Reactor configurations, potential

Figure 10.2 Potential reactor configurations. (a) CSTR in series using two soluble enzymes, (b) Packed bed reactor (PBR) configurations using immobilized and soluble enzymes. (1) PBR divided in sections using both enzymes immobilized, (2) PBR...

It is important to attain as high an area as possible for a membrane reactor. Configurations with multilayer planar membranes, coiled membranes, or as multiple tubes also can be used for similar processes with potentially very high surface areas, as sketched in Figure 12-6. 

Membranes that arc catalytically active or impregnated with catalyst do not suffer from any potential catalyst loss or attrition as much as other membrane reactor configurations. This and the above advantage have the implication that the former requires a lower catalyst concentration per unit volume than the latter. It should be mentioned that the catalyst concentration per unit volume can be further increased by selecting a high "packing density" (surface area per unit volume) membrane element such as a honeycomb monolith or hollow fiber shape. 

Immobilization of lipases on hydrophobic supports has the potential to (1) preserve, and in some cases enhance, the activity of lipases over their free counterparts (2) increase their thermal stability (3) avoid contamination of the lipase-modified product with residual activity (4) increase system productivity per unit of lipase employed and (5) permit the development of continuous processes. As the affinity of lipases for hydrophobic interfaces constitutes an essential element of the mechanism by which these enzymes act, a promising reactor configuration for the use of immobilized lipases consists of a bundle of hollow fibers made from a microporous hydrophobic polymer (137). 

Immobilization is the process of adhering biocatalysts (isolated enzymes or whole cells) to a solid support. The solid support can be an organic or inorganic material, such as derivatized cellulose or glass, ceramics, metallic oxides, and a membrane. Immobilized biocatalysts offer several potential advantages over soluble biocatalysts, such as easier separation of the biocatalysts from the products, higher stability of the biocatalyst, and more flexible reactor configurations. In addition, there is no need for continuous replacement of the biocatalysts. As a result, immobilized biocatalysts are now employed in many biocatalytic processes. 

The rising need for new separation processes for the biotechnology industry and the increasing attention towards development of new industrial eruyme processes demonstrate a potential for the use of liquid membranes (LMs). This technique is particularly appropriate for multiple enzyme / cofactor systems since any number of enzymes as well as other molecules can be coencapsulated. This paper focuses on the application of LMs for enzyme encapsulation. The formulation and properties of LMs are first introduced for those unfamiliar with the technique. Special attention is paid to carrier-facilitated transport of amino acids in LMs, since this is a central feature involved in the operation of many LM encapsulated enzyme bioreactor systems. Current work in this laboratory with a tyrosinase/ ascorbate system for isolation of reactive intermediate oxidation products related to L-DOPA is discussed. A brief review of previous LM enzyme systems and reactor configurations is included for reference. 

Potential photocatalysts, radiation sources and auxiliary equipment pertinent to the photocatalytic studies developed at the Chemical Reactor Engineering Centre (CREC) using Photo-CREC reactors, ai e reported in this chapter. The discussion about the auxiliary equipment can be relevant, however, to photocatalytic studies in general when other reactor configurations are used. 

To demonstrate the potential complexity involved when dealing with multiple reactor designs, consider Figure 1.5, which proposes a number of different reactor configurations (reactor structures) that might be used. For simplicity, the configurations are limited to combinations of a maximum of three reactors, using PFRs and CSTRs only. 

Figure 5.10 shows a generalized representation of the reactor network synthesis problem. It is assumed that a single feed is available. The volumetric flow rate of the feed is given by Q. On the other end of the network, a combined product stream of concentration C exits the network, which may be composed of potentially many mixtures of product streams within the network. Since the constant density assumption is enforced, the volumetric flow rate of the product stream is also Q. The goal is to determine the specific reactor configuration within the box that optimizes C. 

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