(383q) Exploring in-Situ Adsorption for Ammonia Separation: Insights from High-Pressure and High-Temperature Conditions

Ammonia (NH₃) is important across various industries, such as fertilizers, explosives manufacturing, and nitrogen-containing chemicals. The production of bulk ammonia is mainly through Haber-Bosch (HB), a high-energy, intensive reaction process (200 to 400 ºC and 100 to 200 bar); separation from unreacted reagents (N₂, H₂) produces a condensed output stream at -20 ºC, followed by reheating the gases up to the synthesis conditions to be returned to the reactor. A possibility to reduce the energy consumption of the separation stage is the use of in-situ adsorption at HB temperature and pressure conditions, as opposed to cryogenic. However, the absence of experimental NH₃ adsorption data under actual HB conditions impedes a comprehensive assessment of the feasibility of such separation in situ. The main objective of this research is to determine ammonia adsorption capacity and selectivity at HB-relevant conditions, as well as the mechanistic aspects that will impose limitations on multicycles upon temperature and pressure. Ion-exchanged forms of type A, X, and Y zeolites were selected due to established thermal and chemical stability, widespread industrial utility, and commercial availability. In general, X zeolite has shown the highest affinity toward NH₃ at any pressure and temperature (up to 15 bar and 150 ˚C), with the extra framework cations dominating the interactions with NH₃. A practical comparison to determine the most promising adsorbents could involve evaluating their working capacity, defined by the difference in adsorbed amounts between the adsorption stage at 15 bar of ammonia and the desorption stage at 1 bar. In this regard, X zeolites exhibited a working capacity approximately 77% higher than LTA zeolites and 20% higher than Y faujasites at 150 ºC, making the X-type version of faujasites a strong candidate for in-situ adsorption recovery process during HB.