Production of ethylene oxide

Details Production of ethylene oxide Production of ethylene oxide

1992-02-19

1994-08-09

Evans, Joseph E.

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549523, 549534, C07D30110, C07D30132, C07D30304

Patent

active

053367910

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the production of ethylene oxide.
It is known front U.S. Pat. No. 4,822,926 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 European Patent No 0003642 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 a significant proportion of the oxides of nitrogen can be removed by contacting the gas stream flowing from the reactor with aqueous alkali prior to recovery of the ethylene oxide from the reaction gas stream.
Accordingly, 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 treated by contacting it with an aqueous alkaline quench solution, thereby removing nitrogen oxides and/or organic nitrogen containing compounds from the gas stream, and subsequently recovering ethylene oxide from the gas stream.
The accompanying FIG. 1 is a diagrammatic illustration of apparatus and process for carrying out the invention.
The stream of reaction gas is treated with an aqueous alkaline quench solution. Prior to the contact with the quench solution there is no substantial condensation of water from the gas stream. Suitably the gas stream is contacted with 0.01 to 5% and preferably 0.05 to 0.5% of its own volume of an alkali solution, for example a sodium and/or potassium hydroxide end/or carbonate solution, preferably having a pH of 7.1 to 9.5 and more preferably 7.5 to 9 as finely divided droplets with a residence time of the gas 0.05 to 30 seconds. Contacting with a stream of aqueous alkali may also be carried out by passing the gas stream through the liquid for example as such or as liquid flowing over porous packing. The temperature of the stream of aqueous alkaline quench liquid is suitably 10.degree. C. to 40.degree. C. The temperature of the gas stream at the start of the treatment with the aqueous alkaline quench solution is typically from 50.degree. C. to 100.degree. C. The quench additionally serves the purpose of cooling the reaction gas to a temperature of typically 20.degree. C. to 50.degree. C., close to the temperatures typically used in ethylene oxide absorbers.
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 compounds such as nitromethane, 2-nitroethanol and nitroethylene.
We have found that this procedure is effective to remove a surprisingly high proportion of the nitrogen containing compounds, particularly the inorganic nitrogen containing compounds, in the gas stream. It is further effective to remove the formaldehyde that can be formed by homogenous reactions in the stream of reaction gas in the presence of nitrogen oxides. The quench thus serves an additional purpose in at least reducing the amount of formaldehyde reaching the ethylene oxide removal

REFERENCES:
patent: 4822900 (1989-04-01), Hayden
patent: 4822926 (1989-04-01), Dye

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