To produce ethylene oxide (EO) from ethylene and oxygen in a direct oxidation process.
In the direct oxidation process, ethylene and oxygen are mixed with recycle gas and passed through a multi-tubular catalytic reactor (1) to selectively produce EO. A special silver-containing high selectivity catalyst is used that has been improved significantly over the years. Methane is used as ballast gas. Heat generated by the reaction is recovered by boiling water at elevated pressure on the reactors shellside; the resulting high-pressure steam is used for heating purposes at various locations within the process.
EO contained in the reactor product-gas is absorbed in water (2) and further concentrated in a stripper (3). Small amounts of co-absorbed ethylene and methane are recovered from the crude EO (4) and recycled back to the EO reactor. The crude EO can be further concentrated into high-purity EO (5) or routed to the glycols plant (as EO/water feed).
EO reactor product-gas, after EO recovery, is mixed with fresh feed and returned to the EO reactor. Part of the recycle gas is passed through an activated carbonate solution (6, 7) to recover CO2, a byproduct of the EO reaction that has various commercial applications.
Most EO plants are integrated with (mono) ethylene glycol, (M)EG production facilities. In such an integrated EO/(M)EG facility, the steam system can be optimized to fully exploit the benefits of high-selectivity EO catalyst.
When only high-purity EO is required as a product, a small amount of technical-grade MEG inevitably is co-produced.
Yields: Modern plants are typically designed for and operate CRI EO catalyst at a molar EO catalyst selectivity of 91%–92% with fresh catalyst and 89–90% as an average over three years of catalyst life, resulting in an average EO production of about 1.4 tons per ton of ethylene. However, the technology is flexible and the plant can be designed tailor-made to customer requirements or different operating times between catalyst changes.