Acta Phys. -Chim. Sin. ›› 2014, Vol. 30 ›› Issue (2): 251-256.doi: 10.3866/PKU.WHXB201312243

• THEORETICAL AND COMPUTATIONAL CHEMISTRY • Previous Articles     Next Articles

CH4, CO2 and H2OAdsorption on Nonmetallic Atom-Decorated Graphene Surfaces

LIU Xiao-Qiang1, TIAN Zhi-Yue1, CHU Wei2, XUE Ying1   

  1. 1 Key Laboratory of Green Chemistry and Technology of the Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, P. R. China;
    2 College of Chemical Engineering, Sichuan University, Chengdu 610065, P. R. China
  • Received:2013-11-04 Revised:2013-12-24 Published:2014-01-23
  • Contact: XUE Ying E-mail:yxue@scu.edu.cn
  • Supported by:

    The project was supported by the National Key Basic Research Program of China (973) (2011CB201202) and National Natural Science Foundation of China (21173151).

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Abstract:

As an unconventional gas, coalbed methane (CBM) is a desirable alternative energy source to conventional fossil fuels such as coal, oil, and natural gas. In this work, non-metallic atom X (X=H, O, N, S, P, Si, F, or Cl)- decorated Gr (graphene) (X-Gr) was used to represent the surface models of coal with structural heterogeneity. Using density functional theory, the adsorption of the CBM component Y (Y=CH4, CO2, H2O) on X-Gr was systematically investigated. The results indicate that CH4, CO2, and H2O are weakly bound to X-Gr, and the interactions between the adsorbate and the surface can be described as physisorption, which was identified through the density of states and electronic density difference analysis. Furthermore, CH4 has very large adsorption energies to H- and Cl-decorated graphene. The dopants X, such as N, O, F, and Cl, are very good adsorbents for CO2 and the influence of the dopants N and Cl cannot be ignored for the adsorption of H2O. In general, the adsorption energies of H2O on X-Gr are larger than those of CO2, while CH4 has the lowest adsorption energies, namely, the order of adsorption is H2O> CO2>CH4. Consequently, the injection of H2O or CO2 into methane-rich coal seams strongly enhances the CBM recovery efficiency via competitive adsorption with CH4 on the coal surface. The results provide a molecular-level insight into the interactions between CBM and X-Gr, and might offer useful information for recovery and purification of coalbed methane.

Key words: Density functional theory, Coalbed methane, Nonmetallic atom-doped graphene, Adsorption