Mass loss and evolved gas analysis in thermal decomposition of solid urea

The effect of different oxygen concentration and heating rates on the mass loss and the formation of gaseous products (NH3, N2O and CO) during the thermolysis process of solid urea was studied and discussed by experiments, and the production mechanism of N2O and CO was also explored and proposed. Experimental results show that there were four major stages of mass loss in each TGA curve and two sharp endothermic peaks in each DSC curve, and the peaks reflected urea melting and its decomposition. Little NH3 was found in the exhaust gas at temperatures prior to 140 °C, confirming that little urea decomposed before the melting point, but above that the NH3 production dramatically increased. The presence of O2 lowered the highest NH3 yield, possibly resulting from the oxidation of partial generated NH3. At the same experimental condition, the N2O production was approximately twice the CO production, but O2 accelerated the formation of both of them, and more O2 promoted more formation. The higher heating rate resulted in the less reaction time for urea thermolysis. Therefore, it not only led to the thermolysis process moving to the high temperature zone, but also brought about higher gaseous products concentration.