Non-linear isothermal packed bed adsorbers: Comparison of Peclet and cell numbers

Adsorption and desorption curves were generated by the axial dispersion and cell models for both equilibrium and non-equilibrium systems having the Langmuir type of isotherm. Ethylene-helium and methane-helium on 5A zeolite were selected to represent the equilibrium system as the mass transfer resistance is small in these systems, while ethylene-helium on 4A zeolite and oxygen-helium on carbon molecular sieve having strong intracrystalline diffusion resistances were selected as the non-equilibrium processes. The time to change the dimensionless exit concentration level between 0.99 and 0.01 (τ_0.99-0.01) was chosen as the criterion to find a correspondence between the Peclet number in the axial dispersion model and N, the number of cells in the cell model. Computations were performed to estimate τ_0.99-0.01 for all the systems by both models for various values of the non-linearity parameter λ. For both the equilibrium and non-equilibrium processes, the ratio of Peclet number to N changes from a value of 2 at low λ to unity when λ is high (λ = 0.85) during adsorption. However, this ratio can be taken for 2 for all values of λ during desorption.