| 摘要 |
Hollow pellets consisting essentialy of cyanuric acid are produced by repeatedly contacting solid pellets of urea with finely divided crude cyanuric acid at a temperature no higher than 160 DEG C. to give porous hollow pellets of urea cyanurate (claimed per se) which are then heated to 190-310 DEG C. to give hollow pellets of cyanuric acid. Preferably, as the first stage, the urea containing not more than 50% by weight biuret is heated to 125-160 DEG C. at atmospheric pressure for 15-45 minutes with cyanuric acid finer than 35 U.S. mesh in a horizontal rotating drum optionally with 5-20% by weight of a finely divided inert powder (ammelide preferred to melamine, kieselguhr, expanded silica or ground limestone as other examples). Preferably, as the second stage, the pellets of urea cyanurate are heated for 10-90 minutes in a rotary reactor which is at 230 DEG C. near the inlet and 300 DEG C. at the exit, at a pressure 100-760 mm. Hg.abs. Some (50-75%) of the pellets, comprising for example 85-98% cyanuric acid and 2-15% ammelide, are preferably ground to a fine powder and recycled for the production of more hollow urea cyanurate pellets and the remainder removed as product or for further purification e.g. by hyrdrolysing the ammelide to cyanuric acid with strong mineral acid.ALSO:Hollow pellets of urea cyanurate (claimed per se) are prepared by repeatedly contacting solid pellets of urea with finely-divided crude cyanuric acid at a temperature no higher than 160 DEG C. These may then be heated to 190-310 DEG C. to give hollow pellets of cyanuric acid. Preferably, as the first stage, the urea containing not more than 50% by weight biuret is heated to 125-160 DEG C. at atmospheric pressure for 15-45 minutes with cyanuric acid finer than 35 U.S. mesh in a horizontal rotating drum optionally with 5-20% by weight of a finely-divided inert powder which may be melamine, kieselguhr, expanded silica, ground limestone, but is preferably ammelide. The pellets of urea cyanurate are substantially spherical and have a wall thickness 25-80% of the diameter of the central hollow portion.
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