No abstract

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 50kHz), a power of 100W, a time of 30min 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 20kHz (40.32% and 53.17%) and acid hydrolysis resulted in maximal yields of glucose at 40kHz (33.32% and 48.07%). Enzymatic hydrolysis of bagasse and wheat straw pretreated with [Bmim]OAc-ultrasound show maximal yields of glucose at 28kHz and acid hydrolysis at 50kHz. Combination of ultrasound with [Bmim]OAc is more effective than [Bmim]Cl in terms of the yields of reducing sugar.

Low‐cost bagasse and microcrystalline cellulose were used as the raw materials to prepare solid acid catalysts via incomplete carbonization and sulphonation. The solid acid synthesized from microcrystalline cellulose (C‐SO3H) exhibited better catalytic performance than that synthesized from bagasse. C‐SO3H was characterized by various techniques to study the reaction conditions of the catalytic transformation from glucose and fructose to 5‐hydroxymethylfurfural (5‐HMF). The conversion of glucose was 73.29 ± 0.74 %, and the conversion of fructose reached a maximum of 98.85 ± 0.01 %. The selectivity and yield of 5‐HMF reached maxima of 65.04 ± 0.28 % and 64.29 ± 0.27 %, respectively. Using C‐SO3H as the catalyst, the conversion of glucose followed second‐order kinetics at various temperatures, while the conversion of fructose followed first‐order kinetics. The activation energies of the glucose and fructose transformations were 73.75 and 51.87 kJ · mol−1, respectively.