acetaldehyde synthesis

[El_Zorro]

I'd like a few bee's thoughts/opinions on my thinking about patent US 1892011.

So what I got from that patent was that you just pass a stream of ethanol vapor and water vapor over a metal catalyst at whatever temp it takes to start the reaction, according to them anywhere from 120°-300°C.  Not too hard, I guess.  They said that the metal catalysts that could be used were nickel, copper, and cobalt.  Now this is where I start thinking.  Heating mantles are available that are designed to fit around glass tubing, they're just about condenser-sized.  So you can just get a glass blower to make a glass tube, about condenser sized, and with correct joints.  Now you just have to figure out how to get a metal catalyst in there, and also provide copious amounts of surface area, as well as allowing the vapors to pass through.  So what about those copper coated scrub pads?  You could just stretch one out and stuff it in there.  The patent said the the catalyst eventually gets contaminated with metal oxides and hydrates, so no sweat, you just pull that one out and stuff another $1 pad in there.  And you could just have a custom glass joint attached to the inlet joint of the reactor tube to accomidate two separate flasks, one for the water, and one for the alcohol, that way you could keep a good amount of water coming into the tube, because I think that just a mix of water and alcohol wouldn't give off enough water vapor.  And as lugh said in some post I read, you can just lead a tube from the end of the apparatus to a glass of water or something, and when hydrogen bubbles start appearing,(oh yeah, hydrogen is produced) then you have the right reaction temp.  Pretty simple.

So what are you bee's thoughts on this?  The patent claims 95%+ yeilds on several substrates, so I think it merits looking into, especially if an apparatus could be built as easily as that.

My only other question is, I guess there would be a lot of water condensed at the other end, so how easy is it to separate acetaldehyde from water?  acetaldehyde's boiling point is significantly lower than water's but will is form azeotropes, or stay dissolved, or something like that?

[roger2003]

If you look to

Patent US1124347

there are a lot details for preparing catalyst pp.

[urushibara]

I don't see why this wouldn't work, much the same reaction can be done with toluene, and it's not even an alcohol.

also, removing the water - perhaps mix with another solvent with a way lower or way higher bp and dry it and then fractional distil?

[Mountain_Girl]

Ullmann's Encyclopedia of Industrial Chemistry:

Introduction
Acetaldehyde (ethanal), CH3CHO [75-07-0], was observed in 1774 by Scheele during reaction of black manganese dioxide and sulfuric acid with alcohol. Its constitution was explained in 1835 by Liebig who prepared pure acetaldehyde by oxidation of ethanol with chromic acid and designated this product “aldehyde,” a contraction of the term “alcohol dehydrogenatus.”
blah blah

Physical Properties
Acetaldehyde, C2H4O, Mr 44.054, is a colorless liquid with a pungent, suffocating odor that is slightly fruity when diluted.
bp at 101.3 kPa = 20.16 °C
Relative density = 0.8045-0.001325T (T in  °C)
blah, blah.. 
Acetaldehyde is completely miscible with water and most organic solvents. It forms no azeotrope with water, methanol, ethanol, acetone, acetic acid, or benzene. Binary azeotropes are formed with butane (bp –7 °C, 84 wt % of butane) and diethyl ether (bp 18.9 °C, 23.5 wt % of ether).

Production
For the production of acetaldehyde, ethanol can either be dehydrogenated or oxidized in the presence of oxygen. Between 1918 and 1939, dehydrogenation took precedence over oxidation because of the simultaneous production of hydrogen. Later, however, the catalytic vapor-phase oxidation of ethanol became the preferred process, probably because of the long catalyst life and the possibility of recovering energy.

Dehydrogenation of Ethanol:
In the first work on ethanol dehydrogenation, published in 1886, ethanol was passed through glass tubes at 260 °C.

CH3CH2OH(l) ^__> CH3CHO(l) + H2(g)

Improved yields are obtained in the presence of catalysts such as platinum, copper, or oxides of zinc, nickel, or cobalt. In later patents, zinc and chromium catalysts [34], oxides of rare earth metals [35], and mixtures of copper and chromium oxides [36] have been reported. The lowest amounts of decomposition products are obtained using copper catalysts. Frequent regeneration of the catalysts is required, however.

Process Description:
Ethanol vapor is passed at 260 – 290 °C over a catalyst consisting of copper sponge or copper activated with chromium oxide in a tubular reactor [37]. A conversion of 25 – 50 % per run is obtained. By washing with alcohol and water, acetaldehyde and ethanol are separated from the exhaust gas, which is mainly hydrogen. Pure acetaldehyde is obtained by distillation; the ethanol is separated from water and higher-boiling products by distillation and flows back to the reactor. The final acetaldehyde yield is ca. 90 %. Byproducts include butyric acid, crotonaldehyde, and ethyl acetate.

Oxidation of Ethanol:
Oxidation of ethanol is the oldest and the best laboratory method for preparing acetaldehyde. In the commercial process, ethanol is oxidized catalytically with oxygen (or air) in the vapor phase.

CH3CH2OH(g) + 1/2O2 ^__> CH3CHO(l) + H2O(l)

Copper, silver, and their oxides or alloys are the most frequently used catalysts.

blah,blah...

El_Zorro:
1)Patent links can be written [patent]patent number with no space between letters & number[/patent].

2)What nefarious use has a masked warrior for acetaldehyde ?
If it's for acetic anhydride, maybe you should just go the more direct ketene route since the equipment requirements don't seem that different..hmm ?

[roger2003]

Acetaldehyde is very important for the biotransformation of PAC an L-Pac (benzaldehyde + acetaldehyde)

Can you post the references from Ullmann ?

[Aurelius]

Post 427759

(SpicyBrown: "Re: i did read, after a google search, that...", Chemistry Discourse)

[El_Zorro]

Ha!  That info makes me very happy, Mountain Girl.  I guess all I gotta do is stick the post-reaction mix in a hot water bath and distill off the acetaldehyde.  And the fact that this method seems to give the catalysts a shorter life isn't much of a stumbling block, either.  With copper as a catalyst, and the form of copper being a $1 scrub pad, then the catalyst is cheap to purchase, and it's obvious when there's a large buildup of the oxide, because it's green.

Mountain Boy:
No, I'm not going to use the acetaldehyde for acetic anhydride production.  But I'm going to be a little tight-lipped about what I am going to use it for.  Sorry, but the masked man does have to keep a few secrets.

[ragnaroekk]

temperature: 270°C
catalyst: copper coprecipiated with zinc on celite or pumice and reduced with hydrogen (ammonia should work also for prereduction). Scrubber pads work - it depends on the amounts of acetaldehyde you want to make in the end.
setup: EtOH boiler -> nozzle -> reaction tube -> condensor for condensing EtOH -> into water for to get the a-dehyde -> either catching the very pure hydrogen over water or better end the line with an  -> aspirator. Closed line, the sucking of the aspirator and the nozzle as flameback arrestor make this very easy and safe. Plain drinking alcohol can be used (I use cheap vodka) the water doesnt hurt but help in the reaction. I don´t know if denaturated alcohol is useable - depends on the denaturants, I use vodka (predistilled) thats ok for me.
Yield per pass is uninteresting - this runs alone overnight, no problem. Interesting is IMHO the fact that at 270°C selectivity is over 95%. The best workup is the one that has not to be done.


the information for this was taken from patents (posted elsewhere already) and most helpful was this:

Anorganisch-chemisches Institut der Technischen Universität München
Hochselektive Katalysatoren
zur Gasphasendehydrierung
von Alkoholen
Markus Ludwig Gitter
Teiweiser Abdruck der von der Fakultät für Chemie der Technischen Universität
München zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
genehmigten Dissertation.
A.D. 2002

And it won´t be acetaldehyde Mr. Zorro is after but some more substituted or to substitute compound. There are nice reactions in the tube available for this purpose. Dehydrogenation - oxidation couples and else. Tz, tz.... secrets, secrets....

[roger2003]

You have specifications for preparing the (Cu/Zn/Silica)catalyst ?

[El_Zorro]

I was thinking that two boilers might be required, one for the EtOH, and one for the H2O, because I'm not sure the azeotrope that would distill out if you just used a mix of EtOH and H2O would contain enough water vapor to adequately drive the reaction forward.  In the patent that I linked to, they said that the reaction works without water vapor, but with lower yeilds.  They theorized that it was because the formed hydrogen just rehydrogenated the formed aldehyde.  So as long as there's enough water vapor present, according to them, you get 95%+ yeilds of the aldehyde.

So what, just two 5 liter flasks connected to a custom Y adapter, which in turn is connected to a 24/40 jointed tube, which is packed with copper-coated scrub pads.  This tube is connected to a condenser, which has a vacuum adapter hooked up, with another 5 liter  flask as the reciever.  Using denatured alcohol, the only real byproduct produced that I can think of would probably be formaldehyde, from the dehydration of methanol.  Other than that I don't think there would be any real problems.  Denatured alcohol costs a few bucks per gallon.  Tap water could be used.  Both five liter boilers would be filled half-full, as is good pracice for any flasks with boiling liquids.  They each have their own heating mantles, and they boil their contents up into the reactor tube, which has a heating mantle around it.  There are mantles mad specifically for tubes, but now it seems that heating mantle tapes are becoming more popular.  Whichever one is used, it doesn't matter.  So according to , then the reactor tube temp should be 270°C, and then the water, acetaldehyde, and any excess EtOH is condensed in the condenser.  When the run is finished, the reciever flask is put on a heating mantle, and slightly warmed.  I was wondering if distilling the acetaldehyde through a NaOH drying tube would hurt the acetaldehyde in any way.  If so, other drying agents could be used.  So the acetaldehyde is distilled, and kept in a well-sealed container.

The method of acetaldehyde production on Rhod's site says that acetaldehyde has to be polymerized in order to be stored, because it's so volitile, it will evep through just about any kind of lid.  I was thinking that just putting it in a glass container, like a 20L carboy,  and cutting out a little section of rubber to use as a gasket, and make sure you cap it tight.

The only other thoughts I had on this is, the amount of cooling that would be needed at the condenser for this.  If the acetaldehyde was going to be condensed there along with everything else, then the cooling water used would have to be cold, and stay cold, (below 20°C) which would take a lot of ice for a recirculating pump, given the amount of water that has to be cooled.  And then the reciever flask would have to be kept in an ice/water bath.  So I think that if my little setup worked, then it would be fine for a fairly medium-scale operation, but not for a continuous large-scale operation.  If that patent is right, then running a few liters of EtOH through in one overnight run would give a few liters of acetaldehyde to be distilled the next day.  Then it could be put in a 4L glass bottle and stored in the freezer.

What are you other bee's thoughts on this?

[ragnaroekk]

Exactly because of the extreme volitility of the a-dehyde I would recommend to bubble the acetaldehyde in cold water first and to distill it later what makes the procedure much easier as you don´t need and low-temp condensor dring runtime of the tube but only during the following distillation. And you would have to redistill anyways for an anhydrous pure product.
Why did you mention the oxide before? Catalyst is plain coppermetal in dehydrogenation. If a oxidative dehydrogenation would be applied (with oxygen supplied) the oxide would be the right catalyst.
The precipitation of the copper/zinc on celite is so easy and does not call for anything hard to get that I couldn´t understand not to use it. Surface area and activity - no need to say more. But it´s your choice of course. You need to oxidate and reduce your scrubberpads in the tube for getting results worth mentioning after my experience. (I tried it with thin copperwire before doing it right).
The use of a separate steam boiler is absolute right and recommended! Damned are there no secrets on this world?    
Think "Venturi nozzle"  or the steamboosters in industry.

this principle:



You may say I complicate it in a unnecessary way. Maybe. The advantages are some safety added (flameback function) and most important a constant ratio of mix of steam and EtOH independent from the pressure of both (over a limited range of course). This helps for a constant temperature in the tube as the temperature depends mostly on the amount of water (steam) passing through.
I admit this aims for a device which runs unwatched overnight or even longer. If it isn´t intended to use it in such a way it may be made more simple, agreed.

Zorro: The dimensions of the tube in a setup you described are 80mm length and 22mm inner diameter. Don´t forget the fucking nozzle! Open path between EtOH boiler and tube is an absolute no no!
Also the glassblower isn´t needed here - ask your plumber. This is metalwork IMHO.

[roger2003]

@ ragnaroekk

I found the link to your ref. dissertation:

http://tumb1.biblio.tu-muenchen.de/publ/diss/ch/2002/gitter.pdf

[El_Zorro]

I mentioned the oxide before because if plain copper metal was used, then eventually it would become contaminated with oxides and hydrates from reacting with the steam.  All I was saying was that it would be easy to know when it was time to recharge the catalyst, because the oxides and hydrates would most likely be a green color.  Pretty fucking obvious.

And I just had a thought.  Wouldn't it make it a hell of a lot easier to manufacture acetic anhydride if instead of bubbling a gas into GAA, and guessing when the reaction was complete, you poured an excess of liquid acetaldehyde into GAA?  IMHO, that would make it much easier, since the BP's for acetaldehyde and acetic anhydride are fairly far apart, it would make the separation of the two much easier than trying to separate GAA and acetic anhydride.  Just a thought.

[roger2003]

Degussa H 1201
Fixed Bed Catalyst - Copper/Chrome on Silica 
  
Description 
H 1201 is a highly active Cu-Cr catalyst for dehydrogenation of alcohol to carbonylic compounds or hydrogenation of ketones to alcohols, respectively.
The special silica carrier will not lead to dehydratisation reactions.
H 1201 is also available in smaller sizes.
 
Active Component (s)  Cu,  Cr 
Shape Granules, 4 - 7 mm
Support silica

Infos:
 

http://www.degussa-catalysts.com/catalysts/reactions/solution/reactions.html

See also:

Patent US3956475

Dehydrogenation of Alcohols to Aldehydes or Ketones
Fixed Bed Catalysts 
 
EtOH --> acetaldehyde 
 
Comments to reaction scheme:
Primary and secondary alcohols can be dehydrogenated to give corresponding aldehydes and ketones. The type of catalyst depends on the alcohol. Slow poisoning may occur due to side reaction products and water. The reaction can be carried out in vapor or liquid phase.
 
Base metal: Copper chromite, Copper alumina, ZnO/CuO catalyst choice depends on reactant)
 
Conditions
Temperature range [ºC]  200-450 °C
Pressure range [bar]  1-3
 
 
 
References:
Weissermel, K., Arpe, H. -J., Industrielle organische Chemie, 4. Auflage, Weinheim, VCH, 1994
Peloso, A.; Moresi, M.; Mustachi, C.; Soracco, B., Can. J. Chem. Eng., 57(2), 1979, 159-64
Henry, J. P., Marcinkowsky, A. E., US 4220803
Teichner, S., Echevin, B., US 3956475
Gifhorn, A., Rabl, H.-P., Meyer-Pittroff, R., DE 19640604

[Disciple]

This seems the easiest way, for me at least.
A while ago in the holidays i converted an old 5L stovetop pressure cooker into a dodgy solvent still (Moonshine? :-P ) yeh well, This was achieved by brassing on a 20cm length of approx inch diameter copper pipe, to help purity/separation. at the top of this was soldered a reducer to a smaller diameter 6M length of copper piping(i'd recommend longer, and a decent width,its amazing how much shorter it appears after its coiled). this was then siliconed through a bucket   filled with ice water as coolant. When my thoughts turned to   the synth of acetaldehyde, it seemed the perfect apparatus. simply have a lenght of uncoiled pipe before the major condensing part and with this section running over your hot stovetop either in an oil bath or for those confident/foolish ones straight over the gas flame.
PRECAUTION make sure all joints are sealed, and ensure condenser outlet is far from any naked flames preferably venting into water for redistillation later. This apparatus allows the quick, easy production of acetaldehyde.
 
What would other bee's recommend to flush out oxides? preferably added to the mix periodically while distilling. Thinking an acid, (phosphoric,oxalic). Hmmm

{disclaimer} I can't guarantee the safety for anyone less than a perfectionist. Not that i'm guaranteeing the safety of anyone.

[roger2003]

Apparatus for the conversion of alcohol to carbonyl compounds

Patent US3284170

[psyloxy]

Acetaldehyde from ethyl toluensulfonate

Yield     89% 
Reagent   O2   
Catalyst  CuCl/kieselguhr   
Solvent   hexane   
Time      45min
Other     heating

Ref: Hashemi, Mohammed M.; Beni, Yousef Ahmadi; JRPSDC; J.Chem.Res.Synop.; EN; 7; 1999; 434 - 435

[cha0sad]

[stratosphere]

what is wrong with a EtOH/HOCl synth of ethanal?

in practice i have gotten decent yields using H202 with a catalytic amount of HCl (about 10%mol ratio HCl:H202) and then distilling off the ethanal, smells barfingly strong of over ripe fruit.

a fair amount of glycol is also formed but  distillation easily seperates the 2.