Effects Of Ultrasonic And Supercritical Carbon Dioxide Pretreatment On Lignocellulose And Hydrolysis Results

The development of green chemistry and exploitation developing renewable energy sources are the two efficient ways to meet the energy crisis and environmental pollution. Biomass has potential application value for its advantages of clean and renewable. Supercritical carbon dioxide is the most attractive green solvent because it is readily available, inexpensive, and mild critical condition.In this paper, corncob, rice straw and corn stalk were used as raw materials and pretreated by ScCO2and ultrasonic. The effects of ScCO2and ultrasonic on the preparation of reducing sugar and various factors in the pretreatment were investigated. Various factors of high pressure CO2in strengthening subcritical hydrolysis were studied and being analyzed from the aspect of thermodynamics. The main work and results are as follows:1. Effects of ScCO2pretreatment temperature, moisture content, pressure and time on the reducing sugar by hydrolysis were investigated. The results showed that the reducing sugar yield of corncob, rice straw, corn stalk was39.6%,36.6%,28%, respectively, with the optimal condition of100℃,50%moisture content, CO2pressure15MPa and30min. Compared the control sample respectively increased by13.4%5.7%,5.5%. The dilute hydrolysis condition was160℃,40min, liquid-solid ratio50:1, mass fraction1%sulfuric acid catalyst. The results of orthogonal analysis of various factors of ScCO2pretreatment, were showed that pretreatment temperature and moisture content affected the reducing sugar yield significantly. The increasing pretreatment temperature could improve the reducing sugar yield. But higher temperature may result in small molecules degradation and producing byproduct. Increasing moisture content also improves reducing sugar yield, but but excessive water content had little improvement.2. Effects of ultrasonic power and time in the ultrasonic pretreatment lignocellulose have investigated. The results showed that neither the increase of ultrasonic power nor the time could improve the reducing sugar yield. The reducing sugar yield improved3-4%using the ScCO2combined ultrasonic than that of single method. In addition, the sequence of these two methods had no effect on the reducing sugar yield. The optimal condition of ultrasonic pretreatment was ultrasonic frequency59kHz, ultrasonic power90W and20min. Dilute acid hydrolysis condition was160℃,40min, liquid-solid ratio50:1, mass fraction1%sulfuric acid catalyst. The yields of reducing sugar were corncob38.3%, rice straw37.5%, corn stalk 30.5%, which have improved12.1%,6.6%and8%compared with control sample, respectively.3. Exploration of hydrolysis conditions for the high pressure CO2in strengthening subcritical hydrolysis with rice straw and corn stalk as raw materials. Effects of hydrolysis temperature, time, liquid-solid ratio, CO2pressure and stirring speed on reducing sugar yield have been studied. The results showed that both high temperature with short time and low temperature with long time could result in higher reducing sugar yield. The addition of CO2could decrease the heating time and to reducing energy consumption. The reducing sugar yield by using corn stalk was16%, with hydrolysis condition190℃,40min, liquid-solid ratio50:1, CO2partial pressure of8MPa, stirring speed1000r/min, which was1.8%higher than that of without CO2and relatively increases by12.7%. The changing of liquid-solid ratio did not affect the reducing sugar yield. The addition CO2could increase the reducing sugar yield without etching apparatus and had simple post-process, which has a certain guiding significance of industrial production.4. The calculation results of the thermodynamic and pH value of H2O/CO2binary system showed that the water mole fraction was low when the partial pressure of CO2was high at low temperature. The lower pH value of H2O/CO2binary system would be obtained at lower temperature and higher partial pressure of CO2, which would in favor of hydrolysis. The selection of appropriate hydrolysis temperature and partial pressure of CO2would reduce the consumption of energy and equipment investment.