Ethylbenzene
Ethylbenzene is an organic compound with the formula C6H5CH2CH3. It is a highly flammable, colorless liquid with an odor similar to that of gasoline. This monocyclic aromatic hydrocarbon is important in the petrochemical industry as a reaction intermediate in the production of styrene, the precursor to polystyrene, a common plastic material. In 2012, more than 99% of ethylbenzene produced was consumed in the production of styrene.
Ethylbenzene occurs naturally in coal tar and petroleum. The dominant application of ethylbenzene is its role as an intermediate in the production of polystyrene. Catalytic dehydrogenation of ethylbenzene gives hydrogen and styrene. Ethylbenzene hydroperoxide, a reagent and radical initiator, is produced by autoxidation of ethylbenzene.
Ethylbenzene is added to gasoline as an anti-knock agent to reduce engine knocking and increase the octane rating. Ethylbenzene is often found in other products, including pesticides, cellulose acetate, synthetic rubber, paints, and inks. Used in the recovery of natural gas, ethylbenzene may be injected into the ground.
Ethylbenzene is produced on a large scale by combining benzene and ethene in an acid-catalyzed chemical reaction. In 2012, more than 99% of ethylbenzene was produced in this way. Small amounts of ethylbenzene are recovered from the mix of xylenes by superfractioning, an extension of the distillation process.
On June 3, 2014, an explosion occurred in the Dutch Moerdijk industrial area. This happened in a chemical reactor operated by Shell which overheated due to an exothermal runaway reaction between the metal oxide catalyst and ethylbenzene.
Ethylbenzene is found mostly as a vapor in the air since it can easily move from water and soil. A median concentration of 0.62 parts per billion (ppb) was found in urban air in 1999. A study conducted in 2012 found that in country air the median concentration was found to be 0.01 ppb and indoors the median concentration was 1.0 ppb. It can also be released into the air through the burning of coal, gas, and oil. The use of ethylbenzene in the industry contributes to ethylbenzene vapor in the air. After about three days in the air with the help of sunlight, other chemicals break down ethylbenzene into chemicals that can be found in smog. Since it does not readily bind to soil it can also easily move into groundwater. In surface water, it breaks down when it reacts with chemicals naturally found in water. Generally, ethylbenzene is not found in drinking water, however it can be found in residential drinking water wells if the wells are near waste sites, underground fuel storage tanks that are leaking, or landfills.
As of 2012, according to the EU Dangerous Substances Directive, ethylbenzene is not classified as hazardous to the environment. Ethylbenzene is a constituent of tobacco smoke.
Certain strains of the fungus Cladophialophora can grow on ethylbenzene. The bacterium Aromatoleum aromaticum EbN1 was discovered due to its ability to grow on ethylbenzene.
Acute (short-term) exposure to ethylbenzene in humans results in respiratory effects, such as throat irritation and chest constriction, irritation of the eyes, and neurological effects such as dizziness[2]. Chronic (long-term) exposure to ethylbenzene by inhalation in humans has shown conflicting results regarding its effects on the blood[2]. Animal studies have reported effects on the blood, liver, and kidneys from chronic inhalation exposure to ethylbenzene[2]. Limited information is available on the carcinogenic effects of ethylbenzene in humans[2]. In a study by the National Toxicology Program (NTP), exposure to ethylbenzene by inhalation resulted in an increased incidence of kidney and testicular tumors in rats, and lung and liver tumors in mice[2]. EPA has classified ethylbenzene as a Group D, not classifiable as to human carcinogenicity[2].
Ethylbenzene may cause cancer in humans[4]. It causes tumors in the kidneys, lungs and liver of animals as well as severe inner ear damage[4]. The International Agency for Research on Cancer classified ethylbenzene as a possible human carcinogen[4]. When rats were fed high doses of ethylbenzene over long periods of time, they experienced severe damage to the inner ear[4]. Rats developed kidney tumors and mice developed lung and liver tumors in a two-year study[4].
A person can come in contact with ethylbenzene from skin contact with consumer products (including gasoline and automotive products, carpet glues, varnishes, paints and tobacco products), by drinking contaminated water, or by breathing in contaminated air[4]. In indoor air, the concentration of ethylbenzene is higher than the concentration of outdoor air[4]. National Health and Nutrition Examination Survey (NHANES) 2014 data indicate that ethylbenzene is detectable in the blood of the general U.S. population[4].
Ethylbenzene is a clear, colorless liquid[5]. It is used as a solvent, in making other chemicals (especially Styrene), and in the rubber and plastic industries[5]. Ethylbenzene can affect you when inhaled and by passing through the skin[5]. Ethylbenzene should be handled as a CARCINOGEN-- WITH EXTREME CAUTION[5]. Contact can irritate the skin and eyes[5]. Prolonged or repeated exposure can cause drying and scaling of the skin with redness and blisters[5]. Inhaling Ethylbenzene can irritate the nose and throat[5].
Citations:
[1] https://en.wikipedia.org/wiki/Ethylbenzene
[2] https://www.epa.gov/sites/default/files/2016-09/documents/ethylbenzene.pdf
[3] https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=382&toxid=66
[4] https://www.healthvermont.gov/sites/default/files/documents/pdf/ENV_CDP_100_41_4_Ethylbenzene.pdf
[5] https://nj.gov/health/eoh/rtkweb/documents/fs/0851.pdf