Abstract: A process for the preparation of urea from ammonia and carbon dioxide at an elevated temperature and pressure having a reaction zone and a stripping zone. In the reaction zone, carbon dioxide and a portion of the ammonia are converted to ammonium carbamate, and a portion of the ammonium carbamate is converted to urea, the combined conversions resulting in a net formation of heat. In the stripping zone, a urea product stream containing unconverted ammonium carbamate is heated by heat exchange with the reaction zone to decompose a portion of the ammonium carbamate. In the reaction zone, the conversion of ammonium carbamate into urea is continued until the quantity of urea formed is at least 50 percent of that quantity of urea that would be obtained at equilibrium under the reaction conditions present in the reaction zone.

Abstract: An improved process for the preparation of urea from carbon dioxide and excess ammonia at elevated temperature and pressure. The urea solution from the urea synthesis zone is heated and stripped at an elevated pressure to decompose a portion of the ammonium carbamate contained therein and the ammonium and carbon dioxide containing off-gas produced is condensed in a first condensation zone. The stripped urea solution is heated at a reduced pressure in a decomposition zone to decompose a further portion of ammonium carbamate, and the ammonia and carbon dioxide containing off-gas thereby produced is condensed in a second condensation zone to form an aqueous ammonium carbamate solution.

Abstract: An improved process for the removal of urea, ammonia, and carbon dioxide from dilute aqueous solutions thereof by hydrolyzing the urea, and thereafter desorbing ammonia and carbon dioxide. The dilute solution containing urea is passed into the top portion of a reaction column and caused to flow downward and countercurrent to a heating and stripping gas while maintaining the reaction column at a pressure of between about 10 and 30 bar, and a top column temperature of between about 170.degree. and 220.degree. C. and a bottom column temperature of between about 180.degree. and 230.degree. C. The resulting liquid stream removed from the bottom of the reaction column, comprised of a substantially urea-free aqueous solution of ammonia and carbon dioxide, is introduced into a desorption zone wherein, at a pressure of between about 1 and 5 bar, ammonia and carbon dioxide are removed therefrom.

Abstract: An improved process for the removal of urea, ammonia, and carbon dioxide from process condensate derived from coupled urea and ammonia syntheses by hydrolysis of urea and desorption of ammonia and carbon dioxide. Process condensate poor with respect to ammonia is treated at a pressure of between about 15 and 42 bar and a temperature of between about 200.degree. C. and 320.degree. C. in a reaction column with steam to form a gas mixture containing ammonia, carbon dioxide, and water vapor, and an aqueous liquid virtually free of urea, ammonia, and carbon dioxide.

Abstract: Unreacted free ammonia and ammonium carbamate are removed from a urea synthesis solution efficiently by first heating the solution up to 205.degree.-250.degree. C and then, in a second, separate step, stripping the heated solution with a stripping gas but under adiabatic conditions to remove the unreacted materials. The process is applied as an integral part of a continuous urea preparation.