Preparation Of Pitch-based Carbon Catalyst And Its Catalytic Upgrading Of Coal Pyrolysis Tar

Catalytic upgrading of coal pyrolysis gaseous tar is an effective way to improve the quality of tar and the yield of light aromatics.Carbon-based catalysts have a wide range of raw materials,low cost,and their pore structure can be modified through preparation conditions,and metal-loaded can further improve their catalytic activity.Therefore,carbon-based catalysts are widely used in tar catalytic cracking.In this study,a porous carbon-based catalyst was constructed using pitch,the largest proportion of tar,as the raw material.The medium-temperature coal pitch was modified by cross-linking and activation methods to prepare porous resin catalyst（RC）,and the high-temperature coal pitch was modified by mixed acid oxidation（OCTP）with a mixture of sulfuric acid and nitric acid.The influence of activation temperature on the pore structure of the two carbon-based catalysts was investigated,and the correlation between pore structure and catalytic activity was analyzed.On the basis of the optimal activation temperature,different concentrations of Ni（C₂H₃O₂）₂·4H₂O solution were impregnated on the catalyst to investigate the effect of the loading amount of Ni on the structure and performance of the catalyst.In addition,the rich oxygen-containing functional groups on the oxidized surface of high-temperature coal pitch provide active sites for Ni exchange,After high-temperature calcination,the oxygen-containing groups on the surface will be greatly reduced.Therefore,Ni loading was carried out before carbonization and activation,and the influence of the order of Ni loading on Ni/OCTP catalytic performance was analyzed.The result of research showed that:（1）Different crosslinking agents have little effect on the pyrolysis of tar from RC catalytic coal pyrolysis,and the yield of BTEXN in the catalytic product is less increased than that of raw coal,but both RC（PXG）and RC（TPAL）can reduce the yield of phenolic compounds and aromatic hydrocarbons with alkyl side chain.（2）The higher activation temperature,the larger specific surface area of the asphalt-based catalyst and the more developed pore structure.When the activation temperature is 850℃,the catalyst achieves the best catalytic effect.The output of BTEXN in the catalyzed product of RC850 is 1.5 times that of raw coal,and the total amount of BTEXN in the catalyzed product of OCTP850 is 1.8 times of that of raw coal.（3）The pore structure of RC850 is greatly affected by the loading of metal Ni,The addition of Ni will reduce the specific surface area and the number of pores of RC850;high temperature makes Ni crystallites agglomerate,the dispersion of Ni on the surface of RC850 decreases,and the size of Ni microcrystals increases significantly,resulting in poor performance of high loading Ni/RC catalyst,Moreover,the acidity of the catalyst becomes weaker after loading Ni,and the amount of acid decreases,so the contribution of the loading metal to the improvement of Ni/RC catalytic activity is small.To maximize the catalytic activity of Ni/RC,it is necessary to achieve a balance between Ni loading and pore structure.（4）The order of Ni addition has a greater impact on the catalytic performance of Ni/OCTP.When Ni is loaded before carbonization and activation,the rich oxygen-containing functional groups on the surface after oxidation of high-temperature coal pitch provide active sites for Ni exchange.Compared with OCTP850,the specific surface area increased significantly,which was conducive to the mass transfer and diffusion of the reactants in the catalyst channel and the contact with the active site.Therefore,the catalytic activity was significantly higher than that of the Ni loaded samples after carbonization activation,which promoted the formation of light aromatic hydrocarbons.Compared with raw coal,the total amount of BTEXN in pyrolysis products after Ni5%/OCTP treatment increased to 2.2 times that of raw coal,and significantly promoted the cracking of phenolic compounds,and the cracking rates of phenol and trimethylphenol were 64%and 67%,respectively.（5）The catalyst can crack condensed ring aromatics and phenols into light aromatics,and can also promote the scission of side chains of aromatic hydrocarbons with side chains.The aliphatic compounds can provide hydrogen components for the process and realize the conversion of various components of coal pyrolysis tar,thus increasing the yield of light aromatic hydrocarbons.