Verfahren zur Herstellung von Harnstoff

摘要

1,131,906. Synthesizing urea. SUMITOMO CHEMICAL CO. Ltd. 7 Feb., 1967 [15 Feb., 1966], No. 5875/67. Heading C2C. A method for synthesizing urea by reacting ammonia with carbon dioxide at elevated temperature and pressure comprises reducing the pressure of the reaction product from the urea synthesis step to 25-50 kg./cm.2g. in an ejector type pressure-lowering apparatus, heating the reaction product in a first stage decomposition step, separating a generated gas from the reaction product, heating the reaction product in a second stage decomposition step under a pressure of 5-15 kg./cm.2g, separating the generated gas from the reaction product, heating the reaction product in a third stage decomposition step under a pressure of atmospheric to 3 kg./cm.2g. and further separating the generated gas, while absorbing the separated gas obtained from the first stage decomposition step under the pressure of said step in an aqueous solution obtained by absorbing in an aqueous absorption liquid the separated gas obtained from the third stage decomposition step, utilizing the absorption heat generated in said absorption of the separated gas obtained from the first stage decomposition step as a heat source for the second and third stage decomposition steps, introducing the gas-liquid mixture formed in said absorption into a medium pressure absorption step to subject the mixture to absorption treatment, reusing the resulting aqueous ammonium carbamate solution for urea synthesis, and returning the gas separated through the second stage decomposition step to the ejector type pressure-lowering apparatus. The reaction product, after separation from the gas generated under a pressure of 25-50 kg./cm.2g. in the first stage decomposition step may be further reduced in pressure to 15-25 kg./cm.2g., a gas generated is separated and introduced into the medium pressure absorption step and the reaction product is then further introduced into the step subsequent to the first stage decomposition step. The aqueous absorption liquid employed to absorb the gas separated from the third stage decomposition step may be water or an aqueous urea solution. A suitable form of apparatus is described for effecting the process.