Effects of Temperature and Pressure on the Thermolysis of Morpholine, Ethanolamine, Cyclohexylamine, Dimethylamine, and 3-Methoxypropylamine in Superheated Steam

Alkalizing amines such as cyclohexylamine and dimethylamine have great potential for protecting steamwater cycles against corrosion, but their thermal stability is limited and anionic decomposition products are a concern because of increased corrosion risk. In this study, morpholine, ethanolamine, cyclohexylamine, dimethylamine, and 3-methoxypropylamine were exposed to temperatures of 500, 530, and 560 degrees C at pressures of 9.5, 13.5, and 17.5 MPa to investigate the effects of temperature and pressure on amine thermolysis kinetics. The surface/volume ratio of the reactor tube was 0.4 mm(-1), close to the value for superheater tubes in steamwater cycles. All amines thermolyzed by first-order kinetics, with the exception of dimethylamine. The Arrhenius constants E-a, ln(A), and Va were obtained from the experimental data for all investigated amines. The effect of pressure on the thermolysis kinetics was less pronounced than in previous studies and was different for each amine. Dimethylamine did not degrade below 20% and 10% at 500 and 530 degrees C, respectively, despite the application of longer retention times, suggesting the synthesis might occur. Limited practical data showed some promise for the applicability of the model to steamwater cycles. More plant data are needed to fully validate the model. In all cases, thermolysis of the amines led to the formation of between 150 and 600 ppb organic acid anions. In most cases, the concentrations increased linearly with increasing degradation percentage. Acetate and formate were found to be major degradation products, with some propionate and traces of glycolate. Cationic degradation products were ammonia and some amines, meaning that the complete thermolysis of an amine does not necessarily lead to acidic conditions