Urea prodn. from ammonia and carbon dioxide - with purifcn. of carbon dioxide to remove hydrogen

摘要

In the prodn. of urea from NH3 and CO2, the gaseous CO2 is pretreated to remove H2 by reaction with O2 or air in the presence of a Pd catalyst, and the resulting H2O is sepd. Removal of H2 eliminates the risk of explosive gas mixts. being formed, esp. in urea synthesis installations employing high-press. scrubbers. Typically the compressed CO2 feed is cooled from 150 degrees C to ambient temp. and passed to a centrifugal separator to remove H2O and oils. The gas is then heated by heat exchange with steam or the off-gas from the oxidn. reactor, and passed through 2 parallel-connected oil absorbers, e.g. packed with Al2O3, SiO2 or active C. The gas is then fed into the oxidn. reactor contg. a bed of Pd catalyst. The O2 or air needed for oxidn. is added to the gas before it is heated. The purified gas is passed through a cooler and a separator to remove H2O.