Supercritical methane

The models of Matranga, Myers and Glandt [22] and Tan and Gubbins [23] for supercritical methane adsorption on carbon using a slit shaped pore have shown the importance of pore width on adsorbate density. An estimate of the pore width distribution has been recognized as a valuable tool in evaluating adsorbents. Several methods have been reported for obtaining pore size distributions, (PSDs), some of which are discussed below. 

Thus, while models may suggest optimal pore spuctures to maximize methane storage, they give no indication or suggestion as to how such a material might be produced. On the other hand, simple measurement of methane uptake from variously prepared adsorbents is not sufficient to elucidate the difference in the pore structure of adsorbents. Sosin and Quinn s method of determining a PSD directly from the supercritical methane isotherm provides an important and valuable link between theoretical models and the practical production of carbon adsorbents... 

R. F. Cracknell, D. Nicholson and K. E. Gubbins, Molecular Dynamics Study of the Self-Diffusion of Supercritical Methane in Slit-shaped Graphitic Micropores, J. Chem. Soc. Faraday Trans. 91 (1995) 1377-1383. 

The 32-term Modified Benedict-Webb-Rubin (MBWR) equation of state proposed by Younglove and Ely was used to represent the / VT-behavior of supercritical methane and, in particular, to compute p. The experimental data agree within 2% with these values at the temperature 333 K, as shown in Figure 3(a). 

Sosin, K.A., Quinn, D.F., and MacDonald J.A.F. (1996). Changes in PSD of progressively activated carbons obtained from their supercritical methane isotherms. Carbon, 34, 1335—41. 

On the other hand, the structure of adsorbed supercritical methane (CH4) in an adsorption-desorption equilibrium state gives a methane inclusion crystal even at... 

In the subsurface the density of a gas increases with depth, despite increasing temperature, because of the pressure-induced compression. When a fluid s critical temperature (Tc) and pressure (pc) are exceeded there are no longer separate gas and liquid phases only a single supercritical fluid can exist. For methane Tc = -82.6 °C and pc = 4.6 MPa, whereas for carbon dioxide the corresponding values are -31.0°C and 7.4MPa (a typical phase diagram is shown in Fig. 4.28). A supercritical fluid has a much higher density than a gas and many of its properties are intermediate between those of a gas and a liquid. Consequently, supercritical methane and carbon dioxide are potentially excellent solvents for oil. 

Figure 8.23 Performance of the dynamic extraction of the trimethyl borate-methanol azeotrope mixture using supercritical methane (Unterreiner, McHugh, and Krukonis, 1991).

Diguet, R., R. Deul, and E. U. Franck. 1987. Static dielectric constant and density of supercritical methane-methanol mixtures to 200 MPa. Ber. Bunsenges. Phys. Chem. 91 551-556. 

Unterreiner, J. M., M. A. McHugh, and V. J. Krukonis. 1991. Breaking the trimethyl borate-methanol azeotrope with supercritical methane. Ind. Eng. Chem. Res. 29 740-745. 

Note that this limit is to be taken along a vapor-liquid saturation curve with temperature held constant. If pure-component i is supercritical at the mixture T, then pure i does not exist in VLE at T, and the limit in (12.1.9) is undefined. This occurs for supercritical methane in Figure 12.3. 

Lin, K., Cox-Stouffer, S., Jackson, T. (2006). Structures and phase transition processes of supercritical methane/ethylene mixtures injected into a subcritical environment. Comb. Sci. Tech., 178, 129-160. 

A.M. van Hest, G.A.M. Diepen, Solubility of naphthalene in supercritical methane, in The Physics and Chemistry of High Pressures, Symposium Papers, Soc. Chem. ind., London, 1963, 10. 

L. Zhou, Y. P. Zhou, M. Li, P. Chen, Y. Wang. Experimental and Modeling Study of the Adsorption of Supercritical Methane on a High Surface Carbon. Langmuir. 16 (2000) 5955-5959. 

Fig. 14 Heat flux thermograms obtained under 100 MPa during isobaric T scans at 0.833 rtiK s on heating (downward exothermic peaks) and cooling (upward endothermic peaks) for a MDPE sample pressurized under supercritical methane (SCCH4 initial and SCCH4 final) and under Hg...

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