KOH.(H2O)x
x=4 MP -32.7°C
x=2 MP 35.5°C
x=1.5 and 1 MP 143°C
(Pickering, J.C.S., 1893, 63, 890)
At about 200°C I can't really see much more than small amounts of Carbonate forming.
If you are really bothered by small amounts of carbonate, heat the KOH in an inert atmosphere/vacuum, or heat the KOH higher than 1000°C to rid the CO2
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