Membrane Reactors with Whole Cells

Membrane Reactors with Biological Catalysts 3.1.3.1 Membrane Reactors with Whole Cells 

In this reactor the product could be synthesized with a space-time yield of 64 g d with an excellent enantiomeric and diastereomeric excess ee and de 99%). The biocatalyst consumption could be decreased 30-fold to 15 gproduct gwcw by using the membrane reactor as compared with a batch reactor. The corresponding (2S,5S)-hexanediol can also be obtained via biocatalysis [20]. 

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Membrane Bioreactors with Membrane as Bio reactor 310 Enzyme Membrane Reactor 311 Whole-Cell Membrane Bioreactor 312 Membrane Bioreactors with Membrane as Separation... 

EC 5.1.3.8). While cascade coupling of the epimerization to a NeuA-catalyzed carboligation suffers from the combination of two unfavorable equilibria [24], the alternative coupling to PEP-dependent NeuS is more productive, as demonstrated by a whole-cell approach to the production of 1 [25]. Also, KDN 3 has been produced on a 100 g scale from D-mannose (8) and 5 using a pilot-scale enzyme membrane reactor with an overall crystallized yield of 75% (Scheme 17.5) [26]. 

Fig. 3.1.4 whole-cell biotransformation with a membrane reactor. 

Applications of whole-cell biocatalytic membrane reactors, in the agro-food industry and in pharmaceutical and biomedical treatments are listed by Giorno and Drioli [3], Frazeres and Cabral [9] have reviewed the most important applications of enzyme membrane reactors such as hydrolysis of macromolecules, biotransformation of lipids, reactions with cofactors, synthesis of peptides, optical resolution of amino acids. Another widespread application of the membrane bioreactor is the wastewater treatment will be discussed in a separate section. 

Another favorable aspect of stirred batch reactors is the fact that they are compatible with most forms of a biocatalyst. The biocatalyst may be soluble, immobilized, or a whole-cell preparation in the latter case a bioconversion might be performed in the same vessel used to culture the organism. Recovery of the biocatalyst is sometimes possible, typically when the enzyme is immobilized or confined within a semi-permeable membrane. The latter configuration is often referred to as a membrane reactor. An example is the hollow fiber reactor where enzymes or whole cells are partitioned within permeable fibers that allow the passage of substrates and products but retain the catalyst. A hollow-fiber reactor can be operated in conjunction with the stirred tank and operated in batch or... 

G. Catapano, G. lorio, E. Drioli, and M. Filosa, Experimental analysis of a cross-flow membrane bioreactor with entrapped whole cells Influence of trans-membrane pressure and substrate feed concentration on reactor performance, J. Membrane Sci 55 325 (1988). 

As was described above in a number of MBR processes the membrane, in addition to performing the separation functions previously discussed, also acts as a host for the biocatalysts (whole cells or enzymes) which are immobilized in the membrane s pore structure. Concerns with such MBR configurations include membrane biofouling, mass transport limitations and biocatalyst activity loss and denaturation. In the two sections that follow we discuss further some of the key aspects of MBR for biochemical synthesis. We classify these reactors into two types, namely whole-cell and enzymatic MBR. 

Product Recovery. Comparison of the electrochemical cell to a chemical reactor shows the electrochemical cell to have two general features that impact product recovery. CeU product is usuaUy Uquid, can be aqueous, and is likely to contain electrolyte. In addition, there is a second product from the counter electrode, even if this is only a gas. Electrolyte conservation and purity are usual requirements. Because product separation from the starting material may be difficult, use of reaction to completion is desirable ceUs would be mn batch or plug flow. The water balance over the whole flow sheet needs to be considered, especiaUy for divided ceUs where membranes transport a number of moles of water per Earaday. At the inception of a proposed electroorganic process, the product recovery and refining should be included in the evaluation to determine tme viabUity. Thus early ceU work needs to be carried out with the preferred electrolyte/solvent and conversion. The economic aspects of product recovery strategies have been discussed (89). Some process flow sheets are also available (61). 

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