γ-戊内酯/水体系下稀酸预处理对玉米秸秆酶解特性的影响

Structure and enzymatic hydrolysis of corn stover with dilute acid pretreatment in γ-valerolactone/water system

γ-戊内酯预处理可以打破纤维原料的抗降解屏障,改善底物的可降解性能。目前,有关戊内酯预处理对木质纤维原料水解特性和结构变化的研究较少。本试验在戊内酯/水体系下,采用硫酸和硫酸氢钠预处理玉米秸秆,研究了其对底物水解特性和结构的影响。结果表明,戊内酯/水体系能够脱除底物中的半纤维素和木质素。硫酸的催化效果优于硫酸氢钠,硫酸浓度分别为75和150 mmol/L时(120℃下进行预处理1 h),底物中纤维素相对含量从34.82%增至57.41%和72.57%,150 mmol/L硫酸预处理时半纤维素和木质素脱除率为92.0%和77.4%,纤维素酶(10 U/g底物)水解得率分别为52.4%和65.6%。对预处理前后玉米秸秆结构表征结果显示,戊内酯预处理后玉米秸秆纤维表面受到破坏,表面O/C明显增加,木质素和半纤维素被脱除,玉米秸秆结晶度增加。该试验表明戊内酯/水体系下稀硫酸预处理可高效溶出玉米秸秆中的半纤维素和木质素,提高纤维素酶水解效率,具有一定的应用前景。

Pretreatment is one of the most important steps in biomass utilization,but there is a lack of economical and effective technologies for pretreating the enzymatic conversion of lignocellulosic biomass.γ-valerolactone (GVL) has been recognized as a safe,sustainable organic solvent,which could be used in biomass pretreatment to disrupt the complex structure of lignocelluloses and improve the degradability of biomass.However,there was limited reports focusing on the enzymatic hydrolysis and structural changes of the γ-valerolactone/water system for pretreatment of biomass.In this work,the hydrolysis capacity and structure of γ-valerolactone/water pretreated corn stover were studied.The results showed that the catalysis of sulfuric acid was better than that of sodium bisulfate.When the concentrations of sulfuric acid were 75 mmol/L and 150 mmol/L (120 ℃,1 h),the content of cellulose increased from 34.82% to 57.41% and 72.57%,respectively,and the high delignification was obtained (62.7% and 77.4% of the lignin were removed,respectively).Nearly 52.4% and 65.6% of hydrolysis yields of corn stover were unexpectedly obtained after the hydrolysis by 10 U/g DM cellulases,respectively.Besides,the GVL pretreated Avicel had a lower hydrolysis yield (<16%) compared with unpretreated Avicel (26.7%),which might be caused by the transesterification of the GVL with the hydroxyl groups in cellulose.The scanning electron microscope (SEM) analysis showed that the fiber surface of the pretreated corn stalk was damaged,and the significant decrease of lignin and hemicelluloses related bands in the Fourier Transform infrared spectrometer (FT-IR) spectra indicated that the hemicelluloses and lignin were partially removed during the pretreatment.The X-ray diffraction (XRD) analysis results showed that the crystallinity of corn stover increased after the pretreatment,but the crystallinity of Avicel had no significant change before and after the pretreatment.The X-ray photoelectron spectroscopy (XPS) analysis showed that the O/C ratio increased from 0.35 to 0.55 and 0.67 after the pretreatment,suggesting that the lignin content of fiber surface decreased after the pretreatment,which benefited to the hydrolysis of cellulases.The results suggested that the dilute acid pretreatment in γ-valerolactone/water system removed lignin and hemicellulose from corn stover efficiently,and further improved the hydrolysis yield.It was concluded that this proposed method has a promising future for the biomass pretreatment.