Enzyme-based processes

In the development of cell or enzyme-based processes, many process configurations exist, including batch, fed batch and continuous operation. In general, the conversion and the separation processes (downstream processing) are regarded as separate units, and most industrial processes are based on this approach. In the last decades, however, more attention is paid to the integration of conversion and separation, leading to the development of membrane bioreactors [49, 50], and some of these concepts have reached an industrial scale. The membranes used for this type of reactors are almost exclusively polymeric, as temperatures seldomly exceed 100 °C for obvious reasons. 

Enzyme-based processes for the resolution of chiral amines have been widely reported [2, 3] and are used in the manufacture of pharmaceuticals, for example, BASF s process for chiral benzylic amine intermediates. Scheme 13.1 [4]. The methods used are enantioselective hydrolysis of an amide and enantioselective synthesis of an amide, both of which are kinetic resolutions. For high optical purity products the processes depend upon a large difference in the catalyzed reaction rates of each enantiomer. 

The use of enzymes is the newest development in bleaching technology. At least one enzyme-based process developed in Finland has been applied commercially. The process uses xylanase to make lignin more vulnerable to oxidation by attacking the surrounding poly-... 

The splitting of fats/oils can be done either in a batch (Twitchell process) or in a continuous (Colgate-Emery process) mode the enzyme-based processes are still under development for commercial applications. A comparison of these processes follows.9a,b... 

Aiteromem, A. L. (2008). Sustainable textile manufacturing with new enzyme based processes, Int. Dyer, 7,15-19. 

Green Biocatalysts for Production of Atorvastatin Codexis, Inc. has developed an enzyme-based process that has greatly improved the yield, efficiency, and safety record for manufacture of atorvastatin, the key building block for Lipitor , one of the world s best-selling drugs, that lowers cholesterol by blocking its synthesis in the liver. The new enzymatic process is dramatically faster and more efficient than previous methods, and also reduces cyanide-related waste, the use of solvents, and the need for purification equipment. 

Scouring and bleaching of cotton fabrics are also attractive targets for enzyme-based processes, due to the severe environmental impact of these processes. These processes are also very energy demanding. Raw cotton contains about 10% of impurities. Pectins, waxes and coloured components can all be partially removed from raw cotton by enzymatic treatments but the residual seed coating remains a problem. 

A recent review has highlighted the role of membrane technology for ISPR and presents numerous biotechnological examples [20]. In particular, it is emphasized that operation with whole-cell systems using a submerged (internal membranes) rather than a recycle loop affords many benefits such as avoidance of shear stress, oxygen deficiencies, and fluctuations in process conditions. For whole-cell processes, flux values of around 1-70 and 30-80 l/(hm ) were found for internal and external processes, respectively. For enzyme-based processes, flux values of 1 0 1/ (h m ) were found. 

Why are modern enzyme-based processes for manufacturing pure enantiomers more sustainable (environmentally friendly) than traditional synthetic routes used by the pharmaceutical industry ... 

Whereas the above features of an enzyme-based process are advantageous for biofuel generahon, the following section will focus on enzyme applications in biorefineries. 

Enzyme conversions are more specific and controlled compared to acid hydrolysis. This is dne to the specificity of the enzymes for certain substrates or chemical bonds. The final result is that enzyme-based processes yield better-quaUty syrups. The most common and widely used enzymes with their specific activity are a-amylase, P-amylase, pullulanase, amyloglucosidase, cyclodextrin glycosyl-transferase, and glucose isomerase (Guzman Maldonado and Paredes Lopez 1995, Hobbs 2003, Kruger et al. 1987, Teague and Brumm 1992, Woods and Swinton 1995). 

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