Production of ethylene oxide

Details Production of ethylene oxide Production of ethylene oxide

1993-02-19

1995-01-24

Evans, Joseph E.

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549538, C07D30132, C07D30304

Patent

active

053844203

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the production of ethylene oxide.
It is known from U.S. Pat. No. 4,822,920 to produce ethylene oxide by reacting ethylene with oxygen in the presence of a silver containing catalyst and a chlorine containing reaction modifier in the absence of nitrate and/or nitrite forming substances in the gas phase and to spray the gas stream flowing from the reactor with aqueous alkali. This cools the gas stream and removes impurities such as oxalic acid, aldehydes and aldol products. Some ethylene oxide is inevitably removed and at least partly hydrolysed to ethylene glycol during this step.
It is also known from our European Patent No 3642 that ethylene may be oxidised with oxygen to ethylene oxide in the presence of a silver containing catalyst and a nitrate or nitrite forming substance which is in the gas phase simultaneously with a chlorine containing reaction modifier. The gas stream from the reaction generally comprises unreacted materials, impurities, H.sub.2 O, oxides of nitrogen and other gases as well as ethylene oxide.
The oxides of nitrogen, though not dangerous in themselves tend to react with other components derived from the reaction in subsequent purification sections of process plant to produce solid or liquid organic nitrogen compounds which may accumulate in cold parts and represent an explosion hazard and/or contaminate the product of the process.
We have found that oxides of nitrogen and other nitrogen containing compounds can be removed by condensing water from the reaction gas stream when the nitrogen containing compounds can be concentrated in the condensate. Further removal of nitrogen containing compounds can be effected by subsequent treatment with an aqueous wash prior to recovery of the ethylene oxide.
This invention provides a process in which a gas stream from a reaction in which ethylene oxide is produced by reacting ethylene with oxygen which gas stream comprises oxides of nitrogen and steam is cooled preferably in a zone to which no liquid is introduced to form a condensate comprising at least 70% and preferably at least 80% for example at least 90% of water by weight, condensed water is removed and ethylene oxide is then recovered from the gas stream.
In the accompanying drawings, FIGS. 1 and 2 are diagrammatic illustrations of apparatus and process for carrying out the invention.
In order to secure the required water content of the condensate steam may if necessary be added as such or in the form of droplets comprising water and optionally are alkaline but which preferably comprise only volatile substances and more preferably consist of water only which are substantially completely evaporated before the condensation step. However, the requisite water content may usually be secured by an appropriate amount of cooling.
It is desirable that no added liquid be present during the condensation stage. We believe without wishing to be bound by this explanation that such added liquid is antagonistic to the production of a desirable misty condition of the gas stream otherwise produced during the condensation and which is very efficient in the removal of oxides of nitrogen. Aqueous mist present in the incoming gas stream may be beneficial in itself but difficult to control.
After the condensation step and before the recovery of ethylene oxide the gas stream may be contacted with a stream comprising water for example an aqueous alkali solution or preferably water free from alkali, preferably as a spray to wash impurities from it.
The oxides of nitrogen may comprise NO, NO.sub.2, N.sub.2 O.sub.4, N.sub.2 O.sub.3 and/or N.sub.2 O.sub.5 and organic nitrogen containing compounds can include nitromethane, 2-nitroethanol and nitroethylene.
We have found that this procedure is remarkably effective in that a surprisingly high proportion of the nitrogen containing compounds in the gas stream are removed in the condensed water and a subsequent wash with water or alkali will not only remove other impurities but will also more easily bring the remaining concentration of oxides of

REFERENCES:
patent: Re25933 (1965-12-01), Huckins
patent: 4469492 (1984-09-01), Lagana et al.
patent: 4822900 (1989-09-01), Hayden
patent: 4822926 (1989-04-01), Dye

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