ACTIVATED CARBONS FROM LIGNOCELLULOSIC MATERIALS BY CHEMICAL AND OR PHYSICAL ACTIVATION - AN OVERVIEW

Four series of activated carbons prepared from lignocellulosic materials (almond shells and olive and peach stones) by either physical activation-gasification (uncatalysed and iron catalysed) in CO2 or in a water-nitrogen mixture-of chars or direct chemical activation with ZnCl2 of the precursor were selected to show the comparative behavior of the activation procedures. Activation with CO2 opens and widens the microporosity of the char with even a shift to meso- and macroporosity, the ablation of the exterior of the particle being very important at high burn-off; the final activated carbon has a well developed micro- and macroporosity, with a relatively small contribution of mesoporosity. The iron catalysed CO2 gasification and gasification with water-nitrogen mixture produce carbons with a well developed macroporosity, although the latter has the advantage of maintaining a well developed micro- and mesoporosity. Direct chemical activation of the precursor with ZnCl2 produces, in only one step, a larger yield of activated carbon having microporosity as well developed as in the CO2 gasification of the char, with the advantage of producing a much larger mesopore volume.