“…The F H H model then yields the following dependence of the thickness of the layer on the fugacityfof the vapor: temperature dependence which indicates that the assumptions on which the F H H model is based, viz. an incompressible liquid and the step density profile (6), break down when the critical point is approached. Table 3 Parameters of the Frenkel-Halsey-Hill Eq.…”
Section: Sub-critical Isothermsmentioning
confidence: 99%
“…Physical adsorption of gases near their critical region has been investigated previously by other authors but these studies were made o n ill-defined surfaces like fused silica [ 5 ] , silica gel, alumina [6], or on highly porous solids like activated carbon and molecular sieving carbon [7]. In these cases adsorption is mainly a process of pore-filling and depends mainly on the pore size distribution of the adsorbent.…”
The surface excess amount of ethylene adsorbed on graphitised carbon black has been measured over a pressure range from 1 to 120 bar using a high pressure microbalance technique. The data span a range of temperatures from 263 to 323 K (0.93 ≤ T/Tc ≤ 1.14) and a range of bulk densities up to ρ/ρc=1.7. The results show the transition from the low‐temperature behavior (T < Tc) with multilayer adsorption on approaching the saturation pressure, to the situation above the critical temperature Tc when the surface excess isotherms Γσ(P) exhibit a pronounced maximum at a pressure Pmax > Pc. The dependence of Pmax on temperature, and the variation of Γσ with temperature along the critical isochore, is determined quantitatively. The surface excess is discussed in terms of an operationally defined exponential density profile of the fluid at the interface. The dependence of the decay length of this profile on the bulk density and on temperature is shown.
“…The F H H model then yields the following dependence of the thickness of the layer on the fugacityfof the vapor: temperature dependence which indicates that the assumptions on which the F H H model is based, viz. an incompressible liquid and the step density profile (6), break down when the critical point is approached. Table 3 Parameters of the Frenkel-Halsey-Hill Eq.…”
Section: Sub-critical Isothermsmentioning
confidence: 99%
“…Physical adsorption of gases near their critical region has been investigated previously by other authors but these studies were made o n ill-defined surfaces like fused silica [ 5 ] , silica gel, alumina [6], or on highly porous solids like activated carbon and molecular sieving carbon [7]. In these cases adsorption is mainly a process of pore-filling and depends mainly on the pore size distribution of the adsorbent.…”
The surface excess amount of ethylene adsorbed on graphitised carbon black has been measured over a pressure range from 1 to 120 bar using a high pressure microbalance technique. The data span a range of temperatures from 263 to 323 K (0.93 ≤ T/Tc ≤ 1.14) and a range of bulk densities up to ρ/ρc=1.7. The results show the transition from the low‐temperature behavior (T < Tc) with multilayer adsorption on approaching the saturation pressure, to the situation above the critical temperature Tc when the surface excess isotherms Γσ(P) exhibit a pronounced maximum at a pressure Pmax > Pc. The dependence of Pmax on temperature, and the variation of Γσ with temperature along the critical isochore, is determined quantitatively. The surface excess is discussed in terms of an operationally defined exponential density profile of the fluid at the interface. The dependence of the decay length of this profile on the bulk density and on temperature is shown.
“…This model reasonably describes the high-pressure maximum observed in the excess isotherms with two temperature-independent parameters. 17 Carbon dioxide adsorption on DeGussa IV (1699 m 2 /g) where H = 15.5 Å and ε fs / k = 77 K. Data of Chen et al (ref ). 18 Adsorption of CO 2 on ACK carbon (983 m 2 /g) where H = 15.4 Å and ε fs / k = 109 K. Data of Ozawa et al (ref ). 19 Adsorption of methane on activated carbon (AX-21) where H = 11.7 Å and ε fs / k = 59 K. Data of Zhou et al (ref ).…”
Section: Resultsmentioning
confidence: 99%
“…Adsorption of CO 2 on ACK carbon (983 m 2 /g) where H = 15.4 Å and ε fs / k = 109 K. Data of Ozawa et al (ref ).…”
The simplified local density approach (SLD) is extended to the Elliott-Suresh-Donohue (ESD) equation of state for the modeling of gas adsorption on activated carbon, providing significant improvement in quantitative modeling compared to the SLD approach using the Peng-Robinson equation of state or the van der Waals equation. Compared to the Peng-Robinson and van der Waals equations, the ESD equation more accurately represents the temperature dependence of adsorption.
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