The methane adsorption of water-preadsorbed carbons of different micropore widths w at 303 K was measured. Although the amount of adsorption of supercritical methane on microporous carbon at 303 K was less than 9.4 mg g-1 at 101 kPa, the presence of the preadsorbed water enhanced noticeably the methane adsorption at 303 K even under subatmospheric pressure. The adsorption increment of methane reached a maximum at 1-2 h after introduction of methane and decreased gradually to a steady value after 20-50 h. The adsorption increment of methane depended on the fractional filling φw of micropores by the preadsorbed water. The maximum increment of 110 mg g-1 for w = 1.1 nm at a methane pressure of 2.6 kPa was obtained at φw = 0.34, corresponding to the estimated adsorption amount at 21 MPa of methane (130 mg g-1). The methane-adsorption increment increased linearly with φw until φw = 0.35, indicating the formation of the stable methane - water clathrate of which the composition of methane to water is 1:2. Thus, the nano-order hydrates of methane should be formed in the micropore. The plausible model of the nanohydrate was proposed on the basis of the experimental results and simulation of methane adsorption.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry