The rise in usage of portable oxygen concentrators in the medical field as a viable alternative to oxygen tanks has increased the demand for rate enhanced adsorbents that allow for the operation of a rapid pressure swing adsorption process necessary for these devices. Rate enhanced adsorbents are developed specifically to lower the heat and mass transfer resistance of the adsorbent with the aim of reducing the cycle time at which a PSA process can efficiently operate. However, not all rate enhanced adsorbents exhibit the same rate characteristics due to differences in the size and formation of the adsorbent along with the amount and type of binder used to form the particle. Thus, determining how to efficiently utilize a specific rate enhanced adsorbent in a rapid pressure swing adsorption process requires an appropriate process evaluation that determines a range of suitable operating conditions with a particular focus on reducing cycle time (minimizing BSF) and identifying appropriate adsorption/desorption pressures. This study illustrates one method to evaluate a rapid PVSA process using a rate enhanced adsorbent while demonstrating a process that provides a high purity product (97% oxygen using argon free air) and extremely favorable recoveries (50-60% at pressure ratios between 4-5) with a BSF under 100 lbs. /TPD oxygen.
Using a commercial Li-X zeolite, a lab-scale two column PVSA system was used to assess the ability of the adsorbent for use in a rapid PVSA process. The evaluation included first examining the effect of cycle time on the oxygen recovery at a range of pressure ratios (varying from 2.5-7 by changing the desorption pressure). The adsorption/desorption pressure, amount of gas used for the feed and purge steps, and product purity were maintained as the cycle time was reduced. This provided a method in which any change in oxygen recovery was almost solely assessed to the reduction in cycle time and not variations in other process parameters. It also allowed for the determination of a kinetic limit for how fast the adsorbent could be used while still providing a high level of performance. Additionally, a range of adsorption pressures were examined to determine an ideal operating range using rapid PVSA for this adsorbent.