Abstract: 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 of 45mL, the straw particle of 3 g, the hydrolysis temperature of 210 ℃, the hydrolysis time of 10 min 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 hemicellulose 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.

Key words: lignocellulose, dilute acid hydrolysis, lignin, rich lignin layer