Porosity Development during CO2 and Steam Activation in a Fluidized Bed Reactor

摘要

Steam- and CO_2-activated carbons from a Spanish HV bituminous coal char were obtained at 800--900 deg. 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 m2/g at 50/100 burnofffor 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 m2/g at 50/100 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 mny be to a partial diffusion control in the CO_2 gasification reaction, under fluidized bed conditions.