Styrene

History

Around 1835, the Pharmacie N Berlin ois Eduard Simon acquires Styrax, a resin also called “liquid amber” exit of the Liquidambar orientalis , a tree pushing with the the Middle East. This resin underwent treatments and was mixed, in particular with perfume. By distilling this resin, Simon obtains a colorless liquid which he baptizes styrene in reference in the name of the resin. By heating this liquid, it obtains a new substance, which it supposes being of the Oxyde of styrene. However, the Chemist S British John Blyth and August Wilhelm von Hoffmann discover in 1845 by ultimate analysis that the composition of the matter did not change during the transformation. It should be waited until 1866 so that Marcellin Berthelot provides a correct interpretation of the phenomenon: it is about a reaction of Polymérisation. Hermann Staudinger, whose work related to mainly the chemistry of the Polymère S, written in his thesis that the heating of the liquid involves a chain reaction which results in the appearance of Macromolécule S of Polystyrène.

Physicochemical properties

The styrene has a pleasant, detectable odor between 0,43 mg/m and 866 mg/m. It is little soluble in water, but it has a good solubility in the Acétone, the ether, the Disulfure of carbon and the alcohol S. the styrene evaporates easily. The Molecule of styrene having a grouping vinyl, and thus a double linking, it can polymerize. The liquid styrene starts to polymerize with the room temperature by forming a yellow liquid viscous. It can be stabilized by the addition of 50 ppm of Hydroquinone. However, stabilization is not possible that in the presence of small quantities of Oxygène. The Polymérisation is very clearly accelerated by the Lumière. The styrene must thus be stored with the expenses in opaque containers.

Chemical reactions

The chemical behavior of styrene is similar to that of the Benzène, the styrene being however more reactive. It reacts mainly during reactions of the ridicalizing substitution type, of aromatic substitution électrophile (for example sulphonation or nitration) as well as ridicalizing addition. The reactions of the nucleophilic substitution type are definitely less frequent. It oxidizes in Oxyde of styrene.

The styrene reaction of with respect to the reactions of Polymérisation is rather unusual: it can undergo polymerizations of the ridicalizing type, just like of anion or cation polymerizations. It thus can copolymériser with Chlorure of iron by cation polymerization. The styrene alone polymerizes by a ridicalizing mechanism to form polystyrene. This last reaction is more easily initiated a presence of a peroxide.

Production

Before 1930, date on which manufactoring processes of styrene start to be developed, it is obtained by separation at the time of the Raffinage of oil.

There exist mainly two manufactoring processes of styrene on an industrial scale. The first is a process of the catalytic dehydrogenation type. The styrene is manufactured by heating with 600 - 650°C of ethylbenzene (EB) in the presence of a Catalyze ur, generally of the ferric oxide or Hydroxyde of potassium. The Chemical reaction is reversible (it is a chemical balance) and Endothermique. The output is increased while working under reduced pressure.

CHCH ←→ CHCH + H

The second process, less used, is carried out in several stages. Ethylbenzene is initially oxidized with 150°C under a pressure of 2 bar. The formed product (a peroxide) reacts then with Propène to 115°C under high pressure and in the presence of Silice to form α-phényléthanol. This last undergoes then a dehydration with 200°C approximately in the presence of Alumine to form styrene.

In 1996, the worldwide production of styrene was of approximately 20 million tons.

Use

The styrene is used as Monomère to manufacture plastic the most important S. is the Polystyrène (the styrene is the only monomer). Many others are produced by copolymerization (use of several monomers), in particular the Acrylonitrile butadiene styrene or ABS, the rubber or the latex containing Styrène butadiene or SBS, as well as Polyester S unsaturates. The production of styrene in particular increased very quickly with the USA during the Second world war to meet the needs for synthetic rubber for the army. The styrene is also used in small quantities as additive in perfumes or drugs. It is also a Solvant, used in particular for the resin polyester synthesis.

Effects on health

The inhalation of concentration S high of styrene can cause disorders of the nervous system, such as depression or difficulties of concentration, muscular weakness , nausea S as well as an irritation of the eyes, Nez and throat.

Studies on animals revealed that the styrene vapor breathing during short durations involves a damage of the nasal partitions. A longer exposure causes damage with the Foie. No data is available concerning the effect on the human health of the presence of weak styrene concentrations in the air breathed for long periods.

There are also only few data on the effects on the human health of an exposure to styrene by ingestion or contact with the skin. The studies on animals showed that the ingestion of high styrene concentrations over several weeks causes damage with the Foie, with the Rein S, with the Cerveau and with the Poumon S. the direct contact on the rabbit skin involves an irritation.

The studies on animals also showed a negative effect of the exposure tovery high styrene rates for short periods on the reproduction and the development of the Fœtus. No data is available for the man.

According to the International agency of research on cancer, the styrene could be Cancérogène for the man. Several studies carried out on a population of paid exposed to styrene highlighted a risk of Leucémie. Studies on animals showed that the styrene is slightly cancerogenic by inhalation or ingestion.

Effects on the environment

On the scale of MARPOL, the styrene has a toxicity B, i.e. which it is toxic but not very persistent in the environment. It persists in a seamen circle during a few days, and is little bioaccumulable. On the other hand, in low dose, the styrene can induce a modification of color or taste of marine food.

Sentences of risk and councils of prudence

Rules Labelling

R: 10 (Flammable)
R: 20 (Harmful by inhalation)
R: 36/38 (Irritating for the eyes and the skin)
S: 2 (To preserve out of the range of the children)
S: 23 (not to breathe gases/fume/vapors/aerosols (term (S) suitable (S) to indicate by the manufacturer))

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