超低酸预处理结合酶解提高玉米秸秆糖化效率

Pretreatment by extremely low acid hydrolysis combed with enzymolysis improving saccharification efficiency of corn stalk

为提高纤维素酶解糖化的效率,该文采用超低浓度硫酸水解预处理废弃玉米秸秆。重点考察了不同酸浓度、反应温度、反应时间条件下超低浓度酸水解及后续酶解的总还原糖、葡萄糖及木糖的产率,详细叙述了总还原糖及各种单糖在酸水解及酶解过程中的转化规律,通过正交试验确定酸水解的最佳工况为酸浓度0.1%,反应温度160℃,反应时间55 min,搅拌180 r/min,固液比1∶10。酸水解后进行酶解(酶用量5%,pH值4.6,时间24 h,温度50℃)得到还原糖、葡萄糖、木糖产率分别为56.22%、16.97%、18.83%。通过红外光谱和纤维素分析仪对酸水解和酶解后的残渣进行分析可知,纤维素、半纤维素的转化率分别为88.52%、95.18%,进一步计算还原糖、葡萄糖、木糖的转化率为88.11%、44.86%、72.49%。该方法较大程度避免了还原糖在酸水解过程中的降解,保证了半纤维素还原糖的转化效率,进一步提高了总还原糖的产率,为超低酸水解在燃料乙醇领域提供了新的应用途径。

Corn straw is one of the most abundant agricultural and forest residues containing cellulose, hemicellulose, and lignin. About 2.24×108 tons of corn straw are produced per year in china, most of which is burned or lost in farmland, and only a small part is used as feed for livestock. Because corn straw is abundant in cellulose, it can be used as a substitute for grain to produce fuel-ethanol, which can be a significant contribution for relieving the crisis of resource and foodstuff shortage. The process of producing fuel-ethanol includes pretreatment, enzymatic hydrolysis, fermentation, and distillation. Cellulose, hemicellulose, and lignin in corn straw form stable polymers, which hardly dissolve in water, dilute acid, dilute alkali, and most organic solutions. Each component interrelates with all the others. Because of the complex configuration, hemicellulose and lignin will hinder the degradation of cellulose. To utilize the cellulose, corn straw must be pretreated. To improve the reduction of sugar yield in corn straw, the hydrolysis method of using extremely low sulfuric acid followed by enzymolysis is employed to treat corn stalk. To investigate the mechanism of reducing sugar conversion in acid hydrolysis and enzymolysis, the yield of totally reduced sugar, glucose and xylose was analyzed with acid hydrolysis followed by enzymolysis under different acid concentrations, temperatures and reaction times. Acid concentrations 0.1%, 160℃, 55 min, 180 r/min, solid-liquid ratio 1：10 was confirmed by orthogonal experiment. Through acid hydrolysis followed by enzymolysis （enzyme 5.0%, pH 4.6, 24 h, 50℃）, the yield of totally reduced sugar, glucose, and xylose was 56.22%, 16.97%and 18.83%, respectively. The concentration of totally reduced sugar, glucose, and xylose was 62.46, 18.85 and 20.92 g/L, respectively. After acid hydrolysis and enzymolysis treatment, the corn stalk component was analyzed by infrared spectral and the Van Soest methods. The conversion of cellulose and hemicellulose was 88.52% and 95.18%, respectively. The conversion of totally reduced sugar, glucose, and xylose was 88.11%, 44.86% and 72.49%, respectively. Extremely low acid pretreatment can hydrolyze hemicellulose into monosaccharides and degrade the crystalline structure of cellulose. The pretreated cellulose with high porosity can be hydrolyzed by cellulose efficiently. This method can avoid degradation of monosaccharides, improve reduced sugar yield and increase the conversion efficiency of corn straw cellulose.