Studies On The Hydrodeoxygenation Reaction And Related Catalysts In Biomass Conversion

The increasing demand for energy,the growing depletion of non-renewable fossil resources and the consequent greenhouse gases and air pollution have forced people to explore green and renewable new sources of energy.Biomass resources are currently the only renewable organic carbon resources,with the characteristic of large in quantities,widely distributed,cheap and easy to get,attracting widespread interests in academia and industry,and it is considered to have the potential to replace fossil resources to provide chemicals and fuels.The development of biomass-based high value-added chemicals and liquid fuels not only addresses the current environmental and human threats posed by unreasonable use of biomass,but also achieves waste recycling and increases the added value of the overall industry chain,which will promote the construction of China’s agricultural modernization.Biomass is constituted of three components:cellulose,hemicellulose and lignin,cellulose is formed by glucose through β-1,4-glycosidic bond,hemicellulose is a polymer composed of five carbon sugar and six carbon sugar,lignin mainly contains the following structure:β-coumaryl alcohol,coniferyl alcohol and sinapyl alcohol,which is more difficult for depolymerization than cellulose and hemicellulose.The hydrolysate which contains six carbon sugar,five carbon sugar and lignin residue could be obtained through the acid hydrolysis of biomass.Hexose can be converted into the platform compound 5-hydroxymethylfurfural and levulinic acid by catalytic dehydration.Five carbon sugar can be transformed into platform compound levulinic acid through catalytic conversion.Lignin can be catalyzed into a series of phenolic derivatives.The 5-hydroxymethylfurfural,levulinic acid and phenolic derivatives can be converted into 2,5-dimethylfuran,y-valerolactone and cycloalkanes by catalytic hydrodeoxygenation,which could be used as liquid fuels for the development of renewable biofuels.However,there are still many problems in the existing catalytic systems,such as poor catalyst reactivity,low selectivity,complicated catalyst preparation process,harsh reaction conditions and low cycle performance.Therefore,it is very important to develop novel catalyst systems with high activity and high selectivity for the above hydrodeoxygenation process and to achieve efficient conversion to the corresponding liquid fuel molecules under mild conditions.In this thesis,a series of catalytic systems which is easy for preparation,highly active and low cost were designed.The regulation of the product distribution was carried out through regulating the synthesis of the catalyst.The thesis was divided into the following four parts:In Chapter 1,the composition,structure,and utilization of biomass are described.The development of biomass-based 5-hydroxymethylfurfural,levulinic acid and phenolic derivatives,as well as the progress of hydrodeoxygenation of biomass derived compounds into liquid fuels and chemicals,is followed.In Chapter 2,the perovskite type oxide supported Ni catalyst was used to catalyze the hydrogenolysis of 5-hydroxymethylfurfural into 2,5-dimethylfuran.The catalyst with different Ni content in perovskite was prepared by citric acid complex method.It was found that the LF-N20 catalyst could convert 5-hydroxymethylfurfural to 2,5-dimethylfuran in 98.3%yield.The effects of reaction temperature and hydrogen pressure on the reaction results were investigated.The catalyst could be used for 5 times without obvious decrease in activity,and the possible reaction mechanism was proposed according to the kinetic experiment and the intermediate experiment.In Chapter 3,the commercial zeolites loading Pt catalyst was used to catalyze the preparation of γ-valerolactone from ethyl levulinate.Pt nanoparticle was loaded on a series of zeolites and used for the hydrogenation of ethyl levulinate intoγ-valerolactone,among them,Pt/ZSM-35 showed the best performance,and 99%ofγ-valerolactone was obtained.The reaction temperature,the hydrogen pressure and the reaction solvent on the reaction results were investigated.The relationship between the microstructure of the catalyst and the reaction results was explored according to XRD,XPS,TEM and BET analysis.Finally,the stability of the catalyst was studied,and the activity of the catalyst was slightly decreased in the third run.In Chapter 4,the hydrodeoxygenation of lignin-derived phenolic compounds into alkanes over carbon nanotubes supported Ru catalyst in biphasic system was introduced.The traditional hydrodeoxygenation of phenolic derivative is usually carried out in a single phase solvent system.The use of biphasic solvent system allows the cycloalkanes produced by hydrodeoxygenation in the aqueous phase to rapidly transfer into the organic phase,thus avoiding further breakage of C-C bond,which will reduce the yield.In this chapter,Ru/CNT was synthesized by impregnation method,and eugenol was hydrodeoxygenated in water/n-dodecane biphasic system to obtain propylcyclohexane in 94%yield,while in pure water system the yield was only 56.5%and in pure n-dodecane solvent the yield of only 4%,which also confirms the advantages of biphasic system.In this biphasic catalytic system,lignin-derived phenolic monomers and dimers can be hydrodeoxygenated into the corresponding alkanes.The development of this biphasic system also extends the new idea of biomass hydrodeoxygenation.In summary,this thesis mainly uses the important compounds derived from biomass as the research object,and designs different catalytic systems to realize the efficient hydrodeoxygenation of these compounds into the corresponding target products,and the catalysts can be recycled.The relationship between the structure of the different catalysts and the activity and selectivity was studied through the characterization of the catalyst.The developed catalytic system also promoted the catalytic conversion and application of biomass.