Preparation Of Mn/Fe₂O₃-Al₂O₃ Catalyst And Its Performance On Steam Catalytic Cracking Of Coal Tar

Under current China's energy status and environmental pressure,how to utilize abundant coal resources efficiently and cleanly has become one of urgent issues to be solved.Coal pyrolysis is the key technology for coal utilization and other conversion processes,such as gasification and liquefaction.However,the tar produced by coal pyrolysis usually has high content of pitch.The characteristic reduces the quality of tar and increases the difficulty of processing.Therefore,it is necessary to upgrade tar to improve its utilization value.Catalytic cracking of tar in steam atmosphere?steam catalytic cracking?was developed as a potential way of tar processing.The key of the process lies in the design of catalyst.In this paper,Mn/Fe₂O₃-Al₂O₃ catalyst was synthesized by coprecipitation method.Then,the catalyst was tested to investigate steam catalytic cracking of NMH coal tar in two fixed bed reactors.The research can provide technical support and theoretical basis for tar catalytic upgrading and the design of catalysts used in steam catalytic cracking.The effects of loading amount of Mn,space velocity and regeneration times on the yield and quality of light tar were investigated in the steam catalytic cracking.The optimum processing parameters were obtained from the above investigation.Combining with various characterization methods,it was found that Mn loading on Fe₂O₃-Al₂O₃?FA?is beneficial to increase the specific surface area of the catalyst,and more active sites are formed.The formation of Fe-Mn solid solution?Fe₃Mn₃O₈?further promotes oxidative cracking of tar.The light tar content and yield reach to maximum on Mn₂FA.The conversion of pitch increases with the decrease of space velocity,and the maximum yield of light tar?66.6 wt.%?was obtained at 1.96 h^-1.Moreover,it was found that the catalytic activity shows more stable due to the formation of Fe-Mn solid solution after repeated regeneration,which indicates that the regeneration performance can be effectively optimized by loading Mn.The effect of carrier gas flow rate was firstly investigated without catalyst in the in-situ steam catalytic cracking of coal pyrolysis tar.At low gas flow rate,secondary cracking of tar produces light components,resulting in a decrease in tar yield.However,both the light tar content and yield increase,and the yield of light tar reaches to maximum at 100 mL/min.Subsequently,the in-situ upgrading performance of the catalyst was carried out.The fraction distribution and composition tar products were characterized to study the composition changes in steam catalytic cracking upgrading process.Thr use of catalyst contributes to produce more light tar.The results of NMR and GC/MS analysis show that the condensed aromatic hydrocarbons undergo partial cracking in steam catalytic crackingof tar.The long side chains are oxidized and fractured to form aliphatic components with oxygen functional groups.The content of light components including benzenes and aliphatics increases,which leads to the improvement of tar quality.