Hodgkinson - the answer to your chemistry problem

[WotTheFook]

Hi,

Your problem is perhaps you are getting an azeotrope of the alcohol and the water, the alcohol will also be hygroscopic and will gradually absorb water.

The answer (using kitchen stuff you should have around) is to heat some table salt or baking powder to make it anhydrous (to drive off the water of crystallisation).

Then you allow it to cool and add it to the alcohol. You should stand a much better chance of removing the final water content that way.

BTW, I was an industrial chemist for 25 years in the oil industry.

:-D

WTF

[Karlos]

^^ What he said :-)

If you can buy a big load of epsom salts (that's hydrated magnesium sulfate), then you can bake it dry and grind it into a powder. If you stick this into your alcohol it will mop up any excess water even more effectively than the above salts.

[Hodgkinson]

Hi there and thanks for the comment(s)!

I've just processed about 500ml of raw isopropyl alcohol today, using just the salting-out technique followed by basic distillation. I used a water bath (Pan) for the boiling flask as suggested by another member - This enabled much better control over the temperature of the mixture and helped to prevent the flask from running dry as it did when I tried it with direct heat, however, the process took about 4 1/2 hours to finish! (Decided to re-use the cooling water from the condenser to water the garden in the process...).
About 25cm3 of initial mixture remained in the boiling flask, probably mostly alcohol, which had to be discarded due to the process slowing down unbearably towards the end. Oddly, the mixture in that flask had turned slightly brown/orange - Presumably residue from the new rubber bungs used.
Density test on the distillate to follow, hopefully.

@WTF/Karlos:
Ah, I'd read about the magnesium sulphate idea over on the instructable (And got some evaporating dishes just in case). However, im at a loss as to how to remove the hydrated/anhydrous magnesium sulphate afterwards - Simple filter paper or is another distillation step required?
How easy would it to be to reuse it?

@WTF:
Eg, just use a drying agent for the whole process? Or bake the "Salting-out" salt before use to mop up additional water?

Thanks,
Hodgkinson.

[WotTheFook]

@ Hodgkinson

I would bake the powder (whichever you decide to use) just before you use it and add it to the distilled alcohol, followed by a filtration process.

You may also be able to percolate the alcohol through a filter paper containing the anhydrous powder, although you are risking the powder caking up and blinding the filter.

Once the alcohol has flashed off the powder, you should be able to re-use it, as all you are doing is removing and adding back the water of crystallisation to the powder.

You could also pack a column with a drying agent and attach it above the distillation flask, to remove the water as it distills. The problem with this is you may not know that your drying agent is spent, unless you use something like copper sulphate or cobalt chloride, which change colour with the water of crystallisation present. Copper sulphate goes from white to blue, cobalt chloride goes from blue to pink.

[Karlos]

About 25cm3 of initial mixture remained in the boiling flask, probably mostly alcohol, which had to be discarded due to the process slowing down unbearably towards the end. Oddly, the mixture in that flask had turned slightly brown/orange - Presumably residue from the new rubber bungs used

During my degree I often made "intractable black tar" at the end of fractional distillation of any substance that required heating :-D

Have you ever thought of buying IPA from a proper supplier? Of course, these days you'd probably be tagged as a terrorist suspect for doing so, but...

[WotTheFook]

@ Hodgkinson

The slowing down you describe towards the end of your distillation is direct evidence of an azeotrope forming, i.e. the alcohol and water form a constant boiling point mixture (it will be below 100C) and you end up at a point where you can't separate them by distillation.

Are you planning to scale up this process? If so, I would read up about a company called Chemstar that used to be local to where I work. They had the bright idea of distilling ink to recover the solvent and sell it back to the printers, all went well until a fire started one night and the results were catastrophic :-o .

http://carrbrookvillage.users.btopenworld.com/cowbury.htm

http://www.hse.gov.uk/comah/sragtech/casechemstar81.htm

I am a Health & Safety Manager by trade; I would be negligent if I didn't urge you to be careful with what you are doing and keep a fire extinguisher handy.

[Hodgkinson]

So the magnesium sulphate, even when hydrated, won't pass through the filer paper? (I'll probably try this out on the recent batch - I assume that the drying agent behaves in the same way as the videoed one on Wikipedia?)
Re the cobalt chloride paper, I've got some of the stuff already. The only problem is that it seems to be so sensitive to even the slightest bit of water present (Ah, blue to pink, ligand change, whoever said that messing about in the kitchen wasn't chemistry revision?)

I suppose we might be able to find IPA available commercially, and probably far cheaper than the combined equipment/gas/salt cost, but that’s beside the point :-D we can get the alcohol free  :crazy: :lol: and the whole projects been well worth all the effort!

Re safety, yeh, gas flame + alcohol vapours = Explosion hazard. Unfortunately we don't have a fire extinguisher (Should really get one, at least for the garage), but I have arranged so that any vapours that are not condensed pass outside through a flue tube to prevent build-up of vapours within the room. I've also made an open-box arrangement of gauzes, which can be used as a safety screen when any flasks are being directly heated for one reason or another.

Btw, we might be getting about 300ml or so every couple of months of the alcohol, so there's little room for growth there!
Re the azeotrope, all the way through the process the temperature of the vapours, just above the liquid level, remained between 82-86 degrees C. Towards the end the temperature crept up a little higher (NB. The distillation isn't really to separate the alcohol from the water, it’s just to get rid of the dissolved salt).

Hodgkinson.

[Hodgkinson]

Right, I now have 500g of magnesium sulphate heptahydrate to try out :crazy:

:bump: So the magnesium sulphate, even when hydrated, won't pass through the filer paper?

(Just checking ;-) )

Hodgkinson.

[WotTheFook]

It shouldn't get through the filter paper; go for it!!

[Hodgkinson]

Thanks! :insane:

(Will get A2 exams out the way first...)  

[Hodgkinson]

Hi again!

A2 Exams are now out of the way!

I tried a little experiment earlier today. I mixed (Dissolved?) MgSO4 in excess water (Just water, no alcohol yet), filtered the solution, and evaporated off the filtrate.

No residue was left on the filter paper, and loads came out in the evaporating dish.

I guess that I have a fair amount to learn about the finer points of drying agents. How can the hydrated MgSO4 be separated from the solution by filtration, even when MgSO4 dissolved in water goes straight through the filter paper?

Photos of MgSO4 experiment (Large images):
http://www.booni.info/chemistry/recycle_project/dissolve1.jpg
http://www.booni.info/chemistry/recycle_project/dissolve2.jpg

Photos of recent tinkering to help improve the efficiency of the “indirect heating” method (Large images):
http://www.booni.info/chemistry/recycle_project/tin1.jpg
http://www.booni.info/chemistry/recycle_project/tin2.jpg
http://www.booni.info/chemistry/recycle_project/tin3.jpg
http://www.booni.info/chemistry/recycle_project/tin4.jpg

PS. I’ve arranged to test the distilled alcohol for density Monday next week. I'll post on the results.

PPS. Not sure yet if I’ll upload photos of the full setup for obvious “legal misunderstanding issues” here in the UK…Besides, it’s an ongoing tinkering opportunity…

PPPS. Anyone know where I might be able to get a hydrometer from that will go down to the density of IPA?

:-D Hodgkinson.  

[WotTheFook]

Eh?

Magnesium sulphate is soluble to a degree in water, it's one of the salts that make water "hard". That test proved nothing.

MgSO4 is insoluble in alcohol and it's this property we are exploiting as the drying agent. Dry some out in the oven then add it to some alcohol, it won't dissolve, but it can be filtered out.

For a hydrometer, you will need something in the range 0.750 to 0.800 as the SG if IPA is about 0.790, if memory serves. Try the Scientific Glassblowing Company in Oldham or BDH / Fisher Scientific (easily Googled), they should carry these in stock.

If you get stuck, PM me and I'll give you my phone number.

[Hodgkinson]

Thanks for the advice.

EDIT: Doh. Now I get how it works. So, when the anhydrous form is added to the alcohol, its function is to effectively mop up the water left in the alcohol. When all the water has been absorbed, no water is left to dissolve the hydrated MgSO4, so it stays as a solid (Having absorbed all the water, and as a result it has nothing left that it is capable of dissolving into) in the now ~ pure alcohol?
I was trying to figure out how the the MgSO4 diddn't dissolve in the water and go straight through the filter paper...But there isn't any water left... :-)

All this is a learning curve for me, so im figuring out these things as I go along.

Heh, I really need to get myself a pestle and mortar - I also tried dehydrating some of the magnesium sulphate today just to find a congealed mass in the bottom of the evaporating dish :-D
I follow from the previous posts that MgSO4 behaves much in the same way (Visually) as the videos on Wikipedia of Na2(SO4) ?

I'll have a look at them companies :-)

Hodgkinson.

[Hodgkinson]

I've just dehydrated *loads* of the MgSO4 and added it to the distilled product. With it not being a fine powder, it’s difficult to distinguish whether any more is required or not, so I've just added the whole lot.

I'll filter it in a bit (Looks like I might need to make my own Buchner app. if I’m going to do this on a larger scale...) then test it along with the raw stuff and distilled stuff.
The results should be interesting!

PS. Did I mention I’ve applied for a Chemical and Process Engineering (With Fuel Technology) Degree at Sheffield (Starting this September)? :crazy:

[WotTheFook]

@ Hodgkinson

You could also use Sodium Carbonate (Soda Ash) as the drying agent, the anhydrous salt works just the same as Magnesium Sulphate. If I recall correctly, Soda Ash doesn't cake up as much as MgSO4.

I agree, a Buchner funnel or some sort of vacuum filtration like some Millipore kit would help things along nicely, it can get expensive though. For the vacuum side of things, get a venturi to fit onto the tap to generate the vacuum, it's cheaper than a pump and there are no parts to break.

I get the feeling your learning curve is going to get a lot steeper starting in September..... :-o  :-)