Conversion Of Biomass To Ethyl Levulinate Catalyzed By Protic Ionic Liquid

With the increasing environmental pollution and energy crisis,renewable and clean resources are vigorously developed and utilized.Among them,the preparation of chemicals via highly selective catalytic liquefaction under mild conditions from widely available and inexpensive cron stalk is one of the important ways to utilize biomass in a high-value way.Protonic ionic liquids are new catalysts with stable structure,tunable acidity,and easy recovery.As effective catalysts,ionic liquids can integrate several processes into a single step,including the decomposition of lignocellulosic biomass and the hydrolysis of sugars.In this dissertation,a one-pot conversion and graded conversion reaction systems were systematically constructed for the utilization of biomass components in order to address the problems of unutilized lignin,low product selectivity,and complicated catalyst recovery process in the current research direction of catalytic liquefaction of lignocellulosic components.The selective catalytic conversion from polysaccharides in lignocellulosic biomass to ethyl levulinate and the separation of lignin and its application were investigated.The reaction performance and laws of these systems were studied,and the preliminary reaction mechanism was proposed based on the experimental data.The details of the research contents are as follows:（1）A one-pot method was used to liquefy lignocellulosic biomass to ethyl levulinate and extract lignin from corn stalk as raw material and a protonic ionic liquid as the catalyst.To explore the coupling between lignocellulosic biomass and ionic liquids,and the mechanism of lignin extraction and separation.It was found that the highest yield of ethyl levulinate was 24.72%and the yield of extracted lignin was up to92.45%with[C₃H₆SO₃Hmim]HSO₄ content of 8 mmol,corn stalk of 4 g,reaction temperature of 200°C,reaction time of 1.5 h and solvent（ethanol to water volume ratio:3:1）of 100 m L.The liquefied residue of corn stalk was analyzed by scanning electron microscopy（SEM）,thermogravimetry（TG）,Fourier infrared spectroscopy（ATR-FTIR）,and X-ray diffraction（XRD）,and a certain degree of lignin condensation occurred during the liquefaction process,and the solid residue produced was humus and carbon residue.In addition,the two-dimensional nuclear magnetic resonance（2D-HSQC）analysis of hydrocarbons of lignin showed that lignin has a stable structure,which provides a preferable basis for its high-value application.（2）A two-step"lignin-first"process was used to remove lignin from corn stalk with protonic ionic liquid[B2-HEA][OAc]as the pretreatment agent,followed by intensive and oriented conversion of lignocellulosic biomass to ethyl levulinate using alcoholic liquefaction technology.The effects of pretreatment temperature and time on the pretreatment efficiency were firstly investigated.The highest recoveries of cellulose and hemicellulose up to 83.78%and 67.20%were obtained at the maximum biomass loading（liquid-solid ratio of 10:1）,pretreatment temperature of 150°C and pretreatment time of5 h.Meanwhile,the delignification rate could reach 70%.Secondly,the optimal liquefaction conditions for the conversion of pretreated corn stalk to ethyl levulinate were investigated,and the maximum yield of ethyl levulinate was up to 48.97%when the liquefaction temperature was 200°C and the pretreatment time was 1.5 h.（3）Environmentally friendly and recyclable carboxymethylated lignin nanospheres（CLNPs）were synthesized via the modulation and self-assembly of the carboxy-functionalized lignin-solution interface using the lignin isolated and recovered in（1）as the raw material.The CLNPs adsorbent had a high carboxyl content and specific surface area with an average diameter of 107 nm.The adsorption capacity of CLNPs for Cr（VI）was 165.4 mg·g^-1 and the removal rate was 99.27%.The adsorption kinetics of Cr（VI）is in accordance with the quasi-secondary model and the adsorption process is close to the chemisorption process of monomolecular layer.The adsorption mechanism is the complexation of CLNPs and Cr（VI）.The adsorbed Cr（VI）ions were easily removed from CLNPs adsorbent in Na OH solution of 0.1 M.The adsorption of metal ions by CLNPs have favorable reusability and great potential for application in wastewater treatment.