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Manufacture of styrene from ethylbenzene
Summary
The manufacture of styrene from ethylbenzene is a direct dehydrogenation reaction using an iron oxide based catalyst. ...
Introduction
In 1994 the worldwide production of the styrene monomer totalled 14 million tons. ... The main process of producing styrene is through the direct dehydrogenation of the aromatic, ethylbenzene. However, the monomer is also produced on a smaller scale through the manufacture of propylene oxide.
Therefore, before the manufacture of styrene can be looked at the production of the reactant, ethylbenzene (from now on also referred to as EB) must first be considered. 99% of the total ethylbenzene produced is used for the manufacture of styrene with 95% of this being produced through the alkylation of benzene with ethylene. The reminder is produced from the distillation of crude oil. This is a relatively obsolete method as it is very hard to separate EB from other, mainly aromatic, C8 compounds due to the very similar boiling points (bp1. ...
Chemistry of the process
Production of ethylbenzene
This alkylation is an exothermic reaction (DH0298=-114 kJ/mol) that normally takes place in the liquid phase in the presence of an acid catalyst (85% of the worlds production of EB uses AlCl3/HCl as a Lewis acid in a Friedel-Crafts system). ...
The production of EB is not limited to the Lewis acid/Friedel-Crafts method, as recently molecular sieves have been employed in the vapour phase to separate EB from crude oil, and now zeolites such as H-ZSM-5 are used as very effective catalysts for the alkylation reaction. ...
Production of styrene
The direct dehydrogenation of EB is a reversible endothermic reaction (ΔH°298 = +124. ... Steam use is also advantageous because it inhibits the build up of coke (formed from product condensation) on the catalyst and the reactor, and keeps the iron oxide of the catalyst in the correct oxidation state. ... This will give a single-pass conversion as high as 50%-70% with selectivity to styrene of about 90%-95%. ...
Without the use of a catalyst temperatures of between 700°C and 800°C need to be used, but this will reduce single-pass conversions to 20%-30% with yields of styrene not exceeding 50%-60% (molar). This is poor performance is through the plenitude of unwanted side reactions (such as extra alkylations of the styrene to form methylstyrene) encouraged by the higher temperature.
Approximate Word count = 1872
Approximate Pages = 7.5
(250 words per page double spaced)
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