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- PublicationAccès libreOn the characterization of microporous carbons by immersion calorimetry alone(1997)
;Centeno, Teresa A.Immersion calorimetry is a useful tool for the characterization of solid surfaces in general, but in the case of microporous solids it usually requires complementary information, obtained from an adsorption isotherm. This article demonstrates the possibilities and the limitations of this technique when used alone. It appears that the use of a standard value for the enthalpy immersion does not always provide a reliable assessment of the total surface area.
- PublicationAccès libreOn the use of standard DRK isotherms in Dubinin’s t/F method(2000)
;Hugi-Cleary, DeirdreIt is shown that the adsorption of benzene, carbon tetrachloride, dichloromethane and nitrogen by a typical non-porous carbon black follows the Dubinin–Radushkevich–Kaganer equation. The requirement for temperature invariance is fulfilled, with an average characteristic energy Eo=10.8 kJ mol−1. This expression is compared with the standard isotherms for benzene and carbon tetrachloride at 293 K proposed by Dubinin and used as a reference in the so-called t/F method, which leads to the non-porous surface area of active carbons. It appears that Dubinin’s isotherm contains inconsistencies, which are compensated for internally. Alternative DRK expressions, applicable to different vapours, are therefore proposed. The present study also shows the limits of Dubinin’s method with respect to comparison plots at higher relative pressures.
- PublicationAccès libreDynamic adsorption, in active carbon beds, of vapour mixtures corresponding to miscible and immiscible liquids(1999)
;Lavanchy, AndréIt is shown that the combined Myers–Prausnitz–Dubinin theory (MPD) can be extended to the adsorption of ternary mixtures from an air stream. When combined with a computer model developed for dynamic adsorption, it provides a satisfactory agreement with the experimental breakthrough curves in active carbon beds. On the other hand, as illustrated by a mixture of water and 2-chloropropane vapours, MPD is no longer valid when the corresponding liquids are not miscible. In this case, binary adsorption can be described with a relatively good precision by assuming independent co-adsorption of the vapours. This, in turn, leads to satisfactory previsions for dynamic adsorption.
- PublicationAccès libreMicroporosity in carbon blacksMicroporous carbon blacks can be characterized by the same techniques as activated carbons, using the classical DR equation and comparison plots based on non-porous materials. The CO2 adsorption isotherm at 273 K, combined with computer modelling, also leads to an assessment of microporosity. The results agree with independent techniques such as immersion calorimetry into liquids of variable molecular dimensions and a modified Dubinin equation. The study also confirms that the comparison plots based on N2 (77 K), CO2 (273 K) and C6H6 (293 K) do not necessarily lead to overlapping results for the total micropore volume and the external surface area of the carbons.
- PublicationAccès libreWater adsorption by activated carbons in relation to their microporous structure(2003)
;Slasli, Abdou ;Jorge, M. ;Seaton, N. A.The present paper examines the adsorption of water by microporous carbons in the absence of specific interactions. The modelling of water adsorption for 293 and 310 K, using variable pore size distributions (PSD), shows that the type V isotherms follow the Dubinin–Astakhov (DA) equation and fulfill the requirement for temperature invariance. Furthermore, the parameters of the DA equation can be related in a simple way to structural properties of the model carbons. For a number of well-characterized carbons, the type V isotherms generated by combining model isotherms with the corresponding PSDs are in good agreement with the limiting isotherms at 293 and 310 K derived on the basis of a recent development of Dubinin’s theory. This approach will provide the basis for further studies including specific interactions.
- PublicationAccès libreRecent developments in Dubinin's theory(1998)Dubinin's theory, developed in successive stages between 1947 and 1971 and extended to immersion calorimetry in the 1980s, has recently found new applications. It has been shown that water adsorption by microporous carbons, corresponding to type IV and V isotherms, can be described by the Dubinin-Astakhov (D-A) equation. The extension to immersion calorimetry is also valid and provides information on the interaction between water and oxygen-containing surface groups. The D-A equation has also been combined successfully with the theory of Myers and Prausnitz, which leads to a satisfactory description of static and dynamic adsorption of binary mixtures by active carbon beds.
- PublicationAccès libreMicropore sizes in activated carbons determined from the Dubinin–Radushkevich equation(2001)
; ;López-Ramón, M. V. ;Hugi-Cleary, DeirdreGuillot, André
- PublicationAccès libreDynamic adsorption of vapour mixtures in active carbon beds described by the Myers-Prausnitz and dubinin theories(1997)
;Lavanchy, AndréThe adsorption of binary vapour mixtures from air by active carbon beds can be predicted with a good accuracy by adapting a model developed earlier for single vapours. This model is based on a semi-implicit finite difference scheme. Multiple adsorption of vapours is described by the combined theories of Myers-Prausnitz and of Dubinin (MPD), which have already been applied successfully to static adsorption. A good agreement is found between the predicted and the experimental breakthrough curves of the systems 2-chloropropane + chlorobenzene and carbon tetrachloride + chlorobenzene on two activated carbons at 298 K and under different experimental conditions.
- PublicationAccès libreThe comparison of experimental and calculated pore size distributions of activated carbonsActivated carbons are disorganized materials with variable pore size distributions (PSD). If one assumes that the porosity consists mainly of locally slit-shaped micropores, model isotherms can be obtained by computer simulations and used to assess the PSD on the basis of experimental isotherms. In the present study, CO2 isotherms have been measured at 273 K on seven well-characterized microporous carbons with average micropore widths between 0.65 and 1.5 nm and analysed with model isotherms obtained with standard Monte Carlo simulations. The resulting PSD are in good agreement with those obtained from a modified Dubinin equation, from liquid probes of molecular dimensions between 0.4 and 1.5 nm, from STM and from modelling based on CH4 adsorption at 308 K. The present study validates the determination of micropore distributions in active carbons based on CO2 isotherms, provided that no gate effects are present.
- PublicationAccès libre