An innovative auto-catalytic esterification for the production of phytosterol esters: experiment and kinetics

Abstract

An innovative auto-catalytic method was proposed to synthesize phytosterol esters from phytosterols and long-chain fatty acids without adding any catalyst and solvent. The effects of reaction temperature, molar ratio of oleic acid/phytosterols, reaction time and carbon-chain length of the fatty acids on the reaction were investigated. The results showed that the conversion, the yield and the selectivity of the reaction were increased with the increase in reaction temperature, molar ratio and a decrease in the length of carbon chains of fatty acids. The selectivity was decreased on prolonging the reaction time. A high conversion (99.1%) with a high yield (94.9%) and selectivity (95.8%) was achieved under a molar ratio of oleic acid/phytosterols of 3 : 1, a reaction temperature of 220 °C and reaction time of 4 h. The properties of the phytosterol oleic esters by autocatalysis conformed to the quality indices of phytosterol esters from the China Ministry of Health and were superior to the commercial product. The kinetics suggested that the reaction order was 2 and the reaction activation energy was 58.75 kJ mol⁻¹. The auto-catalytic process, omitting the separation step for catalysts and solvents, could be considered as a promising process to synthesize phytosterol esters.