Abstract: A process for isolating liquid urea and its thermal decomposition products from the off-gas of melamine synthesis, which gas has been freed from melamine by fractional condensation and then been washed with molten urea, wherein the off-gas, containing 2-10 kg of melt per kg of pure gas, is passed at 8-30 m/sec tangentially into the upper part of an axially symmetrical separation zone. As a result of the rotation imparted to the gas/liquid mixture, the two phases are separated from one another, and both pass downward through the separation zone. The gas and liquid are separately taken off at the bottom end of the separation zone. The residence time of the gas mixture in the separation zone is not less than 0.5 second.

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: To isolate ammonia from gas mixtures containing ammonia and carbon dioxide, the gas mixture is first partially absorbed in a solvent, with residence times of at most 0.1 second, and the non-absorbed gas is then separated from the solution obtained. The solution is then subjected to a first desorption stage, in which only the ammonia present in an excess over a molar ratio of 3 parts of ammonia to 1 part of carbon dioxide is expelled by heating, and the entrained carbon dioxide is washed out of the expelled ammonia by means of solutions containing free ammonia. The solution remaining after the first desorption stage is substantially freed from ammonia and carbon dioxide in a second desorption stage and the expelled gas, containing solvent, together with fresh gas mixture is fed to the adsorption stage, while the solvent obtained from the second desorption stage is employed for the absorption.