Study On Treatment Of Hemicellulose From Corncobs By Steam Explosion

Recently, the human being concerns the exploitation of low-cost, reborn energy, with the oil, coal, natural gas gradual dry up. Plants fiber is a natural, renewable resource. Lots of countries want to translate plants fiber into the energy and chemical products which people need. China is a big agricultural country and has rich crop straw resources. Successful performance of rational development and comprehensive utilization work for crop straws in China will be positive significance. Not only for the improvement of agricultural ecological environment, increasing of resource utilization level, but also for realization of pluralistic energy resources, as well as safetyguard of national energy safety and reduction of environmental pollution.Corncob is a kind of cheap renewable lignocellulosic resource in China, annual output of corncob can reach to more than 2000 Million tons. However, few of them were used as fIeed and chemical industrial product, and most of them were burnt. The structure of corncob was complex, cellulose and hemicellulose were bounding by lignin, hemicellulose covalent binding with lignin, cellulose has high orderd crystal structure, all of that made corncob hard to use.The steam explosion is a treatment technology which is used to translate plants fiber into the energy and chemical products that people need. The research subject of this work was taken corncob as raw material, focused on steam explosion process and the optimized conditions of the corncob hemicellulose separation. The advanced analytic techniques including SEM, X-ray diffraction spectrum, IR spectrum and UV spectrum were applied to investigate the effects of steam explosion on major components, appearance and structure of corncob. On this basis, the main influencing factors of steam explosion technology were investigated by single factor experiment, and steam explosion process conditions were optimized by response surface method. Besides, In order to improve the corncob hemicellulose separation efficiency, the technology of repeated steam explosion, water prepreg, high temperature and steam explosion united treatment on corncob hemicellulose were also discussed.The main results of this work can be summarized as follows:(1) The objective of this study is to evaluate the effects on the corncobs treated by steam explosion.The main composition, crystallinity and enzymatic hydrolysis of the lignocellulosic residues were studied. The corncobs were firstly steamed at 1.5MPa for 60s, 120s, 180s, 240s, 300s, respectively, and then exploded. The results showed that no significant differences in the content of cellulose and lignin were observed during the various steam explosion pretreatments, while the content of hemicelluloses was found to be decreased obviously. The SEM indicated that the microstrueture of corncobs presented rupture after steam explosion. The crystal structure of corncob after explosion treatment was analyzed through wide angle X-ray diffraction(XRD), and crystallinity index and crystallite size of fibers were calculated according to the Gauss theory and Scherrer equation. The results showed that treated fibers still showed the characteristics of cellulose I, steam explosion treatment increased the crystallinity index of corncob fibers firstly, and then as the intensity of treatment increased, crystallinity index fell again, but still higher than that of corncob raw fibers.(2) The effect of steam explosion pressure and dimensional pressure time on the degradation rate of corncob hemicellulose, cellulose and lignin was studied by single factor experiment and response surface methodology. Three model equations for steam explosion pressure and dimensional pressure time on the degradation rate were built. Based on the three models and SAS9.0 statistical software, the basic areas were defined for cellulose without degradation: steam explosion pressure X₁<2.0MPa and dimensional pressure time X₂<155.7s; and found the range with the greatest degradation rate of hemicellulose condition: steam explosion pressure X₁=1.6MPa, dimensional pressure time X₂=113s. In the process condition, the degradation rate of hemicellulose was 44.8 %, the degradation rate of lignin was 18.7 %, obtained results in good agreement with the model prediction, indicating that the model is reasonable and effective. Under this condition, the field of TRS, DRS, Xylan, DP, Monosaccharides was 42.3%, 9.5%, 39.4%, 4.5, 1.9, and Furfural was 0.44%. Monosaccharides were mainly xylose with less amounts of arabinose and glucose.(3) Under the condition, steam explosion pressure (1.6MPa) and dimensional pressure time (113s), cellulose was almost no degraded. Under this condition, corncob was processed again. The degradation rate of hemicellulose was 58.3%, the degradation rate of cellulose was 1.2%, the degradation rate of lignin was 22.4%. Under the condition, the yield of total sugar (TRS) was 53.2%, the yield of reducing sugar (DRS) was 39.3%, the dissolution rate of xylan (XS) was 26.1%, the average degree of polymerization (DP) was 1.4, the yield of monosaccharides was 20.3%, the yield of furfural was 6.8%. The dissolution rate of xylan was decreased by 13.3%, average degree of polymerization was decreased, but a considerable amount of furfural was producted.(4) The steam explosion-cooking process conditions was studied by single factor and orthogonal experiment. The results showed that different importance factors influence of TRS dissolution rate:cooking temperature>liquid-solid ratio>cooking time. The optimum experiment conditions for xylan dissolution rate were obtained with the cooking timing 120min, solid to liquid ratio 1:15 and cooking temperature 100℃.Under the condition, the degradation rate of hemicellulose was 86.7%, the degradation rate of cellulose was 0%, the degradation rate of lignin was 28.3%, the yield of total sugar (TRS) was 80.2%, the yield of reducing sugar (DRS) was38.9%, the dissolution rate of xylan (XS) was 73.4%, the average degree of polymerization (DP) was 2.1, the yield of monosaccharides was 6.4%, the yield of furfural was 0.44%. The dissolution rate of xylan was increased by 34.0%, average degree of polymerization was decreased.(5) The prepreg method using water-steam explosion process conditions was studied by single factor and orthogonal experiment. The results showed that different importance factors influence of TRS dissolution rate: liquid-solid ratio>prepreg time>prepreg temperature. The optimum experiment conditions for TRS dissolution rate were obtained with the prepreg timing: 4h, solid to liquid ratio: 1:4 and prepreg temperature: room temperature.Under the condition, the degradation rate of hemicellulose was 84.2%, the degradation rate of cellulose was 1.8%, the degradation rate of lignin was 32.7%, the yield of total sugar (TRS) was 78.6%, the yield of reducing sugar (DRS) was 3.0%, the dissolution rate of xylan (XS) was 75.4%, the average degree of polymerization (DP) was 7.2, the yield of monosaccharides was 3.0%, the yield of furfural was 0.18%.The dissolution rate of xylan was increased by 36.0%, average degree of polymerization was increased.