Comparative Microfluidic Screening of Amino Acid Salt Solutions for Post-Combustion CO2 Capture

The CO₂ absorption capacity and rate of the potassium salts of glycine, taurine, proline, and lysine were compared with MEA by tracking the volume change of an entrained CO₂ gas plug as it traveled through a microfluidic channel (see figure 1). The potassium salt of lysine, which contains two primary amine functional groups, exhibited the highest rich CO₂ loading, >50% higher than MEA. The salts of glycine, and taurine exhibited similar absorption capacity to MEA, and the salt of proline exhibited the lowest absorption capacity (see figure 2). The trend in absorption capacities of the potassium salt of lysine and MEA was also observed in a set of breakthrough experiments in a continuously stirred reactor vessel. Experiments were conducted to compare the CO₂ absorption capacity on the basis of both constant molar concentration (0.5M) and constant mass fraction (30%) of the absorbent molecule and the significance of this difference are highlighted. Specifically, the higher molecular weight of lysine is identified as a drawback to its use. Raman spectroscopy was used to analyze the neat absorbent solutions as well as the microfluidic reactor effluent and spectral features of carbamate, carbonate, and bicarbonate were identified in the effluent spectra. The effectiveness of the microfluidic reactor as a volume and time efficient screening tool is demonstrated. The results suggest further work should be done to evaluate the efficacy of the alkali salt of lysine as a post-combustion CO₂ capture absorbent as it has potential to match or possibly improve upon the CO₂ loading of MEA while offering advantages such as low toxicity and lower volatility.