| In order to solve the environmental problems caused by the excessive use of fossil fuels and relieve conflicts between the growing shortage of fossil resources and the increasing demand of energy due to economic growth,it is imperative to find new alternative energy sources for fossil resources.Lignocellulosic biomass has attracted extensive attention around the world due to its wide distribution,high content,low cost and renewability.Abundant cellulose and hemicellulose are contained in biomass,which can be hydroylized into monosaccharides.One of the main ways of conversion and utilization of biomass is to further convert the monosaccharides into biofuels and high value-added bio-based chemicals.Due to the complex structure of biomass,especially the presence of lignin,it is difficult to hydrolyze cellulose by cellulase effectively.In order to fully utilize the cellulose,an effective pretreatment step must be employed to break the lignin seal and release the polydaccharide.However,the common problems with the traditional methods of lignin removal are serious environmental pollution,poor solution recoverability,high energy consumption and high enzyme dosage.In this paper,corn stalks were used as raw materials,and easily recoverable solvents such as dioxane,ammonia and p-toluenesulfonic acid were used as pretreatment agents.The regularitie of lignin removal under acidic?alkaline environment were systematically studied.The effects of lignin removal on enzymatic hydrolysis performance by different pretreatment methods were investigated.It is hoped that it can overcome the shortcomings of traditional pretreatment methods and provide theoretical support for the estalishement of sugar molecular platform.The main research results are as follows:(1)Due to its excellent solubility of dioxane to lignin,acidic dioxane was used to remove lignin from corn stover,and then coupled with acid to pretreat corn stover.The effect of volume ratio of dioxane to water,reaction temperature,reaction time and acid concentration on glucose yield of enzymatic hydrolysis were investigated.This method could significantly improve the hydrolytic efficiency of cellulase.As the reaction conditions were improved,the removal of lignin increased,improving the enzymatic hydrolysis performance of cellulose.The optimal conditions were 120 ?for 40 min with 1 wt%HC1 in the first stage followed by 130?,12.6 wt%ammonium hydroxide,3.0 MPa 02,40 min in the second stage.The total yield of glucose and xylose were 71.5%and 82.8%,respectively,with a low cellulase dosage at 3 FPU/g of substrate.This method could significantly reduce the dosage of cellulase and achieve higher sugar yield under low enzyme dosage.(2)Dioxane use as a solvent for pretreatment is costly,and its efficient recovery is difficult.Aqueous ammonia was chosen as a substitute solvent for dioxane due to its low cost and easily to be recovered.During the pretreatment process of dilute acid combined with aqueous ammonia wet oxidation(AWO),the effects of oxygen pressure,reaction temperature,reaction time and aqueous ammonia concentration on glucose yield of enzymatic hydrolysis were investigated.This method could significantly improve the hydrolytic efficiency of cellulase.As the reaction conditions increased,the lignin removal increased,improving the enzymatic hydrolysis performance of cellulose.The optimal conditions were 120? for 40 min with 1 wt%HC1 in the first stage followed by 130 ?,12.6 wt%ammonium hydroxide,3.0 MPa 02 40 min in the second stage.The total yield of glucose and xylose were 71.5%and 82.8%,respectively,with a low cellulase dosage at 3 FPU/g of substrate.Compared with aqueous ammonia pretreatment under the same conditions,this method can significantly reduce the dosage of cellulase and achieve higher sugar yield with low enzyme dosage.The acid and alkali produced during the pretreatment process could be neutralize each other,reducing the environment pollution.(3)The main disadvantages of the AWO pretreatment method were the lower solubility of oxgen in water and the higher input cost of pressure resistant equipment.Therefore,the hydrogen peroxide due to its excellent permeability and stronger oxidability was used as the oxidant to replace of the oxygen.Dilute acid combined with aqueous ammonia hydrogen peroxide was used to pretreat corn stover.During the pretreatment process,the effects of the dosage of hydrogen peroxide,reaction temperature,reaction time and aqueous ammonia concentration on glucose yield of enzymatic hydrolysis were investigated.This method could significantly improve the hydrolytic efficiency of cellulase.As the reaction conditions increased,the lignin removal increased,improving the enzymatic hydrolysis performance of cellulose.The optimal conditions were 120? for 40 min with 1 wt%HC1 in the first stage followed by 130 0C,58.5%(v/v)mmonium hydroxide,6%(v/v)hydrogen peroxide,40 min in the second stage.The total yield of glucose and xylose were 68.8%and 83.1%,respectively,with a low cellulase dosage 3(?)glucose and xylose at low enzyme dosages were achieved.(4)The three pretreatment methods mentioned above could significantly improve the enzymatic hydrolysis efficiency of the cellulose,but the reaction temperature was higher,and the energy consumption required was also higher.P-toluenesulfonic acid,an easily recoverable organic stong acid,could remove lignin at a temperature lower than the boiling water temperature quickly and efficiently.Then p-toluenesulfonic acid was used to pretreat corn stover.As the reaction conditions increase,the lignin removal increases,and the enzymatic performance of cellulose increases.The optimal condition was 80°C for 10 min with 71 wt%p-methylbenzene sulfonic acid.68.5%glucose yield with a low cellulase dosage at 5 FPU/g of substrate was obtained at that optimal condition.The pretreatment method using p-methylbenzene sulfonic acid coud realize the separation of cellulose and lignin quickly and effectively,and also achive solvent circulation. |
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