Membrane reactors Biological applications

Reaction engineering helps in characterization and application of chemical and biological catalysts. Both types of catalyst can be retained in membrane reactors, resulting in a significant reduction of the product-specific catalyst consumption. The application of membrane reactors allows the use of non-immobilized biocatalysts with high volumetric productivities. Biocatalysts can also be immobilized in the aqueous phase of an aqueous-organic two-phase system. Here the choice of the enzyme-solvent combination and the process parameters are crucial for a successful application. 

This Part will be focused on the fundamentals and applications of membrane-assisted transformation processes, i.e. membrane reactors. Two separate chapters are dedicated to the fundamentals of membrane reactors using traditional chemical catalysts at high temperature (>200 °C) and catalysts of biological origin or biomi-metic at low temperature (<100 °C). 

The possibility of having membrane systems also as tools for a better design of chemical transformation is today becoming attractive and realistic. Catalytic membranes and membrane reactors are the subject of significant research efforts at both academic and industrial levels. For biological applications, synthetic membranes provide an ideal support to catalyst immobilization due to their biomimic capacity enzymes are retained in the reaction side, do not pollute the products and can be continuously reused. The catalytic action of enzymes is extremely efficient, selective and highly stereospecific if compared with chemical catalysts moreover, immobilization procedures have been proven to enhance the enzyme stability. In addition, membrane bioreactors are particularly attractive in terms of eco-compatibility, because they do not require additives, are able to operate at moderate temperature and pressure, and reduce the formation of by-products. 

The porous ceramic membrane can be used to either separate biologically reacting material in reactors, or carry catalysts, microbes or enzymes to influence the desired reactions. An overview of the Japanese efforts for the establishment of membrane reactors in the "Aqua Renaissance 90 Project" are summarised by Kimura [95] a very recent review was written by Zaman and Chakma [96]. The preparation of microporous membranes (pore diameters smaller than 2 nm) for the application in membrane reactors is described by Keizer et al. [97] and Julbe et al. [98], however without detailing the membrane reactor itself. 

Pervaporation membrane reactors (PVMR) are an emerging area of membrane-based reactive separations. An excellent review paper of the broader area of pervaporation-based, hybrid processes has been published recently [3.1]. The brief discussion here is an extract of the more comprehensive discussions presented in that paper, as well as in an earlier paper by Zhu et al [3.2]. Mostly non-biological applications are discussed in this chapter. Some pervaporation membrane bioreactor (PVMBR) applications are also discussed additional information on the topic can be found in a recent publication [3.3], and a number of other examples are also discussed in Chapter 4. 

Abstract Biocatalytic membrane reactors are widely used in different industrial applications including those of the food industry, and in fine chemical, biological, biomedical and pharmaceutical productions, environmental treatments and so on. The application of biocatalytic membrane reactors to research in these fields has an important effect on our daily lives, as well as on the professional environment concerned. This chapter considers the value of using biocatalytic membrane reactors, based on traditional and novel methods, for enzyme- and cell-immobilization moreover, characterization and assessment of their performance is carried out. Finally, the chapter describes their applications in biotechnology, such as hydrolysis, organic synthesis, production of bio-ethanol, pharmaceutical products, optical resolution and medical fields such as artificial organs. 

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