NaOH activation of anthracites: effect of hydroxide content on pore textures and methane storage ability

Abstract The present paper is the continuation of a previous work dealing with the activation of anthracites with NaOH at various temperatures, ranging from 600 to 830 °C [A. Perrin et al., Carbon 42 (2004) 2855]. In this latter article, the pore textures were accurately investigated through the adsorption isotherms of four probe molecules characterised by their increasing molecular diameters, namely CO 2 , N 2 , C 6 H 6 and CCl 4 , and the methane storage capacities were measured and discussed accordingly. In the present paper, the same kind of study is carried on, keeping the activation temperature constant at 730 °C (which was previously found to lead to the highest density of adsorbed methane), but changing the mass ratio NaOH/anthracite, R , from 1 to 3. The changes occurring for each kind of pores and the specific volumes of different micro- and meso-pore families are measured and discussed. Just like in our previous work, two separate mechanisms of porosity development are evidenced. Mass ratios NaOH/anthracite R  ⩽ 2 mainly lead to the creation of micropores of effective widths close to the optimal value for methane storage, i.e., 0.8 nm. While higher values of R mainly lead to the widening of already existing pores. Methane storage isotherms at 20 °C were measured up to 3.5 MPa for the investigated materials. Linear correlations between various textural parameters and methane storage capacities were given. Additionally, a number of results previously reported in the literature were confirmed by the present work.