Production Of P-xylene Through Catalytic Transformation Of Sawdust

Biomass,as a renewable energy with abundant reserves,is the best alternative to fossil energy in fuel and chemical industry.p-Xylene is one of the most important chemical raw materials in petrochemical industry.The production of biomass based p-xylene has important academic and industrial significance.In this paper,a one-step process was developed to transform biomass(sawdust)into p-xylene.The main findings are as follows:1.The selectivity and yield of p-xylene in the catalytic cracking of lignocellulosic biomass(sawdust)are closely related to the acidity,reaction temperature and methanol addition.The alkylation of benzene and toluene,and the isomerization of m-xylene and o-xylene to p-xylene can be promoted by adjusting the acid ratio and pore structure of catalysts by means of loading different elements(such as La,Mg,Ce,Zn)on molecular sieve catalyst HZSM-5.The selectivity of four modified catalysts for p-xylene was 20%La2O3/HZSM-5>20%MgO/HZSM-5>20%ZnO/HZSM-5>20%CeO2/HZSM-5>HZSM-5.2.The highest p-xylene yield,20.7 C-mol%,with a p-xylene/xylenes ratio of 91.6%was obtained by the co-catalytic pyrolysis of sawdust with 50 wt%methanol over the 20%La2O3/HZSM-5(80)catalyst.(The reaction temperature was 450 ?,the flow rate of carrier gas(nitrogen)was 200cm3/min,and the mass ratio of catalyst to sawdust was 2:1).3.The deactivation and regeneration mechanism of the catalyst in the process of catalytic cracking was studied in detail.The deactivation of the catalyst was caused by the reduction of the acidity of the catalyst due to carbon deposition.The activity of the catalyst can be restored by regenerating the catalyst at 600 ? with oxygen,owing to that the carbon deposits on surface of catalyst was removed.4.On the basis of product identification and catalyst characterization,the mechanism of catalytic pyrolysis of lignocellulosic biomass(sawdust)to p-xylene was discussed in this paper:(a)the pyrolysis of lignocellulosic biomass into oxygenated organic compounds;(b)catalytic pyrolysis of oxygenates into aromatic monomers;(c)the alkylation of light aromatics to xylenes;(d)the isomerization of m/o-xylenes to p-xylene.