Methane storage in activated carbon fibres Original Research Article

Methane storage in two series of activated carbon fibres (ACF) has been studied. The two series have been prepared by activation with CO2 and steam of a petroleum-pitch based carbon fibre. Methane isotherms have been carried out in a gravimetric system up to 4 MPa. ACF are very promising materials for this purpose because they are essentially microporous activated carbons. The paper analyzes the different correlations found in the literature between methane storage capacity and parameters related with the porous texture. Our best correlation is found with the total micropore volume, noting that this micropore volume has to include both the narrow microporosity (size lower than 0.7 nm) and supermicroporosity (size between 0.7–2.0 nm). This statement is specially relevant for samples in which N2 adsorption has diffusional limitations. Steam activation produces lower micropore volumes than CO2 and, hence, lower storage capacities. Methane storage capacities of 163 v/v are reached with the ACF prepared by CO2 activation. The delivery of methane obtained for the best samples is about 143 v/v. This value is very close to that aimed for a commercial application of space-filling shapes of activated carbons.