ACTIVATION OF LIGNOCELLULOSIC MATERIALS - A COMPARISON BETWEEN CHEMICAL, PHYSICAL AND COMBINED ACTIVATION IN TERMS OF POROUS TEXTURE

The influence of the chemical activating agent:raw material ratio in the preparation of activated carbons from almond shells by chemical activation with ZnCl2 has been studied. Selected aqueous mixtures were kept in contact for 5 h and after filtering the remaining solution and drying, the impregnated almond shells were pyrolysed under N2 flow. The main effect of this impregnation was the development of microporosity in the activated carbons as a result of the pyrolysis process increasing the activating agent:raw material ratio to a value of 2 enhancing the micropore volume. By this procedure carbons with surface areas ranging from 420 to 1211 m2 g-1 have been obtained. The subsequent activation of one of the low surface area carbons with CO2 produces a development in the overall range of porosity giving rise to apparent surface areas of > 2300 m2 g-1. Comparing activation with CO2 of carbonized almond shells and ZnCl2-activated carbons from almond shell it is shown that the differences are not in the range of porosity developed but in the global yields, always being larger in the latter.