Thermolysis of Morpholine in Water and Superheated Steam

Amines show great potential for protecting steam-water cycles against corrosion, but their thermal stability is limited and acidic decomposition products are a concern due to increased corrosion risk. In this study, morpholine (hydro)thermolysis is simulated at boiler (352 degrees C, 17.5 MPa) and superheater (490 degrees C, 17.5 MPa) conditions with an experimental stainless steel flow reactor. Thermolysis under superheater conditions was more rapid than hydrothermolysis under boiler conditions. Organic acid anion decomposition products increased linearly over time, while the thermal decomposition of morpholine followed first order kinetics. Further experiments under superheater conditions were performed at 470, 490 and 510 degrees C, with pressures of 9.5, 13.5, and 17.5 MPa. With the kinetic rate constants for morpholine thermolysis in dry steam derived empirically, the activation energy of the decomposition reaction was 160.0 (+/- 2.0) kJ/mol, the pre-exponential factor was e(21.7 (+/- 0.66)) s(-1), and the activation volume was 896 (+/- 36) cm(3)/mol. This led to a model capable of predicting the observed pressure and temperature dependent thermolysis of morpholine under the investigated conditions. Care must be taken when using the model results to calculate morpholine stability in the SWC, because wall effects during (hydro)thermolysis require further investigation.