Membrane Reactors for the Production of Biochemicals

The concept of coupling reaction with membrane separation has been applied to biological processes since the seventies. Membrane bioreactors (MBR) have been extensively studied, and today many are in industrial use worldwide. MBR development was a natural outcome of the extensive utilization membranes had found in the food and pharmaceutical industries. The dairy industry, in particular, has been a pioneer in the use of microfiltra-tion (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. Applications include the processing of various natural fluids (milk, blood, fruit juices, etc.), the concentration of proteins from milk, and the separation of whey fractions, including lactose, proteins, minerals, and fats. These processes are typically performed at low temperature and pressure conditions making use of commercial membranes. 

MBR are finding fertile ground for application in biochemical synthesis [4.1, 4.2] for the production of a broad spectrum of products. These range from food, liquid fuels (e.g., ethanol), and plant metabolites, to fine chemicals, including medical products, flavoring agents, food colors, fragrances, etc. Biochemical synthetic processes are important in the pharmaceutical industry, because they allow the production of complex molecules, like hormones, which cannot be produced safely and efficiently with the more conventional techniques [4.3]. 

Catalytic Membranes and Membrane Reactors. By J. G. Sanchez Marcano and Th. T. Tsotsis Copyright 2002 Wiley-VCH Verlag GmbH ISBN 3-527-30277-8 

The way membranes (in various forms, i.e., cylindrical, coaxial, flat-sheet, spiral-wound, and hollow fiber, etc.) couple with the bioreactor depends on the role the membrane performs. As with catalytic and pervaporation membrane reactors, the simplest configuration consists of two separate but coupled units, one being the bioreactor the other the membrane module. The biocatalyst (e.g., enzymes, bacteria, yeasts, mammalian cells) could, in this case, be suspended in a solution and continuously circulated through the 

A different application involves using the membrane for the delivery of one of the reactants (e.g., bubble-free aeration [4.14]). One recent example of such an application is that reported by Onken and Berger [4.15]. They used a microporous polypropylene hollow-fiber membrane for the controlled addition of oxygen in the biotransformation of cit-ronellol into 3,7-dimethyl-1,6,7-octanetriol by Cystoderma carcharias. 

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