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UK researchers create graphene-based sieve that can remove salt from seawater

bbc.com

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Re: UK researchers create graphene-based sieve that can remove salt from seawater

#51

Post by jessriedel »

marmshallow wrote: post #42
jessriedel wrote: post #15

Earlier quoted context omitted.

Desalinization is already with about a factor of 2 or 3 of the thermodynamic optimum, so improvements can't be revolutionary. Desalinization mostly needs cheap clean energy.

Can you describe this thermodynamic optimum or link me to something? Curious

> A state-of-the-art facility is now within a factor of two of the theoretical energy minimum, and only 25 percent higher than the realistic minimum for the current reverse osmosis process. In short, it’s going to be tough to squeeze too much more energy out of reverse osmosis, and we’re unlikely to find an alternative method of desalination that will provide a significant boost over that.

> But that doesn’t mean that there are no other ways of getting better output for our energy. The total process of desalination turns out to require three to four times the theoretical minimal energy use, since the salt water must be pumped and pretreated, the membranes maintained, and the resulting brine handled afterwards. Some of these things might be amenable to further improvements, and there has been work put into developing membranes that don’t clog up as easily or better pre-filtering of biological materials.

http://arstechnica.com/science/2011/08/desalinization-is-thi...

More: http://science.sciencemag.org/content/333/6043/712

https://www.researchgate.net/profile/Menachem_Elimelech/publ...

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#52

Post by jessriedel »

throwaway91111 wrote: post #38
jessriedel wrote: post #15

Earlier quoted context omitted.

Desalinization is already with about a factor of 2 or 3 of the thermodynamic optimum, so improvements can't be revolutionary. Desalinization mostly needs cheap clean energy.

Also, waste is a major problem, environmentally.

Are you talking about the brine? This is trivial if you just put a pipe a few hundred yards out to sea. The concentration is diluted extremely quickly. (The only exception is if your desalination plant is below sea level because then you have to pump the brine up hill, which costs some energy.)

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#53

Post by ChuckMcM »

M_Grey wrote: post #5

I swear I've heard about this before... is this one of those stories that emerges about a technology that never seems to enter the market? That "super slick" coating for condiment container interiors is another that springs to mind.

I was thinking the same thing although I've been unable to locate the paper that I recall reading about it. There are lots of papers which discuss nano-pores in graphene as membrane but I recall something that required a current in the graphene.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#54

Post by johncolanduoni »

jessriedel wrote: post #49
leot wrote: post #44

Earlier quoted context omitted.

Even with forward osmosis?

Not really. Basic thermodynamics tells you that if your only input is water with a certain salt concentration and your output is water with a lower salt concentration (plus either brine -- very salty water -- or dry salt), then there is a minimum free energy cost. > Based on thermodynamic principles and practical kinetic requirements, the theoretical minimal energy for desalination with FO is always higher than that…

> A strict 1-particle-to-1-particle replacement can (I think) have arbitrarily low free energy cost

Even better, it can have a (theoretical) energy gain if you use a substance with a lower heat of mixing than (sea) salt and water.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#55

Post by jessriedel »

johncolanduoni wrote: post #54
jessriedel wrote: post #49

Earlier quoted context omitted.

Not really. Basic thermodynamics tells you that if your only input is water with a certain salt concentration and your output is water with a lower salt concentration (plus either brine -- very salty water -- or dry salt), then there is a minimum free energy cost. > Based on thermodynamic principles and practical kinetic requirements, the theoretical minimal energy for desalination with FO is always higher than that…

> A strict 1-particle-to-1-particle replacement can (I think) have arbitrarily low free energy cost Even better, it can have a (theoretical) energy gain if you use a substance with a lower heat of mixing than (sea) salt and water.

OK, but then, forgetting about desalination, you'd be able to just build a power plant with this substance and sea water, right? The fact that very few such plants exit then tells us that it would probably be cheaper to just do your desalination with reverse osmosis powered by a conventional power plant.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#56

Post by adrianratnapala »

desireco42 wrote: post #47

This is all fine, but if it isn't inert and if it 'leaks' graphene, it can be super toxic as well. I don't want to pu-pu it, but it is legitimate concern.

I didn't know that graphene was toxic. I should stop licking my pencils.

And from what little chemistry I know, I though graphene oxide was rather inert.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#57

Post by throwaway91111 »

jessriedel wrote: post #52
throwaway91111 wrote: post #38

Earlier quoted context omitted.

Also, waste is a major problem, environmentally.

Are you talking about the brine? This is trivial if you just put a pipe a few hundred yards out to sea. The concentration is diluted extremely quickly. (The only exception is if your desalination plant is below sea level because then you have to pump the brine up hill, which costs some energy.)

I mean, I sure hope so.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#58

Post by johncolanduoni »

jessriedel wrote: post #55
johncolanduoni wrote: post #54

Earlier quoted context omitted.

> A strict 1-particle-to-1-particle replacement can (I think) have arbitrarily low free energy cost Even better, it can have a (theoretical) energy gain if you use a substance with a lower heat of mixing than (sea) salt and water.

OK, but then, forgetting about desalination, you'd be able to just build a power plant with this substance and sea water, right? The fact that very few such plants exit then tells us that it would probably be cheaper to just do your desalination with reverse osmosis powered by a conventional power plant.

Baring some yet undiscovered and very bizarre (but thermodynamically viable) chemistry that requires you to involve saltwater in a practical implementation, yes. Otherwise saltwater (which has a positive heat of mixing) is just fighting your actual process.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#59

Post by krastanov »

adrianratnapala wrote: post #56
desireco42 wrote: post #47

This is all fine, but if it isn't inert and if it 'leaks' graphene, it can be super toxic as well. I don't want to pu-pu it, but it is legitimate concern.

I didn't know that graphene was toxic. I should stop licking my pencils. And from what little chemistry I know, I though graphene oxide was rather inert.

The naive (very hand-wavy) explanation for the toxicity of graphene (nanotubes to be specific, not sheets in general) is not chemistry, rather the nanotubes physically rupturing cell organelles. Same with asbestos: small rigid particles that cut everything else in pieces.

Re: UK researchers create graphene-based sieve that can remove salt from seawater

#60

Post by _coldfire »

Jach wrote: post #33
m0zzie wrote: post #25

Earlier quoted context omitted.

Is that really still true in the world we live in today though? Previously we were unable to instantly share information so freely and collaborate with people around the world with so little effort. I'm not saying it shouldn't take time to develop these things, but surely the 30-40 year timeline is significantly reduced due to information sharing today?

I'd question the 30-40 years figure. I suspect "it depends". Check out the book "Skunk Works" sometime and marvel at what they managed to do on the frontiers with such small numbers of people and crappy computers (with relatively small budgets and tight deadlines to boot). Peter Thiel riffs on this idea a lot. Despite our incredible advances in computing and networks, it seems like progress in everything else has slo…

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