kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
Ethanol From Ether De/Re-Hydration Process
So I was thinking, as ethanol has a boiling point relatively close to that of methanol and other denaturants used in the industry, and diethyl ether
has such a vastly distant boiling point from dimethyl and methyl-ethyl ethers, one ought to be able to make reagent ethanol from the denatured variety
by converting it ether, distilling it, and then converting it back to ethanol. The process would go something like this:
Sulfuric acid is added to denatured alcohol, and ethers are distilled out. Dimethyl ether condenses out -23°C, with the help of a brine cooled
condenser hooked up to some peltiers or a phase change pump. Methyl-Ethyl ether then condenses out at 7.4°C similarly. Diethyl ether then condenses
out at 34.6C. In practice this could be done with a continuous fractionating still, or with a cascade of three continuous reflux stills, or a cascade
of three batch reflux stills. It could also be done in three steps with a single still but that would be more work. For a continuous still, the
steam feed would consist of ethanol, while H2SO4 is fed in from the middle and runs out the bottom containing water. The water could be distilled out
from that and the same H2SO4 cycled back in, if one wanted to get that elaborate. I have a hybrid two stage continuous/batch still which could at
least separate the diethyl ether from the dimethyl/methyl-ethyl ether blend. I put together this still mainly for distilling solvents and nitric
acid, but the feed sources aren't fully chemically compatible just yet.
The purified diethyl ether would then be fed into a continuous still from the side while a stochiometric amount of water in the steam feed hydrates
it, as the column would be packed with solid catalyst. I am not sure exactly what solid catalysts might be appropriate (though I'm sure someone here
does), but I know an alternative could be to include phosphoric or sulfuric acid in either of the incoming process streams to catalyze the reaction.
The acid catalyst would then run out the bottom with any waste waters. This step could produce at least 190 proof ethanol which could then be easily
dehydrated with zeolite or something to make anhydrous reagent ethanol. Anhydrous ethanol could possibly be produced directly here if the amount of
water could be carefully controlled, and the conversion complete.
An alternative to the continuous rehydration is to feed diethyl ether and water vapors into a cooled flask or separatory funnel containing the
catalyst, condensing out ethanol in a batch process. If sulfuric acid is used in this process, it could be neutralized with copper oxide in order to
distill out the ethanol without dehydrating it again. Copper sulfate can then be recycled to SO3/oleum/H2SO4.
If desired, the dimethyl ether could be similarly rehydrated to obtain pure methanol. I'm not sure what the equilibrium or proportions of
methyl-ethyl ether would look like or if the methyl and ethyl groups would be mobile in the solution at all. I'm sure someone here knows this though.
The absolute boiling point of methyl-ethyl ether is only 91% that of dimethyl ether, while the boiling point of dimethyl ether is only 81% that of
diethyl ether. Compare this to the boiling point of methanol being 96% that of ethanol.
http://www.chrisf.4hv.org/projects/chem/HPIM1363.JPG
http://www.chrisf.4hv.org/equipment/HPIM1355.JPG
http://www.chrisf.4hv.org/equipment/HPIM1356.JPG
The mind cannot decide the truth; it can only find the truth.
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
I dare say that you will never condense out the Me2O. Otherwise it seems like a cumbersome but doable process. Except that CuO+H2SO4 will make water,
and just to annoy us chemists water tends to come off things as azeotropes even when it SHOULD stay stuck to them (ie. CuSO4).
Ediat- Sorry. but actually, no, 'rehydrating' an ether is not that easy. I don't know how you do that. If you ever work it out you could sell the
method to drugos so they can turn codeine into morphine.
[Edited on 27-10-2007 by Antwain]
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
| Quote: |
I dare say that you will never condense out the Me2O. |
-23C isn't that hard to achieve. A CaCl2 brine cooled condenser could work down to almost -50C as long as you've got a cooler than can reach that.
Another, option, wasteful as it may be, would be a dewar condenser containing liquid propane or another refrigerant. I have a variety of
fridge/freezer condensers and have been working on retrofitting some of them, including a -50C 6000BTU/hr cascade for condensing chlorine. If nothing
else, the Me2O could be piped out and burned, and used to heat the still, or something.
You're right the process is cumbersome, but it should work for extracting from E85 fuel and such too as the other hydrocarbons won't react and have a
much lower boiling point than the ethers. Really, it should work for about any source of ethanol, but is definately only practical if you really need
some pure reagent ethanol and don't wish to pay for taxed alcohol, or have a 20ft still.
edit:
| Quote: |
Sorry. but actually, no, 'rehydrating' an ether is not that easy. I don't know how you do that. If you ever work it out you could sell the method to
drugos so they can turn codeine into morphine. |
I thought I read somewhere that ether could be rehydrated to alcohol much as it is dehydrated from alcohol, and that sulfuric or phosphoric acids
could catalyze the hydration. It would be a little like the catalytic hydration of alkenes, but simpler.
[Edited on 26-10-2007 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
Well, yes, it CAN be done, but the conditions would (i imagine) be most awful. Since ethers are very unreactive it would have to be hot,possibly very
hot, like >150*C. which means gas phase or very high pressures (or both maybe?) anyhow I know I wouldnt like to work with ether at 150*C, because I
don't like dying in an explosion  but I don't know what apparatus your have
available. I will leave it to someone more knowledgeable to tell you whether it is actually impossible, or just very hard.
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
I've found that usually you have a choice between either difficult process conditions or expensive catalysts, though often both are required, like in
the Contact Process (which I do intend to carry out sometime as well, but at least its feedstocks and products are not explosively flammable). I
could have sworn the ether hydration was not that hard though. I guess we will see what others have to say.
The mind cannot decide the truth; it can only find the truth.
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
C-> M conversion and what is this shit?
| Quote: | Originally posted by Antwain
Ediat- Sorry. but actually, no, 'rehydrating' an ether is not that easy. I don't know how you do that. If you ever work it out you could sell the
method to drugos so they can turn codeine into morphine.
[Edited on 27-10-2007 by Antwain] |
quite do-able as a matter of fact .. the very thing came up in my reading last week and is covered in US Treasury Department Supplement No. 103,
Chemistry of the Alkaloids of Opium. I don't know for sure but I doubt if the Rhodium/Hive/Wetdreams cabal would have missed it.
But what the hell is all that apparatus? Is that what you propose to do it in? What are the gas hookups? What is the guage for? It all looks like
a movie set. And why is it strapped to the wall like that?
I've gotta say this seems the long way around. I think you end up with the worlds most expensive ethanol and it still has water in it. Be better off
making it from oxidation of ethene with sulfuric acid. Or is that one of you gasses?
[Edited on 26-10-2007 by chemrox]
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
@kilowatt- I admit to not knowing how difficult this will be, just have a gut feeling that it won't be simple.
@chemrox- I didn't know that. I thought that in addition to its lower addictiveness, one of the main benefits of codeine that made it ok to sell OTC
was its inertness. Also oxidation of ethylene would give ethylene oxide or similar would it not? alkenes and alcohols have the same oxidation state in
organic chem, don't they?
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
Well I daresay it would be slightly easier than the catalytic hydration of ethylene. It should be fun, anyhow, I am curious how well it might work out.
| Quote: |
Also oxidation of ethylene would give ethylene oxide or similar would it not? |
It depends how far you oxidize it. Ethanol is typically made industrially by oxidizing ethylene over a solid acid catalyst at like 100psi and 300°C.
Ethylene oxide is made in two steps with the chlorohydrin process, or can be made by oxidizing ethylene with hydrogen peroxide under some conditions
which I'm not sure of.
| Quote: |
But what the hell is all that apparatus? Is that what you propose to do it in? What are the gas hookups? What is the guage for? It all looks like a
movie set. And why is it strapped to the wall like that? |
It is indeed what I intend to do it in, as well as any other chemicals I want to distill. Haven't you ever seen a continuous still? The stainless
tank is a pressurized wash tank where chemicals are fed into the still between the rarefaction column and rectification column by controlling the
regulator on it. I now actually have a needle valve on the incoming line itself so it is easier to control. The aluminum tank with insulation on it
is the boiler which provides steam feed to the bottom of the rarefaction column. It provides the heat for the distillation and runs out the
separatory funnel at the very bottom with the lowest fraction. The gauges read pressure to make sure everything is at a safe level. The second
fraction which has been reduced in volume then runs into the middle flask to be distilled again, removing the highest fraction. Sometimes this stage
is not necessary, but for batch distillations it is the only stage used while the more difficult to operate continuous stage is closed off. I made it
specifically for vacuum distilling white fuming nitric acid from aqueous Ostwald nitric acid or sulfuric acid/sodium nitrate solution, but also to be
versatile enough to distill almost anything. For nitric acid the boiler will be replaced with my 4L reaction kettle and either aqueous nitric acid
will come in at the steam feed while conc. sulfuric runs in from the side to get fuming nitric acid out and water/sulfuric out the bottom, or nitrate
salt solution will come in the side while sulfuric acid/water comes in the steam feed to get sulfate solution out the bottom and aqueous nitric out
the top to be distilled to fuming nitric with concentrated sulfuric in the second stage. Another option may be to use an oleum as the steam feed
while the nitric acid or nitrate solution comes in the side, since oleum and SO3 boil at a much lower temperature than H2SO4. It will need some other
work too like nickel plating any metal fittings and addition of further control devices. Right now if is very tedious to get the thing running
perfectly. For now I use it for distilling off-the-shelf solvents, and it works quite well once you get it in tune. What's wrong with mounting it to
the wall? I have no other good way to mount an 8' tall set of glassware.
[Edited on 27-10-2007 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
A little off topic, but are you familiar with sucrose fermentation?
Also, cleaning up ethanol from E85 fuel seems like it would be MUCH simpler.
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
Why do you even need to condense the methyl ethyl ether and the dimethyl ether? If you don't care about them as a final product, why not just pipe
them out of your work area as gases? Also the ether you collect will probably still be contaminated with these 2 ethers, as they are both soluble
within diethylmether. So you would need to devise a way of removing these two ethers from the ether you produce. Which would likely involve
refluxing you crude ether while blowing a gas through the solution.
As pointed out, fermentation would be more practical. Even the hydrolysis of ethyl acetate would be more practical.
In fact, you will probably obtain a better product by simply 'cleaning up' denatured ethanol which is bought from a hardware store. If the ethanol is
denatured with say 6% methanol, and you distill off around 10% of the alcohol even in an inefficient still the other 90% of alcohol left in the
distilling flask would be very methanol free.
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
And 3A sieves may absorb the remaining methanol after the water is removed, but I've read conflicting info on that. It seems clear that 3A, 4A sieves
have a preferential affinity for water over either methanol or ethanol, but maybe there is selective absorption after the water is gone?
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
And... If you need Et2O as a solvent, a few percent of dissolved MeOEt isnt going to affect the results. Again, for most needs as a solvent *a few
percent* of MeOH in EtOH is not going to have a detrimental affect. It has similar properties, except that polar substances are slightly more soluble
(negligable effect in small concentration. As per adding ethanol to a water solution... I have done this with a CuSO4 solution and it knocks ALL the
colour out, zero solubility even though there is 20%+ water there).
If you need reagent ethanol, then I would suggest buying reagent ethanol...If its a reagent you probably wont need to use much so the cost is
acceptable. Or if you were so inclined to buy OTC products then I would recommend a Polish drinking product called "95" (95% ). Bad as tarrifs are this will still only cost 2-3 times as much as chemical
supplier ethanol. Or in some cases, it would be cheaper. It all comes down to a balancing act of your time, your money and the quality of your
product.
As smuv pointed out, you could hydrolise ethyl acetate. This may be cost effective for you if you have a cheap source of EtOAc. Basic hydrolysis is
easy since it can only proceed one way and sequesters the acetate, certainly easier than playing with ethers.
[Edited on 28-10-2007 by Antwain]
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
With those elaborate apparati of yours you should be able to separate ethanol and methanol directly with a column without problems. The only important
thing would be to use a proper column head, use a high reflux ratio, and wait until equilibrium has established in the column before slowly starting
to tap off product.
Be glad that your denatured ethanol contains no MEK, as does mine (in germany). This is COMPLETELY IMPOSSIBLE to separate by fractionation. Chemical
methods would have to be applied to remove it.
On the other hand, our denatured ethanol contains NO methanol.
You could also try to separate methanol and ethanol by forming esters with an organic acid (preferably a high-boiling or especially low-boiling one-
have a good difference in the boiling points of products and towards the alcohols) whose boiling points differ more than those of the alcohols.
Hydrolysis of the pure ethyl ester would then give very pure ethanol, after dewatering of the aqueus alcohol thus obtained.
This process would also remove MEK, so it is of potential interest to me as well if I ever need high-purity ethanol.
Here are the boiling points of the lower aliphatic esters of methanol and ethanol (in °C):
Formate 32,0 54,3
Acetate 57 77
Propionate 80 99
You see, the b.p. difference is about 20°C in all three examples- notably larger than the 13,6°c of EtOH/MeOH.
Acetic and propionic acid are not convenient to use here due to their boiling points being too close to the alcohols.
Formic acid would be a good choice, since the esters boil lower than both alcohols, allowing for their continual removement from the equilibrium and
therefore high yields.
Be careful though, the esters might form azeotropes with the alcohols.
Hydrolysis of alkyl formates is rapid in basic medium. You could also react the formate with ammonia solution, giving an aqueous solution of formamide
as a valuable byproduct (formamide is difficult to get from ammonium formate). Or conventional hydrolysis with NaOH-solution, giving sodium formate as
byproduct which also has its uses.
Ethyl formate smells very nice, I like the smell a lot. Methyl formate on the other hand has only very weak smell.
It depends on the price and availability of formic acid where you live.
Your proposed ether process seems really... "unfeasible" to me.
For one, the diethyl ether synthesis using sulfuric acid is difficult to do with yields of more than 30% in the lab. The ethanol also needs to be
introduced deep below the surface of the sulfuric acid, as dripping the alcohol on the acid causes the alcohol to instantly evaporate without
reacting. The reaction also needs close temperature control.
The rehydration of the ether is also a difficult operation. Those catalysts tend to rather dehydrate ethanol to ether or even ethene if temperature or
other parameters are not strictly controlled. Low conversion per pass would have to be used.
Your ether process is probably not applicable except on a very large scale- and one would never even consider doing it, as methanol and ethanol can be
separated far more economically using a good column.
One last idea: Methanol esterifies markedly faster with most acids than ethanol.
Boric oxide (the anhydride of boric acid) reacts readily with methanol at room temperature under evolution of heat.
If you use, say, the amount of B2O3 theoretically needed to convert all of the methanol into trimethyl borate plus a good excess, you should get quite
a good separation of MeOH and EtOH after removing the volatile ester by distillation.
Repeating this process once or twice. I would be interested in the purities (residual methanol content) of the ethanol thus obtained.
There are also the obvious methods of course, like purchasing pure ethyl acetate (industrially made by catalytic dimerization of ethyl acetate, so no
denaturants are present) and hydrolyzing it,
and fermentation (may produce methanol as well if no proper yeast culture is used, also higher alcohols).
[Edited on 28-10-2007 by garage chemist]
[Edited on 28-10-2007 by garage chemist]
[Edited on 28-10-2007 by garage chemist]
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
Interesting methods, garage chemist. I had thought of the possibility of partially oxidizing ethanol and methanol to acetic and formic acids
respectively and reducing them back, but those two have closer boiling points than ethanol and methanol themselves, not to mention the inherent
difficulty of the conversions. Your ester process could potentially work quite well, as long as the azeotropes don't disallow it.
The thing is, even though my distillation setup may seem all fancy at first, the columns aren't actually that tall, having only perhaps 2-3
theoretical plates each. Its purpose is to allow quasi-continuous fractionating distillation procedures, and I would need a very tall space, not to
mention a small fortune for the columns, to set up a similar apparatus with much higher separation capabilities. I got all that stuff for a great
price on ebay. It's excellent for a lot of distillations but when you get stuff with close boiling points it's probably not quite as effective as I
would like. This is the reason for my wanting to use chemical conversions to widen the boiling points or otherwise chemically extract. Granted, I do
have full control over the reflux ratio with my setup and can make it as high as I want. I could also run stuff through it as many times as I please
to get higher purity. Nonetheless a chemical conversion step like the ester process could make things go faster/easier if all the reactions are easy
and cheap enough to carry out.
| Quote: |
Or if you were so inclined to buy OTC products then I would recommend a Polish drinking product called "95" (95% ). |
We have 95% ethanol here too, for relatively cheap compared to other booze. However, I am not remotely inclined to use OTC products for chemistry if
I can make suitable ones myself for cheaper. There are much better things to do with drinking products anyway, such as drinking them. In regard to both this and the commercial ethyl acetate idea, I don't generally like
to buy reagents reagents this way. They are expensive, and are getting harder and harder to obtain all the time. I do all my chemistry under the
assumption that someday a regular citizen will NOT be able to buy ANY chemicals (beyond certain staple ones like NaCl, gypsum, fuel products,
distilled water, automotive products, etc.) due to increased government regulations and other "phasing out" of chemical products. For example, I
would not count on being able to buy HCl or H2SO4 from a commercial source years from now, and anyone who relies on these commercial products for home
chemistry without being able to make their own will probably find themselves out of business one day. About the only non-consumer chemicals I ever
buy are ones that contain uncommon elements like lithium, bromine, iodine, cesium, mercury, etc. I also have a good stock of chemicals that are still
cheaper to buy than they are to make, such as nitrate and carbonate salts, sulfuric acid, acetone, urea, etc, but I have plans to synthesize from
scratch too when they become unavailable/illegal. It would already be difficult to obtain a reagent like ethyl acetate for a reasonable price, as it
is not something you can pick up in bulk at the grocery or hardware store.
The only way to get ethyl acetate, as far as I'm concerned, is as garage chemist described, by esterfying ethanol and acetic acid, with said acetic
acid being distilled from vinegar or made by fermentation. Of course, if I did fermentation, I could just use it to make ethanol itself. The nice
thing about the ester process though is that an amount of acetic acid can be used over and over again to purify something cheap like E85 by acidifying
the resultant sodium acetate (from the alkali hydrolysis) with HCl. Admittedly the process is still rather round-about in comparison to distillation
without chemical conversions. I see we have another thread on E85 separation, which I have been following as well.
I have some 4A zeolite, perhaps I could try that to further purify after plain distillations.
One of my biggest issues is time, since I feel overwhelmed by my other and more important chemistry projects, and very seldom get to actually work on
them. I need to finish my fused alkali salt cell first thing when I get the chance, then I need to set up apparatus for the Contact Process with SO2
coming from the firing of gypsum with coke and silica and being liquefied out from CO2 by a compressor), the Ostwald Process, metal casting furnaces,
chlorate cell and associated oxygen generator, amalgam cell for NaOH/KOH production and an associated UV pulsed HCl furnace. Distillations take a
long time and use a lot of energy especially when there is a lot of water involved and I want to keep that to a minimum and be able to use my
glassware for more important things. It feels like all work and no play because I spend so much time and effort making reagents that I hardly have
time to use them for what I want, like making exotic rocket propellants and the like.
The mind cannot decide the truth; it can only find the truth.
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
I wish you luck, but the more I ponder the getting of ethanol out petrol, the more I am convinced that it is going to be a pain in the proverbial.
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
Can someone interpret the data at the bottom of this page?
http://en.wikipedia.org/wiki/Methanol_%28data_page%29
I am trying to see if methanol/water forms an azeotrope, but that data seems to imply a zeotrope. But I don't know. Also, it gives data for the 2
phase system ethanol/methanol. Nope I can't work out what they are saying, and it would be more complicated in a 3 phase system.
But here was my idea... as you guys probably know ethanol/ water forms a 95/5 azeotrope... but add some xylene and you can distill a different
azeotrope without water. I don't know how they seperate the xylene from the ethanol, but they can (i think??? or does EtOH anhyd have lots of xylene
in it?). Anyhow, I pose the question to someone who knows what the hell is going on
- can something be added to methanol/ethanol to azeotrope with one of them and allow them to be seperated?
|
|
|
leu
Hazard to Others
Posts: 368
Registered: 13-10-2005
Member Is Offline
Mood: No Mood
|
|
Methanol and water don't form an azeotrope at atmopheric pressure
[Edited on 28-10-2007 by leu]
Chemistry is our Covalent Bond
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
Yes, it looked that way. So its a zeotrope then? note* "a zeotrope" (not=) "azeotrope"
Looking at the data one more time. If I was faced with your problem I would get the lowest methanol conc. methylated spirits i could. if it is less
then 20% then just do a crappy reflux and distill until half of it is gone. As long as the solution at the bottom is not boiling violently then all
your methanol will be gone.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
