(709g) Argon Purification by Cascaded PSA System Using Cation Exchanged Zeolite X as Oxygen Selective Adsorbent

This work deals with conceptual design of a PSA process for the purification of an argon stream with oxygen as minor component. As a precursor to this, we had developed an oxygen selective zeolite X adsorbent. The oxygen selectivity was optimized by suitable cation exchange. The best adsorbent was characterized for its adsorption thermodynamics for argon/oxygen as well as kinetics. Analysis of the experimental gravimetric adsorption data as well as breakthrough curves using suitable models was used to quantify adsorption thermodynamics as well as kinetics. With this adsorbent-adsorbate system characteristic parameters available, PSA systems with 2 or more beds and known PSA cycle configurations were tried using a comprehensive PSA process simulator. The process performance was characterized using conventional purity-recovery-throughput definitions. A single PSA system did not yield acceptable performance for a suitable process. A novel concept of cascaded PSA systems was evaluated using simulation studies. In this conceptual design, oxygen-rich extract of one PSA system (primary system) was treated in another suitably designed PSA system (secondary system) in series so as to get a raffinate stream similar in composition to the feed to the primary PSA system. With this, overall recovery of argon could be enhanced significantly. The concept was extended further to treat oxygen-rich extract of the secondary PSA system in a tertiary PSA system to get raffinate similar in composition to the feed to the secondary PSA system and so on. The recovery improved further. The concept of cascading was studied through extensive simulations to arrive at an overall system with desired purity and recovery parameters. The paper describes stagewise results in this conceptual process design exercise and offers some guidelines for optimal design of such cascaded PSA systems.