CO2/H2 separation by amino-acid ionic liquids with polyethylene glycol as co-solvent

• PEG was used as a co-solvent to intensify CO2 absorption in AAILs.
• AAILs-PEG mixed solvents have high CO2 solubility with reduced viscosity.
• AAILs-PEG mixed solvents are thermally stable at elevated temperatures (up to 413 K).
• CO2 absorption mechanism and intensification effect in AAILs-PEG400 were discussed.

In this work polyethylene glycol 400 (PEG400) was introduced as a co-solvent to intensify CO2 separation and reduce the viscosity of amino-acid ionic liquids (AAILs) while maintain their unique properties, i.e. undetectable vapor pressure, high thermal stability and excellent CO2 solubility. The thermal gravimetric analysis indicated that AAILs, PEG400 and their blend solvents were stable at above 523 K and showed negligible weight loss at 373 K for 300 min. The viscosity of the mixed solvents decreased to be about half of that of pure AAILs at 298 K. The CO2 solubility in the mixed solution was measured over a range of pressures from 100 to 1700 kPa and of temperatures from 333.15 to 413.15 K at 40 K intervals. The ideal CO2/H2 selectivity reached 110 at 333.15 K and 100 kPa. PEG400 as a co-solvent may have created a better gas-liquid interface, which promotes the mass transfer and intensifies the CO2 sorption in AAILs. A CO2 absorption mechanism in AAILs-PEG400 was proposed accordingly to explain the intensification effect with evidence from the FTIR results.