Basf Aktiengesellschaft

Ernst-Juergen Schier

Hans Henning Schneehage

Dieter Fromm

Bernd Leutner

Fritz Beck

Hans-Ulrich Schlimper

Heinz Nohe

Hans Gettert

Klaus Borho

Wolfgang Vodrazka

Dietmar Werner

Winfried Dethlefsen

Hermann Dieter Fromm

Alfred Widmann

Martin Molzahn

Klaus Blanck

Anton Jungbauer

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.

Isolation of liquid urea from the off-gas of the synthesis of melamine

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.

Melamine quality by reactivation of the melamine synthesis catalyst

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.

Simultaneous destruction of trace components in the reaction off-gas

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.

Isolation of pure ammonia from gas mixtures containing ammonia and

Pinacol is manufactured by electrolytic hydrodimerization of acetone in a compartmented cell using a catholyte which contains from 10 to 90% by weight of acetone, from 1 to 60% by weight of water and from 1 to 50% by weight of a quaternary ammonium salt.

Electrochemical manufacture of pinacol

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Altleiningen, Germany

Ernst-Juergen Schier