The Pretreatment And Enzymatic Hydrolysis Of Sugarcane Bagasse And Its Conversion To Platform Chemicals

Biomass is the most plentiful renewable resources on the earth, can be derived to liquid fuels and chemicals, which can replace the petroleum-based chemicals. The carbohydrates in biomass(including cellulose and hemicellulose) could be converted into a variety of bio-based chemicals via biological or chemical pathways, and much attention have been paid on this. Recently, the production of glucose and xylose from biomass, and the conversion of these sugars to hydroxymethylfurfural(HMF) and furfural has attracted more and more concerns. HMF and furfural are important intermediates and energy chemicals having high reactivity and widespread application in many fields. Because of the sealed structure of lignocellulose biomass composed of cellulose, hemicellulose, and lignin, the enzymatic hydrolysis efficiency of biomass is low, pretreatment is required to disrupt the intact structure, and improve the efficiency of enzymatic hydrolysis.In this study, sugarcane bagasse was pretreated by liquid hot water pretreatment, dilute ammonia pretreatment, subcritical CO2 pretreatment and ethanol/water pretreatment, the total sugars obtained from pretreatment and enzymatic hydrolysis were used to determine the optimal pretreatment conditions. Then the raw material, pretreated solids, and enzymatic residues were characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), Scanning electron microscopy(SEM) and Thermogravimetric analysis(TG), to determine the variation of cellulose, hemicellulose, and lignin in sugarcane bagasse, and the specific results were summarized as follows:For liquid hot water pretreatment, sugarcane bagasse were pretreated at 180℃ for 30 min and after the enzymatic hydrolysis of pretreated solids, 19.64 g and 32.75 g glucose based on 100 g raw material could be obtained, representing 70.29 % of xylose and 79.20 % of glucose, the total sugars recovery were 75.60%, and about 84.26% of acid-insoluble lignin(AIL) could be obtained from enzymatic residues. For dilute ammonia pretreatment, sugarcane bagasse were pretreated at 170℃ for 60 min with 15 % dosage of ammonia and after the enzymatic hydrolysis of pretreated solids, 13.22 g and 34.19 g glucose based on 100 g raw material could be obtained, representing 47.29 % of xylose and 82.68 % of glucose, the total sugars recovery were 68.41%, and about 61.64 % of AIL could be obtained fromenzymatic residues. For subcritical CO2 pretreatment, sugarcane bagasse were pretreated at 160 ℃ for 100 min with 5MPa CO2 and after the enzymatic hydrolysis of pretreated solids, 17.71 g and 35.24 g glucose based on 100 g raw material could be obtained, representing 63.36 % of xylose and 85.25 % of glucose, the total sugars recovery were 75.60 %, and about 94.92 % of AIL could be obtained from enzymatic residues. For ethanol/water pretreatment, sugarcane bagasse were pretreated at 190 ℃ for 45 min with 60/40 ethaol/water and 5% dosage acetic acid, and after the enzymatic hydrolysis of pretreated solids, 17.68 g and 40.68 g glucose based on 100 g raw material could be obtained, representing 71.90 % of xylose and 93.04 % of glucose, the total sugars recovery were 85.43 %, and about 49.11 % of AIL could be obtained from enzymatic residues. During the pretreatments with liquid hot water and subcritical CO2, most hemicelluloses were degraded, for the pretreatments with dilute ammonia and ethanol/water, lignin and hemicellulse could be degraded in a certain degree. After the four pretreatments, the crystallinity of pretreated solids were increased, the structure became loose, together with many fragments on the surface, indicating that the cellulose bacame more accessibile for enzyme. From the mass balances, we can know that although some components were lost during the pretreatment and enzymatic hydrolysis, the recovery of total sugars and AIL were still high.To determine the effects of lignin on the enzymatic hydrolysis of cellulose fibers, five different lignins were isolated from different biomass by various methods. When the enzyme load was low, the enzymatic hydrolysis of cellulose fibers could not be depressed by ethanol lignin and calcium lignosulfonate, however, it could be depressed by the alkali lignin and enzymatic residue lignins, and their inhibition on the enzymatic hydrolysis of cellulose fibers decreased as the enzyme load increased. Different isolated lignin will have different effects on the enzymatic hydrolysis of cellulose fibers, it is because that the differences of biomass resources, pretreatment methods, and isolation methods lead to the diverse chemical structures and properties in lignin.Furthuremore, we investigated the conversion of pulp sheet to HMF and furfural with solid catalysts. Compared with SO42-/Ti O2, SO42-/Ti O2-Al2O3 has higher thermostability, the mol ratio of Ti/Al in catalysts and the calcination temperatures can affect the crystalline structure, sulfur content, and their acidity. During the conversion process, the effects ofreaction temperature, time, and the dosage of catalyst on the yields of HMF and furfural were also implemented. When the reaction temperature, time, and catalyst were 220 ℃, 30 min, and 5 wt%, the conversion of pulp sheet was 70.69 %, and the yields of HMF and furfural were 8.85 % and 4.54 %, respectively, and the mol yields of them were 14.12 % and 35.42 %, respectively. The catalyst activity decreased gradually as the recycle number increased.