Biochemical reaction engineering

Previous chapters in this volume have been concerned with chemical reaction engineering and refer to reactions typical of those commonplace in the chemical process industries. There is another class of reactions, often not thought of as being widely employed in industrial processes, but which are finding increasing application, particularly in the production of fine chemicals. These are biochemical reactions, which are characterised by their use of enzymes or whole cells (mainly micro-organisms) to carry out specific conversions. The exploitation of such reactions by man is by no means a recent development—the fermentation of fruit juices to make alcohol and its subsequent oxidation to vinegar are both examples of biochemical reactions which have been used since antiquity. 

The active biochemical constituents of cells are a particular group of proteins which have catalytic properties. These catalytic proteins, or enzymes, are in some ways similar to inorganic catalysts but are distinctive in other, quite important respects. Enzymes are very powerful catalysts, capable of enhancing the overall rates of reactions much more markedly they are much more specific than the average inorganic catalyst. 

Furthermore, the conditions under which the reactions proceed are typically mild, temperatures, for example, being generally under 100°C and frequently below 50°C. Enzymes are water-soluble but are frequently bound to membranes within the cells or retained in the microbe by the cell walls. The structure of those cell walls is such that they permit the ingress of nutrients, or substrates, and the egress of the by-products of the cell s growth. Enzymes usually retain their catalytic activity when isolated from the cell and are often used as such, thus removing the need for 

There is an increasing number of areas where bioreactors are serious alternatives to conventional chemical reactors, particularly when their mild conditions and high selectivity can be exploited. In the pharmaceutical industry micro-organisms and enzymes can be used to produce specific stereo-isomers selectively, a very desirable ability since it can be that only the one isomer (possibly an optical isomer) may possess the required properties. In such applications the limitations of bioreactors are clearly outweighed by the advantages in their use. The fact that the products are formed in rather dilute aqueous solution and at relatively low rates may be of secondary importance and it may then be economically feasible to employ multiple separation stages in their purification. 

Many of the problems encountered in the processing of biological materials are similar to those found in other areas of chemical engineering, and the separation processes used are frequently developments from counterparts in the chemical industry. However, biological materials frequently have rheological properties which make then difficult to handle, and the fact that their density differs little from that of water and the interfacial tensions are low can give rise to difficulties in physical separation of product. 

Proteins are key ingredients to life and to biochemistry. They are linear polymers of amino acids. The general formula for an amino acid is 

Chemical Reactor Design, Optimization, and Scaleup, Second Edition. By E. B. Nauman Copyright 2008 John Wiley Sons, Inc. 

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The Impact of Interdisciplinary Study on Biochemical Reaction Engineering... 

Coulson, J. M. and Richardson, J. F. (1979) Chemical Reactor Design, Biochemical Reaction Engineering Including Computation, Pergamon Press. 

BIOCHEMICAL REACTION ENGINEERING 5.3. CHEMICAL COMPOSITION OF CELLS... 

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