This study is to investigate the potential use of ionic liquids (ILs) as physical solvents for selective CO₂ capture from post water-gas-shift reactor streams at elevated pressures and temperatures. The equilibrium gas solubility (x*) and the volumetric mass transfer coefficients (k_La) for CO₂, H₂ and a gas mixture (CO₂, H₂, CH₄, CO, Ar) in three ILs (TEGO IL K5, TEGO IL P51P and TEGO IL P9) were determined. The data were obtained in an agitated reactor, equipped with sight-windows, in wide ranges of pressure, temperature, mixing speed, and liquid height.

Under the operating conditions investigated, the CO₂ solubilities in the three ionic liquids increased with pressure at constant temperature and decreased with temperature at constant pressure. Also, the volumetric liquid-side mass transfer coefficients of CO₂ increased with mixing speed, pressure, and temperature and decreased with liquid height. At 500 K, the CO₂ solubilities in the TEGO IL K5 were greater than those in the other two ILs. Under similar operating conditions, the CO₂ solubilities in the three ILs were greater than those of H₂, which reflects the selective nature of ILs to capture CO₂. In addition, the ILs appeared to have negligible vapor pressure up to 500 K, which presents an advantage over conventional physical solvents currently employed for CO₂ capture from post water-gas-shift reactor streams.

This study demonstrated the thermal stability of the ILs and highlighted their ability to selectively capture CO₂ at temperatures up to 500 K and pressures as high as 30 bars.

ACKNOWLEDGMENT

The technical effort was performed in support of ongoing Carbon Dioxide research at the National Energy Technology Laboratory of the U.S. Department of Energy under RDS contract DE-AC26-04NT41817.