GB1124868A - Preparation of urea - Google Patents

Abstract

Urea is extracted from the synthesis mixture obtained in the synthesis of urea from ammonia and carbon dioxide in a synthesis reaction vessel at elevated temperature and pressure by expelling the products contained therein which have not been converted into urea at a pressure of 100-300 atmospheres with a gas mixture which, before the expulsion commences, consists in larger part by volume of carrier gases which are inert as regards the urea synthesis and in smaller part by volume of ammonia or carbon dioxide. The expulsion process may be carried out either in a separate apparatus to which the synthesis mixture is fed from the reaction vessel or in the reaction vessel itself, suitable inert gases being nitrogen, hydrogen and mixtures thereof. The inert carrier gas may be circulated, in which case unconverted reaction constituents may be partially stripped off in an after-connected absorber condenser with approximately total absorption of one of the reaction constituents, while part of the other reaction constituent is recirculated again with the carrier gas to the expulsion apparatus. The present process may be operated in conjunction with an ammonia synthesis process wherein, for example, the gas mixture obtained in the ammonia synthesis may be withdrawn before or after partial separation of the ammonia and may then be returned to the ammonia synthesis as a charging gas after passing through the expulsion and stripping apparatus of the present urea extraction. Suitable forms of apparatus are described for both batchwise and continuous operation of the process of the present invention.