Production of high quality biodiesel from waste acid oil obtained during edible oil refining using ion-exchange resin catalysts

This study was aimed at the continuous production of high quality biodiesel fuel, which fully satisfies international specifications, from waste acid oil with free fatty acids (FFA) content of >95 wt%. First, the effect of water on the esterification of FFA with the cation-exchange resin catalyst was discussed. Then, a simple method for pretreating the resin without drying, only supplying alcohol of 1.5 cm3/g (wet resin), was proposed. Second, the operating conditions for the continuous esterification of FFA to biodiesel were established. The complete conversion of FFA was achieved at the mole ratio of alcohol:fatty acid residue of 2:1 and sufficient residence time. Subsequent processing with an anion-exchange resin catalyst for the transesterification of triglycerides in the oil was necessary to produce high quality biodiesel. The biodiesel productivity with acid oil was about 8.5 times higher than that with triglyceride-rich oil. This process demonstrated a commercially feasible route to high quality biodiesel.