Research On Pretreatment Of Lignocellulose And Hydrolysis Reaction In Liquid Hot Water

Due to the foreseeable depletion of fossil fuels and the environmental issues, the exploitation and utilization of lignocellulosic materials as renewable resources has been highlighted for its enormous quantity and renewable characteristics. Through the hydrolysis of lignocellulosic to obtain ethanol is the main way of utilizing biomass. Based on the existing hydrolysis methods, exploring green and efficient hydrolysis pathways for lignocellulose to obtain high yield of fermentable sugars is the focus of the current work. Liquid hot water (LHW) and supercritical carbon dioxide (scCO2) have attracted extensive attention from domestic and international academic circles as green solvents for its excellent solvent properties and mass transfer characteristics. Chemical reactions performed in LHW and scCO2have increasingly become a hot topic. This work mainly focused on studying the conversion technology with these two solvents.In order to obtain high fermentable sugar yield and raw material conversion, a two-step hydrolysis of lignocellulose method by LHW combined with maleic acid was proposed, and the reinforcement effects of lignocellulose hydrolysis by ultrosound/scCO2coupling with pretreatment was also examined. Mechanism of lignocellose hydrolysis in LHW and the intensification of enzymatic hydrolysis by ultrosound/scCO2pretreatment were elucidated by using characterization techniques, such as X-ray diffraction (XRD), high performance liquid chromatography (HPLC), and scanning electron microscopy (SEM), as well as thermodynamic calculations. The main results are as follows:1. Effects of reaction time, reaction temperature, maleic acid concentration, and reaction pressure on the reducing sugar yield by two-step hydrolysis were investigated. It was confirmed that high conversion ratio of cellulose and glucose selectivity unification could be achieved by choosing appropriate pressure. The results showed that the total sugar yield of corncob and cornstalk at the optimum condition in two-step method were48.3%and36.3%, respectively, while the total sugar yield of corncob and cornstalk were30%and11%in one-step hydrolysis, respectively. It seemed that the two-step hydrolysis was more efficient than one-step hydrolysis. Besides, the total sugar yield in the second hydrolysis step of corncob coupling CO2with maleic acid achieved51.3%, indicating that CO2could play a catalytic role in the hydrolysis of cellulose. 2. Effects of pretreatment temperature, ultrasonic pretreatment time, and CO2pressure, on the corncob and cornstalk with ultrosound/scCO2and coupling pretreatment were studied. The results showed that the corresponding enzymatic hydrolysis sugar were63%and87%when using the scCO2pretreatment and ultrosound/scCO2pretreatment on corncob, which were increased51%and65%by comparing with the blank sample, respectively. The results of sugar yield and SEM pictures showed that pretreatment process for corncob is more effective than cornstalk, demonstrating that different pretreatment methods were needed toward to different raw material.3. Effects of pretreatment temperature, CO2pressure, moisture content and pretreatment time on corncob with LHW coupling scCO2were investigated and maleic acid was used as evaluation method. SEM characterization results confirmed that the significant destructive effects of corn cob.cellulose using CO2explosion after removing hemicellulose with LHW. The sugar yield corresponding optimum pretreatment conditions was28.7%, and the relative increment was35.5%compared with the blank sample. These results verified the feasibility to evaluate the effect of pretreatment using maleic acid.4. The phase equilibrium constant and pH value of CO2-H2O binary system were calculated using equation of state-activity, and equilibrium constant empirical formula, The differences of pH value between the calculation and experimental results was within1%. The changes of reducing sugar yield could be well explained though the above theoretical calculations, The results can provide theoretic reference for the further investigation on the mechanism of pretreatment and hydrolysis process.