Molecular simulation studies of hydrocarbon and carbon dioxide adsorption on coal

Abstract

Sorption isotherms of hydrocarbon and carbon dioxide (CO 2 ) provide crucial information for designing processes to sequester CO 2 and recover natural gas from unmineable coal beds. Methane (CH 4 ), ethane (C 2 H 6 ), and CO 2 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 CH 4 , C 2 H 6 , and CO 2 sorption on dry coal when pressure is over 6 MPa. CO 2 is more closely packed due to stronger interaction with coal and the stronger interaction between CO 2 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 T c 2 /P c ) in the Peng-Robinson equation of state is an important factor affecting the sorption behavior of hydrocarbons. CO 2 injection pressures of lower than 8 MPa may be desirable for CH 4 recovery and CO 2 sequestration. This study provides a quantitative understanding of the effects of temperature on coal sorption capacity for CH 4 , C 2 H 6 , and CO 2 from a microscopic perspective.

Molecular Insights on the CH4/CO2 Separation in Nanoporous Graphene and Graphene Oxide Separation Platforms: Adsorbents versus Membranes

“…The addition of the second membrane layer nearly doubles the adsorption of CH 4 (Figure 6). You et al 61 and Zhang et al 45,62 have similarly obtained the adsorption isotherms for Gas Transport Properties. To examine the CH 4 /CO 2 separation efficiency in the NPG and NPGO membranes, the diffusion coefficient, permeance, flow, and selectivity of the gaseous species were calculated.…”

“…The addition of the second membrane layer nearly doubles the adsorption of CH 4 (Figure ). You et al and Zhang et al , have similarly obtained the adsorption isotherms for CH 4 on coal, which has graphite-like surface structures. They also report a drop in the CH 4 adsorption with an increase in the CH 4 partial pressure.…”

Laboratory Characterization of Shale Oil Storage Behavior: A Comprehensive Review

“…Therefore, molecular simulation is widely used to study the oil adsorption behavior in shales. The molecular simulation methods to study adsorption behavior in organic-rich shales have been well-documented in the literature; − therefore, they are not repeated in this review.…”

The effect of coal grain size on the sorption of hydrocarbons from gas mixtures

“…The micropores become accessible for the sorbed molecules if mesopores and macropores are present. These pores are treated as transport pores . Thus, the porous structure is another important feature of coal contributing to the sorption characteristic.…”

“…These pores are treated as transport pores. 35 Thus, the porous structure is another important feature of coal contributing to the sorption characteristic. The results indicate that the porous structure of coals tested was composed of micropores and mesopores in the amount quantified by the results of the pore size distribution analysis on the basis of nitrogen sorption isotherms.…”