Wow! I was actually in the middle of distilling 99% isopropyl alcohol that is roughly 3 years old. I had distilled roughly 250ml without incident I
browsed and found this! The only reason I was distilling isopropyl was because it was cloudy with what I presume is denatonium benzoate. I did not
want to burn the impurities into my new round bottom flask so I was never planning on distilling to dryness. I am not sure when distilling to dryness
is ever a good idea. Anyways, after this thread I made a strong ferrous sulfate solution acidified with sulfuric acid. I added it to the remaining
250 that I was about to distill and stirred.
When I applied heat the ferrous sulfate started to produce bubbles at 35 Celsius similar like hydrogen peroxide decomposition. Judging
about what I saw any peroxide that was present was pretty dilute as definitely less than 1%. The temperature then rapidly rose to 80 Celsius and
water clear isopropyl alcohol came over 2 drops a second. The ferrous sulfate precipitated to the bottom and it became more a grey green color. I
stopped distillation when I received 250 ml of clear distillate. I discarded roughly 100 ml of fluid into fire pit for incineration. Although
initially I saw some peroxide action, nothing suggested that such a hazard exists. Maybe a preliminary heating with acid ferrous sulfate then
distillation is feasible. But then again 99 % isopropyl alcohol is cheap and widely available. I just had cloudy alcohol that I wanted clear for
solvent dyes.
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