Patent GB-655101-A (GB)
Title: Process for making ketene
IPC: C07C45/88
Filed: 1948-10-12
Abstract: <PICT:0655101/IV (b)/1> In processes in which ketene is prepared from ketones by the thermal decomposition of the ketone vapour at an elevated temperature in a reaction zone, the surfaces of the reaction zone which are in contact with the ketone vapour are constructed of a steel alloy containing from 22 to 27 per cent chromium and from 12 to 22 per cent nickel, the balance being substantially iron.  The reaction vessel may be in the form of a single tube or a coil and is preferably constructed entirely of the alloy, but if desired those surfaces in contact with the hot reactant gas may be lined with the alloy.  The steel alloy should preferably contain less than 0.25 per cent of carbon.  In carrying out the invention a ketone such as acetone or methyl ethyl ketone is first vaporized and then preheated and the preheated vapour passed into the reaction vessel.  In an example described with reference to the drawing, acetone is vaporized in vaporizer 2 and preheated to about 1150 DEG  F. in preheater 4 which may be a steel alloy containing 18 per cent chromium and 8 per cent nickel, and then passed to pyrolyser 6 which is a tube constructed of a steel alloy containing 25 per cent chromium and 20 per cent nickel.  The temperature of this chamber may be maintained at 1200 DEG  to 1500 DEG  F., preferably at 1300 DEG  F., and the contact time of the acetone is from 0.25 to 0.75 second.  The effluent gases are immediately introduced into the absorbing tower 8 where they are passed countercurrent to glacial acetic acid introduced through line 9. The bottom of the absorber also acts as a soaker for the completion of the reaction between the ketene and acetic acid.  A mixture of acetic acid and acetic anhydride is removed through line 10 and passed to fractionator 11 where the acetic acid and acetic anhydride are separated, the former being recycled to the absorber through line 15 and condenser 16 and the latter withdrawn through line 14 as product.  Unconverted acetone, some acetic acid and fixed gases (largely methane, carbon monoxide and ethylene), are passed overhead to condenser 13 where the bulk of the acetone is condensed and recycled through line 23.  The mixture of fixed gases and uncondensed acetone are passed by line 17 to scrubber 18 where they are contacted countercurrently with glacial acetic acid.  Alternatively the acetone may be recovered by scrubbing with water and then fractionating, the acetone being returned to the system by returning it to line 23.  In operation a positive gauge pressure of about five pounds is maintained on the apparatus with an inlet temperature of the gas to the cracking zone of about 950 to 1200 DEG  F. and an outlet temperature of 1200 DEG  to 1500 DEG  F., when acetone is being cracked.  The pyrolysis temperature should be between 1100 DEG  and 1500 DEG  F.  Specifications 627,810 and 629,211 are referred to.ALSO:In a process in which ketene is prepared from a ketone by the thermal decomposition of the ketone vapour (see Group IVb), the surfaces of the pyrolysis chamber are made of a steel alloy containing from 22 to 27 per cent chromium and from 12 to 22 per cent nickel, the balance being substantially iron.  The alloy should preferably contain less than 0.25 per cent of carbon.  In an example, acetone is preheated in a preheater made of a steel alloy containing 18 per cent chromium and 8 per cent nickel, the balance being substantially iron, and then pyrolysed in a chamber constructed of a steel alloy containing 25 per cent chromium and 20 per cent nickel.  Specifications 627,810, [Group IV(b)], and 629,211 are referred to.