What is put in/taken out of alcohol to make it “denatured.” Why bother doing this process?
They add a little methanol (Wood alcohol) to ethanol (grain alcohol). Not enough to alter the physical/chemical properties of ethanol, but just enough to “poison” it so that the alcohol isn’t taxed as liquor.
I’ve often wondered about everclear. The stuff is … uhh … “fully natured alcohol”, i.e. 100% ethanol with none of that nasty methanol mixed in. Does this mean it’s taxed as liquor? But it’s for industrial cleaning, rather than drinking, right (notwithstanding the preferences of certain college students)? What I’m getting at, is what non-drinking purposes would be spoiled by methylating spirit, thus necessitating the use of everclear?
Huh? I thought Everclear was a liquor intended for drinking. Not straight, now, but for mixing?
Ethanol is denatured in several different ways depending on what it is to be used for. The most common denaturents are methanol, kerosene, and benzene/petrolleum distillates.
Denaturants can cause problems when they are found in alcohol used as a solvent for chemical synthesis (e.g. ethyl vs methyl esters), in biological extractions where methanol is far harder on cell membranes than ethanol, and in various chromatographic applications.
Non-denatured 95% ethanol (aka everclear), as well as anhydrous (100%) ethanol are available, without taxation, to chemical laboratories.
Ethanol is denatured in several different ways depending on what it is to be used for. The most common denaturents are methanol, kerosene, and benzene/petrolleum distillates.
Denaturants can cause problems when they are found in alcohol used as a solvent for chemical synthesis (e.g. ethyl vs methyl esters), in biological extractions where methanol is far harder on cell membranes than ethanol, and in various chromatographic applications.
Non-denatured 95% ethanol (aka everclear), as well as anhydrous (100%) ethanol are available, without taxation, to chemical laboratories.
My chem teacher denatures the 95% ethanol* she gets for use in the lab with phenalpthalein (sp?), an acid-base indicator…which also used to be the “gentle” ingredient in Ex-Lax. They can always tell who’s been nipping the lab alcohol 
*–Everclear and other brands of “pure” ethanol are actually 95% ethanol, 5% water because that mixture boils at a lower temperature than 100% ethanol. Therefore, 95% is as good as you can get by distillation. You want better than that, it gets really expensive to produce (molecular sieves and such).
Boris: AFAIK it is sold in liquor stores and taxed as such.
I’m pretty sure Everclear is intended to be used as a “spike” for drinks, although I understand some lunatics drink it straight. Why would they sell an “industrial cleanser” in a liquor store?
During Prohibition there was a “ring” in my ome town in New Jersey that bought denatured alcohol and distilled out the ethanol, which they then took to New York City and sold. Considering that “denaturing” was often done with benzene (carcinogen) or methanol (more immediate health effects), this is a scary prospect. Big operation – they did this at a chemical plant, with the collusion of government officials.
Sometimes you just gotta use the straight stuff. When I was in Utah I needed absolute ethanol for my experiments. This was tough to get, especially in Utah – Absolute (“un-denatured”) alcohol is subject to state liquor laws, and each bottle bore a liquor tax stamp. It was the one item that required in-person signing out at the supply center.
Mmm… azeotropic…
Might also add that for people like myself that only use non-recreational alcohol for cleaning lab equipment, denatured ethanol works just as good as 100% ethanol and is a hell of a lot cheaper. (Although for my purposes ethanol is not quite as good or as cheap as acetone, my liver feels safer in an acetone-free lab.)
It is possible to get past the azeotrope using distillation techniques. This, however, would require multiple columns and either a higher pressure column or the addition of a third component to the mixture as an entrainer. Unless you needed high purity ethanol on a mass scale, other techniques such as molecular sieving and pervaporation remain more cost efficient.