Co-adsorption of n-butane/water vapour mixtures on activated carbon fibre-based monoliths

Water-n-butane co-adsorption experiments on Activated Carbon Fibre based Monoliths (ACFMs) under equilibrium and dynamic conditions were performed at 30degreesC. ACFMs proved to be better adsorbents than active carbon particles for the dry adsorption of n-butane at low concentration levels. The presence of water vapour in the gas stream has a negligible influence on n-butane adsorption for values of relative humidity (RH) equal to or below 25%. Higher water pressures cause a significant loss of adsorption capacity in ACFMs. Equilibrium water adsorption on ACFMs can be described by the Do and Do model [Carbon 38 (2000) 767] modified in order to account for both the variable size of the water aggregates on acid centres and the variable size of the clusters detached from the aggregates and inserted into the micropores. The model results show close agreement between the amounts of active sites for adsorption calculated by the model and the number expected from subjecting the ACFMs to different pre-treatments. The equilibrium of co-adsorption of water and n-butane can be described by a pore filling concept according to which the volume occupied by both gases adsorbed together from the gas mixture is approximately equal to the volume occupied by the pure component adsorbed separately to a greater extent. Pre-moistening of the monolith has little effect on its effective n-butane adsorption capacity (breakthrough time) during dynamic adsorption experiments. For values of relative humidity equal to or below 25%, the effective n-butane adsorption capacity of the monoliths was better than that of active carbon powder. Moreover, the monoliths produced a much lower pressure drop in the system. At these conditions, adsorption efficiency for the ACFMs never showed values below 85%. (C) 2003 Elsevier Ltd. All rights reserved.