Application of acidic ionic liquids for the treatment of acidic low grade palm oil for biodiesel production

Employing low quality feedstocks for biodiesel production can present cost reduction opportunities due to its wide availability and cost effectiveness. However, most low quality feedstocks have high free fatty acid (FFA) content which is not feasible for biodiesel production through direct transesterification due to soap formation. Thus, a pre-treatment step through FFA esterification could reduce the FFA content while simultaneously yielding fatty acid methyl esters (FAME). In this study, the catalytic activity of ten ionic liquids (ILs) were screened for the esterification of FFA in acidic crude palm oil (ACPO). 1‑butyl‑3-methylimidazolium hydrogen sulfate as IL exhibited the highest catalytic activity and was further investigated to determine the optimum operating parameters such as IL dosage, molar ratio, reaction temperature and time. Single factor optimization was employed for the laboratory scale batch esterification reaction. The FFA content was reduced from 10.77% to less than 1% using the following optimum conditions: 4% IL to oil, molar ratio of 10:1 (methanol to oil), 120 min reaction time and 60 °C reaction temperature. Under optimum conditions, the IL can be recycled five times with minimal loss in catalytic activity, highlighting its feasibility as an industrial catalyst for esterification of acidic oils and fats.