Surface excess amounts in high-pressure gas adsorption: Issues and benefits

Jean Rouquerol (1) , Françoise Rouquerol (1) , Phillip Llewellyn (1) , Renaud Denoyel (1)

1 MADIREL - Matériaux divisés, interfaces, réactivité, électrochimie

This paper introduces a calculation procedure aimed at improving the accuracy and meaningfulness of high-pressure gas adsorption data obtained by either adsorption manometry or gravimetry. The procedure is based on the Gibbs model and avoids the usual simplifying assumption that the well-defined Gibbs Dividing Surface (the GDS) coincides with the ill-defined adsorptive-accessible surface of the microporous adsorbent. Instead, it makes a clear distinction between the two surfaces and introduces the concept of “Gibbs exclusion volume” (i.e. the volume enclosed by the GDS) which is shown to be central in the calculation of the surface excess amount and useful to avoid any confusion with the adsorbent volume. It is shown, in the case of methane adsorption on gas shale, how this procedure avoids introducing the uncertainty due to the dead volume determination in an inter-laboratory comparison. The conditions for a surface excess isotherm to be a useful intermediate step in the assessment of the amount adsorbed are stressed and illustrated.

Keywords: Gibbs adsorption model; Gibbs exclusion volume; Amount adsorbed; Surface excess amount; Dead space; Buoyancy correction

Domains: Chemical Sciences

Jean Rouquerol, Françoise Rouquerol, Phillip Llewellyn, Renaud Denoyel. Surface excess amounts in high-pressure gas adsorption: Issues and benefits. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016, 496, pp.3 - 12. ⟨10.1016/j.colsurfa.2015.10.045⟩. ⟨hal-01476943⟩