Operation of enzyme reactors

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 

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

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As a consequence of enzyme deactivation, conversion may drop during the continuous operation of enzyme reactors. To maintain a constant degree of conversion, two methods can be employed according to the [E] x-concept (see above) ... 

Operation of Enzyme Reactors Under Inactivation and Thermal Optimization... 

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. 

From a practical point of view, a prolonged operation of a reactor with enzyme in suspension is not feasible. Procedures to retain the enzyme in the tubular reactor have been developed in order to maintain high enzymatic activity and to avoid enzyme washout. A plug-flow reactor operated with immobilized enzyme is known either as a fixed bed reactor or a fluidized bed reactor, depending on the characteristics of the flow pattern and the immobilized enzyme. Since mechanical stirring is not required in plug flow reactors, the support material is not damaged by the impeller, which may be a drawback in CSTR with immobilized enzyme. 

Enzyme immobilisation allows the construction of enzyme reactors in which the enzyme can be reused. Furthermore, the process operate continuously and can be readily controlled. Enzyme reactors currently in use include those illustrated in Figure 2.1. 

A variety of immobilization methods were tested for industrial purposes, from which aminoacylase immobilized by ionic binding to DEAE-Sephadex was chosen. Through chemical engineering studies on aminoacylase columns we designed an enzyme reactor for continuous production. Since 1969, we have been operating several series of enzyme reactors for the production of L-methionine, L-valine, L-phenylalanine and so forth. With this immobilized enzyme system, L-amino acids can be produced more economically con cured to the conventional batch system using native enzyme as shown in Fig. 1. 

Temperature is a variable of paramount importance in any bioprocess. Temperature optimization of bioreactor operation is a complicated task since many variables and parameters are involved that are strongly dependent on temperature. Besides, temperature exerts opposite effects on enzyme activity and stability. Then, thermal optimization of enzyme reactor operation requires that temperature explicit functions for all parameters involved be determined and validated. Optimization wifi... 

Mathematical models, especially when coupled with computer techniques, are a very effective tool in searching for optimal operating conditions in the design, operation and control of enzyme reactors. The study of a reliable model for the enzyme reaction system is of significant importance for the industrial application of the biocatalyst. The model has to be effective in a wide range of values of the process variables. 

During operation, the immobilized enzyme loses activity. Most commercial enzymes show decay as a function of time (Eig. 12). The glucose isomerase ia a reactor is usually replaced after three half-Hves, ie, when the activity has dropped to around 12.5% of the initial value. The most stable commercial glucose isomerases have half-Hves of around 200 days ia practical use. To maintain the same fmctose content ia the finished symp, the feed-flow rate is adjusted according to the actual activity of the enzyme. With only one isomerization reactor ia operation, the result would be excessive variations ia the rate of symp production. To avoid this, several reactors at different stages ia the cycle of enzyme decay are operated ia combiaation. 

Biocatalysts in nature tend to be optimized to perform best in aqueous environments, at neutral pH, temperatures below 40 °C, and at low osmotic pressure. These conditions are sometimes in conflict with the need of the chemist or process engineer to optimize a reaction with respect to space-time yield or high product concentration in order to facilitate downstream processing. Furthermore, enzymes and whole cells are often inhibited by products or substrates. This might be overcome by the use of continuously operated stirred tank reactors, fed-batch reactors, or reactors with in situ product removal [14, 15]. The addition of organic solvents to increase the solubility of substrates and/or products is a common practice [16]. 

Free Enzymes in Flow Reactors. Substitute t = zju into the DDEs of Example 12.5. They then apply to a steady-state PFR that is fed with freely suspended, pristine enzyme. There is an initial distance down the reactor before the quasisteady equilibrium is achieved between S in solution and S that is adsorbed on the enzyme. Under normal operating conditions, this distance will be short. Except for the loss of catalyst at the end of the reactor, the PFR will behave identically to the confined-enzyme case of Example 12.4. Unusual behavior will occur if kfis small or if the substrate is very dilute so Sj Ej . Then, the full equations in Example 12.5 should be (numerically) integrated. 

Enhanced thermal stability enlarges the areas of application of protein films. In particular it might be possible to improve the yield of reactors in biotechnological processes based on enzymatic catalysis, by increasing the temperature of the reaction and using enzymes deposited by the LB technique. Nevertheless, a major technical difficulty is that enzyme films must be deposited on suitable supports, such as small spheres, in order to increase the number of enzyme molecules involved in the process, thus providing a better performance of the reactor. An increased surface-to-volume ratio in the case of spheres will increase the number of enzyme molecules in a fixed reactor volume. Moreover, since the major part of known enzymatic reactions is carried out in liquid phase, protein molecules must be attached chemically to the sphere surface in order to prevent their detachment during operation. 

Aim of this work was to optimise enzymatic depolymerization of pectins to valuable oligomers using commercial mixtures of pectolytic enzymes. Results of experiments in continuous and batch reactor configurations are presented which give some preliminary indications helpful to process optimisation. The use of continuous reactors equipped with ultrafiltration membranes, which assure removal of the reaction products, allows to identify possible operation policy for the improvement of the reaction yield. 

The rates of many enzyme reactions are strongly dependent on both pH and temperature. Construct a CS that learns to keep conditions within a simple reactor within the limits 6 < pH < 9 and 27 < T < 41. You will need both to write the classifier system itself and a small routine that represents the environment. Test the operation of your system by including a method that periodically adds a random amount of acid or base, or turns on a heater or chiller for a short period. 

Though cycle time plays an important role in the SBR for the decolorization process, not many reports are found in the literature. The long retention times are often applied in the anaerobic phase of the reactor studies, such as 18 and 21 h. In several studies, it was reported that there is a positive correlation between the anaerobic cycle time and the color removal [30, 31]. Indeed, in combined anaerobic-aerobic SBRs, since bacteria shifted from aerobic to anaerobic conditions, or vice versa, anaerobic azo reductase enzyme can be adversely affected by aerobic conditions, which is essential for aromatic amine removal, thereby resulting in insufficient color removal rate. To investigate the effect of cycle time on biodegradation of azo dyes, inar et al. [20] operated SBR in three different total cycle times (48-, 24- and 12-h), fed with a synthetic textile wastewater. The results indicated that with a... 

Figure 4.11 Effect of inhibition of enzyme 2 by cofactor A and of enzyme 1 by cofactor B (i.e., product inhibition) on the concentration of B in the basic system when operated as a fed-batch reactor. For the central and right panels the inhibition constants are indicated on top of each section. In the left panel, inhibition by products was not considered, and—indicates that the parameter is not applicable. Data presented in the left panel are taken from Figure 4.4. The values used for all other parameters ares given in Table 4.1, set I.

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