Highly selective amino acid salt solutions as absorption liquid for CO2 capture in gas-liquid membrane contactors

The strong anthropogenic increase in the emission of CO2 and the related environmental impact force the developments towards sustainability and carbon capture and storage (CCS). In the present work, we combine the high product yields and selectivities of CO2 absorption processes with the advantages of membrane technology in a membrane contactor for the separation of CO2 from CH4 using amino acid salt solutions as competitive absorption liquid to alkanol amine solutions. Amino acids, such as sarcosine, have the same functionality as alkanol amines (e.g., monoethanolamine=MEA), but in contrast, they exhibit a better oxidative stability and resistance to degradation. In addition, they can be made nonvolatile by adding a salt functionality, which significantly reduces the liquid loss due to evaporation at elevated temperatures in the desorber. Membrane contactor experiments using CO2/CH4 feed mixtures to evaluate the overall process performance, including a full absorption/desorption cycle show that even without a temperature difference between absorber and desorber, a CO2/CH4 selectivity of over 70 can be easily achieved with the sarcosine salt solution as absorption liquid. This selectivity reaches values of 120 at a temperature difference between absorber and desorber of 35 °C, compared to a value of only 60 for MEA under the same conditions. Although CO2 permeance values are somewhat lower than the values obtained for MEA, the results clearly show the potential of amino acid salt solutions as competitive absorption liquids for the energy efficient removal of CO2. In addition, due to the low absorption of CH4 in sarcosine compared to MEA, the loss of CH4 is reduced and significantly higher CH4 product yields can be obtained