Research On Supercritical Carbon Dioxide And Ultrasonic Pretreatment Of Lignocellulose To Enhance Enzymatic Hydrolysis

The increasing depletion of fossil raw materials and environmental crisis resulted from its use promoting the development of renewable energy. Biomass as alternative energy for the fossil raw materials, because of its wide distribution, huge production, low cost, renewable and other advantages and has become a hot research. Lignocellulose hydrolysis for reducing sugar, and then producing fuel ethanol by fermentation is an important direction of biomass energy utilization. On the basis of existing hydrolysis technology, exploring green and efficient pretreatment technology to obtain a higher reducing sugar yield is the focus of the current work. SCCO2is the first selection of supercritical solvent because it is environmentally friendly, chemical properties stability and cheap and easy to get, and has a broad application prospect in the field of supercritical fluid technology.In this paper, the pretreatment technologies of lignocellulosic biomass are discussed. Research is mainly focused on the SCCO2pretreatment of corn cob, sorghum stalk, corn stalk and rice straw, using enzymatic hydrolysis to evaluate the effect of pretreatment, and the reinforcement effects of corn cob and corn stalk hydrolysis by ultrasonic pretreatment, SCCO2coupling ultrasonic pretreatment and scCCb pretreatment with water and ethanol as cosolvent were also examined. Clarify the mechanism of pretreatment by XRD, SEM and other characterization results, the main results are as follows:1. Effect of pretreatment time, temperature, pressure and water-dry weight ratio in the SCCO2pretreatment process on the reducing sugar yield of enzymatic hydrolysis were studied with corn cob, sorghum stalk, corn stalk and rice straw as raw material, and exploring the optimum pretreatment conditions of different materials. The experimental results show that for different kinds of lignocellulose, the effect of SCCO2pretreatment is different, the reducing sugar yield of different materials at its best scCO2pretreatment conditions were as follows:63.2%of corn cob,54.1%of sorghum stalk,50.2%of corn stalk and57.3%of rice straw, compared with the untreated sample increased by49.6%,44.4%,34%and28%, respectively. The SEM characterization results of the sample before and after SCCO2pretreatment showed that SCCO2pretreatment significantly destroy the microstructure of the material, improving the contact surface area of cellulose enzyme for cellulose, thereby increasing the reducing sugar yield of raw material. 2. Effect of ultrasonic time, temperature and solvent ratio in the ultrasonic pretreatment process on the reducing sugar yield of enzymatic hydrolysis were studied with corn cob and corn stalk as raw materials, and exploring the optimum pretreatment conditions of different materials. The experimental results show that the reducing sugar yield of corn cob and corn stalk at its best ultrasonic pretreatment conditions were15.9%and21.5%, respectively, compared with the untreated sample relative increased by16.9%and32.7%, respectively.3. Effect of ultrasonic time in the scCO2combined with ultrasound pretreatment process on the reducing sugar yield of enzymatic hydrolysis were studied with corn cob and corn stalk as raw materials, and exploring the optimum ultrasonic time. The experimental results show that the reducing sugar yield of corn cob and corn stalk at its best scCO2combined with ultrasound pretreatment conditions were66.5%and54.4%, respectively, compared with the untreated sample increased by52.9%and38.2%, respectively. The SEM characterization results of the sample after the scCO2combined with ultrasound pretreatment and pure scCO2pretreatment showed that scCO2combined with ultrasound pretreatment can be more damage the surface structure of lignocellulose than the pure scCO2pretreatment, thus improving the reducing sugar yield.4. With corn cob and corn stalk as raw material, using the scCO2pretreatment with water-ethanol as co-solvent, investigating the effect of ethanol-water volume ratio on the reducing sugar yield of enzymatic hydrolysis in the best water-dry basis weight ratio, and exploring the optimum ethanol-water volume ratio. The experimental results show that the reducing sugar yield of corn cob at its best ethanol-water volume ratio was60.5%, compared with the reducing sugar yield of scCO2pretreatment reduced by2.7%, and the reducing sugar yield of corn stalk at its best ethanol-water volume ratio was53.5%, compared with the reducing sugar yield of scCO2pretreatment increased by3.3%, a significant increase did not happen, and even the reducing sugar yield of corn cob was decreased, therefore, still need further study.