| Huangling coal is a tar-rich coal with a tar yield of more than 7%.In this paper,the catalytic pyrolysis of Huangling tar-rich coal was carried out by bimetallic modified USY molecular sieve,and the key factors affecting the secondary catalytic pyrolysis were systematically analyzed,striving to achieve the synergistic effect of intermetallic and USY hydrogenation sites,aiming to increase the light components in tar while reducing the yield of polycyclic aromatic hydrocarbons(PAHs),laying a foundation for improving coal conversion efficiency.Huangling coal has the overall characteristics of low ash,ultra-low sulfur,high calorific value,high hydrogen content,and medium-high tar yield(11.98%).Kaolinite and quartz are the main minerals found in Huangling coal.The raw coal is relatively rich in aliphatic compounds.The thermal behavior of Huangling coal was studied by distributed activation energy method(DAEM),and it was found that a single-step reaction occurred in the coal pyrolysis at the weight loss of 460 ℃～560 ℃,and the activation energy changes sharply in the pyrolysis stage when the conversion rate was greater than 0.6.The sum of yields of benzene,toluene,xylene and ethylbenzene in Huangling coal rapid pyrolysis tar was 33.57%,of which the yields of BTXE were 11.81%,13.80%7.31%and 0.96%,respectively.Magnesium,nickel and zirconium were loaded respectively on the USY by excess impregnation method.The characterization by XRF,SEM,NH3-TPD and other means showed that the loading of metal did not change the phase of USY,and the specific surface area of molecular sieve decreased and the acid content of Ni,Zr modified USY increased under this condition.They were used in the catalytic pyrolysis of Huangling coal,it was found that the distribution of products was still dominated by monocyclic aromatic hydrocarbons,PAHs and phenols;the types of organic substances in the products reduced,the content of monocyclic aromatic hydrocarbons increased,and the highest yield of tar components was transferred from T to B compared with the conventional pyrolysis of raw coal.By comparison,it was found that Zr-USY had the best effect of naphthalene-increasing and phenol-reducing,the yield of naphthalene was 2.32 times that of raw coal,and the phenols decreased from 15.55%to 11.17%;the content of BTXE increased the most in the catalytic pyrolysis product by Zr-USY,from 33.57%that of raw coal to 43.96%,and the yields of BTXE reached 17.05%,15.85%,9.87%and 1.19%,respectively;the content of PAHs in the catalytic pyrolysis product by NiUSY was the lowest,indicating that it was beneficial to the ring-opening cracking of heavy components.Bimetal modified USY were prepared with different Ni loadings based on Zr-USY,and it was found that the loading of Ni increased the specific surface area,the amount of weak acid and the content of strong acid of Zr-USY by characterization.They were used in the catalytic pyrolysis of Huangling coal,and it was found that the distribution of aliphatic compounds,PAHs and phenols was more uniform,the synergistic effect between Zr-Ni and USY acid sites promoted the hydrogenation and ring-opening cracking of PAHs and reduced the catalytic activity of 3Zr-USY for naphthalene and its derivatives,exhibiting a "naphthalen-decreasing"phenomenon and resulting in the reduction of PAHs.The yield of B in the catalytic pyrolysis product was the highest when the Ni loading was 2%,reaching 19.45%,which was 1.65 times that of the raw coal;and the content of PAHs was the lowest.It was obtained that 3Zr/2Ni-USY had high catalytic activity for B and can ensure the ring-opening cracking of heavy components in the catalytic pyrolysis to achieve tar upgrading. |
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