Graphene/PVDF flat-sheet membrane for the treatment of RO brine from coal seam gas produced water by air gap membrane distillation

Abstract

Brine management of coal seam gas (CSG) produced water is a significant concern for the sustainable production of CSG in Australia. Membrane distillation (MD) has shown the potential to further reduce the volume of CSG reverse osmosis (RO) brine. However, despite its potential, the lack of appropriate MD membranes limits its industrial use. Therefore, this study was aimed on the fabrication of a robust membrane for the treatment of real RO brine from CSG produced water via an air gap MD (AGMD) process. Here, graphene/polyvinylidene fluoride (G/PVDF) membranes at various graphene loadings 0.1–2.0wt% w.r.t. to PVDF) were prepared through a phase inversion method. Surface characterization revealed that all G/PVDF membranes exhibited favorable membrane properties having high porosity (>78%), suitable mean pore size (<0.11µm), and high liquid entry pressure (>3.66bar). AGMD test results (feed inlet: 60.0±1.5°C; coolant inlet: 20.0±1.5°C) for 24h operation indicated a high water vapor flux and salt rejection of 20.5L/m2h and 99.99%, respectively for the optimal graphene loading of 0.5wt%, i.e., G/PVDF-0.5 membrane (compared to 11.6L/m2h and 99.96% for neat PVDF membrane). Long-term AGMD operation of 10 days further revealed the robustness of G/PVDF membrane with superior performance compared to commercial PVDF membrane (85.3% final normalized flux/99.99% salt rejection against 51.4%/99.95% for commercial membrane). Incorporation of graphene has resulted to improved wetting resistance and more robust membrane that has the potential for the treatment of RO brine from CSG produced water via AGMD.