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Wires turn salt water into freshwater
Phys.Org ^
| June 8, 2012
| Lisa Zyga
Posted on 06/10/2012 10:10:32 PM PDT by Kevmo
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To: Kevmo
Youre as useless as a 2 story outhouse. You might outlive having to clean it out with good venting.
41
posted on
06/11/2012 11:29:28 AM PDT
by
listenhillary
(Courts, law enforcement, roads and national defense should be the extent of government)
To: Kevmo
Forward osmosis uses the thermodynamic law of entropy to separate solids from a fluid. Using a vessel separated into two compartments by a membrane filter, you put a dirty liquid on one side and clean water on the other. The water passes through the membrane until the percentage of solids on both sides is the same. Doesn't sound very useful, diluting the dirty liquid. Why use a filter at all, just add clean water to the dirty. Diluting isn't separating anything.
42
posted on
06/11/2012 1:31:12 PM PDT
by
Toddsterpatriot
(Math is hard. Harder if you're stupid.)
To: listenhillary
Doesn’t ‘brackish water’ = Marine estuary? No more shrimp? No more sharks?
43
posted on
06/11/2012 1:44:06 PM PDT
by
txhurl
(Scott Walker is my President.)
To: carriage_hill
>>> Salts already banned in NYC, so its a cakewalk from there on in. <<<
Cakes are next on the ban list.
To: AFreeBird
45
posted on
06/12/2012 8:34:54 AM PDT
by
politicianslie
(Obama: Our first Muslim PRESIDENT,destroying America $1 Trillion at a time! And America sleeps)
To: txhurl
There are aquifers that contain brackish water.
46
posted on
06/13/2012 7:47:52 PM PDT
by
Moonman62
(The US has become a government with a country, rather than a country with a government.)
To: Kellis91789
Nanoporous graphene could outperform best commercial water desalination techniques
June 22, 2012 by Lisa Zyga
(Top left) Hydrogenated and (top right) hydroxylated graphene pores. (Bottom) Side view of the simulated nanoporous graphene filtering salt ions and producing potable water. Image credit: Cohen-Tanugi and Grossman. ©2012 American Chemical Society
(Phys.org) -- Although oceans and seas contain about 97% of Earths water, currently only a fraction of a percent of the worlds potable water supply comes from desalinated salt water. In order to increase our use of salt water, desalination techniques must become more energy-efficient and less expensive to be sustainable. In a new study, two materials scientists from MIT have shown in simulations that nanoporous graphene can filter salt from water at a rate that is 2-3 orders of magnitude faster than todays best commercial desalination technology, reverse osmosis (RO). The researchers predict that graphenes superior water permeability could lead to desalination techniques that require less energy and use smaller modules than RO technology, at a cost that will depend on future improvements in graphene fabrication methods.
Water permeability of various desalination techniques. The graphene nanopores can reject salt ions with a water permeability 2-3 orders of magnitude higher than commercial reverse osmosis (RO) techniques. Image credit: Cohen-Tanugi and Grossman. ©2012 American Chemical Society
Because those carbon atoms at the pore edge would be quite reactive without passivation, in one way or another under realistic experimental conditions they will likely have some form of chemical functionalization, Grossman said. This can be controlled to some extent, so we wanted to explore the two limits of hydrophobic vs. hydrophilic edge chemistries. If we had no functional groups (just bare carbon) then within a short time water molecules would dissociate at the pore edge and likely either hydrogenate or hydroxylate those carbons.
The scientists compared the two chemistries, along with different pore sizes, of nanoporous graphene in their simulations by running saltwater with a salinity of 72 g/L over the membranes, which is about twice the salinity of average seawater (about 35 g/L).
They found that, although the largest nanopores could filter water at the highest rate, large nanopores allowed some salt ions to pass through. The simulations identified an intermediate range of nanopore diameters where the nanopores were large enough to allow the passage of water molecules but small enough to restrict salt ions.
The simulations also showed that the hydroxylated graphene significantly enhances the water permeability, which the scientists attribute to the hydrophilic nature of the hydroxyl groups. Since, in contrast, the hydrogenated pores are hydrophobic, water molecules can flow through only when in a limited number of highly ordered configurations. But hydrophilic groups allow water molecules to have a greater number of hydrogen-bonding configurations inside the pores, and this lack of restrictions increases the water flux.
Overall, the results show that nanoporous graphene can theoretically outperform RO membranes in terms of water permeability, which is expressed in liters of output per square centimeter of membrane per day and per unit of applied pressure. Whereas high-flux RO has a water permeability of a few tenths, the simulations showed that nanoporous graphenes water permeability ranged from 39 to 66 for pore configurations that exhibited full salt rejection (23.1 Å2 hydrogenated pores and 16.3 Å2 hydroxylated pores). Graphene with the largest hydroxylated pores reached 129, but allowed some passage of salt ions.
The scientists explain that there are two main challenges facing the use of nanoporous graphene for desalination purposes. One is achieving a narrow pore size distribution, although rapid experimental progress in synthesizing highly ordered porous graphene suggests that this may soon be feasible. The other challenge is mechanical stability under applied pressure, which could be achieved using a thin-film support layer such as that used in RO materials.
Computationally, we're looking at a range of other potentially new ways to engineer membranes for desalination and decontamination, Grossman said. Experimentally, we are currently fabricating nanoporous membranes and hope to test their desalination performance in the coming months.
More information: David Cohen-Tanugi and Jeffrey C. Grossman. Water Desalination across Nanoporous Graphene. Nano Letters. DOI: 10.1021/nl3012853
Journal reference:Nano Letters
Copyright 2012 Phys.org
47
posted on
06/22/2012 6:00:03 PM PDT
by
Kevmo
(SUCINOFRAGOPWIASS: Shut Up, CINOs; Free Republic Aint a GOP Website. It's A Socon Site.)
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