Analysis of urea pyrolysis in 132.5-190 °C

Urea pyrolysis in the temperature range from 132.5 to 190 degrees C was studied in a self-designed fixed-bed experimental system, and the products in solid and gaseous phases were systematically analysed by a liquid chromatography-mass spectrometer (LC-MS) and an online mass spectrometer (MS), respectively. Experimental results showed that in 132.5-160 degrees C, urea was only involved in consumption reactions. The formation reactions of biuret and cyanuric acid (CYA) rather than the decomposition reaction of urea occupied the main part of urea consumption. Above 160 degrees C, the dominant reaction of CYA turned from formation to decomposition, while the conversion temperature point of biuret was 170 degrees C. The (N)H3 production fluctuated in 132.5-170 degrees C but kept rising in 170-190 degrees C. The decomposition reaction of biuret above 170 degrees C accounted for the sustained rising. The HNCO production decreased from 132.5 to 160 degrees C but increased from 160 to 190 degrees C. The decomposition of CYA in 160-190 degrees C was responsible for the decrease. The detailed analysis data and related discussion of urea pyrolysis pathways in 132.5-190 degrees C contributed to the efficient utilization of urea in low-temperature urea-SCR process.