Production of Ethylene Oxide

Process Selection , Process Evaluation and process Flow Diagrams

Ethylene oxide is produced industrially by the oxidation of ethylene with either pure oxygen or air . The primary difference between the two processes is the sequencing of absorbers and desorbers in the separation train . Ethylene and oxygen (or air ) are reacted at 10-30 atmospheres and 400-500F in a fixed bed catalytic reactor . The catalyst bed consists of large bundles of many tubes that contain supported silver catalyst spheres or rings . The tubes are 6-12 meters long and 20-50 millimeters in diameter . In the oxygen

process , the reactor off-gas is fed to CO2 scrubbers , then to ethylene oxide scrubbers , which absorb the ethylene oxide into the liquid phase . The ethylene oxide is recovered from the liquid in a desorber and distilled to remove water . In the air process no CO2 scrubbing is used because the gas purge of inerts (mostly N2 ) is sufficient to remove the CO2 . The reactor operates at a low conversion however , so unreacted ethylene is fed to a secondary fixed bed reactor then separated . Ethylene oxide purity is typically greater than 99 .5 15

Figure 1 is a process flow diagram (PFD ) showing combined pure oxygen- and air-based systems . 15 Figure 1 . Simplified process plow of ethylene oxidation15

Catalyst pellets are designed to favor selective oxidation (epoxidation over sites . Silver is supported on pure aluminum oxide with pore diameters ranging 0 .5-50 micrometers and specific surface area less than 2 m2 /g The motivation for designing this catalyst is that a less active catalyst will promote the partial oxidation of ethylene to ethylene oxide , but it will promote neither the the subsequent oxidation of ethylene oxide . Catalyst is operated with alkali metal promoters , usually cesium , and chlorine-containing inhibitors . Alkali metal promoters are dissolved in the catalyst by adding an...