Evaluation Of Enzymatic Hydrolysis And Characterization Of Lignin About Mixed Solvent Pretreatment System

The rapid development of economy and society has intensified the dependence on fossil energy.In recent years,more and more scientists focused on the search for a novel renewable energy.Among so many renewable energy,biomass energy has many advantages in substitution of oil.Biomass pretreatment is not only the start of biorefinery process,but also the most critical technical difficulty.In this paper,the downstream products(ethanol,acetone and n-butanol)and the concentrated aqueous solution from the pervaporation and gas stripping process were reused circularly in the pretreatment.After several process iterations,the efficiency of biomass pretreatment and the sugar yield were improved significantly.The reaction temperature,solvent cost and energy consumption of pretreatment were reduced obviously.The key innovation parts were listed as follows:(1)The aqueous solution of ABE fermentation products was used as pretreatment solvent to explore the viriation of pretreatment results and highest sugar yields.At the optimized conditions of the one-component solvent pretreatment systems,the total sugar yield was about 300g/kg.From the ternary pretreatment system of mixed ABE solvent,it can be found that n-butanol has better effect of removing lignin and hemicellulose under the same condition.Meanwhile,it also had higher enzymatic hydrolysis efficiency which was consistent with the Hildebrand solubility parameter.With the increase of butanol concentration,total sugar recovery of residue decreased.Under the balance with enzymatic hydrolysis efficiency,three component ratio under the condition of the highest sugar yield is 25%of ethanol,25%of acetone and 50%of n-butanol.(2)Based on the idea of mixed solvent system and coupling with separation process,this paper proposed that the aqueous solutions after primary pervaporation and primary gas stripping were used for pretreatment.And the addition of a little inorganic alkali such as sodium hydroxide can solve the problems such as high reaction temperature and low delignification in the second chapter to a certain extent.The highest total sugar yields under these two pretreatment systems were around 320 g/kg biomass.Compared with the organic pretreatment without alkali in the second chapter,sugar yield was improved a little,and the reaction temperature was reduced by more than 40℃.Compared with the traditional alkali pretreatment,50%of the alkali dosage was avoided.However,the loss of sugar is still serious.The pretreatment system should be optimized to improve sugar yield and economic feasibility further.And the performance of ethanol batch-cycle pretreatment was investigated to prove its feasibility.Batch-cycle pretreatment can avoid unnessary solvent dilution and concentration steps to reduce energy consumption.Owing to the fluctuation of ethanol concentration around 50%w/w,the pretreatment effect of each batch also changed,but the efficiency of enzymatic hydrolysis was more than 90%.After five batches of black liquor pretreatment,the total sugar yield of enzymatic hydrolysis was still above 300 g/kg biomass.Under the condition of ensuring ethanol concentration,the batch-cycle pretreatment is basically feasible.(3)Herein,the pretreatment process using low-concentration organic alkali was investigated in order to substitute inorganic alkali such as sodium hyoxide.On the one hand,low boiling point and volatile nature of ethylenediamine(EDA)were beneficial to solvent recovery.On the other hand,it could also change crystal structure of cellulose to increase the efficiency of enzymatic hydrolysis.In the two ethylenediamine systems explored in this paper,the sugar yield was more than 400 g/kg.Compared with the second chapter system,the problem of serious sugar loss has been further alleviated.Compared with the organic solvent/water system without alkali,the yield of sugar was increased by about 15%.(4)In order to increase the total sugar yield further,the novel two-step pretreatment technology(Sulfuric acid followed by alkaline ethanol)was developed to avoid the difficulties such as the bad utilization and massive loss of xylan.In the first step,1%H2SO4 was used for pretreat corn stalk to remove xylan.In the second step,with the addition of a little sodium hydroxide,ethanol solution of 50%w/w derived from primary pervaporation coupled with ethanol fermentation was used for pretreatment to improve enzymatic hydrolysis efficiency.In the first step,the removal rates of xylan,glucan and lignin were 83.94%,19.08%and 20.20%,respectively.The concentrations of glucose and xylose in acidic black liquor were 4.52 g/L and 17.37 g/L,respectively.Under ideal conditions,the yields of glucose and xylose in the first step were 173.67 g/kg and 45.15 g/kg,respectively.And the enzymatic hydrolysis efficiency of total sugar was 81.39%.Under the ideal condition,the yields of glucose,xylose and total sugar per kilogram of corn straw were 259.85 g,186.46 g and 446.31 g,respectively.Compared with the organic solvent system without alkali,the yield of sugar increased by about 30%.