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macckone
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HVAC pumps actually require a pretty good duty cycle.
Purging a large system takes overnight to do it properly.
The cheapest chinese ones might not make it but anything that honors the warranty will.
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macckone
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Also aspirator pumps with vacuum pump oil are a thing.
The viscosity can be an issue, a cheap fountain pump won't cut it.
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Heptylene
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If you're going through the trouble of building an oil aspirator with liquid pump, tank, etc. then just buy a cheap rotary vane pump.
Alternatively, look for used PTFE diaphgram pumps (e.g. KNF). They don't require a trap and typically go down to 100-10 mbar, which is sufficient for
filtration and some vacuum distillation.
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Fyndium
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When you say "sufficient for ... some vacuum distillation", what vacuum is exactly desired for higher bp (200-300+C) stuff? I've been under impression
that the range of 5-30mbar is pretty decent for most amateurish tabletop purposes.
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Tsjerk
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I always use water with my aspirator and I get the vacuum down very close to the vapor pressure of the water used easily. This pressure is somewhere
around 20 mbar depending on the season. This vacuum is sufficient for any vacuum distillation I ever did so I never bothered using cooled water.
Using 4 degrees water would get the vacuum down to around 10 mbar
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Fyndium
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I suspect that glass joints may leak to the extent it limits the vacuum. Bleeder tube can also reduce the potential a little. I might wanna do a
boiling test in a scrupulously well sealed apparatus to see the extent of the pump and aspirator to exclude issue in them.
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Heptylene
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Quote: Originally posted by Fyndium  | | When you say "sufficient for ... some vacuum distillation", what vacuum is exactly desired for higher bp (200-300+C) stuff? I've been under impression
that the range of 5-30mbar is pretty decent for most amateurish tabletop purposes. |
Well take cinnamaldehyde as an example (atmospheric BP 249 °C). Using a online boiling point calculator you can estimate the boiling point at other pressures. (this probably uses the Clausius-Clapeyron relation) You also need
the enthalpy of vaporization for cinnamaldehyde (45 kJ/mol).
At 100 mbar, cinnamaldehyde boils at ~154 °C and at 10 mbar at ~88 °C. I'd say it's still a bit high, and some compounds would decompose at these
temperatures (not cinnamaldehyde though).
On your comment about joints, they really don't leak much. I did some testing with 14/23 and 29/32 joints with corning grease, and even at 0.006 mbar
they don't have visible leaking. In fact the limiting factor at these vacuum levels was off-gassing from my PVC piping.
I'd say greased glass joints are leak-tight for all practical purposes in chemistry.
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Panache
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Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
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Ha!
What about a NaK molten eutetic like the fast breeder nuclear reactors use as coolant. Might as well make it a challenging en g ineering setip,
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