Competitive Sorption of CO₂ with Gas Mixtures in Nanoporous Shale for Enhanced Gas Recovery from Density Functional Theory

Abstract

CO 2 competitive sorption with shale gas under various conditions from simple to complex pore characteristics is studied using a molecular density functional theory (DFT) that reduces to perturbed chain-statistical associating fluid theory in the bulk fluid region. The DFT model is first verified by grand canonical Monte Carlo simulation in graphite slit pores for pure and binary component systems at different temperatures, pressures, pore sizes, and bulk gas compositions for methane/ethane with CO 2 . Then, the model is utilized in multicomponent systems that include CH 4 , C 2 H 6 , and C3+ components of different compositions. It is shown that the selectivity of CO 2 decreases with increases in temperature, pressure, nanopore size, and average molecular weight of shale gas. Extending the model to more realistic situations, we consider the impact of water present in the pore and consider the effect of permeation of fluid molecules into the kerogen that forms the pore walls. The water−graphite interaction is calibrated with contact angle from molecular simulation data from the literature. The kerogen pore model prediction of gas absolute sorption is compared with experimental and molecular simulation values in the literature. It is shown that the presence of water reduces the CO 2 adsorption but improves the CO 2 selectivity. The dissolution of gases into the kerogen matrix also leads to the increase in CO 2 selectivity. The effect of kerogen type and maturity on the gas sorption amount and CO 2 selectivity is also studied. The associated mechanisms are discussed to provide fundamental understanding for gas recovery by CO 2 .

Modeling Lower Critical Solution Temperature Behavior of Associating Dendrimers Using Density Functional Theory

“…In the current work, a simple weighting is used and the expression for y ij [ρ ̅ k ( r 1 )], the cavity correlation function for homogeneous hard sphere fluid, is only needed at contact and can be found in the work of Tripathi and Chapman ,,,,− …”

Deformation of Nanoporous Materials in the Process of Binary Adsorption: Methane Displacement by Carbon Dioxide from Coal

“…Equations , , and provide a general thermodynamic methodology for predicting the adsorption stress and strain induced by mixture adsorption based on the theoretical adsorption isotherms, which depend on the sample volume, V , which varies due to the deformation. The theoretical adsorption isotherms can be determined by different means, similarly as it is done for single component systems: in particular, by using molecular level models of density functional theory , and Monte Carlo simulations, , or common phenomenological equations with parameters fitted against the experimental data, like Langmuir, Dubinin–Radushkevich, and Derjaguin–Broekhoff–de Boer, among others. Note that the sample volume, adsorption isotherms, thermodynamic potential, and other extensive characteristics can be expressed in the reduced units, as is customary in the adsorption literature, per unit mass of adsorbent.…”

Modeling Hydrocarbons Adsorption in Amorphous Nanoporous Carbonaceous Materials

“…Conventional methods of pore structure characterization rely on oversimplified slit-shaped and cylindrical pore models, which do not capture the nanoscale specifics of carbon disordered structures. [12][13][14][15][16][17][18][19][20][21] Considerable effort has been devoted to developing theoretical and computational methods for generating molecular models of amorphous carbons. 22 The Hybrid Reverse Monte Carlo (HRMC) method uses MC simulations to reproduce the experimental radial distribution functions (RDF).…”