Have you ever wondered why grain alcohol like Everclear or Graves are only 95% ethanol (190 proof)? I have. I assumed it was an ROI thing. My theory figured the increased cost to distill the alcohol to such a purity would force up the price, which customers would not bear. Apparently, there’s a different reason altogether, and it’s a chemistry thing.
The yeast that creates alcohol dies at around 14% concentration. This is why beers and wines are rarely found even above 18- or 20-proof. In order to make stronger drinks, the water-alcohol mixture is distilled, which is really just another word for evaporating them. Alcohol boils at a far lower temperature than water, so if you collect the vapor and recondense it, you end up with a lot more alcohol than water.
But a funny thing happens as water is left behind. The more alcohol there is in the solution, the higher its boiling point (and the lower of that of the water). Somewhere around 95% or 96% alcohol, they converge, and the two liquids boil at the same time (at only 173°F). Simple distillation will not allow you to do any better.
So what if you need absolutely pure alcohol? There is an option. You can add benzene to the mixture. This changes the behavior of the solution, and allows the alcohol to boil away again. Unfortunately, benzene is terribly harmful, even in extremely tiny amounts. Bone marrow damage, a weakened immune system, severe liver disease, and a highly increased chance of cancer are some of the fates that would await you if you were unsatisfied with 190-proof grain alcohol.