Preparation of activated carbons for storage of methane and its study by adsorption calorimetry

Abstract

The scope of this investigation is to relate textural and surface characteristics of activated carbon prepared from Cerrejon coal (Colombia) to their methane quantity adsorption. Sub-bituminous coal from the Cerrejon coal mine in Colombia was used as a raw material for the preparation of pore size-controlled activated carbon adsorbents. A subsequent chemical treatment was carried out, after making a physical activation with CO2. Samples were treated with CO2 flow at 850 °C by varying activation time to achieve different burn-off activated carbons. The samples chemically activated with H3PO4 under CO2 atmosphere showed higher activation rates, surface area, and micropore volume compared to other activation methods, although not all the samples prepared by this method presented storage quantities methane in function of surface area development. Moreover, it was shown that using small proportion of KCl and H3PO4 creates an initial narrow microporosity. Further physical activation grantees better development of pore structure. In terms of pore size distribution, the combined preparation method resulted in a better and more homogenous pore size distribution than the conventional physical activation method. Controlling the pore size of activated carbon by this combined activation technique can be utilized for tuning the pore size distribution. Storage studies of methane up to 60 bar were realized. It was concluded that the high surface area and micropore volume of activated carbons do not unequivocally determine methane capacities. Adsorption microcalorimetry is a useful technique to follow the process of the adsorption reaction of CH4, and its results are in agreement with the results found study by adsorption at high pressure.