Synergetic effect of sustainable protic deep eutectic solvent and sonochemical extractor for extractive transesterification of biodiesel from Chlorella salina

Abstract

Sustainable one-pot biodiesel production by sonochemical extractive transesterification (SET) in Chlorella salina was achieved with protic deep eutectic solvents (pDES). Six pDES were prepared with quaternary ammonium salts as hydrogen bond acceptors and organic acids as hydrogen bond donors. The eutectic mixture formed with choline chloride and lactic acid having moderate density and viscosity yields maximum FAME (90.8 % (w/w)) than the counterparts with higher density. Response surface methodology-based optimization was carried out and 25 % (w/v) of biomass load, 62.5 % (v/v) of DES/methanol ratio, 338 K of ultrasound temperature and 25 min of ultrasound time were identified as optimal conditions for biodiesel production. The resulting biodiesel was found to have an acceptable density (870 g cm−3), viscosity (4.24 mm2/s), acid value (0.31) and iodine index (62 mg/kg biodiesel) as per the EN 14214 standard. Further characterization by FTIR and GC–MS reveals that 90 % of methyl esters have lower carbon chains (<19) resulting in superior quality biodiesel. The activation energy for first order kinetics in the extractive transesterification process was observed as 28.304 KJ/mol. The positive values of Gibb’s free energy and Enthalpy and the negative value of Entropy indicate the process to be non-spontaneous, endothermic and endergonic in nature.