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Journal ArticleDOI

Theoretical analysis of a packed bed membrane reactor

15 Dec 2001-Chemical Engineering Journal (Elsevier)-Vol. 84, Iss: 3, pp 475-483

AbstractAn annular reactor packed with matrices in which the catalysts/enzyme/microorganisms are immobilized, has been simulated and the results indicate that the overall resistance and hence the conversion depend upon the Thiele modulus and another parameter, α. This parameter characterizes the ratios of the diffusion times and the ratios of length scales of the bulk liquid phase and the solid phase in the reactor shell. Analytical solutions can be obtained for linear reactions and a simplified semi-analytic method has been used for obtaining concentration profiles for nonlinear reactions.

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Citations
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TL;DR: The results showed that the CCM structure had a significant effect on the acid conversion, and the conversions obtained from the model are in good agreement with the experimental data.
Abstract: A novel composite catalytic membrane (CCM) was prepared from sulfonated polyethersulfone (SPES) and polyethersulfone (PES) blend supported by non-woven fabrics, as a heterogeneous catalyst to produce biodiesel from continuous esterification of oleic acid with methanol in a flow-through mode A kinetic model of esterification was established based on a plug-flow assumption The effects of the CCM structure (thickness, area, porosity, etc), reaction temperature and the external and internal mass transfer resistances on esterification were investigated The results showed that the CCM structure had a significant effect on the acid conversion The external mass transfer resistance could be neglected when the flow rate was over 12 ml min−1 The internal mass transfer resistance impacted on the conversion when membrane thickness was over 1779 mm An oleic acid conversion kept over 980% for 500 h of continuous running The conversions obtained from the model are in good agreement with the experimental data

42 citations


References
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Journal ArticleDOI
Abstract: Methane steam re-forming is one of the most important chemical processes in hydrogen and syngas production. Simulation of reactors with parallel-flow and counterflow configuration has been performed to study the methane steam re-forming reaction in a packed-bed inert membrane reactor (PBIMR). In this kind of reactor complete methane conversion can be achieved by means of the total removal of hydrogen from the reaction products. In the model a dense Pd membrane was simulated, assuming an infinite permselectivity to hydrogen. Membrane reactor performance was compared to that of a conventional fixed-bed reactor. The effect on the degree of conversion was analyzed for different parameters such as temperature, reactor pressure, feed and sweep flow rate, feed molar ratio, membrane thickness, and space velocity. Comparison with experimental data of Shu et al. (1994) showed a good agreement. An analysis of the results indicated that the choice of operating conditions requires a complex process strategy.

138 citations

Journal ArticleDOI
Abstract: Theoretical analyses of mass transfer in hemodialyzers which contain flowing blood and dialysate streams separated by a semi-permeable membrane are presented. Semi-infinite parallel-plate and cylindrical tube geometries are considered. Solutions are obtained in terms of well-known functions, a method which avoids difficulties associated with computing the higher eigenvalues encountered in previous analyses. Applications of the mathematical model to systems used in clinical practice are discussed.

131 citations

Journal ArticleDOI
TL;DR: The advantages and limitations of using membrane bioreactors for entrapping whole cells and enzymes, including single, laminated and microporous, for the conversion of optically active enantiomers are reviewed.
Abstract: Integrating the properties of synthetic membranes with biological catalysts such as cells and enzymes forms the basis of an exciting new technology called membrane bioreactors. The impetus behind this marriage comes from the recent spectacular advances in recombinant DMA and cell fusion technologies and the need to develop competitive bioprocessing schemes to produce complex and active biological molecules. The advantages and limitations of using membrane bioreactors for entrapping whole cells and enzymes are reviewed. Various membrane configurations such as microcapsules, hollow fibers, and flat sheets are compared. Several different entrapped membrane bioreactors, including single, laminated and microporous, for the conversion of optically active enantiomers are described. As with new and exciting technologies, the future of membrane bioreactors in biotechnology will depend on their ability to produce desired molecules at competitive costs.

114 citations

Journal ArticleDOI
TL;DR: A numerical finite difference solution for nonlinear Michaelis-Menten reaction kinetics is shown to agree with the analytic solution, as Km/C0, the ratio of the Michaelis constant to the initial substrate concentration, becomes large (> 100).
Abstract: The behavior of an immobilized enzyme reactor utilizing asymmetric hollow fibers is simulated using a theoretical model. In this reactor, an enzyme solution contained within the annular open-cell porous support structure of the fiber is separated from a substrate flowing through the fiber lumen by an ultrathin dense membrane impermeable to enzyme but permeable to substrate and product. The coupled set of model equations describing the behavior of this reactor represents an extended Graetz problem in the fiber lumen, with diffusion through the ultrathin fiber skin and reaction in the microporous sponge region. Exact analytic expressions for substrate concentration profiles throughout an idealized fiber which incorporate the membrane and hydrodynamic mass transfer resistances are obtained for a first-order enzyme reaction, and numerical techniques for their evaluation are given. This analysis is extended to yield a numerical finite difference solution for nonlinear Michaelis-Menten reaction kinetics, which is shown to agree with the analytic solution, as Km/C0, the ratio of the Michaelis constant to the initial substrate concentration, becomes large (> 100).

107 citations

Journal ArticleDOI
Vassilis Gekas1
TL;DR: Artificial membranes, due to their interesting properties (high surface area per unit volume, possibility to combine separation with chemical reaction etc).
Abstract: Artificial membranes, due to their interesting properties (high surface area per unit volume, possibility to combine separation with chemical reaction etc) have interested biotechnologists in their attempt to find carriers for the immobilization of biocatalysts Various systems and modes of operation have been used with the biocatalyst either in soluble or in insolubilized form Progress in the above fields over the past decade is summarized and discussed

82 citations