Methane and Carbon Dioxide Adsorption on Illite

Abstract

The adsorption of CH4 and CO2 onto illitic clay was investigated at the temperatures 298, 313, 328, 358, and 423 K (25, 40, 55, 85, and 150 °C) over a range of pressures up to 50 MPa using grand canonical Monte Carlo (GCMC) simulations. Our simulation results showed spontaneous and exothermic adsorption behavior of illite for CH4 and CO2 with enthalpy changes of −3.50 kJ/mol and −25.09 kJ/mol, respectively. Our results indicated that the interlayer counter cations (K+) play an important role in CO2 adsorption. Methane adsorption is mainly affected by the clay surface layers rather than the interlayer counter cations. The density and volume of CH4 and CO2 in their adsorbed phase at saturation were extrapolated from the linear portion of the excess adsorption isotherm. The resulting values were compared with available experimental data, and possible factors causing inconsistency were described. We discussed some issues associated with the Langmuir fit to experimental excess adsorption data in the case of low pressures. Our findings may provide some insights into gas adsorption behavior in illite-bearing shales.

Investigation of the factors influencing methane adsorption on illite

“…This conclusion is in accord with the results of the isothermal adsorption experiments performed by Ji et al who found that high temperatures impeded methane adsorption by illite. This observation was also reported by Mosher et al, Zhang et al, and Xiong et al, who found that the methane adsorption capacities of carbon and minerals decreased with increasing temperature. Furthermore, Figure A shows that the range of maximum pressure was between 16 MPa and 18 MPa when the temperatures were between 313 K and 373 K, which is in disagreement with previous reports .…”

“…These studies indicated that the GCMC method has been proven to be an effective method for investigating of the microcosmic adsorption mechanisms of adsorbents and have obtained some knowledge regarding methane adsorption by clay minerals. In addition, Zhang et al and Chen et al studied the adsorption behaviors of CH 4 , CO 2 , and their mixtures of illite using the GCMC and MD methods. In these studies, the total gas amounts and excess adsorption amounts of clay minerals were used to investigate the methane adsorption capacity.…”

Numerical Simulation of Gas Production from Gas Shale Reservoirs—Influence of Gas Sorption Hysteresis

“…This is a typical characteristic of the excess adsorption of supercritical fluids on solids [28]. The maximum excess adsorption occurs at a certain pressure where the rate of densities of the adsorbed and free phases is changing at the same rate with pressure [26,28]. Moreover, significant hysteresis can be seen between the adsorption and desorption isotherms for each sample.…”

“…A constant adsorbed phase density (ρ ads ), obtained as the value of the bulk gas density (ρ bulk ) at which the measured excess adsorption isotherm is zero [26], was applied for the conversion of excess sorption isotherms to absolute isotherms. At zero excess adsorption, the adsorbed gas is identical to and indistinguishable from the free bulk gas, and as such, the adsorbed phase density at saturation can be taken as the density of the bulk gas at this point [26].…”

“…A constant adsorbed phase density (ρ ads ), obtained as the value of the bulk gas density (ρ bulk ) at which the measured excess adsorption isotherm is zero [26], was applied for the conversion of excess sorption isotherms to absolute isotherms. At zero excess adsorption, the adsorbed gas is identical to and indistinguishable from the free bulk gas, and as such, the adsorbed phase density at saturation can be taken as the density of the bulk gas at this point [26]. Thus, adsorbed phase density at saturation was achieved, in this study, by plotting the excess adsorption isotherm as a function of bulk gas density and then extrapolating the decreasing linear trend of the excess adsorption isotherm to the bulk gas density axis [26][27][28].…”