I concentrated 50% rubbing alcohol to 90%+ that I can use if our supply of hand sanitizer runs out.
It was pretty easy too.
Dump and mix pure salt (non iodized) into the rubbing alcohol. You need to keep adding salt intil it won't dissolve any further - the water becomes super saturated with salt. This in turns makes the water more dense than the alcohol, and the water will fall to the bottom, while the alcohol will rise to the top. I removed the alcohol on top with a turkey baster and put back in the rubbing alcohol container. The method is pretty efficient. From a 16 oz bottle of 50% rubbing alcohol I was able to extract around 7.5 oz of alcohol.
This method would probably work with vodka or everclear, but it would be incredibly expensive considering the additional taxes on consumable alcohol.