Novel Physical Solvents for Selective CO₂ Capture from Fuel Gas Streams at Elevated Pressures and Temperatures

Three perfluorinated compounds (PFCs), PP10, PP11, and PP25, manufactured by F2 Chemicals Ltd., U.K., were investigated as physical solvents for selective CO 2 capture from synthesis gas or syngas streams at elevated pressures and temperatures. The equilibrium solubility, the hydrodynamic, and the mass-transfer parameters of CO 2 in the solvents were measured in a 4-L ZipperClave agitated reactor under wide ranges of operating conditions: pressures (6−30 bar), temperatures (300−500 K), mixing speeds (10−20 Hz), and liquid heights (0.14−0.22 m). The CO 2 solubilities in the three solvents decreased with an increasing temperature at constant pressure and followed Henry’s law. The CO 2 solubilities in PP25 were greater than those in PP10 and PP11. The volumetric liquid-side mass-transfer coefficients ( k L a ) of CO 2 in the PFCs increased with mixing speed, pressure, and temperature. Also, the gas−liquid interfacial areas of CO 2 in the three PFCs appeared to control the behavior of k L a . This study proved the thermal and chemical stability and the ability of the PFCs to selectively absorb CO 2 at temperatures up to 500 K and pressures as high as 30 bar. A preliminary conceptual process design using PP25 for selective CO 2 capture from hot-shifted gas with pressure-swing and pressure−temperature-swing regeneration options was devised [a temperature-swing option was also examined but is not reported here because it is outside the context of the present study, which involves a physical solvent process benchmark (Selexol) for which temperature-swing regeneration is not a viable option]. The pressure−temperature-swing option led to greater PP25 solvent loss but a more favorable (more negative) net enthalpy than the pressure-swing option. However, for either regeneration option to be economically viable, the PP25 solvent must be completely recovered from the process.