Work

Ammonia Adsorption at High Temperature and Pressure Using Sodium Containing Aluminosilicates: Selectivity over Nitrogen and Multicycle Working Capacities

Year: 2025

Type: article

Abstract: Separating NH 3 from N 2 and H 2 using adsorption onto porous materials at elevated pressures and temperatures has been proposed as a promising alternative to optimize the Haber–Bosch (HB) synthesis process. However, experimental data on NH 3 adsorption at high pressure are scarce and necessary to properly evaluate NH 3 adsorption as a possible and viable separation option. Using commercial Na-LTA, Na-X, and Na-Y zeolites (Si/Al 1.00, 1.26, 2.80, respectively), we evaluated the NH 3 equilibrium adsorption up to 15 bar and temperatures of 323, 373, 423, and 473 K. N 2 adsorption isotherms were measured at 323 and 473 K. All the zeolite samples were activated at 673 K to ensure complete dehydration. At 36 bar total pressure and 473 K, ideal adsorbed solution theory (IAST) predicts selectivity for NH 3 over N 2 of 265, 234, and 211 for Na-LTA, Na-X, and Na-Y, respectively. Separation factors based on IAST and kinetic selectivity are estimated as 128, 39, and 46, respectively. The enhanced selectivity of Na-LTA is attributed to diffusion limitations for N 2 stemming from its narrower pore size. NH 3 working capacities through 5-cycle PSA tests at 473 K directly correlate with the Si/Al ratio, with Na-Y zeolite achieving the highest working capacity at 2.50 mmol cm –3 . However, VSA tests with desorption via dynamic vacuum for 10 min yielded a working capacity of up to 8.83 mmol cm –3 for Na-X. Gibbs ensemble Monte Carlo simulations are carried out to investigate the adsorption of NH 3, N 2, H 2, and their mixture in Na-LTA. Analysis of the simulation trajectories indicates that the NH 3 molecules bind strongly to the Na + cations and displace nitrogen in mixtures.

Source: Industrial & Engineering Chemistry Research

DOI: 10.1021/acs.iecr.4c04621

Authors: Cristian Aristizabal-González, Juan C. Muñoz-Senmache, Prerna, J. Ilja Siepmann, Michael Tsapatsis, Arturo J. Hernández-Maldonado

Institutions: University of Puerto Rico-Mayaguez, University of Minnesota, Johns Hopkins University, Johns Hopkins University Applied Physics Laboratory

Language: English

Topic: Zeolite Catalysis and Synthesis

Subfield: Inorganic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: green

Funder: U.S. Department of Energy

Award: MEMBRANE-CATALYST CO-DESIGN FOR TRANSFORMATIVE MANUFACTURING