Prediction of competitive adsorption on coal by a lattice DFT model

Abstract

Adsorption is one of the main mechanisms involved in the ECBM process, a technology where CO 2 (or flue gas, i.e. a CO 2 /N 2 mixture) is injected into a deep coal bed, with the aim of storing CO 2 by simultaneously recovering CH 4 . A detailed understanding of the microscopic adsorption process is therefore needed, as the latter controls the displacement process. A lattice DFT model, previously extended to mixtures, has been applied to predict the competitive adsorption behavior of CO 2 , CH 4 and N 2 and of their mixtures in slit-shaped pores of 1.2 and 8 nm width. In particular, the effect of temperature, bulk composition and density on the resulting lattice pore profiles and on the lattice excess adsorption isotherms has been investigated. Important insights could be obtained; when approaching near critical conditions in the mesopores, a characteristic peak in the excess adsorption isotherm of CO 2 appears. The same effect could be observed neither for the other gases nor in the micropores. Moreover, in the case of mixtures, a depletion of the less adsorbed species close to the adsorbent surface is observed, which eventually results in negative lattice excess adsorption at high bulk densities.

CO2-wettability of low to high rank coal seams: Implications for carbon sequestration and enhanced methane recovery

“…In summary, once injected, CO2 will occupy the smallest pores (micropores of coal matrix) and brine will occupy larger pores (cleats), and as a result brine will be watered-out. In addition, it is experimentally proven that methane wettability of coal is lower than that of CO2 [34], and the sorption capacities of CO2 relative to CH4 on the coal surface are 1.1 -9.1 times higher depending upon the coal rank [31,[79][80][81]. Thus methane, which was adsorbed on the coal surfaces, will be displaced rather easily by CO2.…”

Measuring and modelling supercritical adsorption of CO2 and CH4 on montmorillonite source clay

“…The LDFT model has been applied successfully to reproduce measurements of subcritical and supercritical adsorption on various porous materials, including commercial sorbents (e.g. zeolites, silica and carbons [49,50,51]) and geosorbents, such as coal [52,53] and shale [54]. One of the distinctive features of this approach is that information on the microscopic structural properties of materials, such as the pore sizes and pore volume, are direct inputs to the model.…”

Molecular simulation studies of hydrocarbon and carbon dioxide adsorption on coal

“…Understanding the mechanism of CH 4 , C 2 H 6 , and CO 2 sorption on coal is a key factor for CO 2 storage and hydrocarbons recovery. Sorption of gases in coal has been studied for decades (Bae and Bhatia 2006;Billemont et al 2011Billemont et al , 2013Brochard et al 2012aBrochard et al , 2012bBusch and Gensterblum 2011;Busch et al 2003Busch et al , 2004Day et al 2008;Fitzgerald et al 2005;Gensterblum et al 2014;Goodman et al 2007;Krooss et al 2002;Li et al 2010;Ottiger et al 2008;Pini et al 2009Pini et al , 2010. Theoretical models have been developed and improved to study gas sorption on coal by several authors (Connell et al 2010;Lu and Connell 2007;Lu et al 2008;Pan and Connell 2007, 2012Sakurovs et al 2007; Vandamme et al 2010).…”