Patent ID: 7893298

Claim:
Method for concentrating an aqueous ammonium carbamate stream, which has been formed in a process for the preparation of urea, comprising: (a) providing an aqueous ammonium carbamate feed stream that has been formed in a CO 2 process for the preparation of urea and 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. % H 2 O; (b) increasing pressure of the aqueous ammonium carbamate feed stream to a pressure between 1.0 MPa and 7 MPa and thereby form an aqueous carbamate stream of increased pressure; (c) subjecting the aqueous carbamate stream of increased pressure to a condensation step by contacting the aqueous ammonium carbamate stream of increased pressure with a gas stream, wherein the gas stream has been formed in a process for the preparation of melamine and consists essentially of NH 3 , CO 2 and optionally H 2 O and has a lower H 2 O content than the aqueous ammonium carbamate stream of increased pressure, to cause the gas stream to be absorbed in the aqueous ammonium carbamate stream of increased pressure in such a way that a concentrated ammonium carbamate stream is formed that contains between 15 and 35 wt. % H 2 O; and (d) separating and discharging the concentrated ammonium carbamate stream.