always, improves the reliability of an interlock system. The paper also demonstrates how common cause failures can greatly reduce the chances of an interlock system performing when needed.
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  • 6
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 159-170 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Quantum's Deer Park Ethylene Plant was built with a philosophy of risk management which was based on loss prevention. To this end, the plant incorporates a number of concepts designed to effect early detection containment and dispersion of hydrocarbon releases. Features include a gas detection grid system, water curtain in the furnace/boiler area with open path IR detector, extensive deluge systems on equipment and in pipe racks, remote television monitoring, large portable monitors (as well as the more standard plant safety systems such as hydrants), fixed monitors, and foam generators.The systems described are monitored by means of a graphic panel and alarm console located in the Central Control Room. This centralized facility enables the operator to monitor and activate the proper subsystems and provide a visual interface between the operator and the physical plant.
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  • 7
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thionyl chlorie is routinely shipped in galvanized drums. The compatibility of this drum for the storage of a mixture of thionyl chloride and ethyl acetate was investigated by thermochemical studies, condensed phase and off gas analysis. The chemical incompatibility of the ternary mixtures (thionyl chloride/ethyl acetate/zinc) resulted in an exothermic runaway reaction with extensive gas evolution, which has not been heretofore described in the literature. Storage in a drum was simulated in a half-liter, high pressure containment vessel. Adiabatic calorimeter data are also presented to illustrate the mass transfer process involved in the induction period and the runaway reaction characteristics. Ethyl acetate is inert with thionyl chloride. However, in the presence of metallic zinc, an equimolar amount of each component are consumed by the reaction to generate ethyl chloride (g), sulfur dioxide (g), acetyl chloride (l) and sulfur (s). It was also found that the rate of gas evolution is highly dependent on the molar ratio of the thionyl chloride or ethyl acetate to metallic zinc in the solution. Based on the semi-batch process experiments, the reaction mechanism is proposed. A potential hazard indication based on the oxygen balance for the reaction mixture is also discussed. Data on similar ternary mixtures are presented.
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  • 8
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 139-145 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper reports results from a U.S. Bureau of Mines study of the flammability of various metals and other elemental dusts dispersed in air. The data are useful for evaluating the explosion hazards in the minerals and metals processing industries. The dusts studied included boron, carbon, magnesium, aluminum, silicon, sulfur, titanium, chromium, iron, nickel, copper, zinc, niobium, molybdenum, tin, hafnium, tantalum, tungsten, and lead. The dusts were chosen to cover a wide range of physical properties - from the more volatile materials such as magnesium, sulfur, and zinc to the highly “refractory” materials such as carbon, niobium, molybdenum, tantalum, and tungsten. These flammability studies were conducted in the Bureau of Mines 20-L explosibility test chamber, using strong pyrotechnic ignitors. The parameters measured included the minimum explosible concentrations, maximum explosion pressures, and maximum rates of pressure rise. All of the elemental dusts ignited and burned as air-dispersed dust clouds except the nickel, copper, molybdenum, and lead. In general, the dusts with the highest explosion pressures and rates of pressure rise were also those with the highest calculated, adiabatic flame temperatures and/or the ones that vaporized most easily, but this was not true in all cases. The effect of particle size on flammability was studied for the aluminum and iron dusts. The minimum explosible concentrations were relatively independent of particle size below 30 μm, but the highest explosion pressures and rates of pressure rise were found at the finest sizes tested.
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  • 9
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    New York, NY [u.a.] : Wiley-Blackwell
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 10
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 171-175 
    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 new means for modeling blast effects of all types of reactants including vapor cloud explosions has been developed and verified against empirical data. Methods such as the TNT-equivalency model are still being widely used to simulate vapor cloud explosions and blast effects. However, many limitations exist in the accuracy of those models. Use of such flawed models could potentially provide for deleterious results from an explosion such as loss of property and/or life as well as the ramifications of liability. This should be of extreme interest to not only the chemical process industry, but also to insurerers who must understand the nature of the risk that is being under written, government safety compliance organizations and the legal profession which must either defend or litigate liability cases resulting from explosions.The computer code, CMBWAT, models the physics of detonations and deflagrations occurring in the reaction zone and the resulting shock wave which attenuates with distance. It computes static and stagnation pressure, velocity and the shock wave impulse delivered to target surfaces within the flow field, all as a function of time, both for the incident and reflected waves. Data resulting from these analyses are used to examine the structural response of the object due to the resulting shock and to determine proper risk mitigation solutions to minimize damage effects. The model can also examine the physics of solid or vapor reactants including nuclear explosions.Systems Integration Corporation has developed this code which was independently verified against actual test data by Sandia National Laboratory. The Nuclear Regulatory Agency is currently revising its REG GUIDE 131 as a result of this work.
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  • 11
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 177-182 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An approach is presented to accurately design emergency relief systems for even the most complex chemical reactions. Two examples illustrate how large differences in relief requirements can result if small, but important, aspects of the calorimetry data are overlooked. Although both simple and rigorous kinetic models may seem to predict calorimetry data reasonably well, these examples demonstrate the importance of well-designed experiments, optimization algorithms, rigorous kinetic modeling, correct physical properties, and dynamic simulations.The first example shows how the inclusion of a subtle equilibrium reaction in the kinetic model will allow venting of an intermediate species, decreasing the reactant available for the highly exothermic irreversible reaction. The second example emphasizes the importance of a rigorous model for the decomposition of a large molecule where bond cleavage can occur between repetitive groups.This example takes advantage of the tempering effect of intermediate decomposition products which are accounted forwith the rigorous model.
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  • 12
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 183-189 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The dust explosibility characteristics of Lycopodium, Cornstarch, Pittsburgh Bituminous Coal and Calcium Sterate were measured in a 1 m3 spherical explosion chamber at ambient pressures, ambient temperatures and at three different turbulence levels. Explosibility parameters measured were the maximum pressure, maximum pressure rate of rise and the initial pressure rate of rise. Propane explosibility and Hybrid explosibility (Cornstarch in the presence of propane) were also measured. For the hybrid system, the lower limits of explosibility and the effect of low propane concentrations on the explosibility of optimum Cornstarch concentrations were investigated. Finally, a relationship between maximum pressure rate of rise and initial pressure rate of rise was sought in order to lay a foundation for explosion suppression and explosion venting engineering methodologies.
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  • 13
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    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 13 (1994), S. 190-201 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The VDI Guideline 3673 “Pressure Release of Dust Explosions” published in June 1979 [1] describes one of the possible constructional protective measures against the effect of dust explosions and provides details on the venting area requirements of vessels and silos. Thanks to the results of extensive explosion trials conducted in the last ten years on the problems addressed above, important gaps in our knowledge have been filled and new findings gained which have made a revision of the above guidline necessary. The contents of the new version are reported and attention drawn to modifications compared with the first version.
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  • 14
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 15
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 16
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1-1 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 17
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    AIChE Journal 40 (1994), S. 2-10 
    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 coating flow of a reactive fluid on an inclined plane is studied. The fluid viscosity steadily increases due to a sustained cross-linking reaction. Using well-known long wave approximations and a simple kinetic relation, we find that the linear stability of a uniform coating is affected not only by the inclination angle but also by the reaction order. In the weakly nonlinear limit, a generalized Kuramoto-Sivashinsky (K-S) equation is derived. Two interesting cases are identified in the limit of creeping flow. One is when surface tension is moderate and a generalized Burger's equation results, and the other is when the surface tension is large and the traditional K-S equation is recovered when the inclination angle is greater than 90°. The solution in this case represents a shock-like traveling wave down the incline and it appears to be unique for reacting coating flows.
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  • 18
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 11-18 
    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 dynamic evolution of the cluster-size distribution (CSD) in the precoalescence stages of nucleation and growth for sizes within and beyond the nucleation barrier layer (NBL) has been obtained. The existence of several universal kinetic laws of nucleation is predicted. In the precoalescence stages of nucleation, the CSD for sizes within and beyond the NBL obeys dynamic scaling relations. In a range of sizes beyond the NBL, the CSD exhibits a universal power law behavior, the exponent of which depends only on the interphase monomer transfer mechanism. Based on the results for the CSD, a general foundation is developed for nucleation kinetic measurements including the determination of the nucleation barrier and the inter-facial monomer transport rate by measuring the CSD. A preliminary comparison with an experimental study confirms the predicted dynamic scaling and the power law behavior of the CSD in the early stages of nucleation and growth.
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  • 19
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    AIChE Journal 40 (1994), S. 29-39 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: To test the ability of different turbulence models to predict the turbulent momentum transport in the viscous sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: -u′v′+ = Aky+3. The results of 2-D computer simulations using four different low Reynolds number k-∊ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k-∊ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the viscous sublayer.
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  • 20
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    AIChE Journal 40 (1994), S. 19-28 
    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 theoretical model for the process of bubble and drop formation in flowing liquids, applicable for both terrestrial and microgravity environments, has been developed by using a force balance. The contact angle variation at the nozzle due to the bubble motion and the added mass coefficient of the bubble moving through a pipe have been theoretically analyzed, considering bubble motions during its expansion and detachment stages. Predictions of bubble size of the model show satisfactory agreement with available experimental results in the case of normal gravity. The effects of the nondimensional variables on bubble and drop size are evaluated in microgravity conditions. In microgravity, the bubble is detached from the nozzle only by the liquid flow drag, and in the region of low liquid velocity the bubble size becomes much larger than that in normal gravity.
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  • 21
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    AIChE Journal 40 (1994), S. 40-49 
    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 dynamic affinity adsorption oflysozyme through stacked flat-sheet cellulose membranes with immobilized cibacron blue 3GA was studied and compared to three affinity-membrane models: diffusion model to explore the importance of axial and radial diffusion; variation model to study the effects of pore-size distribution or thickness variation; and stack model to investigate the effects of stacking flat-sheet membranes. For the diffusion model, when Per 〉 0.1, radial diffusional resistance is significant, but when Pez 〈 25, axial dispersion must be considered. For the variation model, increasing pore-size distribution or nonuniform membrane thickness greatly broadens the breakthrough curve. The stack model shows that the stacking of membranes significantly sharpens the breakthrough curves by averaging out the flow dispersion due to pore-size distribution or thickness variation.
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  • 22
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    AIChE Journal 40 (1994), S. 50-64 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Monitoring and control of batch pulp digesters, which convert wood chips to pulp by Kraft process are discussed. The Kappa number, which represents the extent of delignification, is the key controlled variable, which cannot be measured on-line and must be estimated through secondary liquor measurements. Given a fixed batch time, the final Kappa number should be as close to the target Kappa number as possible, despite errors in the initial state estimates and input disturbances. To fulfill this objective, a state-observer-based model-predictive controller is designed using a detailed nonlinear dynamic model of the digester. The extended Kalman filter (EKF) using on-line measurements of various liquor characteristics is capable of recovering from significant errors in the initial state estimates. In addition, the EKF is shown to be robust to the errors in the covariance matrices and most model parameters, but quite sensitive to some model parameter errors. Coupled with the EKF, a finite-horizon model predictive controller (MFC) based on successive linearization of the nonlinear pulping model, is found to work efficiently for controlling the Kappa number and batch time.
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  • 23
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    AIChE Journal 40 (1994), S. 65-72 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When multicomponent, multistage separation problems are solved on parallel computers by successive linearization methods, the solution of a large sparse linear equation system becomes a computational bottleneck, since other parts of the calculation are more easily parallelized. When the standard problem formulation is used, this system has a block-tridiagonal form. It is shown how this structure can be used in parallelizing the sparse matrix computation. By reformulating the problem so that it has a bordered-block-bidiagonal superstructure, it can be made even more amenable to parallezation. These strategies permit the use of a two-level hierarchy of parallelism that provides substantial improvements in computational performance on parallel machines.
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  • 24
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    AIChE Journal 40 (1994), S. 73-87 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental results using a pulsed tubular reactor are presented. The use of a pulsation source eliminates the reactor fouling and plugging issue that has occurred in previous investigations. Startup data and steady-state profiles are presented. Comparisons in monomer conversion and particle-size distribution for batch, CSTR and tubular reactor are made. The influence of pulsation on the particle-size dis-tribution is discussed. It is shown that high-conversion latex with a narrow particle size distribution can be produced continuously in the pulsed tubular reactor.
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  • 25
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    AIChE Journal 40 (1994), S. 88-96 
    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 dynamic model for emulsion polymerization in a tubular reactor has been developed and compared with experimental data. The model uses an axial dispersion coefficient to fit experimentally measured residence time distributions and to represent axial mixing during reaction. Very general emulsion polymerization kinetics are assumed so that a wide range of monomers and operating conditions can be handled. Orthogonal collocation on finite elements was chosen as the numerical solution technique. Comparisons show good agreement between model and experiments for two different monomers.
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  • 26
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    AIChE Journal 40 (1994), S. 120-130 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Spatiotemporal patterns existing in a one-dimensional fixed-bed reactor with oscillatory or excitable kinetics are analyzed to develop the methodology of motion identification and classification. The reactor model accounts for a local (solid-phase) oscillator and a global (gas-phase) convective interaction. The local oscillator incorporates a fast and diffusing surface temperature and a localized activity as its dynamic variables. Such kinetics admit a traveling pulse solution or homogeneous oscillations in a uniform medium. In a fixed-bed reactor, the local conditions in the bed (the phase plane character) vary along the system. The response of an excitable bed to local perturbations depends on its location (at inlet or outlet) and the nature of the initial steady state ( ignite or extinguished). The main spatiotemporal-sustained patterns in the bed are: almost homogeneous oscillations that appear as parallel bands in the time-space contour map; oscillatory fronts that emerge from the reactor exit, and aperiodic motion that appears as split-bands. Pattern selection is determined by the phase planes spanned by the reactor and the ratio of the two slowest time scales: front residence time and period of oscillations.
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  • 27
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    AIChE Journal 40 (1994), S. 97-111 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Phase transition during an exothermic multiphase reaction was studied experimentally using a single catalytic pellet reactor. Cyclohexene hydrogenation (to cyclohexane) and disproportionation (to benzene and cyclohexane) on Pd/Al2O3 comprised the test reaction system. The steady-state behavior of the pellet exposed on part of its surface by a flowing liquid rivulet containing the liquid reactant (cyclohexene) and the other part by a flowing gas containing the gaseous reactant (hydrogen) was examined. Measurements included the pellet weight (liquid holdup), degree of external wetting, center and surf ace temperature and overall reaction rates. Two regimes observed are: a low-rate regime for all hydrogen gas-phase concentrations in which the partially wetted pellet is filled mostly with liquid and nearly isothermal; a high-rate regime for hydrogen concentrations exceeding a critical value in which the pellet is filled only partially with liquid and the pellet temperature rise is considerable. Benzene formation was observed in this state. The difference in overall cyclohexane formation rates between the two states was as high as a factor of 20 for the same bulk conditions. Over the range where multiple states were observed, the steady state of the pellet depended on whether the pellet was pref tiled with the reactive gas mixture or with liquid cyclohexene. The range over which the high-rate state was sustained was the largest for the most active catalyst and declined as the catalyst slowly deactivated. Data features are interpreted using the theoretical foundations of the half-wetted catalytic slab model (Harold and Watson, 1993).
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  • 28
    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 mechanistic background to the understanding of the hydrodynamics of high-pressure bubble column reactors in both the homogeneous and heterogeneous flow regimes is discussed. An important parameter determining the stability of homogeneous bubbly flow in a bubble column is shown to be the Richardson-Zaki exponent in the bubble swarm velocity relationship Vswarm = v∞(1-∊)n-1. Experimental data for the bubble swarm velocity were obtained in 0.05- and 0.1-m-dia. bubble columns with various gases (helium, air, argon, sulfur hexafluoride) using water as the liquid phase. Bubble swarm velocity data show that with increasing gas density the Richardson-Zaki exponent value decreases; physically this means that increasing gas density reduces interaction between neighboring bubbles and, consequently, reduces chance of propagation of instabilities. This rationalizes the experimental observation that the influence of increased gas density ρG is to delay the transition from homogeneous bubbly flow to churn-turbulent flow: increasing ρG increases the regime transition velocity. A stability analysis rationalizes the observations. The hydrodynamics of bubble columns in the churn-turbulent regime is considered to be analogous to that of a bubbling gas-solid fluidized bed, and the two-phase theory of gas-solid fluid beds is extended to describing bubble columns by identifying the “dilute” phase as the fast-rising large bubbles and the “dense” phase as the liquid phase with entrained small bubbles. A simple coalescence rationalizes experimental large-bubble holdup data.
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  • 29
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thermolysis of coal yields a complex mixture of many extract products whose molecular-weight distribution (MWD) varies with time for continuous-flow, semi-batch experiments. A laboratory flow reactor with a differential fixed bed of coal particles contacted by supercritical tert-butanol was used to provide dynamic MWD data by means of HPLC gel permeation chromatography of the extract. The experimental results, multipeaked, time-dependent MWDs of extract molecules, are interpreted by a novel mathematical model based on continuous-mixture kinetics for thermal cleavage of chemical bonds in the coal network. The parameters for the MWDs of extractable groups in the coal and the rate constants are determined from the experimental data. The effect of temperature on the kinetics of the extraction is explained in terms of one- and two-fragment reactions of the extractable groups in the coal. At lower temperatures (613 and 633 K) single-fragment reactions dominate, but at higher temperatures (653 and 673 K) more bonds in the coal are broken and the two-fragment reactions become significant. Also, the detailed MWDs are related to conventional lumped data for the thermolytic extraction process. The results yield information about the structure of coal, as well as the kinetics and mechanism of supercritical thermolytic reactions.
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    AIChE Journal 40 (1994) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 31
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    AIChE Journal 40 (1994), S. 745-755 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Local heat-transfer measurements are performed using a special heat-transfer probe in gas-liquid and gas-liquid-solid systems with viscous Newtonian liquids as the continuous phase. Effects of viscosity on bubble-liquid and bubble-liquid-solid interactions affecting local heat transfer are studied through heat-transfer experiments with simultaneous flow visualization in a simplified system involving single bubbles or a chain of gas bubbles moving in viscous liquids and liquid-solid systems. Effects of viscosity on bubble wake and local heat transfer are examined with reference to heat transfer in freely-bubbling beds (bubble columns and three-phase fluidized beds). The kinematic viscosity of the fluid greatly influences the nature of flow in the wake which affects local heat transfer in the bed. The local heat transfer decreases with the viscosity due to the rapid decay in the circulation strength of the bubble wake caused by increased viscous dissipation of vorticity. Local heat transfer due to cyclic/periodic injection of bubbles is significantly enhanced due to increased bubble-wake interactions which rapidly accelerate bubbles and increase average bubble rise velocity. Heat transfer in simplified liquid and liquid-solid systems with single- and chain-bubble injections characterizes the local heat-transfer performance of freely-bubbling beds (bubble columns and three-phase fluidized beds). A mechanistic model developed accounts for the heat-transfer behavior in bubble columns and three-phase fluidized beds with viscous liquids.
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  • 32
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    AIChE Journal 40 (1994), S. 756-766 
    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 falling liquid film has become a popular means of transferring heat and mass from a vapor to a binary liquid, especially in gas-fired heat pump systems. Ideally, the required amount of heat and mass transfer can be accomplished by using a simple cylindrical tube; however, increasingly stringent size and weight requirements for the machine prohibit use of the simple cylindrical surface, and other more complex surfaces with higher absorption capacities have been sought. In this article, absorption of a single component and condensation of a binary mixture on an axially fluted tube is considered. The solution to the problem hinges on the energy equation, although the entire energy transfer process is mass-transfer-limited. Significant mass transfer is limited to a thin layer near the liquid-vapor interface. Solutions to the energy equation are obtained for both the conduction- and convection-dominated regimes. In the latter, significant heat transfer occurs within a thin layer near the liquid-vapor interface which contains the mass transfer layer; this “boundary layer” structure does not appear to have been recognized in previous work in this area. Using the present results, the capacity of a given tube may be predicted as a function of governing geometrical and physical parameters. The principal objective of this work is to develop the theoretical tools from which computations may be carried out during a design process. The theoretical results may be applied to mixtures typical of application in the absorption heat pump industry.
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    AIChE Journal 40 (1994), S. 777-785 
    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 desorption profiles of various organics from soil and activated carbon using dense liquid and supercritical carbon dioxide were modeled. The model accounts for effective diffusion of the organics in the solid pores, axial dispersion in the fluid phase, and external mass transfer to the fluid phase from the particle surface. This model, involving partial differential equations, is solved using the orthogonal collocation on finite elements. The model is able to predict the experimental data quite well without any adjustable parameters. The importance of each parameter depended on the system, although adsorption equilibrium and the effective pore diffusion of the organic were the most significant parameters in all the systems investigated.
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    AIChE Journal 40 (1994), S. 767-776 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Liquid-liquid dispersions are commonly used for separations and reaction systems, because the added interfacial area due to dispersion aids in mass transfer and chemical reaction rates. Transient coalescence experiments have been performed for a wide range of dispersed-phase fractions and impeller speeds. A similarity transformation of the experimental drop-size distribution is possible for most of the experiments. The drop-size-dependent coalescence frequency is obtained from an inverse problem procedure previously developed. Over the range of drop sizes encountered in our experiments, the coalescence frequency increases with increases in the size of the coalescing drops, the dispersed-phase fraction, and the impeller speed. For a dispersephase system of neutrally buoyant droplets of benzene/carbon tetrachloride in water, the coalescence frequency is K(v, v′)= 3.72 (10-3)φ1.42N20.52(v1/2+v′1/2) as a function of dispersed-phase fraction, φ, impeller speed, N2, and volumes of the coalescing droplets, v and v′. The results are compared with previous models for the coalescence frequency. Models predicting an eventual decrease in coalescence rates with drop size are disqualified unless this decrease occurs beyond the sizes observed in our experiments.
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    AIChE Journal 40 (1994), S. 786-798 
    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 new approach for developing fundamental equations of oxygen permeation through thin mixed-conducting oxide ceramic is presented considering both surface reactions on membrane-gas interfaces and the diffusion of charged species in the bulk oxide. The essence of this work is the coupling of surface reactions with the bulk diffusion using a novel approach which differs from the conventional Wagner. Theory applicable only to limited cases. With this approach, fundamental equations based on various permeation mechanisms can be derived for oxygen permeation through thin mixed-conducting oxide membranes, which is impossible using conventional approach. In general, the final results are a complex implicit equation correlating the oxygen permeation flux to the driving force, membrane thickness, and rate constants with physical significance in each step. Somewhat simpler theoretical oxygen permeation equations are obtained for some special cases (mixed-conducting membranes with a rate-limiting step, ionic-conducting membranes, ionic-conducting membranes with a reducing agent in permeate side). Theoretical results derived using this new approach agree excellently with the experimental oxygen permeation data. It is theoretically and experimentally shown that for ionic conductors, the surface permeation parameter measured by the dynamic permeation method is directly related to the oxygen isotope exchange rate constant measured under equilibrium conditions.
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    AIChE Journal 40 (1994), S. 1223-1237 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Heavy metals like Cu2+, Cr6+, and Hg2+ were removed successfully from wastewater and concentrated in a strip aqueous solution for recycle using the hollowfiber-contained liquid membrane (HFCLM) technique. Using cotransport, Cr6+ and Hg2+ present as anions in the feed solution were transferred individually through a liquid membrane containing tri-n-octylamine in xylene and concentrated in an alkaline solution on the strip side. The removal efficiency of each heavy metal was studied as a function of the aqueous feed flow rate in an HFCLM permeator. Copper present as cation Cu2+ was removed and concentrated by countertransport using LIX84 in n-heptane as the liquid membrane. The efficiency of copper removal was studied as a function of feed copper concentration, feed flow rate, strip flow rate, and area ratio between the feed fiber set and strip fiber set. The strip side flow rate did not affect the Cu2+ transfer rate. A theoretical model presented predicts the copper transport rate from the feed solution to the strip solution in an HFCLM permeator with a variable feed to strip-side membrane area. Both feed aqueous boundary layer and interfacial complexation reaction on the feed side dominate the observed Cu2+ removal process through LIX 84 in n-heptane for feed concentration levels used 90-500 mg/L. It was verified by providing two times larger liquid-liquid interfacial area in the feed aqueous side or in the strip aqueous side. The model can be used to design the membrane area required on the feed and strip fiber sides to remove essentially all of the copper from a given wastewater stream.
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    AIChE Journal 40 (1994), S. 1238-1245 
    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 quantitative determination of porosity and saturation distributions in porous media using unclear magnetic resonance imaging techniques is addresed. A method based on multiple image acquisitions with extrapolation within a model of transverse relaxation was investigated for new experimental situations. The determination of saturation was validated with limestone and sandstone samples. Experimental evidence for dependencies of transverse relaxation and linewidth on saturation is discussed, as well as their impact on image resolution and quantitation. An automatic production measurement device for independent verification of average saturations during dynamic experiments is investigated.
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Devonian shales and other unconventional resources can be highly fractured and may have significant amounts of gas stored by adsorption. Conventional experiments are not well suited for characterizing the properties important for describing gas storage and transport in these media. Here, X-ray computed tomography scanning is used to determine gas storage in dynamic gas flow experiments on Devonian shale samples. Several important properties are obtained from these experiments, including fracture widths, adsorption isotherms, and matrix porosities and permeabilities.
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    AIChE Journal 40 (1994), S. 1254-1261 
    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 fourth-generation X-ray computer-assisted tomography (CAT) scanner was used for the study of fluidized and trickle beds. A variety of exploratory experiments were performed, and images of density and holdup were obtained in three dimensions as a function of time. The gas/solid fluidized beds were glass bead/nitrogen and polyethylene/nitrogen systems. The trickle bed was a glass bead/nitrogen/water system. The algorithms presented can be used to determine holdup from X-ray absorption data. These algorithms - extensions of similar algorithms used for the calculation of fluid saturations in porous media - are applied on data of CAT scanner images as they are generated by the scanner and after they are transferred to a workstation. The results of the presented tests demonstrate how detailed holdup calculations can be performed in a chemical reactor. Radial and longitudinal variances of the holdup can be easily defined. The proposed algorithms can assist in the design of chemical reactor prototypes.
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    AIChE Journal 40 (1994), S. 1268-1272 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 40 (1994), S. 1262-1267 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Magnetic resonance imaging is used to make nondestructive experimental measurements of fluid flow velocity and rock porosity inside a brine-filled Casper sand-stone sample during brine injection. Two-dimensional images of these values are obtained in arbitrary cross sections, with pixel sizes on the order of 1 mm2. The data are then statistically analyzed to find the variation of the average interstitial velocity as a function of porosity, as well as frequency distributions for both the velocity and porosity. The results show that as local porosity increases, the local flow velocity increases, according to the empirical relationship, V = 0.0669 φ + 0.0055. Thus, higher porosity regions of the core are better contacted by the displacement fluid. Results also imply bypassing of fluid around the perimeter of the core, indicating the need for a coreholder capable of sustaining higher overburden pressures on the order of 225 psi (1.55 MPa).
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    AIChE Journal 40 (1994) 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 40 (1994), S. 849-861 
    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 systematic methodology applicable to the optimal design of stable process systems is presented. It is based on the formulation of a parametric problem that provides bounds on the optimal stable solution and an iterative algorithmic approach that attains convergence of the bounds in a finite number of iterations. The bounds on the optimal stable solution are based on analytical expressions of bounds on the eigenvalues of the Jacobian matrix using the concept of the measure of the matrix. When extended to the synthesis problem of reactor networks, the approach is able to couple the optimization problem with stability issues even in cases where the number of reactors is large and the reaction mechanism is described by a general complex reaction scheme. Furthermore, since at the synthesis level the reactor network represents an exhaustive superposition of the existing structural and operational alternatives, the approach fully exploits these alternatives and coordinates a weighted optimal search that improves the objective and accommodates a stable reactor network. This approach is not restricted to the synthesis of reactor networks and can be applied to the design of total process flowsheets.
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    AIChE Journal 40 (1994), S. 312-320 
    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 statistical thermodynamics model based on the original work of van der Waals and Platteeuw is presented for structure-H hydrates. The model is an extension of the hydrate prediction method generalized by Parrish and Prausnitz for structure-I and-II hydrates. Four structure-H-forming systems, methane+ adamantane, methane+ neohexane, methane+isopentane, and methane+methylcyclohexane, were considered. Optimized Kihara core parameters are presented for each of the large hydrocarbon guest molecules. The optimized reference chemical potential difference and reference enthalpy difference for structure-H hydrates are also presented. The results show good agreement with the experimentally determined phase-equilibria conditions. A sensitivity analysis is presented for the parameters in the model, and their relative order of influence on the accurate evaluation of the quilibrium pressure is determined.
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    AIChE Journal 40 (1994), S. 321-333 
    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 mathematical model has been developed to predict the coupled hydrodynamics and high-molecular-weight protein transport in mammalian-cell hollow-fiber bioreactors (HFBRs). The analysis applies to reactors with isotropic ultrafiltration membranes under startup conditions when the extracapillary space (ECS) is essentially unobstructed by cells. The model confirms the experimental finding that secondary ECS flows, engendered by the primary flow in the fiber lumens, can cause significant downstream polarization of ECS proteins at typical mammalian-cell HFBR operating conditions. It also reveals that the osmotic activity of the proteins, by curtailing transmembrane fluid fluxes, can influence strongly the outcome of the polarization process. In fact, at order-of-magnitude higher protein concentrations and/or lower recycle flow rates, the secondary flow velocities can be reduced by as much as six orders-of-magnitude throughout the ECS, thereby virtually eliminating the polarization problem. This result has important implications for improved reactor startup procedures.
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    AIChE Journal 40 (1994), S. 334-348 
    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 motility of a population of swimming bacteria can be characterized by a random motility coefficient, μ, the operational equivalent of a diffusion coefficient at the macroscopic level and in the absence of interacting chemical gradients. At the microscopic level, random motility is related to the single-cell parameters: speed, tumbling probability, and index of directional persistence (related to the angle a cell's path assumes following a change in direction). Various mathematical models have been proposed for relating the macroscopic random motility coefficient to these microscopic single-cell parameters. In separate experiments, we have measured motility at both the cell-population and single-cell levels for Escherichia coli. The agreement of these results shows that the macroscopic transport behavior of a population of motile bacteria can be predicted from straightforward microscopic observations on single cells.
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    AIChE Journal 40 (1994), S. 349-360 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mixing effects in protein precipitation processes are very poorly understood. They impact apparent protein solubility, protein structure in precipitates, particle size, morphology and recoverable activity. In this work, a model is proposed to describe the impact of mixing on protein solubility in precipitation processes. A series of semibatch-mode precipitation experiments were performed using bovine liver catalase and ammonium sulfate to test model predictions. The process variables studied include initial protein supersaturation, agitation rate, and rate of addition of salt solution to the initial protein solution. The mixing model parameters were estimated independently with the aid of a series-parallel dye reaction. The results showed good agreement between model and experiment. The initial protein supersaturation was the most important variable at the 1-L scale. The influence of mixing on recoverable activity was also examined. Scale-up guidelines are suggested based on model simulations and experimental results.
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    AIChE Journal 40 (1994), S. 369-372 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 40 (1994), S. 373-377 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 40 (1994), S. 361-364 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Various phenolic compounds in aqueous buffer solutions were contacted batchwise with powdered activated carbon. Relatively slow, but continual, decreases in the solution phenolic concentrations were measured over a period of several weeks. The decreases were due to oxidative coupling reactions of the phenolics which occurred on the carbon surface subsequent to adsorption. The effects of time, pH, dissolved oxygen, and the molecular nature of the phenolic were determined.
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    AIChE Journal 40 (1994), S. 380-381 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 40 (1994), S. 1524-1534 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Isobutene is the only product of the uncatalyzed and acid-catalyzed dehydration of tert-butanol in compressed liquid water at 250°C. The uncatalyzed dehydration reaction is fast: equilibrium is established after about 30 s. Only one of many chemically-motivated kinetic models is able to fit all the experimental data. This model presumes a heterolytic dehydration mechanism that involves protonated alcohol, carbocation, di-tert-butyl ether, and protonated ether as intermediates. The model permits tert-butanol to dissociate as both an Arrhenius acid and a Bronsted acid while catalyzing its dehydration to isobutene. The pKa of tert-butanol at 250°C is predicted to be about 9, whereas its value at normal temperature and pressure is 18. This 109 increase in the Ka value of tert-butanol hints of the promising new world of reaction chemistry in near- and supercritical water.
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    AIChE Journal 40 (1994), S. 1558-1573 
    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 general molecular-based formalism developed rigorously establishes microscopic bases of the supercritical solubility enhancement in terms of well-defined molecular correlation function integrals by unambiguously splitting the mixture's properties into short-(finite) and long-range (diverging) contributions. Consequently, the short-range nature of the solute's and solvent's residual chemical potentials is proved and the change of the solvent's local environment around an infinitely dilute solute and its finite contribution to solute mechanical partial molar properties are interpreted in terms of the short-range solute-solvent and solvent-solvent direct correlation function integrals. The solute-induced effect on the system's microstructure and thermodynamics approaches zero as the mixture approaches ideality or the solute becomes an ideal gas particle. At the solvent's critical conditions, the solute-induced effect on the solute's partial molar properties shows no compressibility-driven singularity, though along the critical isotherm it can exhibit a finite extremum or a change of curvature near critical density, depending on the type and strength of solute-solvent interactions. The utility of the proposed solvation formalism is illustrated using statistical mechanical integral equation calculations for three simple models of infinitely dilute near-critical mixtures: pyrene-CO2, diterbutyl nitroxide-ethane, and Ne-Xe.
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    AIChE Journal 40 (1994), S. 1601-1610 
    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 effect of imposed large-amplitude oscillations on turbulent drag is studied. The system consists of water flow through a straight 5.08-cm pipe. The velocity gradient at the wall is measured with flush-mounted electrochemical mass-transfer probes. Newly developed numerical algorithms are used to analyze the probe performance in the presence of unsteady flows. Sinusoidal oscillations are at large enough frequencies, ω+ = 0.0138-0.0506, that a pseudo-steady-state approximation cannot be made. The ratio of the time-averaged velocity gradient at the wall, with and without oscillations, S̄, varies between 1.00 and 1.03, provided flow reversal does not occur. However, two experiments in which reversed flows existed at the wall for an appreciable period of time show drag reductions of 7 and 13%.Imposed nonsinusoidal oscillations are also studied for a period of favorable pressure gradient, about twice longer than that of unfavorable, and two sudden changes in the pressure gradient. Experiments at Re = 9,700 with T0 of 2.00, 2.45, and 3.46 s, and at Re = 19,200 with T0 = 3.46 give values of S̄ = 1.04-1.08. At Re = 19,200 and T0 = 2.00, 1.50, 1.00 s, drag reductions are 10-15%. This phenomenon could be associated with the speed with which a flow adjusts to sudden changes in the pressure gradient.
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    AIChE Journal 40 (1994), S. 1618-1628 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Separating mixtures of α-amino butyric acid (ABA) and isoleucine (Ile) by displacement chromatography with a cation exchange resin and an alkaline displacer leads to the formation of a displacement train, in which only ABA is recovered as a pure component, while Ile is recovered in a mixed band with ABA. The purity of the Ile band depends on the concentration of the displacer, and essentially pure Ile is obtained when the displacer concentration is reduced to a low value. The observed behavior is explained by considering the nonideality of the equilibrium uptake of these amino acids by the resin. An equilibrium model, representing the pure component isotherms, predicts variable selectivity and the occurrence of selectivity reversal in the two-component system. Analyses using this model based on the theory of coherent waves and a numerical solution of the conservation equations for the displacement chromatography process agree with the observed behavior, predicting the formation of “azeotropic” bands during the development of the displacement train. Such analyses are used to determine under what conditions a complete separation may be obtained for a given experimental system.
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  • 58
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1639-1649 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Elliptical basis function (EBF) networks are introduced as a new nonparametric method of estimating probability density functions for process data. Unlike Parzen window density estimators that use identical hyperspherical basis functions, the EBF method uses elliptical basis functions adapted to the local character of the data. This technique overcomes the spikiness problem associated with Parzen windows, where in high dimension, they can fail to produce smooth probability density estimates. The EBF estimator produces valid density functions that converage to the underlying distribution of the data in the limit of an infinite number of training examples. A technique based on statistical cross validation is introduced for evaluating different density estimators. The criterion is a measure of how well the density estimator estimates the density of data not used in the training. The EBF density estimation method and the evaluation technique are demonstrated using several examples of fault diagnosis.
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  • 59
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1685-1696 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most existing adsorption models do not properly consider steric hindrance effects of preadsorbed solutes. As a consequence, the models often fail to represent the adsorption kinetics and equilibria accurately. In this work, we extend the random sequential adsorption concept for irreversible adsorption to analyze reversible adsorption on a continuous surface and a random site surface. Based on simulation results of these processes, general kinetic equations for one-component adsorption are developed. The equations are used to correlate chromatography frontal curves of lysozyme and isotherm data of ethane adsorption on activated carbon and ethylene adsorption on a molecular sieve. The significance of the equations, as compared with the Langmuir equation, lies not only in their ability to correlate the experimental data more accurately, but in the physical significance of the adsorption parameters such as the maximum adsorption capacity obtained from the correlation. Our study shows that steric hindrance effects alone result in nonlinear Scatchard and Hill plots with negative cooperativity.
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  • 60
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Four noncubic equations of state, (EOS) and five activity coefficient models are applied to binary polymer and solvent solutions. Solvent activities at intermediate concentrations and equilibrium pressures are predicted with the perturbed-soft-chain theory (PSCT), group-perturbed-soft-chain theory, (GPSCT), group-contribution-lattice fluid (GCLF) EOS, GC-Flory EOS, UNIFAC-FV, entropic-FV and GK-FV models, “new” UNIFAC, and modified Flory-Huggins model. Free-volume activity coefficient models (UNIFAC-FV, entropic-FV) are simpler and, when applied to polymer solutions, more accurate than the EOS. Activity coefficient models are restricted to low-pressure calculations and require accurate values of pure-component volumes. Mixture parameters for activity coefficient models and GC-Flory EOS have been previously evaluated from experimental vapor-liquid equilibrium data for mixtures with only low-molecular-weight compounds. The GC-Flory EOS, though more complicated than activity coefficient models, provides equally good or in some cases better predictions. The application of GC-Flory EOS developed as an activity coefficient model is restricted to low-pressure calculations. On the other hand, PSCT and GCLF developed as “true” EOS provide reliable equilibrium predictions using mixture parameters evaluated solely from pure-component properties together with standard mixing and combining rules. PSCT EOS performs generally better than GCLF EOS for polymer solutions considered in this study.
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  • 61
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 62
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 445-462 
    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 molecular weight distribution (MWD) estimator for batch methyl methacrylate solution polymerization is implemented experimentally for on-line control and estimation of the MWD. The estimator is based on an extended Kalman filter and provides current estimates of the entire MWD, reaction temperature, monomer conversion, and initiator conversion. It uses a detailed polymerization model, on-line monomer conversion measurements, temperature measurements, and periodic, time-delayed measurements of the MWD from an on-line size-exclusion chromatograph. The estimator is shown to perform well with several on-line MWD estimation experiments. Real-time feedback control of the molecular weight is presented by utilizing the on-line MWD information. Temperature, monomer-addition, and simultaneous temperature and monomer-addition control are investigated experimentally to achieve a specific constant weight-average molecular weight. The on-line feedback control is effective in rejecting realistic disturbances which deteriorate molecular weight control.
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  • 63
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1794-1803 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Time-dependent viscous flows driven by capillarity act to minimize the surface area of a fluid bounded in a plane geometry with initial gradients in surface curvature. These free-surface flows are solved by a finite-element model applied to describe the viscous sintering of two-dimensional ceramic particles. The numerical model is validated by comparison to the analytical solution obtained by Hopper (1990) for the coalescence of two infinite cylinders of equal cross section and is applied to several other geometries pertinent to the study of particle sintering for which analytical results are not available. Details of the flow fields and morphological evolution lend insight to the physical behavior of these systems and provide a basis for the more complete understanding of viscous sintering phenomena.
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  • 64
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1804-1813 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fouling of tube surfaces from flowing solutions or suspensions is examined. A new approach to the removal aspects of this process is presented linking removal to the morphological and mechanical characteristics of deposit microstructure. A simplified description of deposit microstructure is employed, involving a collection of geometrically similar roughness elements. A dynamic situation is envisioned whereby these elements grow due to deposition and suffer breakage under the action of hydrodynamic forces. A mathematical model for the macroscopic fouling behavior based on the techniques of population balances is obtained and numerically analyzed. The behavior found is in agreement with experimental evidence.
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  • 65
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1850-1864 
    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 closed-loop strategy for terpolymer composition control in semicontinuous emulsion polymerization of high solids content systems is presented. This strategy is based on a nonlinear adaptive controller that calculates the flow rate of the more reactive monomers to be added into the reactor to produce a terpolymer of a given composition. The nonlinear adaptive controller is based on a simplified mathematical model of the process that includes the on-line estimation of an adjustable parameter. The addition of a conventional feedback proportional-integral (PI) controller to the prediction of the nonlinear controller was studied by simulation. It is shown that the contribution of the PI controller is negligible. The controller was checked by computer simulation and also experimentally verified during the semicontinuous emulsion terpolymerization of high solids content (55 wt. %) of vinyl acetate, methyl methacrylate and butyl acrylate.
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  • 66
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1900-1900 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 67
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1876-1891 
    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 filtration of colloidal gels, consisting of octadecyl-coated silica spheres in hexadecane, is examined experimentally using CAT scanning. A number of interparticle strengths are explored, with significant differences in qualitative behavior relative to the filtration of stable dispersions. For stiff gels, the transmission of stresses from the cell wall to the dispersion results in a fracturing phenomenon during consolidation on a length scale substantially larger than the particle size. For more pliant gels, the radial propagation of stress is more local to the wall region and gravitational effects play a prominent role. The existing theory of network consolidation is compared against our experimental results for pliant gels, independent of the form of the constitutive functions for the sedimentation velocity and yield stress. Though our measurements seem consistent with the theory at early times, deviations at later moments question whether a compressive yield stress is actually present.
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1892-1900 
    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 phase and chemical equilibria of flue-gas/water systems containing sour gases such as HCl, HF, SO2, SO3, NOx and volatile heavy metal compounds such as Hg, HgCl2, and SeO2 are calculated from thermodynamic standard data using the Gibbs free energy minimization method. The Pitzer/Debye/Hückel equation is used for the activity coefficients of the ions in the aqueous solution. The inhibition of certain oxidation reactions is considered by a proper formulation of the atom matrix. The comparison of the calculated equilibrium values to experimental data from a coalfired power plant show that concentrations of most pollutants at the outlet of the absorbers are close to the equilibrium values of one single theoretical stage. The extension of the Gibbs free energy minimization to multistage countercurrent absorbers gives the concentration profiles of various components.
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  • 69
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1901-1910 
    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 flow and retention of 0.1% w/w aqueous solutions of pepsin, bovine serum albumin (BSA), lipase, γ-globulin, and invertase with molecular weights of 36,000, 67,000, 80,000, 150,000, and 270,000 dalton (g/mol) are studied when they are tangentially filtered through an inorganic microporous membrane with a nominal pore size of 0.02 × 10-6 m made by Anopore, with transmembrane pressure differences up to 100 kPa. The data were analyzed within the frame of the film layer theory for the concentration polarization phenomenon. This allows the mass-transfer coefficient to be obtained for the cell used as a function of the feed circulation speed and the molecular weight of the solute. Apparent and true retention curves obtained lead to a size exclusion radius smaller than the nominal one but very similar to that obtained from scanning electronic photographs.
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