Non-isothermal adsorption in a bidisperse adsorbent pellet

The kinetics of adsorption in bidisperse pellets has been largely studied under isothermal condition. But due to large heat of adsorption, the isothermal models may lead to erroneous results. The present paper proposes a non-isothermal bidisperse model, taking into account two scale mass diffusion (macro—micropore diffusion) and one scale heat diffusion (the temperature within the microparticles is assumed uniform). This model is solved numerically, yielding the sorption uptake and temperature evolution. It turns out that considering the simultaneous macro—micropore diffusion is only necessary for 10⁻⁶ < α < 10⁻¹ (α is the ratio of macropore and micropore diffusional resistances). The macropore diffusion should be rate limiting if the parameter α > 10⁻¹ and the micropore diffusion become rate limiting if α < 10⁻⁶. On the other hand, heat effect may make the isothermal assumption quite erroneous when the diffusion in the macropores and micropores is rapid and the heat transfer between the adsorbent and the ambient sorbate is small.