Chemical Properties
Styrene is a colorless or yellow, sweet odor liquid. 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.
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.
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].
Air & Water Reactions
Highly flammable. Insoluble in water.
Health Hazard
Exposures to styrene induce adverse health effects, which include irritation to the eyes,
mucous membrane, loss of appetite, vomiting, and nausea. Prolonged exposure results in
skin damage in the form of dermatitis, rough, and fi ssured skin.
Health Hazard
Moderate irritation of eyes and skin. High vapor concentrations cause dizziness, drunkeness, and anesthesia.
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.
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.
First aid
If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.
Shipping
UN2055 Styrene monomer, stabilized, Hazard Class: 3; Labels: 3-Flammable liquid.
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.
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 ppmv, respectively (Leonardos et al.,
1969). Experimentally determined detection and recognition odor threshold concentrations were
220–640 μg/m3 (52–150 ppbv) and 64 μg/m3 (15 ppbv), 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.
Definition
ChEBI: A vinylarene that is benzene carrying a vinyl group. It has been isolated from the benzoin resin produced by Styrax species.
Preparation
Prepared from ethylbenzene or from phenylethanol.
Production Methods
Styrene is made by dehydrogenation of ethylbenzene at high temperature using metal catalysts: C6H5CH2CH2(g)→ C6H5CH = CH2(g) + H2(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.
Aroma threshold values
Detection: 3.6 to 80 ppb
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.
Flammability and Explosibility
Flammable
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).
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.
Toxics Screening Level
The Initial Threshold Screening Level (ITSL) is 1000 μg/m3 with an annual averaging time.
