Na plus -gated nanochannel membrane for highly selective ammonia (NH3) separation in the Haber-Bosch process

Currently, cryogenic condensation is the predominant process for recovering ammonia (NH3) in the Haber-Bosch (HB) process, which is highly energy intensive. To be more compatible with the reaction conditions in the HB process and thus minimize the pressure and temperature swing during reactant recycling, energy-efficient technologies for NH3 extraction at elevated temperature and pressure are greatly needed. In this work, the Na+-gated nanochannel membrane, shown exclusively for water conduction in our previous work, also exhibited highly NH3-selective performance, with NH3/H2 selectivity as high as 4,280 and NH3/N2 selectivity > 10,000 at temperature up to 250 degrees C and pressure up to 35 bar. Excellent stability of the Na+-gated nanochannel membrane was demonstrated during a 100-h run in ternary NH3/H2/N2 gas mixture at 200 degrees C and 35 bar, consistent with structural characterization by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transfer infrared (FTIR) spectroscopy. A techno-economic analysis (TEA) was conducted for the HB process using the Na+-gated nanochannel membrane and the traditional HB process with condenser. Under the optimized separation conditions, > 80 % energy savings and approximately 20 % reduction of the net NH3 production cost can be achieved, demonstrating the great potential of the Na+-gated nanochannel membrane for NH3 separation in the HB process.

Automated summary

Cryogenic condensation is currently used to recover ammonia (NH3) in the energy-intensive Haber-Bosch (HB) process, but there is a need for more energy-efficient technologies for NH3 extraction at elevated temperature and pressure. This study demonstrates that a sodium-gated nanochannel membrane, previously known for its exclusive water conduction abilities, also shows highly selective performance for NH3. Techno-economic analysis shows that using this membrane can lead to more than 80% energy savings and a 20% reduction in net NH3 production cost in the HB process.