Chemical—biochemical processes

At present most bioprocesses in the organic chemical industry are actually mixed chemical/biochemical processes. In such processes, chemically synthesised educts (chemical precursors) are biotransformed and then re-enter chemical synthesis. The main reason for this approach is that, in general, higher volumetric productivities can be achieved with chemical catalysts. 

Table 2.3 Possible drawbacks of bioprocesses and mixed chemical/biochemical processes compared to purely chemical synthetic processes.

These sources of multiplicity are very frequent in actual chemical/biological processes. Chapter 7 highlights examples of multiplicity, bifurcation, and chaotic behavior for a number of experimental and industrial chemical/biochemical processes. We also include Appendix 2 on multiplicity and bifurcation at the end of the book. 

Here, we give a very simple presentation of the necessary components for developing model (design) equations for chemical/biochemical processes. Full details and generalization will be given in Chapter 3. 

Optically inactive starting materials can give optically active products only if they are treated with an optically active reagent or if the reaction is catalyzed by an optically active substance The best examples are found m biochemical processes Most bio chemical reactions are catalyzed by enzymes Enzymes are chiral and enantiomerically homogeneous they provide an asymmetric environment m which chemical reaction can take place Ordinarily enzyme catalyzed reactions occur with such a high level of stereo selectivity that one enantiomer of a substance is formed exclusively even when the sub strate is achiral The enzyme fumarase for example catalyzes hydration of the double bond of fumaric acid to malic acid m apples and other fruits Only the S enantiomer of malic acid is formed m this reaction... 

As the experimental tools for biochemical transformations have become more pow erful and procedures for carrying out these transformations m the laboratory more rou tine the application of biochemical processes to mainstream organic chemical tasks including the production of enantiomerically pure chiral molecules has grown... 

The biological response to chemical insult may take numerous forms, depending on the physicochemical properties of the material and the conditions of exposure. Listed below are some of the more significant and frequendy encountered types of injury or toxic response they may be defined in terms of tissue pathology, altered or aberrant biochemical processes, or extreme physiological responses. 

One development involves the use of vitamin B 2 to cataly2e chemical, in addition to biochemical processes. Vitamin B 2 derivatives and B 2 model compounds (41,42) cataly2e the electrochemical reduction of alkyl haUdes and formation of C—C bonds (43,44), as well as the 2inc—acetic acid-promoted reduction of nitriles (45), alpha, beta-unsaturated nitriles (46), alpha, beta-unsaturated carbonyl derivatives and esters (47,48), and olefins (49). It is assumed that these reactions proceed through intermediates containing a Co—C bond which is then reductively cleaved. 

Aerobic (i) Having molecular oxygen as a part of the environment, (ii) Growing only in the presence of molecular oxygen, as in aerobic organisms, (iii) Occurring only in the presence of molecular oxygen, as in certain chemical or biochemical processes such as aerobic respiration. 

If the definition of work is limited to mechanical work, an interesting simplification is possible. In this case, AE is merely the heat exchanged at constant volume. This is so because if the volume is constant, no mechanical work can be done on or by the system. Then AE = q. Thus AE is a very useful quantity in constant volume processes. However, chemical and especially biochemical processes and reactions are much more likely to be carried out at constant pressure. In constant pressure processes, AE is not necessarily equal to the heat transferred. For this reason, chemists and biochemists have defined a function that is especially suitable for constant pressure processes. It is called the enthalpy, H, and it is defined as... 

Within the chemical industry, micro-organisms and enzymes are often used as catalysts. It is possible for a unit operation in an essentially chemical production process to be a biochemically catalysed step giving rise to a mixed chemical/biochemical production process. The products of these reactions include organic chemicals, solvents, polymers, pharmaceuticals, and purfumes. Mixed chemical/biochemical production processes are continuously innovated and optimised, mainly for economical reasons. 

The Bioreactor is the major equipment used in biochemical processes. It differs totally from a simple chemical reaction vessel. To control physical operating parameters and microbial environmental conditions, there are several influential variables ... 

Chemical Engineering, Volume 3, Third edition Chemical Biochemical Reactors Process Control Edited by J. F. Richardson and D. G. Peacock... 

---