Effect of pyridine extraction on the tar characteristics during pyrolysis of bituminous coal

Extensive research has shown that coal has an extractable small molecular compound, which was associated with non-covalent bonding coal molecules. In addition, the reactivity of coal extract and residue is different. In this work, a bituminous coal was acid washed and extracted by pyridine to destroy the electrostatic interactions and hydrogen bonds. The pyrolysis behavior of the extracts and residue was studied by thermogravimetry (TG) and a fixed bed reactor. The H/C atomic ratio for the pyridine extract was significantly higher than that of raw coal, indicating hydrogen-rich components. The pyridine extract (E1) gave a higher tar yield of 44.41%, as well as more gas, while the tar yield of residue (R1) was lower than raw coal in an N₂ atmosphere. However, the residue gave more than two times the amount of tar under H₂ than that of N₂ because developed porous structure was formed by pyridine extraction, which would facilitate hydrogen diffusion into the pore structure and reduce the polycondensation reaction.