Sorption isotherms of hydrocarbon and carbon
dioxide (CO2) provide crucial information for designing
processes to sequester CO2 and recover natural gas from
unmineable coal beds. Methane (CH4), ethane (C2H6), and
CO2 adsorption isotherms on dry coal and the temperature
effect on their maximum sorption capacity have been
studied by performing combined Monte Carlo (MC) and
molecular dynamics (MD) simulations at temperatures of
308 and 370 K (35 and 97 C) and at pressures up to
10 MPa. Simulation results demonstrate that absolute
sorption (expressed as a mass basis) divided by bulk gas
density has negligible temperature effect on CH4, C2H6,
and CO2 sorption on dry coal when pressure is over 6 MPa.
CO2 is more closely packed due to stronger interaction
with coal and the stronger interaction between CO2 molecules
compared, respectively, with the interactions between
hydrocarbons and coal and between hydrocarbons. The
results of this work suggest that the ‘‘a’’ constant (proportional
to Tc
2/Pc) in the Peng–Robinson equation of state
is an important factor affecting the sorption behavior of
hydrocarbons. CO2 injection pressures of lower than
8 MPa may be desirable for CH4 recovery and CO2
sequestration. This study provides a quantitative understanding
of the effects of temperature on coal sorption
capacity for CH4, C2H6, and CO2 from a microscopic
perspective.