kaymatt
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Copper Chromite Oxide Catalyst Preparation
I have made several attempts at this preparation method as outlined in a Hive entry but the results have been less than stellar so I sourced the original journal entry to find out where I might be waltzing to a samba beat, metaphorically speaking. As a result of this investigation, I have a
number of questions.
Call out to forum boffins, your expertise and experience in such matters is hereby requested and will be deeply appreciated upon kind delivery. I have
paraphrased the original text here for clarity of purpose.
"If excessive temperatures are reached during the decomposition of the copper ammonium chromate the activity of the catalyst is seriously affected."
Ok, so what amounts to "excessive temperatures"?
"A batch of copper ammonium chromate (herein referred to as CAC) was prepared in the usual manner and separated into three portions."
"Portion I was fired to 320C in a muffle furnace and in a short time, the temperature in the mixture reached 635C"
Indicating that a strong exothermic reaction takes place at some early, though not specifically identified, point along the
temperature/time-of-addition graph. Hydrogenation of ether using this product revealed a yield of just 30.5%. This correlates well with another
chemist known to me who used an oven that fell some way short of the required 350C target temp.
Question 1. Correct me if I'm dancing out of time here, but perhaps by heating to a lower end temperature, you end up lingering at certain temperature
ranges for longer than you should, allowing an expected exothermic reaction to proceed for longer than is advisable?
"Portion II was powdered and added in small portions (How small? The literature is unclear) to a one-litre three-necked flask equipped with a
stainless steel crescent stirrer that scrapped close to the bottom of the flask (the Hive entry mentions a Herschberg type stirrer. You can jury-rig
something similar by removing the propellors off a standard overhead stirring rod and fashioning a wire propellor using nichrome wire, ingenuity and
some amount of patience). The flask was partially immersed in a Woods Metal bath heated at 400C. The time of addition was 15 minutes. The mixture was
heated and stirred at 400C for fifteen minutes after all the complex was added. It was then passed through a 200-mesh screen with the aid of a camel
hair's brush. Hydrogenation of ether revealed a yield of 88.3%"
Now we're talking!
Portion III was treated by the same method as portion II, only at 350C. Hydrogenation of ether revealed a yield of 92.1%.
So, in order to achieve pay dirt, I must exercise a 350-400C temperature range control over my flask heat source.
Question 2. The use of a Woods Metal bath may be more essential than I previously thought. Liquid Woods alloy would cling to every micron of glass
surface, thus creating uniform heat transference to the "small portions" of CAC. I've just been using a heating mantle which, as I'm sure you're all
aware, are dotted with small air pockets between each braid of heat-conducting mesh. They also often experience a wide variation in temperature from
the centre to the outer rim. I can hit the target with little difficulty, but not uniformly. How about if I try placing the mantle on a 30 degree
incline so the relatively cold centre spot is taken out of the equation and the location of the small portion CAC is somewhere that I know the temp
will never stray south of 350C?
Question 2a. Or am I simply over-emphasising the essentialism of Woods Alloy in this reaction?
Question 3. This may sound like a dumb question, but will standard-issue copper chromite from my friendly neighbourhood chemical supply chain work to
the same yields as portion III described here? I only ask because i recall reading somewhere that there are all sorts of variants of copper chromite
that are specific to different dehydrogenation processes.
Thank for your attention on this necessarily long-winded post
[Edited on 26-7-2019 by kaymatt]
[Edited on 26-7-2019 by kaymatt]
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Tsjerk
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What I deduct from your analysis and my rememberings of the topic is that it might be helpfull to either do this with small quantities, or with the
copper ammonium chromate spread over a large area.
I can imaging the compound has to be able to lose energy when the exothermic reaction takes place, otherwise it will go above the 350 degrees
recommended. I'm pretty sure the exothermic phase is obligated to go through, but when doing so, make sure it does it in a orderly fashion.
Are you using copper sulfate? See note 10, I guess washing with plenty of water also takes care of any sulfate left.
I don't think uniform heating is important, just get it to 350 in about half an hour and leave it there for another half an hour. I think the stirring
is also not too important as long as the amount is small enough or it spread over a large enough surface.
[Edited on 26-7-2019 by Tsjerk]
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Johnny Windchimes
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https://www.youtube.com/watch?v=4L5AGGfxFBc
Should help
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Tsjerk
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Check the filtration problems at around minute 6; this can be prevented by first boiling the suspension. I read that somewhere, forgot the source
though. I just gravity filtered through coffee filter.
Edit: after boiling before filtering the crushing seen at minute 8 is also a lot less tedious. I used an empty beer bottle to role over the dried
coffee filter and gained a fine dust.
Edit2: I didn't do the acid wash Doug did, but I did add a pinch of barium hydroxide to capture any soluble copper present after washing the copper
ammonium chromate with a bunch off water (possible because of the boiling before filtering... otherwise this would take ages.
I also noticed Doug is quite gentle when heating the sample with the burner, good idea I think.
[Edited on 11-8-2019 by Tsjerk]
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