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'Salting Out' Isopropyl Alcohol?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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'Salting Out' Isopropyl Alcohol?

Unread postAuthor: mark.f » Wed Oct 08, 2008 9:05 pm

It's interesting, I was just reading around on isopropanol and came across a little ditto on Wikipedia.

Basically, it says you can add a salt to an aqueous solution of isopropyl alcohol, and it will bring the actual alcohol into a separate layer that can be extracted.

I think this would be good for purifying the consumer 70-91% concentration stuff for fueling launchers. While it would make the fueling a little more piddly (requiring an even SMALLER amount of alcohol than what you would already have to measure out using the diluted stuff), there might be a few benefits.

Just letting you guys know. The wikipedia article says almost any salt will do, but obviously sodium chloride (table salt) is the most available.
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Unread postAuthor: starman » Wed Oct 08, 2008 10:03 pm

Cool info. Still a lot of effort there ....and doesn't beat the cheap and utterly and readily available and easy to use propane.
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Unread postAuthor: Lentamentalisk » Wed Oct 08, 2008 10:34 pm

its easier to make a ghetto metering system. ie syringe.
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Unread postAuthor: jimmy101 » Thu Oct 09, 2008 2:11 am

To get this to work you really wouldn't be doing a "salting out", at least not in the traditional chemical sense.

Isopropyl alcohol (IPA) and water are miscible in all proportions. If you add salt you will force most of the IPA out of the water. But the IPA will still contain a fair amount of water and the water will still contain a fair amount of IPA.

If you just dumped a bunch of table salt into the 70-91% IPA the salt will form a brine layer and pull out most, but not all, of the water. This technique is really not "salting out", though it is similar. Instead you are just using the salt as a drying agent. I doubt any amount of salt will get the water concentration below about 5%.

I really don't think it is worth the effort. Even at 70% IPA / 30% water it still works just fine as a spudgun fuel. There is so little fuel/water in the gun that the water won't do anything. Of course, if your not sure if the IPA is 70% or 90% it kind of messes up your calculation on the amount to use.

If you've got the stuff laying around it's worth a try. Off hand, I can't think of any way to tell if it has actually done any good. There are several ways to assay for water content but none that I can think of that you can do with junk laying around out in the garage.

It is much easier to just use a fuel with insignificant amounts of water in it. Gasoline, kerosene, mineral spirits, acetone, etc. generally have very little water in them.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 09, 2008 4:43 am

Or you can work where I do and have isopropanol available by the 200 litre drum ;)
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Unread postAuthor: mark.f » Thu Oct 09, 2008 9:03 am

It was just an idea I wanted to toss around. I'd probably wind up just using 91% if I ever used alcohol to fuel a cannon.

EDIT - question removed. I'll just ask my chemistry teacher tomorrow.

Thanks for the help!
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Unread postAuthor: nivekatoz » Thu Oct 09, 2008 5:26 pm

Im not a combustion cannon guy, but I herd you could use ETHER, starter fluid for carborators as propellent.. You could also use butain or propane ,propane might be the cheapest.
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Unread postAuthor: mark.f » Thu Oct 09, 2008 6:32 pm

nivekatoz, I have made 6 propane/MAPP/butane/Starting Fluid combustion cannons. :wink:

EDIT - 7 if you count the one I made out of a JIF peanut butter jar.
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