The General Equation of Supercritical Gas Adsorption Isotherm

Effects of Surface Structure and Temperature on the Surface Mediation, Layer Concentration and Molecular Projection Area: Adsorption of Argon and Nitrogen onto Graphitized Thermal Carbon Black

This paper is devoted to an investigation of the effects of surface structure (structure-less or structured) on the description of the adsorption isotherm and the isosteric heat of nitrogen and argon adsorption onto graphitized thermal carbon black. It was found that the surface structure had little effect on the adsorption of either argon or nitrogen at 77 K and 87.3 K. The variation of the monolayer coverage concentration was also investigated as well as the concentrations of higher layers as a function of pressure and temperature. Finally, the commonly used values for the molecular projection area of nitrogen and argon for graphitized thermal carbon black (16.2 Å2 and 13.8 Å2) were revisited. For this material, a value of 15.5 Å2 is recommended for nitrogen at 77 K, while for the case of argon at the same temperature the recommended values of 13.8 Å2 and 12.94 Å2 are suggested for the reduced pressure range (0.1–0.2P/P0) and (0.25–0.35P/P0), respectively. A value of 14 Å2 for argon at 87.3 K is suggested for the BET plot over the reduced pressure range of 0.1–0.2P/P0.

Pore Characterization of Carbonaceous Materials by DFT and GCMC Simulations: A Review

A review is given of the pore characterization of carbonaceous materials, including activated carbon, carbon fibres, carbon nanotubes, etc., using adsorption techniques. Since the pores of carbon media are mostly of molecular dimensions, the appropriate modern tools for the analysis of adsorption isotherms are grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT). These techniques are presented and applications of such tools in the derivation of pore-size distribution highlighted.

Evaluation of 1-Site and 5-Site Models of Methane on Its Adsorption on Graphite and in Graphitic Slit Pores

In this paper, we evaluate the performance of the 1- and 5-site models of methane on the description of adsorption on graphite surfaces and in graphitic slit pores. These models have been known to perform well in the description of the fluid-phase behavior and vapor-liquid equilibria. Their performance in adsorption is evaluated in this work for nonporous graphitized thermal carbon black, and simulation results are compared with the experimental data of Avgul and Kiselev (Chemistry and Physics of Carbon; Dekker: New York, 1970; Vol. 6, p 1). On this nonporous surface, it is found that these models perform as well on isotherms at various temperatures as they do on the experimental isosteric heat for adsorption on a graphite surface. They are then tested for their performance in predicting the adsorption isotherms in graphitic slit pores, in which we would like to explore the effect of confinement on the molecule packing. Pore widths of 10 and 20 A are chosen in this investigation, and we also study the effects of temperature by choosing 90.7, 113, and 273 K. The first two are for subcritical conditions, with 90.7 K being the triple point of methane and 113 K being its boiling point. The last temperature is chosen to represent the supercritical condition so that we can investigate the performance of these models at extremely high pressures. We have found that for the case of slit pores investigated in this paper, although the two models yield comparable pore densities (provided the accessible pore width is used in the calculation of pore density), the number of particles predicted by the 1-site model is always greater than that predicted by the 5-site model, regardless of whether temperature is subcritical or supercritical. This is due to the packing effect in the confined space such that a methane molecule modeled as a spherical particle in the 1-site model would pack better than the fused five-sphere model in the case of the 5-site model. Because the 5-site model better describes the liquid- and solid-phase behavior, we would argue that the packing density in small pores is better described with a more detailed 5-site model, and care should be exercised when using the 1-site model to study adsorption in small pores.