CHANGES IN PSD OF PROGRESSIVELY ACTIVATED CARBONS OBTAINED FROM THEIRSUPERCRITICAL METHANE ISOTHERMS

When relatively high pressure methane isotherms at room temperature ar e measured on carbons, differences in the overall uptake are very obvi ous. They are believed to be due to differences in the total pore volu me and, also, the pore size distributions (PSDs) of these carbons. A r ecently developed [1] method for determining a PSD) of a carbon adsorb ent based on the high pressure methane isotherm was used to analyze tw o series of PVDC carbons, progressively activated, one with steam, and the other with CO2. Notable similarities in the properties of both se ries were observed. Methane uptakes (at 600 psi) per unit mass rose co ntinuously from similar to 90 mg CH4/g in unactivated samples to simil ar to 190 mg CH4/g at 65% weight loss. Considered on the ''per unit ma ss of the original sample'' basis, the uptakes exhibited a maximum of similar to 98 mg CH4/1 g original sample, at about 15% weight loss, af ter which they decreased steadily down to similar to 63 mg CH4/1 g ori ginal sample, at 65% weight loss. This would suggest that, in samples activated beyond 15% weight loss, the extent of changes to the porous structure is outweighed by the loss of adsorbent material during activ ation. The size of the average micropore also increased during activat ion, from an initial value of similar to 6.5 to similar to 14 Angstrom A at 65% weight loss. Interestingly, at 15% weight loss it was found to be similar to 8 Angstrom, which is close to the optimum determined by Matranga et al. [2]. The analysis also suggests that all the change s were due to alterations to the existing pores and that no new pores were created during the activation. Copyright (C) 1996 Elsevier Scienc e Ltd.