Ultrasound-ionic liquid enhanced enzymatic and acid hydrolysis of biomass cellulose

The purpose of this paper was to investigate the effect of ultrasound-ionic liquid (IL) pretreatment on the enzymatic and acid hydrolysis of the sugarcane bagasse and wheat straw. The lignocellulosic biomass was dissociated in ILs ([Bmim]Cl and [Bmim]AOC) aided by ultrasound waves. Sonication was performed at different frequencies (20, 28, 35, 40, and 50   kHz), a power of 100   W, a time of 30   min and a temperature of 80   °C. The changes in the structure and crystallinity of the cellulose were studied by Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The amounts of the total reducing sugars, glucose, cellobiose, xylose and arabinose in the hydrolysates were determined. The results of FT-IR, XRD and TGA revealed that the structure of cellulose of both biomass samples remained intact after the pretreatment, but the crystallinity decreased. The enzymatic and acid hydrolysis of the biomass samples pretreated with the ultrasound-IL result in higher yields of the reducing sugars compared with the IL-pretreated sample. Enzymatic hydrolysis of bagasse and wheat straw pretreated with [Bmim]Cl-ultrasound resulted in maximal yields of glucose at 20   kHz (40.32% and 53.17%) and acid hydrolysis resulted in maximal yields of glucose at 40   kHz (33.32% and 48.07%). Enzymatic hydrolysis of bagasse and wheat straw pretreated with [Bmim]OAc-ultrasound show maximal yields of glucose at 28   kHz and acid hydrolysis at 50   kHz. Combination of ultrasound with [Bmim]OAc is more effective than [Bmim]Cl in terms of the yields of reducing sugar.