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Sauron
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[*] posted on 23-3-2007 at 21:08


Thanks, @leu. Unfortunately this while interesting is not helpful. @Hector has all but totally discarded (on my advice) the ketene process. The patent you attached involves vac.disitllation of 83-85% Ac2O with AcOH for rest plus traces of diketene.

The recommended prep, vinyl acetate over PdCl2 -> acetic anhydride + acetaldehyde, is conducted in AcOH as solvent. Therefore unlike the system above, in this process and after removal of acetaldehyde and unreacted vinyl acetate, which are lower boiling, the mixture is predominantly AcOH containing a relatively small amount of Ac2O. Since AcOH boils 23 deg C lower than the anhydride, distillation would be lengthy and tedious.

Therefore we are looking at liquid-liquid extraction of the Ac2O from the AcOH with a solvent that is immiscible with the acid but that will dissolve the anhydride.

@hector2000 needs to produce 20 L/day anhydride and this scale is too large for bench and way too small for an industrial process. He is presently using Merck acetyl chloride and anhydr. sodium acetate to make 50 L/day Ac2O but is having problems with the Merck acid chloride turning ywllow then red and passing that contaminant on to the anhydride.
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[*] posted on 23-3-2007 at 22:30


I don't think of Merck as an industrial supplier of something like acetyl chloride. I think of them more as a supplier to research and educational institutions. Am I wrong here?

If I'm correct in the above it seems like 20L/day would be a large acetyl chloride customer for Merck. On that basis Hector ought to be able to work with Merck to work out Merck's apparent quality problem for Hector. Has that been tried Hector?

It just doesn't seem right that Merck grade acetyl chloride would be of poor quality. Merck is a pharmaceutical manufacturer and maker of fine chemicals. They ought to have quality down to a gnat's ass.

Hector: What is the grade anyway? Technical? lab grade?, or what?




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Sauron
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[*] posted on 23-3-2007 at 22:50


I think you will find that Merck sells lots of chemicals in bulk just as Aldrich does, Acros does, Eastman does, Carlo Erba does, Panreac does, and so on. A cursory look at the websites or print catalogs will reveal request cards for bulk quotes and/or lists of bulk products from all of these companies. None of these companies could survive on just the research and educational markets.
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[*] posted on 23-3-2007 at 22:58


OK, so maybe Hector's 20L/day order is no big deal to Merck. It still seems strange that Merck would have a quality problem with their acetyl chloride, unless, of course it is due to something unique in Hector's process, and no other customers complain.



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Sauron
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[*] posted on 23-3-2007 at 23:13


@Hector's process is to add AcCl to NaOAc anhydr. Perhaps the (stainless?) steel vessels are being attacked by the acid chloride. That's what he thinks. I am not so sure. FeCl2 is not red. He is getting first yellow then red.
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[*] posted on 23-3-2007 at 23:27


That sounds right. Note the discussion on this page relating to color. http://jchemed.chem.wisc.edu/jcesoft/cca/CCA3/MAIN/CLFE/PAGE...
There is probably water in the reaction vessel somewhere, although that isn't the only problem since the steel vessels are not inert.




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Sauron
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[*] posted on 24-3-2007 at 00:22


@Hector, please take note. Try avoiding any contact between the acetyl chloride and the acetic anhydride with iron, steel or stainless steel. The red color may be FeCl3, the yellow color FeCl2.

When you open fresh bottles acetyl chloride transfer the liquid out of the bottle without pouring it over the metal part. Use a siphon system of something intert like glass or PTFE. Store the acetyl chloride like I told you in brown glass with inert plastic caps away from light and heat. Do not use metal vessels for reaction with NaOAc. Do not stir with metal. If you do this you should not have color problem, anhydride should be water white.
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[*] posted on 24-3-2007 at 01:52


You are buying reagent grade acetyl chloride from Merck in a 200 L drun. This is PE lined steel. I think we all assumed you were buying many many 1 L or 2.5 L bottles. How silly of us! Anyhow the "for synthesis" grade of Merck is as good as it gets.
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[*] posted on 24-3-2007 at 09:27


I think that is a very good experiment you are trying, ie, conducting the process on a lab scale using no metal vessels or equipment. That should help in isolating the cause of the discoloration.

In fact, why not do it on a small scale with just glassware. See if the color remains or disappears.




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[*] posted on 24-3-2007 at 10:09


The CO2 + acetate routes, one gives Na2CO3 and the other NaHCO3, basically treat a solution or suspension of sodium acetate with high pressure CO2 at slightly elevated temperatures 30 - 60 C, then cooling to 0 C or below, letting it sit for awhile, and separating the carbonate/bicarbonate from the liquid containing acetic acid and acetic anhydride. At that point the anhydride must quickly be separated from the aqueous materials, solvent extraction being the best.

It works, I've tried it, but it does not seem to have made it commercially. I suspect loses of anhydride were too high for the quality of the product. A version using up-to-date methods might be practical, but you'de be doing full blown R&D.
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[*] posted on 24-3-2007 at 12:22


This patent mentions the use of toluene :P

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[*] posted on 24-3-2007 at 12:25


Toluene is also within the specified class of aromatic hydrocarbons mentioned in this patent :P

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[*] posted on 24-3-2007 at 16:42


I am very dubious of the CO2/acetate method, as the extraction of anhydride has to be done fast enough to preclude hydrolysis. So mostly it's a good way to make acetic acid, because that's what most of the Ac2O formed will turn into. You've got seconds to minutes of half life to seperate solids and extract the anhydride and dry it. The key parameter is the temperature dependent half life of Ac2O in water. To give yourself half a chance of recovering even part of the anhydride, you need to use only near-freezing water.

@hector2000, I gave you CAS number of cyanuric chloride. You want the Merck number? They sell it, and you buy from Merck in bulk. Yes it is a common chemical particularly in agro-chemical industry for making triazine pesticides.

[Edited on 25-3-2007 by Sauron]
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[*] posted on 24-3-2007 at 17:38


There are a variety of methods that have been patented for the production of acetic anhydride that have never been commercialized for one reason or another that may be most suitable for a cellulose acetate manufacturer in a restrictive country such as Iran :( The procedure that makes the most sense would be to hire a chemical engineer to evaluate the various processes in terms of the cost of what materials and equipment are available and compare that to the profits that can be gained to see if any such process is economically feasible and then decide what to do at that point :P For example, there's a little known process that uses acetic acid in a copper still that may be perfectly suited for your purposes since acetic acid can be produced by the destructive distillation of wood along with methanol, this way you could reduce your dependence on Merck :cool:

[Edited on 25-3-2007 by leu]

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[*] posted on 24-3-2007 at 18:19


@leu, please don't overlook the simple fact that @hector's requirement is barely larger than large bench scale. He is talking 20 L a day. He is not looking to invest millions in a giant industrial operation. Heb has two tasks:

1. Find a suitable less costly and less problematic alt. to his present acetyl chloride-sodium acetate process. Note that lab grade AcCl Merck costs him only $6 US/Kg (or maybe L) as he buys it in 200 L drums. I am sure that we all wish we could get it for that price. In my case I can't buy it at any price.

2. He has a wee problem with contamination (we think Fe(II)/Fe(III) chlorides in present process. If we can help him eliminate this problem then he can at least stick with what he has if we can't find him a cheaper route.

He is cool to my suggestion of vinyl acetate route because of cost of PdCl2 catalyst, He would need about 4 Kg PdCl2 and that isn't cheap. However, it is a one time capital cost as it is reusable, it's heterogeous catalyst and is not consumed.

If he prepares his own PdCl2 from say 2 Kg Pd metal what is spot market price for Pd? This would be a lot cheaper than buying PdCl2 commercially. PdCl2 is c.59% Pd. The spot market price for a troy oz is about $350. So $23 a gram roughly. $46,000 for 2 Kg. So something less than $10 per L catalyst cost first year. What is catalyst life cycle? Other than mechanical losses it will not go away. If this was a hydrogenation we would talk about poisoning of catalyst but, it isn't. Is it reasonable to anticipate a catalyst life of more than a year? If so then amortized catalyst cost/L plummets rapidly. $5/L 2 years $2.50/L 4 years.

(If he makes 100 L (Ac2O) a week that is 4800 L/year (we must deduct Ramadan when he cannot work.) So he has all that product over which to amortize his catalyst cost.)

Hmmm, I guess it is easy to see why this Pd(II) process can't compete economically. Oh well. too bad, it looked good otherwise.

------------------------

Acros sells cyanuric chloride for $34/Kg for 1 Kg pack. Now @hector you can probably improve considerably on that by buying in bulk just as you do with acetyl chloride. Acros price for acetyl chloride $45/L in 2.5 L pack. So I would not be surprised if you can get CC for $5/Kg in 200 Kg pack. Get a quote from Merck and find out.

One Kg CC makes about 1.4 Kg acetyl chloride. That's about 1.25 L as the density of AcCl is 1.1

Therefore, making acetyl chloride from cyanuric chloride is competitive with your cost of the Merck product, assuming your cost for AcOH is low.

I did not calculate in the cost of energy to distill the acetyl chloride from the AcOH, but, AcCl boils at 51 C compared to 117 C for the acid, a 66 degree spread, so this is an easy seperation. A simple distillation will suffice, maybe two at most.

Merck's product number for cyanuric chloride is 802815.



[Edited on 25-3-2007 by Sauron]
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Sauron
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[*] posted on 24-3-2007 at 22:36


I believe both acetic acid and acetic anhydride are totally miscible with benzene and toluene. So you can't extract anhydride from acetic acid with those.

So far the only solvent we have found that will do this job is CS2.

Acetic acid is practically insoluble in CS2.

Acetic anhydride is miscible with CS2 in certain proportions.

There may be other solvents that will work, but we haven't identified them as yet. I would think that sulfur containing hydrocarbons like thiophene, sulfolane etc are strong candidates. Someone else suggested monochloropentanes. But unless we can find examples in the literature you will have to experiment, or someone will have to experiment, to find this out. So far the standard texts on laboratory and industrial solvents have been useless. I will keep on looking.

By the way benzene is a bad carcinogen.
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[*] posted on 24-3-2007 at 23:19


That Daicell patent is concerning treatment off offgases from ketene process.

Look at data sheets for AcOH and Ac2O and you will see both are miscible with benzene. That means they dissolve in all proportions. Benzene is useless for you in liquid phase seperation of AcOH and Ac2O. Do not be confused by that patent.

The CO2 acetate process involves treatment of aqueous sodium acetate solution with CO2. It appears to me that solid CO2 in snowflake form would be best, as you want the water as cold as possible to slow the hydrolysis of Ac2O formed. You have very blittle time to extract Ac2O into organic phase (chloroform is best) before the Ac2O will react with water forming AcOH. And the AcOH will react with sodium carbonate or bicarbonate formed to produce more sodium acetate so this process goes in a circle. If and only if you can efficiently extract Ac2O into a hydrophobic organic phase will this be productive of Ac2O for you. To me it sounds like a Chinese fire drill. It's like a dog chasing his own tail.

[Edited on 25-3-2007 by Sauron]

[Edited on 25-3-2007 by Sauron]

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[*] posted on 25-3-2007 at 01:01


Put that question aside for the moment.

Here are two US patents from 1930s.

First one says vinyl acetate + acetic acid over conc sulfuric acid as catalyst, gives acetaldehyde and acetic anhydride. Claims 77% conversion and 95% recovery of the anhydride formed. No PdCl2 required.

Other catalysts suggested include phosphoric acid, sulfonic acids like p-toluenesulfonic acid (the example they give is benzenesulfonic acid), etc. as I know you have a problem with sulfuric acid.

This would be very cheap and easy. No acetyl chloride needed. No PdCl2 needed. You should try this. No sodium acetate needed. So no more 3 day drying oven.

Don't thank me, thank @S.C.Wack who pointed these out in another thread.

The second patent says that heating trichloroethylene (which they call methyl chloroform) and water in an autoclave (pressure reactor) to 75-150 C for 10 hours gives excellent yields of AcOH, AcCl, or Ac2O depending on ratio of trichloroethylene:water.

1 part trichloroethylene to 1 part water -> acetic acid

2 parts trichloroethylene to 3 parts water -> acetic anhydride

1 part trichloroethylene to 2 parts water -> acetyl chloride

When I say parts read mols.

Catalyst: H2SO4 (AcOH only), FeCl2 anhydrous, ZnCl2, CoCl2, etc.

Hydrochloric acid by product.

This patent was to Dow Chemical.

If you can still get 1,1,1-trichloroethylene in Iran you may want to try this

[Edited on 25-3-2007 by Sauron]

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Sauron
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[*] posted on 25-3-2007 at 02:22


In the first reaction you start with vinyl acetate and acetic acid. Supposedly 77% of the VA reacts so that means 77% of the acetic acid does. Therefore 23% of AcOH is left. So you have a mixture of acetaldehyde (but you take that off during the reaction), VA (distill it off), a lot of Ac2) and a little acetic acid. Much easier to seperate by distillation than in the PdCl2 catalyzed process.

In the second reaction we are told that the conversions are very high percentages, so in case of acetic anhydride you will have minor amounts of trichloroethylene, water, and a lot of HCl. The HCl is gasous rather than aqueous. You offgas it from the liquid product with vacuum. Once again this purification by distillation is easy.

Am I sure of this reaction? I haven't tried it yet. But you can read the patents for yourself. Just try them. They look simple.

2 CH3-CCl3 + 2 H2O -> (CH3-C=O)2O + 6 HCl
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[*] posted on 25-3-2007 at 04:28


I named that a little wrong, it is 1,1,1-trichloroethane.

Industrially making Ac2O out of vinyl acetate makes little sense because vinyl acetate is made from Ac2O.

However, if this patent is geuine and reaction works, this is a good way to make Ac2O on a scale from lab bench to your 50 L/day as the VA is cheap, the catalysts are cheap (various transition metal chlorides) and the conditions are not harsh.

The acetaldehyde you condense and oxidize to AcOH

The byproduct ethylidene diacetate you add to the pot for next batcg as it behaves just like VA + AcOH

The Ac2O yield is higher than in the Gulf Research PdCl2 cat. process.

And the product is more easily worked up.

This really looks good if it works. Easy enough to find ut. We are all hoping it does because if so we can use it too. For many of us both acetaldehyde and Ac2O are highly desirable.

Good luck!

[Edited on 25-3-2007 by Sauron]
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[*] posted on 25-3-2007 at 09:28


I noticed that it was mentioned by using CC or TCT acetyl chloride could be formed... I was under the impression that this would form chloroacetic acid instead of the acetyl chloride.
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[*] posted on 25-3-2007 at 19:09


I think you are confusing TCT with TCCA. And then misremembering what TCCA does.

TCT (CC) chlorinates carboxylic acids to acid chlorides; and it chlorinates alcohols to alkyl chlorides. It is 2,4,6-trichloro-s-triazine. Its three chlorines are on carbon.

TCCA is trichloroisocyanuric acid. Its three chlorines are on nitrogen.

Both of them form cyanuric acid upon hydrolysis, TCCA by rearrangement.

TCCA can be regenerated with chlorine. TCT cannot.

TCCA is swimming pool chlorinator.

TCT is trimer of cyanogen chloride and is feedstock for triazine pesticides.

TCCA selectively chlorinates secondary alcohols only.

TCT chlorinates primary and secondary alcohols.

The structures of both have been posted here previously. So don't let the similar acronyms fool you.
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[*] posted on 26-3-2007 at 00:17


interesting patent -- vinyl acetate is available everywhere ... should be nice if it works out..
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[*] posted on 26-3-2007 at 00:39


I'm not too thrilled with a -8 C flash point though. On the other hand it's not as bad as ether (-30 C) or CS2 (-45 C)

Through the kindness of another member I obtained the following abstract for ref. 4 of the Gulf Research 1962 paper (see above) on PdCl2 catalyzed hydrolysis of vinyl acetate

"Acetylation of isopropenyl acetate catalyzed by mineral acids.
Jeffery, E. A.; Satchell, D. P. N..
Chemistry & Industry (London, United Kingdom) (1960), 1444.

Abstract

The HCl- and HBr-catalyzed acetylation of HOAc to Ac2O was examd. kinetically, the HOAc acting as the solvent so that the deficit of isopropenyl acetate (I) reacted completely. Use of AcOT resulted in negligible labeling of the Me group of the HOAc. Thus the following reaction scheme was preferred: (a) I + HCl -> AcCl + Me2CO (rate-detg. step), (b) AcCl + AcOH .->. Ac2O + HCl (fast), rather than (a) I + HCl -> CH2:CO (II) + Me2O + HCl (rate-detg. step), (b) II + AcOH -> Ac2O (fast), (c) Ac2O + HCl .->. AcCl + AcOH (fast). The AcCl was the real acetylating agent rather than II. Other tracer expts. with H2SO4 catalyst showed that II was not involved in this case either. "



[Edited on 28-3-2007 by Sauron]
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[*] posted on 27-3-2007 at 19:37


As we are using some unfamiliar terms I thought it would be useful to insert a sketch

Only vinyl acetate is inexpensive.

From structure you can see why isopropenyl acetate produces acetone along with acetic anhydride, rather than acetaldehyde.

[Edited on 28-3-2007 by Sauron]

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