https://doi.org/10.1021/acs.iecr.2c02344
“Certain degradation compounds need to be monitored, either from an emission or a health perspective, or both, and many of these compounds are formed in tiny amounts. Until more research on the potential effects of specific components is done, their presence, even in very concentrations, requires monitoring. An example here is nitrosamines, a group of generally carcinogenic compounds. (121) However, few studies are available for the nitrosamines that are typically formed in the CO2 capture process. For some, there are indications of them being less carcinogenic than, for example, N-methyl-N-nitroso-methanamine (NDMA); which is a nitrosamine that is found in some processed foods. If the specific toxicity or carcinogenicity of the identified nitrosamines is not tested, a generalization is made by putting them in the same class as nitrosamines that already have been tested, such as NDMA. The formation of nitrosamines depends on the molecular structure of the amine, and all aqueous amine solutions in a CO2 capture process will result in some nitrosamine formation. Stable nitrosamines are formed from secondary amines. Nevertheless, to some extent, nitrosamines are formed from all aqueous amine solvent systems. This is because the primary or tertiary amines are observed to form secondary amines, and these degradation compounds can, in turn, form nitrosamines, meaning that the nitrosamine formation in primary and tertiary amines typically is much lower than in secondary amines. Many solvent-specific nitrosamines formed are nonvolatile compounds and will, therefore, primarily be contained in the solvent. For several of the smaller nitrosamines (often not solvent specific), which have been of interest to other applications than CO2 capture, (standardized) analytical methods are available. These are often referred to as the EPA mix (water analysis EPA 521 (122)), and include nitrosamines such as NDMA, N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA), N-nitrosopyrrolidine (NPYR), and N-nitrosopiperidine (NPIP). A group methodology for analyzing nitrosamines exists. However, in a round-robin test conducted in the OCTAVIUS project, this method did not give reliable quantification of the nitrosamine content in the range of 0.1–1.2 mg N-NO/kg sample. (123) The same work shows that the laboratories were able to give reliable results for nitrosamine in the sulfamic matrix. Further, only a few laboratories could analyze low levels of nitrosamines in the solvent matrix and the whole specter of nitrosamines requested in that work. In carbon capture and storage (CCS) research, many studies related to nitrosamines have been conducted, and these studies give information about the formation and decomposition in the process. They have highlighted factors contributing to the formation and mapped nitrosamines in many open solvents. (124) Work has also been done looking into the mitigation technologies based on adjusting the process conditions (temperature in the desorber), inhibitor use, and nitrosamine destruction (e.g., catalytic hydrogenation or with ultraviolet (UV) light). (125) Many of the mitigation methods will be challenging to use in industrial scale. For example, the effect of UV-light is reduced significantly in solvent with discoloration. Formation of nitrosamines in nonaqueous or water-lean solvents that include an amine has not been adequately investigated.