Free fatty acids esterification for biodiesel production using self-synthesized macroporous cation exchange resin as solid acid catalyst

Using high free fatty acids (FFAs) contents oil as the raw material for biodiesel production can reduce the production cost and make fully use of the bio-oil resources. Macroporous cation exchange resins contain numerous acid sites to catalyze heterogeneous esterification reactions to reduce the FFAs contents and prevent the saponification reaction. This study focuses on the synthesis and performance tests of the macroporous resin catalysts and its water deactivation mechanism. Self-synthesized macroporous cation exchange resins have a surface area of 185 m2 g−1 with an average pore diameter of 9.7 nm and the ion exchange capacity is 3.37 ± 0.11 mmol g−1. Owing to their pore structure, macroporous resin performs better than gel-type resin in low methanol concentration or high FFAs contents, but they show physical instability in reusability tests. The FFAs conversion reaches 97.8% (substrate oil with acid value of 64.9 mg KOH/g) under 100 °C and a methanol/FFAs molar ratio of 15:1 with 10 wt% catalyst loading. Water that originally exists in oil or that is produced in the reaction deactivates differently on the activity of the resin, but this deactivation can be decreased by increasing the reaction temperature. In this study, a linear relationship between original water content and esterified FFAs was identified and differences in deactivation models were investigated.