Three-dimensional porous carbon materials as catalysts for upgrading coal pyrolysis volatiles to boost light tar

Abstract

The large proportion of heavy components in volatiles from coal pyrolysis is liable to entrain dust and form coke, resulting in the difficulty of separating oil from dust, which thus causes the blocking of technical pipelines. Carbon-based catalysts (BC and BHC) and metal-modified carbon-based catalysts (Fe-BC, Ni-BC, Fe-BHC and Ni-BHC) were prepared for the upgrading of volatiles from coal pyrolysis. This three-dimensional interconnected macroporous carbon material is primarily derived from the pyrolysis of the blend of a biochar and a caking coal. The results show that the metal-modified carbon-based catalysts aid in activating small molecules, such as CH4, CO2, and H2O, increasing in-situ hydrogen donation while cracking polycyclic aromatics, macromolecular oxygen-containing compounds, and N, S-containing heterocyclic compounds. This thus increases the selective catalysis of benzene, naphthalene, biphenyl, and anthracene and improves tar quality. The unactivated Fe-BC and Ni-BC catalysts exhibit high selectivity for light oil with a boiling point below 170 °C. In contrast, the activated Fe-BHC and Ni-BHC catalysts have a stronger ability to crack heavy tar due to the synergistic effect of metal and carbon defect structures. However, the micropores within the catalysts prevent mass transfer of macromolecular compounds, drastically lowering the tar yield with coke formation. Overall, the unactivated metal modified catalyst with three-dimensional porous structure allows for the synergistic effect of dust removal and upgrading of volatiles while maintaining the tar yield, especially the Fe-BC catalyst with a lower price.