Discussion in 'Chemistry' started by Maqqie, Aug 26, 2008.
What is the difference between ethyl alcohol (ethanol) and dry ethyl alcohol?
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Ethanol is hygroscopic (because of its ability to form hydrogen bonds).
It's so strongly hygroscopic that it can absorb water from the air.
Ethyl alcohol is simply alcohol, with some percentage of water contained within it (I think it's something like 5%-30%).
Dry ethanol on the other hand contains some drying agent to remove all traces of water.
I know that with diethylether they use sodium metal to dry the ether. I don't remember if they do the same with Ethanol or not, because I can;t remember off the top of my head if Sodium will react with Ethanol.
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Ethanol boils at 78.4°C, water boils at 100°C, but the azeotrope boils at 78.1°C, which is lower than either of its constituents. Indeed 78.1°C is the minimum temperature at which any ethanol/water solution can boil. It is generally true that a positive azeotrope boils at a lower temperature than any other ratio of its constituents. Positive azeotropes are also called minimum boiling mixtures ...A well known example of a positive azeotrope is 95.6% ethanol and 4.4% water (by weight). Ethanol boils at 78.4°C, water boils at 100°C, but the azeotrope boils at 78.1°C, which is lower than either of its constituents. Indeed 78.1°C is the minimum temperature at which any ethanol/water solution can boil. It is generally true that a positive azeotrope boils at a lower temperature than any other ratio of its constituents. Positive azeotropes are also called minimum boiling mixtures. ... A well known example of a positive azeotrope is 95.6% ethanol and 4.4% water (by weight).
The corresponding minium temperature at which a solid alloy will melt is called its eutectic. One common commercial eutectic is sold as
Cerobend (phonetically spelled - I think named to suggest "certain bend" but "cero" does suggest "wax" in some languages.). It is compex of low melting temperature metals with melting point less than 100C. Plumbers us it to bend pipes with out them "buckling" -I.e. they fill the pipe solid with cerobend and then bend it as a solid rod. After it is bent as desired gentile heating from one open end first (for safety reasons) will recover most of it. Any that is still addhering to the ID walls, can be washed out with boiling water.
In both cases (azeotropes and eutectics) if you do not start with that mix the boiling or melting phase changes will tend to mover the vapor or melt phase towards the azeotropes and eutectics compositon.
Thus, for example, if you start with 50/50 Etoh / H2O liguid and boil it, the vapor will have more alcohol in it than water. This is true, regardless of which side of the minium temp mix you start with. For example if you buy some pure Etoh reagent and leave it open to the air it so it absorbs 0.1% H2O, you can not remove that water by "boiling it out," even if willing to boil most of your reagent away in the effort. What happens is that the remaining liquid will become 95.6% ethanol and 4.4% water (by weight) and then boil away with no further change in the liquid composition.
I too am not certain, but think Trippyis correct. One way to get the pure Etoh back is to add Na which certainly will react with the H2O to form NaOH and liberate hydrogen. Years ago, around 1900, one well know physics professor at Johns Hopkins (so the legend goes) would occasionally dress in long black cape and go into some of Baltimore's poor neighborhoods at night with tiny pieces of sodium (covered with oil) after rain storms throwing them in puddles and burning the hydrogen. Why I do not know - but bet it did convence many he was indeed the devil, burning water.
Now THAT is "cool."
Another couple of well known eutectic mixtures are solder, and salt and water.
I looked it up, and it turns out I was right.
Although you can use a sodium to dry out ether, adding sodium to ethanol leads to a reaction between the Sodium and the ethanol to produce sodium ethoxide (which is a great thing, because alkoxides are very useful in other reactions).
The 'reccomended method' for drying out Ethanol that i've found involves mixing it with Benzene. Benzene forms an azetrope with alcohol and water that boils at 64.9°C.
I imagine that you could also do it with Cobalt chloride, or silica granules (both of which can be reused by drying in an oven).
Are you stating the for ONLY those two liquids? (my guess) or all three? I suspect that the three would have a slightly lower boil point but that the Benzene and water would be a higher fraction in the vapor than alcohol, but I doubt you can get to pure (reagent grade) alcohol this way. - comments?
I am not much of a chemist - I'm asking for information. I have however spent one summer between undergrad years at Cornell working for the Lion Oil company in Eldorado Ark. - I doubt if it exists anymore. My task used 55 gallon drum of benzene and 55 gallons of Tolulene. On first day, I mixed them into a still. (They have some what similar boiling points.) The remainder of the summer I separated them many times with the small still. (Its column was about 10 feet high as I recall, but that was long ago.)
Point was to evaluate the new, expensive, perforated, curved, tiny, shinny, metal pieces that filled the distillation column. It got 22 "theoretical plates" in my best runs. Lion Oil was considering buy truck loads of it for an major expansion of the oil refinery and want to check the maker's claims. I could hardly believe they trusted a summer student with the job as a lot of money was envolved. At end of summer I wrote my report and returned to Cornell. I never did find out if they bought the "packing" I evaluated for them that summer.
That is the limit of my non academic chemical experience (which in fact was more physics than chemistry).
The Azetrope is a ternary mixture of the water, alcohol, and benzene, yes.
My understanding is that it's a distillation process, and most of the bezene boils off with the water.
I just checked it out, and Wikipedia says much the same thing as my textbook (http://en.wikipedia.org/wiki/Ethanol_purification) under entrainers, although, apparently they use cyclohexane instead - either way, the alcohol has residues on the order of PPM and is unfit for human consumption (according to Wiki).
Essentially this process only works with 95% pure alcohol.
Cool, my job experience is based around my current job (essentially working for the equivalent of the EPA), and some lab prep work I did at a local gold mining for assaying.
Running pure ethanol reduces the amount of get up and go your car will have, but mixing it 1/2 and 1/2 with gasoline is a wise alternative. A little less power, a lot better gas mileage. Ethanol can be made at home!
I do not know about older designs (US's motors) but the flex -fuel models of Brazil (run on any mix of alcohol with sensors measuring the mix and adjusting spark timing, fuel injections, etc.) acutally get about 2 or 3 % more power on 100% alcohol than on 100% gasoline. What you lose is driving range on a full tank, but you save a lot of money so almost all who can use 100% alcohol. I doubt the average driver can even notice the slight power increase.
A popular flex-fuel model is the GOL by VW - .br is the internet extention for brazil. I bet you can confirm the power gain by visit to their web site. Power gain on alcohol is true of all the flex-fuel motors, but I am not much into cars and only can remember that name. (What the local nuts about football yell when a point is made.)
Not exactly sure why there is a power gain, but suspect that they inject about 35% more fuel on each stroke to more than compensate for the 70% lower energy content by volume. You can put more in with the same compression ratio as alcohol has a higher octane than gasoline. (In fact is added to gasonline to raise the octane rating.)
SUMMARY: Your fact is backwards to the truth.
All I know is my car gets significantly worse gas mileage with ethanol mixes.
Plus the bastards charge the same high price for it. It would be one thing if the etOH mix was 25 cents cheaper a gallon or something, but no. Someone who's already sitting on a mountain of money is just adding to it at my expense.
Yes it should get about 30% less if fuel is pure alcohol as there is only 70% as much combustion energy in each gallon. That is why a simple good rule in Brazil is to buy pure alcohol for your flex-fuel car only if the alcohol price is less than 70% of the gasoline price. Just now it is about 45% of the price of gasoline, so all who can use it, do and fill up more often to compensate for the lesser range of a full tank.
A 50% mix should be more than 15% cheaper than gas to be a good deal. etc.
I heard that Ethanol does indeed get worse gas mileage, and still produces the same Carbon dioxide as burning gas. It's just made in the US generally, so it's seen as helping the economy and making oil go farther.
True, if not made from corn. Make it from sugar cane (or cellulose if that can be economically competive, which I am inclinded to doubt)
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