Synthesis of alkenyl succinic anhydrides from methyl esters of high oleic sunflower oil

Abstract

Alkenyl succinic anhydrides (ASA) have been prepared by ene‐reaction of high‐oleic sunflower oil methyl esters with maleic anhydride in a 50% xylene medium. Response surface methodology (RSM) was used to investigate the influence of two factors: reaction temperature and molar ratio between maleic anhydride (MA) and methyl esters (SME). The studied parameters in 8‐h reactions were the methyl oleate conversion, the distillation yield in ASA, and responses allowing the indirect estimation of side reaction products: clarity index and dynamic viscosity. The highest yield in ASA (>70%; clarity index ≈10) was reached for a temperature of 240–250 °C with a molar ratio of 1.5–1.7. But for an industrial application requiring minimized side products (clarity index >40), the optimal synthesis conditions were: temperature between 220 and 235 °C and molar ratio of 1.2–1.35 (yield ≈55%). Such conditions did not provide a medium free of side products, even if xylene decreased their formation. Compared to solvent‐free synthesis, conversion was lower with xylene. With solvent, higher temperatures were needed to reach the same yields. Supplementary heating compensated the reagent dissolution effect that slows down the kinetics of the ene‐reaction. The influence of reaction time at 220 °C with a MA/SME ratio of 1.2 in a 50% xylene medium was studied. A reaction time of 8–10 h provided a good compromise between ASA yield and side products.