Thermogravimetric-gas chromatographic study on effects of hydrogen pressure on coal hydrogenation

Thermogravimetric characteristics and evolution of main gaseous products during hydrogenation of two coals were studied in a thermogravimetry-gas chromatography combined system at 15℃/min, 0.1~5MPa and a final temperature of 1000℃. The results show that the hydrogenation process occurs in four stages: drying and degassing, hydropyrolysis, rapid hydrogasification, and slow hydrogasification. With increasing hydrogen pressure, hydrogenation of volatile radicals is promoted and decomposition of oxygen-containing functional groups forming carbon oxides is inhibited. During hydropyrolysis stage, the weight loss rate increases with hydrogen pressure for FG coal, while the hydrogen pressure has little influence on that for HLE coal. During the rapid hydrogasification stage, the evolution rate of CH₄ increases with hydrogen pressure; for HLE coal the evolution rate of CH₄ doesn't increase with hydrogen pressure any more at high pressures (3~5MPa). The HLE coal with higher oxygen content contains more active sites provided by the oxygen-containing groups in the semi-char. The FG coal with higher H/C atomic ratio is able to provide more hydrogen by itself during hydrogenation reactions. The kinetic data of the slow hydrogasification stage is k₀=2.38×10⁷ (min^-1·MPa^-1), E=231kJ/mol, n=1 for the FG coal and k₀=2.64×10³ (min^-1·MPa^-0.736), E=127kJ/mol, n=0.736 for the HLE coal.