Esters of fatty acids (FAs) and polyethylene glycol 400 (PEG) are valuable chemically derived surfactants. In this work, it is shown that the chemical synthesis of PEG esters can be replaced by enzymatic synthesis under milder conditions and using simpler and more environmentally friendly technology. The main obstacles to enzymatic catalysis in a system of PEG and higher FAs are the high viscosity of the former and the low water solubility of the latter. These problems are solved by selecting organic media and other con ditions of the process mediated by pancreatic lipase. The optimum conditions for the synthesis of PEG esters of FAs are determined: reaction medium, benzene/hexane in a ratio of 2 : 3; optimum temperature, 25°C; water content in the system, no more than 0.2%; FA : PEG molar ratio, 1 : 1.8; reaction time, 48 h. Under these conditions, the yields in synthesizing PEG esters of capric, lauric, and palmitic acids are 80, 78, and 44%, respectively.
Main applications of lipases for the production of esters with different structures are analyzed in the review. The effect of nonaqueous media, methods of lipase immobilization, and substrate specificity on enzymatic esterification is described. Implementations of enzymatic esterification reactions under industrial conditions using two configurations of reactors – with fixed or fluidized bed – are reported. Esters obtained by enzymatic catalysis are systematized with respect to their chemical structure. Lipases are shown to be promising for use in the esterification processes aimed to produce esters with different structures and intended for various purposes.
The esterification activity of some commercial lipases was examined. The comparison of the enzymatic activities was carried out in regard to the synthesis of esters of lower aliphatic acids and alcohols. The highest esterifying ability was shown by the enzyme preparation Novozym 435 which quickly starts the process. The conversion of used acids was 70-82% within 0.5 hours, and reached 90% of conversion in 1 hour of reaction. Similar efficacy shows Novozym 40086. This enzyme preparation provides 90% conversion of the acids in two hours of process. The enzyme preparation Lipozyme TLIM provides conversion of the used acids on 84-90% in three hours of process. The enzyme preparation Lipozyme CALB is less effective on the used acids. Thus, in the synthesis of aliphatic esters the esterifying ability of enzyme preparations in the studied conditions decreases in a row: Novozym 435, Novozym 40086, Lipozyme TLIM, Lipozyme CALB. Pancreatic lipase in the synthesis of butyl butyrate detects an induction period of about 1 hour.
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