Sciencemadness Discussion Board - Vacumm distilation and pump protection

Vacumm distilation and pump protection

Little_Ghost_again - 21-10-2015 at 05:30

Hi I have a couple of questions regarding several vacuum distillations I have lined up.

The first one is regarding sulphuric acid.

I am going to attempt to distill some of my sulphuric acid back! I want to use vacuum distillation with a 2 stage rotary pump, I would appreciate any comments on the following intentions etc.

I want to use reduced pressure so I can use lower temperatures in the distillation, while its a slightly mute point I am mentally more at ease with sulphuric acid below 150C. I appreciate that in practice is something goes very wrong then acid at 100C is going to be little different from an acid shower at 200C.

I want to protect my pump as much as is reasonable, so I intend to have a plain water wash inline with the pump. this will be followed by a alkali wash (probably mag carbonate), I dislike water getting into my pump oil!! its a pain cleaning my pump out so I thought if I add a trap after the alkali one containing pump oil then hopefully this should cop most of the water or vapors.

The next is similar but uses waste engine and other mineral oil waste. I am going to centrifuge first to remove as much water and bits of metal or whatever first. The centrifuge will be run at 5000 RPM for 20 mins.

What I am aiming for is to clear and see how clear I can get the oil from the dark black it is now.
I have absolutely no idea what is in this oil! so I am going to TLC it at each stage just to see if I have removed anything. The only solvent I can think of for this is petrol, anyone got any ideas if this is a good or bad choice?

I will also reduce pressure distill it.

My main question is regarding the fact I dont have a cow or a triangle thing, so each time I want to swap out the collection bottle what is the best way?

Can I simply switch of the pump with the heat kept on and slowly introduce air until the pressure is equal? then I would change the collector and start the pump again, I would prefer not to turn the heat off completely and dont intend going above 160C.

I will use a wash train like above to collect gasses ect before they get to the pump.

On both distillations is it better to use say two libergs connected one after the other without cooling water in the jacket? Or best to use 1/2 condensers with water? The place I am distilling is currently around 4C anyway so i figure an air jacket around the condenser would be best?

Any comments/help welcome

Magpie - 21-10-2015 at 05:40

What's going to keep your wash liquids from evaporating into your pump?

I would think a cold trap would be needed. Cool with acetone/dry ice or liquid nitrogen. Then again I have never tried this. Also remember that the acid is likely to bump severely so you likely will need an ebulliator.

When I did some distillation of sulfuric acid a significant and unanticipated problem was that of condensed water falling back into the acid causing a violent reaction!

[Edited on 21-10-2015 by Magpie]

[Edited on 21-10-2015 by Magpie]

[Edited on 21-10-2015 by Magpie]

Little_Ghost_again - 21-10-2015 at 05:49

Quote: Originally posted by Magpie

What's going to keep your wash liquids from evaporating into your pump?

The last one is pump oil and after that just a plain air anti suck back (I forgot to mention that), I am hoping the wash bottle with pump oil in will pick up most the stuff I dont actually want in the pump.

I am open to better ideas however, reduced pressure distillations are new to me and I dont have a manometer, I dont think for this I will really need one though. I also have a pulled glass tube leading into the distillation pot to help stop bumping.

I am concerned my rubber or silicon tubing isnt going to last very long with the acid one however.

Magpie - 21-10-2015 at 05:53

see my edits above. This sounds like a very dangerous experiment for someone with little vacuum distillation experience. Try it with water first.

Little_Ghost_again - 21-10-2015 at 06:17

Thanks Magpie, Actually most of that is my fault for asking the questions and not adding in the actual detail! The reception vessel will be a RB flask sitting in salt ice slush at around -14C (thats as cold as I can get).

My ebulliator is what I was trying to describe with the pulled glass tube in the dist pot, I couldnt think of the correct word and didnt have Vogel handy! Unless I have my terms mixed up??? The idea being to pull a capillary and control the air into this, the end of the capillary goes into the boiling flask and provides a stream of bubbles that prevent super heating? This is because chips cant be used ?

I Had NO idea about about the water drips back into the acid, Would a clasian adapter help or maybe a steep angle distillation head?

I will try other reduced pressure distillations first as I have a number of solvents l could do with cleaning up a bit.

Apart from Sieves I cant think of much that would take water from sulphuric acid first, I assume things like magnesium sulphate dont stand a chance taking water from conc sulfuric acid?

A couple of thing I will change for the fist acid try however will now be.

Instead of a heating mantle (now worried of the glass giving out should water drip back) i will use an oil bath for heat.

I am only trying to distill to 96%, I dont know how conc the acid is at the moment and it contains some impurities and maybe a little bit of iodine.

I will take this very slowly.

I might actually do the waste oil before the acid, i have done water reduced pressure distillation but I didnt keep the heat going.

Thanks for the help and info on the water, I dont like the idea of water drops back into the acid at all.

Deathunter88 - 21-10-2015 at 07:20

Quote: Originally posted by Little_Ghost_again

I Had NO idea about about the water drips back into the acid, Would a clasian adapter help or maybe a steep angle distillation head?

Thanks for the help and info on the water, I dont like the idea of water drops back into the acid at all.

I have distilled 93% acid to 98% acid a lot recently and have never had the problem of water dripping back into the flask nor with any bumping. BUT this was all done under standard pressure so that might have made a difference. In my opinion, distilling sulphuric acid should be done in the simplest set-up you can manage. More pieces = more places for things to go wrong. Mine was just a 500ml 1 neck RBF, connected with a 75 degree 2 way adapter to a 300mm vigreux column as an air condenser. Then the acid simply dripped into a beaker.

Do whatever you feel comfortable with and take my experience with a grain of salt.

Magpie - 21-10-2015 at 07:59

I would follow Deathunter's recommendation. With vacuum you have added a severe risk - that of implosion. If your glass fails and you have no blast shield it could get ugly.

Sulaiman - 21-10-2015 at 09:52

Little_Ghost_again,

I just wanted to point out that I think that you did not appreciate the comment by Magpie
"What's going to keep your wash liquids from evaporating into your pump?"

the pressure at which sulphuric acid boils below 200C will cause the water in your trap to boil, then probably freeze solid.

Little_Ghost_again - 21-10-2015 at 10:09

Quote: Originally posted by Sulaiman

Little_Ghost_again,

I just wanted to point out that I think that you did not appreciate the comment by Magpie
"What's going to keep your wash liquids from evaporating into your pump?"

the pressure at which sulphuric acid boils below 200C will cause the water in your trap to boil, then probably freeze solid.

Ah I see, No I missed the point he was making. Whats the best wash train to use then?

My concern was using a condenser with water in at such high temps, I also wanted to keep the overall temperature as low as I can. Maybe I should forget doing at reduced pressure and just use a long condenser with no water jacket connected.

Sorry Magpie I didnt get the connection with the wash bottle.
Some of my acid has potassium Iodide in it which is the main reason i am trying to distill it off. I have around 500ml to distill.
I didnt try it in the end today as I thought I would wait for suggestions.

Little_Ghost_again - 21-10-2015 at 10:12

Quote: Originally posted by Deathunter88

Quote: Originally posted by Little_Ghost_again

I will probably do this for the acid and use reduced pressure for the oil.

[Edited on 21-10-2015 by Little_Ghost_again]

Sulaiman - 21-10-2015 at 12:08

Quote: Originally posted by Little_Ghost_again

Ah I see, No I missed the point he was making. Whats the best wash train to use then?

When you find out please let us know as I am in a similar position,
for the professionals amongst us, a dry ice + acetone trap (for example) is just a choice of procedure,
for me the only source of dry ice that I have found is minimum £35 for a block !
I am considering preparing for many assorted distillations, buying a block, then beaver away like crazy for a weekend.
but I have no immediate plans for this.
I have recently tried H2SO4 + ice and NaCl + ice. Although quite low temperatures can be reached
(no data sorry, my thermometers do not go low enough, I'll use a thermocouple next time)
these baths cannot absorb much heat.
I have ordered a couple of ThermoElectricCoolers so I'll be investigating that option eventually.

Little_Ghost_again - 21-10-2015 at 12:20

Having read more and more on distilling sulphuric acid I have a few things to weigh up. I can get 98% tech grade for £25 ltr. while that is alot of money to me I have to balance that against the cost of a new distillation set up if it goes wrong, I searched long and hard and took a long time to build up some decent glassware. Most came from schools or universities getting rid of stuff, the quality is good and to be honest I dont think its worth trying to distill 500ml of acid and having all the risk and agro when for now I can buy it.

So in short for now I wont be doing the acid. i will be doing the oil though.
thanks again for the replies it helped make my mind up and I decided its just not worth it at the moment.

Sulaiman - 21-10-2015 at 13:02

If 96% H2SO4 is good enough then I can recommend apc pure https://www.apcpure.com/product/sulphuric_acid_96
or affiliated atom scientific http://atomscientific.com/products.php?product=Sulphuric_Aci...
you can get a certificate of analysis for your batch,
usually next day delivery.

Coincidentally, I bought 1 litre of drain cleaner from my local hardware shop for under £8, it is viscous enough to be 96% but I have not yet titrated it,
I bought it just to evaluate the otc source, it is orange/red but not as deep a colour as the photo shows.

Little_Ghost_again - 22-10-2015 at 01:20

Quote: Originally posted by Sulaiman

If 96% H2SO4 is good enough then I can recommend apc pure https://www.apcpure.com/product/sulphuric_acid_96
or affiliated atom scientific http://atomscientific.com/products.php?product=Sulphuric_Aci...
you can get a certificate of analysis for your batch,
usually next day delivery.

Coincidentally, I bought 1 litre of drain cleaner from my local hardware shop for under £8, it is viscous enough to be 96% but I have not yet titrated it,
I bought it just to evaluate the otc source, it is orange/red but not as deep a colour as the photo shows.

I have used APC but wouldnt again, I will U2U

Hockeydemon - 24-10-2015 at 01:12

I'm not sure where you're located, but in the states you can purchase Rooto Professional drain cleaner at the local hardware store for a few bucks, and it comes out to about 18 molar (96%) when titrated.