Integrated In-situ Catalytic Cracking With Catalytic Reforming Of Methane For Upgrading Of Coal Pyrolysis Tar

Pyrolysis provides an important route for the staged conversion of coal.However,the tar from coal pyrolysis always owns abundant heavy components,which could block and foul the subsequent apparatus and restrict the industrial application of coal pyrolysis technology.It's necessary to decrease the content of heavy tar.In this paper,a novel tar upgrading process by integrating in-situ catalytic cracking of coal pyrolysis tar with catalytic reforming of methane was proposed.The upgrading catalysts were impleted two roles:the reforming of methane and the cracking of coal tar.By this way,the cracking fragments of tar could be stabilized by the free radicals from catalytic reforming of methane,so that excessive cracking of tar is avoided,and both the light tar content and yield are enhanced.The main work and results are as follows:(1)Ni/Al2O3 with different Ni contents was used as the catalyst for the upgrading of Buliangou coal pyrolysis tar under CH4/CO2 atmosphere,and the influence of Ni content and Ni/Al2O3 dosage on light tar content and yield was investigated.The results showed that with the increasing weight ratio of catalyst to coal,light tar content and yield over Ni/Al2O3 first increase and then decrease,and the variation trend with increasing Ni content is similar to that with catalyst dosage.Compared with Fe and Co,Ni exhibits better performance on tar upgrading.When the weight ratio of Ni/Al2O3 to coal was 0.2,Ni/Al2O3 with 5 wt.%Ni(5Ni/Al2O3)showed the best upgrading performance.Compared with non-upgrading tar,light tar content over 5Ni/Al2O3 increases from 52.8 wt.%to 80.8 wt.%,and light tar yield increases from 8.0 wt.%to 13.1 wt.%at 650 0C.The content of light oil,phenol oil,naphthalene oil and wash oil increases by 120%,1 10%,51%and 32%,respectively,and the average molecular weight of upgraded tar over 5Ni/Al2O3 decreases from 279 amu to 193 amu.Benzenes,phenols and naphthalenes in the upgraded tar are all improved to some extent,and aromatics with 3 or 4 rings decrease.Long-chain aliphatic hydrocarbons also have an obvious decrease,and short-chain aliphatic hydrocarbons increase.At the same time,the side chain of aromatic rings become shorter,and the condensation degree of tar is reduced.(2)Modified char(MC)and activated carbon(AC)were obtained by steam activation and KOH activation of pyrolysis char,respectively.The upgrading effect of char,MC and AC to Buliangou coal pyrolysis tar under CH4/CO2 atmosphere was investigated.Compared with char and MC,AC showes a better catalytic effect in upgrading tar as a result of its higher disorder structure and specific surface area.When the weight ratio of AC to coal was 0.2 and the gas flow rate was 300 mL/min,light tar content and yield increase by 67%and 45%compared with non-upgrading tar,respectively,and the average molecular weight of the upgraded tar over AC decreases to 176 amu.The content of light oil,phenol oil,naphthalene oil and wash oil increases by 120%,161%,84%and 50%,respectively,and the pitch content decreases by 75%.(3)Ni/AC with 5 wt.%Ni was employed to in-situ upgrade coal pyrolysis tar under CH4/CO2 atmosphere.With Ni/AC added,light tar content of Buliangou coal pyrolysis tar increases from 52.8 wt.%to 96.5 wt.%at 650?,and light tar yield increases by 53%.The content of light oil,phenol oil and naphthalene oil over Ni/AC increases by 224%,283%and 132%,respectively,and the average molecular weight of the upgraded tar decreases to 160 amu.Buliangou coal pyrolysis tar can be also upgraded by Ni/AC under CH4/H2O and coal pyrolysis gas atmosphere,indicating the catalytic upgrading process is suitable to different methane reforming methods.When Ni/AC was used to upgrade pyrolysis tars of Naomaohu coal,Yulin coal,Baiyinhua coal and Pingshuo coal,light tar contents all increase to above 95 wt.%,and light tar yields all increase by above 40%.The phenomenon indicated that Ni/AC can be used to different coal samples.Additionally,the integrated upgrading method,which combined catalytic cracking of coal pyrolysis tar and catalytic reforming of methane was put forward to ex-situ upgrading processes.The results showed that light tar contents and yields of coal tar and vacuum residue over Ni/AC increase significantly,and the pitch content has a dramatic decrease.(4)Isotopic trace method was used to explore the catalytic upgrading mechanism.When CD4 was used as the tracer,2H NMR spectrum was employed to evaluate tar samples from coal pyrolysis with and without Ni/AC.When Ni/AC was used as the upgrading catalyst,the deuterium peaks in the upgraded tar are obvious,indicating CD4 takes part in the tar upgrading process.When CD4 and 13CH4 were used as the tracer,respectively,GC-MS was employed to analyze some representative components of light tar.D and 13C can be detected in all the representative components when the upgrading process exists,indicating the free radicals from methane reforming can combine with cracking fragments of tar to form light tar.The above results revealed the catalytic upgrading of tar is an integrated process of catalytic cracking of coal pyrolysis tar and catalytic reforming of methane.