Influence of different chemical reagents on the preparation of activated carbons from bituminous coal

Activated carbons were prepared by chemical activation from bituminous coal with three chemical reagents, ZnCl2, H3PO4 and KOH. The activation consisted of impregnation of a reagent followed by carbonization in nitrogen at various temperatures. A thermogravimetric study showed that these reagents were capable of suppressing the evolution of tarry substances during carbonization. Because of carbon oxidation and gasification mechanisms, activation with KOH resulted in a lower carbon yield than those with ZnCl2 and H3PO4. For each activation process the porosity of the resulting carbons increased with the carbonization temperature to a maximum and then began to decrease with further increase of the temperature. The maximum surface areas obtained from the activation with ZnCl2, H3PO4 and KOH are 960, 770 and 3300 m(2)/g, respectively. The results of the present work suggest that ZnCl2 and H3PO4, which are acidic, are not suitable for preparing high-porosity carbons from bituminous coal, while carbons with very high porosity can be produced with bases such as KOH. An increase in particle size of the coal precursor was found to cause a reduction in both yield and porosity of the resulting carbons. (C) 2000 Elsevier Science B.V. All rights reserved.