WATER ACTIVITY CONTROL IN ENZYMATIC ESTERIFICATION PROCESSES

Lipase-catalyzed (Lipozyme IM 20 and Novozyme SP 435) esterification r eactions in 5-methyl-2-hexanone were studied in order to investigate t he practical application of a water activity control system consisting of a semipermeable silicone tubing and saturated salt solutions. The system used successfully in different reactor configurations [batch, c ontinuous stirred-tank reactor (CSTR), and tubular] was described. The dimensions of the tubing could be calculated given the diffusion coef ficient of water (D-aw) through the tubing, the amount of enzyme, and the maximum accepted increase in water activity. Tubular reactors with continuous water activity control were constructed. The enzyme prepar ation was packed in a silicone tubing which was submerged into a satur ated salt solution. A reactor with Lipozyme was successfully used for two months without any decrease in product yield (72% conversion at a( w) = 0.33). By connecting a second tubular reactor (containing immobil ized lipase and molecular sieves), the yield increased to 95%. A two-s tage tubular reactor was used to catalyze esterification in pure subst rates (equimolar amounts). The yield (after the second reactor) reache d equilibrium (95% ester) at a water activity of 0.33. (C) 1997 Elsevi er Science Inc.