A New Equilibrium Model for the Bazarov Urea Synthesis Process

Abstract

A new equilibrium model for the high temperature and pressure Bazarov urea synthesis process is presented. By including the formation of ammonium hydroxide as an important equilibrium in the process the model can quantitatively predict the yield of urea under the following range of synthesis conditions: NH₃/C0₂ ratios (L) greater than 2, when no excess water is added, in the temperature range 170-210ºC. The model also predicts the observed maximum in urea yield with temperature for a given L> 2. New experimental data for L> 9 are presented that confirm the model's prediction that the yield of urea asymptotically approaches 100% at high L ratios. These data also reveal a pressure dependence for the urea yields which becomes more pronounced with increasing temperature and L ratio. In this region the agreement between theory and experiment is generally within 3% in the pressure range 30-50 MPa.

Enthalpies of reaction for the formation of urea from ammonium carbamate and for the formation of ammonium hydroxide under urea synthesis conditions have been derived, and are 26 and -40 kJ mol^-1 respectively, the former being in good agreement with a value estimated from literature data.