Amine degradation in CO2 capture. I. A review

Post-combustion CO2 capture based on CO2 absorption by aqueous amine solutions is the most mature gas separation technology. A main problem is amine degradation due to heat, CO2, O2, NOx and SOx. This review proposes to make a critical survey of literature concerning degradation, to list degradation products and to discuss mechanisms proposed by authors. Benchmark molecule is monoethanolamine (MEA) but diethanolamine (DEA), N-methyldiethanolamine (MDEA), piperazine (PZ) and 2-amino-2-methylpropan-1-ol (AMP) are also studied. Uses of other amines and amine blends are also considered. In the case of MEA, ammonia, N-(2-hydroxyethyl)-piperazin-3-one (HEPO) and N-(2-hydroxyethyl)-2-(2-hydroxyethylamino) acetamide (HEHEAA) are the main identified degradation products in pilot plants. Among lab studies, the most cited degradation products are ammonia, carboxylic acids, N-(2-hydroxyethyl)-formamide (HEF), N-(2-hydroxyethyl)-acetamide (HEA) and N-(2-hydroxyethyl)-imidazole (HEI) for oxidative degradation, and oxazolidin-2-one (OZD), N-(2-hydroxyethyl)-ethylenediamine (HEEDA) and N-(2-hydroxyethyl)-imidazolidin-2-one (HEIA) for thermal degradation. Numerous degradation products have been identified but some are still unknown. A lot of degradation mechanisms have been proposed but some are missing or need proofs. SOx and NOx effects are still few examined and much work remains to be done concerning volatile degradation products potentially emitted to atmosphere: their identification and their formation mechanisms need further investigations.