VIOLENT POLYMERISATION

Numerous accidents have brought about a violent polymerisation of ethylene. In two examples the conditions were the following ... 

A large number of accidents due to the polymerisation of styrene in storage containers are caused by a temperature which is too high. It is recommended not to store styrene at a temperature greater than 32°C. However, the presence of polymerisation primers, which are placed deliberately or accidentally, is the most frequent cause of violent polymerisations of styrene. 

A temperature of 30-40 C and a moderate pressure are enough to cause a violent polymerisation, which can increase the pressure in the reactor to 1000 -1200 bar. In storage, a low polymerisation can also be dangerous for a different reason. In this case, polymer precipitates in the form of flakes causing the volume to rise, which can eventually cause the storage tanks to detonate. Butadiene can only be stored if it contains a poiymerisation inhibitor, which also plays the role of an oxidation inhibitor. Tert-butylcatechol concentrated at 0.2% is perfect for this use, but rust and water can damage the inhibitor. 

There was a sudden temperature rise after heating ethylene oxide at a moderate temperature. The medium could not be cooled and as a result the equipment detonated. It was assumed that violent polymerisation of epoxide caused the accident. 

Twenty tons of ethylene oxide were contaminated by ammonia accidentally. The tank broke open releasing a fume cloud , which gives rise to a devastating explosion. Again, it is rather difficult to interpret this accident. Indeed, it could be a violent polymerisation, which was the result of the catalytic effect of ammonia or a very exothermic reaction ... 

Finally, in an aromatic series, the effect of allyl chloride on benzene or toluene in the presence of ethyl aluminium dichloride (Friedel-Crafts catalysts) at -70 C is very violent and has led to a large number of accidents. It is thought that the exothermicity of the reaction below (in the case of benzene) caused these accidents, but one can not exclude a violent polymerisation of allyl chloride. 

Accidents are often caused by the violent polymerisation of aziridine. To avoid it, this amine needs to be handled or stored in a diluted solution when it is cold, and alkaline hydroxide in the solid state is present. 

When acid or base traces are present, acrolein gives rise to a very violent polymerisation after a period of induction that varies according to its purity. It decreases rapidly with the quantity of impurities that are present. Even when the acid is not very strong (NO, NO2, SO2, CO2), the polymerisation is violent. Hydroquinone inhibits the polymerisation, but apparently not for very long. 

The violent polymerisation of acryl acid caused a violent fire on a boat that was transporting it. The investigation showed that this acid contained ethylidene norbornene, which is a very oxidisable compound that forms a peroxide in air, which caused the acid polymerisation. 

At 130°C or at ambient temperature and in the presence of bases, malonitrile gives rise to a very violent polymerisation. The stability of this dinitrile in the molten state (mp 32°C) decreases with the temperature rise and its fall in purity. It was assumed that decomposition never occurs below 100 C. However, when this compound was heated to 70-80°C for two months, this caused a very violent detonation. 

Products that are likely to form free radicals also start a very violent polymerisation if the mixture is made in uncontrolied conditions. Primers are usually tert-butyl or benzoyl peroxide or azobis-isobutyronitrile. 

Bromine was added to acrylonitrile in small portions at 0°C and then by heating to 20°C between each portion. After adding half the amount of bromine, the temperature reached 70°C and the container detonated. The accident was explained by a violent polymerisation, catalysed by traces of hydrogen bromide that were the result of the following substitution reaction ... 

SELF-HEATING AND IGNITION INCIDENTS THERMAL STABILITY OF REACTION MIXTURES VIOLENT POLYMERISATION... 

See entries polymerisation incidents, polyperoxides, violent polymerisation... 

A powerfully reducing and reactive solid (m.p., 15°C) of high vapour pressure (b.p., 50°C). Mixtures with air may explode, and contact with water causes violent polymerisation [1], More usually encountered polymeric or as a hydrate. Like formaldehyde, pure glyoxal may polymerise exothermally and ignite in storage [2],... 

Accidental contamination by aqueous ammonia of an ethylene oxide feed tank containing 22 t caused violent polymerisation which ruptured the tank and led to a devastating vapour cloud explosion [1,2], The close similarity to other base-catalysed incidents was stressed [3],... 

See Other POLYMERISATION INCIDENTS, RUNAWAY REACTIONS, VIOLENT POLYMERISATION... 

Contact with the basic solvent causes violent polymerisation of the isocyanate. 

Bromine was being added in portions to acrylonitrile with ice cooling, with intermediate warming to 20°C between portions. After half the bromine was added, the temperature increased to 70°C then the flask exploded. This was attributed either to an accumulation of unreacted bromine (which would be obvious) or to violent polymerisation [1], The latter seems more likely, catalysed by hydrogen bromide formed by substitutive bromination. Chlorine produces similar phenomena, even if the flask stays intact. The runaway is preceded by loss of yellow colouration and accompanied by formation of 3-chloroacrylonitrile and derivatives. It can be suppressed by presence of bases [2],... 

Laboratory Chemical Disposal Co. Ltd., confid. information, 1968 Presence of mineral or Lewis acids, or bases including amines, will catalyse violent polymerisation of this very reactive dimer, accompanied by gas evolution [1], Sodium acetate is sufficiently basic to cause violent polymerisation at 0.1% concentration when added to diketene at 60°C [2],... 

See Other SELF-HEATING AND IGNITION INCIDENTS, PEROXIDATION INCIDENTS See entries POLYMERISATION INCIDENTS, VIOLENT POLYMERISATION See other GLASS INCIDENTS... 

The same idea will explain an experiment in which a styrene phial (20 mmole) was broken at -10 °C into 100 ml of a 6 x 10 3 M solution (C104" content) of the coloured ionic reaction product between AgC104 and 1-phenylethyl bromide (see above). Because of the rather slow initial mixing, the colour of the solution was not completely discharged by the styrene, and a violent polymerisation ensued, at least 100 times faster than the reaction catalysed by an equivalent amount of perchloric acid would have been. 

Most of these monomers are inclined to violent polymerisation unless stabilised. Stabilisation usually involves oxygen as well as the nominal stabiliser. A kinetic study of the process for acrylic and methacrylic acids is reported. 

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