公开(公告)号：BR8603801A

公开(公告)日：1987-03-17

申请号：BR8603801

申请日：1986-08-08

Applicant: STAMICARBON

Inventor： MEESSEN JOZEF HUBERT ,  SPIKEMA RUDOLF

IPC: C07C67/00 ,  C07C239/00 ,  C07C273/04 ,  C07C126/02

Abstract: Process for the preparation of urea in which- a urea synthesis solution containing carbamate and free ammo­nia is formed in a high-pressure part in a synthesis zone at an NH₃/CO₂ molar ratio of up to 4 : 1, a temperature of at least 175 ◊C and the corresponding pressure,- a portion of the carbamate is decomposed in a first decom­position stage at synthesis pressure or lower pressure by a stripping treatment with carbon dioxide while heating is applied, and the gas mixture thus obtained is at least in part condensed and the condensate and the non-condensed por­tion of the gas mixture, if any, are returned to the synthe­sis zone,- in at least two further decomposition stages a further por­tion of the carbamate still present is decomposed and the gas mixture formed is separated, in the first of the further decomposition stages a pressure of 12-30 bar being maintained and heat being supplied,- and the remaining urea-containing solution is processed further by evaporation to a concentrated urea solution and, if desired, solid urea.The gas mixture, formed on expansion of the stripped urea synthesis solution to a pressure equal to or higher than the pressure in the first one of the further decomposition stages, is brought into direct contact in a contact zone with the solution remaining after further amounts of carbamate still present have herein been decomposed and the gases thus formed have been separated. The remaining gas mixture is thereafter discharged from the contract zone and is condensed. The con­densate is returned to the high-pressure part of the urea synthesis.