Researchers claim membrane work will cut cost of desalination

Research engineers at the University of Virginia have developed upgrades to existing polymer membranes which they said may make desalination simpler and less expensive.

Assistant professor in the university's engineering department, Geoffrey M Geise, said the membranes can also be used to help create and store clean energy.

"The desalination membranes that we study work by allowing water molecules to move more rapidly through the polymer compared to salt, resulting in less salt on the product side of the membrane," said Geise.

Ions joined to water molecules move slower through the membrane because they are larger that water molecules alone. And ions are energetically less stable in the membrane phase compared to the water phase, so they are blocked ofrom entering the polymer.

By manipulating the polymer's chemistry, to exploit these effects Geise's team is seeking to maximize the separation efficiency. He says he beliefs his team;s combination of "experimental and computational research capabilities" place it ahead of rival researchers in the field. "A key challenge is understanding how to fine-tune material chemistry to maximize the selectivity of the polymer. That would make water purification as efficient as possible."

Geise said he and this team are developing their understanding of how to minimize the ions that travel through membranes without affecting the amount of water that passes through. They can also design polymer to block the salt from entering the membrane in the first place. "If the salt never gets into the membrane, it cannot move through the membrane and desalination occurs," Geise said.

"By making membranes that are more selective, we can reduce energy consumption by reducing pressure requirements for reverse osmosis or electrical energy requirements for electrodialysis," Geise added.

Geise's research not only looks at water desalination, but also explores how to generate clean energy using similar membranes. The emerging energy generation technology "reverse electrodialysis" turns the electrodialysis process around and uses differences in salt concentrations on either side of a membrane to generate electrical power.

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