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(OP)
thread798-176593: Convert ppmw to ppmv for liquids
I have read that the maximum solubility of water in CO2 at -43C is 180 ppm. On the other hand, I read that the maximum permissible of water in CO2 50 ppmv. These are two different values (non related), however, I would like to know How do I convert from ppm to ppmv for this situation?

You don’t normally use ppmv for miscible liquids. Due to the change in volume of mixing for non ideal liquids, most miscible liquids will “change” density when mixed. Due to this, it is usually easier to handle liquid properties on a mass or molar basis, not a volume basis. ppmv is usually reserves for vapors.

Why do you want ppmv for a liquid?

What pressure do you have?

Gaseous CO2 can be liquefied under pressure provided its temperature is -31 °C. 180 ppm is the same as 180mg/L.

For transporting CO2 gas, the target water content to prevent pipeline corrosion control is 50 ppmv or lower.

What are you trying to determine?

(OP)
Dear TiCl4 and bimr, I think that both of you are correct. You will have corrosion in the presence of CO2 if the water content is above the solubility limit i.e. 180ppm (mg/L) at -43oC. However the specifications of the fluids that I must handle were given in ppmv, one of the fluids has 50 ppmv2 of water in CO2, for this reason I need to convert 50ppmv to ppm.

Hi,
ppm = part per million: 1/1e6
ppm vol = ppm mol
you may want to convert to ppm mass ?

Pierre

(OP)
Hi Pierre,

No, I want to convert ppmw to ppmv.

thanks,

Your writing is sloppy and it’s confusing us.

The OP speaks of 50 ppmv “of water in CO2”.

Your second post says “one of the fluids has 50 ppmv2 [sic] of CO2 [sic]”.

I think I know what you are asking, but . . . can you verify, correctly please.

Good Luck,
Latexman

(OP)
Hi Latexman, the post is now corrected.

50 ppmv H2O * 18.01534 = 900.767
999950 ppmv CO2 * 44.00996 = 44007759.502

900.767 + 44007759.502 = 44008660.269
44008660.269 / 1000000 = 44.008660269

900.767 / 44.008660269 = 20 ppmw H2O
44007759.502 / 44.008660269 = 999980 ppmw CO2

Good Luck,
Latexman

David_Materials,

I think I know what you are asking now. The short answer is that I believe you CANNOT convert between the two values. The corrosion threshold of 50 ppmv of H20 in CO2 is given under consideration of gaseous CO2 with water vapor. It would be a fallacious assumption to think that liquid CO2 with liquid water would have the same threshold for corrosion.

Perhaps some corrosion experts can correct me here, but I believe the mechanism for corrosion for gaseous acids and the mechanism for liquid acids is different. If that is true, then you cannot apply the 50 ppmv threshold data for gaseous CO2 to a liquid CO2 system.

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