Use of laser Raman spectrometry for a quantitative study of the urea synthesis under process conditions. Part II. Measurements under urea synthesis conditions

Abstract

Laser Raman spectrometry has been applied to the in situ quantitative determination of urea and ammonium carbamate concentrations under urea synthesis conditions (120–210 °C, 5–35 MPa, NH₃:CO₂= 5 and H₂O:CO₂= 0). Good agreement was found between urea conversion values measured and those calculated using a recently published expression. To achieve these results, suitable signal processing procedures were developed, potassium nitrate was used as an internal standard and a cell from synthetic sapphire, suitable for high-pressure measurements, was employed. Calibration in a high-pressure cell fabricated from sapphire, which exhibits birefringence, can be achieved through the use of glass capillary tube cells suitable for lower pressures.