Analysis of CH₄ evolution in fast pyrolysis of lignite under H₂ atmosphere

The fast hydropyrolysis of Huolinhe lignite were carried out under pressure in a tubular reactor with a transporter for coal samples. The effect of H₂ on CH₄ evolution and crack of chemical bonds were analyzed. Under pressure fast hydropyrolysis conditions, CH₄ yield was higher under H₂ atmosphere than that under N₂ atmosphere, and increased with increasing temperature and pressure. Compared with N₂ atmosphere, the yield of CH₄ increased by 72.5% under 50% H₂ atmosphere at 900 ℃ and 1.0 MPa. H₂ or H· free radical induced the cracks of aromatic rings, side chains, ether linkages and aliphatic chains in the char, which could promote the coal pyrolysis. The increased yield of CH₄ was mainly due to the external donor H. Below 700 ℃, the action of H₂ with active groups in coal structure affected the pyrolysis of coal; above 700 ℃, hydrogenation of char promoted coal pyrolysis, leading to an increase in CH₄ yield.