Suitable material for high temperature phosphoric acid 1

[RockaRolla]

I'm looking for a material that can stand up to high temperature phosphoric acid. And by high temperature, I'm talking up to 500C, atmospheric pressure.
I doubt there's a metal that'll do, but thought I'd ask. Ceramics are a possibility, too. I'm leaning towards quartz right now. There are definitely issues with quartz, but I'm not finding anything else that looks even remotely suitable.

Any suggestions?

Thanks

 

[strider6]

with that temp is not an easy job... but have a look at this pub from NIDI on materials selection for Phosphoric plant

http://64.224.111.143/technicallibrary/nidi/literature/pdf/415.pdf

hope this help u

S

Corrosion Prevention & Corrosion Control

 

[unclesyd]

You need to come back with a few more details on you process as ortho-phosphoric acid doesn't exist at these temperatures.

 

[SJones]

Yes - it's pyrophosphoric acid which will settle as a viscous liquid or solid. If it's not too contaminated and oxidising, I'm inclined to suggest Alloy 201 (N02201) in the first instance just to get the discussion going.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[unclesyd]

We used a catalyst made from H3PO4 and boric acid which we mixed in 316 SS mixers dumped into 316 SS trays, dried at 400F for 8 hrs, then sintered at 650F for 6 hrs.
The dryer oven were 316 SS lined and the sintering ovens were also 316 SS.
There was never any corrosion noted.

Sjones,
I believe they will have a mixture of pyro and meta phosphoric acid at thie temperature and i would favor the meta form along with some P2O5.

 

[RockaRolla]

Thanks for the input.

The idea of the process is to heat orthophosphoric acid, and use the P2O5 vapor generated.

I've been using this brochure from the Potash Corp as a reference:

http://www.potashcorp.com/media/pdf...fied_phosphoric_acid/PCS_phos_acid_manual.pdf

Figure 12 in it implies that boiling phosphoric gets more concentrated and generates a higher percentage of P2O5 as vapor up to pretty high temperatures (the graph goes to 800C), and at atmospheric pressure. That sounds a bit fantastical to me, especially considering what you describe, Unclesyd. Is their info wrong? Or is something else going on? The listed figure is based on an old paper prepared for the TVA, and I've tracked it down, should have a copy in a day or two.

I'm trying to test some of this. I can get the temperatures I need in a test rig I've built, but I haven't a clue what material to make a vessel from, which is why I'm here.

 

[unclesyd]

In our process the phosphoric acid in the catalyst is converted to P2O5 and is used as a dehydrating agent. As far as I know the P2O5 didn't enter into the reaction equation.
The boric acid is a reaction promoter and also a dehydrating agent in the catalyst.

The chemistry of catalyst wasn't ever studied in depth as if the compound was right there was a high selectivity and yield in the process. Aside from the complexity of the chemistry the analytical techniques were severely lacking.
Immediately prior to shutting down this process I found out that this catalyst could be regenerated by running it though a Pyrolysis oven. This would burn off the carbon and dehydrate the phosphoric and boric acid.

The chemistry of catalyst wasn't ever studied in depth as if the compound was right there was a high selectivity and yield in the process. Aside from the complexity of the chemistry the analytical techniques were severely lacking.

 

[TVP]

Do you plan to allow this reaction to equilibrate, or will you siphon off the P₂O₅, as this will obviously affect the reaction substantially. The corrosion of Ni or other metals will depend a great deal upon the concentration of any other species present, e.g. F^- is extremely detrimental.

 

[RockaRolla]

I plan to siphon off the P2O5, and flow it through a process chamber. I realize that this will concentrate any impurities present in the H3PO4, and create lifetime issues with whatever material and/or design I choose.
I'm hoping to extend that lifetime. I'm also hoping to win the lottery. The more I learn, the more I see that might be the more likely scenario....

 

[TomEun]

In addition, please find the MTI Materials Selector below.

http://www.mtiproducts.org/maseforhachm1.html

MTI MS-7: Phosphoric Acid