Sciencemadness Discussion Board - Gas-phase apparatus construction

Gas-phase apparatus construction

picketfence - 15-1-2007 at 13:38

http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...

Has anyone ever constructed this?

The article details a safe gas-phase apparatus for the pyrolysis of acetone to ketene - which is not what I'm interested in particularly due to the fact that if I needed acetic acid I'd just use vinegar and I have no requirement for the anhydride. Rather I'm wondering if there are any issues with the actual construction of this apparatus.

Where would you get a combustion tube suitable? and the choice of glass isn't exactly perfect for my liking - quartz would be better/safer.

You could construct a quartz combustion tube with a quartz tube with a short section of narrower diameter quartz tube (as found in radiator heaters) at each end for the inlet and outlet and adhere these with industrial high temperature adhesive.

In the diagram, what's 'B' called? Why is there a stopcock used above B, which collects the unreacted acetone?

Why is there a three-way stopcock used at the far right?

[Edited on 15-1-2007 by picketfence]

Magpie - 15-1-2007 at 21:00

I have never tried to make ketene but will take a crack at a couple of your questions.

The stopcock at "B" would be mostly closed as you collect acetone above it then open it periodically to drain the acetone. Or perhaps it could just be "cracked" open to keep a liquid seal. If you just left it open you would blow out everything including the gaseous ketene. Edit: Actually that valve looks more like a needle valve, which would allow fine adjustment for draining the acetone yet keeping the liquid seal.

I imagine the 3-way valve at the far right is to allow you to vent the product gas to the atmosphere at start-up until you're ready to start absorption. Also it could serve as a vacuum breaker at shutdown to avoid any suckback.

What do you mean by:

Quote:

You could construct a quartz combustion tube with a quartz tube with a short section of narrower diameter quartz tube (as found in radiator heaters) at each end for the inlet and outlet and adhere these with industrial high temperature adhesive.

[Edited on 16-1-2007 by Magpie]

Thermal - 15-1-2007 at 21:35

IMHO setups using an electrically heated filament are much preferable.

Sauron - 16-1-2007 at 13:24

The electrical ketene or butadiene lamps suffer from fairly rapid carbonization of the filament so that in practice to keep one running (their output is SLOW) you need a spare filament assy to cgange out while cleaning the crudded up one.

The combustion tube approach is not very safe IMO if you are using open flame burners for obvious reasons but then safe and ketene are two words that can't really be concatonated without destroying all epistomological value of the sentence.

A tube furnace of appropriate length and ID and temperature range is a better way to go. These are often available very cheaply on LabX (I was only bidder on the auction in which I got mine, for the opening bid $70) and I agree that a quartz tube is a far better idea than pyrex for an operating temperature c. 700 C. You might consider Vycor though which will be adequate and ought to cost way less than quatrz, be easier to fabricate connection to and have superior mechanical qualities. The furnace I won for $70 accepts up to 2" OD tubes, is 12" end to end and has a top end of 1100 C.

[Edited on 16-1-2007 by Sauron]

[Edited on 17-1-2007 by Sauron]

[Edited on 17-1-2007 by Sauron]

307873-0m.jpg - 26kB

Magpie - 16-1-2007 at 14:28

Sauron you did indeed get a sweet deal.

I have been occaisionally checking out the tube furnaces on ebay, but they are either too expensive or don't get the temperature I want. It seems the breakpoint is 1100-1200C and I'm looking for 1300C. I have a plan for a homemade tube furnace but it won't be cheap either. It would have a clamshell design. It would use a 1648C castable Mizzou refractory in the center and a Kast-O-lite type material in the annulus (or a castable insulating brick). The container would just be a 16 gallon steel drum. I'm thinking it would be about 18" long and have a bore of around 1.5". It would use Kanthal A-1 elements operating at their maximum allowable temperature. It would have a programmable PID controller and TC for temperature control.

Edit: Corrected refractory temp

[Edited on 17-1-2007 by Magpie]

picketfence - 16-1-2007 at 22:50

sauron you really did get a good deal, what's the inner diameter? It looks rather large! (too large?)

Sauron - 16-1-2007 at 23:18

The ID is 2" (5 cm).

It's 1350 W and draws 11 A @ 110V. My mains are 220 so I put a rather larger stepdown in between that is rated for 3 KW so I don't expect any trouble.

[Edited on 17-1-2007 by Sauron]

307873-1.jpg - 17kB

Fleaker - 17-1-2007 at 19:38

Good price. Those are usually about 3,000 USD for the ones that get to 1200C. I use two such pieces of equipment in the laboratory I work at. One is used for prepping catalyst, other for pyrolysis.

garage chemist - 11-8-2007 at 16:22

I made Ketene a few hours ago by the tube furnace method.
It worked surprisingly well, I didnt use any packing in the quartz tube, just an empty tube at 700°C and acetone vapor.

The ketene was lead into water in order to hydrolyze it to acetic acid and prove the succes of the method.

Here's the acetone evaporator:

The exit end of the furnace, with the excess length of the tube serving as cooling zone (too long, but still worked):

The condensation apparatus to condense unreacted acetone: the vapors are fed into a RBF with a dimroth condenser, the acetone collects in the RBF and the ketene is withdrawn from the top of the condenser:

700°C in the furnace, a dull red glow, the digicam makes it look violet due to its sensitivity to infrared which is emitted in large amounts:

Upon starting to evaporate acetone, a white fog started to appear in the apparatus, and a brisk gas stream is noticed in the washing bottle:

20ml acetone were fed through the furnace, of which 7ml were recovered unchanged in the RBF (less than should be (60-80%), so the speed of distillation was probably somewhat too slow).
The water in the washing bottle definately became acidic! There was some gas evolution when some CaCO3 was added to it, therefore proving that ketene was being generated in this setup.

No soot or coke formation occured inside the tube! The reaction was very clean.

The exit gases from the washing bottle (methane, carbon monoxide, ethylene) were very flammable and burned well.

I carefully wafted the exit gases in order to find out how ketene smelled like. BIG MISTAKE! There was so much unhydrolyzed ketene present that I choked and coughed, it felt like chloropicrin minus the eye irritation. Ketene is a really obnoxious lung and respiratory tract irritant. I also had a stinging sensation in the chest for some time afterwards. Lets hope no delayed toxic effects will follow.
The Ketene also had a very unique and strong acrid smell.
In order to hydrolyze ketene, a washing bottle with sintered glass gas bubbler would have probably been better than a simple washing bottle.

Before any synthesis can be done with the ketene generated by this setup, the corks will have to be replaced by something more gastight.

[Edited on 12-8-2007 by garage chemist]

Magpie - 11-8-2007 at 20:32

Very nice GC! We have been talking about making ketene for years but this is the first time someone has actually done it, IIRC.

garage chemist - 12-8-2007 at 12:32

Yes, it seems like I am the first to make ketene at home and document it. I saw some pictures of a homebuilt ketene lamp in another thread, but it didnt appear to have worked.
The tube furnace method is without a doubt more suited to obtaining useful amounts of ketene than the lamp, and can be run nonstop for 24 hours or more should the need arise (e.g. when gassing acetic acid) without having to change filaments.

I'll try to make acetanilide with the ketene when the teflon endpieces for the quartz pipe are ready. I'd like to use another solvent than ether, since most of the ether will probably be evaporated out of the washing bottle due to the stream of inert gases.
Acetone springs to mind, since ketene has a high solubility in it.
Ethyl acetate would also be a good choice. But both also dissolve acetanilide well, making some sort of workup necessary before the acetanilide can be weighed and yields calculated.

[Edited on 12-8-2007 by garage chemist]

Fleaker - 12-8-2007 at 16:25

Bravo! Now I'm interested, I'd like to give it a shot as well. A clean reaction eh?

I still need to finish up the SO3 work though :-\

bio2 - 12-8-2007 at 17:26

....."Acetone springs to mind, since ketene has a high solubility in it. "..........

Wouldn't this react to isopropenyl acetate.

garage chemist - 12-8-2007 at 21:47

Obviously not, otherwise the ketene would react with the unreacted acetone (about half of the used amount), either in the hot or in the cold zone or in the RBF...

EDIT: I looked it up. Isopropenyl acetate is actually made from ketene and acetone, but a strong acid catalyst is required.
Its absence in my setup is surely the reason why the ketene does not react with the acetone.

[Edited on 13-8-2007 by garage chemist]

not_important - 12-8-2007 at 22:05

Quote:

Originally posted by bio2
....."Acetone springs to mind, since ketene has a high solubility in it. "..........

Wouldn't this react to isopropenyl acetate.

Takes a catalyst to get much yield, H2SO4 is often used. In cold acetone ketene dimerizes and also forms dehydroacetic acid ( 3-Acetyl-6-methyl-2H-pyran-
2,4(3H)-dione, 3-acetyl-6-methylpyran-2,4-dione), SMILES O=C1OC(=CC(=O)C1C(=O)C)C as well as isopropenyl acetate, acetylacetone, and others. Acetyleacetone is also a byproduct of making isopropenyl acetate.

bio2 - 13-8-2007 at 13:54

So, is there any way to stabilize the ketene in a solvent
for short term storage?

not_important - 13-8-2007 at 16:11

SFAIK it reacts with itself within a few hours, it's pretty much a make-it-use-it reagent.

garage chemist - 13-8-2007 at 17:01

On Orgsyn they said it can be stored up to two weeks when liquefied at -80°C:
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5...
It might be stored somewhat longer at liquid nitrogen temperatures.
Also, only the pure ketene gas obtained by cracking diketene is suitable for liquification, the gas prepared from acetone is of course saturated with acetone vapor along with all the other gases it contains.

Ketene has high solubility in acetone (thats the reason why the condensed unreacted acetone should be kept close to its boiling point in the RBF, to minimize ketene loss by dissolution), but it dimerizes completely to diketene overnight, which is a way to prepare diketene in the lab:
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3...

Diketene itself is only stable up to a week, dimerizing a second time to dehydroacetic acid and becoming an orange to brown tar.

Ketene is, just like ozone, a reagent that is best made as needed. Once the apparatus (ozonisator + high voltage source for ozone, and pyrolysis setup or "lamp" for ketene) is made, it is very easy to create a constant stream of the gas.

chemrox - 19-8-2007 at 00:25

I had given up the idea of making it- now I'm reconsidering .. what is the furnace you're using?

garage chemist - 2-9-2007 at 00:55

Its a simple selfbuilt furnace, Ytong (expanded concrete) as the body, covered with refractory mortar on the inside and with 80/20 NiCr 1mm wire as the heating wire in four spirals. 2000 Watt at 230V. Power is regulated by a thyristor circuit.
The furnace did cost maybe 20€ to make, not counting the thyristor circuit and the quartz tube.
Pyrex would probably still be usable at that temperature, but you'd have to be careful to avoid big temperature gradients.

Touche

NERV - 6-10-2007 at 16:43

Awhile back me and Fleaker decided to try garage chemist's acetone pyrolysis to ketene. It worked pretty well. We used one of his swagelock stainless steel reaction tubes and packed it with really fine copper wool. We then filled a RBF with acetone and put it in a mantle and hooked it all up to the reactor tube and set it to bake at 700 celsius. On the product side we set up dual cold water condensors set up reflux style to collect any acetone. The ketene went through and into a gas washing bottle filled with some glacial acetic acid. All of that was in a big beaker filled with ice, which helps the ketene absorb better and saturate the acetic and react. All of the leftover ketene went into a second wash bottle filled with water. Fleaker titrated the slightly acidic solution and found out that it was 0.330M and this was from the second wash bottle. All this tells us was how much ketene escaped to hydrolyze in the second bottle. pH was 3.8 on that solution.

There was a lot of gas produced, and it moved quickly through the system like a gray cloud. This of course was out ketene, ethylene, and carbon monoxide which are byproducts of the pyrolysis and degradation of the ketene.

We used about 250mL of acetone, collected about 100mL of it, used 200mL of glacial acetic acid in the wash bottle, and after fractional distillation (which went shitty, but got 3 fractions) and freezing out the GAA, we got about 62mL of Ac2O. Not bad for 3 hours work, and only an hour of that was spent pyrolyzing, most was spent setting up, titrating, and yelling at Fleaker for almost killing us.

To confirm that we were making some ketene, we took some gas samples from the second bubbler trap and did some FTIR on it and saw that we got some carbonyl in the spectrum. I don't have a scanner here, but if enough of you want the spectrum I can go scan it in. We had a huge peak of carbonyl
at~1750 cm-1, some ethylene bands at 980/1390/1880 or so, big methane at 1380 and 2980ish and a nice big 2130 for CO. 980 was the big absorption band for ethylene, the others were minor. I think the carbonyl one is probably ketene, I don't see acetone making it through two condensors and two bubblers.

I took it home, put it all in the freezer and nothing froze. I figured there's probably a shit ton of acetone and GAA in there. So I did a quick distillation.
After the fractional distillation, I put all the three fractions in the freezer. The first fraction, 30mL mostly acetone (came over at 34-84*C), next 140mL was GAA at 80-100 , then next was GAA and ~100ml GAA/Ac2O mix at 100-102. And I know that its not right--wonder about azeotropes...don't think they exist for this system??

Put all three fractions in the fridge, only the GAA middle fraction froze. Put the other two in the freezer, and the first fraction didn't freeze, took the last fraction a full day to finally freeze. Opened it up and woosh smells like Ac2O. Poured the liquid that didn't freeze and it measured it in a grad cylinder. Probably a few more mls in there stuck in the GAA crystals.

Problems with this reaction included controlling the flow rate, it seemed like about 2/5 of the acetone we put in collected in the air trap. I think the ketene should have had a longer residence time in the glacial to react more. Oh, and probably the biggest mistake was when Fleaker forgot to tighten the apparatus and we had a small fire. Dumbass.

To improve this and make it more of a continuous process I'd say you should use a large equal pressure addition funnel filled with acetone on the input side of things.

Conclusion:
Ac2O from acetone is easy and cheap, and not bad yield wise if you run it all day long.

So you all probably want pictures. We have some.

This is the input side. RBF with mantle.

This is the acetone & copper. (ya its sideways get over it)

This is the GAA.

This is the output side with RBF and condensors and the traps. Note the big beaker with ice, that's where the bubbler with the GAA went.

A shot of the titration.

Pictures of the product.

Picture of the Ac2O and frozen GAA.

Hope you all liked it.

[Edited on 22-9-2002 by NERV]

[Edited on 22-9-2002 by NERV]

garage chemist - 6-10-2007 at 17:51

Very nice, looks good! I like it!
Tube furnaces are cool, arent they? Unfortunately mine broke, I have to build a new one.
There are no azeotropes in the GAA/Ac2O system, but wou will want to use a column next time to get better separation.
You should test your product for presence of Ac2O by reaction with e.g. aniline in aqueous solution and see if it makes any acetanilide (Ac2O reacts with aniline immediately at room temp). Acetanilide would precipitate.
Did you try to smell the ketene?

Fleaker - 6-10-2007 at 18:38

Yes we wafted it and it does not smell very good. Good idea on the acetanilide. That is very easy to do.

Tube furnace insulation: Fiber or Brick?

garage chemist - 8-11-2007 at 11:46

Now that the ceramic tube has been ordered, the tube furnace project continues.
I am still undecided if I should use either ceramic fiber mats or lightweight firebrick as the insulation. Money is a minor factor, none of both offers a significant lower price than the other.
Some considerations were given in this thread:
https://sciencemadness.org/talk/viewthread.php?tid=9412
and I wish to continue the discussion here since this thread is more appropriate topic-wise.

If I use fiber mats, I would get a 25mm 1400°C fiber mat of the dimensions 820mm*610mm (the unit the shops sells the mat in).
The tube of the furnace is 50cm long and 4cm in diameter, but the outer diameter is increased by the heating wire and electric insulation paste on it, so I'll assume it to be 5cm in diameter.
If I apply two layers of the fiber mat, for an insulation thickness of 5cm, the mat piece I gave above would suffice (after cutting to size). If I had to use an additional layer, I would have to get more of the fiber mat.
Is 5cm fiber insulation enough, or would 7,5cm be more appropriate?

I could also get the same dimension of fiber mat, but with 1250°C classification temperature, for somewhat less money, so I could make the insulation thicker. Now that I think of it, this would probably be just as good as the 1400°C mat for my application. I take it that the fiber mats dont fail immediately when their rated temperature is exceeded for a short period of time?

With firebrick, there are two types I can get: both 250x124x64mm in dimension, but one for 1150°C and the other one for 1400°C. Also, the former weighs 0,9kg but the latter 2,2kg!
I would use four of those bricks (with a groove in them for the tube), giving a minimum insulation thickness of about 3cm. Sounds somewhat thin, but I could use cheap rockwool or glass wool as additional insulation if the outside of the furnace gets too hot.
What happens to lightweight firebricks if their temperature rating is exceeded slightly, say if the 1150°C type is used at 1250°C for a short period of time? Will they rapidly fail, or will they just develop some small cracks on the hot side?
And the quite heavy 1400°C ones, do they insulate less good than the 1150°C ones? Is 3cm of insulation too thin?

I'm leaning towards the fiber mat, as the construction of the furnace would be incredibly simple with it, and the furnace would be very lightweight and transportable. But I need to know how thick the insulation should be.
With the firebricks the furnace would be much more rugged and mechanically stable.

What would you use for a tube furnace if you had the choice between kaowool and kiln bricks?

[Edited on 8-11-2007 by garage chemist]

Eclectic - 8-11-2007 at 12:28

You could just wrap your heating element wire around the tube, then put it in a box or pipe with heat resistant end plates and fill the whole thing with diatomaceous earth for insulation. I found 25 lb boxes of snow white DE filter material at Home Depot for $18 each in the pool supply section. Very low density material. It's supposed to be fairly pure silica, so the upper temperature limit should be as good or better than thermal blanket fiber.

[Edited on 11-8-2007 by Eclectic]

garage chemist - 8-11-2007 at 12:49

Silica kills Kanthal wire, the manufacturer warns of this in the technical brochure for the heating wire alloys. No material containing significant amounts of free silica must touch Kanthal wire while in operation, clays and bricks touching the wire must contain at least 45% alumina.
Although I will cover the wire on the tube with an insulation paste, I'd rather not use diatomaceous earth. The connecting ends of the wire would also be in contact with the silica.

Brauer uses the kind of insulation you're proposing with MgO instead of diatomaceous earth, this would work for my furnace. But I have no cheap source for MgO, and it would probably cost more than fiber insulation in the end if I buy the MgO from one of the sources known to me.
Still a good idea.

Fleaker - 8-11-2007 at 16:14

Can't you just simply burn magnesium metal, dissolve in water to hydrolyze any nitride to ammonia, and then heat the resulting magnesium hydroxide to MgO?

not_important - 8-11-2007 at 16:29

Glad you've a source of magnesium metal that is cheaper than any of its salts.

Epsom salts and sodium bicarbonate or carbonate give basic magnesium carbonates as a precipitate. Heating these to 400 C will decompose them to the oxide, provided you have an escape route for the CO2 and H2O.

evil_lurker - 8-11-2007 at 17:03

I noticed one of the local co-op feed stores had feed grade MgO in 50lbs bags.

I didn't check to see how much it was, but I bet $30 would probably get it.

garage chemist - 9-11-2007 at 04:53

I dont have such a source of MgO, but the epsom salts and sodium carbonate (why bicarbonate? the carbonate is way cheaper here) idea would be good to make the MgO that I need for the insulation paste (a mix of MgO and Al2O3 according to Brauer- I'll probably use Al(OH)3 instead of Al2O3 since I only have that and I dont think it is necessary to convert it to the oxide prior to mixing with the MgO).

I now decided on using the ceramic fiber- the cutoffs can be used as carrier for vanadium pentoxide catalyst as shown in the SO3 preparation which I want to attempt too.

Does someone know more about the chemistry of the ceramic fibers? I found a manufacturer datasheet that list 10% ZrO2 in the 1400°C product, and the 1400°C mat contains only 40% alumina while the 1260°C mat contains 46% alumina.

not_important - 9-11-2007 at 05:43

Bicarbonate because it is the most likely to be found pure, in some regions there are no OTC sources of sodium carbonate without additives. Also bicarbonate results in a precipitate closer to MgCO3 than carbonate does, which could be important for some uses although not so in your case.

If you have patience you can wash the precipitate by decantation, you do want to wash it to remove most of the sodium.

Klute - 9-11-2007 at 14:57

You can find magnesium carbonate and/or oxyde in climbing shops (or specialized sports shops) as a talc the climbers put on their hands. Very cheap, I used to make MgSO4 with those with H2SO4, the crystals were nice and white and seemed relatively free of major contaminants other than other carbonates/oxides/chlorides etc. For your use that could be more than enough, check it out. The composition was indicated behind all the products I stumbled on, apparently some climbers prefer the oxyde, others the carbonate. They have different trivial names.
Thought it could help.

Fashist - 27-11-2007 at 01:36

bravo.bravo
finally you success.
you defeat Darn keten lamp method
really nice picture and Equipment.
What is your idea about copper tube?
after heating it wont melt plastic tube?
MAY YIELD INCREASE ?
THX

[Edited on 29-11-2007 by Fashist]

Fashist - 29-11-2007 at 09:19

No Answer?

garage chemist - 29-11-2007 at 15:30

I dont know if a copper tube is suitable. Steel and quartz work, pyrex may work as well if it doesnt become too soft.

You can see more pictures of my tube furnace here:
http://www.versuchschemie.de/topic,9256,0,-Bau+eines+Rohrofe...

This tube furnace has broken, and at the moment I dont have a suitable tube furnace so I cant do any more work with hot tubes until I have built the new tube furnace.

Fashist - 30-11-2007 at 12:21

Thanks Mr Garage Chemist.
Nice Pictures.
You Used What type of Element ?
What Gauge?
What Type(chromel,..)?
How long?

garage chemist - 30-11-2007 at 14:37

The wire is NiCr 80/20, chromel would be a trade name of it, as well as Nikrothal 80, Nichrome etc...
It has 1mm diameter and such a length (18,89m) that it takes up 2000 Watt at 230 Volt. It is wound into 1,2cm diameter spirals (four of them, each 40cm long).
The furnace is good for up to 1000°C, the wire can take 1200°C surface temperature.

[Edited on 30-11-2007 by garage chemist]

Fashist - 1-12-2007 at 11:52

Mr Garage Chemist Thanks
I Have 3 Question(My Name Should Change to Mr Question)
(?)Do you Have Problem with Carbon Dust inside Your Quartz Tube?
(?)Did you Test your Anhydrid With water?(What is it Purity?)
(?)What is YIELD or Output of Your System(ex. 1lit per 24hour or less)?
Thx

Fleaker - 1-12-2007 at 15:14

Yield per day is entirely dependent on how much acetone you put through it and how quickly. With a meter long tube furnace with a 7.6cm diameter tube inside of it, I would guess that one could make 500mL per hour of Ac2O if your system was running at its best.

Fashist - 2-12-2007 at 02:58

MR Fleaker This is Necessary to Cover all of Copper Tube with Steel? or just the Tube Inside Heater?
Thanks

Fleaker - 2-12-2007 at 10:08

You can use copper entirely copper if you want, it will just oxidize on the outside which is exposed to oxygen. We used a stainless steel tube packed with copper wool, and when we opened it, the copper was just as bright and shiny as when we packed it.

Fashist - 2-12-2007 at 10:29

Mr Fleaker you think that My picture and design for making anhydrid is wrong?
Mr not important guide me that my system wont work well.
Wat is your idea?
What ballon and how long tube and.. i should use?
What is your advise for making 5-10lit anhydrid per day?
Really Thanks

Magpie - 4-9-2008 at 19:33

This post is really about the synthesis of Ac2O via ketene reaction with glacial acetic acid. As there have been two major posts about that already in this thread I decided to continue here also.

A few days ago I tried my first Ac2O synthesis using my homemade tube furnace. I'm not sure if I made any Ac2O as I haven't fractionated the product yet. My post here is to ask for your comments on unexpected problems of goo and coke. My equipment configuration is essentially the same as that of my predecessors, garage chemist and NERV, with some subtle differences.

I purged with argon before and after the run and had no fires, and am happy with that aspect. Neither did I smell any ketene as my hood blower was doing its job.

I had to abandon my fritted glass gas dispersion tube as it caused excessive flow resistance (back pressure), so just used a straight open tube in the absorber/reactor column. I fed the furnace with acetone vapor generated on a hot (near boiling) water bath along with some argon. I tried to feed about 3 ml/min acetone to the furnace but didn't get that high a rate. Recovered acetone was 55%.

The biggest surprise was the appearance of quite a bit (1-2 mL) of a translucent white goo collecting in the inlet adapter of the tube furnace. Also there was a liquid in the outlet adapter, but off-color due to absorbed gunk (carbonized material). The inside of the quartz tube had a thin film of coke also. After thinking about these unexpected problems for a while I have come to the following conclusions:

1. The goo collecting in the inlet of the furnace was probably phthlate plasticizer leached from 18" or so of 5/16" ID PVC plastic inlet tubing by the hot acetone vapor.

2. The coke in the furnace probably was plasticizer degradation products.

3. The liquid in the furnace outlet was more plasticizer, possibly mixed with acetone.

I ripped out all of the PVC tubing and threw it away as it stunk like a BBQ gone wrong.

At first I thought that the silicone grease used on the ground glass fittings was being leached out by the hot acetone. This may be a contributor but I think it was mostly plasticizer. Next time I will use LDPE tubing.

Comments, suggestions, questions, and criticisms are welcomed.

[Edited on 4-9-2008 by Magpie]

garage chemist - 8-9-2008 at 09:08

I did not have any goo or coke deposit in the tube.
I only saw a minuscule amount of dark oily droplets in the tube after the experiment, no coke.
What was the temperature you worked at? Too high a temperature could certainly lead to carbonization. If you stayed at 700°C, perhaps try 650°C if the carbonization problem persists even after you changed the plastic parts to something that does not give off plasticiser to the acetone.

As you can see on my pictures with the old tube furnace, I did not use a hose on the inlet, I used a bent glass tube. The acetone vapor only touches glass, PTFE (from the quickfit connector) and the cork at the tube entrance.

At the outlet, I used silicone tubing.

The exit gas contained some white fog/smoke in my experiment. I suspect this to be a high-boiling byproduct that condenses into the fog form as the gas cools down from the high reaction temperature.
It could perhaps be dehydroacetic acid- this is a solid substance that is formed when two molecules of diketene react with each other. But this is just speculaion.

[Edited on 8-9-2008 by garage chemist]

Magpie - 8-9-2008 at 09:49

My tube furnace was supposed to be at 700C, but I cannot measure this directly as I was afraid to insert the TC alongside of the quartz tube. So I just set the amps at 6.2 which gave me 700C when the alumina tube was empty. Where did you place your TC when the quartz tube is in the furnace?

I have high hopes that getting better tubing, say LDPE or even glass, will solve this problem. I looked into buying some silicone tubing but no one locally has it and I would have to buy 25 or 50 feet of it over the internet. I think PTFE tubing would also be great but there again it's high cost and I can't buy it locally.

garage chemist - 8-9-2008 at 12:55

I put the thermocouple alongside the quartz tube and measured the temperature in the middle of the tube furnace, e.g. at the hottest spot.
Perhaps you really had too high a temperature. Also, if the flow rate is too low, there will also be increased decomposition of the ketene to CO and ethylene. Rapid emoval of the reaction gases from the hot zone is desirable, and the excess acetone vapor is supposed to do that.

Magpie - 20-9-2008 at 18:47

I thought I would post pictures and results of my 2nd ketene attempt for discussion. Although the operability was improved, ie, no goo in the quartz tube and less char, I still did not produce any Ac2O. I acertained this via fractional distillations and freezings of the absorbent, GAA.

This time I used 1/4" (6mm) polyethylene tubing and nylon connectors. I also inserted the TC to the midpoint of the furnace and measured a temperature range of 710-730C for the 1 hour run. Acetone feed rate was 2mL/min, and acetone recovery was 38%.

I think the low flow rate was my main problem. Next time I will load the quartz tube with broken porcelain (per OrgSyn) or copper mesh (per NERV) to improve heat transfer and reduce residence time in the furnace. Also I will increase the acetone feed rate hopefully to 4mL/min. I may be limited in my feed rate by how fast I can push gas through my absorber. Also I will place the absorber in an ice bath.

I have 3 pictures to post. I apologize for having to use 3 posts to show them.

Comments, questions, and critique are welcomed.

[Edited on 20-9-2008 by Magpie]

ketene, inlet.jpg - 63kB

Magpie - 20-9-2008 at 18:48

2nd picture:

[Edited on 20-9-2008 by Magpie]

keten, outlet.jpg - 92kB

Magpie - 20-9-2008 at 18:50

3rd picture, the quartz tube:

[Edited on 20-9-2008 by Magpie]

quartz tube.jpg - 39kB

Klute - 21-9-2008 at 03:45

Thank you very much for posting thoses pictures! It's a pity it didn't work, but such details really clear things up for those how have never attempted this.. Your furnace is beautifull!

Looking forward to hear more!

Barium - 21-9-2008 at 05:17

Quote:

Originally posted by Magpie
Acetone feed rate was 2mL/min, and acetone recovery was 38%.
I think the low flow rate was my main problem. Next time I will load the quartz tube with broken porcelain (per OrgSyn) or copper mesh (per NERV) to improve heat transfer and reduce residence time in the furnace. Also I will increase the acetone feed rate hopefully to 4mL/min.

The following notes in the procedure from Org.Syn. may hold the answer to your results:

"4. With an electric combustion furnace, wherein a temperature of 695–705° is maintained, consistent yields of 35–40 per cent ketene are produced. The best rate of flow in such a case is 4–6 cc. per minute, with recovery of 60–80 per cent of the original acetone as distillate. Although yields of ketene ranging above 45 per cent have been obtained frequently with this apparatus, they could not be duplicated consistently.

5. The thermal decomposition of ketene into carbon monoxide and ethylene is prevented, as far as possible, by the rapid removal of ketene from the hot tube, which is accomplished by the undecomposed acetone vapor. About half the acetone originally used should be collected unchanged as distillate by the vertical condenser. The yield of ketene will fall considerably if less distillate is formed.

S.C. Wack - 21-9-2008 at 06:00

All this is in the literature.

"In order to obtain good yields of ketene from acetone it seems to be essential to decompose only a small fraction of the acetone. Factors such as the temperature of decomposition (provided it is not much below 600°), time in the furnace and the presence of inert gases do not appear to have any very appreciable effect on the yield of ketene except in so far as they affect the fraction of acetone decomposed.

Laboratory Preparation.
Ketene can be prepared conveniently by dropping acetone directly from a separatory funnel into a quartz [or Pyrex, but not iron - JACS 47, 1427 (1925)] reaction tube heated in the range 650-750°. The rate of introduction of the acetone is adjusted so that from 10-40% of the acetone is decomposed."

JACS 56, 1760 (1934)

Magpie - 26-9-2008 at 12:12

Thank you Klute.

Run #3 was in progress today. Everything was going well, adding acetone at 4mL/min, when all of a sudden I saw no bubbles in the GAA absorber/reactor. Checking all connections the cause was apparent: the polyethylene hose had sagged and was perforated just at the outlet of the furnace. See picture below. I don't know if this was caused by ketene, or hot gases, or both. But the glass at that end never was hot to the touch. When I saw that perforated PE tube I was very glad I had a good hood fan. I had completed about a third of my planned addition of 240mL acetone to dose 80mL of GAA.

Also, I lost my acetone vaporizer due to massive cracking (luckily not breached, however). I had it really hot so I could be sure and get the acetone vaporized immediately upon addition from the dropping funnel. I guess this is what happens when you violate the rule of "do not distill to dryness." In that regard I was probably lucky that I aborted the run. I might have had an acetone fire otherwise.

I was happy the way the run was progressing and recovery of acetone was 61.3%. Now it is back to the drawing board.

I had the quartz tube loaded with broken porcelain per OrgSyn. I figured if nothing else this would cut down on residence time in the furnace. Furnace temperature ranged from 689-711C. When the furnace cools off I'll post a picture of the tube to show any char.

droopy hose.jpg - 64kB

Magpie - 26-9-2008 at 19:25

Here's the picture of the quartz tube packed with broken porcelain from Run #3. As you can see there is virtually no char.

I gave some thought to what temperature would be best for the GAA ketene absorber/reactor. From an absorbtion standpoint an ice-bath might be best. But from a reaction standpoint a high temperature, such as the 80C specified in the Chem E project posted by not_important in the acetic anhydride thread, might be prefered. I suppose it depends on wheter the conversion to Ac2O is mass transfer limited or kinetics limited. Not having a strong opinion either way I left the column at room temperature. Any thoughts?

I am pleased that I was able to achieve the OrgSyn feed flow and acetone parameters and no char. I haven't fractionated the product yet so don't yet know whether I was successful overall. But I obviously have some equipment issues to resolve before I can continue.

[Edited on 26-9-2008 by Magpie]

quartz tube.jpg - 38kB

watson.fawkes - 27-9-2008 at 14:30

You might try a dry run with compressed air to see if it's just purely a temperature issue. Do note, however, that the heat capacities for nitrogen and oxygen are different than that of acetone and ketene.

Magpie - 27-9-2008 at 15:38

Watson that is a good suggestion. But I feel that I have to deal with it no matter the cause, and high temperature is most likely it. My plan is to make a jumper out of glass tubing, butt the ends right up to the hose barbs on the adapters, and hold the joints together with heavy wall rubber vacuum hose, as per OrgSyn. When all else fails I try following the procedure.

What is your opinion on the best temperature for the GAA/ketene absorber/reactor?

Fleaker - 28-9-2008 at 09:54

Magpie, earlier in the thread, NERV and I used an ice bath to cool our GAA, the gas was also bubbled through a frit, not just a plain tube. This produces many small bubbles. It's in the pictures. It worked OK. I don't remember the final yield for the reaction, we got 60 some mL of Ac2O from 250 mL acetone.

Magpie - 28-9-2008 at 10:29

Thanks Fleaker. I have a fritted tube also but have been using just an open tube. It seemed like I was producing so much gas (in the first two runs) that I didn't think I could use it. I'll give it a try. On run #3 most (61.3%) of the acetone was recovered so the gas production (ketene, methane, ethene, etc) may actually be less voluminous. It did appear so as I recall.

Yes, for temperature of the GAA absorber/reactor, you were successful with an ice-bath. This is a strong argument for using same.

[Edited on 28-9-2008 by Magpie]

Waffles SS - 9-12-2009 at 06:34

How Control acetone flow rate in Quartz tube?

Magpie - 9-12-2009 at 08:50

Quote: Originally posted by Waffen SS

How Control acetone flow rate in Quartz tube?

With a pressure equalizing funnel. See photo upthread.

Waffles SS - 9-12-2009 at 09:37

I did it one time and my rb flask break
First i heat my flask and then add acetone drop by drop
Flask temp was 100c
Now i control flow rate by temp of heater
I use 2lit flask,1meter 2mm(inside diameter)Quartz tube with Copper wire inside,50cm in furnace(temp 700c)
My ketene yield is little and my recover acetone is Yellow!

[Edited on 9-12-2009 by Waffen SS]

Magpie - 9-12-2009 at 10:32

Quote: Originally posted by Waffen SS

I did it one time and my rb flask break
[Edited on 9-12-2009 by Waffen SS]

Initially I was heating a 500mL RBF with a mantle to serve as acetone vaporizer. My RBF cracked too - ouch! So I switched to hot water bath heating. But this is a pain also. The best vaporizer I believe would use an oil bath with closed loop temperature control.

I have invested a lot of time and money into trying to get this ketene method to work. I never did get any Ac2O. It's also a very risky method. I have now switched to S2Br2 for making Ac2O.

Waffles SS - 9-12-2009 at 11:11

But i got Anhydrid, now i am working for best perfomance.
If you like i can share my Result and Pic.
Also i am working on control flow rate part with new idea.
Final Product contail 3 componet after fraction distil:first come in ~100 that is soluble in water and has less density(i dont know what is that).second acetic acid. third acetic anhydrid.
Your acetic acid and acetone should be dry for best result.
I believe best vaporizer is metal flask.

[Edited on 9-12-2009 by Waffen SS]

Magpie - 9-12-2009 at 11:29

Quote: Originally posted by Waffen SS

But i got Anhydrid, now i am working for best perfomance.

What proof do you have that it is actually Ac2O? Try reacting it with aniline if you have any.

What is the yield?

The only significant variable that I have not yet tried is use of copper internals in the quartz tube. This was used by Fleaker/NERV in their succesful run.

Waffles SS - 9-12-2009 at 13:18

Quote: Originally posted by Magpie

What proof do you have that it is actually Ac2O? Try reacting it with aniline if you have any.
What is the yield?

Proof:
-Boilng point:138c-141c
-React with water(produce acetic acid)
-Odor(strong acetic acid)
-If you add one drop anhydrid to water it will fall at bottom like oil and will disappear after a while.

Unfortunately i dont have aniline but i am sure that is anhydrid.
Now yield is little but i am improving it.
I used 1800cc acetone and recover 1500cc and got 30cc anhydrid.
Yield is little because most of ketene escape from absorber and i should use 2 or 3 absorber also i should contol
flow rate better.
Recover acetone is yellow and i guess ketene decompose cause that also there is unknown componet that has lower boiling poin(~100) that i dont know what is that yet.

[Edited on 9-12-2009 by Waffen SS]

DSC00473.JPG - 88kB

entropy51 - 9-12-2009 at 16:28

Waffen, are you seriously attempting to make ketene outside of a fume hood? I can't tell for sure.

You say the ketene escapes the wash bottle. Does it by any chance go into the air that later enters your respiratory tract?

If so, I hope your health and life insurance is very, very good.

[Edited on 10-12-2009 by entropy51]

Magpie - 9-12-2009 at 20:30

That's an interesting looking tube furnace Waffen. Is it homemade?

I also managed to get a few mL boiling in the range 136-138C from my last ketene run. I didn't have any aniline at the time to test it. But I did do some other tests shown in the link below, with mixed results. When I produced Ac2O with S2Br2 I knew I had relatively pure Ac2O right off the bat, without even testing it. "A true huntsman knows a hunting dog, just as a true hunting dog knows a huntsman." or something like that.

http://www.chemistry.ccsu.edu/glagovich/teaching/316/index.h...

Waffles SS - 10-12-2009 at 00:10

Quote: Originally posted by entropy51

Waffen, are you seriously attempting to make ketene outside of a fume hood? I can't tell for sure.

You say the ketene escapes the wash bottle. Does it by any chance go into the air that later enters your respiratory tract?

If so, I hope your health and life insurance is very, very good.

[Edited on 10-12-2009 by entropy51]

Yes Ketene is very toxic,i burn final mixed gas(ketene,methane,..)by burner and ketene in this temp decompose depend on your temp.

Furnace is self made and has digital display.
Now flow rate is low because little char produce in quartz.i am working on it.
Also i build complete system by copper metal but i have problem with that.

Waffles SS - 14-12-2009 at 02:53

Quote:

acetic anhydride is also prepared by the reaction of ketene with acetic acid at 45–55 °C and low pressure (0.05–0.2 bar)
wikipedia

I think cold aceic acid will not produce good yield Ac2O.
We should heat washing bottle to 45-55c.
I got better yield When i heat my washing bottle to 50c.
Does ketene react with anhydrid acecic?
Ketene react with my PE tube and i think it absorb water from PE and remain char.

[Edited on 14-12-2009 by Waffen SS]

peach - 2-7-2010 at 13:56

You don't need a fume hood if you select scrubbers / washes properly. Use a wash, after the one for (partial) absorption, containing something it will react with to a none harmful form; e.g. if something is exhausting acidic fumes, I'd wash it with a strong base. Wash flasks cost tens of dollars, can actually neutralize exhausts as opposed to absorb them and can be used for other things.

I'm very impressed by all this furnace building and ketening.

[Edited on 2-7-2010 by peach]

JohnWW - 2-7-2010 at 14:37

We have not heard from Waffles SS for a while. Perhaps he has succumbed to his own ketene, which is very toxic (in spite of which the Nazi SS did not think of using it as a poison gas during WW2).

Fleaker - 2-7-2010 at 16:35

That would be most unfortunate, as he was obviously quite capable given his construction of a most admirable tube furnace.

I would like to revisit this experiment on a larger preparative scale.

Jimmymajesty - 4-7-2010 at 07:26

I attach a small bubbler after the main one, and sometimes check it by samling it with a syringe and smell it, when it starts to smell acetic, and the main bubbler heating ceases, I consider the glacial acetic acid => acetic anhydride conversion finished.

The cooling of the main bubbler is essential as ketene to acetic anhydride is very exotherm, If you do not cool it, acetic anhydride will vaporize, and makes it to the second bubbler, so keep it as cool as possible, at mine desing even at -30°C the bubbler inner temp is about +50°C

When I checked the plastic tubing during operation one connection slipped apart, I suddenly breathed out and held back my breath while I fixed the leak.. After a couple of seconds of the leak when the ketene reached my face, it was so intense and painfull like a punch.. especially my eyes burned like hell, I cannot imagine what would ketene do to you after a lungfull of it, it must be very painfull death..

peach - 5-7-2010 at 17:16

Have you ever taken a good lungful of rich HCl(g)? How doest ketene comparuth?

Jimmymajesty - 6-7-2010 at 02:07

HCl, Cl2 and croton aldehyde are nice ones too

Its like a sniff from glacial acetic acid but more permanent.
There are some chemicals which smell you had better not know, including ketene, Ac2O is also a nice one be contented with that

FrankMartin - 6-7-2010 at 16:37

Heating wire (Nichrome) may be investigated here:

http://www.wiretron.com/nicrdat.html

There may be a catalogue available giving Nichrome wire gauges, resistivities and practical examples.

We have made some in-situ heaters using Nichrome and power supplies.

Frank

peach - 8-7-2010 at 08:32

Acetic acid smells really nice, from a distance.

Up close and it's one of those smells that makes you instantly shout "fuck!" and jump back from.

The worst I've ever had from gases has been using 15% industrial bleach. I was cleaning a small lab, about 12ft x 8ft, for a few hours, spraying the bleach on every surface. I was in there for hours, cleaning. The bleach was actually green. Soon after starting, I couldn't smell the chlorination anymore. Hours later, when I left, it felt like someone had hit me in the chest with a baseball bat.

But I was breathing very clearly after that, chloride ions thin the mucus lining and improve oxygenation.

At least with things like HCl(g) and acetic, you smell them and pull away immediately. It's the vapors and gases that hide that I worry about; the ones you can't smell until it's too late.

Like SO2. At least I can smell it from a long way off and, when I get close, it hurts so much I retreat. I'm more bothered about things like mercury sublimation vapors.

Jimmymajesty - 8-7-2010 at 13:09

I have similar experience with chlorine, be careful with that, it is carcinogenic in case of repetitive exposure.

Acidic molecules can ruin your lung very easily, I do not know the exact mechanism, but a little vomit in your lung and you are dead, that is why placing and injured person to its side is of utmost importance.

Its not the terrible acrid smell of ketene that I fear the most, rumours has its carcinogenic, seeing the acylating potential of the molecule, it must be a very nasty one.

I cried fuck many times lately, unfortunately because of makeshift solutions, just do not do experiments in a haste or if you do not have time to build a proper setup, or do not have suitable materials at hand.

SO2 is really a bitch, one slipped apart connection made me choke for hours, during which I coughed up sour mucus from my lung, must be very healthy too. BTW do not use silicone tubing with that, it is like if it wouldnt there.

peach - 15-7-2010 at 15:47

A poor workman blames his tools.

But, for this kind of gas based work, trying to improvise and swap materials too heavily is like trying to carve a work of art with a nail file. Gases are like a different area of chemistry. Beakers and normal containers or seals don't work and all of a sudden you have to start thinking about diffusion, absorption, scrubbers, seals, and compatibilities (as the connecting elements are inevitably not glass and are routinely subjected to elevated temperatures that will damage the polymers they're constructed from, both chemically and mechanically).

It's a worthwhile area to get used to though. It does make me have a lot of sympathy for the guys doing this kind of thing industrially.

"It's, rotted, melted, fallen off, leaked, escaped..... again!"