Pyrolysis behavior and bonding information of coal — A TGA study

Pyrolysis of 34 Chinese coals is studied in a TGA coupled with a mass spectrometer. The mass loss registered in TGA during temperature programmed heating is attributed mainly to devolatilization of fragments generated from cleavage of covalent bonds because retrogressive reactions of small volatile radical fragments do not produce solid products and that of large volatile radical fragments are slow and occur mainly outside of the sample crucible. Each of the DTG curves is fitted by a set of sub-curves and regression using 6 sub-curves yields the best fitting. Each of the 6 sub-curves is assigned to cleavage of a group of covalent bonds in coal, which is validated by model compounds and literature data. The trends in peak temperature and peak area of the sub-curves with respect to changes in C% in the coals are clear and similar to changes in some of the physical properties of coals. The analysis method presented is useful in analyses of coal structure and pyrolysis reactions. Furthermore, TG analysis is suggested to replace proximate analysis due to the rich volatile-temperature information and easy identification of volatiles generated from decomposition of carbonates.