METHOD OF PREPARING CARBAMIDE Russian patent published in 1997 - IPC

FIELD: organic chemistry. SUBSTANCE: carbamide is prepared from carbon dioxide in two synthesis zones in which NH₃:CO₂ molar ratio and pressure are maintained at 2.8-4.5 and 14-19 in first zone and 2.8-3.0 and 14 in second zone, respectively. "Fresh" ammonia and carbon dioxide as well as gas phase containing ammonia and carbon dioxide from first synthesis zone are fed into first synthesis zone, and "fresh" ammonia, carbon dioxide and aqueous ammonium carbonate solution formed by absorption of ammonium and carbon dioxide removed from carbamide melt in both synthesis zones are fed into second zone. Carbamide synthesis melt from second zone is divided into two flows one of which (larger) is treated at two pressure stages. Ammonium carbamate is decomposed and unconverted reagents are removed in first pressure stage with heat supplied at pressure maintained in second synthesis stage in gaseous carbon dioxide current. Second (smaller) flow of carbamide melt from second synthesis zone is treated together with carbamide melt from first synthesis zone. In this case ammonium carbamate is decomposed and unconverter reagents from mixture of melts are removed in first stage at pressure maintained in second synthesis zone in gaseous ammonia being removed, and gaseous flow of the removed reagents is transferred into second synthesis zone. Ammonium carbamate is decomposed and reagents from mixture of melts from both synthesis zones in second stage with heat supplied at pressure of 1.6-2.2 Mpa. In this case, removal is carried out in current of gases from first synthesis zone reactor. All flows of carbamide melt from both synthesis zones are finally treated in the last stage with heat supplied at pressure of not higher than 0.4 Mpa. Gas and water flows containing unconverted reagents removed from carbamide melts from the both synthesis zones are also directed to second synthesis zone. EFFECT: more efficient preparation method. 2 cl, 2 dwg, 3 tbl