Evaluation and optimization of VPSA processes with nanostructured zeolite NaX for post-combustion CO₂ capture

We present a comprehensive experimental and simulation study on a low-cost and efficient CO₂ capture technique using nanostructured zeolite NaX in a vacuum pressure swing adsorption (VPSA) process. The nanostructured zeolite NaX adsorbent has a high CO₂ adsorption capacity, a relatively high adsorption and desorption rate, and a large CO₂ selectivity over N₂. Therefore, it is suitable for post combustion CO₂ capture from dry flue gas. A series of nanostructured zeolite NaX pellets are prepared with different ratios of binder material and at different sintering temperatures. The results from mechanical properties, adsorption isotherms, kinetics and breakthrough experiments demonstrate that nanostructured zeolite material prepared with a low ratio of binder that sintered at 500 °C has the best separation performance for a CO₂/N₂ mixture. In addition, the results indicate that the nanostructured zeolite NaX samples lead to a better separation performance compared with the commercial microsized zeolite NaX. Process optimization studies employing the above adsorbents were performed to minimize the energy consumption of the process for a specified product purity and recovery rate. The decision variables include the feed pressure, blowdown pressure, evacuation pressure, feed flow rate, and length to diameter ratio of the adsorption bed. The effect of cycle time was investigated independently due to the need for synchronization of the multi-bed configuration. The optimization results indicate that the energy consumption of the process with nanostructured zeolite is about 30% lower while achieving a higher CO₂ purity and productivity compared with a process employing a commercial microsized zeolite.