Scientists cook up new recipes for taking salt out of seawater

water
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As populations boom and chronic droughts persist, coastal cities like Carlsbad in Southern California have increasingly turned to ocean desalination to supplement a dwindling fresh water supply. Now scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) investigating how to make desalination less expensive have hit on promising design rules for making so-called "thermally responsive" ionic liquids to separate water from salt.

Ionic liquids are a liquid salt that binds to , making them useful in forward osmosis to separate contaminants from water. (See Berkeley Lab Q&A, "Moving Forward on Desalination") Even better are thermally responsive ionic liquids as they use thermal energy rather than electricity, which is required by conventional reverse osmosis (RO) for the separation. The new Berkeley Lab study, published recently in the journal Nature Communications Chemistry, studied the chemical structures of several types of ionic liquid/water to determine what "recipe" would work best.

"The current state-of-the-art in RO desalination works very well, but the cost of RO desalination driven by electricity is prohibitive," said Robert Kostecki, co-corresponding author of the study. "Our study shows that the use of low-cost "free" heat—such as geothermal or solar heat or industrial waste heat generated by machines—combined with thermally responsive ionic liquids could offset a large fraction of costs that goes into current RO desalination technologies that solely rely on electricity."

Kostecki, deputy director of the Energy Storage and Distributed Resources (ESDR) Division in Berkeley Lab's Energy Technologies Area, partnered with co-corresponding author Jeff Urban, a staff scientist in Berkeley Lab's Molecular Foundry, to investigate the behavior of ionic liquids in water at the molecular level.

Using and dynamic light scattering provided by researchers in the ESDR Division, as well as molecular dynamics simulation techniques at the Molecular Foundry, the team made an unexpected finding.

Scientists cook up new recipes for taking salt out of seawater
Berkeley Lab scientists investigating how to make desalination less expensive have hit on promising design rules for making so-called "thermally responsive" ionic liquids to separate water from salt. Credit: Berkeley Lab

It was long thought that an effective ionic liquid separation relied on the overall ratio of organic components (parts of the ionic liquid that are neither positively or negatively charged) to its positively charged ions, explained Urban. But the Berkeley Lab team learned that the number of water molecules an ionic liquid can separate from seawater depends on the proximity of its organic components to its positively charged ions.

"This result was completely unexpected," Urban said. "With it, we now have rules of design for which atoms in are doing the hard work in desalination."

A decades-old membrane-based reverse osmosis technology originally developed at UCLA in the 1950s, is experiencing a resurgence—currently there are 11 desalination plants in California, and more have been proposed. Berkeley Lab scientists, through the Water-Energy Resilience Research Institute, are pursuing a range of technologies for improving the reliability of the U.S. water system, including advanced water treatments technologies such as desalination.

Because forward osmosis uses heat instead of electricity, the can be provided by renewable sources such as geothermal and solar or industrial low-grade heat.

"Our study is an important step toward lowering the cost of desalination," added Kostecki. "It's also a great example of what's possible in the national lab system, where interdisciplinary collaborations between the basic sciences and applied sciences can lead to creative solutions to hard problems benefiting generations to come."

Also contributing to the study were researchers from UC Berkeley and Idaho National Laboratory. The Molecular Foundry is a DOE Office of Science User Facility that specializes in nanoscale science. This work was supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy.


Explore further

Desalinating water in a greener and more economical way

More information: Hyungmook Kang et al, Molecular insight into the lower critical solution temperature transition of aqueous alkyl phosphonium benzene sulfonates, Nature Communications Chemistry (2019). DOI: 10.1038/s42004-019-0151-2
Citation: Scientists cook up new recipes for taking salt out of seawater (2019, July 31) retrieved 23 August 2019 from https://phys.org/news/2019-07-scientists-cook-recipes-salt-seawater.html
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Jul 31, 2019
North American "Scientists" only need 100 1000 megawatt fission plants to remove the salt from seawater.

Jul 31, 2019
Our sun produces limitless freshwater for free

Where does the salt go
If it's put back near the seawater that's about to sieved
that's increasing the salinity of the seawater

When all is said and done
The sun is evaporating the seawater
Forming rain clouds
Raining down on the land
Running in streams, rivers, lakes, underground caverns
As fresh water
Till it eventually runs back into the sea
To be evaporated by the sun
So
For all this high cost of freshwater
The sun is evaporating
Millions of square miles of seawater
Turning into freshwater
For free

Oh! This Irony, we're short of freshwater, that is prohibitively too expensive to produce!

Jul 31, 2019
When our Sun giveths for Free
Shootist> North American "Scientists" only need 100 1000 megawatt fission plants to remove the salt from seawater.

We could borrow those Giga watt power stations, which are keeping our fusion reactors, fusion fires burning!

Oh! The irony of ironies, even our free fusion energy reactors, are prohibitively expensive!

Aug 01, 2019
Always seemed like the simplest solution to me would be to pump the sea water to the dry salt lake beds in the eastern CA and NV desert, and use them as natural, large-scale solar stills. You would just need to construct large, transparent shields to allow the sunlight to penetrate while catching the evaporating fresh water. No moving parts and no adverse bi-products except salt (which is already there in high concentration from the last time the sun separated the salt from the seawater in the lake). You could also, potentially, use the water in that location for irrigation to farm the desert.

Aug 01, 2019
Our sun produces limitless freshwater for free

Where does the salt go
If it's put back near the seawater that's about to sieved
that's increasing the salinity of the seawater

When all is said and done
The sun is evaporating the seawater
Forming rain clouds
Raining down on the land
Running in streams, rivers, lakes, underground caverns
As fresh water
Till it eventually runs back into the sea
To be evaporated by the sun
So
For all this high cost of freshwater
The sun is evaporating
Millions of square miles of seawater
Turning into freshwater
For free

Oh! This Irony, we're short of freshwater, that is prohibitively too expensive to produce!


have you seriously never heard of a drought before? or a desert possibly? It doesn't rain everywhere everyday...

Aug 01, 2019
"have you seriously never heard of a drought before? or a desert possibly? It doesn't rain everywhere everyday..."

Is the perfect place to collect that entire solar desert Sun
To evaporate seawater, to water the desert for farming, drinking and whatever we do with this freshwater, freshly evaporated by solar power

Aug 02, 2019
There are drought conditions in the deserts in Israel, where farms of plentiful food had grown in the kibbutzim not long after it became the State of Israel in ~1948. And now they are searching for a way to attract rain clouds to rain on the desert. The Red Sea is said to be closing up slowly as the eastern part of Africa moves closer to the Near East.
There is a possibility that great amounts of heat is coming up through the regolith of Earth. Coming up from the lower mantle and upper core, that heat could encourage desertification. That extra heat has to go somewhere. This is not the same as volcanism, of course.
In the northern latitudes, that type of heat from the middle of the Earth would cause glaciers to melt, but water and rain would still be available. But closer to the equator where it is hot, it would possibly cause new deserts that are free of vegetation. The using up of water from the available aquifers would eventually remove the only available sources of water.

Aug 02, 2019
"have you seriously never heard of a drought before? or a desert possibly? It doesn't rain everywhere everyday..."

Is the perfect place to collect that entire solar desert Sun
To evaporate seawater, to water the desert for farming, drinking and whatever we do with this freshwater, freshly evaporated by solar power


They already do that in the Los Angeles area of California. There are artificial lakes where seawater is pumped in so that the Sun can evaporate the water and leave the salt. The salt is then taken out to be used for something. Perhaps that salt is sold to companies such as Morton Salt or to be sold as "sea salt".
But if I'm not mistaken, there must be a base of clay or plastics before seawater can be pumped into those artificial lakes, else the seawater would just seep into the ground.

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