Thermodynamic and Experimental Studies of Ethane Solubility in Promising Ionic Liquids for CO2 Capture
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Natural gas is one of the world’s major energy sources and the demand has increased remarkably in recent years. The production of natural gas often requires treatment processes in order to separate CO2 and H2S. CO2 must be removed in order to meet the heating value specifications for sales gas, whereas H2S is removed due to its toxicity and to reduce the overall release of SO2 into the atmosphere during combustion. Ionic liquids have recently been considered the most economically and environmentally friendly solvents for natural gas sweetening. This research aimed at measuring the solubility of C2H6 in six room temperature ionic liquids, N-pentyl-n-methyl pyrroliidinium bis(trifluoromethylsulfonyl)imide, ([p(5)mpyrr][Tf2N]) ; Diethylmethyl(2-methoxyethyl)-ammonium bis(trifluoromethylsulfonyl)imide ([deme][Tf2N]); 1,2,3-Tris(diethylamino)-cyclopropenylium bis(trifluoro methanesulfonyl)imide , ([TDC][Tf2N]); 1-Hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, ([hmim][eFAB]); 1-Butyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphatem, ([bmim][eFAB]); and 1-Ethyl-3- methylimidazolium tris(pentafluoroethyl)trifluorophosphate, ([emim][eFAB]) at 298.15, 313.15, and 333.15 K and at pressure up to 13 bar using a gravimetric microbalance (IGA-003). The experimental solubility of C2H6 in these solvents were well correlated with the standard PengRobinson (PR-EoS), the standard Redlich-Kwong-Soave(SRK-EoS), the SRK-EoS with quadratic mixing rules. Binary interaction parameters for these correlations were obtained. The solubility of C2H6 in ionic liquids followed the same trend with CO2 with lower solubility. The solubility increased with increasing pressure and decreased with increasing temperature. Solubility decreased in the following order: [TCD][TF2N] > [hmim][eFAP] > [bmim][eFAP] >[p(5)mpyrr][Tf2N] >[emim][eFAP] > [deme][[Tf2N]. The two ionic liquids, [emim][eFAP] and [deme][[Tf2N] can be considered promising due to comparably higher CO2/C2H6 selectivity than other ionic liquids studied in this work. It was also observed that CO2/C2H6 selectivity ratio is decreasing with increasing alkyl chain: [emim][eFAP] > [bmim][eFAP] > [hmim][eFAP]. In addition, Henry’s law constants and enthalpies and entropies of absorption for C2H6 in the calculated ionic liquid are also reported.