NH3 separation by ZnCl2 immobilized molten salt (IMS): Experimental and modeling

Abstract

The utilization of membrane-based separation demonstrates significant potential as a means to mitigate energy consumption and emissions in crucial industrial processes such as the Haber-Bosch process. This study systematically explored the performance of ZnCl₂ immobilized molten salt (IMS) membranes, both theoretically and experimentally, for separating NH₃ from N₂ and H₂. Experimentally, the separation characteristics of the ZnCl₂ IMS membrane supported on a 1 μm pore-sized wire mesh were determined when exposed to pure and mixed gases at 300 °C and atmospheric pressure. For the single gas permeation test, the NH₃ permeance was ∼218 GPU, with NH₃/N₂ and NH₃/H₂ ideal selectivities of >10⁷ and >10⁷ were achieved, respectively. In the case of binary mixtures, NH₃ permeance within the range of 1800–2000 GPU was attained at a feed NH₃ partial pressure of ∼5 kPa. The membrane was reasonably stable for ≥640 h under different feed mixtures. The theoretical component examined the transport mechanisms of NH₃ across the ZnCl₂ IMS membranes and employed a mathematical model initially introduced by Xu et al. [J. Chem. Eng. 460 (2023) 141728]. The mathematical model was fitted to experimentally measured NH₃ fluxes as a function of the NH₃ partial pressure (∼10–100 kPa) and membrane thicknesses. The mean absolute percentage error (MAPE) between the model and experimental data was less than 3%. In particular, the model was used to deduce the kinetic and thermodynamic parameters related to the permeation of NH₃ through the membrane.