As almost everywhere in the world, Evonik uses the autoxidation process for hydrogen peroxide production, in which a reaction carrier is cyclically reduced and oxidized. An organic working solution ensures that the reaction carrier always remains in solution so that the process can run continuously. It is important to continually refresh the working solution, otherwise the process would soon fail.
As an extension to the previous process, the working solution should have been treated with sodium hydroxide in an additional regeneration step in Rheinfelden from 2017 on. The new process would have resulted in a corrosive wastewater stream containing a number of organic components and due to its toxicity could not have been discharged into a biological wastewater treatment plant without pretreatment.
To avoid this, a team from the Active Oxygens Business Line devised a method for processing this wastewater stream. They integrated what is known as a Fenton reaction into the process in Rheinfelden. A combination of hydrogen peroxide and iron(II) sulfate is used to fragment the organic components of the caustic solution to the point at which they are biodegradable. While the Fenton reaction itself has been known for more than 100 years, it was the team from Active Oxygens that first succeeded in adapting it for the special conditions in hydrogen peroxide production. Thanks to sophisticated process design and skilful adjustment of reaction parameters, the degradation process is now running optimally and providing even better results than predicted. The wastewater that has been treated in this way is fed to the site’s own treatment plant. A caustic disposal problem has thus been solved.
It was thanks only to the integrated Fenton reaction that the upstream regeneration stage could be realized at all, as a result of which the capacity of the production plant could be increased. It is already clear that the process could also be carried over to other production plants for hydrogen peroxide. And in the future Evonik will also use the process to treat wastewater from other production processes. Another such plant will come onstream in Marl as early as 2020.