Definitions

naphtha

naphtha

[naf-thuh, nap-]
naphtha, term usually restricted to a class of colorless, volatile, flammable liquid hydrocarbon mixtures. Obtained as one of the more volatile fractions in the fractional distillation of petroleum (when it is known as petroleum naphtha), in the fractional distillation of coal tar (coal-tar naphtha), and in a similar distillation of wood (wood naphtha), it is used widely as a solvent for various organic substances, such as fats and rubber, and in the making of varnish. Because of its dissolving property it is important as a cleaning fluid; it is also incorporated in certain laundry soaps. Coal-tar (aromatic) naphthas have greater solvent power than petroleum (aliphatic) naphthas. Originally the term naphtha designated a colorless flammable liquid obtained from the ground in Persia. Later it came to be applied to a number of other natural liquid substances having similar properties. Technically, gasoline and kerosene are considered naphthas.
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e. a distillation product from petroleum or coal tar boiling in a certain range and containing certain hydrocarbons, a broad term encompassing any volatile, flammable liquid hydrocarbon mixture.

Naphtha is used primarily as feedstock for producing a high octane gasoline component (via the catalytic reforming process). It is also used in the petrochemical industry for producing olefins in steam crackers and in the chemical industry for solvent (cleaning) applications.

Etymology

The origin of the word Naphtha is unclear. It is an Ancient Greek word that was used to refer to any sort of petroleum or pitch. The Greeks themselves borrowed the word from the Old Persian words nafata, naft or neft, which were used to describe bubbling oil. Naphtha may also have been derived from the name of the Vedic Hindu and Avestic god Apam Napat, a form of Agni, or fire god.

Naphtha is the root of the words naphthalene and napalm, which is derived from naphtha by mixing under controlled conditions with aluminium salts of palmitic acid (a type of soap).

In older usage, naphtha simply meant crude oil, but this usage is now obscure.

Health and safety considerations

Forms of naphtha may be carcinogenic, and frequently products sold as naphtha contain some impurities, which may also have deleterious properties of their own. Like many hydrocarbon products, because they are products of a refractory process where a complex soup of chemicals is broken into another range of chemicals, which are then graded and isolated mainly by their specific gravity and volatility, there is a range of distinct chemicals included in each product. This makes rigorous comparisons and identification of specific carcinogens difficult, especially in our modern environment where exposure to a great number of such products occurs on a daily basis, and is further complicated by exposure to a significant range of other known and potential carcinogens (e.g., see ).

Below are linked some Material Safety Data Sheet (MSDS) specifications for different "naphtha" products, which contain varying degrees of naphtha, as well as various other chemicals. As well as giving health guidelines, these are some of the few ways to determine what a given product contains.

  • JT Baker VM&P Naphtha MSDS
  • Diggers Shellite MSDS
  • Shell Ronsonol MSDS source1 source2
  • Links to more MSDS for various camping-stove fuels including several that include naphtha

Benzene in particular is a known high-risk carcinogen, and so benzene content is typically specified in the MSDS. But more specific breakdown of particular forms of hydrocarbon is not as common.

Properties of naphthas

Physical properties

Molecular weight range is 100-215 g/mol; specific gravity range is 0.75-0.85 g/cm3; boiling point range is 320-430°F; vapor pressure is < 5 mm Hg (< 5 torr). Naphthas are insoluble in water; colorless (kerosene odor) or red-brown (aromatic odor) liquid; incompatible with strong oxidizers.

Production of naphtha in refineries

Naphtha is obtained in petroleum refineries as one of the intermediate products from the distillation of crude oil. It is a liquid intermediate between the light gases in the crude oil and the heavier liquid kerosene. Naphthas are volatile, flammable and have a specific gravity of about 0.7. The generic name naphtha describes a range of different refinery intermediate products used in different applications. To further complicate the matter, similar naphtha types are often referred to by different names.

The different naphthas are distinguished by:

  • density (g/ml or specific gravity)
  • PONA, PIONA or PIANO analysis, which measures (usually in volume percent but can also be in weight percent):

Different types of naphthas

Paraffinic naphthas

Generally speaking, less dense ("lighter") naphthas will have a higher paraffin content. These are therefore also referred to as paraffinic naphtha. The main application for these naphthas is as a feedstock in the petrochemical production of olefins. This is also the reason they are sometimes referred to as "light distillate feedstock" or LDF (these naphtha types can also be called "straight run gasoline"/SRG or "light virgin naphtha"/LVN). When used as feedstock in petrochemical steam crackers, the naphtha is heated in the presence of water vapour and the absence of oxygen or air until the hydrocarbon molecules fall apart. The primary products of the cracking process are olefins (ethylene / ethene, propylene / propene and butadiene) and aromatics (benzene and toluene). These are used as feedstocks for derivative units that produce plastics (polyethylene and polypropylene for example), synthetic fiber precursors (acrylonitrile), industrial chemicals (glycols for instance).

Heavy naphthas

The "heavier" or rather denser types are usually richer in naphthenes and aromatics and therefore also referred to as N&A's. These can also be used in the petrochemical industry but more often are used as a feedstock for refinery catalytic reformers where they convert the lower octane naphtha to a higher octane product called reformate. Alternative names for these types are Straight Run Benzene (SRB) or Heavy Virgin Naphtha (HVN).

Other applications / descriptions

Naphthas are also used in other applications such as:

  • (as an unprocessed component - in contrast to reforming above) in the production of petrol/motor gasoline.
  • industrial solvents and cleaning fluids
  • an oil painting medium
  • the sole ingredient in the home cleaning fluid Energine, which has been discontinued.
  • an ingredient in shoe polish
  • an ingredient in some lighter fluids for wick type lighters such as Zippo lighters.
  • an adulterant to petrol
  • a fuel for portable stoves and lanterns, sold in North America as white gas or Coleman fuel.
  • historically, as a probable ingredient in Greek fire (together with grease, oil, sulfur, and naturally occurring saltpeter from the desert)
  • a fuel for fire spinning, fire juggling, or other fire performance equipment which creates a brighter and cleaner yet shorter burn.
  • to lightly wear the finish (polish) off guitars when preparing "relic" instruments.
  • to remove oil from the aperture blades of camera lenses, which if present can slow the movement of the blades, leading to overexposure.
  • in medieval times, pots containing naphtha were used in battle as a form of primitive grenade.
  • Naptha is used in the furniture industry on "works in progress" to artificially, and temporarily (until it evaporates) see what the patina will look like when the piece is oiled and/or aged. It is useful in matching adjacent boards for a join, primarily with tabletops, panels and shelves.
  • in the process of extracting pure dextromethorphan from cough syrup
  • fuel in torches used by torch jugglers

Health hazards

“Light naphtha, a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from five to nine carbon atoms per molecule. Heavy naphtha, a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from seven to nine carbons per molecule.” “Almost all volatile, lipid-soluble organic chemicals cause general, nonspecific depression of the central nervous system or general anesthesia.” The OSHA PEL TWA = 100 parts-per-million (ppm); Health Hazards/Target Organs = eyes, skin, RS, CNS, liver kidney. Symptoms of acute exposure are dizziness and narcosis with loss of consciousness. The World Health Organization categorizes health effects into three groups: reversible symptoms (Type 1), mild chronic encephalopathy (Type 2) and severe chronic toxic encephalopathy (Type 3).

Examples in daily life

Shellite (Australia), also known as white gas (North America), white spirit or Coleman fuel, is a water white liquid with a hydrocarbon odour. Shellite has a freeze point less than , and a boiling point of . The composition of shellite is 95% paraffins and naphthenes, less than 5% aromatic hydrocarbons and less than 0.5% benzene. It is highly flammable and due to its low flashpoint is used in many low pressure camping stoves. Shellite is also a fast drying solvent used for cleaning metal, hard plastic and painted surfaces. Ronsonol is a brand name used in North America, and is marketed principally as a refill fluid for cigarette lighters and has a flashpoint of about .

References

See also

External links

Additional Sources

  • McDermott, Henry J. (2004). Air Monitoring for Toxic Exposures (Second Edition) John Wiley & Sons, Inc.

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