Integrated Process Of Coal Pyrolysis With Methane Aromatization For Improving Tar Yield

Coal is the relatively abundant and inexpensive energy source compared with petroleum. Coal pyrolysis to produce hydrocarbons as an alternative fuel source of crude oil has been received considerable attention recently, however, the tar yield from generally coal pyrolysis is low. Hydropyrolysis is an effective method to improve tar yield, but the high cost of pure hydrogen hinders its practical application. Therefore, methane could be the hydrogen substitute in coal conversion into liquid fuel because of its high hydrogen to carbon ratio and low cost.In this work, a new process to integrate coal pyrolysis with methane aromatization (MAP) was put forward for improving tar yield. The effect of experiment conditions including temperature, gas flow rate and Mo loading in catalyst on tar yield, water and char yields was investigated. The results showed that SM coal pyrolysis has the highest tar yield of 21.5 wt.% at the optimum conditions of 700℃pyrolysis temperature,25 mL/min CH4 flow rate,4 wt.% Mo loading in HZSM-5, which is 1.4 and 1.5 times as that in coal pyrolysis under H2 and N2, respectively. Methane aromatization, coal pyrolysis under CH4 and MAP process at different CH4 flow rate were also investigated. The results showed that the sum of the tar yield of coal pyrolysis under CH4 and the hydrocarbons yield of methane aromatization is less than that of coal pyrolysis in the MAP process, which proved the synergistic effect of coal pyrolysis and methane aromatization.It can be inferred from the simulated distillation analysis of the tar under different pyrolysis atmospheres that light component content of the tar from hydropyrolysis is the highest. The content of cut fraction below 200℃in the MAP process is higher than that under N2 pyrolysis. Light oil and carbolic oil have the highest yield in the MAP process. It can be inferred from the GC analysis of Shenmu coal that phenolic compounds, which are more than 40% in the volatile fractions, are the major products of the tars under different pyrolysis atmospheres. The composition of tar derived from coal pyrolysis under different atmospheres was not vividly different. However, it turned out to be a high yield of phenolic compounds in the MAP process.A radical mechanism is considered primarily, the free radicals such as H, CHx and OH coming from the methane aromatization can combine with the radicals coming from coal pyrolysis to avoid condensation between free radicals in coal pyrolysis, thus the tar yield is improved.