I never heard of any chemical plant using (even state-of-the-art) column crystallizers to enrich HP. They use vacuum distillation. Without exception. Why? Because it is less complicated. 98% HP is quite possible. Adding a suitable drying agent to the bottom still, even 100 % HP is, but can be a bit messy too.
JD
Degussa told us they use fractional freezing at their plant in Germany, but that is the only operation I am aware of. X-L Space Systems produced 98% for years without freezing, and FMC does today, so it certainly isn't a necessity.
John Carmack
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