Absorption and Adsorption of Methane and Carbon Dioxide in Hard Coal and Active Carbon

Abstract

The paper shows what can be deduced on sorption mechanisms in hard coals and active carbon by using a theoretical model of sorption of small molecules in elastic submicroporous materials. This model (referred to as the multiple sorption modelsMSM) describes both adsorption and absorption phenomena. Basic assumptions and formulas of the MSM are presented. The computations were performed for isotherms of CO2 and CH4 at elevated pressures on three coal samples of different rank and on an active carbon. Nonideality of the sorbates is handled by an original state equation providing consistent information on fugacity and cohesion energy corresponding to a given molar volume of sorbate molecules in the sorption system. Surface structure of the studied coals and energetic parameters of the systems determined with MSM are compared to those obtained by using BET and Dubinin-Radushkievitch equations. It was stated that MSM provides more information on surface structure (including submicropores) and clearly explains sorption properties of hard coals (together with expansion phenomena). It is also applicable to examination and prediction of adsorption on microporous materials (like active carbon).

Carbon dioxide and methane sorption in high volatile bituminous coals from Indiana, USA

“…Milewska-Duda et al (2000) convincingly provide such an explanation based on their modeling study. Their computations give evidence that, while both adsorption and absorption play important role for the storage of both gases, for CO 2 the contribution of pure absorption is comparable to that of the pure adsorption, whereas for CH 4 the pure absorption is much lower.…”

Competitive adsorption equilibria of CO2 and CH4 on a dry coal

“…Therefore, the uptake process of CO 2 can be viewed as a combination of adsorption on the coal's surface and penetration (absorption) into the coal's matrix. Following this idea, Duda and coworkers used a multiple sorption model (including both adsorption and absorption mechanisms) to describe the behavior of coal when exposed to CO 2 and CH 4 (Milewska-Duda et al 2000). It is worth noting that, as we will see later in the discussion section, different representations of the coal's uptake mechanisms of gases, i.e.…”

Characterization of the CO2 fluid adsorption in coal as a function of pressure using neutron scattering techniques (SANS and USANS)

“…There has also been discussion about adsorption mechanisms (e.g. Milewska-Duda et al, 2000) and speculations about the changes in the structure of the matrix of the coal that could result from the absorption of CO 2 (Larsen et al, 1997;Larsen, 2004). Even though there have been numerous studies conducted, important questions about the structural stability as well as adsorption mechanisms and controls on sub-and supercritical CO 2 adsorption in coal remain open.…”