Study On Catalytic Hydrogenation Of Bio-based Levulinate Ester Into γ-Valerolactone

With the rapid development of world economy and society,situations of fossil energy depletion,climate change and environmental pollution have become serious problems in the 21st century.Lignocellulose,as one of the most abundant and inedible biomass resources,can be efficiently converted into small molecule platform compounds,which are able to be further catalyzed to produce biofuels and chemicals.Making full use of lignocellulose in biomass instead of fossil energy to produce liquid fuel and high value-added chemicals is undoubtedly of great significance to reduce the dependence of traditional fossil energy and to alleviate environmental pollution.γ-valerolactone（GVL）,as a biomass-based platform compound for the preparation of high-density liquid fuels and important chemicals,attracts many scholars to develop new methods for its synthesis.At present,one of the main preparation methods of GVL synthesis is catalytic hydrogenation of levulinic acid（ester）.However,there are still many problems in the above-mentioned reaction process,such as:the complex preparation of catalyst,high cost,low efficiency,poor cycle stability,excessive temperature and long reaction time,etc.At present,there are still challenges in large-scale production.Therefore,it is necessary to find simple,green,efficient and economical methods and innovate catalysts for GVL synthesis.In order to solve the problems mentioned above,copper-based catalysts with simple preparation,low cost,anti-toxicity and good selective hydrogenation performance were selected and catalytic hydrogenation of EL to GVL with two different hydrogen source（hydrogen and isopropanol）has been studied,and a green reaction process was developed.This study provides a new idea for the resource utilization of biomass and its derivatives,and also provides a possibility for alleviating the current crisis of fossil energy depletion.First（in Chapter 2）,EL was selected as the model compound of biomass and its conversion intoγ-valerolactone on a commercial-availabe Raney Cu catalyst with gaseous hydrogen as the hydrogen source was studied.The optimum GVL yield of 98.3%and selectivity of 98.7%were successfully obtained at reaction conditions of 0.4 mmol EL,40 mg Raney Cu,4 MPa H₂,160 ^oC and 3 h.The catalyst can be reused for many times and maintains high activity.In addition,the catalytic effect of Raney Cu was analyzed and the possible reaction pathway was proposed.Then（in Chapter 3）,an effective green process for synthesis of GVL by catalytic hydrogen transfer of EL with isopropanol as hydrogen source was explored,in which,a ternary Cu/ZnO/Al₂O₃ catalyst prepared by a coprecipitation method was used as the catalyst.By optimizing the experimental conditions,it was found that under the experimental conditions of 0.2 mmol EL,2 mL isopropanol,30 mg Cu/ZnO/Al₂O₃ catalyst and 140^oC reaction for 2 hours,the yield of GVL was as high as 99.0%and the selectivity was 99.6%.Moreover,the Cu/ZnO/Al₂O₃ catalyst can be reused at least four times and maintains high activity.By preparing the Cu/ZnO/Al₂O₃ catalysts treated at different calcination temperatures,it was found that calcination temperatures affected the catalytic activity and stability of the catalysts significantly.In addition,the structures and surface morphologies of Cu/ZnO/Al₂O₃,Cu/ZnO and Cu/Al₂O₃ catalysts were characterized by XRD,BET,SEM,TEM and H₂-TPR.The effect of different oxide supports on the particle size,specific surface area,surface morphology,catalytic activity and stability were also discussed.Based on the experimental results,the possible conversion pathway of catalytic transfer hydrogenation of EL to GVL was proposed.