EFFECT OF MOLAR WEIGHT OF CARBOXYLIC ACIDS ON THE ENZYMATIC ESTERIFICATION OF GLYCEROL

Abstract

Glycerol is a by-product in biodiesel synthesis, and its current market condition allows the possibility to transform into value-added compounds. In this work, the enzymatic esterification between glycerol and carboxylic acids of different molar weights was studied to obtain glycerides of industrial relevance. Therefore, eight different carboxylic acids were evaluated: formic, acetic, levulinic, caprylic, capric, lauric, stearic, and oleic. Immobilized lipase from Candida Antarctica was employed as a catalyst. Solvent-free reactions were carried out at 65 °C, 450 rpm, at a molar ratio of glycerol: carboxylic acid of 1:1 and a 1,6% enzyme concentration (based on reagents weight). Conversion of carboxylic acids was followed with time by titration. Under these conditions, acids from octanoic to oleic, which initially formed biphasic systems with glycerol, showed high conversions (68%-80%) and initial reaction rates in the same magnitude order. On the other hand, no enzymatic catalysis was observed with formic, acetic, and levulinic acids. Formic acid exhibited a higher rate and 58% of conversion without catalyst. However, for acetic and levulinic acids, conversion was low in uncatalyzed reactions. Then, for these acids, toluene was added as a reaction solvent. As a result, conversions and initial rates increased for these lighter acids, indicating the need for a non-polar media or a biphasic character to activate the enzyme.