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Hey Jacko According to the hyperphysics page (great page) and here it is: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/watvap.html#c2 You see the vapour pressure of water at room temperature is roughly 17 mm of mercury. This is less than 1 inch so you would need better than 29" Hg vacuum to boil off the water. It will be a challenge to get to 29" and it will require a good pump and large diameter piping and good attention to seals and valve types.(read $$) My reactor uses ball valves which are not really suitable for vacuum service (I'm used to talking High Vacuum 10e-12 torr -microns of mercury are gross units to me, but we are talking an order higher than that, mm really gross) so for this purpose I can get away with ball valves. I do everything in the reactor vessel because I have space restictions. Processing begins right after drying the oil in situ. So therefore I use the immersion heater to heat the oil to 50 deg. C while drying and then add the methoxide after venting most of the vacuum. If you interpolate the data from the page you see that at 50 deg. C the vapor pressure rises to around 100 mm which means roughly 26" hg vacuum (29.92" - 4"). This is something which is readily achievable even with a small pumping line (I use 1/4" poly tube from the pump to my liquid trap and 1/2 " condenser to the top of the water tank) and ball valves seem to be up to the task (so far). I can get to 28" with this setup but when the vacuum creeps past the 27" mark I start the process. So the process goes like:
As to your question about what is the acceptable vacuum limit. What you are really asking is how much water can we get away with. I would like to know as well. I do know that a couple of times when I have let the dried oil sit in the reactor (under vacuum but with the pump off and valves closed) for a couple of days before reacting, a small amount of water vapor would re-condense in the tubing which is part of the recirculation system, which is at room temperature outside the insulation jacket. I estimated it was about 1cc (out of a 25 liter batch) or roughly 40ppm water and the batch was fine. Hope this helps Joe [EMAIL PROTECTED] wrote:
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