Department of Chemical and Biomolecular Engineering, Rice University , Houston, Texas 77005, United States.
Langmuir. 2017 Oct 24;33(42):11189-11202. doi: 10.1021/acs.langmuir.7b02055. Epub 2017 Sep 12.
The prediction of fluid phase behavior in nanoscale pores is critical for shale gas/oil development. In this work, we use a molecular density functional theory (DFT) to study the effect of molecular size and shape on partitioning to graphite nanopores as a model of shale. Here, interfacial statistical associating fluid theory (iSAFT) is applied to model alkane (C - C) adsorption/desorption/phase behavior in graphite slit pores for both pure fluids and mixtures. The pure component parameters were fit to the bulk saturated liquid density and vapor pressure data in selected temperature ranges. The potential of interaction between the fluid and graphite is modeled with a Steele 10-4-3 potential that is fit to the potential of mean force from single-molecule simulations. Good agreement is found between theory and molecular simulation for the density distributions of pure components in slit pores. The critical properties of methane, ethane, and their mixtures as well as the shift in bubble point and dew point densities were studied, showing good agreement with simulation. The competitive adsorption of mixtures of normal and branched alkanes in graphite pores was also studied. Heavier components more strongly adsorb up to the point that the entropic penalty due to confinement reduces adsorption.
在纳米尺度孔隙中预测流体相行为对于页岩气/油的开发至关重要。在这项工作中，我们使用分子密度泛函理论（DFT）研究分子大小和形状对石墨纳米孔隙中分配的影响，将其作为页岩的模型。在这里，界面统计关联流体理论（iSAFT）被应用于模拟烷烃（C-C）在石墨狭缝孔隙中的吸附/解吸/相行为，包括纯流体和混合物。纯组分参数拟合到选定温度范围内的饱和液体密度和蒸气压数据。流体和石墨之间的相互作用势能采用 Steele 10-4-3 势能进行建模，该势能拟合自单分子模拟的平均力势能。理论与纯组分在狭缝孔隙中分子模拟的密度分布之间存在良好的一致性。研究了甲烷、乙烷及其混合物的临界性质以及泡点和露点密度的移动，与模拟结果吻合良好。还研究了正构和支链烷烃混合物在石墨孔隙中的竞争吸附。较重的组分在由于受限导致的熵罚减小吸附之前更强地吸附。
