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Stoeckli, Fritz

Nom
Stoeckli, Fritz
Affiliation principale
Fonction
Professeur.e émérite
Email
fritz.stoeckli@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/471

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  • Publication
    Accès libre
    On the Adsorption, by Activated Carbons, of Some Sparingly Soluble Organics from Aqueous Solutions
    (2005)
    Hugi-Cleary, Deirdre
    ;
    Slasli, Abdou
    ;
    Stoeckli, Fritz 
    Activated carbons play an important role in the purification of air and of water. Whereas vapors are adsorbed by a micropore filling process, the removal of sparingly soluble species such as phenol and its derivatives is limited to the coating of the effective surface of the material. This reduces considerably the sorptive capacity of a given carbon, and a suitable description is needed to predict the corresponding equilibrium. It is shown that, in the case of phenol, its derivatives, and a few typical pollutants, the latter process can be described by an extension of the Dubinin-Radushkevich-Kaganer (DRK) equation. A major advantage of this approach is the possibility of calculating the adsorption equilibrium based on simple physicochemical properties of the adsorptives and on the structural characteristics of the activated carbon. It also appears that, by analogy with adsorption in the vapor phase, a scaling factor can be introduced for adsorption from solution.
  • Publication
    Accès libre
    Modelling of water adsorption by activated carbons: effects of microporous structure and oxygen content
    (2005)
    Slasli, Abdou
    ;
    Jorge, M.
    ;
    Stoeckli, Fritz 
    ;
    Seaton, N. A.
    The present paper examines the adsorption of water by microporous carbons containing various amounts of surface oxygen and a smaller proportion of basic centres. The modelling of water adsorption for 293 and 310 K, using variable pore size distributions (PSD), confirms that the overall type IV isotherm is the sum of a type I isotherm associated with the specific interactions, and a type V isotherm reflecting the non-specific interactions. The principle of temperature invariance is followed by these isotherms, which indicates that modelling leads to the Dubinin–Astakhov equation.

    The present approach allows the prediction of water adsorption near room temperature, on the basis of the PSD and the density of oxygen present on the surface area of the micropores. It is assumed, to a first and good approximation, that the pores are slit-shaped and the oxygen distribution is random.
  • Publication
    Accès libre
    Specific and non-specific interactions between ammonia and activated carbons
    (2004)
    Stoeckli, Fritz 
    ;
    Guillot, André
    ;
    Slasli, Abdou
    It is shown that the adsorption of NH3 by activated carbons at different temperatures follows Dubinin's theory and, as in the case of water, for carbons with high oxygen contents one observes an upward deviation in the initial section of the DR plot. This indicates a strong primary adsorption, due to specific interactions. At higher relative pressures, this adsorption is followed by a classical micropore filling mechanism, where NH3 conforms to the pattern of non-specific adsorption. The affinity coefficient β1 (NH3) associated with primary adsorption varies between 0.4 and 1.2. It depends on the characteristic energy E0 and on the ratio between the amount of oxygen present on the surface and the limiting amount of ammonia adsorbed in the micropores. This behaviour had been reported earlier for the adsorption of short alcohols, but with a single DR plot, due to the fact that specific and non-specific interactions were similar. For carbons with little oxygen on the surface, NH3 adsorption leads to a single DR plot, irrespective of the average pore-size.
  • Publication
    Accès libre
    Water adsorption by activated carbons in relation to their microporous structure
    (2003)
    Slasli, Abdou
    ;
    Jorge, M.
    ;
    Stoeckli, Fritz 
    ;
    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.
  • Publication
    Accès libre
    The characterization of microporosity in carbons with molecular sieve effects
    (2002)
    Stoeckli, Fritz 
    ;
    Slasli, Abdou
    ;
    Hugi-Cleary, Deirdre
    ;
    Guillot, André
    The apparent and the real micropore size distributions (PSDs) of molecular sieve carbons can be assessed by combining the adsorption of CO2 at 273 K with immersion calorimetry into liquids of increasing molecular dimensions. On the basis of model isotherms resulting from computer simulations, the adsorption of carbon dioxide, a relatively small probe, leads to the overall PSD of the carbon (essentially the internal micropore system). Immersion calorimetry, on the other hand, reveals the distribution of the pores accessible directly from the liquid phase, that is without constrictions. Liquid CS2 probes the same volume as CO2 and can be used as a reference. The paper describes the case of an industrial molecular sieve carbon obtained by blocking partly the entrance to a relatively broad micropore system, thus limiting its accessibility to molecules with diameters below 0.5–0.6 nm. It is shown how activation by steam at 900 °C removes the constrictions and leads to a gradual overlap of the two PSDs. The distribution of the pore widths on the surface, observed directly by scanning tunnelling microscopy, is also given.
  • Publication
    Accès libre
    Microporosity in carbon blacks
    (2002)
    Stoeckli, Fritz 
    ;
    Guillot, André
    ;
    Slasli, Abdou
    ;
    Hugi-Cleary, Deirdre
    Microporous 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.
  • Publication
    Accès libre
    The comparison of experimental and calculated pore size distributions of activated carbons
    (2002)
    Stoeckli, Fritz 
    ;
    Guillot, André
    ;
    Slasli, Abdou
    ;
    Hugi-Cleary, Deirdre
    Activated 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.
  • Publication
    Accès libre
    Pore size distributions of active carbons assessed by different techniques
    (2000)
    Stoeckli, Fritz 
    ;
    Guillot, André
    ;
    Hugi-Cleary, Deirdre
    ;
    Slasli, Abdou