Nature-Inspired Superhydrophobic Membranes For Membrane Distillation

Membrane distillation (MD) is a membrane technology based on the vapour pressure gradient across the porous hydrophobic membrane. MD offers several advantages such as lower operating pressures and insensitive to feed concentration for seawater desalination.

However, the commercialization of MD process has been constrained mainly by the lack of commercially available high-performance MD membranes and high energy consumption. Current state-of-the-art lab-scale fabrication of superhydrophobic membranes for membrane distillation often involve complex surface modifications and/or the massive usage of nanomaterials. However, these methods are often difficult to be scaled up.

Hence, a pure rheological spray-assisted non-solvent induced phase separation (SANIPS) approach has been developed to fabricate superhydrophobic polyvinylidene fluoride (PVDF) membranes. The resulting membranes are found to have high porosity, superhydrophobic, high liquid entry pressure and hierarchical micro/nanostructures and can be easily scaled up. This facile fabrication method is envisioned to pave the way for large-scale production of superhydrophobic membranes for membrane distillation.

The spraying step in this fabrication approach causes local distortion of the membrane surface and induces a two-stage phase inversion, leading to the formation of multilevel polymeric crystal structures, like the lotus surface. The morphological structures and other membrane properties such as mechanical strength and liquid entry pressure could be tuned by applying spraying materials with different physicochemical properties.

Features of the membrane and module include:

Flat sheet membrane

• Fabricated from commercial PVDF polymer
• Superhydrophobic
• High liquid entry pressure
• One step fabrication of the membrane with online modification of the membrane surface

Modules

• Industrial scale modules available
• Customized modular design

Treatment of high salinity waters in:

• Mining, metal treatment
• Pharmaceutical
• Chemical synthesis
• Oil and gas

Zero-liquid discharge processes

Desalination

Desalination brine treatment

• Treatment of difficult streams which is not possible with other conventional methods
• Usage of waste heat
• High surface area to volume ratio compared to plate and frame membrane distillation as the current work is in the spiral-wound configuration
• Proven method of translating membrane fabrication from lab scale to industrial scale phase inversion (PI) casting line
• Readily available industrial scale process settings to fabricate membrane of one meter in width and several hundreds of meters in length