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.
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.
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, 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.
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.
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.
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:
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).
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).
Naphthas are also used in other applications, such as:
Forms of naphtha may be carcinogenic, and products sold as naphtha frequently contain some impurities that may have deleterious properties of their own. 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.
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.
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, "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 dose response exposures may be impacted (decreased or increased) by chemical, biological, and environmental factors.
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.
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.
Various types of sampling may be used, as noted below.
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.
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.
All links retrieved December 20, 2014.
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