Phosphoric acid activated carbon discs for methane adsorption

Phosphoric acid has been used as activating agent in the preparation of binderless activated carbon discs. The granular precursor was impregnated with different solutions of phosphoric acid, hot pressed in discs, heat treated under a flow of nitrogen and washed with distilled water to extract the excess acid. The role of the impregnation ratio and the temperature of conforming have been analysed. The discs have a bulk density higher than the granular activated carbon because there is a considerable reduction of the interparticle space, the contribution of non-microporous volume being small. The discs exhibit a high volume of microporosity accessible to both nitrogen and methane molecules. Best results (storage capacity of 131, v/v) were obtained when using an impregnation ratio X-p=0.35 g phosphorous/g precursor (maximum micropore volume and minimum interparticle space) and conforming at 100 degreesC (higher temperatures reduce the volume of micropores). Some discs were additionally activated under a flow of carbon dioxide, the maximum methane storage capacity (near 150, v/v) being obtained when burn-off is in the 10-40% range. (C) 2003 Elsevier Ltd. All rights reserved.