| Biomass is the renewable resource that can produce liquid fuel and finechemicals to replace the petroleum-based chemicals. Ethyl levulinate (EL) is regardedas a new biomass-based chemical, with good response characteristics and numerouspotential industrial applications. The direct conversion of biomass into EL isconsidered to be a great development potential conversion pathway due to the simplesynthetic technique and minimal impact on the environment.In this paper, firstly, the processes of conversion of glucose to EL wereinvestigated in different catalyst systems included extremely low sulfuric acid catalystand the mixed-acid catalyst, respectively. Then, the furfural residues were used toproduce EL in mixed-acid catalyst system. Finally, two-step process was carried out,which included the removal of lignin from the furfural residues and the ethanolysis offollow-up residue. The following conclusions:1. The process of EL produced by glucose in extremely low sulfuric acid catalystsystem was investigated. The liquid products were analyzed by GC and HPLC. Thereasonable reaction mechanism of glucose synthesis of EL was proposed, then thekinetic model was established. In the experiment conditions, the kinetics followed asimplified first-order kinetic model. For the main and side reactions, the values ofactivation energy were122.64kJ/mol and70.79kJ/mol, and the reaction orders were0.985and0.998, respectively. In the reaction, the conversion of glucose to EL wasaccelerated by increasing the reaction temperature and acid concentration. However,formation of humins was also promoted by higher temperature. The extremely lowsulfuric acid can offer enough acid sites for the synthesis of EL by extending thereaction time. Extremely low acid system suppressed self-condensation of ethanoleffectively.2. Mixed-acid catalyst system was used for synthesis of EL from glucose, whichconsistied of solid acid USY and extremely low sulfuric acid. According to theanalysis of the liquid products, reaction path was consistent either in solid acid system or in liquid acid system. The mixed-acid catalyst system was found topromote degradation of glucose and synthesis of EL. When the concentration ofsulfuric acid was0.1%and the amount of USY was2%, EL yield was51.47mol%at180℃for120min. In mixed catalyst system, the amount of unit volume diethyl etherdid not increase significantly. The solid acid USY still maintained good activity, andcan be reused more than five times. Mixed-acid catalyst system retained theadvantages of solid acid catalysts and improved the EL yield.3. Furfural residues (FR) were used as feedstock to produce EL in differentcatalyst systems. Mixed acid catalyst resulted in higher EL yield than a single systemwith either USY or sulfuric acid as catalyst. Sulfuric acid concentration was constant(0.1%), effects of different process parameters including reaction temperature,reaction time, ratio of liquid to FR and the amount of USY were studied. Responsesurface methodology was applied to optimize the effects of processing parameters. Atoptimal conditions, the yield of EL was17.23%. Since the fifth cycle of USY, theproduct yield was decreased greatly. The residue was characterized using SEM, thestructure of original feedstock changed to a certain extent and become porous afterreaction by liquid acid catalyst. Mixed-acid catalyst system was efficient for thedegradation of furfural residue and direct synthesis of EL.4. Two-step process was explored included delignification process andethanolysis process. Considering the ligin removing rate and cellulose losing rate,delignification pretreatment conditions were determined. After completion of thedelignification, the lignin was obtained by concentration of the extract, the residuewas used to produce EL. In two-step process, with1g of FR basis,0.1150g of ELand0.1151g of lignin were obtained respectively. |
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