Enzymes as Catalysts in the Fine Chemicals Industry

Applications of biocatalysis in large-scale processes in industry advance only slowly against established chemical processes, even with stoichiometry-based chemistry. Introduction of biocatalysis into existing processes often requires process modifications that are not economical in view of the short life span of the product and/or the low fixed costs of the existing process owing to written-off plant. It should be emphasized that the desire to reduce chemical wastes, imposed by either company policy or governmental measures, needs to be matched by favorable process economics. Therefore, the introduction of biocatalytic options at the very beginning of product and process development is of the utmost importance. 

---

Enzymes are not widely used as catalysts in the fine chemicals industry. Among the reasons for this are their poor stability in aqueous environments and low efficiency as heterogeneous catalysts in liquids when compared with inorganic catalysts. However, the possibility of using enzymes as heterogeneous catalysts in supercritical media opens up new possibilities for chemical synthesis. 

The category Enzymes as industrial catalysts , including the starch-processing, antibiotics and the fine-chemicals industry, is covered in chapter 4. 

In this context, however, asymmetric transformations with chiral metal complexes or enzymes are particularly important. The demand for enantiopure building blocks in the fine chemical and pharmaceutical industries is still hampered by simple asymmetric processes which can be scaled up, as well as by the stability, recyclability, and hence the price of most chiral catalysts (refer also to the chapter by K.-U. Schoning in this volume). Immobilization of effective and robust catalytic systems and their application in continuous flow reactors is regarded as a key for success in this field. 

Enzymes are characterized by unusual specific activities and remarkably high selectivities. They are effective catalysts at relatively low temperatures and ambient pressure. The primary driving force for efforts to develop immobilized forms of these biocatalysts is cost, especially when one is comparing process alternatives involving either conventional inorganic catalysts or soluble enzymes. Immobilization can permit conversion of labile enzymes into forms appropriate for use as catalysts in industrial processes—production of sweeteners, pharmaceutical intermediates, and fine chemicals—or as biosensors in analytical applications. Because of their high specificities, immobilized versions of enzymes are potentially useful in situations where it is necessary to obtain high yields of the desired product... 

The use of industrial enzymes for the synthesis of bulk and fine chemicals represents a somewhat specialized application for biocatalysts relative to their broader uses, as outlined above. Industrial biocatalysis is, however, becoming increasingly relevant within the chemical industry for the production of a wide range of materials (see Table 31.3).1,2,4-8 Broadly defined, a biocatalytic process involves the acceleration of a chemical reaction by a biologically derived catalyst. In practice, the biocatalysts concerned are invariably enzymes and are used in a variety of forms. These include whole cell preparations, crude protein extracts, enzyme mixtures, and highly purified enzymes, both soluble and immobilized. 

Enzymes are perfectly equipped to convert substrates into products in high enantio-, regio-, or chemoselectivity, a property that is commonly used in industry to prepare optically active fine-chemical intermediates [5]. More specifically, lipases appeared as ideal catalysts as a result of their high enantioselectivity, broad substrate scope and stability. In addition, lipases are powerful catalysts for the preparation of polyesters, polycarbonates and even polyamides, as is reviewed in Chapters 4 and 5 of this book. Moreover, a variety of different polymer architectures such as block copolymers, graft copolymers etc have been prepared using lipases as the catalyst (see Chapter 12). 

---