High Throughput Separation By Rapid Pressure Swing Adsorption: Bench Scale Demonstration of Model Binary Gas Mixture

Pressure swing adsorption (PSA) is a cyclic gas separation technique that is just over 50 years old. It has many successful commercial applications including gas dehydration, air separation, hydrogen purification, and solvent vapor recovery. More applications are also on the horizon, including CO₂ capture from flue gas

Traditional, commercial PSA systems utilize cycle times on the order of minutes to tens of minutes, with individual step times no shorter than 0.5 min (30 s) or so. However, since the mid 80’s there has been a great deal of interest in trying to reduce the cycle time to make the columns smaller and thus increase the feed throughput, which is the amount of gas processed per unit time per unit mass of adsorbent. These so called rapid PSA processes have met with limited success, however, until only recently.

Within the past 10 years, SeQual Technologies in San Diego and QuestAir in Vancouver (among less notable others) developed the rapid PSA concept into viable, commercial processes using rotary valve and rotary bed technology, respectively. They both have commercial processes that operate with cycle times on the order of a few seconds, with individual step times of less than 1 s. SeQual has been focusing on medical oxygen technology, while QuestAir has been focusing on hydrogen technology.

However, a paucity of work has been done on other rapid PSA applications; and overall, the understanding of the rapid PSA concept is quite limited with little fundamental information available. This leaves considerable room not only for the development of new theories and mechanisms underlying the rapid PSA concept, but also for the development of new applications for rapid PSA processes. The goal of this project has been to shed some light on both of these notions, theoretically, experimentally and via process modeling.

To this end, a 1-bed rapid PSA system has been constructed and is currently being utilized to separate a model binary gas mixture consisting of 15 vol% CO₂ in N₂ using beaded 13X zeolite over a wide range of cycle times and process conditions. Step times as short as 0.25 s are possible in this 1-bed system under both positive and negative gauge pressures and at different temperatures. A variety of PSA cycle schedules are being studied, including light reflux, heavy reflux and/or dual reflux steps, and including equalization steps with tanks. The ultimate goal is to demonstrate the separation of this model binary gas mixture at exceptionally high feed throughputs. This presentation will discuss the latest results obtained with this unique 1-bed rapid PSA system.