Bio-Petrol?

[Wombat]

at 95% it forms an azeotrope or constant boiling point mixture with water and no purer alcohol will distill off. You need to put in a dessicant to absorb the water.

Nev

[dave45]

Any idea of EROEI? - how much energy does it take to distill a litre of alcohol, compare to the energy content of that litre?

My guess is that it takes a lot !

[basil_brush]

Yes, that's a good point. You could use very small boiling chamber heated by solar radiation. It would be effective but slow, but if it's only for a lawnmower then you can afford to wait weeks for a few litres of alcohol.

Alternatively maybe he could remove most of the water by reverse osmosis.

[dave45]

Alternatively maybe he could remove most of the water by reverse osmosis.

ok - what do i need to have a go at this? I've heard the words before (biology textbooks?) but never seen it as a practical thing - is it?

[Wombat]

REverse osmosis works on the idea that the water molecule is smaller than the ehtanol molecule and it will be forced through a semi-permeable membrane leaving the ethanol behind. I have seen hand powered ones but most are electric. Why not try throwing in some silica gel dessicant? a lot easier and re-usable......

Nev

[basil_brush]

Wombat is right, if you want a really simple homebased method then just use a reusable desiccant. After looking into reverse osmosis more it seems to be harder than it first seems. Often the alcohol goes through the membrane with the water (like when the wine industry uses it to remove alcohol from their product) so you would have to spend ages trying to find the right membrane etc.

Some people have talked about separation by freezing:

http://malaysia.answers.yahoo.com/quest ... 6042001267

But they can't seem to agree on whether it works. You could get some vodka and try freezing it to find out. They also mentioned just letting it stand for some time to separate by gravity and using water based dyes to show which bit is the water, but I'm skeptical of that, surely alcohol mixes too well with water to be able to separate?

Of course, if you use desiccant then you'll need lots of heat to dry it out and recycle it. So your desire to avoid using more energy than what you get from the ethanol looks like a no go. The best you can do is get the energy from the sun, thereby giving you the closest thing to a free lunch. To do either use solar heat to boil and distill your 15% ethanol mixture from the yeast or use desiccant to dry your ethanol and then use solar heat to roast your desiccant and recycle it.



By the way, I was just reading about separating salt and sugar with alcohol (salt does not dissolve in alcohol) and thought: well, alcohol mixes with water because of the electrical attraction of the polarised molecules, so what if you dissolve as much salt as possible into your 15% ethanol in water mixture, the salt ions will likely attract to the water molecules strongly and push the ethanol out of the way, the saturated brine will sink to the bottom and the alcohol will float on top, you can then leave your brine outside to evaporate and recycle your salt. Might be worth a try with some salt and spirits to see if it works. For that matter anything which develops stronger ionic bonds with water than ethanol will cause the ethanol to be excluded and pushed out, because the ethanol cannot mix if the water's ionic bonding points are all taken up by something else. If I recall correctly soap and biodiesel producers throw salt into the liquid mixture to cause the glycerin to precipitate out of the oils. So this this style of technique is definitely worth thinking about.

[basil_brush]

Ok, I've found this:

http://www.haverford.edu/educ/knight-bo ... fwater.htm

Near the bottom it says: "The MSG, an amino acid salt, should dissolve in water, but only partially dissolved in the alcohol. If rubbing alcohol is used instead of pure isopropyl alcohol, you may observe a liquid layer separate out with the un-dissolved salt at the bottom of the jar. There is some water in rubbing alcohol. When that water become saturated with the salt it becomes much more dense than the alcohol and it also become less miscible (soluble) with the alcohol, and separates out as a lower layer."

So it would appear you can use water soluble salts to separate water from alcohol. So buy some cheap vodka and a couple of kilograms of table salt and try it.

[Wombat]

Ok, I've found this:

http://www.haverford.edu/educ/knight-bo ... fwater.htm

So buy some cheap vodka and a couple of kilograms of table salt and try it.

or MSG

Nev

[basil_brush]

Ha, yes, if you can find it, probably the best place to go is a Chinese store. I've seen my Chinese housemate buy a half kilo bag of pure MSG.

How well any particular salt will work depends on its ionic binding strength with water. I don't know that so find a chemist (the technical kind not the pharmaceutical kind) to ask. :)

[Wombat]

Ha, yes, if you can find it, probably the best place to go is a Chinese store. I've seen my Chinese housemate buy a half kilo bag of pure MSG.

How well any particular salt will work depends on its ionic binding strength with water. I don't know that so find a chemist (the technical kind not the pharmaceutical kind) to ask. :)

I used to be but it is over 15 years since I was in the industry....

Nev

[basil_brush]

Looking back at what I wrote earlier, I would be inclined recommend table salt (sodium chloride) rather than MSG. I've read that table salt will not dissolve in alcohol, whereas MSG is partially soluble. Which means you'll end up with a little bit of MSG in your fuel mixture. Unlikely to be a problem, but you might like to recycle 100% of your salt chemical.