Technology

Production of Ethylene Oxide

Production process is based on a catalytic reaction between Ethylene and Oxygen using Silver as catalyst. Silver is unique as a catalyst for this reaction as no other metal until now can compete with Silver, which, in practice, is finely dispersed and deposited on various kinds of porous support materials such as alumina. The exact composition and structure of the support material do strongly influence the process and product quality. It is considered as know-how of the producers and therefore kept secret. Several, but similar, technologies exist for ethylene oxide production. Differences depend mainly on whether air or pure oxygen is used for oxidation. The selectivity now being achieved is over 90%. As the catalyst ages, selectivity decreases. The lifetime of a catalyst is in the range of 2-5 years.

Production steps

• Ethylene is mixed with air or oxygen and passed over a catalyst (finely divided silver on an inert support such as alumina) at 520-550 K and under 15-20 atmospheres pressure. Residence time in the reactor is 1-4 seconds. Two reactions, partial and complete oxidation, take place simultaneously at the catalyst surface. Together with Ethylene Oxide, Carbon Dioxide and Steam are generated as well (Fig. 1). A small amount of 1,2-Dichloroethane is added to the reaction mixture which decreases the unwanted side reaction.
  
  Figure 1 - Two competing reactions for the oxidation of ethylene
  (The enthalpy values are at 523°K and 15 atm).
  
   
• The gas leaving the reactor is cooled by means of steam generation or direct heating of the gas inlet of the reactor. 
• Ethylene oxide and CO₂ are removed from the gas by scrubbing with first water and second an aqueous Potassium carbonate solution. The ethylene oxide dissolves in the solution.
• Ethylene oxide is desorbed from the solution in the desorber and stripped of its low-boiling components.
• Ethylene oxide is finally distilled with separation into water and ethylene oxide.
• The process runs continuously using a recycled gas stream through the reactors driven by compressors, and reloaded before entering the reactor again.

References

1. Siemens Aktiengesellschaft, 2003, Oil & Gas Industry, Process Analyzers in Ethylene Oxide Production Plant.
2. The Essential Chemical Industry - Online, 6^th Oct 2016, Epoxyethane (Ethylene oxide).