2024 AIChE Annual Meeting
(222d) Adsorption of Ammonia Onto Zeolites with Sodium Counterions at High Pressure and Temperature
Authors
Munoz Senmache, J. - Presenter, University of Puerto Rico – Mayaguez
Aristizabal-Gonzalez, C., University of Puerto Rico - Mayaguez
One alternative to reduce the energy footprint required for the production of NH3 via the Haber Bosch (HB) process is the implementation of in-situ adsorption using highly selective and capacity porous adsorbent materials at reaction conditions. This will not only decrease the energy requirement of the separation process (avoid the condensation of the output stream to -20 °C), but it could also increase the yield of the reaction. This study aims to capture NH3 equilibrium and diffusion adsorption data at conditions closer to HB (150 ˚C and 15 bar) with porous zeolite materials. For decades, the efforts have been limited to ambient condition tests, limiting the observation of adsorption mechanisms. As a starting point, sodium-based faujasite type X and Y and zeolite type A (i.e., Na-X, Na-Y, and Na-A, respectively) were considered to establish benchmarks. These adsorbents were chosen due to thermal stability. High-pressure (up to 15 bar) NH3 adsorption tests at 50-150 ˚C revealed that the abundance of Na cations in the zeolites significantly influences interactions with NH3. At the same time, pore size dictates adsorption capacity under high pressure. Notably, Na-X exhibited the highest capacity, surpassing Na-Y and Na-A by approximately 30% at 150 °C and 15 bar NH3 pressure. Furthermore, selectivity values for NH3/N2, estimated through Ideal Adsorbed Solution Theory (IAST) calculations at 50˚C, demonstrated favorable selectivity of 37, 78, and 47 for Na-X, Na-Y, and Na-A, respectively. The temperature increase will only increase selectivity due to the rectangular shape of NH3 isotherms contrasting the predominantly linear N2adsorption isotherms. Finally, regarding irreversible NH3 uptake, faujasite-type zeolites exhibited no hysteresis during complete adsorption/desorption cycles and, therefore, exhibited the utmost working capacity. These findings collectively suggest that Na-X zeolite is a promising adsorbent candidate for separation NH3 at HB conditions.