Equilibrium theory for hysteresis-dependent fixed-bed desorption

The effect of hysteresis on fixed-bed desorption was investigated, based on local equilibrium theory. According to the geometric condition: ∂q/∂y = Δq/Δy, different type isotherms were analyzed to determine the locations of simple waves, shcok waves and/or combined waves. The characteristics, bed profiles and elution curves were constructed for three systems which collectively exhibited isotherm Types I, II, IV and V, and hysteresis loop Types H1, H2 and H4. The effect of hysteresis was ascertained by comparing elution along the adsorption branch of the isotherm with that along the desorption branch. The results showed that hysteresis can increase significantly the time associated with desorption. To attain complete desorption, 10-30% delay was realized by three systems investigated. Moreover, because the elution curves were, in some cases, significantly different, an even greater effect of hysteresis can be realized when complete regeneration is not advantageous.