(530g) Heterogeneous Catalyst Stability during Hydrodenitrogenation in Supercritical Water
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Heterogeneous Catalysis in Liquid Media II
Wednesday, November 13, 2019 - 2:42pm to 3:00pm
We constructed oxygen fugacity-pH diagrams to identify a library of catalytic materials that are thermodynamically stable during HDN of propylamine in SCW at 380-500 oC and 22-38 MPa. Among the materials assessed with the model, Pt/TiO2 was chosen for further study as both Pt and TiO2 are predicted to resist dissolution and changes in oxidation state in the reaction environment. Flow experiments with aqueous feeds of formic acid, ammonia, and propylamine were designed to isolate interactions between the catalyst, the SCW solution, and the reactants and products. When formic acid is in the feed, H2 forms in-situ and Pt/TiO2 is active for HDN of propylamine. Without formic acid, propylamine undergoes hydrolysis to propanol. The catalyst does not exhibit any evidence of oxidation or dissolution during the flow experiments. However, when formic acid is present, corrosion of the stainless-steel reactor tubing occurs prior to the catalyst bed and Fe deposits onto the catalyst. Oxygen fugacity-pH diagrams of Fe predict formation of Fe cations in the presence of concentrated formic acid solutions at temperatures below the critical temperature of water (374 oC), but these cations are much less soluble at higher temperatures. This thermodynamic analysis provides a key insight into the upstream reactor corrosion and subsequent Fe precipitation onto the catalyst. Overall, the experimentally observed hydrothermal stabilities of the catalyst and reactor materials agree with the stabilities predicted by the oxygen fugacity-pH diagrams. The results and methodology applied in this work can be used to improve the design of catalysts and reactor materials for future hydrothermal HDN reactions.
References
- M. Yeh, J.G. Dickinson, A. Franck, S. Linic, L.T. Thompson, P.E. Savage, Technol. Biotechnol. 88 (2013) 12-24.
- Xiong, H.N. Pham, A.K. Datye, Green Chem., 16 (2014) 4627-4643.
- Kritzer, J. Supercrit. Fluids 29 (2004) 1â29.