Hydrolysis Mechanism And Reaction Kinetics Of Rice Straw Under Extremely Low Acid

With the development and progress of modern society, the living standards of humanbeing are greatly improved. However, the contradiction between the requirements formaterial life and spiritual life and the unsatisfying for these requirements become graduallyprominent. Energy shortage and environmental pollution are the main factors for thecontradiction above. Therefore, how to find a new kind of energy to replace fossil resourceto resolve the contradiction has become the focus all over the world. Biomass energy hasthree great advantages on the source, the potential conversion efficiency and environmentalpollution. As a traditional agricultural country, China has a huge space for thedevelopment of biomass energy. The lignocelluloses containing hemicelluloses andcellulose can be hydrolyzed into fermentable sugars which can be further fermented tomanufacture fuel ethanol. The fuel ethanol is an important part of biomass energy. In thisstudy, the hydrolysis of hemicellulose and cellulose in rice straw was studied under hightemperature and extremely low acid, which provide theoretical basis for the industrialproduction of fuel ethanol. The main results were as following.1) Under the sulfuric acid concentration of0.05%, the optimal solid concentration andthe optimal stirring speed of the high temperature and extremely low acid hydrolysis ofrice straw was0.500g/mL and700r/min, respectively. On this basis, there was onesingle-peak on the hydrolysis trend of rice straw at160℃. At the temperature170℃~200℃, there existed double-peak on the hydrolysis trend. When the temperaturereached to210℃, the single-peak trend reappeared. The main reason was that cellulose andhemicellulose in rice straw had it’s own hydrolysis peak and their hydrolysis peakssuperposed and separated as temperature increased, which mainly in the single-peak anddouble-peak on the rice straw hydrolysis trend.2) In semi-continuous tubular reactor, the hydrolysis of sawdust in ethanol/watermixture was studied as well. The results indicated that under suitable conditions of ethanolconcentration and hydrolysis temperature, the reducing sugar concentration also showeddouble-peak as the hydrolysis proceeded. It could be predicted that the double-peak phenomenon has certain universality, and had nothing to do with the type oflignocelluloses.3) Through the analysis of the liquid hydrolyzates of rice straw, it was found that themain products of rice straw hydrolysis were cellotriose, cellobiose, glucose, xylose,pyruvaldehyde. Under the same conditions, reducing sugar concentrations with thehydrolysis time were consistent with the hydrolysis trends of hemicellulose and cellulosehydrolysis in rice straw law. The byproducts of rice straw hydrolysis were mainly furfural,ketones, organic acids, etc.4) Through the solid residues of rice straw hydrolysis for straw, most of thehemicellulose was hydrolyzed, and the structure of lignin was damaged to a certain extent.The cellulose was partly hydrolyzed. Although the degree of polymerization of thecellulose greatly reduced, the crystallinity was relatively high.5) Based on the extremely low acid hydrolysis kinetics of the hemicellulose andcellulose hydrolysis in rice straw (pre-exponential factor and activation energy), thelumped kinetic model for hemicellulose and cellulose as the whole was set up. Bycomparison of calculated and experimental values, there were many differences at thedifferent stages of rice straw hydrolysis, which indicated that the model couldn’t reflect thetrue law of the hydrolysis of the hemicellulose and cellulose in the lignocelluloses. Theeffect of lignin on hemicellulose and cellulose hydrolysis couldn’t be ignored.