https://phys.org/news/2019-07-scientists-cook-recipes-salt-seawater.html
[image in online article]
July 31, 2019
Scientists cook up new recipes for taking salt out of seawater
by Lawrence Berkeley National Laboratory
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 water, 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)
desalination 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 nuclear magnetic resonance spectroscopy 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.
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 ionic liquids 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 thermal
energy 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.
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
=====================================
To subscribe, unsubscribe, turn vacation mode on or off,
or carry out other user-actions for this list, visit
https://www.freelists.org/list/keiths-list
Note: new climate change website is now in pre-launch
Visit https://www.10n10.ca/e/index.shtml