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The effects of pre-treatment and refining of high free fatty acid oil on the oxidation stability of biodiesel

ABSTRACT Although non-edible oil feedstocks with high free fatty acid (FFA) are potential feedstocks for biodiesel production, their utilization may require refining or pre-treatment prior to the production of biodiesel by alkali catalyzed transesterification. In this study, the crude Jatropha curcas oil with 4.54% FFA was either refined (neutralized, deodorized, and fully refining) or pre-treated (acid esterifying and glycolysis) to lower the FFA to less than 1% prior to biodiesel production by homogeneous base catalyzed transesterification. The study revealed that the oxidation stability of the biodiesel varies significantly with the method of either refining or pre-treating the FFA in oil. It was further observed that the biodiesel from re-esterified oil presented the greatest stability, followed by the biodiesel from neutralized, deodorized, acid pre-treated, and fully refined oil in that order. Biodiesel produced from fully refined and acid esterified oil showed the poorest oxidation stability and fail to meet the minimum required induction time of 6 h and 3 h as recommended by the EN 14214 and ASTM D6751 standards, respectively. Both neutralized and re-esterified oil present superior biodiesel oxidation stability with oxidation induction time 8.18 h and 8.24 h, respectively. Although pre-treatment and refining process lowers the FFA in the oil to less than 1% and produces biodiesel with more than 96.5% fatty acid methyl ester content content, the addition of antioxidants in the biodiesel from deodorized, acid esterified, and fully refined oil is inevitable due to poor oxidation stability of the produced biodiesel.