Fertilizer ---->phosphorus pentoxide

[DONMAN]

I just picked up some 0-45-0 also known as (Calcium dihydrogen phosphate). It decomposes at 205~ centigrade. I expect it would go something like this?

2Ca(H2PO4)2 + O2 ---> 2CaO + ?? HPO3 or P2O5 with some H2

My ultimate goal is to make phosphorus pentoxide. Can you give me some input. I know it would be best if I could get my hands on some ammonia phosphate... but I cant... I could synthesize it ....but that's annoying..

[megalomania]

You will end up with phosphorus oxides, not necessarily all phosphorus pentoxide. P2O3, P2O5, H3PO4, and who knows what else may form depending on the conditions of your heating, how much oxygen is available, and the moisture in the environment.

With ample oxygen and low moisture I would say you would get predominantly P2O5.

[kurtz]

I will go out on a limb and propose that there is absolutely no chance whatsoever to obtain any P oxide from any phosphate unless transient reduction of the phosphate with whatever reducing agent occurs first.

Ca(H2PO4)2 - H2O -> CaH2P2O7, calcium dihydrogen pyrophosphate/calcium acid pyrophosphate/CAS# 14866-19-4.

[DONMAN]

Is there an easy test to find out which P oxide have created? All P oxides look the same. I guess I could try reacting it with some alcohol and seeing if it oxidizes it....... Stupid non-ionic, non-organic reactions..... *mumble* *mumble*...

[knowledgehungry]

With enough heat I would imagine that it would go to Phosphorous oxides, because of entropy and such. CaO has much lower entropy(or more, momentary brainfreeze on whether high amounts of entropy have more energy or low amounts have more energy)than CaH2P2O7.

[DONMAN]

Pretty sure high amounts of entropy have more energy. Like when you heat something up you increase entropy.

[kurtz]

If you can find a single reference to the production of any P oxide from any alkali/Ca phosphate by heating in air below 1200C without reducing agents, in any sort of reference (handbook, database, journal, book, patent), in any language, let us know. Until someone finds that such a thing has been demonstrated to be possible, it seems safer to assume that you don't have one. That's just me, I guess.

[Frunk]

Pretty sure high amounts of entropy have more energy. Like when you heat something up you increase entropy.

No, actually when you heat something you increase the level of order, therefore you decrease entropy. Things tend to go towards entropy, things tend to cool down.

Absolute Zero is absolute entropy.

[megalomania]

I found several MSDS sheets yesterday for this stuff that stated phosphorus pentoxides are produced as decomposition products over 200 C. I could give you several references, but you can find them.

Lets start with the Merck index first... The entry for calcium phosphate, monobasic states "decomposes at 200 degrees." There you go kurtz my boy. Merck goes on however... "The products obtained from commercial processes are not pure monobasic calcium phosphate. The superphosphate obtained from the H2SO4 treatment is about 30% CaH4(PO4)2.H2O, 10% CaHPO4, 45% CaSO4, 10% iron oxide, silica, alumina, etc., and 5% water; it contains 18-21% available P2O5."

That's a nasty mix there, and most likely what your fertilizer grade is.

On the other hand the fertilizer code you provided could be triple superphosphate fertilizer, which is formed from a different manufacturing process and is much purer containing 43-50% P2O5 and no calcium sulfate.

Here is a PDF with more than I wanted to know about the stuff... http://www.ams.usda.gov/NOP/NationalList/TAPReviews/monocal.pdf

You guys arn't mixing up your entropy and enthalpy are you? Irregardless, who cares? Your not helping the thread with a pedantic discussion of physics. I am afraid DONMAN that your topic is so esoteric no document on the Internet is going to contain this information. This is a problem long relegated to the shelves of forgotten 19th century chemistry. Heat fertilizer, how dare you? a modern chemist would say...

i doubt anyone alive could actually answer your question. Why? Because they don't teach practical information like this anymore, no industry would bother actually doing this process so it won't appear in any modern reference, and there is nothing free on the Internet that would tell you. I hate to say it but it looks like experimentation with a good deal of chemical analysis is required to really answer your question. That would require a well established laboratory.

[kurtz]

The entry for calcium phosphate, monobasic states "decomposes at 200 degrees." There you go kurtz my boy.

And I told the product in the above post. The action of heat on phosphates is not a mystery, and in fact the old references are often not the best source in this case, as the identification of the products is not easy and the products themselves complicated.

Ya'll aren't actually going to come right out and say that you think that the %P2O5 means that it actually contains P2O5, or that you can just heat it up and magically get P2O5 (mp 330, sublimes @ 360C) are you?

[DONMAN]

hmm... looks like I have my work cut out for me. I will tinker for a few days and report my findings....

[kurtz]

Took on my own challenge and I did find some oxide from phosphate in a search. There were four conversions of phosphate to an oxide (all to P2O5) in the literature up to 1970 or so. One of them doesn't count because it involves transient reduction with carbon. A Polish article claims formation at the anode during electrolysis of Na metaphosphate at 640C. A French article has AlPO4 heated to 1000C. P2O5 vapor forms starting around that temperature, and Al2O3 remains. This is Compt. rend. 234, 1777 (1952), which is freely available at Gallica. And a Berichte article has phosphate, pyrophosphate, and metaphosphate heated a little with SO3, all with the formation of P2O5; i.e. 2 K3PO4 + 9 SO3 -> 3 K2S3O10 + P2O5. I have this article if anyone gives a shit and if there is a thread for it, but it is of course in German.

I should have a thick enough skin to ignore the cries of bullshit upon stating widely accepted facts, but even so I tracked down an article on this for proof of what I said above; and I'd still like to meet Rosco and smack him (see formamide).

"Acid Pyro- and Metaphosphates Produced by Thermal Decomposition of Monocalcium Phosphate"
IEC 39, 1667 (1947)
http://www.box.net/shared/ze6pu5janz

[DONMAN]

That is awesome, thank you so much. Where in the hell did you dig that up!