The most common method of carbon dioxide capture is the use of monoethanolamine – a colorless liquid with a slight ammonia odor, which absorbs CO2 well, but releases it back when heated. This method has some disadvantages: equipment under the impact of such reactions is subject to corrosion, and recover and reuse of the solvent requires a lot of thermal energy.
An alternative is euthetic solvents – non-toxic and unstable mixtures of two or more components with a hydrogen bond between them. One of these components is often choline chloride which is a biocompatible and biodegradable salt, while we can change the other components for “tuning” the physical and chemical properties of the mixture.
The scientists of the Institute of Solution Chemistry of the Russian Academy of Sciences tried to determine how effectively a mixture of choline chloride with amines and amides (nitrogen-containing organic compounds) can capture carbon dioxide. For this, the authors mixed choline chloride, amines or amides, and then heated the resulting mixture and stirred it at 70°C. They placed the prepared solutions one at a time into an experimental cell where carbon dioxide was fed in portions. By the way the mass of the eutectic mixtures changed, the authors determined how much CO2 each of them absorbed.
The experiments showed that mixtures containing amines were 50 times better at capturing carbon dioxide than solvents with amides. The reason was that choline and amine-based solvents interact chemically with CO2 to form stable intermediates. In contrast, solvents with amides only physically dissolve carbon dioxide. In this case, no new compounds are formed, and only weak van der Waals interactions are formed between the solvent and the gas.
“The efficiency of the mixture a choline chloride with one of the amines is comparable to aqueous solutions of amines, but is more environmentally friendly and requires less energy expenditure for absorber regeneration. In the future, we plan to continue searching for even more efficient mixtures for carbon dioxide capture from emission sources,” the Russian Science Foundation quotes Arkady Kolker, Ph.D. in Chemical Sciences.