Patent GB-746507-A (GB)
Title: Improvements in or relating to the pyrolysis of diacyl cyanides
Inventor: REUTER LOUIS FREDERICK
Filed: 1953-09-21
Abstract: Monomeric 1,1-dicyano ethylene and its alkyl 2-substituted homologues, the alkyl group containing from 1 to 4 carbon atoms are obtained by the vapour phase pyrolytic deacyloxyation at 300-800 DEG C., of a diacyl cyanide having the formula R.C.(CN)2.CH2R1, wherein R is an aliphatic acyloxy radical and R1 is hydrogen or an alkyl radical containing from 1 to 4 carbon atoms, the pyrolysis vapours being rapidly condensed by bringing a stream of the hot vapours into countercurrent flow with a moving stream of a cold inert quench liquid, the weight ratio of quench liquid to pyrolysis product being at least 50 to 1 and the said quench liquid being at a temperature not higher than room temperature.  The process may be operated at atmospheric pressure or at pressures slightly above atmospheric and the preferred pyrolysis temperatures are 500-600 DEG C.  The pyrolysis may be carried out in the presence of an inert diluent which may be either a gas or liquid at room temperature.  Specified diluents are the liquid aromatic hydrocarbons or liquid halogen-substituted aromatic hydrocarbons, e.g. benzene, toluene, o-, m-, or p-xylene, monochlorobenzene, dichlorobenzene, and trichlorobenzene.  Inert diluent gases specified are methane, ethane, propane, nitrogen, hydrogen, and helium, and mixtures thereof.  Rapid condensation of the pyrolysis vapours is preferably effected by directing the pyrolysis vapours into a quench zone, which may be a quench nozzle of restricted volume where the hot vapours are met with a relatively large liquid flow of preformed pyrolysis product or an inert liquid diluent such as one of those specified above, or a mixture of both, maintained at a temperature no higher than room temperature.  The pyrolysis vapours should be maintained above the dew point until they are contacted by the cold flow of quench liquid and this may be effected by heating the line through which the vapours pass to the quench nozzle.  The ratio of quench liquid to pyrolysis vapours is preferably about 200 to 1 and may be controlled by adding liquid diluent to the diacyl cyanide fed to the pyrolyzer or by adding the diluent to the quench liquid continuously.  A polymerization inhibitor is desirably incorporated in the pyrolysis product either simultaneously with or soon after the condensation of the vapours.  Specified inhibitors are sulphuric acid, halosulphonic acids, e.g. chlorosulphonic acid, the sulphonyl chlorides, e.g. benzene- or toluene, sulphonyl chloride, and sulphur dioxide.  A specific procedure is described and illustrated and examples are given for the pyrolysis of 1-acetoxy-1,1-dicyano ethane which is fed together with monochlorobenzene into a vaporizer, the vapours being led into a pyrolyzer containing a stainless steel helical coil where they are pyrolyzed at 530 DEG  C., the pyrolysis vapours being then led into a quench nozzle where they are met with a large downward flow of a mixture of monochlorobenzene and cooled condensed crude pyrolysis product.  The results obtained using various pyrolysis temperatures, feed rates and quantities of diluent are tabulated. Other diacyl cyanides specified are 1 - propionoxy - 1,1 - dicyano propane, 1 - propionoxy-1,1-dicyanoethane and 1-acetoxy-1,1-dicyano butane. Specifications 653,468, 677,825 and 746,508 are referred to.