Naphtha ( or ) is a flammable liquid hydrocarbon mixture.
The word naphtha is from Latin and Ancient Greek (), derived from Middle Persian naft ("wet", "naphtha"), the latter meaning of which was an assimilation from the Akkadian nap?u (see Semitic relatives such as Arabic naf? ("petroleum"), Syriac naft?, and Hebrew neft). In Ancient Greek, it was used to refer to any sort of petroleum or pitch.
The book of II Maccabees tells how a "thick water" was put on a sacrifice at the time of Nehemiah and when the sun shone it caught fire. It adds that "those around Nehemiah termed this 'Nephthar', which means Purification, but it is called Nephthaei by the many [literally hoi polloi]."
It enters the word napalm, a contraction of the "na" of naphthenic acid and "palm" of palmitic acid, originally made from a mixture of naphthenic acid combined with aluminium and magnesium salts of palmitic acid. Naphtha is the root of the word naphthalene, and can also be recognised in the word phthalate, and the paint colour phthalo blue.
In older usage, "naphtha" simply meant crude oil, but this usage is now obsolete in English. It was also used for mineral spirits (also known as "Stoddard Solvent"), originally the main active ingredient in Fels Naptha laundry soap. The Ukrainian and Belarusian word (nafta), Lithuanian, Latvian and Estonian "nafta", the Russian word (neft') and the Persian naft () mean "crude oil". Also, in Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Finland, Italy, Serbia, Slovenia, nafta ( in Cyrillic) is colloquially used to indicate diesel fuel and crude oil. In the Czech Republic and Slovakia, nafta was historically used for both diesel fuel and crude oil, but its use for crude oil is now obsolete and it generally indicates diesel fuel. In Bulgarian, nafta means diesel fuel, while neft, as well as petrol ( in Cyrillic), means crude oil. In Nafta is also used in everyday parlance in Argentina, Paraguay and Uruguay to refer to gasoline/petrol. In Poland, the word nafta means kerosene,, as in lampa naftowa "paraffin lamp"; crude oil and (colloquially) diesel fuel are called ropa "pus". In Flemish, the word naft is used colloquially for gasoline.
There is a hypothesis that the word is connected with the name of the Indo-Iranian god Apam Napat, which occurs in Vedic and in Avestic; the name means "grandson of (the) waters", and the Vedas describes him as emerging from water golden and shining "with bright rays", perhaps inspired by a burning seepage of natural gas.
Various qualifiers have been added to the term "naphtha" by different sources in an effort to make it more specific:
One source distinguishes by boiling point:
Light naphtha is the fraction boiling between 30 °C and 90 °C and consists of molecules with 5-6 carbon atoms. Heavy naphtha boils between 90 °C and 200 °C and consists of molecules with 6-12 carbon atoms.
Another source differentiates light and heavy comments on the hydrocarbon structure, but offers a less precise dividing line:
Light [is] a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from five to six carbon atoms per molecule. Heavy [is] a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from seven to nine carbon atoms per molecule.
Both of these are useful definitions, but they are incompatible with one another and the latter does not provide for mixes containing both 6 and 7 carbon atoms per molecule. These terms are also sufficiently broad that they are not widely useful.
Naphtha is used to dilute heavy crude oil to reduce its viscosity and enable/facilitate transport; undiluted heavy crude cannot normally be transported by pipeline, and may also be difficult to pump onto oil tankers. Other common dilutants include natural-gas condensate, and light crude. However, naphtha is a particularly efficient dilutant and can be recycled from diluted heavy crude after transport and processing. The importance of oil dilutants has increased as global production of lighter crude oils has fallen and shifted to exploitation of heavier reserves.
The safety data sheets (SDSs) from various naphtha vendors are also indicative of the non-specific nature of the product and reflect the considerations due for a flammable mixture of hydrocarbons: flammability, carcinogenicity, skin and airway irritation, etc.
Humans can be exposed to naphtha in the workplace by inhalation, ingestion, dermal contact, and eye contact. The US Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit for naphtha in the workplace as 100 ppm (400 mg/m3) over an 8-hour workday. The US National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 100 ppm (400 mg/m3) over an 8-hour workday. At levels of 1000 ppm, which equates to 10% of the lower explosive limit, naphtha is immediately dangerous to life and health.