So i have installed this distillation assembly recently ... i was wondering if any one can suggest me something on the vacuum source .. whether to go
for aspirator or pump ...
I have worked with aspirators before and they dont produce much pressure ot atleast the ones i used did not ... (i am planning to distill off toluene
etc)
while pumps ... they r prone to vapor contamination ... installing a trap and then keeping it cool is an additional task ..
I want to ask u guys ... what would u suggest ? recirculatoing aspirators or vacuum pumps ? if pump then what kind of it ? ... is there any kind of
pump that is immune to contamination vapors ? ...
I want vacuum of upto 350 mm Hg ...
please help me guys !Molecular Manipulations - 4-3-2015 at 07:29
I'd go for an aspirator, especially if you only need about 350 torr.
A vacuum is quite expensive (I got a great deal on one from a friend, $800.00!). they are quite hard to keep in good condition when distilling
corrosive vapors. A trap is good for toluene but anything acidic or oxidizing would be very bad, and only something like a dry ice trap will be
effective at keeping the vapors from doing serious damage. That or a scrubber.
An aspirator can pull a lot more than 350 torr, depending on the temperature (cold water pulls stronger).
BTW, distilling an organic solvent doesn't really constitute this thread being in "organic chemistry", but it's too late for you to change it, a mod
will do it.
[Edited on 4-3-2015 by Molecular Manipulations]qeezur - 4-3-2015 at 07:37
Molecular manipulations,
Thanks friend ... I am in position to get a chinese diaphragm vacuum pump ... and its coming very cheap ... i am not much into the mechanics of pumps
so i was wondering if diaphragm pump would be immune to vapors going inside it ...
I am inclining towards aspirator as well ... but they r not much available here ... Molecular Manipulations - 4-3-2015 at 07:43
If you post a link I'll check it out. There's several different kinds of diaphragm pumps, I think all of them will be fine with toluene but only a
Teflon coated one will survive corrosive acid vapors without permanent damage. Dr.Bob - 4-3-2015 at 07:44
There is a long discussion of this topic in this thread:
lets say harmless vapors go inside the pump, non corrosive organic ones ... would the pump choke or keep working ? 2 years back i used to employ a
vacuum pump on my rotavap and it became victim of same thing. Vapors went inside it and it just died after making sounds and then got turned off ... i
left that lab so i dont know what became of it.
lets say my toluene goes inside it ... would it keep working or there would be some issue with its proper function ?
I dont know if i can post the commercial links here ? (is there a way i can pm u ?) ... its a PTFE diaphragm pump ...
qeezur - 4-3-2015 at 08:16
dr. bob ... thankyou ... i am viewing ur posted link.Molecular Manipulations - 4-3-2015 at 08:23
You could PM me by clicking my username and hitting send U2U, but I'm by no means an authority on the vacuum subject here. Yes you can certainly post
commercial links here, it's just more advertising for the company.
If it is PTFE it will do great with not only organics but practically anything you put in there. But make sure it's completely coated. Dr.Bob - 4-3-2015 at 11:27
Most volatiles that go into a pump will leave the exhaust port. A small amount can condense and clog things, but most pumps will eventually expel
them. A rotary pump runs hot enough to boil off normal volatiles, but char a few things, so those can be the problem. But even a simple trap will
catch most of them. Many rotvaps put out a huge amount of solvent vapor, so they can overwhelm a trap. For rotovaps, I would use a diaphram pump
that is designed for organics. They pull a decent vacuum, enough for all but DMF and DMSO, those usually require a high vacuum or two stage
diaphragm pump to rotovap off. The real pump killers I see are acid chlorides (form HCl in most pumps) and TFA. Those can destroy many pumps.
Most other solvents are no big deal.Molecular Manipulations - 4-3-2015 at 11:46
... indeed the supplier is confirming the PTFE diaphragm ...
Dr.bob ... in order to distill off any high BP solvent above 100C ... i have to get the pressure down to something around 250-300 torr ... and the
device must also be kinda immune to any escaping solvent vapor ...
vs the pump that molecular manpulations posted ...
help me select one please ! keeping in mind that i have to work with the likes of Diglyme, DMF, toluene etc ... careysub - 4-3-2015 at 12:02
I have been thinking of putting together a vacuum pump system for both vacuum bag composites, as well as chemical work.
I was looking at this system set-up: http://www.joewoodworker.com/docs/ProjectEVS.pdf
using the Harbor Freight two stage rotor pump (listed as going down to 22 microns). One or more of the reservoirs included in the system could be
filled with filtering material (I am thinking Drierite, then NaOH pellets, then charcoal) so that they do double duty.
i can understand the theory behind subtracting the said value of 734 torr from 760 ... but if its a vacuum generating device then should not the
vacuum be listed as 24 torr directly ? ... i mean other advertised vacuum devices directly list the minimum negative pressure ...
what i fear is that ... i buy this aspirator and it turns out to be reducing 24 torrs only ... lol
Molecular Manipulations - 4-3-2015 at 12:16
I think they usually say the amount of pressure they reduce, so they would say the vacuum pulls 734 torr, which makes it ~24 torr absolute. They
should specify wether it gauge or absolute. I prefer to use absolute only however.qeezur - 4-3-2015 at 12:22
I think they usually say the amount of pressure they reduce, so they would say the vacuum pulls 734 torr, which makes it ~24 torr absolute. They
should specify wether it gauge or absolute. I prefer to use absolute only however.
i have emailed their technician to clarify whether the 0.098 MPa is abs. or gauge P ... otherwise it will be a hilarious aspirator. aga - 4-3-2015 at 15:04
I use a cheap aircon vacuum pump.
It works, and Nothing lasts forever.chemrox - 4-3-2015 at 16:03
I have a glass aspirator that will pull 35T especially in winter when the groundwater is around 4deg. I'd let it go for the right price. Otherwise the
Nalgene ones work pretty well to around 100T. I think 100T is about the limit of most aircon pumps. Curious to know how Nicodem finds them. The virtue
is they're cheaper than maintaining a good oil vane pump. I don't really like the 'use 'em 'til they burn and buy a new one..' philosophy but there it
is.
The main point is there's no right answer to 'what kind of pump?' without specifying the use or range of pressures. You did that which leaves you with
the cheapest and most attractive option; the aspirator. I haven't found a good metal one yet. The glass ones I came across by accident. I was amazed
when I hooked it up to a manometer.
[Edited on 5-3-2015 by chemrox]qeezur - 4-3-2015 at 23:30
molecular manipulations,
0.098 MPa turned out to be absolute pressure. qeezur - 5-3-2015 at 11:29
I have a glass aspirator that will pull 35T especially in winter when the groundwater is around 4deg. I'd let it go for the right price. Otherwise the
Nalgene ones work pretty well to around 100T. I think 100T is about the limit of most aircon pumps. Curious to know how Nicodem finds them. The virtue
is they're cheaper than maintaining a good oil vane pump. I don't really like the 'use 'em 'til they burn and buy a new one..' philosophy but there it
is.
The main point is there's no right answer to 'what kind of pump?' without specifying the use or range of pressures. You did that which leaves you with
the cheapest and most attractive option; the aspirator. I haven't found a good metal one yet. The glass ones I came across by accident. I was amazed
when I hooked it up to a manometer.
[Edited on 5-3-2015 by chemrox]
by "pulling 35 torr" u mean it reduces 35 torr from 760 to 725 torr ... or it brings down the vacuum to 35 torr (reducing 725 torr) ... ?
