Jw. Wilder et al., Resolving apparent contradictions in equilibrium measurements for clathrate hydrates in porous media, J PHYS CH B, 105(41), 2001, pp. 9970-9972
A conceptual model for hydrate equilibrium in media with broad pore-size di
stributions is used to interpret methane hydrate equilibrium experiments in
silica gel pores with nominal radii of 2, 5, and 7.5 nm, While the hydrate
equilibrium pressure is an intensive property, it is demonstrated that the
presence of a broad pore-size distribution in a porous medium causes the e
xperimental pressures to appear extensive. It is observed that the sample s
ize, the headspace volume, the temperature at which the experiments are sta
rted, and the amount of hydrate allowed to dissociate to establish equilibr
ium at this initial temperature all affect the observed pressure at any giv
en temperature. The pore-volume distribution of the porous medium (not the
nominal pore radius) and the percent conversion of pore-water to hydrate al
so affect the measured equilibrium pressures. As a result, measured equilib
rium pressures at a specific temperature for identical media can be signifi
cantly different, while those for different media may be superposed. These
seeming inconsistencies, their causes, and interpretations are examined and
explained. Apparently fundamental problem,,; in experimental data are remo
ved when the number of degrees of freedom is properly included in the inter
pretation.