Continuous enzyme reactors

For continuous enzyme reactors, that is, CSTR for enzyme reactions, we have Equations 12.31 and 12.32 ... 

Bioreactors utilizing UF hollow fibers appear to have tremendous potential for continuous enzyme reactors and fermentors. 

Based on the optimization of the conditions attained in discontinuous experiments (Mielgo et al. 2003), the degradation of the dye was performed in a continuous enzyme reactor (Ldpez et al. 2004). Different experiments were planned to maximize process efficiency, defined as the ratio between degradation rate and enzymatic consumption. 

The flow diagram of the enzyme reactor for continuous production of the L-amino add is given in Figure A85. The acetyl amino add is continuously charged into the enzyme column through a filter and a heat exchanger. The effluent is concentrated and the L-amino add is crystallised. The acyl-D-amino add contained in the mother liquor is racemised by heating in a racemisation tank, and reused. 

The use of glutaric dialdehyde as a coupling agent bound the enzymes trypsin or glucose-6-phosphate dehydrogenase to the surface. A large part of the enzymic activity was retained (Fig. 4), and the activity was such that the particle-enzyme conjugate could be used in laboratory scale continuous-flow reactors. 

Third, a poly[bis(phenoxy)phosphazene] has been coated on porous alumina particles, surface nitrated, reduced to the amino-derivative, and then coupled to the enzyme glucose-6-phosphate dehydrogenase or trypsin by means of glutaric dialdehyde. The immobilized enzymes were more stable than their counterparts in solution, and they could be used in continuous flow enzyme reactor equipment (25). 

An immobilized-enzyme continuous-flow reactor incorporating a continuous direct electrochemical regeneration of NAD + has been proposed. To retain the low molecular weight cofactor NADH/NAD+ within the reaction system, special hollow fibers (Dow ultrafilter UFb/HFU-1) with a molecular weight cut-off of 200 has been used [32],... 

The food and water processing reactor system has a semibatch feed, continuous chemical reactors, and a semibatch elimination system. Food is chewed in the mouth to small pieces of solid and enters the stomach every 8 hours or so. In the stomach food is further mixed with water, acidified, and mixed with enzymes, which begin reacting it into small particles and molecules. The food mixes in the stomach (volume 0.5 Hter), but its feed is semibatch so we describe it as a transient CSTR. 

This chapter describes the different types of batch and continuous bioreactors. The basic reactor concepts are described as well as the respective basic bioreactors design equations. The comparison of enzyme reactors is performed taking into account the enzyme kinetics. The modelhng and design of real reactors is discussed based on the several factors which influence their performance the immobilized biocatalyst kinetics, the external and internal mass transfer effects, the axial dispersion effects, and the operational stabihty of the immobilized biocatalyst. 

Bioreactors that use enzymes but not microbial cells could be regarded as fermentors in the broadest sense. Although their modes of operation are similar to those of microbial fermentors, fed-batch operation is seldom practiced for enzyme reactors. The basic equations for batch and continuous reactors for... 

Once a polymer is fuUy saturated, the physical tests described above can be conducted with confidence. Naturally, minimizing the evaporation of water should be considered. The one exception in this new category of testing is flow of water through the foam. This is not covered in the standard but will be very important for some applications, particularly in environmental remediation. If the intent is to build a biofilter or a continuous flow enzyme reactor, we must know the hydrodynamic properties of the materials we produce. Since polyurethanes are rarely used in these environments, the flow of water even through a reticulated foam is not described by the manufacturers. Furthermore, if we are to make composites of reticulated foams, the amount of polymer grafted to the surface will have a dominating effect on the flow of water. In a later chapter, we will describe our work in this area. 

Batch-, stirred-tank-, extractive semibatch-, recirculating batch-, semicontinuous flow-, continuous packed-bed-, and continuous-membrane reactors have been used as enzyme reactors, with dense gases used as solvents. 

A continuous stirred-tank reactor (CSTR) is an ideal reactor which is based on the assumption that the reactor contents are well mixed. Therefore, the concentrations of the various components of the outlet stream are assumed to be the same as the concentrations of these components in the reactor. Continuous operation of the enzyme reactor can increase the productivity of the reactor significantly by eliminating the downtime. It is also easy to automate in order to reduce labor costs. 

A main adimntage of immobilized enzyme is that it can be reused since it can be easily separated from the reaction solution and can be easily retained in a continuous-flow reactor. Furthermore, immobilized enzyme may show selectively altered chemical or physical properties and it may simulate the realistic natural environment where the enzyme came from, the cell. 

Similar behavior to that of the nonisothermal CSTR system will be observed in an isothermal bioreactor with nonmonotonic enzyme reaction, called a continuous stirred tank enzyme reactor (Enzyme CSTR). Figure 3.27 gives a diagram. 

A large part of the enzymic activity was retained after immobilization, as illustrated in Figure 3.20. Moreover, packing of the conjugate particles into a chromatography-type column allowed the construction of a continuous flow reactor. Figure 3.20 illustrates that the enzyme molecules continued to catalyze their reactions for long... 

J. Y. Lee, A. Veiayudhan, and M. R. Iadisch, Maintaining constant enzyme activity in a continuous flow reactor, Chem. Eng. J. 

M.-R. Kula and C. Wandrey, Continuous enzymic transformation in an enzyme-membrane-reactor with simultaneous NADH regeneration, Meth. Enzymol. 1987, 136, 9-21. 

A more promising approach for the synthesis of hydrophobic substances with ADHs is published by Kruse et al. [159, 238], They use a continuously operating reactor where the enzyme containing water phase is separated from the hydrophobic substrate-containing organic phase by a membrane. The hydrophobic product is extracted continuously via a hydrophobic membrane into an hexane phase, whereas the coenzyme is regenerated in a separate cycle, that consists of a hydrophilic buffer system. This method decouples advantageously the residence time of the cofactor from the residence time of the substrate. Several hydrophobic alcohols were prepared in this way with (S)-ADH from Rhodococcus erythropolis (Table 16). 

Fig. 7. Effect of enzyme loading on conversion in 50-mm PDMS-E continuous-flow reactors.

Fig. 9. Effect of time on conversions for 1000-mm PDMS-E continuous-flow reactor with various enzyme loadings.

Having confirmed that the immobilization strategy was robust enough to be used in conjunction with a continuous flow reactor, the authors evaluated the immobilization of a second Hisg-tag enzyme, BsubpNBE, and employed the synthesis of 6-O-acetyl-D-glucal 162 (Scheme 44) as a model reaction. 

To demonstrate the synthetic application of this methodology, the authors subsequently demonstrated its use for the preparative kinetic resolutions of a series of 2° alcohols, Table 24, whereby 20 ml solutions of each racemic alcohol were passed through the bioreactor (3.3 h) and found to afford analogous results to those obtained during the initial optimization experiments. The authors successfully demonstrated the use of immobilized and lyophilized enzymes within a continuous flow reactor, presenting a synthetically viable approach to the kinetic resolution of racemic alcohols. 

Figure 6.10 Chromatograms of debranched amylopectins of (a) A-type starches (b) B-type starches analyzed using anion-exchange chromatography a pulsed amperometric detector and an amyloglucosidase enzyme reactor (HPAEC-ENZ-PAD) and (Continued overleaf)...

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