Ether-functionalization of monoethanolamine (MEA) for reversible CO2 capture under solvent-free conditions with high-capacity and low-viscosity†
CO2 capture based on aqueous alkanolamines, in particular, monoethanolamine (MEA), currently represents the maturest technology, but it is still limited by the inherent drawbacks of high energy consumption and low gravimetric capacity due to the involvement of water as solvent. In this work, the ether-functionalization of MEA has been proposed to structurally modify this cheap industrial absorbent for CO2 capture under water-lean conditions. The resulting ether-functionalized MEAs have been employed as solvent-free absorbents with enhanced gravimetric capacities (11–19 wt% at 25 °C and 12–20 wt% at 40 °C) and relatively low viscosities (as low as 311 cP at 25 °C and 105 cP at 40 °C) at the CO2-loaded state. The captured CO2 could be easily stripped out by heating at a relatively low temperature (75 °C). Such novel absorbents also exhibit excess absorption capacity under high operating pressures (20 and 30 bar), owing to the CO2-philic nature of the ether group for additional physisorption. Furthermore, a clear structure–property relationship among these functionalized MEAs has been established through the systematic investigation of their thermodynamic properties and absorption–desorption performance by means of density functional theory (DFT) calculations, 13C NMR spectroscopy, differential scanning calorimetry (DSC) and in situ FTIR analysis. Additionally, these newly identified MEA derivatives possess considerable potential for use in the already existing aqueous alkanolamine infrastructure for further cost saving.