Evaluation of simple and complex models for mass transfer in the non-isothermal adsorption of single and binary component mixtures from an inert carrier gas

The problem of non-isothermal single and binary component adsorption on activated carbon from an inert carrier gas is considered. The adsorbed components are propane and butane. The isotherms for single component adsorption have been experimentally determined and are correlated using linear logarithmic interpolation. In the case of binary component adsorption the equilibrium isotherms are correlated with an accuracy of ± 3% using Ideal Adsorbed Solution Theory. The material and energy balances for a spherical pellet are presented, and two different models are used to describe mass transfer within the particle. These are: a) a simple model based on the definition of effective diffusivity within the particle, and b) a complex model in which the fluxes are described by the dusty gas model expressions. Film mass transfer resistance, at the outer surface of the particle is considered in both models. Heat transfer through the particle is governed by Fourier\u27s law using an effective thermal conductivity. A film resistance to heat transfer is assumed to exist at the surface of the particle. The heats of adsorption are taken to be constant within the range of concentrations and temperatures considered in this work. It is found that the temperature rise incurred by a single pellet under normal operating conditions is negligible. Comparisons of the results from the simple and complex models for varying Reynolds\u27 numbers, particle Sherwood numbers, Nusselt numbers and pressures are found to differ most for the least preferentially adsorbed component. As steady state approaches these differences decrease. Only small differences are evident between the results of the two models for the more preferentially adsorbed component. The main finding is that the improvement due to application of the more complex model to describe the physics of pore diffusion is insufficient to justify its use over the simple model. It is thought that more research should be directed towards the effects of pore size distribution and pore connectivity on the constitutive equations of mass and heat transfer in porous adsorbent particles --Abstract, pages ii-iii