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Old 08-04-2017, 15:27   #31
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Re: Another way to create drinkable seawater?

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Originally Posted by Captain Bill View Post
Ok StuM, I've read all of your articles and some of the original scientific papers these popular articles were based on. I have also understood them, which you have not. .
You clearly have NOT understood them because you continue to refer to Osmosis and think that that is the basis of the technology.


It is not, osmosis and osmotic pressures are irrelevant when you are talking about layers of graphene oxide one atom thick. The water does not pass through the filter due to osmotic pressure.

The second link, if you have indeed read it, makes it quite clear that very powerful capillary action at the molecular level is the prime motive force moving water through the filter, not osmosis. "The latter effect is due to a property that the Manchester scientists call “ion sponging”. Their graphene capillaries suck up small ions as powerful hoovers leading to internal concentrations that can be hundreds of times higher than in external salty solutions."

Here's another fairly long read - the Manchester patent:
https://encrypted.google.com/patents/WO2015075451A1

Buried in it you will find this little gem:
"it is believed that water and solutes pass through capillary-like pathways formed between the graphene oxide flakes by diffusion and that the specific structure of the graphene oxide laminate membranes leads to the remarkable selectivity observed as well as the remarkable speed at which the ions permeate the laminate structure. "

Again clearly illustrating that your obsession with osmotic pressure is irrelevant.
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Old 08-04-2017, 15:33   #32
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Re: Another way to create drinkable seawater?

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Ok StuM, I've read all of your articles and some of the original scientific papers these popular articles were based on. I have also understood them, which you have not. Not one of these people has claimed to eliminated the pressure issue caused by osmotic pressure.
No?
From the previous link:
"The concentration gradient corresponds to a capillary-like pressure of «50 bars, which acts on salt ions against the osmotic pressure. "
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Old 11-04-2017, 01:22   #33
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Re: Another way to create drinkable seawater?

The length and random configuration of the paths require substantial pressure to strip the water molecules at the surface from the ions and then to move the water molecules through the membrane against the osmotic pressure. Thus, the RO filter tends to be energy inefficient."

So what these folks are saying is that the pressure required is that required to "move the water molecules through the membrane against the osmotic pressure"


plus,


that required to overcome the friction pressure generated by moving the water through " the length and random configuration of the paths"


It is obvious that instituting a better "configuration of the paths" might lead to a reduction in the flow motivating pressure required but how does the grapheme generate the pressure required to overcome the osmotic pressure.


Does the grapheme itself somehow generate the pressure drop required or does the osmotic phenomenon just disappear in the presence of grapheme?
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Old 11-04-2017, 04:33   #34
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Re: Another way to create drinkable seawater?

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Originally Posted by RaymondR View Post
The length and random configuration of the paths require substantial pressure to strip the water molecules at the surface from the ions and then to move the water molecules through the membrane against the osmotic pressure. Thus, the RO filter tends to be energy inefficient."

So what these folks are saying is that the pressure required is that required to "move the water molecules through the membrane against the osmotic pressure"
Instead of just taking the quoted text out of context, it may be advisable to actually read the link it came from. That quote was in the itroductory paragraphs and was just an illustration of the pressure required for traditional reverse osmosis. It does not apply to the graphene oxide filter process.

Quote:
plus,


that required to overcome the friction pressure generated by moving the water through " the length and random configuration of the paths"


It is obvious that instituting a better "configuration of the paths" might lead to a reduction in the flow motivating pressure required but how does the grapheme generate the pressure required to overcome the osmotic pressure.

Does the grapheme itself somehow generate the pressure drop required or does the osmotic phenomenon just disappear in the presence of grapheme?
Yes. the very small pores in the very thin graphene oxide layers do it essentially by capillary action.

I repeat myself:
"The concentration gradient corresponds to a capillary-like pressure of «50 bars, which acts on salt ions against the osmotic pressure. "
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Old 11-04-2017, 05:32   #35
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Re: Another way to create drinkable seawater?

Second Law of Thermodynamics: physical processes tend to go from states of low entropy (highly ordered) to states of high entropy (more disordered). To go in the opposite direction (disordered to ordered, high entropy to low) requires work. In this case we're discussing converting salty water (very disordered) to pure water with the solutes removed (more ordered - less random). This requires energy, no matter how it's achieved or what intermediate stages are involved. Speed is negotiable and so is the extra work required to overcome diffusion resistance, but these don't change the bottom line. This is Bill's point and he's correct: there's no free lunch in thermodynamics (or water purification).
However, I'm going to follow the advice I have for Bill: don't get further involved in this discussion. The level of incomprehension is too overwhelming. You're just wasting your time.
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Old 11-04-2017, 12:26   #36
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Re: Another way to create drinkable seawater?

WE seem to have encountered a thought block process here. If I am correct, the impasse results from each sides' refusal to recognize the possibility to the others' understanding of the process, and any real attempt to address it. I am getting a bit over my head in that my science education is dated, although I do like to think I keep up with technologic developments and the science upon which they are based. Anyway, here goes:

I initially believed, and continue to believe -possibly incorrectly- that the graphene membrane identified in the initial post had characteristics -the ability to separate water molecules from certain contaminants such as dissolved sodium chloride, etc.- without the process we typically refer to as reverse osmosis, including pressure and semi-permeable membranes. This was achieved, at least in my belief and understanding, by the happy achievement of a product that both attracted water and had holes of the correct size that the water molecules fit through (or were drawn through by the previously mentioned attraction, if it was on one side only or somehow unequal on the two sides?). The other ions and materials did not have the admission ticket and were excluded.

If I am correct, those of you who disagreed and disagree believe the process is still (reverse) osmosis related, and requires the application of significant outside energy, mechanical for sure, and electrical as a practical matter, beyond the mere movement of water to a place where the potential energy related to gravity can do the rest. I suppose if the water were taken high enough this would always be true, but I think, or at least hope we all understand the point. This seems to be the stalling point for the thermodynamics contingent, so they win the argument that some energy is needed, even to lift a bucket of sea water, but there is a vast difference between amounts required.

Of greatest importance to boaters, especially cruisers, was the potential for this seeming innovation to affect the need to carry water supplies, particularly for longer voyages, and the power (energy) requirements and equipment needed for replenishment without the usual outside sources.

Can any of you confirm that my view is incorrect, without resorting to the assumption that it is impossible? I, to no small extent, still liken the process to a sieve that allows waster to flow through, but not the pasta or peas, rather than reverse osmosis which is, by similar analogy, to potato ricers where the cooked potato is squeezed through holes using hand pressure (yes, I know the analogies are imperfect, but I was attempting to avoid oil filters and the like).
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Old 11-04-2017, 12:54   #37
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Re: Another way to create drinkable seawater?

Here is a video of a similar technology in action. No pumps.

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Old 11-04-2017, 14:53   #38
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Re: Another way to create drinkable seawater?

Quote:
Originally Posted by StuM View Post
Instead of just taking the quoted text out of context, it may be advisable to actually read the link it came from. That quote was in the itroductory paragraphs and was just an illustration of the pressure required for traditional reverse osmosis. It does not apply to the graphene oxide filter process.



Yes. the very small pores in the very thin graphene oxide layers do it essentially by capillary action.

I repeat myself:
"The concentration gradient corresponds to a capillary-like pressure of «50 bars, which acts on salt ions against the osmotic pressure. "
Patience my friend, us dumb old roughneck folk rely upon you soaring intellect folk to digest, interpret and re-present this complex stuff for our edification.

I'll get onto my review of the osmoses and capillary phenomenon just as soon as I can spare a little intellectual capacity from the resolution of the computer to MFD wifi file transfer problem, but I wouldn't hold my breath.

It's very interesting and a very elegant solution if one can use the capillary phenomenon to both provide the motive pressure gradient and the molecular filter media in the one material.

Next question is what sort of productivity is exhibited, say in cc/square cm/hour,by the material in filtering sea to fresh water.

It would appear that if a decent production cost/productivity ratio can be achieved the worlds future fresh water requirement problems are solved.
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Old 11-04-2017, 16:06   #39
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Re: Another way to create drinkable seawater?

The big question: when to sell the watermaker before it's completely worthless?
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Old 13-04-2017, 15:13   #40
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Re: Another way to create drinkable seawater?

I vowed I would avoid this absurd debate, but I guess I'm a sucker. Capillary action is not, repeat not the magical solution to water purification that you imagine.
(1) Capillary action affects liquids, not the ions dissolved in them.
(2) Capillary action is bidirectional. Plants can move water up their stems/trunks using capillary action, because they have elegant ways to remove the water at the top. How does the graphene membrane do this? (It requires energy, in the case of plants provided by photosynthesis.)
Here's the unpalatable truth, which you seem determined to ignore. Removing the ions dissolved in salt water to produce pure (or purer) water is an endothermic reaction (2nd Law!) It doesn't matter where this happens or how or what mental sleight of hand you use to try to avoid the fact, entropy is going to decrease and the energy cost of that must be paid. Whatever its properties, the graphene membrane won't violate the principles of thermodynamics. For heaven's sake find a physicist somewhere who can explain this to you, because I obviously can't.
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Old 13-04-2017, 15:33   #41
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Re: Another way to create drinkable seawater?

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Originally Posted by ajhil View Post
Here's the unpalatable truth, which you seem determined to ignore. Removing the ions dissolved in salt water to produce pure (or purer) water is an endothermic reaction (2nd Law!) It doesn't matter where this happens or how or what mental sleight of hand you use to try to avoid the fact, entropy is going to decrease and the energy cost of that must be paid. Whatever its properties, the graphene membrane won't violate the principles of thermodynamics. For heaven's sake find a physicist somewhere who can explain this to you, because I obviously can't.
No one is ignoring that fact or arguing that no energy is involved. The problem is with the nay-sayers who keep insisting that the same amount of energy will be required as is currently used by RO de-salination.

What we are looking at here is a potential much more energy efficient means of de-salination.

If all of the energy required is because of the endothermic cost of separating the ions, then I've got a great idea for energy generation.
Let's just fill a big tank with river water and dissolve a few Kgs of salt in it. We can then harness nearly as much energy as is required to desalinate the same amount of water with RO.
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Old 13-04-2017, 16:44   #42
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Re: Another way to create drinkable seawater?

I hope I live long enough for this dispute to be resolved by practical application or by its failure to come into being. Preferably 50 or so years beyond the resolution event. Right now I am almost 74.
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Old 13-04-2017, 18:32   #43
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Re: Another way to create drinkable seawater?

I have a water maker,
But I also have a triangular sheet of canvas, 6 ft wide at one end,
I hang it on the transom and it is saggy in the middle, and the pointy end hangs down into the cockpit into a five gallon drum,
Its amazing how much fresh water you can collect in minutes when its raining,
Five minutes and five gallons of fresh water which I put straight into my tanks,
Its only limitations is the size of my water tanks, Which dont take long to fill in heavy rain,
And lack of rain,
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Old 14-04-2017, 01:23   #44
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Re: Another way to create drinkable seawater?

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No one is ignoring that fact or arguing that no energy is involved. The problem is with the nay-sayers who keep insisting that the same amount of energy will be required as is currently used by RO de-salination.

What we are looking at here is a potential much more energy efficient means of de-salination.

If all of the energy required is because of the endothermic cost of separating the ions, then I've got a great idea for energy generation.
Let's just fill a big tank with river water and dissolve a few Kgs of salt in it. We can then harness nearly as much energy as is required to desalinate the same amount of water with RO.
I don't believe there is any endothermic reaction involved in the reverse osmosis method of separating the Na and Cl ions from the water if it is a filtration process. You are not trying to recombine the ions, just filter them out of the water phase.

Might take a fair bit of salt to raise the temperature to boiling point and I'm sure the folks down stream would get pretty pissed off with you.

Mixing salt with ice to reduce the temperature in order to make ice cream was once a common practice.
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Old 14-04-2017, 01:31   #45
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Re: Another way to create drinkable seawater?

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I vowed I would avoid this absurd debate, but I guess I'm a sucker. Capillary action is not, repeat not the magical solution to water purification that you imagine.
(1) Capillary action affects liquids, not the ions dissolved in them.
(2) Capillary action is bidirectional. Plants can move water up their stems/trunks using capillary action, because they have elegant ways to remove the water at the top. How does the graphene membrane do this? (It requires energy, in the case of plants provided by photosynthesis.)
Here's the unpalatable truth, which you seem determined to ignore. Removing the ions dissolved in salt water to produce pure (or purer) water is an endothermic reaction (2nd Law!) It doesn't matter where this happens or how or what mental sleight of hand you use to try to avoid the fact, entropy is going to decrease and the energy cost of that must be paid. Whatever its properties, the graphene membrane won't violate the principles of thermodynamics. For heaven's sake find a physicist somewhere who can explain this to you, because I obviously can't.
My understanding of the method vascular plants use to elevate water and dissolved nutrients is solely dependant upon capillary phenomena and this is the limiting factor in the height trees can grow to in earths gravity. If this is true then if you could grow trees out of graphene then they should be able to grow to in excess of 1,000' if the capillary action generated can exceed the osmotic pressure generated between sea water and fresh???
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