Patent GB-1026407-A (GB)
Title: Production of cyanuric acid and urea cyanurate
IPC: C07D251/32
Filed: 1963-01-10
Abstract: Cyanuric acid is prepared by heating urea cyanurate, preferably in the form of a coating on cyanuric acid granules, at 175 DEG  to 325 DEG  C. in air or other inert atmosphere until cyanuric acid or a mixture of cyanuric acid and a minor amount of ammelide is formed. When urea cyanurate coated cyanuric acid granules are heated, free urea may be present in the ratio of urea to such granules of 1: 10 to 1: 150 by wt. In a batch process at 180-320 DEG  C., in which cyanuric acid particles are coated with urea in a wt. ratio of 10: 1 to 250: 1, the urea is applied at a rate only sufficient for substantially all of the urea to react with the cyanuric acid particles to form a coating of urea cyanurate, and the coating is converted to cyanuric acid by further heating.  In continuous processes, molten or aqueous urea is supplied to an agitated bed of cyanuric acid granules (e.g. 1/20 inch-1 inch diameter) at 220-320 DEG  C. having at least a partial coating of urea cyanurate to maintain a wt. ratio of urea to cyanuric acid granules of 1: 10 to 1: 150 and at such a rate as for the urea to react substantially completely with the cyanuric acid on the surface of the granules. According to examples (1) urea cyanurate (prepared by reacting powdered cyanuric acid with an aqueous urea slurry (see Division C2C) was heated at 210 DEG  C. and the evolved ammonia removed.  The product contained less than 0.01% of ammelide and could be further purified by boiling with 10% sulphuric acid, (3) 100 gms. of cyanuric acid granules ( 1/16 inch- 1/8 inch) were heated to 210 DEG  C. in a vibrating crucible, 6 gms. of molten urea at 140 DEG  C. was sprayed thereon to produce a mixture of cyanuric acid and urea cyanurate which on further heating decomposed to cyanuric acid in 3/16 inch- 3/8 inch granules. (4) In a continuous process cyanuric acid pellets ( 1/20 inch- 1/4 inch) were heated to 270 DEG  C. in a rotating drum having a wall temperature of 500 DEG  C.  Molten urea at 150 DEG  C. was fed through one end of the drum through an axial pipe and effluent gases were withdrawn at the same end and passed sequentially through a urea and ammonia condenser.  The feed ratio of cyanuric acid granules to urea fed at no time fell below 43: 1.  The cyanuric acid granules increased in size as urea cyanurate formed thereon and decomposed to form further layers of cyanuric acid, granules of which were withdrawn from the other end of the drum.  A further example (VI) has the granule bed at 300 DEG  C.ALSO:Urea cyanurate is prepared by contacting urea and cyanuric acid at 180-320 DEG  C., the urea being contacted with hot cyanuric acid in an amount and at a rate sufficient only for the urea to react with the cyanuric acid and to form urea cyanurate.  In Example 1, 64 gm. of powdered cyanuric acid was added to a slurry of 120 gm. of urea in 60 gm. water.  On boiling the slurry dissolved and the solution was thereafter cooled to 10 DEG  C. to crystallize the formed urea cyanurate.  In Example 3, urea cyanuarate is formed as a layer on cyanuric acid granules by spraying atomized molten urea at 140 DEG  C. on to constantly agitated cyanuric acid granules of 1/16 -\ba1/8 -inch diameter at 210 DEG  C.