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

摘要

A simple, semi-empirical, generalized expression was developed for the LDF mass transfer coefficient k as a function of the half cycle time theta (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(theta (c) ) for any system, irrespective of the loading and irrespective of theta (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 theta (c) > 0.3 and the short cycle time limit now valid for theta (c) < 0.01. When evaluating this region for several adsorbate-adsorbent systems, the minimum Glueckauf theta (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 theta (c) less than this minimum Glueckauf theta (c) , this new first-of-its-kind expression can be used to readily provide an accurate value of k = f(theta (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(theta (c) ) from this new expression can be based on either the shortest cycle step in the cycle or a different value of k = f(theta (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.