Characteristics of gas evolution profiles during coal pyrolysis and its relation with the variation of functional groups

Strict relation between the substituents or functional groups attached to the coal macromolecules and the generation of the volatile products, e.g., CH₄, H₂O, CO, CO₂, etc., during the coal pyrolysis is an important but confusing subject. In this paper, quadrupole mass spectrometry, gas chromatography, and ¹³C nuclear magnetic resonance are applied to real-time monitoring the formations of volatile products, off-line quantitative determination of the total products from the pyrolysis of a sub-bituminous coal (SC), and the changes of diverse substitents in the SC along with coke foamation, respectively. These measurements are also performed for the pyrolysis of a caking coal to contrast SC. The qualitative and quantitative data reveal that, during coal pyrolysis, the functional groups related with the formation of CO, i.e., ether, carbonyl, and anhydride, can directly generate CO via bond breaking, or take a detour of the formation of other intermediates via condensation and recombination firstly. Moreover, the formations of CO₂ and CH₄ are related to the direct removal of -COO- and -CH₃, respectively.