(355n) Mixtures of Amino Acid Salts and Ethylene Glycol for CO2 Capture | AIChE

(355n) Mixtures of Amino Acid Salts and Ethylene Glycol for CO2 Capture


Gurkan, B., Case Western Reserve University
The concentration of CO2 in our atmosphere continues to rise due to anthropogenic emission sources such as fossil fuel powerplants and cars, recently surpassing 400ppm which is nearly double the average value from the last 800,000 years. As a result, researchers continue to develop CO2 capture materials to combat this drastic increase. Ionic liquids (ILs) have been of particular interest due to their tunable reactive capture of CO2 and negligible volatility. Since CO2 is acidic, basic anions in ILs have demonstrated CO2 reactivity near a 1:1 molar ratio. Another group of solvents known as deep eutectic solvents (DESs) have been of interest as well due to similarly tunable properties to ILs and high CO2 solubilities. A common hydrogen bond donor in DESs is ethylene glycol which supports a hydrogen bonding network in the liquid and this is credited with the deep melting point depression that is characteristic of DESs. Ethylene glycol has also been shown to react with CO2 in the presence of basic anions.

In this study, natural DESs made from a choline cation and series of amino acid anions (glycine, alanine, proline, and phenylalanine) were mixed with ethylene glycol to yield CO2-reactive solvents. The melting points of the mixtures were measured using differential scanning calorimetry. The resulting phase diagrams indicate eutectic behavior. These solvents were tested for CO2 capacity at various CO2 partial pressures in nitrogen (400 ppm CO2 to 100% CO2 at 1 bar). Choline amino acids show very slow CO2 uptake because they are extremely viscous (>1000 cP). Therefore, dilution with an active solvent such as ethylene glycol improves mass transport of CO2 while maintaining a high CO2 capacity. The CO2 absorption mechanism of these solvents was assessed via quantitative 13C-NMR. These eutectic solvents are made entirely from natural materials that are significantly cheaper and easier to synthesize than most ILs.