In this study, the free fatty acids (FFA) content in acidic crude palm oil (ACPO) was converted to fatty acid methyl esters (FAME) using a choline chloride based deep eutectic solvent (ChCl-DES) for the first time. This DES is composed of a mixture of a hydrogen bond donor (i.e. p-toluenesulfonic acid monohydrate) and a salt (i.e. choline chloride). The pre-treatment esterification stage involved the use of ChCl-DES. A dosage of 0.75 mass ratio of ChCl-DES to ACPO resulted in reducing the FFA of ACPO from 9.00% to less than 1%. The molar ratio of methanol to oil was 10:1 (methanol to oil), at a temperature of 60 C and within 30 min reaction time. Three recycling runs of ChCl-DES were achieved without significant loss in its activity. The yield of the final product after the alkaline transesterification was 92 wt% with 0.07% FFA and FAME content 96 mol%. All other properties have met the international standard specifications for biodiesel quality. The ChCl-DES can be used as a pre-treatment catalyst for a wide range of waste and acidic oils.
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