The reason why 55% hydrofluoric acid is green in color
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The catalyst used in our unit needs to be activated with HF at a temperature of around 300 degrees. The equipment is made of 20# steel; excess HF is blown away by nitrogen to the absorption system, where it is absorbed by water to form 55% hydrofluoric acid. But hydrofluoric acid is green in color; I’m not sure why Requesting help. If it is dissolved in iron, the resulting iron trifluoride should be colorless or pale yellow.
There must be iron ions in the solution. Hydrofluoric acid does not have oxidizing properties; after corroding iron under sealed conditions, ferrous fluoride should be formed, and it is normal for it to appear green. Furthermore, due to the strong chelating effect of fluoride ions, the complexes of divalent iron are also more stable.
OP, is it the color of trivalent chromium? Does hydrofluoric acid turn purplish-red in the later stages of activation? Also, how can the heat exchange problem be addressed when using 55% concentrated hydrofluoric acid? If a heat exchanger is used, is its material graphite?