The chemistry is kind of interesting. If you distill isopropyl alcohol, you can't get more concentrated than 91% because it forms an azeotrope. That is, if you

The chemistry is kind of interesting. If you distill isopropyl alcohol, you can't get more concentrated than 91% because it forms an azeotrope. That is, if you try to distill 91% isopropyl alcohol, the vapors are also 91% concentration, so distillation doesn't get you any further. Thus, 91% isopropyl alcohol is a common product. Similarly, ethanol forms an azeotrope at 95% concentration, so you can't distill higher than that. This is why, for instance, Everclear has a 95% alcohol concentration. (You can produce higher concentrations, of course, but it requires a more expensive process than distillation.) https://en.wikipedia.org/wiki/Azeotrope https://en.wikipedia.org/wiki/Azeotrope