A developed dual-site Langmuir model to represent the high-pressure methane adsorption and thermodynamic parameters in shale

Abstract

Comprehending the mechanism of methane adsorption in shales is a crucial step towards optimizing the development of deep-buried shale gas. This is because the methane adsorbed in shale represents a significant proportion of the subsurface shale gas resource. To properly characterize the methane adsorption on shale, which exhibits diverse mineral compositions and multi-scale pore sizes, it is crucial to capture the energy heterogeneity of the adsorption sites. In this paper, a dual-site Langmuir model is proposed, which accounts for the temperature and pressure dependence of the density of the adsorbed phase. The model is applied to the isothermals of methane adsorption on shale, at pressures of up to 30 MPa and temperatures ranging from 40 to 100 °C. The results show that the proposed model can describe the adsorption behavior of methane on shale more accurately than conventional models, which assume a constant value for the density of adsorbed phase. Furthermore, the proposed model can be extrapolated to higher temperatures and pressures. Thermodynamic parameters were analyzed using correctly derived equations. The results indicate that the widely used, but incorrect, equation would underestimate the isosteric heat of adsorption. Neglecting the real gas behavior, volume of the adsorbed phase, and energy heterogeneity of the adsorption sites can lead to overestimation of the isosteric heat of adsorption. Furthermore, the isosteric heat evaluated from excess adsorption data can only be used to make a rough estimate of the real isosteric heat at very low pressure.

Review of Developed Methods for Measuring Gas Uptake and Diffusivity in Polymers Enriched by Pure Gas under High Pressure

“…Thus, dual sorption is observed for all CB-blended EPDM composites. The dual-mode sorption phenomenon is observed over the entire pressure range up to 90 MPa can be expressed as [ 36 , 37 , 39 , 40 , 41 , 42 , 43 ]: …”

A review on agrowaste based activated carbons for pollutant removal in wastewater systems

“…The variations in adsorption energy across distinct sorbent surface sites are elucidated by modifying the Langmuir isotherm model. This particular model is constructed based on the assumption that the sorbent possesses two types of adsorption sites: strong (type 1) and weak (type 2) sorption sites [71,72]. Experimental adsorption data for liquid-solid adsorption systems can be interpreted using the dual-site Langmuir isotherm model, as expressed in Equation 33:…”