Porosity Development during CO 2 and Steam Activation in a Fluidized Bed Reactor

Steam- and CO 2 -activated carbons from a Spanish HV bituminous coal char were obtained at 800−900 °C in a batch laboratory scale fluidized bed reactor. The N 2 and CO 2 adsorption isotherms and scanning electron microscopy allow for sample characterization. The development of porosity upon activation, using a fluidized bed reactor, is different depending on the activating agent. A much better activation development is attained with steam. Thus, total micropore volume linearly increases with the activation degree, attaining an apparent specific surface area of 1150 m 2 /g at 50% burnoff for steam-activated carbons. Although CO 2 activation also produces a linear increase 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 analysis indicates that CO 2 produces external burning of the carbon particles. This different behavior of CO 2 and steam activation was also observed for several runs carried out with almond shell char. The explanation of this behavior may be to a partial diffusion control in the CO 2 gasification reaction, under fluidized bed conditions.