Naphtha

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Not to be confused with Naphthalene.
Coleman camp fuel, also known as white gas, is a common naphtha fuel used in many lanterns and torches.

Naphtha is a name given to several mixtures of liquid hydrocarbons that are extremely volatile and flammable. Each such mixture is obtained during the distillation of petroleum or coal tar, and occasionally by the distillation of wood. Accordingly, it is known by different names, such as petroleum naphtha, coal-tar naphtha, or wood naphtha.

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.

Contents

Etymology

The origin of the word naphtha is unclear. It was an ancient Greek word that referred to any type 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 god Apam Napat, the god of freshwater, sometimes described as a fire god.

Alternative names

Naphtha is known by various names, depending on its source, composition, uses, and manufacturing company. Some names include ligroin, VM&P Naphtha (Varnish Makers and Painter's Naphtha,[1] Benzin, petroleum naphtha, petroleum spirits, and naphtha ASTM. Another name is shellite (Australia)—also known as white gas (North America), white spirit, or Coleman fuel—which is a white liquid with a hydrocarbon odor. Given its high flammability and low flashpoint (less than -30 °C), it is used in many low-pressure camping stoves. Ronsonol is a brand name used in North America and is marketed as a refill fluid for cigarette lighters.

Properties

To obtain the product known as naphtha, 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. As a result, the product contains a range of distinct chemicals with a range of properties. They generally have a molecular weight range of 100-215, a specific gravity range of 0.75-0.85, and a boiling point range of 70-430 °F. Their vapor pressure is usually less than 5 mm mercury.

Naphthas are insoluble in water. They are colorless (with a kerosene odor) or red-brown (with an aromatic odor). They are incompatible with strong oxidizers.[2]

Generally speaking, less dense naphthas ("light naphthas") have a higher paraffin content. They are therefore also called paraffinic naphtha. The denser naphthas ("heavy naphthas") are usually richer in naphthenes and aromatics, and they are therefore referred to as N&A's.

Production of naphtha in refineries and uses

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):
    • Paraffin content (volume percent)
    • Isoparaffin content (only in a PIONA analysis)
    • Olefins content (volume percent)
    • Naphthenes content (volume percent)
    • Aromatics content (volume percent)

Paraffinic (or light) naphthas

The main application for paraffinic ("light") naphthas is as 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 may 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 vapor 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), and industrial chemicals (glycols, for instance).

Heavy naphthas

The "heavy" naphthas can also be used in the petrochemical industry, but they are more often used as 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).

Additional applications

Naphthas are also used in other applications, such as:

  • in the production of gasoline.
  • in industrial solvents and cleaning fluids
  • an oil painting medium
  • the sole ingredient in the home cleaning fluid Energine, which has been discontinued. You can purchase this type of naphtha at any hardware store.
  • 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 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.

Health and safety considerations

Forms of naphtha may be carcinogenic, and products sold as naphtha frequently contain some impurities that may have deleterious properties of their own.[3] Given that the term naphtha is applied to different products, each containing a variety of distinct chemicals, it is difficult to make rigorous comparisons and to identify specific carcinogens. This task is further complicated by the presence of a number of other known and potential carcinogens in modern environments.[4]

Below are links to some Material Safety Data Sheet (MSDS) specifications for different "naphtha" products, which contain varying proportions of naphtha and other chemicals. Besides giving health guidelines, they provide one of the few ways to determine what a given product contains.

  • Petroleum Ether MSDS[5]
  • Diggers Australia Shellite[6]
  • Shell Ronsonol Lighter Fuel[7]
  • MSDS for camping-stove fuels[8]

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.

According to J. LaDou in Occupational and Environmental Medicine,[9] "Almost all volatile, lipid-soluble organic chemicals cause general, nonspecific depression of the central nervous system or general anesthesia." The U.S. Occupational Health and Safety Administration (OSHA) places the permissible exposure limit (PEL) at 100 parts per million (ppm); and the Health Hazards/Target Organs are listed as eyes, skin, RS, CNS, liver, and 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).

Toxicity

Toxicity dose response exposures may be impacted (decreased or increased) by chemical, biological, and environmental factors.

  • Chemical factors include concentrations of the chemicals, their interactions with one another, dispersability, toxicity, water solubility, particle size, bioavailability, persistence in the body, and so forth.
  • Biological factors include stress, respiratory rate, gender, age, race, individual susceptibility, route of entry, rate of uptake, storage in the body, metabolism, and excretion.
  • Environmental factors can affect chemical and particulate exposures, such as by temperature, air pressure, air quality, and precipitation.

Air sampling for naphthas

Air sampling is conducted to identify and evaluate employee or source exposures of potentially hazardous gases or particulates; assess compliance; and evaluate process or reformulation changes.

Two categories of air sampling equipment exist, they are: direct reading and sample collection.

  • Direct reading equipment provides immediate measurement of exposure concentration.
  • Sample collection equipment takes samples of air over a period of time, and these samples are then weighed and analyzed in a laboratory.

Sample collection involves active and passive air monitoring methods. Active sampling relies on sampling pumps to draw air and chemical vapors or gases to adsorbent filter materials. Passive monitors rely on the collection of gases and vapors through passive diffusion to allow personal sampling without use of pumps.[10]

Sampling types

Various types of sampling may be used, as noted below.

  • Personal sampling: Personal sampling is used to evaluate employee exposure to naphtha. The employee wears the sampling device that collects an air sample representative of air exposure for a specific period of time.
  • Area Sampling: Area Sampling is used to evaluate background exposure to leaks and implement control measures.
  • Grab Sampling: Grab sampling is used to monitor extremely toxic environments over a short period of time, or to determine if additional air monitoring is required for over-exposure.
  • Integrated Sampling: Integrated exposure sampling is used to determine the 8-hour time weighted average exposure because various exposure concentrations are integrated during the sampling period.

Complications

Complications with air sampling can occur in the form of interference with chemicals (alcohols, ketones, ethers, and halogenated hydrocarbons), vapors, sampling media, humidity, temperature, barometric pressure, atmospheric dust, water vapor, and container.

Exposure Control

Primary methods focus on preventing chemical exposures before they occur. Personal protective equipment could include the use of air-purifying cartridges, respirators, and gloves. Engineering prevention controls would include automated handling, enclosure and elimination of harmful substances, isolation, and change of process. Ventilation controls would include local exhaust ventilation and vacuum operations. Administrative prevention controls would include changes in work practices, education, training, job rotation, job reduction, job reassignment, and proper maintenance and housekeeping.

Secondary methods focus on early identification and treatment of chemical exposures.

Tertiary methods include the treatment and rehabilitation of employees overexposed to harmful chemicals in the workplace.

See also

Notes

  1. "NIOSH Pocket Guide to Chemical Hazards": VM & P Naphtha Retrieved August 19, 2007.
  2. NIOSH CAS No.: 8032-32-4, NIOSH "Pocket Guide to Chemical Hazards" 8030-30-6, (September 2005)8002-05-9Retrieved October 12, 2007.
  3. Report of the International Agency for Research on Cancer. Retrieved August 19, 2007.
  4. For instance, see Study of Health Outcomes in Aircraft Maintenance Personnel. Retrieved August 19, 2007.
  5. Mallinckrodt Baker, Petroleum Ether MSDS. Retrieved August 19, 2007.
  6. Diggers Australia, Shellite MSDS Retrieved August 19, 2007
  7. Shell Ronsonol Lighter Fuel MSDS Retrieved August 19, 2007
  8. North American Fire Arts Association. MSDS for various camping-stove fuels including several that include naphtha. Retrieved August 19, 2007
  9. J. LaDou, Occupational and Environmental Medicine, 3rd ed. (Lange Medical Books, McGraw Hill, 2004), 508.
  10. Diffusion is the movement or passage of chemical molecules through a semi-permeable barrier from the source of higher concentration to a lower concentration.

References

  • Burton, D. J. 2002. Burton Field Guide for Industrial Hygiene. Fairfax, VA: AIHA. ISBN 1931504326
  • McDermott, Henry J. 2004. Air Monitoring for Toxic Exposures, 2nd ed. Hoboken, NJ: Wiley-Interscience. ISBN 0471454354
  • Meyer, Eugene. 2004. Chemistry of Hazardous Materials, 4th ed. Upper Saddle River, NJ: Pearson Prentice Hall. ISBN 0131127608

External links

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