两步碱法预处理对玉米秸秆组分及结构的影响

Effects of two-step alkaline pretreatment on components and structure of corn stover

针对乙酸对乙醇发酵的影响及其在预处理过程中的产生机制,采用氢氧化钠-氢氧化钙2步预处理的方法:第1步氢氧化钠预处理实现乙酰基的去除,从源头上将乙酸与"糖"分开;脱乙酰基后的玉米秸秆进一步采用氢氧化钙预处理,提高纤维素酶水解得率。采用红外光谱(FT-IR)、X射线衍射仪(XRD)和扫描电镜(SEM)对玉米秸秆纤维结构特性进行分析。研究结果表明,玉米秸秆经第1步氢氧化钠可实现乙酰基去除率和木聚糖残留率分别为95.2%和87.8%,纤维素基本不被降解。脱乙酰基玉米秸秆第2步氢氧化钙预处理正交试验优化条件为氢氧化钙用量0.100g/g玉米秸秆、温度90℃、时间36h,纤维素酶水解36h后的酶水解得率为85.1%,所得固体渣纤维素和半纤维素的回收率分别为92.1%和65.5%,木质素去除率为63.0%。2步碱法预处理后的玉米秸秆纤维表面出现大量的裂纹和裂片,纤维束间发生分离,纤维素的结晶指数由55.1%上升到60.6%,1245cm-1处的C-O基团伸展振动峰形明显减弱是由于乙酰基的去除,结合酶水解得率的提高也说明预处理达到提高纤维素酶对纤维素的可及度。

Aimed at the effects of acetic acid on ethanol fermentation and its generation mechanism during the pretreatment process,sodium hydroxide combined with calcium hydroxide on the compositions and enzymatic hydrolysis of corn stover were in-vestigated.Corn stover after the first-step NaOH pretreatment could realize the removal of acetyl groups and separate acetic acid from the sugars from the source.The deacetylated corn stover further pretreated by Ca（OH）2 could improve the enzymatic hy-drolysis yield.And the fiber structure characteristics of corn stover were analyzed by Fourier transform infrared spectrometry （FT-IR）,X-rays diffraction （XRD）and scanning electron microscope （SEM）.The results showed that the removal of acetyl groups and the retention ratio of xylan were 95.2% and 87.8%,respectively and cellulose was not degraded after corn stover was pretreated by the first-step pretreatment.The optimal conditions of the second-step pretreatment of deacetylated corn stover by using orthogonal experiment were that calcium hydroxide dosage 0.100 g/g（based on dry corn stover）,reaction temperature 90℃ and time 36 h.The corresponding enzymatic hydrolysis yield of 36 h was 85.1%.The obtained recovery yields of cellulose and hemicellulose in the solid residue were 92.1% and 65.5%,respectively and the lignin remove ratio was 63.0%.The fiber surface was rough and appeared a large number of cracks and slivers,separation occur between fiber bundles of corn stover after two-step alkaline pretreatment.The relative crystallization degree of corn stover increased from 55.1% to 60.6%,and the stretching vi-bration peak of C=O group at 1 245 cm-1 decreased significantly due to the removal of acetyl group.Combined with the increase of enzymatic yield,it also indicated that this two-step pretreatment could improve access of cellulose to cellulase.