Degradation of 2-Amino-2-methylpropanol and Piperazine at CO₂ Capture-Relevant Conditions

The degradation pathways of the nonproprietary solvent blend CESAR1, consisting of 3.0 M 2-amino-2-methylpropanol (AMP) and 1.5 M piperazine (PZ), were studied under oxidative and thermal stress separately. Liquid chromatography coupled with mass spectrometry, using analytical standards of known and suggested degradation compounds, allowed for the identification and quantification of known, proposed, and new degradation products in the solvent. A total of 48 different degradation compounds were quantified in the degraded solvent samples. AMP is highly resistant to oxidative stress compared to PZ, and the single amines degrade more slowly alone than together in the CESAR1 blend, which degrades more than twice as fast as PZ. The main products found in the solvent after oxidative CESAR1 degradation were formic acid, 1-piperazinecarboxaldehyde, ethylenediamine, <i>N</i>-(2-hydroxy-1,1-dimethylethyl)-glycine, formaldehyde, and piperazinone, while the products of thermal degradation were 4,4-dimethyl-2-oxazolidinone, α,α-dimethyl-1-piperazineethanamine, ammonia, 2-[(2-amino-2-methylpropyl)-amino]-2-methyl-1-propanol, 3,4,4-trimethyl-2-oxazolidinone, and acetone. PZ is more resilient under thermal stress than AMP and CESAR1. Fifteen of the compounds included in this study have not previously been quantified in AMP, PZ, or CESAR1. It was found that nitrosamines and nitramines form readily in CESAR1 under oxidizing conditions, even in the absence of nitrogen oxides in the reaction gas, and that <i>N</i>-nitrosopiperazine is one of the ten most abundant degradation species in oxidized CESAR1. At nearly all tested conditions, the total nitrogen concentration of the solvent correlates well with the sum of specific nitrogen-containing compounds, meaning that the most abundant degradation compounds have been identified in this work. At 150 °C, some thermal CESAR1 degradation compounds remain unidentified.