公开(公告)号：DE3162170D1

公开(公告)日：1984-03-15

申请号：DE3162170

申请日：1981-07-13

Applicant: BASF AG

Inventor： BORHO KLAUS DR ,  FROMM DIETER DR ,  SCHIER ERNST-JUERGEN DR ,  SCHNEEHAGE HANS HENNING DR ,  WIDMANN ALFRED DR

IPC: C07C273/10 ,  C07C67/00 ,  C07C239/00 ,  C07C273/12 ,  C07C273/16 ,  C07D251/62 ,  C07C126/08

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.

公开(公告)号：DE3302833A1

公开(公告)日：1984-08-02

申请号：DE3302833

申请日：1983-01-28

Applicant: BASF AG

Inventor： FROMM DIETER DR ,  WIDMANN ALFRED DR ,  SCHNEEHAGE HANS-HENNING DR ,  SCHIER ERNST-JUERGEN DR ,  GRUBE HELMUTH DR ,  MOLZAHN MARTIN DR ,  AUER HEINZ ING GRAD

IPC: C07D251/60 ,  C07D251/56

Abstract: In a process for the preparation of melamine by catalytic rearrangement of urea, the synthesis gases from which the melamine has already been deposited are treated with urea melts. The treatment is carried out in a scrubber which is provided with cooling elements, the urea melt being introduced both above and below the cooling elements. From the gas mixture, which still contains ammonia and carbon dioxide, treated in this way, the ammonia is preferably absorbed in a solvent with contact times of at most 0.1 seconds and the solvent is regenerated again in two following desorption zones with the recovery of pure ammonia. The bottom temperature in the last desorption step is 105 to 120 DEG C. This temperature is maintained by heating a part of the ammonia to 115 to 135 DEG C in the cooling elements of the scrubber and recycling it to the bottom. The virtually ammonia-free solution drawn off from the bottom is initially used for the scrubbing of the carbon dioxide drawn off from the absorption zone before it is employed therein as a solvent.