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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
    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
    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 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
    Reference isotherm for high pressure adsorption of CO2 by carbons at 273 K
    (2001)
    Guillot, André
    ;
    Stoeckli, Fritz 
    It is suggested that the adsorption of CO2 on Vulcan 3G at 273 K and up to 3.2 MPa can be used as a reference isotherm for the characterization of porous and non-porous carbons. The results obtained with the proposed reference are in good agreement with those of the nitrogen (77 K) and benzene (293 K) comparison plots. The external surface areas have also been compared with those obtained from immersion calorimetry into C6H6 at 293 K. It also appears that at low relative pressures CO2 adsorbed on Vulcan 3G follows the Dubinin–Radushkevich–Kaganer equation between 253 and 273 K.
  • Publication
    Accès libre
    Micropore sizes in activated carbons determined from the Dubinin–Radushkevich equation
    (2001)
    Stoeckli, Fritz 
    ;
    López-Ramón, M. V.
    ;
    Hugi-Cleary, Deirdre
    ;
    Guillot, André
  • Publication
    Accès libre
    On the use of standard DRK isotherms in Dubinin’s t/F method
    (2000)
    Hugi-Cleary, Deirdre
    ;
    Stoeckli, Fritz 
    It 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.
  • Publication
    Accès libre
    Dynamic adsorption, in active carbon beds, of vapour mixtures corresponding to miscible and immiscible liquids
    (1999)
    Lavanchy, André
    ;
    Stoeckli, Fritz 
    It 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.
  • Publication
    Accès libre
    On the characterization of acidic and basic surface sites on carbons by various techniques
    (1999)
    López-Ramón, María Victoria
    ;
    Stoeckli, Fritz 
    ;
    Moreno-Castilla, Carlos
    ;
    Carrasco-Marín, Francisco
    Active carbons of different origins have been oxidized with H2O2 and (NH4)2S2O8 and their oxygen surface complexes have been characterized by TPD, classical titration following Boehm's method and by neutralization calorimetry. The net enthalpies of neutralization, determined by immersion calorimetry into NaOH and HCl 2 N lead to −41.1±1.8 and −52.3±2.0 kJ eq−1 for the acidic and basic sites on the surface. Experiments with NaHCO3 lead to −39.7±1.7 kJ eq−1 for the carboxylic groups alone. These results suggest that the surface groups of active carbons can also be characterized by immersion calorimetry. Results are also given for the variation of the pH of the point of zero charge with the total oxygen content of the surface.
  • Publication
    Accès libre
    Dynamic adsorption of vapour mixtures in active carbon beds described by the Myers-Prausnitz and dubinin theories
    (1997)
    Lavanchy, André
    ;
    Stoeckli, Fritz 
    The 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.