Rapid pressure swing adsorption for small scale ammonia separation: A proof-of-concept

In a typical Haber-Bosch process, a gas stream containing 15–20 mol% ammonia is obtained from the reactor effluent, and ammonia is then partially separated in a phase-changing condensation unit. When operating at lower pressure for distributed manufacturing, the single-pass conversion drops to less than 10 mol%, which makes the condensation more cost-intensive. A small adsorber is proposed for concentrating ammonia through rapid pressure swing adsorption (RPSA) that fits the small-scale processing. A mathematical model is developed to evaluate the feasibility of the RPSA process for ammonia separation with high recovery. The ideal adsorbed solution theory, based on the Freundlich single-component isotherm model, is proposed to predict binary isotherms for various commercially available adsorbents. The performance of the RPSA-assisted adsorber is then studied at different process conditions for concentrating ammonia. The effect of various operating variables such as exhaust flow rate, cycle time, and feed pressure, is investigated. The proposed numerical model shows that nearly pure ammonia can be continuously produced at optimized conditions, with more than 95% recovery. This low-pressure RPSA-assisted adsorber can be used to design modular ammonia devices for distributed manufacturing. Our proposed technology can be further extended to concentrate other dilute gas mixtures, such as carbon dioxide.