Hydrogen Sulfide and Carbon Dioxide Removal from Dry Fuel Gas Streams Using an Ionic Liquid as a Physical Solvent^†‡

The mole fraction solubilities (x*) and volumetric liquid-side mass-transfer coefficients (k(L)a) for H2S and CO2 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. CO2 and N-2, as single gases, and a H2S/N-2 gaseous mixture were used in the experiments. The solubilities of H2S and CO2 were found to increase with pressure and decrease with temperature within the experimental conditions used. The H2S solubilities in the ionic liquid (IL) were greater than those of CO2 within the temperature range investigated (300-500 K) up to a H2S partial pressure of 2.33 bar. Hence, the IL can be effectively used to capture both H2S and CO2 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 H2S in the H2S/N-2 mixture created mass-transfer resistance, which decreased k(L)a values for N-2. The k(L)a and x* values of CO2 were found to be greater than those of N-2 in the IL, which highlight the stronger selectivity of this physical solvent toward CO2 than toward N-2. In addition, within the temperature range from 300 to 500 K, the solubility and k(L)a of H2S in the IL were greater than those of CO2, suggesting that not only can H2S be more easily captured from dry fuel gas streams but also a shorter absorber can be employed for H2S capture than that for CO2.