how much methanol in air at a given temperature

[birkATO]

Well, I may have a ChemE degree, but I can't for the life of me remember most of the gas phase equillibrium details that I probably once was tested on. I am working with a process that will consist essentially of a stream of air saturated with methanol and water vapor that will be routed to a condensor at 44°F. This will condense out a lot of the water/methanol. Could someone point me in the right direction to get a rough idea of how much methanol will be in the headspace after passing thorugh the condensor? The idea is that there will be a constant flow of the vapor stream and I need to estimate how much methanol vapor is escaping.

-Ryan Birkenholz, Licensed PE in MN and IA

 

[Compositepro]

The partial pressure of methanol in the air will be equal to the vapor-pressure of methanol at the condensing temperature. This assumes that you get all the vapor down to this temperature.

http://www.erowid.org/archive/rhodium/pdf/methanol.technical.info.pdf

 

[birkATO]

Ah yes, partial pressures coming back to me now. Thanks for the step in the right direction. This should get me in the right ballpark as all I need is a best guess. I will calculate total moles of gas at condensing temp and 1 atm, then use the ratio of methanol vapor pressure/1 atm to determine methanol cocentration, then use that to get moles of methanol, then convert to mass of methanol using MW. I think that is how it is done. I don't work with this stuff much at work these days. Thanks!

-Ryan Birkenholz, Licensed PE in MN and IA

 

[Latexman]

Since the air stream contains more than one condensable component, the partial pressure of methanol in the air will be equal to the vapor-pressure of methanol at the condensing temperature times the mole fraction of methanol in the liquid phase.

You may want to brush up on Raoult's Law, multicomponent gas-liquid systems, dew-point temperature, and dew-point pressure.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[25362]

Due to non-ideality of methanol-water mixtures, the following link may be helpful:

http://vle-calc.com/phase_diagram.h...Mode=isothermal&VLEType=xyp&numberForVLE=6.67