Thread: Compound with less affinity for glycol then methane

Hi guys,

I am new to this forum and this will be my first post. I am struggling with a question for school.
I am searching for a substance that is has a relatively high critical pressure (up to 100 bar) and is gaseouse under standard conditions. This substance has to "like" water more than that it "likes" ethylene glycol. however it seems a simple question, there is not so much to find in leterature. methane is a suitable candidate, but this disolves in EG just too much.

I actually thought to search for polarity. I folowed ''like dissolves like'' but now i don't undersatand the reason that CO2 is dissolving even more in EG then methane... CO2 is also non-polar like methane.. I hope you guys can explain to me how this works?

thanks in advance

Originally Posted by Bipolar

Hi guys,

I am new to this forum and this will be my first post. I am struggling with a question for school.
I am searching for a substance that is has a relatively high critical pressure (up to 100 bar) and is gaseouse under standard conditions. This substance has to "like" water more than that it "likes" ethylene glycol. however it seems a simple question, there is not so much to find in leterature. methane is a suitable candidate, but this disolves in EG just too much.

I actually thought to search for polarity. I folowed ''like dissolves like'' but now i don't undersatand the reason that CO2 is dissolving even more in EG then methane... CO2 is also non-polar like methane.. I hope you guys can explain to me how this works?

thanks in advance

Possibly because the C=O bond is polar, even though the overall molecule is not?

Yes, that is true. and after some research (i did not know that much about molecular polarity) it looks like that even thou CO2 is non polar, EG will atract the polar C=O bond. But still this will even make the search for a compound harder...

Originally Posted by Bipolar

Yes, that is true. and after some research (i did not know that much about molecular polarity) it looks like that even thou CO2 is non polar, EG will atract the polar C=O bond. But still this will even make the search for a compound harder...

Of course CO2 does dissolve in water, too, but I do not know the relative solubility in water and ethylene glycol. How about things such as SO2, H2S, NH3 and so on, or have you already looked at these?

By the way, I find the "Engineering Toolbox" is a good site for data of engineering relevance on various materials. You can find some critical pressures there, certainly.

yes engineering toolbox is one of the sources i have been looking. the problem is that H2S and probably NH3 have a greater affinity for ethylene glycol than methane. which makes them unsuitable.

CO2 dissolves in water via carbenic acids. this however will lowe the pH and negatively affect the EG structure
i have been looking at hydrofluoro -carbons and -olefins. also done a simulation. there is in leterture not so much about this HFC-EG-H2O systems. and the effect of different HFC's. there is only for the HFC-134a, which in comperison with other literature dissolves more in EG then methane (proven also by simulation). so i think i have to look at a smaller hydrofluorocarbon like HFC-32 (difluoromethane). however there is nothing known about this combination in literature.
thanks for your reply

Originally Posted by Bipolar

yes engineering toolbox is one of the sources i have been looking. the problem is that H2S and probably NH3 have a greater affinity for ethylene glycol than methane. which makes them unsuitable.

CO2 dissolves in water via carbenic acids. this however will lowe the pH and negatively affect the EG structure
i have been looking at hydrofluoro -carbons and -olefins. also done a simulation. there is in leterture not so much about this HFC-EG-H2O systems. and the effect of different HFC's. there is only for the HFC-134a, which in comperison with other literature dissolves more in EG then methane (proven also by simulation). so i think i have to look at a smaller hydrofluorocarbon like HFC-32 (difluoromethane). however there is nothing known about this combination in literature.
thanks for your reply

OK. Confess I'm now a bit lost. I thought you were looking for a gas that dissolves better in water than in ethylene glycol. What do you mean by "greater affinity for ethylene glycol than methane" in this context? Does your mystery gas have to have a lower solubility in ethylene glycol than methane does, or do you mean something else?

yes, so the system is this:

methane-EG-water. however, methane (gas) disolves just too much in EG. now i want something better than methane (has to be a gas).
I have looked at the halogenated versions of methane, CH3F and CH2F2, there is just not enough data on a system like this: CH3F-EG-water.

there is one document on C2H2F4 (R-134a)-TEG-Water, this states that fluorine disolves in TEG ( I need EG) and also compared to methane-TEG-water data i can conclude that the halogenated ethane disolves better in TEG than methane. this has two reasons 1) the molecule ethane looks more like TEG than methane, and 2) a polar compound with affinity for water will also have affinity for TEG (so this will have similar effect in EG).

This last conclusion makes me confused, I need a compound with affinity for water (so probably polar) but this compound will also have affinity for EG... so at the moment anny polar compound will be not suitable? it is quit headbreaking

Originally Posted by Bipolar

yes, so the system is this:

methane-EG-water. however, methane (gas) disolves just too much in EG. now i want something better than methane (has to be a gas).
I have looked at the halogenated versions of methane, CH3F and CH2F2, there is just not enough data on a system like this: CH3F-EG-water.

there is one document on C2H2F4 (R-134a)-TEG-Water, this states that fluorine disolves in TEG ( I need EG) and also compared to methane-TEG-water data i can conclude that the halogenated ethane disolves better in TEG than methane. this has two reasons 1) the molecule ethane looks more like TEG than methane, and 2) a polar compound with affinity for water will also have affinity for TEG (so this will have similar effect in EG).

This last conclusion makes me confused, I need a compound with affinity for water (so probably polar) but this compound will also have affinity for EG... so at the moment anny polar compound will be not suitable? it is quit headbreaking

Right. So , as I understand it, you are looking for a 3 component system in which there is a gas (with a critical pressure ~100bar) and two liquids, the liquids being ethylene glycol and water, and you want the gas to be more soluble in water than in ethylene glycol. Is that it?

If so, why do you want to compare the candidate gases with methane?

because, if the candidate gases do a less better job than methane, I can't use them. and the critical pressure has to be high. the gas is applied as a carrier of moisture.

Originally Posted by Bipolar

because, if the candidate gases do a less better job than methane, I can't use them. and the critical pressure has to be high. the gas is applied as a carrier of moisture.

What do you mean by "carrier of moisture"? The vapour pressure of water depends only on the temperature, not on the gas with which the vapour may be mixed.

Yes, do you know the glycol dehydration system? TEG Dehydration: How Does the Stripping Gas Work in Lean TEG Regeneration? | Campbell Tip of the Month

I am aware of the vapor pressure, and according to that i would be able to use more gases as a carrier. but most of the (acid) gases dissolve in EG/TEG. for instance, CO2 would be able but it disolves in EG/TEG. air would be able, but it degrades the EG (because of O2). I would have used an noble gas, but i cant find anything in literature for example on a He-EG-water.

Originally Posted by Bipolar

Yes, do you know the glycol dehydration system? TEG Dehydration: How Does the Stripping Gas Work in Lean TEG Regeneration? | Campbell Tip of the Month

I am aware of the vapor pressure, and according to that i would be able to use more gases as a carrier. but most of the (acid) gases dissolve in EG/TEG. for instance, CO2 would be able but it disolves in EG/TEG. air would be able, but it degrades the EG (because of O2). I would have used an noble gas, but i cant find anything in literature for example on a He-EG-water.

Ah, the light dawns. If you are investigating a stripping process, I think you should post this in the chemical engineering section. There, it is more likely to be read by someone with practical knowledge of stripping as applied in industrial processes.

But meanwhile, from what you now say, it seems to me you want a stripping gas that is INsoluble in ethylene glycol, while its solubility in water is irrelevant (because the stripping action occurs in the gas phase and is thus not gas-dependent). Correct?

exactly. I did not think there was an chemicall engineering section. however, if you know something about somesort of gas, it would really help me out.

Originally Posted by Bipolar

exactly. I did not think there was an chemicall engineering section. however, if you know something about somesort of gas, it would really help me out.

Well I'm not expert at guessing the solubilities of gases in ethylene glycol. Clearly you do not want something reactive either. Like you, I'd have thought one of the inert gases might be a good bet. Or what about nitrogen?

Yes, nitrogen would be appliable but i think it carries less water than methane... however i am not sure..

the thing is, it has to be better than methane in like evry way :P

Originally Posted by Bipolar

Yes, nitrogen would be appliable but i think it carries less water than methane... however i am not sure..

Sorry to needle you on this, but what do you mean by "carries less water"? I've said - and you've agreed - that in the gas phase no particular gas "carries" any more water vapour than any other. The equilibrium vapour pressure of water will depend solely on its temperature. It does not matter what other gas is present.

For your stripping action, the only thing that matters is the ability to provide a boosting pressure, so that boiiing can occur. This enables whatever water is present to evaporate from a larger surface area, due to the surface area of all the bubbles that can then form throughout the liquid. It can therefore evaporate faster, even though the its vapour pressure is not altered.

It's just a kinetic effect, not a thermodynamic one. Isn't it? Or have I missed something?

Originally Posted by Bipolar

the thing is, it has to be better than methane in like evry way :P

Forgive me, but I don't think that sort of general statement will be at all helpful to the analysis of your problem.

Surely you need to specify what properties are important, and focus only on those. Hence my challenging you - above - on this thing you seem to have about the "affinity" of the gas for water. As I've tried to explain, I think it is irrelevant - not needed at all.

If so, that is one constraint fewer. And that will greatly improve your chance of success.

well actually whatmakes me confusing is fir example. air canbe humid right? so it contains an amount if water at a certain pressure and temperature... what you are saying is that no mater the gas, the same amount of moister wil be in lets say helium as that it is in air at the same pressure and temperature?

Originally Posted by Bipolar

well actually whatmakes me confusing is fir example. air canbe humid right? so it contains an amount if water at a certain pressure and temperature... what you are saying is that no mater the gas, the same amount of moister wil be in lets say helium as that it is in air at the same pressure and temperature?

Exactly. The vapour pressure of water is independent of the presence, the partial pressures, and the nature, of any other gases present. Think about it from a kinetic theory viewpoint.

In the liquid phase, you get molecules of a dissolved substance surrounded ("solvated") by molecules of solvent. The degree to which this occurs depends on the "affinity" of the solvent for the solute - and this affects the amount that can dissolve. Whereas, in the gas phase, the molecules of one gas are not associated with the molecules of another: they have too much kinetic energy to stick together. Instead they are free to move, independently, through the space enclosing them.

This is why the solubility of a gas in a liquid decreases to zero as the boiling point is approached. In the gas, the solvation of one substance by another has ceased.

I fully agree to this. I was missled by the fact that I had to search for a gas with affinity for water. So the conclusion of this will be that it actually does not matter if the gas is polar or not? or does the affinity of the gas for water increase the quantity of water vapor in the cariergas?

I also know that if the gas has an affinity for water, it will also have an affinity for the EG. so an other question will be, if i find a suitable gas wich has a huge affinty for water but also dissolves in EG, can i easily remove the "polution".

What do you think?

Originally Posted by Bipolar

I fully agree to this. I was missled by the fact that I had to search for a gas with affinity for water. So the conclusion of this will be that it actually does not matter if the gas is polar or not? or does the affinity of the gas for water increase the quantity of water vapor in the cariergas?

I also know that if the gas has an affinity for water, it will also have an affinity for the EG. so an other question will be, if i find a suitable gas wich has a huge affinty for water but also dissolves in EG, can i easily remove the "polution".

What do you think?

What I have been saying is that the answer to your first question is no, it does not matter what gas you choose, from the point of view of the amount of water vapour it can absorb. Any gas will do equally well.

So that means you can indeed focus your attention on getting the solubility in liquid ethylene glycol that is optimum for your purposes.

thanks man, i have been expanding my research, and did some simulations. at the moment, choosing the right calculations and conditions, i have found Nitrogen to be a verry suitable gas. almost no solubility in EG even at elevated pressures.

I will update more findings when i am done doing some literature research.

Originally Posted by Bipolar

thanks man, i have been expanding my research, and did some simulations. at the moment, choosing the right calculations and conditions, i have found Nitrogen to be a verry suitable gas. almost no solubility in EG even at elevated pressures.

I will update more findings when i am done doing some literature research.

Yes, I took a quick look on the web and saw some commercial nitrogen stripping processes advertised, so it seems to be an established method.