Evolution of structure and pyrolysis behavior of macerals and their interaction based on macro separation of a sub-bituminous coal

High purity vitrinite (PV, 89.40 % vitrinite content), high purity inertinite (PI, 82.38 % inertinite content), and a series of fractions with varying macerals content were obtained from the macro separation of a sub-bituminous coal by the developed Kg-scale density gradient centrifugation separator. The structural characteristics and pyrolysis behaviors exhibited regular variation with the content of macerals. Compared with raw coal (RC), PV had the most abundant alkyl chains and a lower degree of condensation, resulting in the highest tar yield (14.11 %), which was 4.02 % higher than that of RC (10.09 %). The tar contained abundant aliphatics and phenolics. PI contained larger fused aromatics structure and shorter length alkyl side chains. Although tar yield from PI was relatively low (6.02 %), the tar contained the highest three- and four-ring aromatic hydrocarbons, which was more conducive to deriving value-added products. The tar yield from fractions with varying macerals content indicated that an increase in inertinite by approximately 10 % resulted in a 1 % decrease in tar yield. The interaction of the macerals was confirmed and it was affected by the content of vitrinite and inertinite. When the vitrinite and inertinite coexisted with proper proportion, the tar and aromatic hydrocarbons formation could be promoted.