I must admit that partial pressure is not my best subject, but the very first post in this thread shows partial pressures of ingredients depending on the percentage of ethanol. So not only dependant of temperature, but also of the other present substances.engunear wrote:Hmmm. Interesting.
Just to check my sanity, I calculated and plotted the partial pressure of the dominant constituents here. It has been observed that some of us don't understand partial pressure and its role, and I would be the first to agree (I have n=1 evidence of this: me, so don't be offended). Boiling points say one thing, but partial pressure means that things come off below their boiling point.
So I plotted the partial pressure using the equations and constants from http://ddbonline.ddbst.com/AntoineCalcu ... ionCGI.exe" onclick="window.open(this.href);return false;" rel="nofollow
The partial pressure magnitude order follows the boiling points. i.e. methanol > ethanol > water. Not really surprising. But it says to me that the expectation that methanol would concentrate in the heads is not just about boiling point. By "concentrate in the heads" I mean if the concentration in the wash is X, the concentration in the heads is > X.
By the way, if any of you are thinking of learning a computer language, try Python. Even if you are not, but use excel regularly for calculations, try it. Its great for this kind of stuff, and once you get over the hump, you will kick yourself every time you open excel out of habit. I've added the code for the graph FYI. Python is free (comes native on macs), incredibly powerful (e.g. used by US Met office for weather predictions), and fun. OK, I'll stop the off-topic plug.
In this graph at the right side, above 45 %ABV, the volality of methanol is higher than that of ethanol. That is at the start of a run. At the left, the volality of methanol is lower than that of ethanol, that is at the end of a run.