Styrene

Description

Styrene has a characteristic, sweet, balsamic, almost floral odor that is extremely penetrating. Styrene occurs naturally in plants. It was first isolated from a resin called storax obtained from the inner bark of the Oriental sweet gum tree (Liquidambar orientalis) by Bonastre. In 1839, the German apothecary Eduard Simon prepared styrene by distilling it from storax and called it styrol. Simon observed it solidifi ed into a rubbery substance after being stored and believed it had oxidized into styrol oxide. Subsequent analysis showed the solid did not contain oxygen and it was renamed metastyrol. This was the first written record of polymerization in chemistry. In 1845, the English chemist, John Blyth, and the German chemist, August Wilhelm von Hofmann (1818 1892), observed that styrene was converted to polystyrene by sunlight and that styrene could be polymerized to polystyrene by heating in the absence of oxygen. It took another 70 years for the polymerization of styrene to be described by Hermann Staudinger (1881 1965) in the 1920s. This laid the foundation for the commercial polystyrene industry that developed in the 1930s.

Description

Styrene is a sweet-smelling, oily liquid that is almost insoluble in water but is miscible with most organic solvents. Its name comes from styrax (or storax) balsam, the resin of the Liquidambar genus of trees that grow in many places worldwide. M. Bonastre first isolated it in 1831 by distilling the balsam.
Styrene is among the most widely manufactured industrial chemicals: Production is approaching 30 million tonnes per year. Almost all of it is produced by dehydrogenating ethylbenzene; and almost all of it is used to make polystyrene or styrene copolymers, particularly styrene–butadiene rubber and latex. It polymerizes so readily that it forms a resin when it is exposed to the atmosphere.
Styrene has its downsides: It irritates the eyes and mucous membranes and causes more serious problems if it is inhaled or ingested. It has not been classified as a carcinogen, but its carcinogenicity is being evaluated by the US Environmental Protection Agency and the US Department of Health and Human Services. Styrene also contaminates water that flows through cured-in-place pipes.

Chemical properties

Styrene is a colorless or yellow, sweet odor liquid with a penetrating odor. It is produced during alkylation of benzene with ethylene. It is highly reactive and polymerizes rapidly with a violent explosive reaction. This demands proper handling, transportation, and storage by adding polymerization inhibitors in adequate quantities during these operations. Styrene monomer has been extensively used in the manufacture of chemical intermediates, fi lling components, plastics, resins, and stabilizing agents.

Physical properties

Clear, colorless, watery liquid with a penetrating or pungent rubber-like odor. Becomes yellow to yellowish-brown on exposure to air. Experimentally determined odor threshold concentrations in air for inhibited and unhibited styrene were 0.1 and 0.047 ppm_v, respectively (Leonardos et al., 1969). Experimentally determined detection and recognition odor threshold concentrations were 220–640 μg/m³ (52–150 ppb_v) and 64 μg/m³ (15 ppb_v), respectively (Hellman and Small, 1974). At 40 °C, the average odor threshold concentration and the lowest concentration at which an odor was detected were 65 and 37 μg/L, respectively. At 25 °C, the lowest concentration at which a taste was detected was 94 μg/L, respectively (Young et al., 1996). The average least detectable odor threshold concentrations in water at 60 °C and in air at 40 °C were 3.6 and 120 μg/L, respectively (Alexander et al., 1982).

Occurrence

Reported found in cranberry and bilberry, currants, grape, parsley, milk and dairy products, whiskey, cocoa, coffee, tea, roasted filberts and roasted peanuts. Also reported found in fresh apple, guava fruit, pineapple, vinegar, butter, fish oil, black tea, roasted filbert, roasted peanut, soybean, plum brandy, apple brandy, Brazil nut, rice bran, Bourbon vanilla, grapes, peach, strawberry, onion, peas, bell pepper, cassia leaf, cheeses, parsley, milk, boiled and scrambled egg, lean fish, fish oil, cooked chicken and beef, rum, malt and Scotch whiskey, cider, grape, wine, cocoa, coffee, honey, cloudberry, plum, rose apple, beans, trassi, walnut, buckwheat, soursop, watercress, kiwifruit, wild rice, sapodilla fruit, nectarine, okra, crab, crayfish and pawpaw.

History

During the early 1940s, the development of cellular polystyrene took place. Styrofoam was discovered accidentally by Ray McIntire (1918 1996), a Dow chemical engineer in 1944. McIntire was trying to make an artificial rubber for electrical insulation. He was combining isobutene with polystyrene when the isobutene formed bubbles in the styrene, resulting in a light cellular structure. Dow registered the trademark Styrofoam in 1954, but the name is now used generically for foam cellular insulation. World demand for styrene monomer in 2006 is approximately 25 million tons. Styrene has numerous uses. The homopolymer, which is hard and clear, is used for plastic eating utensils, CD/DVD cases, and plastic hobby models. The most common forms of polystyrene is expanded polystyrene (EPS) and extruded expanded polystyrene (XEPS). EPS is produced using a mixture of polystyrene beads, pentane, and a blowing agent. The mixture is heated with steam, causing the beads to expand to 10 to 100 times their original volume as the pentane vaporizes. After this, the mixture is injected into a vacuum mold where heat and a partial vacuum cause further expansion. EPS can be molded into a variety of shapes. The pentane in the foam is replaced by air during the curing process. Extruded expanded polystyrene starts with polystyrene crystals. The crystals are mixed with additives and blowing agents in an extruder. In the extruder, the mix is heated under pressure into a plastic melt. This plastic melt expands through a die into foam. Extruded expanded polystyrene cannot be molded but is produced in sheets. At one time chlorofl uorocarbons (CFC) were the preferred blowing agents used to produce expanded polystyrenes, but they have been replaced by hydrochlorofl uorocarbons because of concerns about CFC's impact on the ozone layer (see Dichlorodifl uoromethane). Styrofoam, produced by Dow, is extruded. Coff ee cups and food packaging are technically not Styrofoam because Dow does not produce Styrofoam as molded expanded polystyrene. EPS and XEPS are used extensively for insulation in the construction industry. Polystyrene is used as a co-polymer with a number of other materials. Examples of co-polymers are acrylonitrile-butadiene-styrene, styrene-acrylonitrile, and styrene-butadiene rubber. Polystyrene is used in paints, coatings, adhesives, and resins.

The Uses of Styrene

Styrene (monomer) is a viscous, highly flammable liquid that evaporates easily and polymerizes readily to polystyrene unless a stabilizer is added. Styrene is used in multiple industries, especially in reinforced plastics (e.g., fiberglass boats), and is widely used to make plastics and rubber, packaging materials (e.g., packing peanuts ), insulation for buildings, plastic pipes, food containers (e.g., takeout containers), and carpet backing) (ATSDR, 2010).

The Uses of Styrene

Styrene polymers and copolymers are usedextensively in making polystyrene plastics,polyesters, protective coatings, resins, andsynthetic rubber (styrene–butadiene rubber)..

The Uses of Styrene

STYRENE, is the simplest and by far the most important member of a series of aromatic monomers. Also known commercially as styrene monomer (SM), styrene is produced in large quantities for polymerization. It is a versatile monomer extensively used for the manufacture of plastics, including crystalline polystyrene, rubber-modified impact polystyrene, expandable polystyrene, acrylonitrile– butadiene–styrene copolymer (ABS), styrene–acrylonitrile resins (SAN), styrene–butadiene latex, styrene–butadiene rubber (SBR), and unsaturated polyester resins.

Definition

ChEBI: A vinylarene that is benzene carrying a vinyl group. It has been isolated from the benzoin resin produced by Styrax species.

Production Methods

Styrene is made by dehydrogenation of ethylbenzene at high temperature using metal catalysts: C₆H₅CH₂CH₂(g)→ C₆H₅CH = CH₂(g) + H_2(g). This is called the EB/SM (ethylbenzene/styrene monomer) process. Styrene can also be made by PO/SM (propylene oxide/styrene monomer) process). This process starts by oxidizing ethylbenzene (C6H5CH2CH2) to its hydroperoxide (C6H₅CH(OOH)CH₃), which is then used to oxidize propylene (CH₃CH = CH₂) to produce propylene oxide (CH₃CH₂CHO) and phenylethanol (C₆H₅CH(OH)CH₃). The phenylethanol is then dehydrated to give styrene and water. Styrene can also be synthesized by reacting benzene and ethylene or natural gas.

Preparation

Prepared from ethylbenzene or from phenylethanol.

Aroma threshold values

Detection: 3.6 to 80 ppb

Synthesis Reference(s)

Journal of the American Chemical Society, 86, p. 4603, 1964 DOI: 10.1021/ja01075a017
The Journal of Organic Chemistry, 46, p. 691, 1981 DOI: 10.1021/jo00317a009

General Description

A clear colorless to dark liquid with an aromatic odor. Flash point 90°F. Density 7.6 lb/gal. Vapors heavier than air and irritating to the eyes and mucous membranes. Subject to polymerization. If the polymerization takes place inside a closed container, the container may rupture violently. Less dense than water and insoluble in water. Used to make plastics, paints, and synthetic rubber.

Air & Water Reactions

Highly flammable. Insoluble in water.

Reactivity Profile

STYRENE MONOMER is a colorless, oily liquid, moderately toxic, flammable. A storage hazard above 32°C, involved in several industrial explosions caused by violent, exothermic polymerization [Bond, J., Loss Prev. Bull., 1985, (065), p. 25]. Polymerization becomes self-sustaining above 95°C [MCA SD-37, 1971]. Presence of an inhibitor lessens but does not eliminate the possibility of unwanted polymerization. Violent polymerization leading to explosion may be initiated by peroxides (e.g., di-tert-butyl peroxide, dibenzoyl peroxide), butyllithium, azoisobutyronitrile. Reacts violently with strong acids (sulfuric acid, oleum, chlorosulfonic acid), strong oxidizing agents [Lewis, 3rd ed., 1993, p. 1185]. Reacts with oxygen above 40°C to form explosive peroxide [Barnes, C. E. et al., J. Amer. Chem. Soc., 1950, 72, p. 210]. Oxidizes readily in air to form unstable peroxides that may explode spontaneously [Bretherick 1979 p.151-154, 164]. Mixing styrene in equal molar portions with any of the following substances in a closed container caused the temperature and pressure to increase: chlorosulfonic acid, oleum, and sulfuric acid [NFPA 1991].

Hazard

Flammable, moderate fire risk, explosive limits in air 1.1–6.1%, must be inhibited during storage. Toxic by ingestion and inhalation. Central nervous system impairment, upper respiratory tract irritant, and peripheral neuropathy. Possible carcinogen.

Health Hazard

Like all other aromatic hydrocarbons, styreneis an irritant to skin, eyes, and mucous membranes and is narcotic at high concentrations.Exposure to its vapors may cause drowsiness,nausea, headache, fatigues, and dizziness inhumans (Hamilton and Hardy 1974). Inhalation of 10,000 ppm for 30–60 minutes maybe fatal to humans.
Absorption of styrene by inhalation isthe major path of absorption into the body.Skin absorption of the liquid is also significant. According to an estimate, contactwith styrene-saturated water for an hour orbrief contact with the liquid may result inabsorption equivalent to 8 hours of inhalationof 12 ppm (Dutkiewicz and Tyras 1968). Itmay accumulate in the body due to its highsolubility in fat. This would happen whenthe metabolic pathway becomes saturated atexposure concentrations of 200 ppm (ACGIH 1986). Mandelic acid and benzoylformic acidare the major urinary metabolites. However,the excretion of mandelic acid was less whenstyrene was absorbed through the skin.
Styrene tested positive in an EPA mutagenicity study. It tested positive in a histidine reversion–Ames test, Saccharomycescerevisiae gene conversion, in vitro humanlymphocyte micronucleus, and Drosophilamelanogaster sex-linked lethal tests (NIOSH1986). Carcinogenicity of styrene in humansis not known. There is limited evidence of carcinogenicity in animals for both the monomerand the polymer..

Fire Hazard

Behavior in Fire: Vapor is heavier than air and may travel considerable distance to a source of ignition and flash back. At elevated temperatures such as in fire conditions, polymerization may take place which may lead to container explosion.

Flammability and Explosibility

Flammable

Contact allergens

The presence of styrene in packaged foods is due primarily to leaching of monomer from polystyrene containers. Polystyrene (PS) is widely used in the manufacturing of food contact materials such as trays for meat, cookies, and candies with disposable plates, cups, etc. and about 50 % of the consumption of PS was related to food packaging and food service articles. During the production process the styrene monomer can become occluded in PS products and may migrate out of these materials into food. The rate of migration of styrene monomer from polystyrene containers depends mainly on the lipophilicity of the food, surface area of the container per volume of food, duration of contact, and food temperature.
Styrene was found in 24 food contact materials from different categories (extruded polystyrene foam, expandable polystyrene, high-impacted polystyrene) at concentrations ranging from 9.3 to 3100 mg/kg, with a mean concentration of 340 mg/kg. This concentration is below the USFDA limit for styrene in food packaging materials which are 5000 mg/kg for fatty foods and 10000 mg/kg for aqueous foods. Moreover, styrene dimers and trimers, which are also residual materials produced during polymerisation, have been detected. Styrene was found in various foods such as yoghurt, croissants, cookies, raw chicken, and raw beef held in contact with PS packaging (meat trays, cookie trays, and chocolate candy trays) at concentrations ranging from 2.6 ng/g in raw chicken to 163 ng/g in sandwich cookies. Styrene is reasonably anticipated to be a human carcinogen. Several international brands start to phase out polystyrene foam packaging from their products.

Safety Profile

Confirmed carcinogen. Experimental poison by ingestion, inhalation, and intravenous routes. Moderately toxic experimentally by intraperitoneal route. Mildly toxic to humans by inhalation. An experimental teratogen. Human systemic effects by inhalation: eye and olfactory changes. It can cause irritation and violent itching of the eyes @200 ppm, lachrymation, and severe human eye injuries. Its toxic effects are usually transient and result in irritation and possible narcosis. Experimental reproductive effects. Human mutation data reported. A human skin irritant. An experimental skin and eye irritant. The monomer has been involved in several industrial explosions. It is a storage hazard above 32°C. A very dangerous fire hazard when exposed to flame, heat, or oxidants. Explosive in the form of vapor when exposed to heat or flame. Reacts with oxygen above 40°C to form a heat-sensitive explosive peroxide. Violent or explosive polymerization may be initiated by alkahmetal-graphite composites, butyllithium, dibenzoyl peroxide, other initiators (e.g., azoisobutyronitrile, di-tert-butyl peroxide). Reacts violently with chlorosulfonic acid, oleum, sulfuric acid, chlorine + iron(IⅡ) chloride (above 50°C). May ignite when heated with air + polymerizing polystyrene. Can react vigorously with oxidizing materials. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes

Potential Exposure

Styrene is used in the production of plastics and polystyrene resins. It is also used in combination with 1,3-butadiene or acrylonitrile to form copolymer elastomers, butadiene-styrene rubber; and acrylonitrilebutadiene-styrene. It is also used in the manufacture of protective coatings; resins, polyesters; in making insulators and in drug manufacture.

Carcinogenicity

Styrene is reasonably anticipated to be a human carcinogen based on limited evidence of carcinogenicity from studies in humans, sufficient evidence of carcinogenicity from studies in experimental animals, and supporting data on mechanisms of carcinogenesis.

Source

Based on laboratory analysis of 7 coal tar samples, styrene concentrations ranged from ND to 2,500 ppm (EPRI, 1990). A high-temperature coal tar contained styrene at an average concentration of 0.02 wt % (McNeil, 1983).
Styrene occurs naturally in benzoin, rosemary, sweetgum, cassia, Oriental styrax, and Peru balsam (Duke, 1992). Identified as one of 140 volatile constituents in used soybean oils collected from a processing plant that fried various beef, chicken, and veal products (Takeoka et al., 1996).
Drinking water standard (final): MCLG: 0.1 mg/L; MCL: 0.1 mg/L. In addition, a DWEL of 7 mg/L was recommended (U.S. EPA, 2000).

Environmental Fate

Biological. Fu and Alexander (1992) observed that despite the high degree of adsorption onto soils, styrene was mineralized to carbon dioxide under aerobic conditions. Rates of mineralization from highest to lowest were sewage sludge, Lima soil (pH 7.23, 7.5% organic matter), groundwater (pH 8.25, 30.5 mg/L organic matter), Beebe Lake water from Ithaca, NY (pH 7.5, 50 to 60 mg/L organic matter), aquifer sand (pH 6.95, 0.4% organic matter), Erie silt loam (pH 4.87, 5.74% organic matter). Styrene did not mineralize in sterile environmental samples. Oié et al. (1979) reported BOD and COD values of 1.29 and 2.80 g/g using filtered effluent from a biological sanitary waste treatment plant. These values were determined using a standard dilution method at 20 °C and stirred for a period of 5 d. When a sewage seed was used in a separate screening test, a BOD value of 2.45 g/g was obtained. The ThOD for styrene is 3.08 g/g. Photolytic. Irradiation of styrene in solution forms polystyrene. In a benzene solution, irradiation of polystyrene will result in depolymerization to presumably styrene (Calvert and Pitts, 1966).
Atkinson (1985) reported a photooxidation reaction rate of 5.25 x 10^-11 cm³/molecule?sec for styrene and OH radicals in the atmosphere. A reaction rate of 1.8 x 10^-4 L/molecule?sec at 303 K was reported for the reaction of styrene and ozone in the vapor phase (Bufalini and Altshuller, 1965).
Chemical/Physical. In the dark, styrene reacted with ozone forming benzaldehyde, formaldehyde, benzoic acid, and trace amounts of formic acid (Grosjean, 1985). Polymerizes readily in the presence of heat, light, or a peroxide catalyst. Polymerization is exothermic and may become explosive (NIOSH, 1997).

storage

Styrene is stored in a flammable liquid storagecabinet, separated from oxidizing substances An inhibitor such as 4-tert-butylcatechol intrace amounts is added to the monomer toprevent polymerization. It is shipped in glassbottles, metal cans, drums, and tank cars.

Shipping

UN2055 Styrene monomer, stabilized, Hazard Class: 3; Labels: 3-Flammable liquid.

Purification Methods

Styrene is difficult to purify and keep pure. 25 1.5441. Usually it contains added inhibitors (such as a trace of hydroquinone). Wash it with aqueous NaOH to remove inhibitors (e.g. tert-butanol), then with water, dry it for several hours with MgSO4 and distil it at 25o under reduced pressure in the presence of an inhibitor (such as 0.005% p-tert-butylcatechol). It can be stored at -78o. It can also be stored and kept anhydrous with Linde type 5A molecular sieves, CaH2, CaSO4, BaO or sodium, being fractionally distilled, and distilled in a vacuum line just before use. Alternatively styrene (and its deuterated derivative) are passed through a neutral alumina column before use [Woon et al. J Am Chem Soc 108 7990 1986, Collman J Am Chem Soc 108 2588 1986]. [Beilstein 5 IV 1334.]

Toxicity evaluation

There has been a general belief that SO is responsible for the bronchiolar tumors (mice) and nasal toxicity (mice and rats) induced by styrene. However, the metabolism of styrene to ring-oxidized metabolites (e.g., 4-vinylphenol) by the CYP2F isoform found in the lung may play a more predominant role than previously thought. CYP2E1 is generally considered the cytochrome P450 isoform primarily responsible for the metabolism of styrene to SO in mice and rats. However, mouse lung toxicity is not attenuated in CYP2E1 knockout mice. Another cytochrome P450 isoform, CYP2F2, is preferentially expressed in mouse Clara cells, which are enriched in the bronchiolar region of the lung where tumors occur. It was recently reported that Clara cell toxicity induced by both styrene and SO in wild-type mice was completely abolished in CYP2F2 knockout mice. Under this mechanism, the cytotoxicity produced by ring-oxidized metabolites of CYP2F2 is thought to lead to increased cell proliferation and the slow development of bronchiolar tumors in the mouse. The absence of tumors in the rat is consistent with the lower level of ringoxidized metabolites produced in this species by comparable styrene exposures, and the lower levels of CYP2F4 in the terminal bronchioles of rats. Humans may be less susceptible than mice to the development of lung tumors since the CYP2F isoform in human lung (CYP2F1) is present at a very low level and is not suspected of catalyzing significant styrene metabolism, observations consistent with the trace levels of ringoxidized metabolites detected in humans. Work in this area is ongoing. The mechanism for the neurotoxic effects of styrene has not been established.

Incompatibilities

Styrene May form explosive mixture with air. A storage hazard above 31C. Upon heating to 200C, styrene polymerizes to form polystyrene, a plastic. Before entering confined space where this chemical may be present, check to make sure that an explosive concentration does not exist. Store in a cool, dry area away from oxidizers, catalysts for vinyl polymers; peroxides, strong acids; aluminum chloride. May polymerize if contaminated, subjected to heat; under the influence of light; and on contact with many compounds, such as oxygen, oxidizing agents; peroxides and strong acids. Usually contains an inhibitor, such as tert-butylcatechol. Corrodes copper and copper alloys. Attacks some plastics, rubber, and coatings.

Waste Disposal

Dissolve or mix the material with a combustible solvent and burn in a chemical incinerator equipped with an afterburner and scrubber. All federal, state, and local environmental regulations must be observed. In some cases, recovery and recycle of styrene monomer is economic and the technology is available.