秸秆中木质素对其超低酸水解过程的影响

The Effect of Lignin in Straw on Hydrolysis Process by Extremely-low Acid

以湖北稻草秸秆为研究对象,研究了超低酸水解木质纤维素的适宜条件,测定了适宜条件下的超低酸法水解15种不同种类秸秆的纤维素及半纤维素的转化率、还原糖得率及结晶度的变化。实验结果表明:秸秆投料量3 g、硫酸投料量45 mL(硫酸质量分数0.05%)、搅拌转速500 r/min、反应温度210℃、反应时间10 min为适宜的水解条件。对15种不同种类秸秆的水解结果统计得到,随着秸秆中木质素含量的增大,纤维素和半纤维素的转化率都逐渐降低,还原糖得率逐渐降低;通过SEM和X衍射分析水解前后的木质纤维素结构,得到了木质素影响水解过程的方式:1)木质素含量越大,纤维素的结晶度越大,纤维素的非晶化越困难,从而影响了纤维素的水解;2)原木质素不溶于反应体系且在酸性条件下相对稳定,富木质素层的木质素阻碍反应物与产物扩散,使富木质素层内的纤维素、半纤维素水解速率降低;3)木质素含量越高,木质纤维素的富木质素层越厚、强度越大,水解时难以从颗粒表面脱落,进一步降低水解速率。

Taking rice straw （Hubei province） as the research object, the optimal condition of straw hydrolysis was investigated. The conversion rate of cellulose and hemicellulose, reducing sugar concentrations and yields, crystallinity of cellulose were determined after the extremely low acid （ acid concentration below to 0.1 wt% ） hydrolysis of 15 kinds of biomass straw under optimal hydrolysis conditions. The results indicated that the condition of the rotation speed of 500 r/min, the sulfuric acid volume of45mL, the straw particle of 3 g, the hydrolysis temperature of 210 ℃, the hydrolysis time of 10 rain and sulfuric acid concentration of 0.05% wt were determined as the optimal hydrolysis conditions. By studying the hydrolysis of the 15 kinds of biomass straw, it was found that with the lignin content increasing, cellulose and hemicellulose conversion rate decreased. This led to the decline of reducing sugar yield. By SEM, X-ray diffraction and composition analysis, the way that lignin affecting the lignocellulose hydrolysis was showed as follows： 1 ） the higher the lignin content, the higher the crystallinity of cellulose, the more difficult for de-crystallization of cellulose, thus the cellulose hydrolysis was confined ; 2） the original lignin was not soluble in the reaction system and was relatively stable under acidic conditions. The lignin in rich lignin layer interfered with the reactant and product diffusion. It slowed down the hydrolysis rate of cellulose and hemicellnlose in rich lignin layer; 3 ） the higher the lignin content, the thicker and the harder the rich lignin layer in lignocellulose, it was difficult for lignin to shed from solid surface and the hydrolysis rate decreased.