Completely dissolving a gas into a liquid

[warfreak131]

Hello PF

I want to dissolve a gas in a liquid. I figured I could create a closed loop vacuum system. I introduce gas into the lines at atmospheric pressure, and then close off the lines, so the intake and exhaust of the vacuum pump are connected. Then I turn the pump on and the gas just runs through the liquid again and again and again until its completely dissolved.

Do you think that would work?

 

[SteamKing]

It's not completely clear what you are trying to accomplish.

A given amount of liquid will be able to hold only so much gas, depending on the ambient temperature and pressure of the liquid. If the liquid reaches its saturation temperature for its pressure, it cannot hold any dissolved gasses at all. This is a consequence of Henry's Law:

http://en.wikipedia.org/wiki/Henry's_law

 

[warfreak131]

Ok, I'll try to clarify. (see attached pic) Let's say I want to re-carbonate soda that's gone flat. I would put soda in a vessel which will allow CO2 to pass through it. And then the CO2 just flows through the soda again and again until its dissolved as much as possible.

If I cool down the liquid, more gas would be able to dissolve correct? Also, if gas makes it through the liquid without dissolving, will at least cool down, making it more likely to dissolve on the second pass?

 

[SteamKing]

You might get some CO2 to re-dissolve, but nowhere near the amount of CO2 the liquid originally contained. That's why soda pop is bottled under pressure: the higher pressure means more CO2 gas is dissolved, and when you open the container and release this pressure, some of the CO2 comes out of solution and makes the bubbles appear.

And using a vacuum pump just means you are lowering the pressure of the liquid, which in turn reduces the saturation temperature of the liquid, which means less gas is going to dissolve in the liquid.

Since you are specifically talking about carbonation, perhaps this article might help:

http://en.wikipedia.org/wiki/Carbonation

 

[warfreak131]

Hmmm, then what would be the best way to maximize the amount dissolved? I was thinking, if I added a 1 way valve into the system, then it would draw in air consistently as long as the system isn't at atmosphere. So if anything happened where the pressure of the soda wasn't at atmosphere, the 1 way valve would allow air in, restoring the pressure.

Otherwise, what's a good way to carbonate something. I know that product soda-stream uses a compressed CO2 cylinder and you just add a few blasts of CO2 to the soda. So would it be better to compress the gas first?

 

[SteamKing]

Yes.