Patent GB-788098-A (GB)
Title: Process for purifying ketene
Filed: 1954-01-19
Abstract: Ketene obtained by the thermal decomposition of acetic acid under reduced pressure is purified, to remove water, acetic acid and acetic anhydride therefrom, by cooling the gaseous reaction mixture at a pressure between about 50 and about 550 mms. mercury to a temperature of not more than 20 DEG  C. but above the solidification temperature of the condensate, separating from the gaseous constituents the liquid thus formed containing the major part of water, acetic acid and acetic anhydride contained in the gaseous reaction mixture, then cooling the gaseous constituents under a pressure between about 600 and about 2000 mms. of mercury to a temperature of not more than 0 DEG  C. but above the solidification temperature of the condensate and separating the liquid thus formed from the remaining gaseous substantially pure ketene.  Preferably the second cooling stage is effected on the delivery side of one or more vacuum pumps in series. In an example, acetic acid containing triethyl phosphate is fed in vapour form through a heated Si-Cr-Al alloy reaction coil and the issuing gases at 730 DEG  C. under 100 mms. pressure are admixed with an equilibrium-stabilizing amount of ammonia and passed through a two-stage cooler employing water and brine at - 10 DEG  C. as coolants, the aqueous condensate is removed and the residual gaseous stream under about 90 mms. pressure is passed into the suction side of a cooled rotary compressor used as a vacuum pump, then delivered under about 620 mms. pressure via a cooler to a second cooled compressor from which the gaseous stream is delivered at atmospheric or higher pressure to another cooler maintained at - 10 DEG  C. and the liquid condensate formed is separated from the remaining purified gaseous ketene.  This ketene may be dimerized in diketene solution.ALSO:Ketene obtained by the thermal decomposition of acetic acid under reduced pressure is purified, to remove water, acetic acid and acetic anhydride therefrom, by cooling the gaseous reaction mixture at a pressure between about 50 and about 550 mm. mercury to a temperature of not more than 20 DEG  C. but above the solidification temperature of the condensate, separating from the gaseous constituents the liquid thus formed containing the major part of the water, acetic acid and acetic anhydride contained in the gaseous reaction mixture, then cooling the gaseous constituents under a pressure between about 600 and about 2000 mms. mercury to a temperature of not more than 0 DEG  C. but above the solidification temperature of the condensate and separating the liquid thus formed from the remaining gaseous substantially pure ketene.  Preferably, the second cooling stage is carried out on the delivery side of one or more vacuum pumps in series.  In an example, acetic acid is thermally decomposed in a furnace and the issuing gases at 730 DEG C. and under 100 mms. pressure, admixed with a small amount of ammonia, are first passed through a two-stage cooling system employing water at 0 DEG  C. and brine at - 10 DEG  C. as coolants, the aqueous condensate formed is removed and the residual gases under about 90 mm. pressure are passed into the suction side of a cooled rotary compressor used as a vacuum pump, then they are delivered under about 620 mms. pressure via a cooler to a second rotary compressor which delivers the gases at atmospheric or higher pressure to another cooler at - 10 DEG  C. and liquid condensate formed is separated from the remaining purified gaseous ketene.