Study of a Fluid/Solid Interface over a Wide Density Range Including the Critical Region. I. Surface Excess of Ethylene/Graphite

Abstract

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.

Adsorption of Carbon Dioxide on Proteins in the Supercritical Region

“…Specovius and Findenegg have stated that density could be a better variable than pressure to explain the behavior of SCF adsorption. 9 ) Hysteresis in the adsorption isotherms of soybean proteins The isotherms of soybean proteins, which differed from those of the other four proteins, did not level off at higher pressures and exhibited hysteresis as shown in Fig. 7.…”

High‐resolution adsorption isotherms of supercritical carbon dioxide on activated carbon

“…Aranovich and Donohue, 1997b and inferences reported by Ž . Specovius and Findenegg 1980 for the near-critical adsorption of ethylene on graphitized carbon black. Parallels have also been drawn between adsorption of supercritical fluids and the phenomenon of local density enhancements around Ž solute molecules in supercritical fluid solutions Subramanian .…”

“…Findenegg's results for the adsorption of ethylene on graphitized carbon black Ž . Specovius and Findenegg, 1980 indicate that the density profile in the interfacial region of a supercritical fluid near an adsorbing surface, becomes long range as the critical point is approached. In microporous materials commonly used in engineering applications, the depth of the density profile is limited by the pore size.…”

“…High-pressure adsorption studies by Findenegg and coworkers on nonporous graphite and controlled pore glass ŽSpecovius and Findenegg, 1980;Findenegg, 1983;Thommes . et al, 1994 revealed some interesting aspects of adsorption in the near-critical region.…”

Adsorption of Carbon Dioxide to Polysaccharides in the Supercritical Region

“…4 MPa by the gravimetric method. The adsorption of CO 2 to two kinds of starches (potato and corn) and to dextrin increasedUnearly with increasing pressure to reach a maximum, and then decreased sharply to constant level at higher pressure.…”