Abstract: An improved process for the preparation of melamine from urea or thermal decomposition products thereof. A melamine containing reaction mixture is cooled with an aqueous medium to form an aqueous product stream containing melamine and reaction by-products. Product melamine is separated from the aqueous product stream leaving a residual aqueous stream which is recycled into the process. A portion of this residual aqueous stream still containing reaction by-product is treated to remove by-products therefrom prior to being recycled to the process.

Abstract: In the synthesis of melamine by conversion of urea in a fluidized catalyst bed, the melamine quality is improved by reactivating the catalyst by treating it, in the fluidized bed, with gases containing steam, in the absence of oxygen, at from 250.degree. to 450.degree. C.

Abstract: The reaction off-gas from the synthesis of melamine consists, after separating off the melamine, mainly of ammonia and carbon dioxide, with traces of hydrogen cyanide, isocyanic acid, urea and residual melamine. To remove these trace components, the off-gas is passed over a catalyst, containing copper oxide and/or iron oxide, in the presence of steam at from 100.degree. to 500.degree. C.

Abstract: An improved method for the preparation of melamine by the conversion of urea and/or thermal decomposition products thereof. The urea and/or thermal decomposition products are converted to melamine in the presence of a gas mixture containing ammonia and carbon dioxide in a reaction zone containing a fluidized bed of catalytically active material. Melamine is desublimated from the melamine containing gas mixture in a desublimation zone by a dry-capture method leaving a desublimator off-gas mixture of ammonia, carbon dioxide and gaseous impurities. A major portion of this desublimator off-gas mixture is compressed and recirculated to the reaction zone as fluidizing gas for the bed of catalytically active material, without intervening treatment to remove gaseous impurities from the desublimator off-gas.

Abstract: An improved process for the removal of urea from urea-containing waste water by hydrolysis and desorption of the ammonia and carbon dioxide thus formed. Urea-containing waste water is treated in a process for the separation of ammonia and carbon dioxide from mixtures thereof, which process has (a) an ammonia separation zone wherefrom ammonia, substantially free of carbon dioxide and water, is obtained, (b) a carbon dioxide separation zone wherefrom carbon dioxide, substantially free of ammonia and water is obtained, and (c) a desorption zone wherefrom water, substantially free of carbon dioxide and ammonia is obtained. The urea is substantially completely hydrolyzed and the ammonia and carbon dioxide produced thereby can be recovered.

Abstract: An improved process for the preparation of melamine from a feed of urea, thermal decomposition products of urea, or a mixture thereof, in the presence of a catalyst and an ammonia-containing gas. The reactor is divided into a lower and an upper reaction zone by a permeable grid or other restriction which reduces the catalyst flow between the two zones to 5 to 75% of what it would have been in the absence of such restriction. The feed is introduced into the lower reaction zone, which is maintained at a temperature of between 325.degree. and 425.degree. C., wherein substantially all of the urea is decomposed into thermal decomposition products, and a major portion of the thermal decomposition products are converted into melamine, which together with the remaining unreacted thermal decomposition products, is passed into the upper reaction zone.

Abstract: Melamine synthesis waste gases are first treated for the removal of melamine by condensation. The waste gases are then treated with urea-containing melts which are cooled indirectly. At least parts of said indirect cooling takes place together with the treatment of the reaction waste gases with the urea-containing melts in a single zone.

Abstract: A two phase sprayer and process are disclosed in which the sprayer has a liquid supply tube surrounded by a coaxial gas or gas mixture supply tube which extends beyond the length of the liquid supply tube where the gas flow surrounds and atomizes the expelled liquid. The sprayer has a unique structure in part characterized by a narrowed taper gas supply tube which converges towards the outlet at an angle of 70.degree.-90.degree. with respect to the sprayer axis. The internally-positioned, coaxial liquid supply tube is chamfered also at a similar 70.degree.-90.degree. angle, the gas and liquid tubes at their outlet being essentially parallel.The joint of the narrowing part of the gas tube and the outflow channel is rounded.