Heavy reaction with hydroperoxide

The first step is oxidation of EB to form EB hydroperoxide. The oxidation is carried out in the liquid phase with a target EB conversion of approximately 13%. Although higher conversions are attractive from an EB recovery and recycle standpoint, there is a significant disadvantage because the EB hydroperoxide selectivity declines sharply. The second step is epoxidation of propylene to form propylene oxide product and 1-phenylethanol. In the last step, the 1-phenylethanol is dehydrated to styrene and water. The dehydrated reaction mixture is typically stripped of light components and rerun in a styrene column to remove heavy by-products, resulting in a purified styrene product. 

The stream from the reaction section is first distilled to remove unconverted propylene, whose recycle, added to the make-up, represents the feed of the first epoxidation stage. Excess propane is also removed by distillation (—50 to 60 trays) to prevent its buildup in tfie synthesis loop. The heavy end of the first column is sent to the purification train for products for which the temperatures cannot exceed 100°C to avoid undesirable degradation. On account of the boiling points at standard pressure of the components present, this makes operation under vacuum necessary. Crude propylene oxide is collected at the top of the first distillation column (50 trays), and r-butyl alcohol at the1bottom, with some hydroperoxide, the catalyst, propylene glycol, aldehydes, esters etc. This stream is sent to a r-butyl alcohol separation column (35 to 40 trays), where the alcohol is recovered at the top. 

However, hydroperoxides can also be isomer-ized by such a reaction pathway. When they interact with free radicals (H-abstraction from -OOH group) or with heavy metal ions (cf. Reaction 3.64), they are again transformed into peroxy radicals. Thus, the 13-hydroperoxide of hnoleic acid isomerizes into the 9-isomer and vice versa ... 

Phenolic compounds known as polyphenols (such as phenohc acids and flavonoids) are easily oxidised by atmospheric oxygen in reactions catalysed by oxidoreductases (o-diphenokO, oxidoreduc-tases). These reactions are known as enzymatic browning reactions (see Section 9.12). Autoxidation of plant phenols catalysed by heavy metal ions (mainly cupric and ferric ions) and oxidation by lipid hydroperoxides lead to similar products. The products of oxidation of the so-called o-diphenok (1,2-dihydroxybenzenes) are o-quinones (1,2-benzoquinones), highly reactive compounds that react with proteins (amino acids) and other food components with the formation of dark-coloured polymeric products resistant to proteolysis. 

Redox reactions of heavy metal ions with peroxides and hydroperoxides in which free radicals are generated are widely used for the initiation of chain polymerization and oxidation reactions. The H2O2 + Fe system known as Fenton s reagent has long ago been used for the hydroxylation and oxidative dimerization of organic compounds. These reactions occur during the catalytic decomposition of peroxides and in complicated processes of catalytic oxidation. 

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