Porosity development during CO2 and steam activation in a fluidized bed reactor

Steam- and CO2-activated carbons from a Spanish HV bituminous coal char wer e obtained at 800-900 degrees C in a batch laboratory scale fluidized bed r eactor. The N-2 and CO2 adsorption isotherms and scanning electron microsco py allow for sample characterization. The development of porosity upon acti vation, using a fluidized bed reactor, is different depending on the activa ting agent. A much better activation development is attained with steam. Th us, total micropore volume linearly increases with the activation degree, a ttaining an apparent specific surface area of 1150 m(2)/g at 50% burnoff fo r steam-activated carbons. Although CO2 activation also produces a linear i ncrease vs burnoff, much lower pore volume values are obtained, reaching an equivalent specific surface area of only 800 m(2)/g at 50% burnoff. SEM an alysis indicates that CO2 produces external burning of the carbon particles . This different behavior of CO2 and steam activation was also observed for several runs carried out with almond shell char. The explanation of this b ehavior may be to a partial diffusion control in the CO2 gasification react ion, under fluidized bed conditions.