No abstract

The adsorption amount of methane on 16 different kinds of materials at 3.5 MPa and 298 K holds a linear relation with the specific surface area. The linear relationship implies that gases are adsorbed monolayerly on the surface of adsorbents at above-critical temperatures. Determination of surface area and calculation of storage capacity of a material are explicitly discussed. It is indicated that methane storage is different from natural gas storage and the difference affects the development of storage material. Natural gas is a mixture and all components other than methane cannot be desorbed when the tank pressure released to atmospheric at ambient temperature, therefore, a storage mechanism other than adsorption might be more suitable.

A PSA cycle complemented with CO 2 displacement was studied for enriching coalbed methane (CBM). The column was first pressurized to the adsorption pressure with feed gas, and then N 2 was produced at column top in step 2. The feed gas switched to CO 2 at the end of step 2, and the adsorbed CH 4 was displaced and pushed to column top by CO 2 becoming the second column-top product in step 3. The CO 2 stream was shut off before it broke through the sorption bed. Then bed regeneration followed. A series of CH 4 /N 2 mixtures containing 17.62 to 51.33% CH 4 was used for feed gas. It was experimentally shown that the product concentration was higher than 90%, and methane recovery was higher than 98% even for the feed of low-methane concentration. Displacement at ambient pressure was shown more efficient than the displacement at adsorption pressure for the enrichment.

The separation between CH 4 and N 2 bears importance in coalbed methane enrichment, and activated carbon is a major adsorbent for industrial PSA (pressure swing adsorption) separation. However, the adsorption of both gases shows supercritical features, and the physicochemical properties are also similar, which results in similar adsorption behavior and renders the separation difficult. To maximize the separation coefficient, the effect of carbon pore structure on the separation was studied and a series of carbons was prepared at different extent of activation. The effect of specific surface area, pore size and pore volume on the separation coefficient was observed and a linear correlation between the separation coefficient and the small pore (0.7-1.3 nm) volume reduced to unit surface area was shown.

Activated carbon with high specific surface area and considerable mesopores was prepared from bamboo scraps by phosphoric acid activation. The effect of activation conditions was studied. Under the conditions of impregnating bamboo with 80% H 3 PO 4 at 80uC for 9 days and activation at 500uC for 4 h, the prepared activated carbon had the highest mesopore volume of 0.67 cm 3 /g, a specific surface area of 1567 m 2 /g, and the mesopore ratio reached 47.18%. The study on adsorption isotherms of CH 4 , CO 2 , N 2 and O 2 on the activated carbon were carried out at 298 K. The considerable difference in the adsorption capacity between CO 2 and the other gases was observed, which would be of interest for the adsorptive separation/purification of gaseous CO 2 from its mixtures, especially from mixtures with N 2 and/or O 2 .