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Caustic Concentrations (NaOH) above 50%

Caustic Concentrations (NaOH) above 50%

Caustic Concentrations (NaOH) above 50%

Very curious on use of materials for caustic concentrations (NaOH) of more than 50%.

I have seen the Caustic Service Chart by NACE (Carbon Steels, Nickel Alloys), but the concentrations are capped at 50%, where I couldn't find any information about what goes beyond that.

Basically, my questions are:
1) Why is the chart capped at 50%?
2) What are the materials used for higher concentrations, and any references like the NACE Caustic Service Chart for such cases?

Do hope you all forgive my lack of knowledge and appreciate the help with pointing me in the right directions.

Thank you!

RE: Caustic Concentrations (NaOH) above 50%

Above 50% caustic, it's a slurry rather than a solution. That's why the max concentration of commercial caustic is 50%.

RE: Caustic Concentrations (NaOH) above 50%

Concentration of NaOH solution is not higher than 50% as any excess NaOH above this limit is crystallizing and solution becomes slurry.

RE: Caustic Concentrations (NaOH) above 50%

Two questions, temperature and can you tolerate any Fe (low ppm)?
If ambient temp with no Fe restrictions then you use steel.
It is hard enough working with a 50% solution that freezes so easily, working with the slurries is extremely problematic as both freezing and erosion are serious issues.

I have worked with caustic evaporators which are fed a slurry of NaOH+NaCl that is then boiled down to concentrate the solution. These are all either Ni200 or E-Brite, nothing else works. So there is a wide range depending on service.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

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