Tar Formation In Process Of CO₂ Reforming Methane Coupling With Coal Pyrolysis

Coal pyrolysis is the basic process of coal combustion, gasification, liquefaction andother coal processing methods. Coal pyrolysis is a method to get components in coal that arerich in hydrogen by heat for chemicals or liquid fuel. The tar yield is not so high by usingconventional coal pyrolysis. For improving the tar yield and desulfurization efficiency of coalpyrolysis, An integrated process of coal pyrolysis with partial oxidation of methane (POM)was studied in this paper.Experiments under different atmospheres were done to compare the pyrolysisperformance. The results show that, partial oxidation of methane coupling in coal pyrolysis(POMP) has high tar yield and high desulfurization degree of coal compared withhydropyrolysis at same pyrolysis conditions.Because of some shortage in the POMP process, such as difficulty to control theoxidation degree in the process, it is necessary to find another suitable oxidant for this process.Considering the similar mechanism of CO₂ reforming of methane and POM, another process,namely CO₂ reforming of methane coupling in coal pyrolysis (CRMP) process, was putforward. The results show that the process is effective in improving the tar yield anddesulfurization of coal besides the mild condition and use of greenhouse gas as feedstock.Based on the CRMP process, a catalyst was added to the coal to form a new process,called CO₂ reforming of methane coupling in catalytic coal pyrolysis (CRMCP) process. Theresults show that the tar yield can be further improved.For understanding the reason of improvement in tar yield, the mechanism of process wasdiscussed in the paper. A radical mechanism is considered primarily, i.e. the free radicals likeH, CH_X coming from the POM, CRM process can combine with the free radicals comingfrom coal pyrolysis to avoid the condensation between free radicals in coal pyrolysis, thenimprove the tar yield of coal pyrolysis.