The Effect Of Acidity And Pore Structure Of Y Zeolites On Catalytic Upgradng Of Coal Pyrolysis Gaseous Tar

Catalytic upgrading of coal pyrolysis gaseous tar is a promising approach to improve the quality of coal tar.Zeolites are often used and Y-type zeolites with 3-dimensional network of accessible micropores and tunable acidities are widely used in this field.They can convert heavy components in coal gaseous tar to high-value light aromatics such as benzene,toluene,ethylbenzene,xylene?m,p-xylene and o-xylene?,and naphthalene?BTEXN?,which are important raw materials in chemical industry and can be used for synthetic plastic,pesticide,fragrance,and so forth.However,little information is available regarding the effect of their pore structure and acidity on catalytic upgrading of coal gaseous tar.Based on this,NaY zeolite has been selected as research object and a series of Y zeolites with different acidity and pore structure were prepared.With the help of XRD,N₂ adsorption-desorption,Py-FTIR,TEM and other characterization techniques,the effect of pore and acidic properties of Y zeolites on the catalytic upgrading of coal gaseous tar was investigated.The main research conclusions are as follows:?1?¹³C NMR and Py-GC/MS were used to analyse the type and proportion of carbon and the pyrolysis properties of three different coal.The total yield and distribution of BTEXN correlates directly to the chemical structure of coal sample.The content of aromatic structure and chemical bonds,such as cycloalkyl,bridged bonds are responsible for the diversity in coal gaseous tar.?2?Incipient wetness impregnation was used to modified Y zeolites,a variety of ZnO loadings were prepared.Their concentration and strength of Lewis acid sites increase with the increasing ZnO loading,especially the strong Lewis acid sites.The pore volumes and specific surface areas increase slightly.Coal sample with different type and proportion of carbon need different content and strength of Lewis acid sites.However,all of them do not exhibit superior catalytic cracking activity compared to NaY zeolite,the total yield of BTEXN is not improved significantly.It is concluded that L acid sites are less important in catalytic upgrading coal pyrolysis gaseous tar.?3?A series of Y zeolites with different B acid sites were prepared by ion exchange of parent NaY zeolite in different concentrations of NH₄NO₃ solution.The framework structure of modified Y zeolites almost unchange,and the medium strong B acid sites change markedly.These zeolites display excellent performance in catalytic cracking gaseous tar from coal pyrolysis.The total yield of BTEXN in three kinds of coal gaseous tar can reach up to 3.2 time,2.8 times and 1.7 times without catalysis.The superior catalytic activity of these Y zeolites are attributed to the increasing medium strong B acid sites,they can markedly convert the polyaromatic hydrocarbons into BTEXN.The medium strong B acid sites are the active sites of catalytic cracking reactions.The different proportion of chemical structure in coal contributes to the diversity of gaseous tar,and the optimum B acid sites and B_Total/L_Totalotal of different coal samples are not the same.?4?Hydrothermaltreatmentwasusedtoprepare mesopore-modification Y zeolites.A part of framework aluminum atoms are expelled from the zeolite lattice and mesopore surface area and pore volume increase with the increasing temperature,the content of Lewis acid sites increase and the proportion of B acid sites decrease constantly during the process,and the structure of zeolites may be destroyed.The results show that the optimum temperature of hydrothermal treatment is600°C,which will contribute to better catalytic activity.The total yield of BTEXN in three kinds of gaseous tar are 5.2 time,6.2 times and 3.3times as that of non-catalytic pyrolysis.Mesopores is conducive to a better performance of zeolites in catalytic cracking reactions,since they can improve accessibility and contribute to the diffusion of reactants and products,and the heavy components can get into the pore of zeolites easily and be cracked into light aromatics like BTEXN.