Studies On Pretreatment Of Wheat Straw By Glycerol

Lignocellulosic materials are the organic compounds with virtues of largest distributing and abundant contents in nature. However, these materials have not been utilized effectively; therefore, it seems to have great significance to study how to effectively utilize these lignocellulosic materials. In this paper, the optimization of the pretreatment-conditions of wheat straw by glycerol was investigated. Meanwhile, the lignin structure of wheat straw and the effect of non-ionic surfactant on the hydrolysis of lignocellulosic materials were also investigated.After cooking in glycerol-water solution, the enzymatic hydrolysis-characteristics of wheat straw can be improved. With preliminary optimization conditions, including the factors such as glycerol concentration, cooking time, cooking temperature and the ratio of the glycerol solution and wheat straw, it was found that the glycerol solution of 70% pretreated wheat straw carried out at 230℃for 1 h with the ratio of the glycerol solution and wheat straw was 20.And after pretreatment, the materials had high cellulose recovery(92%) and removal of lignin(72%). Meanwhile, the cellulose conversion of the pretreated material was up to 41.3%. By comparing with SEM photographs and infrared spectroscopy of the wheat straw and the pretreated wheat, it was found that the complex structure of wheat straw was destroyed including removal some lignin and hemicellulose after glycerol treatment, improved the accessibility of cellulose thus to cellulose enzymes and enhanced the conversion of cellulose in materials.The chemical structure of the lignin separated from wheat straw after being cooked with glycerol solution, was analyzed in this paper. Meanwhile, it was compared with the wheat straw lignin. These two lignins of wheat straw were both composed of three basic units, which were guaiacyl unit, syringyl unit and hydroxyphenyl unit, where the guaiacyl unit was the main unit. The formation of new phenolic hydroxyl and alcohol hydroxyl during the wheat Straw cooking process, caused by the cleavage of aryl-ether linkages which connected phenylpropanoid monomers, resulted in the UV absorption peak of glycerol lignin moved to the long-wave compare with dioxane lignin. It was known from the gel chromatography of dioxane and glycerol lignin that, the number average molecular weight, weight average molecular weight and polydispersity of these two kinds of lignin were 3172 and 2241,6601 and 2361,2.08 and 1.05, respectively. The relative molecular weight of glycerol lignin was smaller and more uniform than dioxane lignin, so glycerol lignin will have a wider use because of the narrow molecular weight distribution.It had been shown that addition of non-ionic surfactant significantly increased the enzymatic conversion of cellulose into soluble sugars. With non-ionic surfactants added, amount of glucose released from the material pretreated by glycerol was increased by 19.3% (Tween80) and 21.2%(PEG6000). And after optimization of the concentration of non-ionic surfactant and the time when join in enzyme system, it was found that we should add cellulase and non-ionic surfactant at the same time for shorter time of enzymatic hydrolysis, and the concentration of non-ionic surfactant was 0.05g(gDM)"1.