How to deal with solubility of water in liquid CO2 by Refprop version 9.1

[Yasuhiro-Komatsu-RGP]

Dear person in charge,

Please let me ask you about how to use Refprop version 9.1.

I would like to calculate and plot solubility of water in liquid CO2.
Can Refprop ver. 9.1 calculate and plot this solubility?
Some AI says that Refprop ver. 9.1 can deal with this problem, however I have not succeeded yet.

Could you please let me know specific procedure of this calculation and plotting?
Specifically, I would like to calculate and plot this solubility at the following condition.

Content of water: 10 to 1000 ppm
Pressure: 0.5 to 3.5 MPa (gauge pressure)
Temperature: -30 to +30 degree C

Even if Refprop can neither calculate nor plot this solubility directly, I really appreciate it if you could let me know another way to deal with this solubility by Refprop ver. 9.1.
For example, "By varying parameters, when the phase of water changes from vapor to liquid (or ice), that point shows the limit of solubility of water."

Thank you very much for your support.

Best Regards,

Yasuhiro Komatsu

[nist-aharvey]

REFPROP 9.1 is not able to perform liquid-liquid equilibrium (or solid-liquid equilibrium for mixtures) calculations. Even the current version, REFPROP 10.0, is not able to perform such calculations.

For a difficult problem like that, it is necessary to figure out the answer outside of the software based on the limited experimental data available. For the system you mention, I find these sources that might be useful:
King, M. B.; Mubarak, A.; Kim, J. -D.; Bott, T. R.
The mutual solubilities of water with supercritical and liquid carbon dioxide
J. Supercrit. Fluids, 1992, 5, 296-302
Hou, S.-X.; Maitland, G. C.; Trusler, J. P. M.
Measurement and modeling of the phase behavior of the (carbon dioxide + water) mixture at temperatures from 298.15 K to 448.15 K
J. Supercrit. Fluids, 2013, 73, 87-96
Kim, S.; Kim, Y.; Park, B. H.; Lee, J. H.; Kang, j. W.
Measurement and correlation of solubility of water in carbon dioxide-rich phase
Fluid Phase Equilib., 2012, 328, 9-12

[Yasuhiro-Komatsu-RGP]

Thank you very much for your explanation. I understand that REFPROP (even the current versioN) is not able to perform the calculation I would have liked to do.

I read 2 literatures (Hou, et al., and Kim, et al.,) you suggested.
I was not able to read the remaining one because this literature does not seem to be collected by the National Diet Library.

With regard to the 2 literture, unfortunately the ranges (pressure, temperature) are not suitable for my interesting.

Thank you very much for your cooperation.

[nist-aharvey]

It would be possible to use the other data to get a rough estimate of the solubility at your lower temperatures.
The first step would be to derive the Henry's constant of H2O in CO2 from the data. This is defined as the ratio of the H2O fugacity to its mole fraction in the CO2 phase. The fugacity to a good approximation is the H2O mole fraction in the water-rich phase (a number close to 1, and exactly 1 if the H2O phase is ice) times the vapor pressure times a Poynting correction for the pressure. If you can get the Henry's constant at a few temperatures, you can extrapolate it to other temperatures -- often ln(H) versus 1/T is a good functional form. Also it is often the case that the Henry's constant of the solute will be proportional to its vapor pressure, so that can be another means of extrapolation and the difference between the two approaches might be an indication of uncertainty (using the vapor pressure is a better approach if the data don't cover enough of a temperature range to see a clear trend). You can then use the extrapolated Henry's constant at other temperatures and reverse the calculation (since you can calculate a fugacity of H2O in the water-rich phase as described above) to estimate the solubility you want. You can use REFPROP to get the vapor pressure of liquid and solid H2O as a function of temperature for use in these calculations, and also the molar volume of liquid water for use in the Poynting correction; you'll have to find the molar volume of ice elsewhere.
This will be approximate, less reliable as you get further away from the temperatures where data exist, but it should at least give you the right order of magnitude..

[Yasuhiro-Komatsu-RGP]

I am sorry for my late reply.
Thank you very much for your suggestion. To my shame, it seems to be difficult to me to calculate following your suggestion.
As another way, I found a paper written by Mr. Song and Mr. Kobayashi in 1987.
I think I will be able to achieve my purpose based on this paper.