Solubility of Methane in the Ionic Liquid 1-Ethyl-3-methylimidazolium Tris(pentafluoroethyl)trifluorophosphate

Previously, we found that the ionic liquid (IL) 1-ethyl-3 methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([emim][FAP]) shows the highest carbon dioxide (CO 2 ) solubility of all ILs studied so far. Therefore, this IL is a very interesting solvent for gas separations, such as the removal of CO 2 from sour gas, as long as the solubility of methane (CH 4 ) in the same IL is sufficiently low. In this work, we present new experimental measurements of the CH 4 solubility in [emim][FAP]. This solubility has been determined by measuring the bubble point pressures for CH 4 concentrations ranging from (5.2 to 15.5) mol % and within a temperature range of (293.30 to 363.42 K) using a synthetic method. The solubilities of CH 4 in [emim][FAP] are compared to the CH 4 solubilities in other ILs. This comparison shows that the solubility of CH 4 in the various ILs slightly decreases in the order: [hmim][Tf 2 N] > [emim][FAP] > [bmim][Tf 2 N]. The solubilities of CH 4 in various ILs are compared with CO 2 solubilities in the same ILs, showing the much lower solubility of CH 4 in all ILs studied. The high solubility of CO 2 compared to CH 4 in [emim][FAP] indicates the possibility of using this IL in separating CO 2 from natural gas. The obtained selectivity for this separation at a temperature of 333.15 K is S = H CH 4 / H CO 2 = 7.74, which is similar to CO 2 /CH 4 separation ratios in other ILs (e.g., S = 8.26 for [bmim][Tf 2 N] and S = 6.10 for [hmim][Tf 2 N]).