I have had the need recently to calculate the partial vapor pressure vs. temperature of one material in a binary solution. I am only interested in the flammable material, so in this case, it is the ethanol in an ethanol-water system. Since I am not near critical points and my temperature range seems reasonable (8 – 25 C), I am using Raoult’s Law modified by the Activity Coefficient.
yethanol*P = xethanol*γ*Pethanolsat
yethanol*P: The partial vapor pressure of ethanol (what I am looking for)
xethanol:Liquid phase mole fraction of ethanol
γ: Activity coefficient for ethanol-water system
Pethanolsat:Vapor pressure of pure ethanol (a function of temperature)
My initial system is 40 volume% ethanol. I calculated the activity-coefficient using the Margules Equation and associated binary-interaction parameters from Perrys. In order to get Pethanolsat, I first tried using the DIPPR 101 equation, but the pressure units were not specified, and my values seemed quite large. I am currently calculating Pethanolsat using Antoine’s Equation, as a result.
Is this an appropriate/correct approach to calculate the partial pressure of the ethanol vapor off of a known ethanol-water system? I’d welcome any improvements or suggestions on “better” equation modifications. Thank you for your time.