Abstract: The invention relates to a method for concentrating an aqueous ammonium carbamate stream, which has been formed in a process for the preparation of urea, has a pressure between 0.20 MPa and 0.9 MPa, a temperature between 35° C. and 95° C., and contains at least 25 wt. % H2O, comprising: a pressure increase step, in which the aqueous ammonium carbamate stream is increased in pressure to a pressure between 1.0 MPa and 7 MPa; a condensation step, in which the aqueous ammonium carbamate stream is contacted with a gas stream, which has been formed in a process for the preparation of melamine and which consists essentially of NH3, CO2 and optionally H2O and has a lower H2O content than the aqueous ammonium carbamate stream, the gas stream being absorbed in the aqueous ammonium carbamate stream in such a way that a concentrated ammonium carbamate stream is formed that contains between 15 and 35 wt. % H2O; a discharge step, in which the concentrated ammonium carbamate stream is separated and discharged.

Abstract: Process for the preparation of a nitrogen-containing compound, comprising the steps of: a) bringing N2, optionally NH3 and optionally a recycle stream together with a carbon- and hydrogen-containing compound or a carbon-containing compound and H2 to form a reaction mixture, whereby the ammonia in the reaction mixture, if present, originates for at least 30 wt. % from the recycle stream; b) bringing the reaction mixture in contact with a catalyst at a temperature lying between 200° C. and 800° C. and at a space velocity lying between 102 and 106 ml/(g.h), said catalyst containing a metal M1 on a support, M1 being chosen from the group consisting of metals in group 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 of the IUPAC Periodic Table of Elements or mixtures thereof, whereby the nitrogen-containing compound is formed; c) optionally separating, subsequent to step b), a portion of between 1 and 99 vol. % off from the reaction mixture, said portion being the recycle stream.

Abstract: The invention relates to a method for concentrating an aqueous ammonium carbamate stream, which has been formed in a process for the preparation of urea, has a pressure between 0.20 MPa and 0.9 MPa, a temperature between 35° C. and 95° C., and contains at least 25 wt. % H2O, comprising: a pressure increase step, in which the aqueous ammonium carbamate stream is increased in pressure to a pressure between 1.0 MPa and 7 MPa; a condensation step, in which the aqueous ammonium carbamate stream is contacted with a gas stream, which has been formed in a process for the preparation of melamine and which consists essentially of NH3, CO2 and optionally H2O and has a lower H2O content than the aqueous ammonium carbamate stream, the gas stream being absorbed in the aqueous ammonium carbamate stream in such a way that a concentrated ammonium carbamate stream is formed that contains between 15 and 35 wt. % H2O; a discharge step, in which the concentrated ammonium carbamate stream is separated and discharged.