Membrane reactors procedure application

Many procedures have been suggested to achieve efficient cofactor recycling, including enzymatic and non-enzymatic methods. However, the practical problems associated with the commercial application of coenzyme dependent biocatalysts have not yet been generally solved. Figure A8.18 illustrates the continuous production of L-amino adds in a multi-enzyme-membrane-reactor, where the enzymes together with NAD covalently bound to water soluble polyethylene glycol 20,000 (PEG-20,000-NAD) are retained by means of an ultrafiltration membrane. 

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 Van Koten group has developed an interesting approach to the assessment of the permeability of nanofiltration membranes for the application of metallodendrimer catalysts in membrane reactors. They have selectively grafted dendrons to organometallic pincers with sensory properties and have used these as dyes in a colorimetric monitoring procedure. 

This chapter gives an overview of the synthesis procedures and applications of zeolite membranes (gas separation, pervaporation, and zeolite-membrane reactors), as well as new emerging applications in the micro- and nanotechnology field. It is important to note that, up to now, pervaporation is the only large-scale industrial application and gas separation is still not implemented at industrial level for zeolite membranes. Related areas such as new zeolite and zeolite-related materials for membranes, alternative supports, and scale-up issues are also discussed. 

This chapter is composed of four sections in the first section, the main economic parameters are introduced. The second and third sections consider the assessment of investment cost and variable cost in particular, a methodology to assess membrane reactor costs and their impact on variable cost is proposed. The last section discusses examples of proposed procedure applications for the reference cases (i.e., systems with more conventional separation technologies) and cases where membrane reactors are applied. 

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