GB654462A - Process of preparing nitriles - Google Patents

Abstract

<PICT:0654462/IV (b)/1> Fatty acids or their esters are converted to the corresponding nitriles by treating them with ammonia, the process including the steps of (a) mixing ammonia with a body of the acid or ester in liquid phase within a liquid phase conversion zone and (b) continuously withdrawing the reaction mixture as vapour from said zone and passing the mixture to a heated vapour phase conversion zone, containing a dehydrating catalyst, to convert the fatty acids and amides in the vapour to nitriles in the presence of those vaporized nitriles which were formed in the liquid phase conversion zone. Suitable starting materials are mixed fatty acids which have been obtained by hydrolysing fat or oil with the Twitchell or autoclave process, caprylic, capric, lauric, myristic, palmitic, stearic, oleic, and linoleic acids, hydrogenated acids or alkyl esters of any of these acids. Activated aluminium oxide is mentioned as a suitable dehydrating catalyst. In the Figure, the feedstock containing fatty acids or their esters is fed continuously by feed pump 10 into a preheater 11 where it is heated to a temperature preferably above 400 DEG F. but below the boiling points of the acids. A temperature of 550 DEG F. is mentioned as suitable, especially when a starting material containing a substantial proportion of stearic acid is used. From the preheater the stock is discharged continuously in liquid form through the control valve 28 into the vaporizing chamber 12, which is preferably fitted with a sight gauge 13. The heating coil 14 supplies the heat necessary for continuous vaporization. Anhydrous ammonia is heated in a preheater 15 to a temperature preferably about 550 DEG F. and is continuously introduced into the lower portion of the liquid fatty substance in the vaporizer 12 by means of the distributer 16. The heat supplied through the coil 14 and the quantity of preheated stock introduced into the chamber 12 are so regulated that the liquid acid stock remains in contact with the ammonia for a period of time preferably averaging over 45 minutes. The vapours issuing from the vaporizer may be passed through the tube heater 17 where they are preferably heated to about 750-800 DEG F. The vapours thus heated are passed through the catalyst chamber 18 and on leaving are condensed in the condenser 20. The mixture passes into the separator 21 where the nitriles and water are separated from excess ammonia. The excess ammonia is preferably recovered and recycled by passing the gas from the separator 21 into the scrubber 22 where a descending stream of cold weak ammonia solution absorbs the ammonia, the non-condensable gases being vented into the atmosphere; the relatively strong ammonia solution from the base of the scrubber is pumped through the heat exchanger 23 and to the ammonia still 24 and from there may be passed through the line 25 and regulating valve 26 back to the preheater 15. Pitch is removed periodically through line 27. Specification 477,463 is referred to.