Catalytic Synthesis Of Bio-Based Para-xylene And Derived Chemicals

At present,bulk chemicals associated with life are mainly derived from nonrenewable fossil resources such as oil,natural gas and coal.Biomass is the only renewable carbon resource on earth.The research and discovery on efficient synthesis of bio-based high-value chemicals is of great significance to promote green chemistry and sustainable development,which accords with the national strategic decision of carbon emission peak and carbon neutralization.However,due to the diversity of biomass composition and structure and the complexity of intermediate products and reaction channels,the directional synthesis of high-value chemicals from biomass is still a challenging scientific and technological problem.In this doctoral thesis,a new way of directional synthesis of bio-based high-value chemicals(2,5-dimethylphenol,terephthalic acid and p-xylene)from lignocellulose was explored and realized,based on the organic coupling of the reaction pathways and the functionalization/broadspectrum design of the catalysts.The catalytic process of selective catalytic cracking of biomass to prepare aromatic intermediates was deeply studied.The regulation mechanism of selective hydroxylation,carboxylation and alkylation of aromatic intermediates were explored.The main findings and innovative achievements are summarized as follows.1.Study on regulation mechanism of selective catalytic synthesis of bio-based 2,5dimethylphenol from cellulose.(1)Based on the organic coupling of selective catalytic cracking of cellulose and selective catalytic hydroxylation of aromatic intermediates(rich in p-xylene),a new strategy for directional synthesis of 2,5-dimethylphenol from cellulose was successfully constructed.(2)The magnetic oxides-modified molecular sieve catalyst(Fe3O4@SiO2@HZSM-5)was designed and prepared.Based on the multi-functional design,including catalyst’s acid site optimization,pore modulation,surface acid removal and magnetism,the selectivity and yield of p-xylene intermediates are dramatically promoted.(3)A magnetic copper-based metal organic frame catalyst(Cu-MOF@Fe3O4)was designed and prepared.It was found that the hydroxylation selectivity of C(sp2)-H bond of alkyl-aromatics was enhanced and the oxidation proportion of C(sp3)-H bond of side chain in alkyl-aromatics was inhibited,based on modulating the valence state of copper ion active center in the Cu-MOF@Fe3O4 catalyst.The selectivity of target product——2,5-dimethylphenol reached 80.2%with high conversion of aromatic hydrocarbons of 90.4%.(4)Based on the analysis of key intermediates(especially OH radical analysis)in the synthesis of bio-2,5-dimethylphenol and the characterization of the catalysts,the structure-activity relationship of the catalyst was preliminarily clarified,and the reaction mechanism of the complex reaction system for the selective synthesis of 2,5dimethylphenol from cellulose were put forward.2.Study on regulation mechanism of selective catalytic synthesis of bio-based terephthalic acid from lignocellulose.(1)Based on the process coupling of selective catalytic cracking of lignocellulose and selective catalytic oxidation(carboxylation)of aromatics intermediates(rich in pxylene),a new route for directional synthesis of bio-based terephthalic acid from lignocellulose was explored and realized.(2)The highly active and selective catalyst(Ga2O3/SiO2/HZSM-5)for biomass catalytic pyrolysis was designed and prepared.The selectivity and yield of p-xylene intermediates were improved through the synergistic effect between the acidic site of molecular sieve and the active site of gallium oxide.(3)The magnetic bimetallic carboxylation catalyst(CoMn2O4@SiO2@Fe3O4)was designed and prepared,which promoted the carboxylation selectivity of p-xylene intermediate through the synergistic action of cobalt ion and manganese ion in the catalyst.The selectivity of terephthalic acid reached 82.3%,with high yield of terephthalic acid of 72.8%.(4)Based on the study of catalytic oxidation process for a series of aromatic model compounds and catalyst characterization,the reaction mechanism of the complex reaction system in the catalytic synthesis of bio-based terephthalic acid from lignocellulose were preliminarily clarified.3.Study on the regulation mechanism of selective catalytic synthesis of p-xylenefrom bio-oil.(1)Compared to the HZSM-5 catalyst,SiO2-modified zeolite catalysts(such as Zn/SiO2/HZSM-5 or Ga/SiO2/HZSM-5)significantly improved the selectivity of pxylene in the selective catalytic cracking of bio-oil.The results showed that the modified molecular sieve increased the isomerization of m,o-xylenes to p-xylene in the pores.At the same time,the reverse isomerization of p-xylene on the catalyst surface is limited due to the elimination of the acid site on the catalyst surface.(2)Based on the study of pyrolysis and catalytic cracking of lignin and cellulose,combined with the characterization of catalysts,the reaction pathways for the selective preparation of p-xylene by the catalytic cracking of bio-oil and lignocellulose were revealed.(3)The catalyst stability and catalyst regeneration methods in the catalytic cracking of bio-oil were studied.The deactivation mechanism of the catalyst was revealed through the characterization of the catalyst before and after the reaction and the analysis of surface intermediates.