Catalytic Pyrolysis Of Lignin For Production Of P-Xylene

P-xylene is an important bulk chemical in petrochemical industry and has been mainly used for the production of terephthalic acid(TPA)that is an important aromatic carboxylic acid for the synthesis of resins and fibers.The production of biomass-based p-xylene is of great significance in both academic and industrial arenas.Lignin,one of three principal components(namely lignin,cellulose,hemicellulose)in lignocellulosic biomass,has been considered to be a potential feedstock for the production of bulk and fine chemicals(especially aromatic compounds),in view of its unique structure,abundant content of aromatic units and huge annual amount.So far,the directional transformation of lignin into the desired high-value-added aromatic platform molecules(e.g.bio-based p-xylene)is still a challenging task.As far as we know,there is few work regarding selective production of p-xylene using lignin.Here,we demonstrated that lignin was directionally converted into p-xylene by a one-pot process.The main results are as follows:This work proved the one step process for the production of p-xylene through the catalytic pyrolysis of lignin into the aromatic monomers,together with the alkylation of light aromatics and the isomerization of xylenes isomers into p-xylene over metal oxides-modified HZSM-5 catalysts.(1)The modified catalysts by adding the La,Mg,Ce,and Zn elements into HZSM-5 promoted the alkylation of light aromatics(like benzene and toluene)into xylenes,and the isomerization of m-/o-xylenes to p-xylene,due to the modulations of the acid strength and the strong acid sites.(2)The 20%La2O3/HZSM-5 catalyst shows high active for alkylation of light aromatics and isomerization of m/o-xylenes to p-xylene during the transformation process.(3)Co-catalytic pyrolysis of lignin and methanol significantly enhanced the production of p-xylene.(4)Under the optimized reaction conditions(Catalyst = 20%La2O3/HZSM-5,T＝450 ℃,WHSV = 0.5 h-1 and catalyst/lignin(in mass ratio)= 2,lignin/methanol(in mass ratio)= 2:1),the highest yield and selectivity of p-xylene obtained by the co-catalytic pyrolysis of lignin with methanol reached 13.9 C-mol%and 54.5 C-mol%with a p-xylene/xylenes ratio of 82.7%,respectively.(5)The deactivation and regeneration mechanism of the catalysts during the catalytic pyrolysis process were investigated in detail.(6)The reaction pathway for the formation of p-xylene from lignin was addressed based on the identified products and the characterization of catalysts.