| The liquefaction of biomass is an effective way to utilize biomass and lessen the immense pressure of energy shortage. By liquefying wheat straw with effective reagent, we can not only utilize agriculture residues, but produce many useful chemicals as well. The liquefaction method using ethylene carbonate (EC) as the liquefied reagent has the rapidest liquefaction speed and the highest yield. Unfortunately, this method has not been widely applied to practice mainly because people have not completely understood the liquefaction mechanism and the liquefied products?properties. The thesis has researched into these two problems. The liquefaction mechanism has been studied from three aspects. At first, the optimum conditions of liquefaction with EC are determined through uniformity design. The result is as follows: the reactive temperature is 160 C the reactive time ranges from 30mm to 75mm EC/WS equals to 5 H2S04/EC equals to 0.0325. Secondly, factors affecting liquefaction have been studied extensively. The following conclusions can be safely drawn from such experiments. (1) Reactive temperature and quantity of liquefied reagent are the most important among all related factors. (2) Different materials behave valiantly during liquefaction due to their differences in lignin structure. For example, the liquefaction speed of softwood is lower than that of hardwood and wheat straw. (3) EG produced by EC can facilitate the liquefaction of lignin, thus accelerate the overall liquefaction procedure. At last, the liquefied residue has been analyzed and it is shown that they are mainly composed of ash, but not carbohydrate. The properties of liquefied products have also been probed in the thesis. As we know, purified liquefied products can be obtained through centrifugal separating, vaporizing, condensing and vacuum desiccating. These products have a number of distinct properties. First, the hydroxyl number is near to that of PFG#4~ Second, though they can hardly be dissolved in any single organic solvent, their solubility in a mixed solvent made up of dioxane and water (v/v=4:1) is considerably high, nearly 100%. Third, carbohydrate can not be hydrolyzed by acid after liquefaction. To understand fi.illy liquefaction mechanism and the properties of liquefied products, we studied on three other materials that related to wheat straw in compositions: lignin, cellulose and carbohydrate. Liquefying them respectively, we found that the liquefaction temperature of lignin is lower than that of cellulose and carbohydrate, but the liquefaction rate of cellulose and carbohydrate are higher than that of lignin at high temperature. And there are some residues after liquefying lignin because of the high content of ash, in contrast, both cellulose and carbohydrate can be completely liquefied. In respect to the liquefied products, It is found that the crystalline part of cellulose disappears, fi.irthermore, its molecular structure is changed, which means that the pyranose ring disappears and ester bond is produced; On the contrary, as to lignin, the ester bond isn抰 produced and the aromatic ring remains. In a word, through research on the liquefaction mechanism and the properties of liquefied products of wheat straw, the thesis objects to provide some theoretical principles for developing liquefaction technology and utilizing liquefied products of wheat straw...
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