No abstract

Three perfluorinated compounds (PFCs), PP10, PP11, and PP25, manufactured by F2 Chemicals Ltd., U.K., were investigated as physical solvents for selective CO2 capture from synthesis gas or syngas streams at elevated pressures and temperatures. The equilibrium solubility, the hydrodynamic, and the mass-transfer parameters of CO2 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 CO2 solubilities in the three solvents decreased with an increasing temperature at constant pressure and followed Henry’s law. The CO2 solubilities in PP25 were greater than those in PP10 and PP11. The volumetric liquid-side mass-transfer coefficients (k L a) of CO2 in the PFCs increased with mixing speed, pressure, and temperature. Also, the gas−liquid interfacial areas of CO2 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 CO2 at temperatures up to 500 K and pressures as high as 30 bar. A preliminary conceptual process design using PP25 for selective CO2 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.

The mole fraction solubilities (x*) and volumetric liquid-side mass-transfer coefficients (k L a) for H 2 S and CO 2 in the ionic liquid, TEGO IL K5, (a quaternary ammonium polyether) were measured under different pressures (up to 30 bar) and temperatures (up to 500 K) in a 4 L ZipperClave agitated reactor. CO 2 and N 2 , as single gases, and a H 2 S/N 2 gaseous mixture were used in the experiments. The solubilities of H 2 S and CO 2 were found to increase with pressure and decrease with temperature within the experimental conditions used. The H 2 S solubilities in the ionic liquid (IL) were greater than those of CO 2 within the temperature range investigated (300-500 K) up to a H 2 S partial pressure of 2.33 bar. Hence, the IL can be effectively used to capture both H 2 S and CO 2 from dry fuel gas stream within the temperature range from 300 to 500 K under a total pressure up to 30 bar. The presence of H 2 S in the H 2 S/N 2 mixture created mass-transfer resistance, which decreased k L a values for N 2 . The k L a and x* values of CO 2 were found to be greater than those of N 2 in the IL, which highlight the stronger selectivity of this physical solvent toward CO 2 than toward N 2 . In addition, within the temperature range from 300 to 500 K, the solubility and k L a of H 2 S in the IL were greater than those of CO 2 , suggesting that not only can H 2 S be more easily captured from dry fuel gas streams but also a shorter absorber can be employed for H 2 S capture than that for CO 2 . † Progress in Coal-Based Energy and Fuel Production.