Adsorbent shaping as enabler for intensified pressure swing adsorption (PSA): A critical review

Pressure swing adsorption is widely applied in industry for hydrogen purification, methane recovery, air separation, biomass upgrading, CO2 recovery, to name a few. To further improve the attractiveness of pressure swing adsorption systems, ongoing research focusses on ways to intensify the process. In particular, improve productivity and reduce the footprint of the system consequently leading to reduced capital and operating costs. The proposed solution is known as fast or rapid cycling which, as the name implies, means to reduce the cycle time. However, there are some challenges to overcome such as mass transfer limitations leading to reduced separation efficiency, as well as increased pressure drop due to high superficial velocities typical to fast cycling. Adsorbent shaping has the potential to overcome these limitations and it is being regarded as a promising process intensification solution for pressure swing adsorption processes offering great flexibility in designing optimized cycles with improved performance. Various adsorbent shapes such as monoliths, laminates, foams and fibers have been studied in literature with monolith structures being the most popular. Most of the published literature on the topic of adsorbent shaping is concentrated on material development and lab-scale testing, modeling, and manufacturing through 3D printing techniques. Performance evaluations generally target reduced pressure drop and enhanced mass transfer kinetics with only a few papers addressing the broader context of process intensification and economic assessments of the potential gained benefits of using structured adsorbents in place of beads or pellets. Although, sorbent shaping is a very promising developing field, there is still significant work to be done for it to reach its full potential. Further research should go beyond shape optimization and lab-scale testing to process optimization and pilot/large-scale testing under cyclic conditions. In this context, newly developed artificial intelligence tools show great promise for the development of intensified cycles based on structured adsorbents by speeding up computation time of complex optimization routines. To date, there are limited industrial applications using structures sorbents. One of the main hurdles for large scale deployments is the labor and time intensive preparation methods currently available, leading to high manufacturing costs. Thus, development of easy, fast and cost-effective manufacturing options through automatization, will expedite the large-scale implementation of structured adsorbents in pressure swing adsorption processes.