METHOD FOR THE PREPARATION OF UREA

摘要

The invention relates to a method for the preparation of urea in a reactor using ammonia and carbon dioxide as starting materials, which method comprises a) bringing the ammonia and carbon dioxide into contact in the reactor under conditions for the formation of carbamate; and b) decomposing the carbamate thus formed to give urea and water, characterised in that the water formed during step b) is removed from the reaction mixture by the use of a water-selective membrane. The water-selective membrane is preferably a pervaporation membrane, such as a porous ceramic membrane. Furthermore, a pressure difference is preferably maintained or applied over the selective membrane. The method can in particular be carried out in a liquid circulating stream which, in addition to the reactants fed to the circulating stream and the carbamate formed in step a), also contains at least some of the water formed in step b) and also the urea formed in step b), the urea being recovered from the circulating stream and the circulating stream being recycled to the reactor.