Deep eutectic solvent (DES) assisted deacidification of acidic oil and retaining catalyst activity: Variables optimization and catalyst characterization

Deacidification is a critical step in alkali catalyzed transestrification of acidic oil for biodiesel production. In this work, optimization of the process variables and insights into the mechanisms of deep eutectic solvent (DES) assistance of deacidification of acidic oil catalyzed by Amberlyst 15 were investigated. Specifically, response surface methodology (RSM) and Box-Behnken Design (BBD) were employed to optimize the three process variables, namely temperature, catalysis loading, and molar ratio of methanol to oleic acid . Furthermore, the catalysts before and after used with and without DES assistance were characterized by FTIR and XRD in order to elucidate the chemical mechanisms involved in the process. Results showed that maximum deacidification rate (DR) of 98.02% was achieved in the deacidification process assisted by DES at the optimal process conditions (temperature 72.02ºC, catalyst loading 5.05 wt%, and methanol to oleic acid molar ratio 33.02), compared to 89.68% of the control (without DES assistance). Data analysis and verification results further confirmed the suitability of BBD and RSM methods in optimizing the process. More interestingly, dramatic higher catalytic activity (DR of 76.33% vs 64.16%) of Amberlyst 15 with DES assistance compared to that of the control after 4 cycles was observed. Finally, FTIR spectra confirmed that less water absorbed onto the surface of Amberlyst 15 with DES assistance was the major reason for higher DR and better catalyst reusability in comparison with the control.