Biocatalyst catalyst costs

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 first prejudice that biocatalysts are too expensive is only partly true. If the cost per mol or per unit weight is calculated they certainly are expensive. For example, penicillin amidase costs 10 000/kg on a bulk scale. On the other hand the cost contribution of penicillin amidase in the splitting of penicillin G is only 1/kg of product11171. In the case of L-aspartic acid production the cost contribution of aspartase is even lower, 0.1 /kg. This demonstrates that it is not the absolute catalyst cost but the cost contribution of the catalyst to the final product cost that has to be considered and compared. This is also true for chemical catalysts e. g., the bulk price of BINAP is 40 000/kg11171. Important parameters influencing the cost contribution are the total turnover number (mol product/mol catalyst) and the turnover frequency (mol product/mol catalyst and unit time). 

Approximately 80% of all catal54ic processes require heterogeneous catalysts, 15% homogeneous catalysts and 5 % biocatalysts [3]. The total commercial value of all catalysts worldwide is over 12 billion EUR. In crude oil refining processes the catalysts costs amount to only about 0.1% of the product value, and for petrochemicals this value is about 0.22%. 

The repeated use of the biocatalyst is often necessary to reduce the catalyst costs. Soluble enzymes can be easily recovered from the reaction mixture using an ultrafiltration step [18,96,97], thereby combining homogeneous catalysis wifli selective enzyme recovery and reuse. Ultrafiltration can be performed from a microliter to a multi cubic meter scale with commercially available ultrafiltration membranes and equipment. For first experi-... 

Figure 5.8 Environmental factors E (top figure) and cost indices Cl (bottom figure) for the biocatalytic (a) and chemical catalytic (b) syntheses of (5)-styrene oxide (Scheme 5.3) including the synthesis of the Jacobsen catalyst and of the bacteria (Scheme 5.4) as further syntheses. Waste produced during biocatalyst synthesis is indicated. However, it has to be considered that biocatalyst and product synthesis cannot be separated.

Lastly, cost is a crucial issue in the commercialization of fuel cells, particularly as performance and lifetimes have improved to the threshold of practicability. The major costs associated with these systems are materials-related, with separator and catalyst materials at the top of the list. It is envisioned that the cost of separator materials will decrease with increased production and competition and as alternative materials are perfected. However, the cost of conventional noble metal catalysts, particularly platinum, is expected only to increase with increased production and demand. Therefore, the cost issue could perhaps be addressed by employing alternative catalysts, including biocatalysts. Enzymes are de-... 

For more expensive enzymes the continuous use of enzymes made possible by their iimnobihsation can result in considerable savings. By comparison typical chemical catalysts represent a smaller proportion of the total manufacturing costs. Thus the catalysts used in ammonia, cyclohexane and styrene manufacture have been estimated to cost approximately only 0.7, 0.6 and 0.6% of the total production costs respectively. Thus biocatalysts are still in general comparatively expensive compared with chemical catalysts. 

Production of polymers contributes to pollution during synthesis and after use. A polymer produced by microorganisms is already a commercial product (Biopol). Unfortunately, however, cellular synthesis remains limited by the cost of downstream processing and the fact that the synthesis is aqueous-based, and it is impossible to perform the synthesis in the absence of a solvent. Recent research describes an enzyme-catalyzed polymer synthesis in which there is no solvent. This bulk polymerization mirrors conventional synthesis but eliminates the needs for extremes of temperature and corrosive acid catalysts. This represents the first rapid and efficient synthesis of polyesters from bulk polymerization under ambient conditions with very low concentrations of a biocatalyst (Chaudhary et al., 1997). 

The manner in which a bioconversion is performed is dictated by the nature of the biocatalyst, the chemistry, involved, and process economics.16 The overall aims of a bioconversion are the same as for any process, to maximize the production of a given material at the lowest overall cost. In some cases this might mean maximizing the volumetric productivity (Qp in units of mol.m3 s l) of the reactor. Alternately, it might be most important to enable the more efficient recovery through maximizing the ratio of desired to undesired products. If the cost of the biocatalyst is limiting then the catalyst productivity (P ) must be maximized, a function of the intrinsic activity of the catalyst itself and the fashion in which it is used. 

Chemical interesterification is conveniently achieved by using alkali metal methylates as a catalyst. Microbial lipases are also used as biocatalysts in enzymatic interesteiification. In contrast to the chemical process, the enzymatic process can be more selective if an enzyme with positional specificity is used, but this reaction is usually much slower and more sensitive to reaction conditions. Recent developments in lipase-catalyzed interesterification have resulted in new industrial applications of this process (255). Nevertheless, the high costs of enzymes and process equipment may limit widespread adoption of this process. 

It is clear that recombinant DNA technology has had a major impact on commercial production of L-aspartic acid. With the exception of a thermophilic process, there would appear little need for further development of a better enzyme, as the currently available biocatalysts are extremely cost efficient [44,45]. Future development will be aimed at L-aspartic acid processes that produce less waste and use cheaper starting materials. Current L-aspartic acid processes require bromine as the catalyst for the isomerization of maleic acid to fumaric acid, while... 

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