History of Urea Process

In the beginning of the twentieth century, urea was produced on an industrial scale by hydration of cyanamide, which can be obtained from calcium cyanamide [13]. After the development of the Haber-Bosch process (see Section 3.2.2), the synthesis from ammonia and carbon dioxide became more attractive [13]. The industrial process based on these reactants has been developed in 1922 and is called Bosch-Meiser urea process after its discoverers [17], which represents the basis for all industrial scale processes nowadays [13]. 

The limited carbon dioxide conversion and the huge amounts of the by-product ammonia salt represent major disadvantages with respect to production of pure urea. Thus, once-through urea synthesis processes do not have any significant industrial relevance nowadays. Modified processes have been developed, which allow recycling of the nonconverted reactants, thus increasing overall conversion and yield. 

However, the handling of the very corrosive ammonium carbamate represents a major challenge [16]. In addition, the aqueous recycle increases the water concentration in the synthesis part, thus impeding the urea formation (see Section 3.3.1). For this reason, the total recycle process is often operated at high molar NH3 CO2 ratio up-to 4—5 to increase carbon dioxide conversion and minimize the aqueous recycle [13]. 

State-of-the-art urea plants based on the stripping technology are designed up to 3850 ton of urea per day. The daily feedstock requirements of such a plant are 2200 ton of ammonia and 2800 ton of carbon dioxide. 

An overview of some commercially used processes with related synthesis conditions is given in Table 3.1. The listed NH3/CO2 ratios refer to the stream composition at reactor inlet 

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