期刊
ENVIRONMENTAL CHEMISTRY LETTERS
卷 12, 期 1, 页码 201-208出版社
SPRINGER HEIDELBERG
DOI: 10.1007/s10311-013-0435-1
关键词
Amino acid ionic liquid; CO2 capture; NMR; Single-crystal X-ray diffraction
资金
- Chevron
- National Science Foundation (NSF-CAREER grant) [CHE-0846680]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [0846680] Funding Source: National Science Foundation
The reversible capture of CO2 from fossil-fueled industries and the absorption of CO2 for natural-gas-sweetening purposes are industrial issues closely related to very important environmental, economical, and technological concerns. Biological amino acids can be used for task-specific ionic liquids for reversible CO2 capture. Several groups have reported efficient and reversible CO2 capture by such ionic liquids under rigorously dry conditions. However, we have observed that CO2 capture by amino acid ionic liquids is hugely impacted by the presence of water. In addition, the amino acid anions appear to play only a transitory role in the CO2 capture in the first minutes of exposure to a wet CO2 stream. Here, we studied the interaction of two ionic liquids-tetramethylammonium glycinate ([N-1111][Gly]) and tetraethylammonium prolinate ([N-2222][Pro])-with CO2 under wet conditions, by C-13-NMR. Results show that CO2 is initially captured in a carbamate form by the amine-functionalized anions of these salts. This capture mode is unambiguously confirmed by a single-crystal X-ray study of the CO2-ionic liquid complex. However, in solution, as additional CO2 is added, the carbamate releases the covalently bound CO2, and the CO2 remaining in solution shifts in form to an equilibrium mixture of carbonate and bicarbonate. Indeed, when the amount of CO2 present in the system exceeds about one-half mole per mole of ionic liquid present, the ionic liquid-carbamate complex is detected in only trace amounts, and the neutralized amino acids are readily identifiable by NMR.
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