Ethylene Oxide Production from Ethylene (Pure Oxygen as Oxidizer)

The process under analysis comprises three major sections: (1) Oxidation; (2) Reagents Recovery; and (3) Products Separation.

Oxidation. Initially, fresh ethylene, methane make-up and oxygen are mixed with recycle gas (recovered downstream). Methane is used as ballast gas to control flammable limits in the process. The mixture is heated by heat exchange with reactor effluent, and fed to the multi-tubular catalytic reactor in which ethylene oxide (EO) is selectively produced over a silver catalyst supported on alumina. The heat from this exothermic reaction generates steam on the reactor shell-side, used for heating purposes throughout the process. Also, part of the ethylene is combusted, generating carbon dioxide and water.

Reagents recovery. The gaseous stream obtained from reactor outlet is counter-currently contacted with cold water in an absorber for the separation of light gases (mainly CO2, unreacted ethylene, oxygen and methane). The bulk of the gaseous overhead stream is directly cycled back to the EO reaction by a compressor. The remainder of the gaseous overhead stream is treated for CO2 removal before being sent back to the reactor. A liquid solution, comprising EO dissolved in water, is withdrawn from the absorber as a side stream.

Products Separation. The EO/water stream from the absorber is fed to the top of a stripper, where EO is separated from water. The stripper bottoms - a water/ethylene glycol mixture - is routed to a column for recovering antifreezing grade ethylene glycol sold as by-product. The overhead gaseous stream, relatively concentrated in EO, is condensed and sent to a light ends removal unit. Crude EO withdrawn from the bottom of this unit is fed to a final purification column for removal of water and heavy impurities. High purity Ethylene Oxide (99.9 wt%) obtained from column overhead is condensed and sent to storage.