Research On The Combination Technology And Mechanism Of MCC And Cellulosic Ethanol

High-valued utilization of lignocellulose resources is the primary target of biomass energy utilization. Currently, there are many difficulties in lignocellulose converted to bioethanol, such as the higher cost and serious pollution of pretreatment, the poorer separation of lignin, and the compact crystalline structure, etc. Microcrystalline cellulose(MCC) is such a product obtained from cellulose by the action of acid and enzymes. MCC is a fine white crystalline powder which offers a lot of advantages such as high reactivity, renewability and biodegradability. In the process of acid hydrolysis of cellulose,hydrolyzing the amorphous regions while retaining the crystalline regions is the key technology for microcrystalline cellulose products.Therefore, the metal ion and ultrasound were used to promote the degradation of the amorphous regions by acid hydrolysis while retaining crystalline regions as much as possible, which is essential to MCC production. Meanwhile, the hydrolysate from amorphous regions could be fermented to produce cellulosic ethanol, improving the utilization efficiency of cellulose and reducing the acid hydrolysis liquid pollution to the environment. This enabled the whole structure and diversified utilization of cellulose.The research on the combination technology and mechanism of MCC and cellulosic ethanol was carried out based on the differences on the natural structures of crystalline and amorphous regions. Studies involved: ultrasonic enhancing acid hydrolysis selectivity of cellulose under Fe3+ ion catalysis; the synergistic effect mechanism of ultrasonic treatment combined with metal ion catalysts on the selective acid hydrolysis of cellulose amorphous regions; the influence of reused hydrolysate on the properties of hydrocellulose; and the impact of thecumulative action on the cellulosic ethanol fermentation in subsequent section.Ultrasonic assisted with metal ion to enhance selective acid hydrolysis of cellulose were discussed. The effect of ultrasonic pretreatment coupled with HCl–Fe Cl3 catalyst was evaluated to hydrolyze the amorphous regions of cellulose. The ultrasonic pretreatment led to cavitation that affects the morphology and microstructure of fibers, enhancing the accessibility of chemical reagent to the loosened amorphous regions of cellulose. The results indicated that appropriate ultrasonic pretreatment assisted with Fe Cl3 can enhance the acid hydrolysis of amorphous regions of cellulose, thus improving the crystallinity of the remaining hydrocellulose. It was observed that sonication samples that were pretreated for 300 W and 20 min followed by acid hydrolysis had maximum of 78.9% crystallinity. The crystallinity was 9.2% higher than samples that were not subjected to ultrasound. In addition, the average fines length decreased from49μm to37μm. Meanwhile, the thesis explored the influence on the properties of hydrocellulose from selective acid hydrolysis, as well as acid concentration, the dosage of metal ion, the temperature and duration of acid hydrolysis which were based on the four factors and three levels orthogonal test. The optimal conditions of ultrasonic synergistic for selective acid hydrolysis of cellulose were 2.5mol/L HCl, 0.3mol/L Fe3+at 80℃ for 50 min, which result in an increased crystallinity of 9.89%,compared with the untreated hydrocellulose(69.69%), and the average fines length decreased from 47μm to 29μm. As a result, the synergistic effect could effectively save the reaction time compared to the pretreatment method. Moreover, the ultrasonic assisted with metal ion to enhance selective acid hydrolysis of cellulose was a series of first order reaction. The results showed that higher temperature benefited the degradation of oligosaccharide, but not so well for producing MCC.A comparative study in horizontal orientation was carried out about the crystallinity, degree of polymerization(DP) and the morphological/structural characteristics of hydrocellulose, for samplesprepared in the presence or absence of ultrasonic treatment. And on this basis we were supposed to further discuss the synergistic effect mechanism of ultrasonic treatment by in-depth analysis of hydrogen bonding mode and intensity, crystal form, chemical structure, specific surface area, crystal cell parameters, the molecular weight distribution etc.The hydrolysate was removed from the selective acid hydrolysis of cellulose, which contained mostly chemical reagents and reducing sugar.By adding hydrolytic reagent, the hydrolysate was then reused to produce hydrocellulose. The properties of hydrocellulose had not been affected by the cumulative action, and the crystallinity of hydrocellulose could be improved with proper circulation to some certain extent. Meanwhile, the content of reducing sugar was continuously accumulated by repeating this procedure, which was beneficial to ferment cellulosic ethanol in the subsequent part. RSM was used to optimize the fermentation technology of cellulosic ethanol.The optimum fermentation conditions were as follows: the saccharomyces cerevisiae inoculum 10%, fermentation temperature34℃, reducing sugar concentration 60g/L, and duration time 64 h. The theoretical value of the ethanol concentration was 12.09g/L, while the actual value was 11.86 g/L. Therefore, the empirical models developed were reasonably accurate, which verified that RSM analysis is indeed a useful technique to predict and optimize the selective acid hydrolysis of cellulose for cellulosic ethanol fermentation. In addition, the metal ion Fe3+ in fermentation liquor had little or no effect on the fermentation process.