(95b) Development of Adsorption-Based Technologies – Thinking Broader Than Process Optimization

The use of adsorption as an industrial separation process developed rapidly in the second half of the 1900s. Most industrial systems separate gases based on equilibrium selectivity wherein some species adsorb more strongly than others. Commercialized equilibrium examples include air pre-purification, hydrogen PSA, and oxygen VSA. Around 1980, nitrogen production from air using kinetic selectivity was commercialized. The adsorbent used, carbon molecular sieve (CMS), has a restrictive opening to the micropore volume, allowing O2 to diffuse to the adsorption sites much more rapidly than N2 and Ar. Air Products commercialized its first N2 PSA product around 1990.

In the decades since the initial plant designs for each product, there have been many refinements to adsorbents, processes, and hardware. In general, large plant designs are mature and most improvements are now incremental due to optimization of only one aspect, such as process.

Developing a next generation N2 PSA process presented a unique challenge since the separation is based on kinetic selectivity, rather than equilibrium. Our goal was to increase productivity 3 times without compromising N2 recovery. For this aggressive goal, we needed to simultaneously develop and optimize adsorbent, process, and plant equipment. The effort required a team with skills in adsorbent R&D, process modeling, valve technology, and adsorption process scale-up.

N2 PSA plants are commonly 2 bed processes with total cycle time on the order of 1-4 minutes. The cycle time must be reduced to achieve significant productivity gains. In turn, a new CMS adsorbent had to be developed to match the much shorter cycle time. Process improvements were achieved by using a rapid cycle PSA system (to increase productivity) and by optimizing the number of beds (7-9) (to maintain high recovery). For hardware, a new rotary valve design was able to affect the process with low void volume. The new N2 PSA system has been successfully commercialized. Three patent applications were co-filed to protect the new product and have since been allowed. The presentation will highlight the various adsorbent developments, process simulation and testing, and hardware integration leading to this new product.