Enzyme reactors batch

Enzymatic Reactors Adding free enzyme to a batch reactor is practical only when the value of the enzyme is relatively low. With expensive enzymes, reuse by retaining the enzyme with some type of support makes great economic sense. As some activity is usually lost in tethering the enzyme and the additional operations cost money, stabihty is very important. However, many enzymes are stabilized by immobilization thus, many reuses may be possible. 

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]. 

If the enzyme charged to a batch reactor is pristine, some time will be required before equihbrium is reached. This time is usually short compared with the batch reaction time and can be ignored. Furthermore, 5o Eq is usually true so that the depletion of substrate to establish the equilibrium is negligible. This means that Michaelis-Menten kinetics can be applied throughout the reaction cycle, and that the kinetic behavior of a batch reactor will be similar to that of a packed-bed PFR, as illustrated in Example 12.4. Simply replace t with thatch to obtain the approximate result for a batch reactor. 

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. 

Pectolytic activity was also studied in batch reactors, following the reaction progress in thermostated quartz cuvettes. The reaction medium (3 cm ) was prepared with 1.5 g/L pectin in the standard buffer and 0.063 mg of enzyme. The absorbance of the reaction mixture against the substrate blank was continuously recorded at the spectrophotometer (Perkin Elmer Lambda 2, USA). Typical reaction time was 15 minutes, but initial reaction rates were estimated considering only the absorbances recorded during the first 200 seconds, range of totally linear response. 

The stirred batch reactors are easy to operate and their configurations avoid temperature and concentration gradient (Table 5). These reactors are useful for hydrolysis reactions proceeding very slowly. After the end of the batch reaction, separation of the powdered enzyme support and the product from the reaction mixture can be accomplished by a simple centrifugation and/or filtration. Roffler et al. [114] investigated two-phase biocatalysis and described stirred-tank reactor coupled to a settler for extraction of product with direct solvent addition. This basic experimental setup can lead to a rather stable emulsion that needs a long settling time. 

High reaction rate in Equation 5.71 is favored by a high concentration of enzymes (CE ) and high concentration of feed (CA). This means that a plug-flow or ideal-batch reactor is favored if both the feed material and enzymes are to be fed to the reactor. 

The patent described a method for the removal of thiophenic compounds from fossil fuels, in which the reacting media might contain organic solvents. Additionally, the biocatalyst may be contacted with the fuel directly either as free enzyme or in its immobilized form. The process could, therefore, be performed either in a batch reactor or in a semi-continuous or continuous manner. Further, it may be performed either as a stand... 

Albuquerque MGE, Lopes AT, Serralheiro ML et al (2005) Biological sulphate reduction and redox mediator effects on azo dye decolourisation in anaerobic-aerobic sequencing batch reactors. Enzyme Microb Technol 36 790-799... 

Kapdan IK, Oztekin R (2003) Decolorization of textile dyestuff Reactive Orange 16 in fed-batch reactor under anaerobic condition. Enzyme Microb Technol 33 231-235... 

Reactions with soluble enzymes are generally conducted in batch reactors (Chapter 12) to avoid loss of the catalyst (enzyme), which is usually expensive. If steps are taken to prevent the loss of enzyme, or facilitate its reuse (by entrapment or immobilization onto a support), flow reactors may be used (e.g., CSTR, Chapter 14). More comprehensive treatments of biochemical reactions, from the point of view of both kinetics and reactors, may be found in books by Bailey and Ollis (1986) and by Atkinson and Mavituna (1983). 

Suppose, at a particular temperature, results for the hydrolysis of sucrose, S, catalyzed by the enzyme invertase (cEo = 1 X 10-5 mol L-1) in a batch reactor are given by ... 

A first application using ferroceneboronic acid as mediator [45] was described for the transformation of p-hydroxy toluene to p-hydroxy benzaldehyde which is catalyzed by the enzyme p-cresolmethyl hydroxylase (PCMH) from Pseudomonas putida. This enzyme is a flavocytochrome containing two FAD and two cytochrome c prosthetic groups. To develop a continuous process using ultrafiltration membranes to retain the enzyme and the mediator, water soluble polymer-bound ferrocenes [50] such as compounds 3-7 have been applied as redox catalysts for the application in batch electrolyses (Fig. 12) or in combination with an electrochemical enzyme membrane reactor (Fig. 13) [46, 50] with excellent results. 

To develop analytical models that describe the performance of a cyclic enzyme system (herein termed the basic system) and a cyclic enzyme system with an external inhibitor (termed the extended basic system) when operated in different modes as a fed-batch reactor or a continuous reactor. These models enable us to design systems and select operational conditions according to needs. 

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.

To avoid massive dilution of the reaction mixture in the fed-batch reactor, the initial reactor volume was rather large relative to the flow rate of the feed streams. However, the initial volume of the reactor affects the amounts of enzymes that are required. As shown in Section 4.1.4.1, large amounts of enzymes are needed for each volume unit in the reactor, and in order to work with reasonable amounts of enzymes, this volume was limited to 50 mL. 

The interpretation of the experimental results presented in Figure 4.69 was extended to include inhibition of the enzyme G6PDH by NADPH with i.NADPH = 0.027 mM. A comparison between experimental and calculated results is shown in Figure 4.70. In this case better agreement is achieved when lower values of Ki oee are employed, the values being in the range obtained in experiments carried out in a fed-batch reactor (0.15 to 1 mM). 

The basic system was operated as a fed-batch reactor and as a continuous reactor. The fed batch was used as a first implementation due to its simplicity of operation. However, in such a reactor dilution takes place during operation and therefore the operation conditions should involve a low flow rate and high volume of reaction mixture. Also, this mode of operation requires sizable amounts of the soluble enzymes, and the total operation time is limited. 

The basic system was implemented experimentally utilizing the enzymes G6PDH and GR in a fed-batch reactor (soluble enzymes) and a packed bed... 

Starting with a sucrose concentration AO = 1.0 millimol/liter and an enzyme concentration Ceo = 0.01 millimol/liter, the following kinetic data are obtained in a batch reactor (concentrations calculated from optical rotation measurements) ... 

If we introduce enzyme (Ceo = 0.001 mol/liter) and reactant (C o = 10 mol/liter) into a batch reactor and let the reaction proceed, find the time needed for the concentration of reactant to drop to 0.025 mol/liter. Note that the concentration of enzyme remains unchanged during the reaction. 

In a number of separate runs different concentrations of substrate and enzyme are introduced into a batch reactor and allowed to react. After a certain time the reaction is quenched and the vessel contents analyzed. From the results found below find a rate equation to represent the action of enzyme on substrate. 

Enzyme E catalyzes the decomposition of substrate A. To see whether substance B acts as inhibitor we make two kinetic runs in a batch reactor, one with B present, the other without B. From the data recorded below... 

Rakels, J.L.L., Paffen, H.T., Straathof, A.J.J. and Heijnen, J.J. (1994) Comparison of enzymatic kinetic resolution in a batch reactor and a CSTR. Enzyme Microbial Technology, 16,791-794. 

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