New linear driving force correlation spanning long and short cycle time pressure swing adsorption processes

Abstract

A simple, semi-empirical, generalized expression was developed for the LDF mass transfer coefficient k as a function of the half cycle time θ c that encompasses and transitions between the well-known regions governed by the long cycle time constant Glueckauf k and the short cycle time dependent k. This new expression can be used to estimate k = f(θ c ) for any system, irrespective of the loading and irrespective of θ c , no matter if k is in the cycle time dependent region or not. A three times wider transition region between the Glueckauf k and the cycle time dependent k was also established, with the Glueckauf LDF limit now valid for θ c > 0.3 and the short cycle time limit now valid for θ c < 0.01. When evaluating this region for several adsorbate-adsorbent systems, the minimum Glueckauf θ c spanned three orders of magnitude from thousands of seconds to just a few seconds, indicating a cycle time dependent k is not necessarily limited to what is normally considered a short cycle time. For virtually any θ c less than this minimum Glueckauf θ c , this new first-of-its-kind expression can be used to readily provide an accurate value of k = f(θ c ). Since the widely accepted half cycle time concept does not apply to the actual simulation of a multi-step, unequal step time, pressure swing adsorption process, the value of k = f(θ c ) from this new expression can be based on either the shortest cycle step in the cycle or a different value of k = f(θ c ) for each cycle step time in the cycle, with validity confirmed either by experiment or by process simulation using the exact solution to the pore diffusion equation.