Isotopically exchangeable organic hydrogen in coal relates to thermal maturity and maceral composition

Hydrogen isotopic exchangeability (Hex) and δDn values of non-exchangeable organic hydrogen were investigated in coal kerogens ranging in rank from lignite to graphite. The relative abundance of Hex is highest in lignite with about 18% of total hydrogen being exchangeable, and decreases to around 2.5% in coals with Ro of 1.7 to ca. 5.7%. At still higher rank (Ro > 6%), Hex increases slightly, although the abundance of total hydrogen decreases. δDn is influenced by original biochemical D/H ratios and by thermal maturation in contact with water. Therefore, δDn does not show an overall consistent trend with maturity.