Hey all, this will be my first post after months of reading and browsing this awesome sight. Chemistry has been a long time interest of mine and ive
decided to finally start experimenting. In any event, I've decided to go microscale for safety reasons. One of the first procedures i want to try is
vacuum distillation....however, a vacuum pump is quite pricey and i feel like setting up an aspirator wastes quite a bit of tap water. I have seen
some of the hand pumps which are available for purchase for >$50 and i was wondering if i could sufficiently use this for partial vacuum in vacuum
distillation. Anyways, i know this may sound dumb but really im starting learning from scratch here. I have an organic chemistry text book, and
Zubrick's lab procedures manual. This question is the only one ive had yet, so any help is much appreciated.chemrox - 19-5-2008 at 23:57
You will develop a helluva grip trying to maintain a vacuum that way. Those had pumps get to oh about 710 if you really work your ass off. A Nalgene
aspirator will take you down to 25-30 mm with cold tap water. An "aspirator pump" will do the same. Look on ebay.. keep looking until you find one
and then make sure its working by asking the right questions. I lucked out; I got one for $40 that works great. I also got a Welch 1400 pump that
pulls 1 mm with half-ass hoses and cost me $25 plus shipping (LabX). So be watchful and patient and let go of a few ideals.. distill a small quantity
and you won't use so much water..S.C. Wack - 20-5-2008 at 01:43
I think that you two are talking about those Harbor Freight thingys widely sold on the internet, but a hand pump such as a tire pump sort of deal is
about as good as an aspirator. But you'd want a steady vacuum for vacuum fractional distillation.evil_lurker - 20-5-2008 at 02:02
All ya need is a harbor freight 1/2 HP clear water pump, some PVC, hole saws, aspirator, and pressure gauge.
An afternoon of work, and $100 later you have something like this:
It'll do 29-30mm on tap water, less than 25 on ice, and even double duties as a condenser coolant pump.Sauron - 20-5-2008 at 02:38
I used to occasionally use a Nalgene hand vacuum pump, with gauge, for filtrations and small scale (like 100 ml) distillations, and found it adequate,
and a great way to exercise your hands.
But a real pump is better. Even an aspirator.ShulginJr - 20-5-2008 at 07:37
hmmmmm I've looked at some of those aspirator pumps on ebay......they look like they are for cleaning dentures or something.....is this what your
talking about?indigofuzzy - 20-5-2008 at 08:17
Quote:
Those had pumps get to oh about 710 if you really work your ass off.
710? as in 710 millibars? or 710 mm hg below atmospheric? (that'd be about 50 mm hg, right)
Or am I totally misreading?MagicJigPipe - 20-5-2008 at 08:57
Evil, does that pump heat your water significantly? Also, where did you get it and how much was it?evil_lurker - 20-5-2008 at 09:03
Harbor freight $30-35 IIRC. Yeah it does heat up the water pretty good. Thats why there are two lines coming out of the green thing. The smaller line
is an inlet where cool water goes in from the well, and the overflow outlet is the braided hose. Works really well... only uses 10-15 gallons per hour
or so and keeps the temps pretty well constant... constant temps, constant vacuum.MagicJigPipe - 20-5-2008 at 09:38
Damn, I also forgot to ask what you used as a baffle, if you needed one.S.C. Wack - 20-5-2008 at 14:52
Quote:
Originally posted by ShulginJr
hmmmmm I've looked at some of those aspirator pumps on ebay......they look like they are for cleaning dentures or something
Sorry to be pushing the off-topic too, but EL, I really like your setup and intend on "upgrading" mine in a simialr way. Using the pump to feed the
condenser is pretty smart, but doesn't the water heat up to much afetr a while to correctly condense low-boiling compounds? I guess if you want to
remove a solvant under slight vacuum you would just aswell better be off using a independant circuit, as my pump heats the water up to 40-45°C after
30-60min turning..
Also, do find singificant advantage in using a small reservoir? I use 20L as it takes longer to heat up, but I'm not sure if I really gain that much
time. Maybe 5L would heat up in just a little less time, and take less place.. Is that your intial design, or have you tried a larger tube beforehand?
Having a second circuit for the condenser could be advantageous in the sense that a small volume, heated up only be the condenser and a small pump,
in a "cold tube" (the things you put your picnic in for it to stay cool, forgot the word), would necesiate much less ice to saty at 5°C for example,
and would take much longer to heat up than if it was used by the aspirator too.
One thing that could be nice would be to feed the condenser with tap water, and evacuate it to the aspirator's reservoir, with an overflow. This way
the aspirator's water would be gradually cooled to some extent, but this prevents keeping a efective amount of water-treatment: I use oxone or TCCA to
avoid molds/algae, which appear pretty quickly otherwise, aswell as a healthy amount of Na2CO3 to stop the rusting that had accured quite severaly
beforehand. Thanks a million to Bio for this tip, which works great! Clear water ever since..
Ideally, it would be nice to be able to switch from one system to another, using the aspirator's water in the condenser when condensing high boiling
vapors, and avoiding water waste, and switching with adequate taps to a independant cold reservoir when condensing low boiling vapors.
Sorry, I'm starting to think out loud.
BTW, how much pressure do you read on your manometer at maximum opening? I get 2.5bar bax, but my mano is attached after 2 90° angles, and just
before a reduction, leading to some pressure lost..
[Edited on 21-5-2008 by Klute]evil_lurker - 20-5-2008 at 18:32
My pump usually pushes around 40-45PSI or thereabouts. The previous system managed to run around 50PSI, but, I think my lower PSI is due to the longer
PVC fitting that screws in the pump restricting the intake flow.
And yes the system is equipped with a constant tap water flow inlet with overflow drain hence no need for a larger resevoir... it only holds like 3-4
liters... the inlet flow produces quite adequate turnover so the temps don't fluctuate very much at all.
My biggest reason for designing the system the way I did was so it would easily fit behind my lattice on the rear of my work bench out of my way.pantone159 - 20-5-2008 at 20:32
evil_lurker, I am also impressed. One of the things I really like about this board is reading about (and seeing) all the lab setups that people make.
