Optimization of ionic liquid 1-ethyl-3-methylimidazolium acetate pretreatment of Napier grass combined with acetic acid and ferric chloride under microwave radiation by response surface methodology

Acidic aqueous ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate/acetic acid in combination with a metal salt (FeCl₃) pretreatment was investigated for the pretreatment of Napier grass. This research focused on the effects of the FeCl₃ concentration (20–100 mM), pretreatment time (10–190 min), and temperature (40–160 °C) during the pretreatment under microwave irradiation on the obtained total sugar yield after subsequent enzymatic hydrolysis. The optimum condition of these variables was determined by response surface methodology and compared with acidic aqueous IL pretreatment. The untreated and different pretreated NG samples were characterized using X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analyses. The effect of the type of anti-solvent (biomass regenerated solvent) on the obtained total reducing sugar yield by enhancing the cellulose content in the pretreated biomass was also studied. The results showed that an acidic aqueous IL could remove more lignin than the other pretreatments. The addition of FeCl₃ in the acidic aqueous IL pretreatment had a significant effect on the total reducing sugar yield.