Analytic solution for adsorber breakthrough curves with bidisperse sorbents (zeolites)



A time-domain solution in the form of infinite series for the break-through curves is derived for zeolite adsorbers. Three diffusion steps are accounted for in the solution: external film, macropore, and micropore. The solution is based on the assumption that the concentration profiles in micropores and macropores are both parabolic.

Based on the analytic solution, a simple criterion is given for the relative importance of the three individual mass transfer resistances. The adsorber behavior is determined by four independent dimensionless parameters. For the commercial zeolite sorbents, the bed behavior is dominated by two parameters: Henry's law constant (K) and the parameter M2, which is the product of the stoichiometric time (L/v) and the time constant for macropore diffusion (Dp/Ro2).

The analytic solution is in good agreement with experimental data for the breakthrough curves of nitrogen and methane carried in helium in 5A zeolite beds. When reduced to monodisperse pores, the solution is also in good agreement with Rosen's exact solution.