Styrene production in plastics & polymers production

Styrene is an important monomer used in the manufacture of plastics such as polystyrene – best known in its expanded form under the brand name Styropor. But it is also found in foams and other insulating materials. Styrene is manufactured on an industrial scale from ethylbenzene. Catalytic dehydrogenation of ethylbenzene is the most common process for this. The first stage involves producing raw styrene. For this purpose, the reaction mixture provided, consisting of fresh and recycled, unconverted ethylbenzene, diluted with water vapour, is directed through a metal oxide catalyst and is dehydrogenated at 600°C to 650°C. The condensable part is then separated and the hydrogen is extracted and compressed. The raw styrene produced contains, among other components, unreacted ethylbenzene. In the first distillation column, benzene and toluene is removed from the mixture at standard pressure. In the second column, unconverted ethylbenzene is removed and fed back into the reactor. Lastly, in a third column under vacuum the styrene is separated from polymers and other residues.

Precise temperature/heat management is particularly key at the heart of the plant, the dehydrogenation reactor, therefore the temperature and the flow of process steam and ethylbenzene need to be precisely regulated to control the process. Further challenges are presented by the increasing tendency of the styrene to polymerise as the temperature rises and the marginal difference in the boiling points of ethylbenzene and styrene. KROHNE offers state-of-the-art measuring technology here for process monitoring, such as complete thermometers for temperatures well above 600°C with resistant thermowell material and in all common thermowell designs. There are also highly sophisticated vortex flowmeters with integrated temperature and pressure sensor, which allow reliable gross/net heat quantity measurement for steam and condensate. And our electronic differential pressure transmitters provide additional process information thanks to integrated measurement of the static pressure.