Study of the influence of pressure on enhanced gaseous hydrocarbon yield under high pressure–high temperature coal pyrolysis

The influence of pressure on the yield of gaseous hydrocarbon products derived from pyrolysis of Fushun and Xianfeng coals have been investigated in an anhydrous and confined system. Pyrolysis was performed in sealed gold tubes at 380°C and under the pressures ranging from 50 to 250MPa for 24h. The results show that the effect of pressure on coal pyrolysis and product generation should not be ignored. For the Fushun and Xianfeng lignite, the yields of gaseous hydrocarbon generation increase by 9.1% and 12.7% when the pressure increases from 50 to 250MPa, respectively. However, the yields of hydrogen gas decrease greatly with pressure. The hydrogen gas yields of Fushun and Xianfeng lignite decrease by 76.5% and 75.9%, respectively, when the pressure increases from 50 to 250MPa. Yields of carbon dioxide gas of Fushun and Xianfeng coals were enhanced with increasing pressure by 7.4% and 8.9% respectively. Data of stable carbon isotope compositions reveal that the methane and ethane carbon isotope values are also affected by pressure, as they become heavier by approximately 1.2‰ (PDB) when the pressure is increased from 50 to 250MPa. Simultaneously, the hydrogen isotope compositions of methane and ethane increase by 10.3‰ and 7.1‰, respectively. Our experimental results suggest that the increase in gaseous hydrocarbon yield is resulted from synthesis of carbon dioxide and hydrogen and pressure serves to facilitate the synthetic process.