GB772145A - A process for purifying ethylene oxide - Google Patents

Abstract

<PICT:0772145/III/1> Ethylene oxide is isolated from aqueous solutions thereof which contain carbon dioxide and other normally-gaseous impurities by separating the mixture in a fractionating column to give a small proportion of vapour fraction which contains all the normally-gaseous impurities and a liquid fraction comprising the purified solution, and then submitting the purified solution to distillation under such conditions that substantially anhydrous ethylene oxide is obtained as distillate. The process is particularly applicable to the working-up of the solutions of ethylene oxide obtained by absorbing in water the products of the catalytic oxidation of ethylene with air. The gaseous products obtained by oxidizing ethylene with air in the presence of a catalyst containing silver are cooled in heat-exchanger 22 and then introduced via line 15 into absorption column 20. Water or recycle solution (see later) is supplied to the top of this column through line 21. The pressure in the absorption column is maintained between 50 and 300 p.s.i.g., the temperature being about 20 DEG -40 DEG C. A gaseous mixture consisting chiefly of ethylene, nitrogen, carbon monoxide, carbon dioxide and oxygen leaves column 20 through line 23 and may be recycled to the convertor, preferably after washing with aqueous alkali to remove CO2. The impure aqueous solution of ethylene oxide withdrawn from the base of column 20 is steam-distilled in column 25 at a pressure of 20-80 p.s.i.g. by steam introduced through line 26. The aqueous liquid withdrawn from the base of column 25 is free from ethylene oxide and may be recycled via line 27 to the top of column 20. The vapours leaving the top of column 25, which comprise ethylene oxide, steam, carbon dioxide and other gaseous impurities, are introduced through line 10 into distillation column 30 which is provided with a heating coil 31 at the base and a cooling coil 32 at the head, and is operated at a pressure of 20-80 p.s.i.g. A gaseous fraction containing carbon dioxide and some ethylene oxide is withdrawn from the top of column 30. The purified aqueous solution of ethylene oxide is withdrawn from the base of column 30 and is fed through line 34 to distillation column 35, which contains about 27 trays. This column is operated at a pressure of 20-80 p.s.i.g., and substantially anhydrous vapours of ethylene oxide leave the head of column 35 and are condensed in condenser 39; part of the condensate is returned to column 35 as reflux, and the remainder is withdrawn from the system as product. The aqueous liquid withdrawn from the base of column 35 may, if desired, be fed into a plant in which any ethylene oxide remaining in it is converted into ethylene glycol.