According to the Gaylord corp's technical bulletin, DMSO has a rt vapour pressure of circa .5 mm Hg, or around 70 Pa, vs 3.2 kPa for water.
Did anyone ever attempt to pull a vacuum using DMSO and an aspirator?
[Edited on 25-6-2019 by Keras]
Attachment: DMSOVapPress.pdf (271kB) This file has been downloaded 340 times
Pumukli - 25-6-2019 at 02:44
I had the same (very similar) idea months ago: why not use ethylene-glycole in a recirculating aspirator system?
Glycol is fairly cheap and has much lower vapour pressure than water (at least it should have, I didn't bothered to check).
Problems I see:
- price of the working fluid (DMSO is not that cheap)
- if it absorbs water then the achievable vacuum will eventually deteriorate
- these fluids has much higher viscosity than water, it may cause problems with the pump
Anyway, my feeling is if it worked we already had seen completed projects, working units in commerce. Do you know such system? I don't. So there's
obviously a stumbling block somewhere what we don't see yet.Keras - 25-6-2019 at 03:19
I agree for the viscosity. In fact, just after the graph plotting partial pressure vs temperature, there's a viscosity graph, too. But I have no idea
how viscosity units translate into the real world, i.e. what is viscous vs. what is not. Tsjerk - 25-6-2019 at 05:31
Fractionated diesel fuel?walruslover69 - 25-6-2019 at 08:11
diesel and Kerosene would probably make good candidates due to their relatively low viscosity. I think you will definitely need a efficient solvent
trap to prevent whatever you are pumping off from mixing with the working fluid. I imagine DMSO could also be very hard or incompatible with the seals
on common pumps. Sulaiman - 25-6-2019 at 09:19
Vacuum pump oil ?DavidJR - 25-6-2019 at 10:24
DMSO sounds like a great way to end up with a big vat of contact poisonKeras - 25-6-2019 at 12:46
DMSO is not that toxic, is it?
I agree kerosene could be a better idea, but it is flammable…
[Edited on 25-6-2019 by Keras]Metacelsus - 25-6-2019 at 12:57
diesel and Kerosene would probably make good candidates due to their relatively low viscosity. I think you will definitely need a efficient
solvent trap to prevent whatever you are pumping off from mixing with the working fluid. I imagine DMSO could also be very hard or
incompatible with the seals on common pumps.
If you need to use a cold trap why the hassle of using a water pump? HVAC rotary vane vacuum pumps can be bought now for less than $60 on Ebay, and to
use them you need a trap. The point of using a water aspirator (in my opinion) is to not have to worry about a trap, at the end if the water is too
contaminated, just change it, it's not as expensive as a vacuum oil change. RedDwarf - 25-6-2019 at 14:32
Ignoring all the hassle of using DMSO, just assuming you'd need a minimum of a couple of liters of dmso to fill the system I really can't see how it'd
be less expensive than buying a vacuum pump.SWIM - 25-6-2019 at 18:49
I like the vacuum pump oil suggestion, but there's always Lucas DOT 4 brake fluid too.
Vapor pressure 10 Pa, boiling point 232 C. 121 C flashpoint.
But if you're really after low pressure and damn the consequences, how a bout a garbage can full of mercury?
(hope you've got a strong floor)happyfooddance - 25-6-2019 at 22:23
For all the emphasis I see on scimad (and elsewhere) regarding ultimate vacuum, I would hope to see even more focus on preventing and eliminating
vacuum leaks.
Because anyone who understands knows this is where true battle lies
Keras - 26-6-2019 at 00:06
BTW do you have any idea of the vacuum that a common, run-of-the-mill vacuum cleaner can pull?happyfooddance - 26-6-2019 at 00:19
Just a few inches of mercury
They move a lot of air though
[Edited on 6-26-2019 by happyfooddance]Sulaiman - 26-6-2019 at 00:24
about 1/5 th pressure reduction, -20kPa relative to atmospheric, +80kPa absolute.
O.K. for vacuum assisted filtration but probably not much else in the lab other than its intended purpose..
A £10 dc motor vacuum pump pulls about -80 kPa (20kPa abs.)
A £40 HVAC vacuum pump can achieve about 10 Pa abs.
My £85 dual-stage rotary gets down to below 1 Pa ... if you believe the specs.
Peristaltic pumps, hand-operated (brake bleed) vacuum pumps etc. are also viable options.
If you have mercury then a Sprengel pump may be viable
(Cody's Lab has a video on YT)Keras - 26-6-2019 at 11:36
The reason I was asking is that I bought those space saving bags you can put duvets into. Once it’s done, you suck the air out using a simple vacuum cleaner and you get something not only
pretty squeezed (packed up, takes less space), but also that looks as if there’s hardly any air left inside.
[Edited on 26-6-2019 by Keras]Ubya - 26-6-2019 at 11:49
The reason I was asking is that I bought those space saving bags you can put duvets into. Once it’s done, you suck the air out using a simple vacuum cleaner and you get something not only
pretty squeezed (packed up, takes less space), but also that looks as if there’s hardly any air left inside.
[Edited on 26-6-2019 by Keras]
you could do it even by sucking air with your mouth (on a small bagbif you don't want to get light headed). 1 atm = 14 psi, so even if you can create
a vacuum of half a atmosphere every squared inch of those bags feels a weight of 7 pounds, you can see why the get so flat happyfooddance - 26-6-2019 at 17:31
What Ubya said.
You can pull a better vacuum with your lungs (I've been doing it with ziplocks of cheese for damn near 30 yrs).
Sulaiman - 26-6-2019 at 18:05
sucking 'cheese-air' sounds ok ... sucking 'duvet-air' sounds less appealing
(mites and their shit etc.)
one thing to be aware of with vacuum storage bags,
they are not hermetically sealed, air slowly leaks in,
then the contents try to resume their natural volume. happyfooddance - 26-6-2019 at 18:11
Also, what Sulaiman saidKeras - 27-6-2019 at 01:00
Hah. I remember bringing back munster from Alsace. It'd better be carried in a vacuum pack, because otherwise I would've been kicked out of the
carriage!
Ok, thanks for all your answers!
[Edited on 27-6-2019 by Keras]Fyndium - 15-9-2020 at 13:09
Not sure what country you're in but for that amount of money you might able able to find a used lab grade pump which typically pull a better vacuum
and have longer duty cycles and lifetimes than Chinese HVAC pumps. https://www.ebay.com/itm/SAVANT-VP-100-VP100-TWO-STAGE-HIGH-...Sulaiman - 15-9-2020 at 16:42
A dual/double stage rotary vacuum pump is nice to have (I have one)
but a single stage is adequate for chemistry use
and can be cheap enough to risk a little damage,
unlike my dual stage rotary which I rarely use due to fear of damage. macckone - 16-9-2020 at 00:27
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.macckone - 16-9-2020 at 00:32
Also aspirator pumps with vacuum pump oil are a thing.
The viscosity can be an issue, a cheap fountain pump won't cut it.Heptylene - 16-9-2020 at 01:20
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.Fyndium - 16-9-2020 at 02:57
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.Tsjerk - 16-9-2020 at 03:20
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 mbarFyndium - 16-9-2020 at 04:37
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.Heptylene - 16-9-2020 at 07:28
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.
