Journal of Membrane Science | 2021
Fabrication of molten nitrate/nitrite dual-phase four-channel hollow fiber membranes for nitrogen oxides separation
Abstract
Abstract Molten salt-ceramic dual-phase membranes have great prospects in the selective separation of nitrogen oxides. A gas-tight KNO3–Ba0.5Sr0·5Co0·8Fe0·2O3-δ (KNO3-BSCF) four-channel hollow fiber membrane was developed in this study. A wide operating temperature window of 350–500\u202f°C with high nitrogen oxides permeance was achieved. The maximum nitrogen oxides permeance reached 9.2\u202f×\u202f10−9\u202fmol\u202fm−2\u202fs−1 Pa−1 under the condition of 1% NO2, 1% CO2 and 20% O2 at 500\u202f°C. The presence of nitrogen oxides was able to suppress the reaction of BSCF oxide with CO2 to form carbonates. Insights on the transport mechanism of nitrogen oxides transport were provided and the existence of nitrite route for nitrogen oxides transport was firstly demonstrated by experiments. An 1800\u202fh long-term nitrogen oxides permeation was running on the KNO3-BSCF hollow fiber membrane while the permeance increased by a factor of ∼40 (5.2\u202f×\u202f10−10\u202fmol\u202fm−2\u202fs−1 Pa−1 to 2.2\u202f×\u202f10−8\u202fmol\u202fm−2\u202fs−1 Pa−1 at 450\u202f°C) due to the partial decomposition of nitrate into nitrite. This nitrite route was also verified in KNO3/KNO2-BSCF hollow fiber membrane constructed by preloading 30\u202fwt% nitrite in molten salt.