Study On Enhanced Enzymatic Hydrolysis And Green Separation Process Of Lignocellulose Pretreatment

Nowadays,the use of fossil fuels has caused great damage to the environment,and the global demand for energy is also expanding.Compared with fossil energy,lignocellulosic resource is an environment-friendly resource with great development potential.However,the complex and stable chemical cross-linking between the various components of lignocellulose also brings many difficulties to its comprehensive utilization.Therefore,it is necessary to destroy the complex structure of lignocellulose through pretreatment and strengthen the enzymatic hydrolysis process.In this paper,tetrabutyl phosphate hydroxide（TBPH）aqueous solution and supercritical carbon dioxide（scCO₂）were used to pretreat corn cobs and corn stalks,and the optimal process parameters were investigated and optimized.Firstly,the TBPH aqueous solution pretreatment method is used,and the yield of enzymatically hydrolyzed sugar,the recovery rate of hemicellulose and lignin,etc.are used as evaluation indicators.Through single factor experiment and response surface analysis,the pretreatment time（0.5-2 h）,temperature（20-80℃）,TBPH aqueous solution concentration（10-40 wt%）and liquid-solid ratio（4-9 wt/wt）were investigated.The effect of pretreatment and component separation,and get the best process conditions.For corncob raw materials,the optimal pretreatment conditions are as followed:pretreatment time of 1 h,temperature of57℃,TBPH aqueous solution concentration of 10 wt%,and liquid-solid ratio of 7 wt/wt.Under these conditions,the yield of enzymatic hydrolyzed sugar is 90.75%,which is about 4times higher than the 22.5%of the unpretreated raw material enzymatically hydrolyzed sugar yield;the best component separation conditions are as followed:pretreatment time of 1 h,temperature of 60℃,TBPH aqueous solution concentration of 20 wt%and The liquid to solid ratio is 6 wt/wt.Under the corresponding conditions,the recovery rates of hemicellulose and lignin were 41.22%and 54.77%,respectively;for corn stalk raw materials,the best pretreatment conditions are as followed:pretreatment time of 1 h,temperature of 80℃,TBPH aqueous solution concentration of 20 wt%and the liquid to solid ratio is 7 wt/wt.Under the corresponding conditions,the yield of enzymatically hydrolyzed sugar was 80.84%,which was about 4.6 times higher than the 17.7%yield of enzymatically hydrolyzed sugar of unpretreated raw material.In addition,the recovery and reuse of the TBPH aqueous solution found that the yield of enzymatically hydrolyzed sugars after 5 batches of use can be maintained at more than 70%,with good recyclability.Secondly,using the scCO₂pretreatment method,taking the yield of enzymatically hydrolyzed sugar as the evaluation index,Investigate the influence of pressure（35-45 Mpa）,time（1-24 h）,temperature（40-70℃）and water content（0-85 wt%）on the pretreatment effect.For corncob raw materials,the best pretreatment conditions are as followed:pretreatment pressure of 40 Mpa,time of 1 h,temperature of 50℃and water content of 75 wt%.Under these conditions,the yield of enzymatic hydrolyzed sugar is 51.28%,and Compared with22.5%of unpretreated raw material,the growth rate of enzymatic hydrolysis sugar is as high as 128%.For corn stalk raw material,the best pretreatment conditions are as followed:pretreatment pressure of 40 Mpa,time of 4 h,temperature of 60℃,containing with a water content of 75 wt%,the yield of enzymatically hydrolyzed sugars obtained under these conditions is 51.65%,which is as high as 192%compared with the 17.7%yield of enzymatically hydrolyzed sugars obtained from unpretreated raw materials.Combined with HPLC,FTIR,XRD and SEM characterization methods,the component content,functional groups,cellulose crystal structure and surface morphology of the samples before and after pretreatment were analyzed.The results show that after pretreatment with TBPH aqueous solution,hemicellulose and lignin in lignocellulosic raw materials are significantly removed;after scCO₂pretreatment,hemicellulose in lignocellulosic raw materials is significantly removed,but the lignin content does not change.In addition,after these two pretreatment methods,the degree of purification of cellulose is increased.The original dense surface morphology of corn cobs and corn stalks is destroyed,which greatly improves the accessibility of cellulose,thereby enhancing the enzymatic hydrolysis process.Combining experimental results and characterization analysis,the mechanism of scCO₂pretreatment under high pressure and low temperature conditions is proposed.