The effect of gasification by air (623 K) or CO2(1098 K) in the development of microporosity in activated carbons

Abstract

The adsorption of nitrogen, benzene, n-butane, iso-butane, 2,2-dimethylbutane and iso-octane has been carried out in two series of activated carbons, one prepared by activation of carbonized olive stones in CO₂ at 1098 K and another by reacting activated carbon (of the same origin) in air at 623 K. Carbons of the former series have narrower microporosity which is gradually developed upon activation, whereas air produces a more considerable widening of the microporosity. Carbons with low burn-off exhibit a molecular sieving effect toward iso-octane (minimum dimension, 0.59 nm). For carbons with medium burn-off, in which molecular sieving is not exhibited (34–52% burn-off), the characteristic curve is coincident for all adsorbates, but for larger burn-off the N₂ data do not fit the characteristic curve. In the case of the latter carbons, with wide and heterogeneous microporosity, only the micropore volume deduced from the higher relative pressure branch of the Dubinin-Radushkevich plot or characteristic curve for N₂ at 77 K (usually in the relative pressure range 0.05–0.25) is coincident with that obtained from the hydrocarbons.