Biodiesel production through electrolysis in the presence of choline chloride-based deep eutectic solvent: Optimization by response surface methodology

In this study, a novel catalyst-free electrolysis method was developed that uses deep eutectic solvents (DESs) as both a supporting electrolyte and a cosolvent for biodiesel synthesis. Various choline chloride–based DESs for biodiesel production were prepared and tested. Among the DESs that were synthesized, DES-2 (choline-chloride-to-ethylene-glycol molar ratio of 1:2) exhibited the highest efficiency for electrolysis-based biodiesel synthesis. The DES-2-assisted electrolysis was then optimized through the application of a response surface methodology to maximize biodiesel yield. The maximal biodiesel yield of 94.71 % was obtained through electrolysis when an electrolysis voltage of 22.06 V, a DES concentration of 7.91 % (w/w), a water amount of 1.44 % (w/w), a methanol-to-oil molar ratio of 25.09:1, and a reaction time of 2 h were applied at room temperature. Notably, DES-2 could be reused for four cycles to achieve a biodiesel yield of > 80 % biodiesel. The properties of the synthesized biodiesel were verified as meeting international standards. This study suggests that electrolysis involving the use of DESs as a supporting electrolyte and a cosolvent is an eco-friendly, cost-effective, and efficient method for biodiesel synthesis.