Co-processing behavior of a sub-bituminous coal with different types of oil

Coal/oil co-processing is an efficient utilization process of coal and heavy oil by coupling direct coal liquefaction with heavy oil hydrogenation conversion. It is an important way for compensating the shortage of oil, balancing the energy structure, and ensuring the national energy security in China. Coal tar, FCC (fluid catalytic cracking) slurry and DCC (deep catalytic cracking) slurry were chosen as oil samples and a sub-bituminous coal was chosen as the coal sample to investigate their co-processing characteristics. The results show that the coal conversion in the co-processing of FCC and coal is the highest, followed by that of DCC and coal, and that of coal tar and coal is the lowest. Further analyses found that the difference of the coal conversion and product composition in coal/oil co-processing is mainly caused by the difference of the aromatic hydrocarbon types and content in the oil samples. The hydrogen donor capacity of the polycyclic aromatic hydrocarbons (PAHs) of the oil samples is the main route to stabilize and protect the free radicals generated in the co-processing technology. The PAHs is favored to combine with the active hydrogen atoms in the reaction system and generated hydrogenated aromatic hydrocarbons, for which has the ability to stabilize the free radicals. It could be deduced from the analysis of the content of the PAHs with 1−5 rings, the FCC with the highest content of 4 ring PAHs has a higher co-processing ability than of the DCC with the highest content of 3 ring PAHs. The aromatic hydrocarbons in coal tar mainly come from the broken bonds of the aromatic structure of the coal, which has good solubility with the coal sample. However, the content of the higher-ring-number PAHs in coal tar is low, and the hydrogen donor capacity is weak, which leads to relatively low coal conversion rate and liquid oil yield when coal tar is co-processed with coal. When FCC and coal tar are mixed as the oil sample for co-processing, the aromatic hydrocarbons in coal tar can ensure the good dispersion of coal, and the higher-ring-number PAHs in FCC slurry can guarantee the hydrogen donor capacity. The synergy of the FCC and coal tar promotes the coal conversion in the coal/oil co-processing.