Equilibrium of Urea Synthesis. II.

Abstract

In the preceding paper (This Bulletin, 45, 1339 (1972)) it was reported that the existence of the maximum equilibrium conversion was not due to the experimental method. For this phenomenon, we have presented the following interpretation. While NH4CO2NH2 is converted to urea and water, it dissociates into NH3 and CO2 in the solution (not in the gas phase), and the degree of the dissociation increases exponentially as the temperature becomes higher, while the conversion to urea gradually increases. Therefore, at a certain temperature, the equilibrium conversion reaches its maximum value. Although it is nearly impossible to prove analytically the dissociation of NH4CO2NH2 in the solution, we are sure of it from the following facts: 1) The dissociation of NH4-CO2NH2 is a great endothermic reaction, even under the conditions of urea synthesis. 2) The value of NH3/CO2which gives the minimum equilibrium pressure at a usual temperature is not always equal to 2.0, but varies with the temperature. 3) The effect of H2O/CO2 on the equilibrium pressure varies with the temperature; that is, when the temperature is lower than about 200°C, an increase in H2O/CO2 reduces the equilibrium pressure, but when the temperature is higher than 200°C, an increase in H2O/CO2 makes the equilibrium pressure higher.

Densities of urea–ammonia–water–carbon dioxide solutions in chemical equilibrium at and above urea synthesis conditions

“…in which dliq=density of the liquid phase in g/cm3, T=('C/lOo), log P=loglo P ( P in atm), and X=mol fraction NH3 (dimensionless); the constants are given in Table 1 version to urea in the liquid phase with increasing temperature. [14][15][16] This problem has been discussed from a thermodynamic viewpoint,l1. 17 and it has been argued that the maximum and the further decrease in the urea concentration in the liquid phase are related to critical phenomena.…”

Projeto Preliminar De Uma Unidade Produtora De Ureia a Partir De Técnicas De Simulação E Otimização De Processos

“…Pesquisadores como Inoue (1972) e Meesen (2012) assumem existir um equilíbrio líquido-vapor e que amônia e o dióxido de carbono reagem na fase líquida. Trata-se de um equilíbrio descrito como altamente complexo que envolve reações químicas, formação de azeótropos e estados supercríticos.…”

New internals for urea production reactors

“…In spite of the world importance of urea production, scant scientific attention appears to have been devoted to the understanding the behavior and optimization of the urea reactor. Some information on the system can be deduced for instance from Refs 5–9. As said before, it is a typical gas–liquid reactor involving not only back‐mixing phenomena, but also significant aspects of heat and mass transfer between the phases.…”