Patent Literature on Epoxidation of Propylene Over Silver Catalysts Using Molecular Oxygen – A Critical Industrial Review

Abstract

AbstractWe summarize the patent literature related to the direct oxidation of propylene‐to‐propylene oxide (DOPO) over silver catalysts. Inventions claiming new compositions, preparation methods, and/or alternative process options are illustrated with data sampled from patent documents. Early claims focused on powders of silver (silver oxide) alloyed with and/or surface‐modified with one‐two promoterswhere silver was in large excess (>80 wt%). In the following decades, inventors refined their approach and pursued alternative bulk synthetic methods supplemented with impregnation to produce formulationscontaining lower amounts of silver in combination with various other transition metals, halides, alkalis and/or alkaline earth elements. Simultaneously, process development has facilitated increased PO selectivity via the co‐feeding of water and/or carbon dioxide at volume percent levels combined with smaller ppmV concentrations of organic chlorides and nitrogenoxides. At the end we briefly discuss how non‐catalytic oxidative routes to propylene oxide provide additional insights for new catalyst development. While these approaches hardly exceed 60 % PO selectivity, they may shed light on design criteria for catalysts capable of achieving that goal. Success in the field will require strong fundamental understanding of the activation of dioxygen on catalytic surfaces to define design requirements for silver catalystswith high selectivity to PO via direct oxidation.