GB1219554A - Production of urea - Google Patents

Abstract

1,219,554. Ammonia synthesis. SUMITOMO CHEMICAL CO. Ltd. 17 Jan., 1969 [23 Jan., 1968], No. 2878/69. Heading C1A. [Also in Division C2] Urea and ammonia are produced by a process which comprises:- (1) reacting ammonia with carbon dioxide at a temperature of 160‹ to 230‹ C. at a pressure of 120 to 400 kg./cm.<SP>2</SP> to give an aqueous urea synthesis product solution containing urea, unreacted ammonia and unreacted carbon dioxide; (2) contacting the said product solution with an ammonia synthesis gas substantially free from carbon dioxide, the contacting being carried out at a pressure equal to or at most 50 kg./cm.<SP>2</SP> below the pressure used in step (1), to produce an aqueous solution substantially of urea and water and a gaseous mixture containing unreacted ammonia and unreacted carbon dioxide, steam and ammonia synthesis gas; (3) mixing the said gaseous mixture with a crude ammonia synthesis gas containing carbon dioxide; (4) contacting the gaseous mixture obtained in step (3) with an absorbing liquid which is selected from one or more of the following: water, an aqueous solution of ammonium carbamate, an aqueous solution of urea, an aqueous urea synthesis product solution and liquid ammonia, the contacting being carried out at a pressure equal to or at most 50 kg./cm.<SP>2</SP> below the pressure used in step (1), to produce an aqueous solution of ammonia and ammonium carbamate and an ammonia synthesis gas substantially free from carbon dioxide; (5) recycling the aqueous solution obtained in step (4) to step (1); (6) recycling part of the ammonia synthesis gas obtained in step (4) to step (2); and (7) using the remainder of the ammonia synthesis gas obtained in step (4) in the synthesis of ammonia.