Ethylene Glycol/Water Mixture - Vapor Pressure
Ethylene Glycol/Water Mixture - Vapor Pressure
(OP)
We are trying to calculate the vapor pressure of an Ethylene Gylcol/Water mixture.
We are using pure ethylene glycol (no additives), and our mixture is 60% EG and 40% H2O.
The Critical Pressure and Temperature of EG is:
Pressure - 1116.8 psia
Temperature - 733.3°F
The Critical Pressure and Temeprature of H2O is:
Pressure - 3199.2 psia
Temperature - 705.2°F
We want to know what the Critical Pressure and Temperature of the mixture will be. Does anyone know how to go about doing this?
We used Raoults Law assuming that the mixture is an ideal mixture, but we did not get the results we were expecting.
See our calculations below:
EG
Molecular Weight - 62.07 g/mol
Density - 1.11 g/cc
Boiling Point - 387.7°F
H2O
Molecular Weight - 18.02 g/mol
Density - 1.00 g/cc
At a volume of 10cc
Weight EG = 6cc*1.11 g/cc = 6.66g
Weight H2O = 4cc*1.00 g/cc = 4.0g
Number of Moles
EG = 6.66g/62.07g/mol = 0.1073 moles
H2O = 4.00g/18.02g/mol = 0.2220 moles
Mole Fractions
EG = 0.1073mol/0.3293mol = .326
H2O = 0.2220mol/0.3293mol = .674
Vapor Pressure of EG at Critical Temp of H2O
Assuming vapor pressure of EG is linear.
EG = (705.2°F-387.7°F)/(733.3°F-387.7°F)*1116.8psia = 1026psia
Combined Vapor Pressure
EG = 0.326*1026psia = 334psia
H2O = 0.674*3199.2psia = 2156psia
EG + H2O = 334 + 2156 = 2490 psia @ 705.2°F
Any help would be greatly appreciated.





RE: Ethylene Glycol/Water Mixture - Vapor Pressure
It will give you a good idea pretty quick if water and glycol is an ideal mixture, I don't think it is.
RE: Ethylene Glycol/Water Mixture - Vapor Pressure
2. The temperature and pressure are so elevated that using Raoult's law for this is too simple. An equation of state will take the pressure into account, but applying a set of nonideal liquid activity parameters would be quite an extrapolation. Mixing very dissimilar materials typically gives mixture critical T and P that are removed from the mole averaged values. The API Technical Data Book gives a qualitative presentation of this for hydrocarbon binaries. I imagine the vendors of antifreeze products have at some time measured the vapor pressure curves for various strengths of EG/water mixtures. Perhaps the Internet has some data published.
RE: Ethylene Glycol/Water Mixture - Vapor Pressure
Good luck,
Latexman
RE: Ethylene Glycol/Water Mixture - Vapor Pressure
Inhibited Ethylene Glycol-based Heat Transfer Fluids"
DOWTHERM SR-1 fluid is a formulation
of 95.4 percent ethylene glycol
and a specially designed package of
industrial corrosion inhibitors. The
fluid is dyed fluorescent pink for leak
detection purposes. It has an operating
temperature range of -60°F
to 250°F (-51°C to 121°C) and
solutions in water provide freeze
protection to below -60°F (-51°C)
and burst protection to below -100°F
(-73°C).
Table 26 has Pv vs temp and concentration. 60% boils at 230F at 760mmHg.