Study On The Production Of Levulinic Acid And Its Esters From Lingocellulosic Biomass Pulp

Lignocellulosic biomass is the only renewable carbon source on the planet,which has great potential to completely replace traditional fossil resources in many fields,such as energy,pharmaceutical and chemical industry.The catalytic conversion of lignocellulosic biomass to high value-added chemicals is one of the most important ways for biomass resource utilization.The lignocellulosic biomass is mainly composed of cellulose,hemicellulose and lignin,and these three components form a compact and complex supramolecular structure.Therefore,the high-efficiency fractionation of the three major components of lingocellulosic biomass is the precondition for the comprehensive utilization of all components of lignocellulosic biomass.In this thesis,the lignocellulosic biomass was pretreated by cooking with active oxygen and solid alkali(CAOSA)to give cellulosic pulp that was used as the starting material for the production of biomass-based platform molecules levulinic acid(LA)and its esters by acid-catalyzed hydrolysis or alcoholysis,respectively.In addition,the separation and purification of LA from hydrolysate coming from the acid-catalyzed degradation of cellulosic pulp was also investigated in this thesis.Firstly,four raw materials were pretreated by CAOSA and the composition of the resulting cellulosic pulps was analyzed to calculate the delignification rate.The difference of micro structure between raw biomass and the corresponding cellulosic pulp was characterized by scanning electron microscope(SEM).Based on the SEM images,the original cell structure of lignocellulo sic biomass was completely destroyed after the CAOSA process,and the initial dense and thick fiber cluster structure was transformed into loose and thin fiber structure.The acid-catalyzed degradation tests of both raw materials and the corresponding cellulosic pulp were performed and compared.Interestingly,LA yields from cellulosic pulps was higher than those from untreated raw biomasses under the same conditions.In addition,the acid-catalyzed degradation of cellulosic pulps gave the solid residue with incompact structure,which can be readily separated by filtration.In comparison,the acid-catalyzed degradation of raw biomasses resulted in severe carbon deposits on the inner wall of the reactor.Furthermore,the reaction parameters for the acid-catalyzed degradation of bamboo cellulosic pulp to LA was optimized by response surface analysis(RSA).The optimized reaction conditions for the acid-catalyzed degradation of bamboo cellulosic pulp were listed as follows:223.2?,3.37 wt%H2SO4,liquid solid ratio 15.9:15 28.2 min,and gave the optimum LA yield of 65.3%form bamboo pulp.Secondly,we further studied the acid-catalyzed alcoholysis of bamboo powder and its cellulosic pulp to produce levulinate esters.We found that bamboo cellulosic pulp showed a better performance for the production of levulinate esters by the acid-catalyzed alcoholysis than that of untreated bamboo powder,especially for the production of ethyl levulinate(EL)in ethanol.In this thesis,we systematically investigated the effect of reaction temperature,reaction time and liquid solid ratio on the acid-catalyzed ethanolysis of bamboo cellulosic pulp in ethanol with dilute H2SO4 concentrations(0.2-2.0 wt%),affording the optimal EL yield of 56.3%.In addition,the production of EL by the acid-catalyzed ethanolysis of bamboo cellulosic pulp was conducted under extremely low H2SO4 concentrations(^10 mmol/L).The reaction parameters were optimized by RSA,and the optimized reaction conditions were listed as follows:210.3 ?,10 mmol/L H2SO4,cellulosic pulp loading 26.2 g/L,126.6 min which offered the optimum EL yield of 62.7%from bamboo pulp.Finally,biomass hydrolysate containing high concentration of LA(around 10 wt%)was prepared by multi-feeding with the supplement of sulfuric acid catalyst.The elimination of the residual sulfuric acid catalyst in the resulting hydrolysate was then performed by alkali neutralization or electrodialysis.The separation/purification of LA was achieved by concentration followed by distillation in vacuum.We found that the residual sulfuric acid could facilitate side reactions such as condensation during the distillation of LA,which greatly reduces the isolated yield of LA.If the sulfuric acid in the neat LA aqueous solution was neutralized by sodium hydroxide,an isolated yield of LA up to 84.5%was achieved after concentration followed by distillation in vacuum.For the hydrolysate coming from the acid-catalyzed degradation of bamboo pulp,an isolated yield of LA greater th an 92%was also obtained after the neutralization of the residual sulfuric acid.Additionally,we further investigated the removal of sulfuric acid with negligible loss of LA by electrodialysis.Notably,the recovered sulfuric acid could be reused.After removing the residual sulfuric acid in the biomass hydrolysate by electrodialysis,an isolated LA yield of 87.1%was obtained after concentration followed by distillation in vacuum.