FTIR study of the evolution of coal structure during the coalification process

A series of coals varying in rank from peat to semi-anthracite was studied by Fourier Transform infrared spectroscopy (FTIR) and curve-fitting analysis in order to gain additional information on coal structure and the main structural changes that take place during the coalification process. Several structural parameters based on FTIR data and curve-resolved bands were calculated. These parameters provide quantitative evidence of the increase of aromaticity and the loss of aliphatic and oxygen-containing structures with increasing maturation. The analysis of the aromatic C---H out-of-plane region (900-700 cm−1) reveals the loss of aromatic substituents up to the stage of bituminous coal and the subsequent increase in the degree of aromatic condensation with increasing coalification. The ratio of aromatic carbons to carboxyl groups (1605 cm−1/1605 cm−1 + 1705 cm−1) appears to be a suitable parameter for assessing the natural maturation of coal. Copyright