Originally By Tony Ackland
Drying EthanolThe maximum purity you will get by distilling alcohol is around 96%. This is because the ethanol and water form an azeotrope. If you do manage to dry your alcohol beyond this, if exposed to air, it will simply suck in moisture from the air, and dilute itself back to th 96.48%. There are however various methods used to dry ethanol beyond there. Its important to do so if using the ethanol as a fuel, or using it to make biofuels. The water can be absorbed from the ethanol using zeolites (a molecular sieve), or even simple corn-grits. Note that you wouldn't use the limestone or copper sulphate techniques for drinking grade ethanol.
Fred writes ...
Ken wrote ...
I got a can of the 4-8 mesh -- little balls of rock about 1/8" dia. -- they absorb about 20% of their weight of water over the course of a few hours. Take a liter of 95% ethanol, throw in 250g of stuff, swirl occasionally, filter out the next day thru a strainer, and presto! Anhydrous ethanol. Not expensive either -- $2.05 a pound US in 10 lb quantities, and reusable indefinitely. You drive off the water under a broiler for an hour.
The easiest way to get water out of ethanol is probably with molecular sieves (3A zeolite). It takes about 10g of sieve for each ml of water. 5kg cost about $100 and canbe reused hundreds, if not thousands of times. You could probably even rig up a solar oven or something to dry the stuff.
Are you talking about the manufactured m.s. balls or the powdered or hammer-milled type here?
-- DAVID REID"
I suppose it wouldn't really matter. Larger mesh beads (1/8", 1/16") would be easier to recover, but it might take a little bit longer to sop up the water and regenerate the sieve. Powder would take more time to recover (you probably can't just decant, you'd probably have to filter) but would be faster in the adsorption and regeneration, I guess.
These are your answer and 3A is definitely the right one but there are a number of problems and obstacles to overcome.
-- DAVID REID"
Quite a high start-up cost though, to dehydrate only 10 litres of 190 proof - although that will give you about 50 litres of biodiesel, if that's why you want to dry it. Also it takes 300-350 deg C to regenerate zeolite, more energy input, but maybe not more so than other methods which require redistilling. Maybe you could utilise the original boiler heat while distilling the ethanol to dry the zeolite.
-- Keith Addison
Molecular sieves work via adsorbtion. There are lots of little H2O binding sites on the surfaces of the molecular sieve particles (or beads, et cetera). H2O molecules 'stick' to these binding sites, EtOH molecules generally don't. Your sieves come wet. Heat them to about 200C for about 1/4 hour to drive off water. You don't have to do this, but you'll get better adsorbtion if you do. Best to do this at reduced pressure, if possible. Dump your dry sieves into the EtOH/H2O solution. Let it stand for 24 hours. Decant. You now have something very close to absolute ethanol. Keep it out of contact with air. It will take up water very rapidly, and you'll be back to 95% in no time.
-- "Greg Ederer"
http://www.bol.bg/zeoweb/zindex.htm - A piece of info about zeolites
http://www.zeolyst.com/html/faq.html - Zeolite FAQ
http://www.mall-net.com/mcs/zeolite.html - Zeolites
http://www.christison.com/zeolite1.htm - Zeolites brochure for website.
There's a great intuitive explanation of molecular sieves at: http://www.science-projects.com/analogies.htm#molsi
First, make sure it's dry, by heating to about 600 deg. F for several hours, thencooling back down in dry air. Toss in the required amount with your hydrous ethanol (molecular sieve zeolite absorbs like 25% of its weight in water) and stand back -- it can get HOT. Takes a few hours to get saturated. Oh, I'm sure the pros will talk all about columns of X dia. and Y length, with flow rates of blah, blah, but the simple ways are best. Good luck -- BTW, I only have free samples of this stuff. Did you actually have to PAY for it, and if so, how much (if you don't mind my asking :-)). Check out http://www.sorbentsystems.com/desiccants_charts.html for some good info and graphs.
If there's ethanol in your gas tank, there's a 50-50 chance that it was filtered through corn grits using a technique developed at Purdue University. When the corn grits get saturated with water you just make more ethanol out of them!
Drying of ethanol vapors - http://www.esb.ucp.pt/~bungah/downstre/vapordry.htm Ladisch and his students at Purdue University found that drying of ethanol vapors saved energy and was economic. The corn industry makes ethanol by fermentation and has corn grits readily available. Passing the wet vapor over corn grits or other drying agents removes most of the water to yield a product that is close enough to absolute ethanol. When the drying agent approaches exhaustion, it is regenerated by heating and reused. Eventually the drying agent breaks down but has potential uses elsewhere in corn processing.
Source: Mike Ladisch; phone 317-494-7022; Internet,ladisch@e...
Check Chapter 12 of the Alcohol Fuel Manual in the Files section at the list Website, "Drying the alcohol". You can access it with your browser (html files). Click on "manual - Alcohol Fuel Manual", the chapters are inside the folder. The file is called "manual12.html - Alcohol Fuel Manual Ch12". The list website is here: http://www.egroups.com/group/biofuel The lime and calcium hydroxide settle out or are left in suspension, so distillation should remove it all. You'll need unslaked lime, ie quicklime (calcium oxide). The masonry shops only sell hydrated lime these days (calcium hydroxide). According to Stephen Mathewson's recommendations in the Alcohol Fuel Manual you'll need 35 pounds of lime per gallon of water = about 10 gallons of 180-proof ethanol.
Here's an old chemistry trick: take the highest grade ethanol you can make and run it through a column packed with dried copper sulphate. In Europe CuSO4 is used to spray wines, so it's quite easy to obtain. 1 molecule of dry CuSO4 takes up 5 molecules of water forming a crystal hydrate: CuSO4*5H2O. If you haven't got a column just toss the crystals into a vessel, add hydrouos ethanol and stirr occasionally. The color of the crystals changes when they are "full". Dry the crystals in an oven (solar possibly) and reuse XXXX times. P.S.: The process is slow.
Always use crystalline hydrate forming compounds:
burned limestone (CaO + H2O = Ca(OH)2)
copper sulphate (CuSO4*5H2O)
sodium carbonate (Na2CO3*2H2O) etc.
-- "Aleksander Kac"