The relationship between benzene carboxylic acids from coal via selective oxidation and coal rank

- The yields of benzene carboxylic acids increase from 18.5% to 51.3% with coal rank.
- Low rank coal benefits the generation of BCAs with a high number of carboxyl.
- With increasing of coal rank, BCAs with a small number of carboxyl increase.
- When the carbon content of coal is > 87%, the structure of coal has a mutation.

The oxidation of coal to produce benzene carboxylic acids (BCAs) was widely researched. However, the relationship between coal rank and BCAs from coal is unknown. In this study, 8 kinds of coal with different ranks were investigated and the effect of coal rank on the BCA yield distribution was studied. The results indicate that with the increase of coal rank, the yield of BCAs increases, and the structure of coal becomes more and more difficult to be degraded. In addition, BCA yield distribution varies significantly with the increase of coal rank. The results of 13C NMR show that with increasing coal rank, the fraction of aromatic carbon (fa) and mole fraction of aromatic bridgehead carbon in aromatic carbon (Xb) both are increased gradually, and alkyl-substituted degree of aromatic ring (δ) and average methylene chain length (Cn) both are decreased. More and more parent structures of phthalic acid, trimellitic acid, hemimellitic acid and prehnitic acid exist in the coal with the increase of coal rank. When the carbon content of coal is > 87%, the structure of coal has a mutation property that more and more circular catenations of aromatic rings exist in the structure of coal.