Study On Catalytic Conversion Of Furfural And Levulinate Into γ-Valerolactone And Reductive Amination Of Levulinic Acid

Currently,fossil resources-petroleum,natural gas,and coal are the main resources for humans.However,these non-renewable fossil fuels have been decreasing in recent years,which would not satisfy human requirement over time.On the other hand,in the process of employing fossil fuels,many poisonous gasses,for example SOx and NOx would be released,which may cause greenhouse effect,land desertification and air pollution.Therefore,searching for new renewable resources instead of fossil fuels has been a big challenge for humans.Biomass is abundant in earth and the only organic renewable carbon resource in nature.Lignocellulose was the main components of biomass,which consist of 40-50%cellulose,15-25%lignin and 20-40%hemicellulose.Among them,hemicellulose mainly exists in plant cell wall and seeds,and it is mainly composed of xylan（>90%）.Furfural and levulinic acid are the downstream products from xylan and xylose,which could be hydrogenated into many value-added chemicals,for example furfuryl alcohol andγ-valerolactone,has become one of the most promising routes in biomass conversion and received considerable attentions.There are two reductive methods in the conversion of furfural and levulinic acid:one is the directly use of H₂,and another is applying organic hydrogen source as reductant.Although H₂ as hydrogen source has made great progress in reduction reaction,there usually exists security problems in transformation,storage and experimental operation.Besides H₂,these organic reductants（formic acid,alcohol and hydrosilane）,also belong to green resource,and usually shows high selectivity in the reduction of unsaturated compounds in appropriate catalyst systems,which could avoid the suffer of high H₂ pressure.In this context,we synthesized a series of biomass-derived chitosan support metal and organoboron catalysts,and applied formic acid,isopropanol and hydrosilane as reductants respectively in the conversion of furfural and levulinic acid.（1）We successfully synthesized a series of chitosan support metal as heterogeneous catalyst by simple methods.Among them,chitosan-Ru demonstrated the best performance in the reduction of furfural into furfuryl alcohol and levulinic acid intoγ-valerolactone with formic acid as hydrogen source.We further applied the efficient chitosan-Ru/HCOOH system combined with acidic ZSM-5 to achieve one-pot conversion of furfual intoγ-valerolactone.After the screening of reaction conditions,for example the dosage of formic acid,additive,catalyst and ZSM-5,the highest yield ofγ-valerolactone could reach up to 79%.In addition,to reduce the reaction cost,we applied this chitosan-Ru/HCOOH/ZSM-5 system to the directly conversion of xylose and xylan,furnishing 37%and 30%yield ofγ-valerolactone respectively.Furthermore,we investigated the mechanism of the one-pot production ofγ-valerolactone.Finally,chitosan-Ru showed the reusable properties in every step of the conversion.（2）In this section,we studied the MPV reduction of biomass-derived platform ethyl levulinate（EL）toγ-valerolactone with isopropanol as hydrogen source.Following the work of the last section,we continued to synthesize some metal catalysts based on chitosan.After their employment in the MPV reduction reaction,we found chitosan-Zr showed an excellent performance in the transformation of ethyl levulinate toγ-valerolactone,achieving 97%yield ofγ-valerolactone at 160oC and 8 h.In addition,this system could be applicable to the reduction of many organic unsaturated compounds,including aromatic,aliphatic and cyclic aldehyde compounds.（3）The transformation of levulinic acid by reductive amination is also a promising route in the valorization of biomass.In this section,we used hydrosilane as reductant and B（C₆F₅）₃ as catalyst to realize the reductive amination of levulinic acid with various anilines.Then,through the control of the dosage of hydrosilane,good results of the switchable synthesis of pyrrolidones and pyrrolidines products were achieved.Furthermore,we studied the reaction route and mechanism of this reductive amination by ¹H NMR experiments.