Denatured alcohol is used as a solvent and as fuel for spirit burners and camping stoves. Because of the diversity of industrial uses for denatured alcohol, hundreds of additives and denaturing methods have been used. Traditionally, the main additive is 10% methanol, giving rise to the term methylated spirit. Other typical additives include isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and denatonium.
Different additives are used to make it difficult to use distillation or other simple processes to reverse the denaturation. Methanol is commonly used because its boiling point is close to that of ethanol. In many countries, it is also required that denatured alcohol be dyed blue or purple with an aniline dye.
The tax-exempt status for denatured alcohol dates from the mid-19th century.
Denatured alcohol is not, in itself, a preferred product — that is, it is not something which would be normally demanded if given the alternative of normal ethanol. Denatured alcohol and its manufacture are a public policy compromise. The supply and demand for denatured alcohol arises from the fact that normal alcohol (specifically ethanol, suitable for human consumption as a drink) is usually very expensive compared to similar chemicals, being highly taxed for revenue and public health policy purposes (see sin tax). As a result, if pure ethanol were made cheaply available as a fuel or solvent, people would drink it.
Denatured alcohol provides a solution to permit legitimate use and manufacture of ethanol, whereby cheap ethanol can be made available for non-consumption use without the risk of it being converted for consumption. The process creates a modified ethanol that is not suitable for drinking, but is otherwise similar to ethanol for most purposes. As a result there is no duty on denatured alcohol in most countries, making it considerably cheaper than pure ethanol. Consequently, its composition is tightly defined by government regulations which vary between countries.
In instances where absolutely pure ethanol is needed at a reasonable non-consumption-taxed price (for example, at chemical research laboratories), tight security procedures are required to eliminate the possibility of conversion for human consumption — specifically, tracking the purchase and distribution of the alcohol and ensuring compliance of workers who handle the pure ethanol.
There are several grades of denatured alcohol, but the denaturants used are generally similar. The formulation for completely denatured alcohol, according to British regulations is typical:
Completely denatured alcohol must be made in accordance with the following formulation: with every 90 parts by volume of alcohol mix 9.5 parts by volume of methanol or a substitute for methanol and 0.5 parts by volume of crude pyridine, and to the resulting mixture add mineral naphtha (petroleum oil) in the proportion of 3.75 litres to every 1000 litres of the mixture and synthetic organic dyestuff (methyl violet) in the proportion of 1.5 grams to every 1000 litres of the mixture.
Denatured alcohol has a variety of common uses:
In the United States, small amounts of denatured alcohol are used in many consumer products such as toothpaste where they are labeled as "SD alcohol XX", where SD stands for "specially denatured" and XX is the formula used in the denaturing process that specifies the denaturants. These formulas for denatured alcohol are found in 27 CFR part 21 of the Code of Federal Regulations. Some of these formulas, such as SD alcohol 38-B, are designed to be unpalatable but otherwise non-poisonous; they are used in applications like mouthwashes where some amount of incidental ingestion is expected. (The specific denaturants in formulas 37 and 38-B closely resemble the active ingredients in alcohol-based mouthwashes like Listerine.)
Despite its poisonous nature, denatured alcohol is sometimes consumed as a surrogate alcohol, which can result in blindness or death if denatured alcohol contains methanol. To help prevent this, denatonium is often added to give the substance an extremely bitter flavor. Substances such as pyridine help to give the mixture an unpleasant odor, and emetic (vomiting) agents such as syrup of ipecac may also be included. In Poland and other European countries denatured alcohol contains only substances having bitter flavor (like acetylsalicylic acid) and odour, and does not contain methanol or any substance of severe toxicity.