GB1217560A - Synthesis of urea - Google Patents

Abstract

1,217,560. Synthesis of urea. MITSUI TOATSU CHEMICALS Inc. 10 July, 1968 [31 July, 1967], No. 33002/68. Heading C2C. A process for the synthesis of urea in two stages comprises reacting ammonia with carbon dioxide at a first urea-forming temperature and pressure in a first urea-synthesis zone to form a first urea-synthesis effluent, expanding said first urea-synthesis effluent to a pressure lower than the said first urea-forming pressure, separating the unreacted ammonium carbamate contained in the said expanded first urea-synthesis effluent as a gaseous mixture of ammonia and carbon dioxide in a distillation column, maintaining the said gaseous mixture at a second urea-forming temperature and pressure in a second ureasynthesis zone to form a second urea-synthesis effluent, separating the unreacted carbamate contained in the said second urea-synthesis effluent as a second gaseous mixture of ammonia and carbon dioxide, and obtaining urea from the said first and second urea-synthesis effluents having the unreacted ammonium carbamate separated, which includes absorbing the said gaseous mixture separated from the said first urea-synthesis effluent in water, an aqueous ammonia solution or an aqueous solution containing ammonia and carbon dioxide in an absorption zone to form an absorbate, subjecting the said absorbate to a distillation at the said second urea-forming pressure in a distillation zone to separate ammonia and carbon dioxide contained therein as a gaseous mixture, and maintaining the said gaseous mixture separated from the said absorbate at the said second urea-forming temperature to form the said second urea-synthesis effluent. Unreacted ammonium carbamate contained in the said second urea-synthesis effluent and separated as a gaseous mixture of ammonia and carbon dioxide may be absorbed in the said aqueous absorbent together with the said gaseous mixture obtained from the first urea-synthesis effluent, and the absorbent, after having the ammonia and carbon dioxide removed therefrom may be recirculated to said absorption zone.