Petroleum naphtha is an intermediate hydrocarbon liquid stream derived from the refining of crude oil with CAS-no 64742-48-9. It is most usually desulfurized and then catalytically reformed, which rearranges or restructures the hydrocarbon molecules in the naphtha as well as breaking some of the molecules into smaller molecules to produce a high-octane component of gasoline (or petrol).
There are hundreds of different petroleum crude oil sources worldwide and each crude oil has its own unique composition or assay.
There are also hundreds of petroleum refineries worldwide and each of
them is designed to process either a specific crude oil or specific
types of crude oils. Naphtha is a general term as each refinery produces
its own naphthas with their own unique initial and final boiling points
and other physical and compositional characteristics.
Naphthas may also be produced from other material such as coal tar, shale deposits, tar sands, and the destructive distillation of wood.
Naphthas may also be produced from other material such as coal tar, shale deposits, tar sands, and the destructive distillation of wood.
The major source of petroleum naphtha in a petroleum refinery
The first unit operation in a petroleum refinery is the crude oil distillation unit. The overhead liquid distillate from that unit is called virgin or straight-run
naphtha and that distillate is the largest source of naphtha in most
petroleum refineries. The naphtha is a mixture of many different
hydrocarbon compounds. It has an initial boiling point (IBP) of about 35 °C and a final boiling point (FBP) of about 200 °C, and it contains paraffins, naphthenes (cyclic paraffins) and aromatic hydrocarbons ranging from those containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.
The virgin naphtha is often further distilled into two streams:
- a virgin light naphtha with an IBP of about 30 °C and a FBP of about 145 °C containing most (but not all) of the hydrocarbons with six or fewer carbon atoms
- a virgin heavy naphtha containing most (but not all) of the hydrocarbons with more than six carbon atoms. The heavy naphtha has an IBP of about 140 °C and a FBP of about 205 °C.
The virgin heavy naphtha is usually processed in a catalytic
reformer, because the light naphtha has molecules with six or fewer
carbon atoms—which, when reformed, tend to crack into butane and lower
molecular weight hydrocarbons that are not useful as high-octane
gasoline blending components. Also, the molecules with six carbon atoms
tend to form aromatics, which is undesirable because the environmental
regulations of a number of countries limit the amount of aromatics (most
particularly benzene) in gasoline.
Types of virgin naphthas
The
table below lists some typical virgin heavy naphthas, available for
catalytic reforming, derived from various crude oils. It can be seen
that they differ significantly in their content of paraffins, naphthenes
and aromatics:
| Crude oil name Location |
Barrow Island Australia |
Mutineer-Exeter Australia |
CPC Blend Kazakhstan |
Draugen North Sea |
|---|---|---|---|---|
| Initial boiling point, °C | 150 | 140 | 149 | 150 |
| Final boiling point, °C | 200 | 190 | 204 | 180 |
| Paraffins, liquid volume % | 46 | 62 | 57 | 38 |
| Naphthenes, liquid volume % | 42 | 32 | 27 | 45 |
| Aromatics, liquid volume % | 12 | 6 | 16 | 17 |
Cracked naphthas
Some refinery naphthas also contain some olefinic hydrocarbons, such as naphthas derived from the fluid catalytic cracking, visbreakers and coking processes used in many refineries. Those olefin-containing naphthas are often referred to as cracked naphthas.
In some (but not all) petroleum refineries, the cracked naphthas
are desulfurized and catalytically reformed (as are the virgin naphthas)
to produce additional high-octane gasoline components.
Other uses
Some petroleum refineries also produce small amounts of specialty
naphthas for use as solvents, cleaning fluids and dry-cleaning agents,
paint and varnish diluents, asphalt diluents, rubber industry solvents, recycling products, and cigarette-lighter, portable-camping-stove and lantern fuels. Those specialty naphthas are subjected to various purification processes.
Sometimes the specialty naphthas are called petroleum ether, petroleum spirits, mineral spirits, paraffin, benzine, hexane, ligroin, white oil or white gas, painters naphtha, refined solvent naphtha and Varnish makers' & painters' naphtha (VM&P).
The best way to determine the boiling range and other compositional
characteristics of any of the specialty naphthas is to read the Safety Data Sheet (SDS) for the specific naphtha of interest.
On a much larger scale, petroleum naphtha is also used in the petrochemicals industry as feedstock to steam reformers and steam crackers for the production of hydrogen (which may be and is converted into ammonia for fertilizers), ethylene, and other olefins. Natural gas is also used as feedstock to steam reformers and steam crackers.
Safety
People can be exposed to petroleum naphtha in the workplace by breathing it, swallowing it, skin contact, and eye contact. The Occupational Safety and Health Administration (OSHA) set the legal limit (permissible exposure limit) for petroleum naphtha exposure in the workplace as 500 ppm (2000 mg/m3) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 350 mg/m3 over an 8-hour workday and 1800 mg/m3 over 15 minutes. At levels of 1100 ppm, 10% of the lower explosive limit, petroleum naphtha is immediately dangerous to life and health.
Other napthas
Mixtures labelled naphtha have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat.
In different industries and regions naphtha may also be crude oil or refined products such as kerosene. Mineral spirits, also historically known as "naphtha", are not the same chemical.
Nephi and naphthar are sometimes used as a synonyms.
Etymology
White gas, exemplified by Coleman Camp Fuel, is a common naphtha-based fuel used in many lanterns and torches
The word naphtha is from Latin and Ancient Greek (νάφθα), derived from Middle Persian naft ("wet", "naphtha"), the latter meaning of which was an assimilation from the Akkadian napṭu (see Semitic relatives such as Arabic نَفْط nafṭ ("petroleum"), Syriac ܢܰܦܬܳܐ naftā, and Hebrew נֵפְט neft). In Ancient Greek, it was used to refer to any sort of petroleum or pitch.
In the Song of the Three Children
the Greek word νάφθα designates one of the materials used to stoke the
fiery furnace. The translation of Charles Brenton renders this as "rosin".
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 нафта (nafta), Lithuanian, Latvian and Estonian "nafta", the Russian word нефть (neft') and the Persian naft (نفت) mean "crude oil". Also, in Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Finland, Italy, Serbia, Slovenia, nafta (нафта 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 (петрол 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.
Types
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.
Uses
Heavy crude oil dilution
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.
Health and safety considerations
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.
