煤层气(矿井瓦斯)是一种有望替代传统化石燃料,如煤、石油和天然气的非常规气体.作为可得的清洁能源,它的利用被认为是节能和经济的选择.在本工作中,非金属原子X (X=H, O, N, S, P, Si, F, Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型.通过密度泛函理论系统地研究了煤层气组分Y (Y=CH4, CO2, H2O)在非金属原子修饰石墨烯上的吸附作用.结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附.态密度和差分电荷密度共同表明了这种弱的相互作用.其中, H和Cl对CH4的作用较大；N、O、F、Cl对CO2的作用较强；N, Cl对H2O的影响不容忽视.总的来说,吸附能大小依次为：H2O>CO2>CH4.因此,在CH4富集的煤层里注入H2O或CO2可以与CH4形成竞争吸附,进而提高煤层气采收率.本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情,并为煤层瓦斯的开采与分离提供了有用的信息.%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-metal ic 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 systematical y 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.
展开▼
