In-situ Catalytic Upgrading Of Tar From Integrated Process Of Coal Pyrolysis With Steam Reforming Of Methane Over Carbon Based Ni Catalyst

Pyrolysis is one of the important means to achieve clean and efficient utilization of coal resources.In our previous work,high tar yield was achieved by coal pyrolysis coupled with steam reforming of methane（CP-SRM）,but the tar has high content of heavy fractions（>360℃）.In order to improve the tar quality by decreasing the heavy tar content on the premise of ensuring high tar yield,in-situ catalytic upgrading of tar from the integrated process of coal pyrolysis coupled with steam reforming of methane was conducted over carbon（KD-9）based Ni catalysts.And the effect of the catalyst and reaction conditions on the tar yield and composition of the coal pyrolysis tar in the in-situ upgrading process were studied.Furthermore,the mechanism of the upgrading process was also explored.The major research contents and results are as follows:Ni/KD-9 catalysts were prepared by impregnation method with activated carbon KD-9 as the support,and the effect of nickel content on light tar yield,feed gas conversion rate and upgrading effect of coal tar under methane and steam（CP-S&M）atmosphere was investigated in an atmospheric fixed-bed experimental apparatus.The results showed that the Ni/KD-9catalyst could enhance the conversion of methane and steam and the yield and content of light tar.The catalyst with a Ni loading of 5 wt%（5Ni/KD-9）exhibits the best upgrading effect,and the highest light tar yield of 12.2 wt%was obtained at 650℃.The content of light tar increases from 53.5 wt%to 73.5 wt%,and the conversion of methane and steam increases with the increase of nickel loading.Catalyst was characterized by Raman spectroscopy,N₂absorption and desorption,XRD,SEM,etc.It was found that the catalyst has the characteristics of many defects,high specific surface areas,and highly dispersed Ni active sites,and the catalyst activity was still stable after repeated use.On the basis of 5Ni/KD-9 catalyst,Ni/Mg O-Al₂O₃ was used as reforming catalyst to conduct the in-situ upgrading experiment of coal pyrolysis tar under steam reforming methane（SRM）atmosphere.The results indicated that 5Ni/KD-9 catalyst can significantly increase the yield and content of light tar compared with un-upgraded tar under SRM atmosphere.The light tar yield of CP-SRM over 5Ni/KD-9 is 18.9 wt%,which is 1.4 times that without catalyst.Moreover,the content of light tar of CP-SRM over 5Ni/KD-9 increases from 53.0 wt%to 77.5 wt%.and the content of C₂,C₃ and C₄ alkyl substituted benzene in tar significantly increases by 0.5,0.6 and 4.0 times.Besides,the content of phenols and naphthalenes in tar also increase dramatically after upgrading under SRM atmosphere.Finally,CD₄,D₂O and H₂¹⁸O were used as tracers to explore the mechanism of catalytic upgrading in CP-S&M process.D-NMR of tar and MS analysis of o-xylene,phenol,p-cresol,1,5-dimethylnaphthalene and 1-decene reveal that 5Ni/KD-9 can catalyze coal tar cracking and SRM at the same time.Small free radicals such as·CH_X,·H and·OH generated by SRM can combine with free radicals from tar cracking,thus avoiding excessive cracking of tar.