| The rapid development of global economy and the society, the rapid expansion of population and the improvement of people's living standards will be resulted in the slowly exhausting of key mineral resources such as oil in the middle of this century, so it is the task to be solved that developing clean renewable energy instead of fossil fuels. It is of great significance that using the lignocellulosic materials such as rich resource and low cost crops straw as raw material to product the fuel ethanol, because of compact structure and high degree of crystallinity, the lignocellulosic materials is difficult to efficient conversion. It is need to take effective pretreatment before alcohol fermentation to improve the efficiency of the subsequent enzyme solution,y-ray irradiation pretreatment has the advantages of easy operation, non-pollution and good effect. It can greatly improve the efficiency of enzymatic hydrolysis by damaging the structure of lignocellulosic materials, slowing the degree of crystallinity and increasing the enzyme accessibility. Rape is one of the most important oil crops in China, and it accounts for more than 40% of the total amount of vegetable oil per year. It's flower can be used for viewing, and it's straw also has many uses. By enzyme hydrolysis of rapeseed straw after irradiating with different doses (OkGy?400kGy? 600kGy,800kGy,1000kGy? 1200kGy), the paper established the technical system of enzymatic hydrolysis and revealed the mechanism by investigating the effects of irradiation dose on the granule properties, group change, molecular structure, molecular weight and molecular weight distribution and the thermal cracking performance so that some valuable data could be provided and laid a theoretical foundation for irradiation technology application in fuel ethanol production using lignocellulosic materials. Results were followed as:(1) The degradation rule of cellulose, hemicellulose and lignin in rapeseed straw with different irradiation doses (0kGy?400kGy? 600kGy?800kGy?1000kGy? 1200kGy) was investigated. It was found that the degradation rate of three main components increased with the increase irradiation doses. At a dose of 1200kGy, the degradation of cellulose, hemicellulose and lignin was 42.57%?69.06% and 4.99%, respectively, it was suggested that the effect of irradiation on the degradation of cellulose and hemicellulose was better, while the lignin has a low sensitivity to irradiation. It was found that irradiation and enzyme had good synergistic effect when enzymatic hydrolysed after irradiation, and the higher the irradiation dose, the better the synergistic effect of the two. After enzymatic hydrolysis of unirradiated rapeseed straw, the degradation of cellulose, hemicellulose and lignin was 12.81%?5.08% and 4.45%, respectively. The degradation rate of the three major components after enzymatic hydrolysis was gradually increased with the increase of irradiation dose. At a dose of 1200 kGy, the degradation of cellulose, hemicellulose and lignin after enzymatic hydrolysis was 79.21%?75.59% and 23.87%, respectively, which was apparently higher than that of single irradiation and single enzymatic hydrolysis. Meanwhile, the enzymatic hydrolysis yield increase with the increase of irradiation dose, and species and contents of sugar compounds were increased.(2) By adopting GC-MS, the number of fatty acids, aromatics and furans were 32, 17 and 5, respectively, which detecting from ethyl acetate fraction in water extract of straw and the species and contents of the products showed different rules with different irradiation doses. There were 22 species of fatty acids in the unirradiated samples, and the content of it was 19.99%, when the irradiation dose was 400 to 1000kGy, the species and contents of fatty acids were changed little. When the irradiation dose reached up to 1200kGy, the type of fatty acids reduced to 14, and the content decreased significantly, which was only 6.23%. There were only 5 species of aromatic compounds in the non irradiated samples, and the total relative content was also very low, only 0.75%. the species and contents of aromatic compounds were obviously increased after irradiation, and the highest species of it was in samples of 1000kGy. while the highest contents of it was in 800kGy irradiated samples. The furan compounds were detected only when the dose reached 1000kGy, and the types of it was different in samples with different irradiation dose.(3) The response surface methodology(Design-Expert8.05b) and center rotation combination design were employed to optimize the process conditions of sodium hydroxide with 400kGy irradiated straw. The optimal pretreatment conditions were determined as follows:sodium hydroxide concentration 2.38%, reaction temperature 100?, reaction time 0.5h. The predicted value of the total reducing sugar was 524.93mg/g, which was in agreement with the experimental value(528.51 mg/g). It was indicated that this model could be use to analyze and predict the total reducing sugar after enzymatic hydrolysis for irradiation and sodium hydroxide pretreated rapeseed straw.(4) The kinetic model about the enzymatic hydrolysis of rapeseed straw with different pretreatment (400kGy irradiated,600kGy irradiated,600kGy irradiated and acid pretreatment,400kGy irradiated and alkali pretreatment) was established, and it was verified that the theoretical value was identical to the experimental value. So it was indicated that this model could describe well the enzymatic hydrolysis process of rapeseed straw after different pretreatment and could laid a good experimental foundation for process engineering of enzymatic hydrolysis of rapeseed straw after different pretreatment.(5) We investigated changes in the physical and chemical properties of rapeseed straw after pretreatment with different doses of irradiation by using SEM, MS2000, XRD, FT-IR, raman spectrometer, ESR, NMR, GPC, elemental analyser and thermogravimetric analyzer and so on. The properties of rapeseed straw were analyzed comprehensively, and the degradation mechanism was preliminarily clarified for irradiated rapeseed straw. It was confirmed that the morphology surface damage and the specific surface area increased, and the particle size, the degree of crystallinity and the grain size decreased with the increase of irradiation dose, and the concentration of free radicals increased. The relative average molecular weight or the average degree of polymerization reduced after irradiation, the molecular weight distribution narrowed down. With the increasing of doses, the content of element O in irradiated rapeseed straw increased slightly, the temperature with the maximum reaction rate in the process of thermolysis reduced, so it was suggested that the reactivity increased. Otherwise, the heat absorption capacity and exothermic ability reduced, suggested that the integrity of rapeseed straw was damaged, and the chemical bond was interrupted.(6) The physical and chemical properties of rapeseed straw were investigated after enzymatic hydrolysis of 96h with different doses, non-irradiated and 800kGy irradiated straw with different time of enzymatic hydrolysis. The experiment probed the change rule in the process of enzymatic dynamic of straw, preliminarily clarified the degradation mechanism of irradiated and enzymatic hydrolysis of rapeseed straw. The degree of surface damage increased with the increase of irradiation dose and the enzymatic time of residues after irradiation and enzymatic hydrolysis, and the degree of crystallinity and the average degree of polymerization reduced. The reactivity of sample increased with the increase of irradiation dose after irradiation and enzymatic hydrolysis, and the pyrolysis weight loss was divided into two steps, while the temperature with the maximum reaction rate in the process of thermolysis of unirradiated rapeseed straw after enzymatic hydrolysis had no significant change, and the pyrolysis weight loss was completed at a time. It was indicated that only the irradiation could change the pyrolysis properties of the sample, and the enzymatic hydrolysis was not. |
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