Abstract
Zeolites are potentially a robust desalination alternative, as they are chemically stable and possess the essential properties needed to reject ions. Zeolite membranes could desalinate “challenging” waters, such as saline secondary effluent, without any substantial pre-treatment, due to the robust mechanical properties of ceramic membranes. A novel MFI-type zeolite membrane was developed on a tubular α-Al2O3 substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N2) permeation and underwent desalination tests with NaCl solutions under different pressures (0.7 MPa and 7 MPa). The results showed that higher pressure resulted in higher Na+ rejection and permeate flux. The zeolite membrane achieved a good rejection of Na+ (~82%) for a NaCl feed solution with a TDS (total dissolved solids) of 3000 mg·L−1 at an applied pressure of 7 MPa and 21 °C. To explore the opportunity for high salinity and high temperature desalination, this membrane was also tested with high concentration NaCl solutions (up to TDS 90,000 mg·L−1) and at 90 °C. This is the first known work at such high salinities of NaCl. It was found that increasing the salinity of the feed solution decreased both Na+ rejection and flux. An increase in testing temperature resulted in an increase in permeate flux, but a decrease in ion rejection.
Highlights
Membranes are the state-of-the-art for water treatment, including most new desalination plants.the reverse osmosis (RO) membranes used for desalination are polymeric-based and have some common problems, such as biofouling, oxidation, metal oxide fouling, abrasion and clay and mineral scaling [1]
The original and desalination tested MFI-type zeolite membrane was characterised by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to determine any changes in membrane structure, morphology and surface elements after long-term desalination testing under different conditions
A novel MFI-type zeolite membrane was developed by deposition of commercially available zeolite seeds on α-Al2O3 substrate followed by secondary hydrothermal growth
Summary
Membranes are the state-of-the-art for water treatment, including most new desalination plants. There have been some studies to date applying different membrane materials, such as zeolites [3,6,7,8,9,10,11], and hybrid organically bridged silica [5] for separation of salt from aqueous solutions. Ceramic membranes made from zeolites have been shown to be promising candidates for desalination of saline water, including seawater, as they possess the nanoporous structure required to reject ions [6,11]. Performance testing of MFI type zeolite membranes working in reverse osmosis demonstrated that high rejections of even the smallest ions, including Na+, are achievable [6,9]. Little work has been carried out to explore the influence of high salinity and temperatures on the desalination performance of zeolite membranes. The effects of NaCl feed concentration, applied pressure and temperature on membrane performance were investigated
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