How to make anhydrous ethanol (100% alcohol)?
Water and ethanol form what is known as an azeotrope. This occurs when a mixture of liquids has a higher or lower boiling point than each of the individual components. In the case of ethanol, a mixture of 95% ethanol to water boils at a lower temperature than pure ethanol. So the concentration of 95%, there is really nothing you can do by distillation that can concentrate the ethanol further.
The method I am going to show and it is the one that is easiest to get to a 100% ethanol at home.
It is pretty simple and what will just be doing is adding a drying agent to the ethanol that soaks up the water.
So now the question of why anyone would even want a 100% ethanol. I personally need it because there is some reactions that I would like to run where I need to use ethanol, but I can’t have any water present. Another major use that I won’t need it for but others may is to add to gasoline. Anyway, now to get started with the preparation.
The first thing I will do is use my hydrometer to verify that the ethanol is actually at 95%. So first it is placed into a grad cylinder and then they pour methanol in until it floats. Hydrometer functions is based on the principle of buoyancy. Water is more dense than ethanol, so the more water that is present the higher the density of the mixture and the more the hydrometer will be pushed out of the liquid. All of this is to say that the concentration of ethanol is directly related to its density and this tool lets us find out pretty easily. So we can see here that it is actually floating a bit above 95% which makes sense because the azeotrope is actually 95.6%
From my drying agent, I use what is known as molecular sieves. these little sieves have very small pores in them which can adsorb water but the pores are too small to allow any other larger molecules to enter. So this means that the small water molecules can find their way in and bind to these little beads, but the ethanol is too big to do this and will be left untouched. I should note that I used 3A molecular sieves because there are different sieves sizes that will adsorb ethanol.
Once the sieves are added, the container should be sealed and allowed to sit overnight. I let it sit for several hours and then tested the concentration and unfortunately wasn’t really that close to 100%. The process of picking up water can be a little bit slow though especially no stirring is happening. Also my sieves were not freshly dried, so I added about 120g more. Because the molecular sieves can be regenerated, there really isn’t a downside in terms of molecular sieve loss by adding more. However when the ethanol is decanted later a lot is going to stick to the seeds and the more that you use the more loss will occur.
The solution is cloudy because of little bits of dust of the molecular sieves but this really isn’t an issue for now. when allowed to sit overnight, you can see all the dust settled to the bottom and were left with a crystal clear solution. So now we pour it in and we can see that it is pretty much 100%.
So next step is to separate the ethanol from the sieves and to do this we are just going to use a coffee filter. All of the wet sieves are dumped into the coffee filter to hope that some of the ethanol drip through. You will notice that a lot of the dust from the sieves actually makes it through. And the amount of dust that you get with your sieves will depend on the source that you buy it from. I bought mine for pretty cheap source and I think it had more dust than usual. Anyway at this point you have to real options. You can let all the dust settle to the bottom and decanted filter again and you should be left with a pretty clear solution or you can distill.
Depending on your ethanol source, you might want to distill it. For example, mine was bought from the store and it has a lot of denaturing agent that can actually be easily removed by distillation. so for this reason, I opted to distill. Note that the final solution of anhydrous ethanol should be stored over sieves, so if you are only reason to distill is to get rid of the dust, it might not be worth your time. I then set up a fractional distillation, but it is probably totally unnecessary and a simple one will more than suffice. In my case, none of the denaturing agents are volatile, so they should all be left behind in the flask. So this is what the upper part of the distillation looked like prior to wrapping it with aluminum foil. The column is in the wrapped with aluminum foil to insulate it and help the ethanol pass over. You can see that the receiving flask is packed with sieves to keep the ethanol that comes over dry.
Eventually all the ethanol comes over and should be pretty much 100%. At the bottom of the distillation flask were left with a mixture of the denaturing agents and the molecular sieve powder. So to test out the ethanol concentration, we again pull out our trusty hydrometer. So we can see here that the hydrometer float is very nicely at the 100% mark.
So now we have some nice 100% ethanol and we transferred to an appropriate container.
Anyway, once the ethanol is added then I dumped in a bunch of sieves just to keep it dry. it is then capped, sealed off and were left with our nice 100% ethanol. One thing to note is that the sieves dust really shouldn’t be a problem as long as you don’t shake the bottle a lot before you use it. If you remain gentle when you pour it all the dust should remain near the bottom. Anyway, that is it for now and remember to store the ethanol somewhere safe.
FULL VIDEO SOURCE: NileRed
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3A MOLECULAR SIEVE FOR ETHANOL DEHYDRATION
Ethanol dehydration typically occurs in a PSA unit. Water is adsorbed into the molecular sieve from the ethanol-water feed.
