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Styrene

|Section2={{Chembox Properties | Formula = C8H8 | MolarMass = 104.15 g/mol | Appearance = colorless oily liquid | Odor = sweet, floral | Density = 0.909 g/cm3 | Solubility = 0.03% (20°C) | MeltingPtC = -30 | BoilingPtC = 145 | Viscosity = 0.762 c P at 20 °C | RefractIndex = 1.5469 | VaporPressure = 5 mmHg (20°C) | MagSus = -68.2·10−6 cm3/mol }} |Section3={{Chembox Structure | Dipole = 0.13 D }} |Section7={{Chembox Hazards | ExternalSDS = MSDS | MainHazards = flammable, toxic | FlashPtC = 31 | NFPA-F = 3 | NFPA-H = 2 | NFPA-R = 2 | NFPA-S = | RPhrases = | SPhrases = | PEL = TWA 100 ppm C 200 ppm 600 ppm (5-minute maximum peak in any 3 hours) | ExploLimits = 0.9%-6.8% | IDLH = 700 ppm | LC50 = 2194 ppm (mouse, 4 hr)5543 ppm (rat, 4 hr) | REL = TWA 50 ppm (215 mg/m3) ST 100 ppm (425 mg/m3) | LCLo = 10,000 ppm (human, 30 min)2771 ppm (rat, 4 hr) }} |Section8={{Chembox Related | OtherFunction_label = styrenes;related aromatic compounds | OtherFunction = Polystyrene, Stilbene; Ethylbenzene }} }} Styrene, also known as ethenylbenzene, vinylbenzene, and phenylethene, is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid that evaporates easily and has a sweet smell, although high concentrations have a less pleasant odor. Styrene is the precursor to polystyrene and several copolymers. Approximately 25 million tonnes (55 billion pounds) of styrene were produced in 2010. New Process for Producing Styrene Cuts Costs, Saves Energy, and Reduces Greenhouse Gas Emissions, U.S. Department of Energy.

Occurrence, history, and use

Natural occurrence

Styrene is named for storax balsam, the resin of Liquidambar trees of the Altingiaceae plant family. Styrene occurs naturally in small quantities in some plants and foods (cinnamon, coffee beans, and peanuts), and is also found in coal tar.

History

In 1839, the German apothecary Eduard Simon isolated a volatile oil from the resin (called storax or styrax (Latin)) of the American sweetgum tree (Liquidambar styraciflua). He called the oil "Styrol" (now: "styrene").Simon, E. (1839) "Ueber den flüssigen Storax (Styrax liquidus)" (On liquid storax (Styrax liquidus), Annalen der Chemie, 31 : 265–277. From p. 268: "Das flüchtige Oel, für welches ich den Namen Styrol vorschlage, … " (The volatile oil, for which I suggest the name "styrol", … )For further details of the history of styrene, see: F. W. Semmler, Die ätherischen Öle nach ihren chemischen Bestandteilen unter Berücksichtigung der geschichtlichen Entwicklung volitile oils according to their chemical components with regard to historical development, vol. 4 (Leipzig, Germany, Veit & Co., 1907), § 327. Styrol, pp. 24-28. He also noticed that when Styrol was exposed to air, light, or heat, it gradually transformed into a hard, rubber-like substance, which he called "Styroloxyd" (styrol oxide, now: "polystyrene").(Simon, 1839), p. 268. From p. 268: "Für den festen Rückstand würde der Name Styroloxyd passen." (For the solid residue, the name "styrol oxide" would fit.) By 1845, the German chemist August Hofmann and his student John Blyth (1814–1871) had determined Styrol's empirical formula: C8H8.Blyth, John and Hofmann, Aug. Wilh. (1845) "Ueber das Styrol und einige seiner Zersetzungsproducte" (On styrol and some of its decomposition products), Annalen der Chemie und Pharmacie, 53 (3) : 289-329 ; see p. 297. Note that Blyth and Hofmann state the empirical formula of Styrol as C16H8 because at that time, chemists used the wrong atomic mass for carbon (6 instead of 12). They had also determined that Simon's "Styroloxyd" — which they renamed "Metastyrol" — had the same empirical formula as Styrol.(Blyth and Hofmann, 1845), p. 312. From p. 312: "Analyse sowohl als Synthese haben in gleicher Weise dargethan, dass Styrol und die feste glasartige Materie, für welche wir den Namen Metastyrol vorschlagen, dieselbe procentische Zusammensetzung besitzen." (Analysis as well as synthesis have equally demonstrated, that styrol and the solid, glassy material, for which we suggest the name "metastyrol", possess the same percentage composition.) Furthermore, they could obtain Styrol by dry-distilling Metastyrol.(Blyth & Hofmann, 1845), p. 315. In 1865, the German chemist Emil Erlenmeyer found that Styrol could form a dimer,Erlenmeyer, Emil (1865) "Ueber Distyrol, ein neues Polymere des Styrols" (On distyrol, a new polymer of styrol), Annalen der Chemie, 135 : 122–123. and in 1866 the French chemist Marcelin Berthelot stated that Metastyrol was a polymer of Styrol.Berthelot, M. (1866) "Sur les caractères de la benzine et du styrolène, comparés avec ceux des autres carbures d'hydrogène" (On the characters of benzene and styrene, compared with those of other hydrocarbons), Bulletin de la Société Chimique de Paris, 2nd series, 6 : 289–298. From p. 294: "On sait que le styrolène chauffé en vase scellé à 200°, pendant quelques heures, se change en un polymère résineux (métastyrol), et que ce polymère, distillé brusquement, reproduit le styrolène." (One knows that styrene when heated in a sealed vessel at 200°C, for several hours, is changed into a resinous polymer (polystyrene), and that this polymer, when distilled abruptly, reproduces styrene.) Meanwhile, other chemists had been investigating another component of storax, namely, cinnamic acid. They had found that cinnamic acid could be decarboxylated to form cinnamène (or cinnamol), which appeared to be Styrol. In 1845, French chemist Emil Kopp suggested that the two compounds were identical,Kopp, E. (1845), "Recherches sur l'acide cinnamique et sur le cinnamène" (Investigations of cinnamic acid and cinnamen), Comptes rendus, 21 : 1376-1380. From p. 1380: "Je pense qu'il faudra désormais remplacer le mot de styrol par celui de cinnamène, et le métastyrol par le métacinnamène." (I think that henceforth one will have to replace the word "styrol" with that of "cinnamène", and "metastyrol" with "metacinnamène".) and in 1866, Erlenmeyer suggested that both cinnamol and Styrol might be vinyl benzene.Erlenmeyer, Emil (1866) "Studien über die s.g. aromatischen Säuren" (Studies of the so-called aromatic acids), Annalen der Chemie, 137 : 327–359 ; see p. 353. However, the Styrol that was obtained from cinnamic acid seemed different from the Styrol that was obtained by distilling storax resin: the latter was optically active.Berthelot, Marcellin (1867) "Sur les états isomériques du styrolène" (On the isomeric states of styrene), Annales de Chimie et de Physique, 4th series, 12 : 159–161. From p. 160: "1° Le carbure des cinnamates est privé de pouvoir rotatoire, tandis que le carbure du styrax dévie de 3 degrés la teinte de passage (l = 100 mm)." (1. The carbon atom of cinnamates is bereft of rotary power the ability to rotate polarized light, whereas the carbon of styrax deflects by 3 degrees the neutral tint the relative orientation of the polarized quartz plates at which the light through the polarimeter appears colorless (length = 100 mm). further details about 19th century polarimeters, see: William Spottiswode, Polarisation of Light, 4th ed. (London, England: Macmillan and Co., 1883), [https://archive.org/stream/polarisationofli00spotrich#page/52/mode/2up/ pp. 51-52.) Eventually, in 1876, the Dutch chemist van 't Hoff resolved the ambiguity: the optical activity of the Styrol that was obtained by distilling storax resin was due to a contaminant.van 't Hoff, J. H. (1876) "Die Identität von Styrol und Cinnamol, ein neuer Körper aus Styrax" (The identity of styrol and cinnamol, a new substance from styrax), Berichte der deutschen chemischen Gesellschaft, 9 : 5-6.

Industrial production from ethylbenzene

The modern method for production of styrene by dehydrogenation of ethylbenzene was first achieved in the 1930s. The production of styrene increased dramatically during the 1940s, when it was used as a feedstock for synthetic rubber. Because styrene is produced on such a large scale, ethylbenzene is in turn prepared on a prodigious scale (by alkylation of benzene with ethylene). Ethylbenzene is mixed in the gas phase with 10–15 times its volume of high-temperature steam, and passed over a solid catalyst bed. Most ethylbenzene dehydrogenation catalysts are based on iron(III) oxide, promoted by several percent potassium oxide or potassium carbonate. Steam serves several roles in this reaction. It is the source of heat for powering the endothermic reaction, and it removes coke that tends to form on the iron oxide catalyst through the water gas shift reaction. The potassium promoter enhances this decoking reaction. The steam also dilutes the reactant and products, shifting the position of chemical equilibrium towards products. A typical styrene plant consists of two or three reactors in series, which operate under vacuum to enhance the conversion and selectivity. Typical per-pass conversions are ca. 65% for two reactors and 70-75% for three reactors. Selectivity to styrene is 93-97%. The main byproducts are benzene and toluene. Because styrene and ethylbenzene have similar boiling points (145 and 136 °C, respectively), their separation requires tall distillation towers and high return/reflux ratios. At its distillation temperatures, styrene tends to polymerize. To minimize this problem, early styrene plants added elemental sulfur to inhibit the polymerization. During the 1970s, new free radical inhibitors consisting of nitrated phenol-based retarders were developed. More recently, a number of additives have been developed that exhibit superior inhibition against polymerization. However, the nitrated phenols are still widely used because of their relatively low cost. These reagents are added prior to the distillation. Improving conversion and so reducing the amount of ethylbenzene that must be separated is the chief impetus for researching alternative routes to styrene. Other than the POSM process, none of these routes such as obtaining styrene from butadiene have been commercially demonstrated.

Other industrial routes

From ethylbenzene hydroperoxide

Styrene is also co-produced commercially in a process known as POSM ( Lyondell Chemical Company) or SM/PO ( Shell) for styrene monomer / propylene oxide. In this process ethylbenzene is treated with oxygen to form the ethylbenzene hydroperoxide. This hydroperoxide is then used to oxidize propylene to propylene oxide. The resulting 1-phenylethanol is dehydrated to give styrene: :

From toluene and methanol

Styrene can be produced from toluene and methanol, which are cheaper raw materials than those in the conventional process. This process has suffered from low selectivity associated with the competing decomposition of methanol. Exelus Inc. claims to have developed this process with commercially viable selectivities, at 400-425 °C and atmospheric pressure, by forcing these components through a proprietary zeolitic catalyst. It is reported Peter Taffe, ICIS.com, 21 Jan 2008 (based on an paper given at The 6th European.Aromatics & Derivatives Conference – Antwerp, Belgium - 14-15 November, 2007.) that an approximately 9:1 mixture of styrene and ethylbenzene is obtained, with a total styrene yield of over 60%.Stephen K. Ritter, Chemical & Engineering News, 19 March 2007, p.46.

From benzene and ethane

Another route to styrene involves the reaction of benzene and ethane. This process is being developed by Snamprogetti S.p.A. and Dow. Ethane, along with ethylbenzene, is fed to a dehydrogenation reactor with a catalyst capable of simultaneously producing styrene and ethylene. The dehydrogenation effluent is cooled and separated and the ethylene stream is recycled to the alkylation unit. The process attempts to overcome previous shortcomings in earlier attempts to develop production of styrene from ethane and benzene, such as inefficient recovery of aromatics, production of high levels of heavies and tars, and inefficient separation of hydrogen and ethane. Development of the process is ongoing. Styrene/Ethylbenzene 07/08-4 Report, ChemSystems, March 2009, p.64-73.

Laboratory synthesis

A laboratory synthesis of styrene entails the decarboxylation of cinnamic acid: C6H5CH=CHCO2H → :C6H5CH=CH2 + CO2 Styrene was first prepared by this method.R. Fittig und F. Binder "Ueber die Additionsproducte der Zimmtssaure" in "Untersuchungen über die ungesättigten Säuren. I. Weitere Beiträge zur Kenntnifs der Fumarsäure und Maleïnsäure" Rudolph Fittig, Camille Petri, Justus Liebigs Annalen der Chemie 1879, volume 195, p 56-179.

Polymerization

The presence of the vinyl group allows styrene to polymerize. Commercially significant products include polystyrene, ABS, styrene-butadiene (SBR) rubber, styrene-butadiene latex, SIS (styrene-isoprene-styrene), S-EB-S (styrene-ethylene/butylene-styrene), styrene- divinylbenzene (S-DVB), styrene-acrylonitrile resin (SAN), and unsaturated polyesters used in resins and thermosetting compounds. These materials are used in rubber, plastic, insulation, fiberglass, pipes, automobile and boat parts, food containers, and carpet backing.

Health effects

Styrene is regarded as a "known carcinogen", especially in case of eye contact, but also in case of skin contact, of ingestion and of inhalation, according to several sources.http://www.atsdr.cdc.gov/tfacts53.pdf Styrene is largely metabolized into styrene oxide in humans, resulting from oxidation by cytochrome P450. Styrene oxide is considered toxic, mutagenic, and possibly carcinogenic. Styrene oxide is subsequently hydrolyzed in vivo to styrene glycol by the enzyme epoxide hydrolase. The U.S. Environmental Protection Agency (EPA) has described styrene to be "a suspected toxin to the gastrointestinal tract, kidney, and respiratory system, among others". On 10 June 2011, the U.S. National Toxicology Program has described styrene as "reasonably anticipated to be a human carcinogen". However, a STATS author describeshttp://stats.org/stories/2011/styrene_crosshairs_sept14_11.html a review that was done on scientific literature and concluded that "The available epidemiologic evidence does not support a causal relationship between styrene exposure and any type of human cancer".Boffetta, P., et al., Epidemiologic Studies of Styrene and Cancer: A Review of the Literature, J. Occupational and Environmental Medicine, Nov.2009, V.51, N.11. Despite this claim, work has been done by Danish researchers to investigate the relationship between occupational exposure to styrene and cancer. They concluded, "The findings have to be interpreted with caution, due to the company based exposure assessment, but the possible association between exposures in the reinforced plastics industry, mainly styrene, and degenerative disorders of the nervous system and pancreatic cancer, deserves attention". The Danish EPA recently concluded that the styrene data do not support a cancer concern for styrene.Danish EPA 2011 review http://www.compositesworld.com/cdn/cms/uploadedFiles/danish_epa_styrene_review(2).pdf Various regulatory bodies refer to styrene, in various contexts, as a possible or potential human carcinogen. The International Agency for Research on Cancer considers styrene to be "possibly carcinogenic to humans". Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 82 (2002), Some Traditional Herbal Medicines, Some Mycotoxins, Naphthalene and Styrene, pp. 436 - 550. Chronic exposure to styrene leads to tiredness/ lethargy, memory deficits, headaches and vertigo.http://www.epa.gov/ttnatw01/hlthef/styrene.html The U.S. EPA does not have a cancer classification for styrene, linkhttp://www.epa.gov/iris/subst/0104.htm US environmental protection agency. Section I.B.4 relates to neurotoxicology. but it has been the subject of their Integrated Risk Information System (IRIS) program. EPA IRIS track styrene page The U.S. National Toxicology Program of the U.S. Department of Health and Human Services has determined that styrene is "reasonably anticipated to be a human carcinogen". Styrene entry in National Toxicology Program's Thirteenth Report on Carcinogens

References

External links

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Styrene, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Styrene&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany