Study On The Catalytic Conversion Of Biomass Sugar To Prepare Levulinate And ?-valerolactone

Glucose and xylose are important monosaccharides obtained by acid hydrolysis of lignocellulosic biomass.They are basic organic chemical raw materials.The development of new technologies to promote the conversion and utilization of biomass sugars is of great significance for solving the energy crisis.Levulinate and?-valerolactone are important biomass-based energy chemicals with excellent reaction characteristics and wide application value.Biomass sugar can be directly converted to synthesize levulinate and ?-valerolactone.The development of a low-cost,multifunctional catalytic system is the key to effectively achieving the above conversion.In this thesis,a series of researches on the one-pot conversion of biomass sugar to synthesize levulinate and ?-valerolactone have been developed.Corn stover is used to prepare metal-loaded sulfonated carbon catalyst,which is used to catalyze the conversion of xylose and glucose to acetyl.Propionate;on this basis,a composite catalyst combined with zeolite was synthesized for the selective synthesis of levulinate and ?-valerolactone for the conversion of xylose.The above reaction process was optimized and controlled and the mechanism was explored.First,using corn stalks as a carbon source,a Zr and Al bimetal doped sulfonated carbon-based solid acid catalyst(Zr Al@CS-MSA)was prepared by a hydrothermal sulfonation process.The results show that the generated metal hybrids are uniformly embedded in the carbon support,and the sulfonic acid groups are grafted into the carbon framework,which improves the porosity of the catalyst and the utilization rate of the active sites of the catalyst.The catalyst maintains the amorphous carbon structure and has good thermal stability.It was applied to the catalytic conversion of xylose to prepare levulinate esters,and it was found that the Br?nsted acid of Zr Al@CS-MSA can effectively dehydrate xylose into furfural,and use alcohol as a hydrogen donor under the action of the active metal center of Zr Al@CS-MSA Promote the transfer and hydrogenation of furfural to produce furfuryl alcohol,and then obtain levulinic acid ester through acid-catalyzed alcoholysis.The process conditions were optimized and adjusted,and the macro-reaction kinetics of the conversion of xylose to levulinate was constructed.It was found that using Zr Al@CS-MSA to catalyze the conversion of xylose in n-butanol,a 57.1% yield of butyl levulinate can be obtained.The apparent activation energy of transfer hydrogenation of furfuryl alcohol to levulinate is 65.49 k J/mol,which is the main rate-limiting step of the entire series reaction.The synthesized catalyst can be reused many times and has good stability.The reaction effect of Zr Al@CS-MSA catalyst on the direct conversion of glucose to levulinate was further studied,and the influence of different process conditions on the conversion of glucose to levulinate was explored.The study found that: using 10 g/L glucose as a substrate and reacting in n-butanol at 190°C for 24 h,a47.4% yield of butyl levulinate can be obtained.The increase of the reaction temperature and the extension of the reaction time are beneficial to increase the yield of levulinic acid ester.Using the above catalytic system to convert glucose and xylose at the same time,the yield of levulinate ester can reach 45.6%,which provides a reference way for directly using biomass sugar components to prepare levulinate ester by one-pot method.Finally,using a mixture of zeolite and corn stover as a carrier,a two-step process of high-temperature calcination and sulfonation was used to prepare a single metal-doped sulfonated carbon composite solid acid catalyst(Zr@C/?-MSA),and it was applied to catalysis Converting xylose into selective synthesis of levulinate and?-valerolactone.Studies have shown that Zr@C/?-MSA doped with a small amount of Zr can achieve efficient conversion of xylose into levulinate,and increasing the content of Zr can effectively promote the conversion of levulinate to ?-valerolactone.The use of n-butanol as a solvent is beneficial to the selective synthesis of levulinate esters,while the use of isopropanol as a solvent is beneficial to the formation of?-valerolactone.Subsequently,the reaction effect of Zr@C/?-MSA catalyzed synthesis of ?-valerolactone was discussed,and the process conditions were optimized and adjusted,and the macro-reaction kinetics of the conversion of xylose to?-valerolactone was constructed.The results showed that after 48 hours of reaction at190?,?-valerolactone with a yield of 43.2% can be obtained.The catalyst has good reusability and stability.In summary,this paper has developed an effective multifunctional catalyst for the conversion of xylose and glucose to levulinate esters,and clarified the relevant reaction process mechanism.On this basis,a new type of catalytic system was constructed to convert xylose to selectively prepare levulinate and ?-valerolactone,providing theoretical and technical guidance for the preparation of high-value energy chemicals from biomass sugars.