After reading 10finger's post in the nitric acid thread about using his catalytic reactor to produce aldehydes from alcohols i decided to do some more research. According to what i found it should be fairly easy to do this conversion as all that is needed is a stream of alcohol vapors over a heated copper catalyist. I constructed something that was similar to a distillation rig out of some copper gas tubing, and .5" galvanized pipe nipple as the catalyist tube. If anyone is interested i will give specific dimensions of the setup. I used strands of copper from a copper pot scrubber as the catalyist. Anyways i took some denatured alcohol solvent that i had on hand (which is roughly 95% ethanol, from what i gathered from the MSDS on it) and ran it through the rig. i found that i got many bubbles at the receiving vessel when i heated the catalyist pipe as the distilled alcohol had collected for a bit. unfortunatly i could not get the reaction self-sustaining and i had to heat the catalyist during the whole process. the liquid that i got after this unfortunatly had a boiling point very close to ethanol and not the 70F boiling point of acetaldehyde that i should have obtained per the reaction:
CH3CH2OH --> CH3CHO + H2
my best guess is that bubbles observed in the receiving vessel came from the hydrogen being produced. unfortunatly, the boiling point of the liquid that came over was not characteristic of acetaldehyde nor was there a pungent fruity, apple smell that some have described.
WTF? wheres this guy getting all this from!? ... heres a link that has some useful info on it <a href="http://www2.cemr.wvu.edu/~wwwche/publications/projects/large_proj/Acetaldehyde.PDF" target="_blank">http://www2.cemr.wvu.edu/~wwwche/publications/projects/large_proj/Acetaldehyde.PDF</a>
so why didnt this work out the way we wanted it to?
i'm guessing that the effiency of the catalyist was not high enough to produce a siginifant amount of acetaldehyde, and the condenser was cold enough, it remained around 50-60F during the whole operation and the receiving vessel was placed in an ice bath, so i dont imagine that the condenser was to blame. if i can find a source of methanol i'll try that to see if i can get any formaldehyde out of it.
I've also read about a lab demonstration where a copper penny is heated by a torch and placed over some alcohol vapors and it carries out a similar process. i preformed this experiment myself using a coil of 14 guage copper wire which i placed in a stream of ethanol vapors coming from just the boiler in my contraption. I quickly found that red hot was TOO hot and ignited the vapor stream (instant flamethrower!) the required temp. seems to be just below red hot, and when i placed the coil in the stream it had a "shimmering" appearence and the ethanol vapors which were visible in the air could not be seen after the coil was placed in the stream. i let the coil cool outside the stream and placed it back in cool and the shimmering effect was not seen and the ethanol vapors could still be seen in the air.
my conclusion: that the coil did catalytically convert the vapor and it was a self sustaining reaction where the coil did not need any extra heat to keep things going. the reason for the vapors not being visible could be because they were converted to a vapor of a MUCH lower boiling point.
I beleive that this process should be feasable on a lab scale, however i have found little information on the subject as far as catalyist configurations, dimensions, and other specifics. any suggestions/links would be very appreciated because im out of new ideas to try at the moment.

You are going to have lots of trouble condensing CH3CHO. It's too volatile to easily condense. Any CH3CHO that you produced probably escaped your condensation unit as a vapor. Try dehydrogenating CH3OH. Formaldehyde is much easier to condense.

<small>[ August 06, 2002, 05:36 PM: Message edited by: Pu239 Stuchtiger ]</small>

After consulting some literature i found that pure formaldhyde has a boiling point of -19.5C and acetaldhyde has a BP of 20C. As i dont have access to dry ice i dont think i'll be able to get formaldhyde to fully liquify, although i figure i can bubble the vapors through some water to produce a solution (or into an ammonia solution to just produce hexamine!). I think the next trial i do i will fill my condenser( which is simply a large ~1gal tin with some coils of tubing in it) with ice to see if there is any improvment that way. Even still i need to work out the problem that it seem that a large portion of the ethanol was not converted the first time through, based on the BP of the liquid that i get out of it. I'm thinking of arranging it so that the condenser is above the catalyist pipe so i have a sort of reflux arrangement. the hydrogen comes out of the top of condenser(hopefully along with the acetaldhyde vapors) as the unreacted ethanol falls back down to the catalyist. the only difficulty i can forsee in this case is warming the water in the condenser to above the BP of the acetaldhyde but maintaing it below the BP of the ethanol. When i get around to it i think i'll give this a try.

Fuck. That was stupid of me not to look that up.

I have studied this problem to a small extent a few years ago as it applies to formaldehyde production. I have proposed a prototype catalytic process based on the available industrial information, but I have not built it. I am going to assume that acetaldehyde synthesis will require similar conditions to formaldehyde synthesis.

Your first consideration is the reaction temperature. I have here a proposed rxn temp of 300-400 degrees C, and I have another reference that suggests 450-650 degrees C. That is quite hot and will require plenty of heating if using a torch. My prototype design suggests using an improvised furnace bed for the catalyst pipe. This is just some hot burning coals packed inside either a converted grill or some bricks. Basically this setup allows you to run a length of pipe through a bed of hot coals. How long the pipe should be you may experiment to find out, but keep in mind the contact time of alcohol over the catalyst should be about 0.01 seconds.

Your second consideration is the choice of catalyst. Copper sponge is quite coarse, so this will reduce your relative contact time. You can compensate by slowing down the gas flow, or increasing the length of the pipe. Again, experimentation is in order depending on your conditions. I doubt you have any vanadium pentoxide, or molybdenum oxide laying around, so your best choice of catalyst is taken. This reaction requires a metal oxide and mixtures are better. There are other formulas that have been used over time, but by far the best (for a budget conscience improvised lab) is a combination of copper oxide and iron oxide along with copper and iron. The formulation I have is a mix of copper sponge and steel wool along with rust and copper oxide. You can use rusted steel wool and oxidized copper sponge to give yourself a nice catalyst. The steel wool will also increase your surface area a good bit (reducing the length of pipe needed and thus the size of a heating apparatus.

Your third consideration is the ratio of air to alcohol. It is very important to use an excess of air in this reaction, so you will need to supply some kind of forced air, or a supply of oxygen. The literature recommends reacting 30% by volume of methyl alcohol up to 50%. Industrially they can determine how effective their system is running by the amount of hydrogen they get. Your best bet is to force as much air as you can get into the system. Since every system is different, this is one of those things you have to optimize with experimentation.

Your fourth consideration is what to do with the product once it exits the catalyst chamber. A cooling bath is one way, but I would highly recommend bubbling the exit gas into a liquid solvent. Water works equally well for formaldehyde and acetaldehyde, as does the alcohol you are using. You will get unreacted alcohol anyway, so why not use it to condense you vapors. Using alcohol allows you to get a much colder bath anyway, which is quite important for acetaldehyde, less so for formaldehyde.

There are a few miscellaneous concerns you may have to address just to cover all of the bases. Safety is at the top of this list. You are working with flammable vapors, oxygen, and plenty of heat, so make sure everything is sealed tight. This can form an explosive mixture… you have been warned. For formaldehyde at least you get waste formic acid that will act to form paraformaldehyde. The presence of methyl alcohol does slow this down. I don’t know if this is a big problem on the small scale, but you now know. Sodium hydroxide is recommended to neutralize the formic acid.

There you have it. I hope this information helps you in your experiments.

There's lots of easier ways to do this, you know. First of all, acetaldehyde is available at hardware stores like the big orange store <img border="0" title="" alt="[Wink]" src="wink.gif" /> as slug killer. Nearly 100% paraldehyde (acetaldehyde trimer, depolymerized by heating)

As for oxidation of alcohols to aldehydes, check out:

<a href="http://www.rhodium.ws/chemistry/acetaldehyde.html" target="_blank">http://www.rhodium.ws/chemistry/acetaldehyde.html</a>

Also, it has been discussed and found that copper chromite is a great dehydrogenation catalyst and is really well suited for the dehydrogenation of alcohols to aldehydes and ketones. One could also use a hydrogenation catalyst like 10% Pd/C or Pt/C and agitate in vacuum, forcing the equilibrium far to the left and causing dehydrogenation of the alcohol to the aldehyde. This has been exploited before clandestinely in many advanced labs.

Two methods however that should be avoided are oxidation with KMnO4 and also oxidation with hypochlorite. KMnO4 produces carboxylic acids, in this case acetic acid (worthless waste of $ here) and hypochlorite will induce the haloform reaction to produce formic acid and chloroform, also undesired here.

If you just HAVE to go catalytic, use the hydrogenation catalysts or the copper chromite in vacuum or with oxygen. Works great and works clean.

PrimoPyro

100% paraldehyde slug killer?!
2% metaldehyde is what we've got in England! I looked into that as a source very briefly, but decided it wasn't worth the trouble.

"One could also use a hydrogenation catalyst like 10% Pd/C or Pt/C and agitate in vacuum" - what kind of temperature does this need?

Iron oxide, copper oxide, chromium oxide, vanadium pentoxide, etc are all available quite cheaply from ceramic manufacturer suppliers, as are the hydroxides.

Ouch, only two percent? Im sorry. I can mail you some lug killer if you dont think it'll be confiscated by your customs. :p

What temp? I dont know specifically, I will have to check the books and opinions at home. I know of people uysing this, but I never had to. I used other methods that obviated this entire need, so Ive never done it.

Most hydrogenation conditions run at easily reachable temperatures, ranging from 20C to 100C or so. I doubt this would be any different. I would think colder would be better once the reaction has started, because this would keep the gas pressure on the low side which will help drive the reaction forward.

Or you can use a vacuum pump of course, in which case I'd let the dehydrogenation occur to an extent, cold. Then warm the chamber, then vacuum the gas out to attain lower pressure, then re-cool the chamber to lower the pressure even more.

PrimoPyro

I don't believe I missed that at my local 'orange' hardware store... According to my Great Chemical Survey the only product I found in the pest killing aisle worth noting was poison peanuts (2% zinc phosphide, 98% inert; 4oz/$3.96). Excellent work for 4 hours of meticulous searching eh? The Survey is 2.5 years old now, so maybe it is time for an update.

I find chromium compounds quite hard to come buy on the OTC marketplace. I have plenty myself, and I can get them from chemical supply houses, but can most people? The point of the totally catalytic method is to enable the synthesis for as many people as possible for as far into the future as possible. Chromium compounds are expensive and dangerous, that means in 10 years they will be illegial if not sooner when the DEA rapes our rights again. All we have left is copper pipe and rusty steel wool.

I have never been to a ceramic supplier, but it seems a trip is in order...

Thanks for all the info you've all provided. I beleive i have most all of the 4 points that mega mentioned except for the air flow aspect.

With the limited amout of information i gleaned from searching the web i found no mention of O2 entering into the dehydrogenation reaction. I assume that it interacts with the catalyist somehow to "replenish" it or something. Currently, i have no provision for the inclusion of air into the system. As it sits now its a rather gas tight setup.

I soldered the tube from the boiler (a pint sized paint can) and used a compression fitting method to mate the copper tubing to the galvanized pipe caps which i drilled holes in. This arrangement is MUCH safer than the method i used before where i simply soldered a 3/4" copper pipe as the catalyist pipe. When i heated it up (suprise!) the solder melted and i had flames shooting out of the tube coming from the boiler... I think i'll simply drill another hole in the top of the boiler and hook up another tube from there to an air compressor, although i need to find a reliable way of regulting the air stream.

Also, another problem that introducing an air stream into the reactor is the fact that if the catalyist is heated too much, a simple combustion reaction will take place at the ignition point of the alcohol. According to MSDS sheets i dug up, ethanol ignites around 425C and methanol at 385C. This gives me a relativly narrow temperature range to work with as i have seen the required temp. is 300C at the lowest.

A cursory search for OTC methanol yeilded gas line antifreeze and wind sheild washer antifreeze as possible sources. Most wind sheild washer antifreze lists the freezing point at -25F, which is MUCH higher than the freezing point of methanol. This leads me to beleive that much of this product is simply water. I have seen little of gas line antifreeze although i suspect there are some interesting additives in it that would not be so desireable. Is there any possibility of successfully using these as they are or do i need to distill them before use?

The catalyst end of things seems to be pretty much taken care of now, as i managed to blacken some copper pot scrubbers by carefully heating them by a propane torch. I assume the black coating is CuO. I also have some steel wool "reclining" in a bath of water for a while so it will rust. There are no pottery supply houses around where i live(that i know of) so i dont think i'll be able to get something as interesting as vandium pentoxide although there has to be mail order places that sells it.

Thanks for all the info, hopefully i didn't ask TOO many questions this time around :)

It would be nice to find a way to make PE without acetaldehyde.
Anyway if you do a patent search for acetaldehyde, ethanol oxidation etc., you will find a lot of info on this subject. There are many types of catalysts that are used for this reaction but copper is probably the most readily available. IIRC the requirement is for copper and not copper oxide but perhaps at 300* the copper oxidizes so it is really the catalyst. The temperature of the catalyst is usually around 300*C. I believe that oxygen is needed for the reaction because the ethanol molecule loses two atoms of hydrogen which combine with the oxygen to form one molecule of water. In all the patents I have seen oxygen is a requirement for the reaction. If you were using the standard method of making acetaldehyde from ethanol you would use an oxidizer such as sodium dichromate or potassium permanganate.
As for the reaction times on the catalyst, .01 seconds is not very long and I have recently learned that this is a requirement in a lot of catalytic reactions of this type. I would think that the layer of catalytic material would have to be very thin to achieve this or the gas would have to be moving rapidly. In my experiments I assumed that more catalyst was better and my copper sponge was 2 or 3 inches long. This may have been one of my mistakes. I can only assume that once the ethanol is dehydrogenated to acetaldehyde you want to remove it from the catalyst surface before it can be converted back into ethanol. Or it may be that it is further oxidized to acetic acid.
Another problem with my experiment was that the condenser was not sufficient to cool the acetaldehyde from 300*C down to less than 21*C. I think that what little acetaldehyde made was mostly lost. I have since learned that one way to capture the acetaldehyde is to lead it into cold water. It would then have to be distilled out but the temperatures would be more manageable.

Sorry to tell you blazter that if you got all four of megas points you have two complete wrong, one maybe and at least one - the last you have right.

Point one:
There are for true two different ways practiced in industry. One is a dehydrogenation and the other is a oxidative dehydrogenation. The second one the oxidative resembles very much to the methanol to formaldehyde process with temperatures between 450�C and 550�C, a silver screen or bed catalyst and oxygen supplied. This process is to be run at 3atm pressure and is autotherm. Yields are up to 50% with ~90% selectivity.
The other process, a plain dehydrogenation is carried out at 270�C to 330�C with a prereduced coppercatalyst. The catalyst may be promoted by Cr2O3, ZnO or CoO, but copper alone works. Yields are due low temperature limited to 30% to 50% but selectivity goes up to &gt;95%. Heat has to be supplied but hydrogen is yielded as byproduct which is clean enough for direct use in hydrogenations.

Point two:
The right catalyst is already named. Vanadiumcatalysts are mainly useful in toluene to benzaldehyde in gaseous phase reactions as I remember.

Point three:
Excess oxygen will give you overoxidation and ruin the whole reaction.

!! The right amount of oxygen is the difficulty in the oxidative dehydrogenation and makes it not recommended for the engaged amateur. This and the higher temperature needed, the more expensive catalyst and the problematic pressure tell that dehydrogenation over prereduced copper is the way to go. !!

Point four:
Absolute right. Catch acetaldehyde in water or alcohol, hydrogen may be collected over water, rapid cooling boosts yields.

Thats it. If there are questions please ask, it is not only theoretical knowledge I can provide on this.
Sorry mega that my first post is to be this way, I cant help it.
ORG

Most of my information comes from:
"Hochselektive Katalysatoren zur Gasphasendehydrierung von Alkoholen"
von Markus Ludwig Gitter
Abdruck der von der Fakult�t f�r Chemie der Technischen Universit�t
M�nchen zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigten Dissertation. A.D. 2002

Not to worry, the conditions I described were for formaldehyde, not acetaldehyde. I stated I was just assuming (for the lack of sources at the time) that acetaldehyde would be the same. As you have so accurately pointed out, the reaction is clearly different.

About the vandium pentoxide, you can order it from

Sorry, editted to protect the source from abuse by kewls. It's easy enough to find though, a ten minute google search will give plenty of places. ~MrC.

It is usefull if you want to test the production of sulphuric acid.

<small>[ January 17, 2003, 01:38 PM: Message edited by: Mr Cool ]</small>

Most metal oxides that are useful as catalysts are also available quite cheaply at ceramics supplier's shops, including vanadium pentoxide, chromium oxide, copper oxide, etc...
A typical price for V₂O₅ is �5 for 100g, enough to last a long time!

Yes I knew one of the mods would edit the post.
It is good to keep the god damn kewls away from chem. sources.

Well anyway they are a very good chem. supplier, they can even ship to Finland!

My catalytic reactor would be in better shape if I�d just knew how to connect the glass tubing to the metal tubing of the reactor it self.

They ship to finland, too? I never knew that!
I've used them for things before too (for legal experiments), so I have a particular interest to keep the source safe! A nice, friendly chemical supplier is so rare these days...

After letting this project languish for several months I've finally managed to get together some supplies to revive it. I've been able to obtain some molybdenum oxide (MoO2) through an instructor who's sponsoring this project for me. In addition I have found several bottles of methanol gas line antifreeze quite cheaply and have several liters of it on hand. The setup has remained pretty much the same though I have drilled out the lid and have a tube for forcing air through set up. I have procured an old fish tank aerator which will hopefully give enough airflow (I measured about 500ml in 50 seconds via displacement method). On top of all this I am trying to obtain a thermocouple!

With luck I'll be able to borrow a digital cam and take some pics of the setup. Right now I'm at a bit of a loss on how to prepare the actual catalyst though. The MoO2 is in the form of a very fine black dust. I'm thinking mixing a bit of it with steel wool should be sufficient. There are also several patents that I've found which describe this process and I'll list a few of them below for everyone's viewing pleasure:

1,709,853 - Catalytic Oxidation of Organic Compounds in Vapor Phase
1,851,754 - Process of Producing Formaldehyde Through Vapor Phase Oxidation
1,913,405 - Formaldehyde Synthesis and Catalyst Preparation
2,849,492 - Unsupported Catalyst for the Oxidation of Methanol to Formaldehyde

Anyways, my instructor seemed to forget that MoO3 was called for in one of those patents which included an easy preparation. From what i've read so far MoO2 isn't all that soluable so I don't think I can "make a dilute solution of MoO3 and add to a solution of a water soluable iron salt" as was described in 2,849,492 :mad:

Anybody have any ideas for converting the MoO2 into a solid material which would work as a catalyst?

Edit-spelling mistrakes!

<small>[ March 07, 2003, 08:47 PM: Message edited by: blazter ]</small>

Blazter, I use a thermocouple for a gas appliance and a voltmeter. They cost about $5.00. You need to calibrate it to the temperature you want by finding a material that has a known melting point. For instance, for a temp of around 900C I used silver. Melt the material, insert the thermocouple and note the voltage at which the material starts to solidify.

<small>[ March 07, 2003, 06:34 PM: Message edited by: 10fingers ]</small>

OK, some good news and bad news. The good news is that I've procured a type K thermocouple. The bad news is that at present I have no viable means to measure the output voltage from it. Using a digital multimeter which was supposed to read out to .001 volt it only changed from .000 volt to .003 volt when I held a lit match under the thermocouple. According to a table I have, 3mV corresponds to around 80*C. For some reason the meter seems to be severely lowballing the reading. Right now I'm trying to find a simple circuit that will amplify the voltage to something useful. I know that it's possible to buy an IC which amplifies and linearizes the thermocouple signal, but all the outlets that have this only seem to cater to major manufacturers. :rolleyes:
Anybody have any ideas as to what sort of circuit could be developed to help me out here? I know theres a few EE people lurking about, any help would be greatly appreciated :)

You should get more than 3mV out of when holding a match under it. I just tried the one I have and it gives 12mV with a match.
IIRC when I was using it at high temps it gave out over 100mV.
There may be something wrong with your meter or your thermocouple. Try heating the thermocouple with a torch and see what you get.
You really shouldn't need an amplifier but if you do it's easy to make one out of a transistor and a few resistors. Let me know and I can give you a circuit diagram for one.

You may want to check with Omega Engineering at <a href="http://www.omega.com" target="_blank">www.omega.com</a> as they seem to be the authority on this stuff. I am eagerly awaiting their next catalog(s).

I'm pretty sure you can buy a thermocouple adapter for your meter. This will include cold-junction compensation, and linearisation, calibration etc and would by far be the easiest way to go.

I think Analog Devices do a chip for thermocouples, I seem to recall an application note with a nice little circuit. AD595 ?

Ouch! what a price - just looked it up in the RS catalogue - try NZ$200 for an adapter for -50C to 1000C <img border="0" title="" alt="[Eek!]" src="eek.gif" /> . You can buy a whole digital thermometer for half that.

*Edit - breaking news!*
Better still heres a chip from Linear Technology, the LT1025
<a href="http://www.linear.com/pub/q_srch.html?target=lt1025&pub_type=All&product_family=All&x=20&y=10" target="_blank">LT1025</a>
Have a look at the application note AN28 for some simple circuits. LT will sell online with a credit card.

<small>[ March 09, 2003, 07:05 PM: Message edited by: Tuatara ]</small>

or order AD595 as free sample from analog devices.
It works the same way as LT1025.

The cheaper AD597 has less accuracy, but has a setpoint capability (used as a on-off thermostatic control) but is also available as free sample!

<a href="http://www.analog.com" target="_blank">www.analog.com</a>

/rickard

I'm a car enthausiast and in many hi-po cars and in indy cars they use methanol as a fuel
This could be a very discrete source for buying the alcohol for this porcess in quantities above aprox 5 ltrs. As it is prolly priced by the ltr but only sold in smallest amount of something like 5-10 ltrs.

I'm not sure what impurities would exist in car grade methanol or what types of dyes but a simple fractional distilation would yield a clean relatively pure product.

A look at the MSDS from the co. producing or selling the stuff would most probable yield the relevant constituents and their conc. If the constituents other than methanol were relativly unreactive or deemed inconsequential if reacted in the catalytic reactor, for the formaldehyde's future use, then it could be used as is for this process.

I imagine for the production of hexamine it wouldn't matter if the methaol had a small amount of dye and maby some sulfur or ethanol in it. (just pulling ideas out of the air for potential impurities)

For explosive production it may not be a problem.
Afterall we use many tech grade precursors and dyed products in the synth or our explosives.
My HCL contains a substance which turns multiple colours depending on what it is mixed with. Ie when spilt on concrete bricks is bubbles green. Works fine in AP manufacture.

Aussies can just buy a QM1526 from Jaycar/Electus for around $AUD30.. good to 1000'C apparently..
I bought 6 or so QM1538 for work, and they work fine, with nice stainless K-Types included..

Multimeter (http://www1.electusdistribution.com.au/productView.asp?ID=6402&CATID=12&keywords=&SPECIAL=&form=CAT&SUBCATID=72)

saves stuffing around with AD595's etc.

I've just attempted the catalytic dehydrogenation of ethanol. I used an approximately 80cm long piece of 6mm ID copper tubing. This was heated, most likely to a much higher temperature than 300C, over a length of about 10cm. A Bunsen and a camping stove were used.

I used methylated spirits as my ethanol source, distilling into the pipe, previously purged with argon. The output from this pipe connected to a three-necked flask, with a reflux condenser and a stopper in the other necks. A short length of plastic tubing took the gases coming out of the top of the reflux condenser into an empty Dreschel (gas drying) bottle, surrounded by a 50:50 ethylene gycol/water mixture, initially at -20C. The output from the bottle was fed back into the flames of the burners, using a copper pipe with gauze to prevent flashbacks.

My hope was that acetaldehyde vapor would not easily condense in the reflux condenser, and be sprayed into the cold Dreschel. Unused ethanol etc. would condense into the three-neck. After distilling about 1L of meths across I found approx 0.8mL of something in the bottle... quite a pitiful yield. It had a very strong smell, reminiscent of formaldehyde in some ways, it's quite hard describing smells, and I've never smelt pure acetaldehyde to compare with. I cannot be sure if it was acetaldehyde, with more I may have been able to try a decent density measurement. The best I could get was 0.7g for approx. 0.8mL but the errors there are huge. I have a feeling I have made a little bit of crude acetaldehyde with any luck.

I will try gently re-distilling the condensate which came over to see if there is any acetaldehyde in that, it's sitting in the freezer at the moment. A task for tomorrow perhaps.

After reading through some posts and webs, I have a feeling the most likely cause for the (probable) failure was absence of oxygen, as the set up I was using was suited to an oxidative dehydrogenation, as described by organikum. Also, perhaps the temperature was too high and decomposition occured, or the copper pipe as the catalyst was not best suited to the conditions.

I will try to get hold of some metal oxides and go via a standard dehydrogenation, as I do not like the idea of red hot metal, ethanol and oxygen. Speaking of the metal oxides, I have found a nice little site:

http://cssjweb.chem.eng.himeji-tech.ac.jp/jcs/v4n3/a2/text.html

Of particular interest is the table listing the selectivity of various metal oxide catalysts for dehydration or dehydrogenation. It would seem that MnO, SnO, CdO, Mn3O5 and MgO are the best, with 100% selectivity for dehydrogenation. Tin oxide is available at ceramics suppliers, however it is expensive, and I don't see the others on my suppliers site (MnO2 but no MnO)

I reckon zinc oxide is the real winner; 95% selectivity and cheap, about �5 will get you 10 times as much as ZnO as V2O5, and it's better suited to this process!

If I had to guess at your mode of failure I would say it is the pipe. The available catalytic surface is very very very low using a straight pipe. I don�t remember where the website is now, but I remember seeing some chemical engineering drawings of how this works. I think they call this setup a laminar flow, in plain English that is a straight flow. The reactants tend to stay where they are in a laminar flow as they pass through. That means the gas at the surface of the pipe remains at the surface, meaning your product (after it is formed) prevents further reactant from coming in contact with the catalyst.

The opposite of a laminar flow, the technical name of which I forget, is a turbulent flow. This causes a constant mixing of reactant and product that maximizes reactant contact with the catalyst. A turbulent flow, like a copper sponge for example, has a much greater surface area.

Thanks for the advice mega. I'm working on a large catalyst chamber (ID 28mm) which will mean cutting the original tube in half to fit it to either end of the chamber. Right now the thin tube is pretty much unsuited to cramming with anything else. The tube is bent at one end so that it curves into the condenser flask, so pushing a rod through to get things out is not possible.

The chamber should also come apart close to one end so that the catalyst sponge, oxides etc can be changed relatively easily. I can see this involving some high temperature welding in order to make a gas tight seal that will take a fair bit of heating. Hopefully I will be able to open it up with the welding torch and change the contents.

Before I make any modifications, I'm going to do a run or two with it as a ketene generator, as that's what it was originally intended for. I realise that there is catalytic action of copper in this process too, but I hope that the high temperature pyrolysis will be enough to form significant quantities of ketene. I'll report any findings in one of the acetic acid -> acetic anhydride threads.

Back OT, I re-distilled the condensate in the three-neck flask and collected a few fractions (sorry, no bp's available). The fractions smelt nothing like the substance I collected in the Dreschel bottle, so it doesnt like any acetaldehyde (if that's what it is) collected in the flask.

There are glassware supplyers that sell combustion pipes made of borosilicate glass, specially for such reactions. At least they sell em here, cheap.. one example is 40 cm long, thick walled pipe with 2 cm id..
Anyway, since those have low heat transfer, one could use just corcs with outleading pipes to connect this to the rest of the system. Theese would be easy to clean/change out.

Btw, how would one prepare "workable" catalyst from powdered? I mean, one can't just use it in powdered form, since this would most likely cake togther because of adsorbtion of byproducts (though maby not if temp is throughly controlled).

Thanks frogfot. I've just checked my catalogues and I can get similar things to what you described. They are alumina-porcelain combustion tubes, which according to my data book have a thermal conductivity of 12 to 26 W m^-1 K^-1 though I'm not sure if this means good or bad thermal conductivity, I'll have to sit down and work it out.

I've now obtained some copper plated kitchen scourers to improve surface areas. How to make a workable powdered catalyst? I've wondered about this recently and I thought that maybe one could heat the wire sponge or scourer up to a bright orange temperature and 'dip' it in a 'bath' of the oxide powder. With any luck, some oxide may stick to the wire.

I'm just guessing right now, as soon as I get some powders I'll experiment and see what I can come up with.

[Edit] I've just found that a higher thermal conductivity value means better conductivity. Copper has a value of 350 at approx 1000K, so 12 to 26 doesn't look so bad, especially as these values tend drop with higher temperatures.

[Edit 2] I've had a play around with some red hot wire and a few spare oxides I had lying around and the oxide 'bath' idea just isn't gonna happen by the looks of it. On the other hand, my tub of fire cement caught my eye and I thought perhaps one could make small balls of this and dust them with oxide before they set: home made oxide catalyst on a ceramic support!

Somebody recently posted a procedure to make lead acetate, but a byproduct of this was copper powder. You react calcium oxide or hydroxide (lime) with acetic acid (vinegar) to make calcium acetate. Mix the calcium acetate solution with copper sulfate solution (copper sulfate is sold as a root killer in hardware stores) to precipitate insoluable calcium sulfate, leaving copper acetate in solution. You will need to filter this solution to remove the calcium sulfate of course. Add lead metal (bullets, fishing sinkers, batteries, etc) to the copper acetate and copper powder will precipitate while lead is taken up as the acetate. All of the necessary chemicals, vinegar, lime, root killer, lead, can be purchased at Wal Mart.

I have also seen something called bronzing powder sold in craft stores. This is a small jar of finly powdered copper meant to add a gold finish to craft projects or be mixed with plastics and polymers to add weight and gold color. There is also a craft product called gold leaf that is actually extremly thin sheets of copper. This leaf crumbles easily into a granular powder.

What mega described reminded me of the famous 'silver tree' demonstration, where a coil of copper is inserted into silver nitrate solution, some of the copper being taken up as copper nitrate and the silver is deposited on the wire.

I had some copper sulphate solution left over from and electroplating experiment so I tried dipping a little iron wool into it. The result being fine copper coated iron wire, and I expect the copper grows a lovely crystal structure with a large surface area. I found that having the wire wool in the solution for five seconds was enough for a layer of copper to form. Ten seconds and a thicker layer forms but much of this tends to crumble off later. Anything longer than ten seconds and the entire structure is crumbly as too much iron is taken up. Perhaps one would be better off with coarse iron wool, but extra fine is all I have to experiment with for the time being.

After five seconds in the sulphate solution the wire was dipped into a bowl of water and then into acetone before being pressed in a towel and allowed to dry. I put a loose length of this into an old Liebig condenser, the jacket filled with crushed perlite as a heat reservoir, and used this in place of the copper tubing, in the apparatus I described above. I also decided to collect any acetaldehyde by bubbling it though water, and heating by burner was replaced with heating by paint stripper gun.

After a run of distilling approximately 500mL of meths I detected a strong smell of something unlike meths or acetic acid in the gas drying jar, it's a shame I don't have a pure sample known to be acetaldehyde to do some comparisons with. I also tried a run using some zinc oxide coated balls of fire cement with the same notable smell present in the gas drying bottle at the end.

I believe I've read somewhere that acetaldehyde doesn't form any kind of azeotrope with water so I'll try a few more runs so I have plenty of potential acetaldehyde and when I get round to some fractional distillations, I'll include them.

I read an intersting old journal article today for a precursor chemical I am adding to my website. The article concerned some early methods of catalytic reactions. As part of the published experiments the article hinted at a ketene generator. I checked The Forum and The Hive for every post related to ketene generation and all seem to use varients of the method published in Vogels. That being nichrome wire.

From experience I can say it is rather difficult to reliably get a catalyst wire to stay at red heat over extended periods of time. Most people don't have the electrical equipment or the nichrome to try either.

The following method seems more applicapable to a wider audience. The catalyst of choice is alumina on pumice (volcanic rock available at any landscaper or hardware store that sells landscaping or gas grill rocks). The pumice is broken down to 3-5 mm sized bits and soaked in a saturated solution of aluminum sulfate. It is then washed with ammonium hydroxide (household ammonia) to precipitate alumina on the pumice. The catalyst is dried by strongly heating.

The catalyst is loaded into a suitable pipe and heated to 500 C. Acetone is passed through the pipe in the usual manner and forms ketene. A blowtorch can heat a steel pipe to 500 C in about 40 minutes in my experience.

This exact same setup can make a variety of chemicals just by varying the reaction temperature and the starting reagent. Ether for one can be made by passing ethyl alcohol through at 240-260 C. At 300-350 C you get ethene. Mixing ammonia and carboxylic acids at 500 C will yield nitriles.

Does anyone think this setup could also work for the production of formaldehyde from methyl alcohol? The temperature would have to be high enough to avoid the formation of dimethyl ether...

There is no catalyst for the pyrolysis of acetone to ketene. This requires plain high temperatures, 650�C to 800�C. Aluminiumsulfate for example is told to suppress further decomposition, thats the function of it.
A good a working way to do this is to use a coppertube either with small diameter say 3mm and about 70cm length or with larger diameter and filled with porcelain shards (10cm length, hot zone). A batwing propane burner should suffice, it suffices for sure with the small diameter tube which is safer too.
The trick is cool down the ketene to below 500�C as fast as any possible to prevent polymerisation. If you want acetic anhydride venting the ketene directly into acetic acid at about 80�C to 100�C is ok. The excess acetone distills out immediately and can be condensed for reuse. The ketene reacts with the acid to form the anhydride. At this temperature this reaction is fast.
Scrubber and ventilation are a must have at the end of the line. Ketene DOES NOT react fast with cold water! So scrubb with hot water and dont forget the methane....
Iron and nickel as noble metals catalyze the complete decomposition of the acetone and are to be avoided. This is well documented in literature.
Yes I know Vogels ketene-lamp, but I know also nobody who got this working in a way which produces more than traces of ketene. But I know that the porcelain-shard filled tube and that the small diameter copper tube work well.

Methanol to formaldehyde goes by silver precipitated onto copper, copper scrubpads are ok. Copper on iron or better zinc works too, but with lower yields. The surface area made by precipitation from a metal-salt is the key.
Temperature is lower here, about 500�C.

I thought the usual method of producing ketene was the pyrolysis of acetic acid (rather than acetone) in the presence of AlPO4 at 700�C. I have, however, seen a reference to the use of acetone instead. To produce it from acetone would involve the loss of a -CH3, which requires more vigorous conditions. It is used chiefly in the manufacture of acetic anhydride by reaction with another molecule of acetic acid (which is why acetic acid is the preferred starting compound), and in the manufactire of aspirin.

Bugger.

Both, acetic acid and acetone are used for producing ketene, the process is almost identical. For the interested amateur acetone is the favored starting compound as costs are not so important here as in industry where acetic acid is preferred for being cheaper.
The acetic acid process has the disadvantage of producing water as byproduct which reacts with the ketene back to acetic acid if not separated quickly.

Ketene is useful for production of diketene whats more stable, acetic anhydride as described above and it can be used in Grignards directly. Just some examples.