MACROSCOPIC EVIDENCE OF ENHANCED FORMATION OF METHANE NANOHYDRATES INHYDROPHOBIC NANOSPACES

The methane adsorption of water-preadsorbed carbons of different micro pore 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 enhanc ed noticeably the methane adsorption at 303 K even under subatmospheri c 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 phi(w) of micropores by the preadsorbed water. The maximum increment of 110 mg g(-1) for w = 1.1 nm at a methane pres sure of 2.6 kPa was obtained at phi(w) = 0.34, corresponding to the es timated adsorption amount at 21 MPa of methane (130 mg g(-1)). The met hane-adsorption increment increased linearly with phi(w) until phi(w) = 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-o rder hydrates of methane should be formed in the micropore. The plausi ble model of the nanohydrate was proposed on the basis of the experime ntal results and simulation of methane adsorption.