Comments on the Artificiality of Actual Amount Adsorbed

Sircar, Shivaji

doi:10.1021/acs.iecr.8b00852

Cited by 9 publications

(7 citation statements)

References 34 publications

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“…The amount adsorbed cannot be determined directly and must be estimated from the experimental measurements of GSE using assumptions about the nature of the adsorbed phase. 22−24 The relationship of GSE (n ex ) for the adsorption of gas and the absolute or actual amount adsorbed is defined 23 by the equations below…”

Section: Concept Of Gibbs Surface Excessmentioning

confidence: 99%

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Perspectives of Gas Adsorption and Storage in Kerogens and Shales

Thomas

2023

Energy Fuels

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Shale gas from unconventional resources will contribute to meeting the energy demand during the transition to a net-zero carbon economy. In this minireview, the current status of understanding methane adsorption on kerogens and shales is discussed in relation to methane storage capacity. Standard subcritical adsorption studies provide characterization data (micropore volumes, total pore volumes, surface areas, and pore size distributions) for the porous structures of shales and kerogens. However, supercritical methane adsorption measurements under simulated geological conditions are necessary to assess realistic methane adsorption storage capacities. Supercritical methane adsorption on shale and shale components (kerogens and clays) under high pressure and temperature conditions that simulated geological conditions is compared. Kerogen structural characteristics are discussed in relation to supercritical methane isotherms and isobars. The contribution of adsorbed methane gas relative to “free” or compressed gas to the total gas stored in shale is considered. The importance of kerogens in both storage of the adsorbed phase and as the source of methane is highlighted, and the areas where knowledge and understanding are deficient are identified, in particular, the relationship of kerogen type and maturity with supercritical methane adsorption under simulated geological conditions. The competitive adsorption of water on methane capacity is also an area where more detailed studies are necessary. These are challenges to address gaps in the current knowledge and understanding, which require future research.

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Section: Concept Of Gibbs Surface Excessmentioning

confidence: 99%

“…The Gibbs surface excess is the only measurable experimental quantity for the adsorption of pure gases and mixtures. 23 It can be used unambiguously to describe all practical aspects of adsorption. 22 Absolute isotherms can be calculated from the surface excess isotherm using eqs 2 and 3.…”

Section: Supercritical Methane Adsorption Under Simulated Geologicalmentioning

confidence: 99%

Perspectives of Gas Adsorption and Storage in Kerogens and Shales

Thomas

2023

Energy Fuels

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“…On the other hand, the GSE framework can be conveniently used to study many topics of practical interest such as the pure and multigas adsorption equilibria and heats, adsorbate mass transfer into adsorbent particles, formulation of mathematical models for adsorptive separation processes, etc . The GSE framework can also be conveniently used to estimate the amount of gas stored in a vessel packed with an adsorbent and the optimum pressure to maximize the amount of stored gas …”

Section: Uniqueness Of Gsementioning

confidence: 99%

“…13,14 A recent publication has dealt with the artificiality of AAA caused by the above-described assumptions. 6 The following three artifacts were pointed out:…”

Section: ■ Uniqueness Of Gsementioning

confidence: 99%

“…16 The GSE framework can also be conveniently used to estimate the amount of gas stored in a vessel packed with an adsorbent and the optimum pressure to maximize the amount of stored gas. 6 A differential thermodynamic heat of adsorption called iso-NET heat (q, kcal/mol) for a pure ideal gas can be defined analogous to eqs 7 and 8 for the NET framework:…”

Section: ■ Uniqueness Of Gsementioning

confidence: 99%

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Uniqueness of Gibbsian Surface Excess

Sircar

2019

Ind. Eng. Chem. Res.

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The Gibbsian surface excess (GSE) can unequivocally measure the extent of adsorption of a gas on a solid adsorbent. A differential iso-excess heat of adsorption based on the GSE thermodynamic framework provides a physically and thermodynamically consistent description of the adsorbent heterogeneity or homogeneity. The actual amount adsorbed (AAA) cannot be experimentally measured. It must be estimated from the experimental GSE by making extraordinary assumptions regarding the nature of the adsorbed phase. Thus, the AAA is a model dependent variable. A differential iso-steric heat of adsorption based on the AAA thermodynamic framework can be misleading and artificial. The NET amount adsorbed (NAA) is an experimental variable. It is also directly related to GSE. Thus, it provides no further insight into the adsorption system vis a vis the GSE. A differential iso-NET heat of adsorption based on the NAA thermodynamic framework can be misleading and fictitious.

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