Experiment and Mechanism of Co2 Capture by Low-Energy Functional Ionic Liquid Phase Change Absorbent: Phase Change Breaks Low Viscosity-High Load Limit

Abstract

To overcome the limitations between low viscosity and high loading in the rich phase via phase change, three novel multi-site ionic liquids were prepared and mixed with ethylene glycol butyl ether (BEN) and water, respectively. The experimental results indicated that a 3:4:3 (mass ratio) mixture of diethylenetriamine-imidazole ([DETA+Im-]), BEN and H2O (3H4B3DM) was the best liquid-liquid phase change absorber. The volume of the rich phase was only 38.44% with a viscosity of 46.37 mPa·s and a maximum loading of 5.72 mol kg-1. 13C NMR and FTIR spectra showed that the CO2 absorption products, mainly carbamate and carbamic acid, were highly aggregated in the rich phase. DFT calculations showed that BEN in the rich phase formed a dimer with the absorption products, facilitating the reaction. Thermodynamic energy barrier calculations show that H2O lowered the reaction energy barrier by two-proton transfer and acted as a “hydrogen bonding bridge” around the ion clusters. This action disrupted the robust hydrogen bonding network within the rich phase and reduced the viscosity. The absorption products have an uneven charge distribution due to polarity differences, which induce phase change behavior. Compared to 30 wt% MEA, the regeneration energy consumption of 3H4B3DM is reduced by 55.5%, and the corrosion rate in the rich phase is reduced by an order of magnitude to 0.084 mm·a-1. This high regeneration capacity, energy saving properties, and corrosion resistance make 3H4B3DM a highly prospective phase change absorbent.

Keywords: CO2 capture, Phase change absorber, Ionic liquid, Mechanism, DFT calculation