Natural and low-cost deep eutectic solvent for soap removal from crude biodiesel using low stirring extraction system

Biodiesel is a sustainable, clean fuel that has drawn attention from academia and industrial sectors due to the rise in global energy demands. Biodiesel production is accompanied by impurities such as soap, glycerol, alcohol, and catalyst. Soap content, being one of the major impurities, must be removed from biodiesel to prevent engine deposit and fuel filter plugging. Purification of biodiesel is therefore a critical processing step that requires continuous improvement to meet international standards. In this study, ammonium-based DESs were used as the extractant for the first time in removing soap from palm oil-based biodiesel using a low stirring extraction system. The study investigated the effect of different DESs, DES:biodiesel molar ratio, stirring speed, and extraction time on the removal of soap. The results showed that ammonium salt-aqueous glycerol-based DES emerged as the best DES with the highest soap content removal from biodiesel. The extraction efficiency was found to be positively dependent on the DES:biodiesel ratio, extractant stirring speed, and extraction time. A combination of DES:biodiesel molar ratio of 3:1, 170-rpm extractant stirring speed, and 40-min extraction time in the low stirring extraction system can achieve the soap content in biodiesel to EN 14214 and ASTM D6751.