Biocatalytic reactors

G. J. Eye, J. M. Woodley, (Advances in the selection and design of two liquid phase biocatalytic reactors), in Multiphase Bioreactor Design, J. M. S. Cabral, M. Mota, J. Tramper (eds.), Taylor Francis, Fondon, pp. 115-134, 2001. 

Catalytic and biocatalytic reactors are exceptionally rich in bifurcation and instability problems. These can come from many sources, of which we outline a few below. 

This source of multiplicity is probably the most intrinsic one in catalytic and biocatalytic reactors, for it occurs due to the nonmonotonic dependence of the intrinsic rate of reaction upon the concentration of reactants and products. Although a decade ago, nonmonotonic kinetics of catalytic reactions were considered the exceptional case, today it is clear that nonmonotonic kinetics in catalytic reactions are much more widespread than previously thought. The reader can learn more about various examples from the long list of catalytic reactions exhibiting nonmonotonic kinetics [71-76]. 

The previous notes give our readers the minimal information that is necessary to appreciate the possibly very complex bifurcation, instability and chaos behavior of chemical and biological engineering systems. While the current industrial practice in petrochemical petroleum refining and in biological systems does not heed the importance of these phenomena and their implications on the design, optimization and control of catalytic and biocatalytic reactors, it is more than obvious that these phenomena are extremely important. Bifurcation, instability and chaos in these systems are generally due to nonlinearity... 

It is obvious that these briefly discussed phenomena (bifurcation, instability, chaos, and wrong directional responses) may discover unexpected shortcomings in the current design, operation and control of industrial catalytic and biocatalytic reactors. This merits extensive theoretical and experimental research as well as specific research of industrial units. 

Ferreira, B.S., Fernandes, P. and Cabral, J.M.S. (2001) Design and modeling of immobilized biocatalytic reactors, in Multiphase Bioreactor Design (eds J.M.S. Cabral, M. Mota and J. Tramper), Taylor and Francis, London, UK, pp. 85-180. 

A general review of continuous processing/process intensification in the pharmaceutical industry has been made by Rubin ef a. [22], while the use of PI novel technologies to reshape the petrochemical and biotechnology industries has been analyzed by Hahn [23] and Akay [24], respectively. Recent advances in biotechnology process intensification have also been reviewed by Choe ef al. [25] and Akay et al. [26]. The use of monoliths as biocatalytic reactors to achieve PI by smart gas-liquid contact has been reviewed by Kreutzer ef al. [27]. 

The development of hollow fibers with diameters down to about 100 microns makes possible "tube-and-shell" reactors with a high surface-to-volume ratio. Biocatalytic reactors can segregate enzymes or cells either within the hollow fiber lumen,46 within the shell surrounding the outer surface of the fibers,44 45 57-59 or within the porous membrane support.42 45 47 53... 

Molecular separation along with simultaneous chemical transformation has been made possible with membrane reactors [17]. The selective removal of reaction products increases conversion of product-inhibited or thermodynamically unfavourable reactions for example, in the production of ethanol from com [31]. Enzyme-based membrane reactors were first conceived 25 years ago by UF pioneer Alan Michaels [49]. Membrane biocatalytic reactors are used for hydrolytic conversion of natural polymeric materials such as starch, cellulose, proteins and for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industries. Membrane bioreactors for water treatment were introduced earher in this chapter and are discussed in detail in Chapters 2 and 3. 

The combination of a resin and covalently supported IL with SCCO2 was also used in the KR and dynamic kinetic resolution (DKR) of 1-phenylethanol with vinyl propionate catalyzed by Candida antarctica lipase B (CALB) [125]. The IL molecule covalently supported on Merrifield resin was realized through the reaction of 1-butyl imidazole with chloromethylated resin. Subsequently, NTf2 was introduced via ion exchange. Under improved conditions, the conversion of 1-phenylethanol was 50% with 99.9% ee to the product. In order to develop a more efficient process, the KR of 1-phenylethanol was tested on a flow system, and it remained stable for 6 days with 99% ee Moreover, by combing two fixed-bed reactors loaded with the supported enzyme (biocatalytic reactor, CALB-SILLP (SILLP, supported ionic liquid-like phase) 11, 150 mg) and an additional one with an acid zeolite (chemical racemization catalyst, 100 mg). Figure 2.40, the DKR of 1-phenylethanol... 

Figure 2.40 Experimental setup for the continuous DKR of 1-phenylethanol using a combination of consecutive blocatalytic-chemocatalytic-biocatalytic reactors.

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