Urea synthesis from carbon dioxide and ammonia - recovers urea from vapours of urea concentration stage to avoid pollution

摘要

Urea prepn. from CO2 and NH3 under pressure is by passing the prod. through several NH4 carbamate decompsn stages with gradual reduction of pressure to decompose and separate unreacted NH4 carbamate, them contg. the urea soln., pref. at 60-200 mm Hg pressure. The exit vapours from the concn. stage contg. water, entrained urea, NH3 and CO2 are sepd. to form a 1st condensate of urea, CO2 and NH3, and a 2nd condensate contg. the rest of the CO2 and NH3. The 2nd condensate is distilled to recover CO2 and NH3 gas and water. A pre-condensation may pref. be carried out before the 1st condensation stage by indirect cooling. The 2nd condensation is pref. carried out in two stages. The 1st condensate is pref. used as a water wash in the urea process, partic. for the exit dust from the urea pastille formation stage, which is thereafter passed through a resinous filter. Loss of urea and water pollution are avoided.