Innovative NH3 separation over immobilized molten salt membrane at high temperatures

Abstract

In industry, CO2 emissions can be mitigated by replacing conventional ammonia separation techniques withenergy-efficient systems. In this study, a ZnCl2 immobilized molten salt (IMS) membrane was synthesized and evaluated for the potential separation of NH3 from a gas mixture containing N2 and H2. The membrane was prepared via the direct deposition technique, and several permeation tests were performed to evaluate its permeation characteristics at atmospheric pressure with temperatures ranging from 290 °C to 325 °C. For single gas permeation at 300 °C, NH3 permeance was found to be as high as 182 GPU, with NH3/N2 and NH3/H2 ideal selectivities of 11,375 and > 107, respectively. For binary mixtures (10 %/90 % NH3/N2 and NH3/H2), NH3 permeance as high as 825 GPU was achieved at the same operating conditions. Remarkably, higher permeance (∼1100 GPU) was obtained by feeding ternary mixtures (11 %/67 %/23 % NH3/H2/N2) at a temperature of 325 °C. An exceptionally high NH3 purity (99.9 %) was achieved in the permeate stream. The IMS membrane exhibits prolonged stability, working for more than 180 h with no significant performance loss. This pioneering study shows that the ZnCl2 IMS membrane can be used to separate NH3 at high temperatures with a potential application for treating downstream ammonia in the industrial Haber Bosch process.