Pervaporation of ammonia solution with γ-alumina supported organosilica membranes

• Pervaporation of ammonia-solution using γ-alumina supported organosilica membranes was explored.
• Hybrid silica membrane exhibited ammonia selective transport at low ammonia concentration.
• Membrane degradation started to occur at high feed temperature and high ammonia concentration.
• Significant changes in crystalline γ-alumina structure undermined the functional silica separation layer.

In this work, pervaporation of ammonia-solution using γ-alumina supported organosilica membrane (HybSi®, Pervatech) was explored to understand ammonia removal performance and material stability in this unique high pH environment. During the testing of synthetic ammonia solution of 50 mg/L at 45 °C (pH 10), the hybrid silica membrane showed a preference towards ammonia transport over water, with an ammonia separation factor up to 12 and flux of 4.3 kg m−2 h−1 stable in a continuous testing period of 7 h. At an ammonia concentration of 1000 mg/L (pH 11), the membrane initially exhibited separation preference towards ammonia at 45 °C, then gradually reversed to water selective after increasing to 70 °C, where a significant flux decline was observed. The membrane degradation was investigated by FTIR, porosimetry, SEM and XRD. Only slight change in organosilica chemistry and structure was evident, however more significant degradation was observed in the supporting γ-alumina layer. The changes in crystalline alumina structure, porous properties and physical structure undermined the functional silica separation layer. Therefore while the organosilica membrane appeared stable in the high pH aqueous ammonia environment, membranes for ammonia pervaporation applications should consider alternative supporting layers to γ-alumina.