| Lignocellulose is abundant,renewable resource with low price and high carbohydrate content.It is meaningful for alleviating the resource and energy crisis if lignocellulose can be converted to liquid fuels and bulk chemicals through bioprocessing.Eucommia ulmoides Oliver(EU)is a unique economic tree species in China.It not only has important medicinal value,but also contains natural macromolecular polymer-gutta-percha.When one ton of gutta-percha was extracted form EU seed shell,about nine tons of solid residues will be produced.As a lignocellulosic resource,however,there are few literatures on the utilization of the residues now,which resulted in the resource waste and environmental problem.Based on the above background,to realize resource utilization of the solid residues from guttapercha extraction of EU seed shell,the thesis investigated the feasibility of bioconversion of the residues for producing chemicals and comprehensive utilization,including pretreatment of the residues prior to enzymatic hydrolysis,enzymatic saccharification and fermentation of the residues to produce cellulosic ethanol,enzymatic conversion to produce sodium gluconate,and activated carbon production by using lignin precipitated from pretreatment wastewater and the residues obtained from enzymatic saccharification and fermentation steps as raw materials.The main contents and results of this thesis were as follows:1.On the basis of the determination results of chemical compositions of the residues,the improvement of enzymatic digestibility of the residues by ammonium sulfite pretreatment and soda-anthraquinone(soda-AQ)pretreatment were studied,and found that the pretreatment with soda-AQ was suitable for the residues.After pretreatment with 24%NaOH and 0.05%anthraquinone at 165℃ for 90 min,the conversion rates of cellulose and xylan in pretreated substrate at 72 h of enzymatic hydrolysis reached 83.9%and 71.5%respectively when cellulase dosage was 30 FPU/g substrate.Scanning electron microscope observation,analysis of crystallinity,specific surface area and porosity of raw materials before and after pretreatment were conducted and found that cell wall structure destruction,the increase in specific surface area,pore size and porosity of substrate should be part reasons for the improvement of enzymatic digestibility after soda-AQ pretreatment.2.By comparing the enzymatic hydrolysis efficiencies of the lignocellulosic residues with different sources cellulase,it was found that the cellulase produced by Trichoderma reesei SCB18 was suitable and used in the subsequent fed-batch Quasisimultaneous saccharification and fermentation process to produce cellulosic ethanol.By optimizing the cellulase dosage,fed-batch methods,the optimal enzymatic hydrolysis and fermentation process for producing ethanol was obtained and follows,the pretreated residues were firstly pre-hydrolyzed for 12 h under the conditions of 10%of initial solid concentration and 35 FPU/g of cellulase dosage,then adding yeast to hydrolysis system for further saccharification and fermentation.During the fermentation process,5%(w/v,on total system volume)of substrate was fed at 12 h,24 h,36 h and 48 h,respectively,and the final solid concentration in reaction system was 30%.Using this process,the highest ethanol yield of 53.6 g/L was reached at 120 h of fermentation time,and the ethanol conversion rate reached 66.2%based on glucose content of pretreated raw material.3.The enzymatic hydrolysis process of pretreated EU seed shell residues on the high solid concentration was optimized,and the hydrolysates containing glucose obtained by enzymatic hydrolysis was used to produce sodium gluconate by enzymatic conversion with glucose oxidase and catalase.When the dosage of glucose oxidase and catalase were 60 U/g and 1600 U/g(on dry substrate weight),respectively,the concentration of sodium gluconate in the reaction system reached 77.9 g/L,and the conversion rate of sodium gluconate was 87.8%.4.The feasibility of preparing activated carbon using the solid residues from guttapercha extraction of EU seed shell,alkali lignin precipitated from pretreatment wastewater,and residues from saccharification and fermentation steps as raw materials,respectively,were preliminarily studied.It was found that the specific surface area of the activated carbon prepared from phosphoric acid activated alkali lignin reached 1129.5 m2/g,the methylene blue adsorption value was 135 mg/g,reaching the national standard of first-class activated carbon(GB/T 13803.2-1999),and the iodine adsorption value was 564.4 mg/g,reaching the standard of GB 29215-2012.All the results showed that it is feasible to realize the comprehensive utilization of solid residues from gutta-percha extraction of EU seed shell by combination the processes of pretreatment,production of cellulosic ethanol or sodium gluconate,and preparation of activated carbon. |
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