Study On Microwave Pyrolysis Of Low Rank At CH₄-CO₂ Atmosphere

This work investigated the temperature rising characteristics of coal and its semi-coke to heat up in the microwave field, studied the catalytic property of the semi-coke prepared from Shenmu coal pyrolyzed at 650℃ for catalytic CO₂ reforming of CH₄ under microwave heating; investigated the effect of the ratio of CO₂/CH₄ and reaction temperature on gas conversion and product composition in reformation process, explored the catalytic and deactivation mechanism of semi-coke in microwave field. A integrated process of coal pyrolysis and CO₂ reforming of CH₄ under microwave heating was designed, and the products distribution and tar formation mechanism was studied during the process. In the integrated process, a bit of added semi-coke was used as microwave absorber and catalyst of CO₂ reforming of CH₄. The main conclusions are as follows:（1） The microwave absorption capacity of Shenmu bituminous coal was weak,which was difficult to reach the pyrolysis temperature in microwave field. But its semi-coke pyrolyzed at 650℃ was a better microwave absorber.（2） Under microwave irradiation, the catalytic activity of semi-coke reduced quickly. However, CH₄ conversion increased significantly and the life of the activated semi-coke extended through adding CO₂.（3） Semi-coke could participate in the coal pyrolysis process as microwave absorber and catalyst for CO₂ reforming of CH₄ simultaneously in the process of microwave pyrolysis. The tar yield of Shenmu coal during the integrated process reached the maximum at 700℃, which were 1.97 times and 1.47 times than that under N2 and CH₄ atmosphere with the same conditions. The tar yield of Xinjiang coal during the integrated process reached the maximum at 650℃, which were 1.47 times and 1.3times than that under N2 and CH₄ atmosphere with the same conditions. It was mainly because that the added semi-coke and new char from coal pyrolysis can catalyze CO₂ reforming reaction of CH₄, in which the active free radicals were generated. Those free radicals coupled with the radicals procuced during coal pyrolysis, thereby improved the tar yield.（4） GC-MS results of tar showed that: tar had very complex composition, which contained more than 100 compounds. CH₄ and CO₂-CH₄ atmosphere could improve the quality of the tar. CH₄ could promoted the content of polycyclic aromatic hydrocarbons containing benzene and anthracene in pyrolysis tar. In CO₂-CH₄ atmosphere, the aromatics content in Shenmu coal pyrolysis tar increased, the content of long-chain aliphatic hydrocarbons decreased.