Biochemical reactors Catalyst

Biochemical reactors can be operated either batchwise or continuously, as noted in Section 1.5. Figure 7.1 shows, in schematic form, four modes of operation with two types of reactors for chemical and/or biochemical reactions in Uquid phases, with or without suspended solid particles, such as catalyst particles or microbial cells. The modes of operation include stirred batch stirred semi-batch continuous stirred and continuous plug flow reactors (PFRs). In the first three types, the contents of the tanks arc completely stirred and uniform in composition. 

Reactors can be broadly classified as chemical or biochemical. Most reactors, whether chemical or biochemical, are catalyzed. The strategy will be to choose the catalyst, if one is to be used, and the ideal characteristics and operating conditions needed for the reaction system. The issues that must be addressed for reactor design include ... 

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). 

Several types of reaction may be carried out in a chromatographic reactor. The reaction can be chemical or biochemical, taking place on the stationary phase, in the mobile phase, or both. The stationary phase must be chosen to have a good retention (affinity) for at least one component of the reaction system, and in some cases it has to act as a catalyst or catalyst support. Chromatographic reactors are particularly suited to enzyme-catalysed reactions such as the inversion of sucrose and biosynthesis of dextran, to various... 

Most liquid phase chemical and biochemical reactions, with or without catalysts or enzymes, can be carried out either batchwise or continuously. For example, if the production scale is not large, then a reaction to produce C from A and B, all of which are soluble in water, can be carried out batchwise in a stirred tank reactor that is, a lank equipped with a mechanical stirrer. The reactants A and B are charged into the reactor at the start of the operation. The product C is subsequently produced from A and B as time goes on, and can be separated from the aqueous solution when its concentration has reached a predetermined value. 

Trickle-bed reactors are widely used in hydrotreating processes, i.e., hydrodesulfurization of gasoline and diesel fuel, in petroleum refining, chemical, petrochemical, and biochemical processes. The knowledge of hydrodynamic parameters is vital in the design of a TBR because the conversion of reactants, reaction yield, and selectivity depend not only on reaction kinetics, operating pressure, and temperature, but also on the hydrodynamics of the reactor. Special care is also required to prevent flow maldistribution, which can cause incomplete catalyst wetting in some parts... 

Enzymes facilitate many biochemical reactions, serving as a catalyst-i.e., the enzyme itself is not consumed in the reaction. In fact, it must be separated from the products of the reaction. In the past, the enzyme was discarded and fresh enzyme was charged to the reactor with substrate. Obviously, the economics of such a reactor can be improved dramatically if the enzyme can be recovered and reused. One way of doing this is to immobilize the enzyme on a column of glass beads substrate is fed into one end of the column and products are withdrawn from the other end. Because the enzyme is affixed to the stationary phase, it does not contaminate the product and may be used over and over again. 

Fixed bed reactors, especially TBRs, are heavily used in industrial practice. They are used by the petroleum, petrochemical, and chemical industries for waste treatment and processing, biochemical and electrochemical processes, and hydrotreatment. Catalysts provide a mechanism to accelerate and channel very complex processes, which would normally require high pressures and/or... 

This review paper is concentrated on problems in scaling-up multiphase catalytic fixed bed reactors such as trickle-bed or packed bubble column reactors, in which two fluid phases (gas and liquid) pass concurrently through a bed of solid (usually porous) catalyst particles. These types of reactors are widely used in chemical and petrochemical industry as well as in biotechnology and waste water treatment. Typical processes are the hydrodesulphurization of petroleum fractions, the butinediol syntheses in the Reppe process for synthetic rubber, the anthrachinon/hydrochinon process for H202 production, biochemical processes with fixed enzymes or the oxidative treatment of waste water under pressure. 

Enzyme and microbial kinetics involve the study of reaction rates and the variables that affect these rates. It is a topic, that is critical for the analysis of enzyme and microbial reacting systems. The rate of a biochemical reaction can be described in many different ways. The most commonly used definition is similar to that employed for traditional reactors. It involves the time change in the amount of one of the components participating in the reaction or of one of the products of the reaction this rate is also based on some arbitrary factor related to the system size or geometry, such as volume, mass or interfacial area. In the case of immobilized enzyme catalyzed reactions, it is common to express the rate per unit mass or per unit volume of the catalyst. 

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