Kinetics and pathways for nitrosamine formation in amino acid-based carbon dioxide capture systems

Amino acids are emerging as alternative solvents for absorption-based CO₂ capture, but their potential to form the harmful byproducts nitrosamines is not well understood. This study investigated the formation of nitrosamines from model amino acids sarcosine, proline, and taurine under desorber- and absorber-relevant conditions. Special attention was paid to the effects of base and the formation of volatile nitrosamines. Under simulated desorber conditions, all three amino acid solvents with organic base monoethanolamine (MEA) formed more total nitrosamines than those with inorganic base sodium hydroxide (NaOH). Increasing base concentration decreased the formation of N-nitrososarcosine (NSAR) in both NaOH- and MEA-based sarcosine solvents. By measuring NSAR formation under varying base concentration and CO₂ loading, it was shown that both sarcosine carbamic acid (SARCOOH) and deprotonated sarcosine (SAR⁻) contributed to NSAR formation. Volatile nitrosamine N-nitrosodimethylamine (NDMA) was detected in sarcosine solvents at levels three orders of magnitude lower than NSAR. Kinetic modeling showed that 61%–110% of the accumulated NDMA was formed through NSAR decomposition. NDMA formation from NSAR was promoted by increasing MEA concentration, but suppressed by increasing NaOH concentration. Under simulated absorber conditions, NaOH- and MEA-based solvents formed total nitrosamines at similar rates for sarcosine, proline, and taurine. In sarcosine solvents, NDMA formed at levels three orders of magnitude lower than NSAR, similar to that under desorber conditions.