MODELING OF THE INTERACTION OF NITROGEN-DIOXIDE WITH ACTIVATED CARBON .1. ADSORPTION DYNAMICS AT THE SINGLE-PARTICLE SCALE

The adsorption dynamics of nitrogen dioxide on activated carbon are measured using a microbalance technique. A theoretical model, incorporating the mechanisms of micropore, macropore and concentration dependent sorbed phase (surface) diffusion, with nonlinear equilibrium (dual Langmuir isotherm), is fitted to the experimental NO2 adsorption dynamics over a range of temperatures, concentrations and particles sizes. The data are well fitted by the model over the temperature range 298-373 K, with typical extracted values of the diffusivities at 298 K being: D/R(mu)2 = 0.003 s-1 (micropore), D(P) = 0.038 cm2/s (macropore) and D(SO) = 1.0 X 10(-6) cm2/s (surface); with micropore and surface diffusion activation energies of 14.8 and 11.0 kJ/mole, respectively. The influence of the NO2/N2O4 ratio on the adsorption dynamics is also discussed. At temperature higher than 373 K, significant reaction of NO2 with activated carbon results in consumption of the carbon.