Vapor–Liquid Equilibrium of Aqueous Urea Solution from Dynamic Vapor Sorption Measurements at 283.15–343.15 K

Abstract

Urea solution as a biopolymer denaturing agent and source of nitrogen fertilizer has a key role in some industries, and it seems necessary to study the phase behavior of this system. This work aims to investigate the vapor–liquid equilibria (VLE) of aqueous urea solutions over a wide range of concentrations and temperatures. For this purpose, water activity measurements were performed for the aqueous urea solution using the dynamic vapor sorption (DVS) technique at 283.15–343.15 K in the various urea concentrations. The results showed good agreement between obtained data using DVS and the isopiestic technique at 298.15 K. The conductivity value of the urea solution at 298.15 K revealed that this system is a very weak electrolyte solution. Thereby, a combination of Pitzer’s extension of the Debye–Huckel function (PDH) to cover the ion interaction and some local composition models including Wilson, nonrandom two-liquid (NRTL), nonrandom factor (NRF), modified Wilson-NRF, and NRTL-NRF to point to physical interaction was considered to correlate the experimental activity data. It was revealed that increasing the temperature led to increasing the accuracy of NRTL-NRF and NRF models and other models can correlate the experimental data at any temperature in this range well.