FIELD: chemistry.
SUBSTANCE: method comprises the step of carbamating by preparing an N-substituted carbamate starting from an organic primary amine, urea and an organic hydroxy compound in accordance with a carbamation reaction and then recovering the first gaseous phase component comprising urea and/or a carbonyl group-derived urea derivative, an organic hydroxy compound and ammonia. Then the condensation step follows by condensing the first component of the gaseous mixture with a condenser. Thereafter, the isocyanate is obtained, where the N-substituted carbamate is pyrolysed. Next, the ammonia absorption step is carried out by water absorption of the second gaseous phase component discharged from the condenser in the form of a gaseous phase component containing ammonia as the main component and producing water with absorbed gas. The ammonia purification step is then carried out by heating the water with the absorbed gas to separate ammonia from the water with the absorbed gas, where the ammonia obtained in the ammonia purification step is further burned for heat recovery and the heat recovered in this way is used as the heat source in the carbification stage and/or in the isocyanate preparation step.
EFFECT: method allows to efficiently extract ammonia and use it for heat recovery used in the carbamide stage or in the isocyanate preparation stage.
7 cl, 22 dwg, 40 ex
