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March 17, 2013

Graphene with nanometer holes could be super efficient for desalination and drop in replacement at existing desal plants by the end of 2013

Lockheed's new Perforene membranes, made of graphene (sheets of pure carbon only one atom thick), are 500 times thinner than filters currently on the market. This means less energy is required to push water through the membrane, making reverse osmosis more efficient. John Stetson, head engineer for the project, told Reuters that it would require approximately 100 times less energy than other membranes.

But working with such a thin material presents new problems, and engineers are still trying to find the best way to produce nanometer-wide holes in the membranes quickly and on a large scale without tearing the product. The added difficulties of manufacturing will probably factor into cost, but Lockheed says desalination plants wouldn't need to change their infrastructure to use Perforene. The prototype expected by the end of this year will be a drop-in replacement for filters currently in use.

A 2012 patent by Lockheed for Perforated Graphene Deionization or Desalination

A separation arrangement isolates chlorine, sodium and possibly other ions from water. The ion-laden water is applied to at least one graphene sheet perforated with apertures dimensioned to pass water molecules and to not pass the smallest relevant ion. The deionized water flowing through the perforated graphene sheet is collected. The ions which are not passed can be purged. In another embodiment, the ion-laden water is applied to a first graphene sheet perforated with apertures dimensioned to block chlorine ions and through a second graphene sheet perforated with apertures dimensioned to block sodium ions. The concentrated chlorine and sodium ions accumulating at the first and second perforated graphene sheets can be separately harvested.



A method for deionizing water carrying unwanted ions, said method comprising the steps of: providing a sheet of graphene with plural apertures selected to allow the passage of water molecules and to disallow the passage of a selected one of said unwanted ions, to thereby generate perforated graphene; pressurizing said water carrying unwanted ions to thereby generate pressurized water; applying said pressurized water to a first surface of said perforated graphene, so that water molecules flow to a second side of said perforated graphene sheet in preference to ions; and collecting said water molecules from said second side of said graphene sheet.

* nanoholes for disallowance chlorine ions is nominally nine nanometers.
* nanoholes are nominally spaced apart by fifteen nanometers.
* nanoholes to disallow sodium ions is nominally six nanometers.
* sodium nanoholes are nominally spaced apart by fifteen nanometers.

The graphene is backed with a grid of polytetrafluoroethylene.


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