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Outlook of amine stability research

https://doi.org/10.1021/acs.iecr.2c02344

“There are several lessons that we would like to summarize in the nine following points:

(1)

Absorption of CO2 using chemical solvents is a chemical process where unwanted side reactions forming degradation compounds will occur. A more stable chemical solvent is the goal. Alternatively, clever use of degradation mitigation technology is needed.

(2)

For MEA, loss of 0.21–3.65 kg MEA per ton of CO2 captured has been observed for various MEA campaigns at different capture pilot plants. (5) The proprietary solvents in the market typically show lower amine loss. Anyhow, for the operation of the technology, information regarding which amines the solvent contains and which degradation compounds are present, and in which amount, should be made available for risk assessment. This will most likely be needed in many countries as input to emission permits.

(3)

There are no shortcuts to be taken. The chemical stability of new solvents has to be tested on a lab scale, preferably in cycled systems, to identify major compounds as input to emissions permits and health and risk assessments before large-scale piloting. This requires lab facilities and analytical instruments for identifying degradation compounds such as a combination of IC, LC–MS, and/or GC–MS. Degradation and corrosion are show-stoppers if mitigation technologies cannot be used. Batch experiments are easier to perform and can give an initial starting point for identifying degradation products and potentially eliminate really unsuitable amines and solvent blends before costly cycled system testing is performed.

(4)

Degradation compounds can be divided into different groups:

a.

more general components, like ammonia, smaller alkylamine, aldehydes, and smaller acids

b.

solvent-specific degradation compounds, including larger amines (e.g., diamine, methylated/alkylated amine, demethylated/alkylated amine etc.)

c.

cyclic structures (imidazole, piperazinone, oxazolidinone, imidazolidinone etc.)

d.

amino acids (some acids) and amide

e.

nitrosamines and nitramines

 

(5)

Some degradation compounds require monitoring both in the solvent and gaseous phase. At least nitrosamine, nitramine, aldehyde, ammonia, alkylamine, and potentially other volatile compounds should be monitored. It is also wise to keep an eye on the health of the solvent as input to the operation of the plant. Some generalized methods can easily be conducted on-site. I.e., amine titration and analyzing for heat stable salts are simple methods which would give feedback daily or weekly. Monitoring specific degradation compounds often requires both offline and off-site methods. The optimal combination of on-site and off-site analysis depends on the solvent and the specific industrial site.

(6)

Knowledge about the degradation and degradation mechanisms of MEA and other conventional amines and amine blends is essential for elucidating degradation compounds for new amines. However, it should be remembered that each solvent will have solvent-specific degradation compounds that should be known before large-scale piloting/demonstration. Thus, a good understanding of amine degradation and degradation mechanisms is needed to predict which compounds are formed.

(7)

For full-scale implementation, analyzing all compounds is not necessary from an operational or environmental perspective, but the focus should be kept on the compounds that require monitoring from operational or environmental/health perspectives.

(8)

Knowledge of degradation behavior will also help to operate the plant in a way that minimizes solvent degradation. This will also faciliate the selection of solvent specific management and degradation mitigation technologies.

(9)

All aqueous amine solvents form nitrosamines. The concentration of nitrosamines will depend on the amine structure, where a secondary amine structure is particularly inclined to form a high concentration. Primary and tertiary amines may form secondary amine degradation products and are, therefore, also prone to nitrosamine formation. The hazard classification of nitrosamine is based on the group of compounds, and specific toxicity information for the solvent-specific nitrosamine observed in amine solvents does not exist. However, some initial results show that some solvent-specific nitrosamines are less carcinogenic than NDMA. Thus, analyzing for solvent-specific nitrosamines can reduce the overall risks compared to assuming that all nitrosamines are equally hazardous.

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