This invention relates to urea and to a method for preparing urea from ammonia and carbon dioxide or their immediate products of reaction. In all of the applications, so far tried, of said method for the preparation of urea, the procedure has been more or less as follows : In an autoclave under pressure carbamate of ammonium or carbon dioxide and ammonia in the required proportions are heated, with or without additions of catalyst, to a temperature above 130° C, the final product being removed from the autoclave after the transformation and the urea separated. Continuous operation has also been suggested by gradually introducing into the autoclave at operating pressure, carbon dioxide and ammonia in quantities equivalent to the urea continuously removed from the apparatus. The cost of this latter operation is obviously high, both as regards cost of installation and power required for heating and compression.
I nave now found that the expense of supplying the necessary, thermic energy may be dispensed with entirely, while the costs of both power for compression and of installation can be considerably reduced by grafting the production of urea on to the production of synthetic ammonia, that is to say by inserting an apparatus for making urea in an installation (preferably a closed circuit one) for the synthesis of ammonia.
For example in an apparatus for the production of synthetic ammonia such as is described in U. S. Patents No. 1,478,549 and No. 1,478,550 the gaseous mixture leaving the catalytic tube contains a high percentage of ammonia at a temperature of about 250° C. and under a .pressure of about 800 at. If compressed carbon dioxide is now introduced into this gaseous mixture at the aforesaid pressure, urea is rapidly obtained.

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1928 Casale 1670341 Urea Process combined NH3 – urea.pdf