tmb - 4-5-2011 at 14:20
Hi. I want to work out the pressure produced by alcohols when heated in a pressure vessel.
I have spent many hours reading physical chemistry books on vapor pressures, the Clausius–Clapeyron equation etc., but it seems like their only
interest is in discussing theoretical pure-mathematics, rather than any practical use.
Essentially I want to heat, for example, 1 litre of IPA in a 2 litre pressure vessel to 200C. How could I calculate the pressure that this would
produce?
I want to calculate this because, naturally, I need to make sure that the vessel can withstand the pressure!
Would heating 1.5 litres of methanol (in a 2 litre vessel to 200C) produce the same pressure as heating 1 litre of methanol under the same conditions?
(Because the vapor pressure is only a factor of temperature?)
I will only be using pure alcohols, so no difficulties with partial pressures of water-ethanol, for instance.
Hopefully someone can help with some good practical information and general guidance, without too many theoretical coefficients for perfect gases 
Thanks.
Magpie - 4-5-2011 at 14:27
Look up the vapor pressure of the alcohol at 200C. Or calculate it from the Clausius-Clapeyron equation for a theoretical value. For methanol see:
http://www.sciencemadness.org/talk/viewthread.php?tid=14652
tmb - 4-5-2011 at 14:45
Hi. Thanks. From that page:
"Therefore I felt there was adequate factor of safety for a test of methanol at 215C which would give a vapor pressure of ~ 760 psia. "
So this is the pressure it produces regardless of the quantity of liquid originally-added? And, in turn, regardless of the size of the container? So 1
litre of methanol in a 2 litre vessel at 215C produces the same pressure as 1.5 litres or 1.8 litres of methanol under the same conditions? Is that
right?
I will look into the references on that page. Thanks for your help.
Magpie - 4-5-2011 at 15:49
Yes, as long as there is some liquid in the vessel, the pressure is the vapor pressure.
tmb - 4-5-2011 at 23:38
Great. Thanks for your help.