Investigation of hydrogasification of low-rank coals to produce methane and light aromatics in a fixed-bed reactor

• Pressurized hydrogasification of three low-rank coals in a fixed-bed reactor.
• Increased yields of methane, BTX and naphthalene with increasing hydrogen pressure.
• Complicated changes of CO2, CO and phenol yields with hydrogen pressure.
• Concerted influences of hydrogen pressure and coals on S/C molar ratio in char.
• A power model to fit the char hydrogasification rate with pressure.

The hydrogasification of three low rank coals (YX lignite, XD lignite and ZD subbituminous coal) was carried out in a fixed-bed reactor to investigate the effects of hydrogen pressure on the formations of gaseous, liquid and char products. The reactor was typically heated at a rate of 15 °C/min up to 700 °C with a holding time of 60 min under various hydrogen pressures up to 5 MPa. The yields of BTX (i.e., benzene, toluene, and xylene) and naphthalene increased with increasing hydrogen pressure up to 5 MPa for all three coals, but more significant for XD and ZD coals. The compositional analysis of char revealed that the chars produced by the hydrogasification had higher molar ratios of H/C and lower molar ratios of N/C than those produced by the pyrolysis in N2 atmosphere, whereas the former chars had higher or lower molar ratios of S/C than the latter chars from case to case depending principally on coals. The apparent reaction rate constants of the chars hydrogasification in the isothermal stage as a function of hydrogen pressure were found to follow a power equation of the power exponents varying with coals.