Ethylene Oxide: A Catalyst and Process Development Success Story

A retrospective look into the rich history of ethylene oxide (EO) catalyst and process development is presented. This Review is written from the Shell Technology perspective, focusing on the major inventions ranging from the first heterogeneous catalysts to currently practiced process technology. The authors describe the major inventions related to the heterogeneous (gas–solid) epoxidation of ethylene with molecular oxygen over silver-based catalysts. This includes silver-only, chlorine-moderated, alkali-promoted, NO_x-promoted, and rhenium-promoted catalyst systems. General information related to catalyst support materials, preparation methods, and catalyst testing are described. A deeper dive into the effects of gas phase components and the reaction mechanism schemes is also presented, with much of the focus taken from the plethora of academic studies published over the decades of this seemingly simple reaction. Many aspects of EO process development are also covered in this Review, ranging from reactor design, evolution of the overall EO production process, to the manufacture of monoethylene glycol (MEG)─the primary derivative of ethylene oxide. Here, both thermal and catalytic routes to the MEG are described. The very important topics of safety related to feed components, product EO, and unit operation are addressed. Lastly, we discuss the current state of the art and prospects for future improvements with regard to the sustainability of EO and MEG production.