Activated carbons from bituminous coal: effect of mineral matter content

A bituminous coal from Puertollano Basin (Spain) was selected on the basis of previous study as the most suitable raw precursor to prepare activated c arbons. in fact, this coal gave the best results among a total of 10 differ ent Spanish coals that covered a wide range of coal rank. Its initial ash l evel (19 wt%) was decreased in the coal mine facilities by different intens ive hydropneumatic washing, yielding fractions with 12 and 8 wt% ash. Anoth er fraction was also obtained from the original coal with 5 wt% ash by an H Cl/HF washing treatment. These four coals were carbonised at 850 degrees C and activated at 850 degrees C for different activation times in steam and carbon dioxide, to analyse the effect of ash level on the porosity developm ent of the resulting carbons. Contrary to what might be expected (catalysis effect,, pore blocking and impediment of suitable porosity development), t he initial ash level does not affect the porosity development. Those sample s with a lower ash (at the same burn-off degree) yield higher micropore vol umes. But when the results are presented in terms of dry ash free basis, th e same porosity development is attained regardless of the initial ash level . Comparing the behaviour of steam and carbon dioxide as activating agents, the pore structure and pore volumes attained are quite similar, though the pore sizes of steam samples are slightly wider than those of carbon dioxid e samples. The Dubinin-Stoeckli equation applied to experimental adsorption isotherm was used to follow the porosity development during activation for each reactive gas. (C) 2000 Elsevier Science Ltd. All rights reserved.