Zeolite monoliths for air separation part 2: Oxygen enrichment, pressure drop and pressurization

Experiments have been carried out on two individual idealized steps in a pressure swing cycle in order to compare the performance of a novel absorbent monolith with that of a packed bed of commercial pellets containing the same weight of adsorbent. The application is the production of oxygen-enriched air using 5A zeolite. For feed pressures up to 3.8 bar, maximum oxygen compositions in the constant pressure production step up to 100% and 52% were achieved for the monolith with the previous step being carried out (1) by purging the column with pure oxygen at 1 bar, and (2) by evacuating the column, respectively. For virtually all experimental conditions studied, the separative performance of the monolith was found to be somewhat inferior to that of the bed of pellets, this being due largely to the former's poorer film mass transfer coefficient together with the virtual independence of this coefficient on velocity. To its advantage, however, the pressure drop through the monolith was found to be 3-5 times lower than that through the equivalent packed bed and consequently the time to pressurize the monolith was found to be 3-5 times faster than for the bed of pellets. This experimental feasibility study has demonstrated that the novel zeolite monolith configuration shows good potential for the production of oxygen-enriched air of low-to-medium purity, in a low energy, short cycle time, pressure swing process. The challenges associated with both improving and modelling the performance of the monolith are described.