Fabrication of 3-(trihydroxysilyl)-1-propanesulfonic acid membranes with superior affinity and selectivity for NH3 permeation over H2 and N2 at 50–300 °C

Ammonia (NH3) produced by Haber-Bosch process is separated through the condensation process, which needs a large amount of energy consumption. Membrane separation technology is compelling for achieving energy-saving and efficient NH3 separation. Therefore, 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) was applied, for the first time, to fabricate sulfonic silica-based membranes and evaluated for NH3 selective permeation. The amorphous siloxane network can be formed by simple condensation of silanol (Si-OH) under sulfonic acid (-SO3H) self-catalysis, as confirmed by the results of Fourier transform infrared spectroscopy and X-Ray diffractometry. Moreover, TPS xerogel powders dried from TPS sols showed excellent thermal stability and dense structure via thermogravimetric and N2 adsorption analyses. Importantly, an intensive NH3 adsorption amount of ∼3.0 mmol g-1 for TPS xerogels from NH3 adsorption and temperature-programmed desorption was twice higher than the reported oxidized (3-mercaptopropyl)trimethoxysilane xerogels (∼1.41 mmol g-1), which was ascribed to the inherently stronger proton-acidic -SO3H groups in TPS. Finally, TPS membranes prepared using TPS solutions diluted with ethanol expressed superior NH3-selective permeation based on favorable molecular sieving and NH3 adsorption-diffusion via single and binary gas permeation, especially remarkable NH3 permeance of ∼2.6×10-7 mol m-2 s-1 Pa-1 and excellent NH3/N2 selectivity of 266 at 300 °C.