Use of acid cation-exchange resin for catalytic conversion of soybean acid oil to biodiesel

Soybean acid oil (SAO), a by-product of soybean oil refining, contains large amounts of free fatty acids (FFAs). In the present work, the esterification of FFAs in SAO with methanol over four strong acid cation-exchange resins to synthesize biodiesel was studied in a batch reactor. The effects of external and internal diffusion, catalyst amount, methanol/FFAs ratio, and temperature in the esterification over the optimal resin (LS-50) were assessed. After 140 min, the esterification reached equilibrium, and high FFAs conversion (91.02 %) was obtained under the optimized conditions. Based on the obtained data, the reaction kinetics was studied, and the kinetics of the optimized FFAs esterification catalyzed by LS-50 fitted well to the pseudo-homogeneous (P–H) kinetic model. LS-50 could be successfully reused for at least 8 cycles, and its deactivation mechanism was also investigated. The fuel property parameters of the synthesized biodiesel conformed to the standards for biodiesel in the US (ASTM D 6751-03).