ADSORPTIVE CONTROL OF WATER IN ESTERIFICATION WITH IMMOBILIZED ENZYMES - II - FIXED-BED REACTOR BEHAVIOR

Experimental and theoretical studies are conducted to understand the d ynamic behavior of a continuous-flow fixed-bed reactor in which an est erification is catalyzed by an immobilized enzyme in an organic solven t medium. The experimental system consists of a commercial immobilized lipase preparation known as Lipozyme as the biocatalyst, with propion ic acid and isoamyl alcohol (dissolved in hexane) as the reaction subs trates. A complex dynamic behavior is observed experimentally as a res ult of the simultaneous occurrence of reaction and adsorption phenomen a. Both propionic acid and water are adsorbed by the biocatalyst resul ting in lower reaction rates. In addition, an excessive accumulation o f water in the reactor leads to a rapid irreversible inactivation of t he enzyme. A model based on previously-obtained adsorption isotherms a nd kinetic expressions, as well as on adsorption rate measurements obt ained in this work, is used to predict the concentration and thermodyn amic activity of water along the reactor length. The model successfull y predicts the dynamic behavior of the reactor and shows that a maximu m thermodynamic activity of water occurs at a point at some distance f rom the reactor entrance. A cation exchange resin in sodium form, pack ed in the reactor as a selective water adsorbent together with the cat alyst particles, is shown to be an effective means for preventing an e xcessive accumulation of water formed in the reaction. Its use results in longer cycle times and greater productivity. As predicted by the m odel, the experimental results show that the water adsorbed on the cat alyst and on the ion exchange resin can be removed with isoamyl alcoho l with no apparent loss in enzyme activity. (C) 1998 John Wiley & Sons , Inc.