Impact of flue gas contaminants on monoethanolamine thermal degradation

The buildup of flue gas contaminants in amine-based postcombustion CO ₂ capture processes is an important concern due to its potential impact on solvent degradation and reclaiming. In this research, in order to explore the impact of flue gas contaminants on solvent thermal degradation, sodium nitrite, fly ash, sodium sulfate, and sodium thiosulfate were each added into carbon-loaded 5.0 M monoethanolamine (MEA) solution and the solutions were exposed to high-temperature degradation conditions. MEA degrades significantly more in the presence of nitrite (5000 ppm) than MEA alone at the same amine mole concentration. The MEA degradation activation energy of MEA-nitrite solution is calculated and found to be approximately one-seventh of that of MEA solution without nitrite. Addition of nitrite not only enhanced generation of several MEA thermal degradation products but also induced formation of diethanolamine (DEA) and N-(2-hydroxyethyl)piperazin-3-one (HEPO), which have been known to form during MEA oxidative degradation. Interestingly, fly ash was observed to inhibit nitrite-induced MEA degradation and greatly increase the MEA degradation activation energy of MEA-nitrite solution. This led to a reduction in accumulation of several degradation products. Fly ash, sodium sulfate, and sodium thiosulfate by themselves were not shown to impact MEA thermal degradation rate.