Abstract
SINTEF Materials and Chemistry has recently designed an advanced laboratory test rig for studies of solvent degradation. This solvent degradation test rig (SDR) emulates the process conditions observed in an absorber/stripper configuration designed for CO2 capture. Aqueous solvent is degraded by cycling in a combined absorber and stripper setup with realistic temperatures and CO2 loadings of the solvent in addition to a defined synthetic flue gas mixture. A 14 week test campaign with degradation of 30 wt.% 2-ethanolamine (MEA) was performed in the rig. Comparison between group methodology and specific nitrosamine analysis of the solvent showed that 42% of the nitrosamines were unidentified species. This indicates that many of the MEA degradation products are likely precursors for nitrosamine formation. Two nitrosamines were identified in the solvent; nitrosodiethanolamine (NDELA) and the nitrosamine of the degradation product N-(2-hydroxyethyl)-glycine (HEGly): nitroso-(2-hydroxyethyl)-glycine (NHEGly). 56% of the total nitrosamine was identified as NHEGly, while 2% was NDELA. Nitrosodimethylamine (NDMA) was detected in the absorber gas emission, but was below the quantification limit in the solvent. Results indicate that the degradation of nitrosamines and nitramine in the solvent is highly temperature dependent, and that the levels of total nitrosamines and MEA-nitramine are significantly reduced by elevated stripper temperature. The results show that the SDR results give a realistic picture on the solvent degradation to be expected in a real CO2 capture plant; degradation products formed in the SDR MEA solvent reflects those previously found in pilot plant studies. This demonstrates how the SDR enables bench-scale studies of solvent process degradation previously only available from pilot plant studies. SDR results should provide valuable input to health and environmental risk evaluations for different solvent systems for CO2 capture.
