Inverse Gas Chromatography: Effects of the Experimental Temperature and Molecular Structure on the Solubility Parameters of 1-Alkyl-3-methylimidazolium Hydrogen Sulfate ([C_nMIM][HSO₄], n = 4, 6, and 8)

Abstract

Thermodynamic parameters at infinite dilution for thirty-one organic solutes in a series of imidazolyl hydrogen sulfate ionic liquids (ILs) were determined by inverse gas chromatography (IGC). The IGC characterization was carried out at temperatures ranging between 303.15 and 343.15 K for determining the Hildebrand solubility parameter (δ 2 ) as well as the Flory−Huggins interaction parameter (χ 12 ∞ ), the activity coefficient at infinite dilution (γ 12 ∞ ), and the thermodynamic functions. In addition, based on the γ 12 ∞ results, the selectivity and capacity were directly calculated for two separation problems (hexane/benzene and hexane/thiophene). Under the different effects of the three ILs, it was found that the values of χ 12 ∞ and γ 12 ∞ were significantly different for the solutes tested, but all the values follow a certain pattern: they increase with temperature or decrease with temperature. As the temperature increased, the solubility parameters of the three ILs showed a linear decrease trend. The solubility parameters of the three ionic liquids at room temperature were obtained by extrapolation as δ 2([BMIM][HSO4]) = 24.15 MPa 1/2 , δ 2([HMIM][HSO4]) = 24.10 MPa 1/2 , and δ 2([OMIM][HSO4]) = 23.66 MPa 1/2 .

Infinite Dilution Activity Coefficients and Thermodynamic Properties of Various Organic Solutes in a Choline Chloride + Oxalic Acid Deep Eutectic Solvent

“…A column was prepared following a previously reported method. ,,, The examined DES was dissolved in methanol, to which silicon alkylation 102 white monomers (80–100 mesh) were added to prepare a stationary phase coated with 30% DES (0.54 g, with an estimated uncertainty of 0.0005 g). − The stationary phase was placed in a rotary evaporator to remove superfluous volatile solvents and then placed in a vacuum drying oven at 323.15 K for 8 h. A vacuum pump was used to fill the prepared stationary phase into a stainless-steel column (1200 × 2 mm I.D.) that had been previously cleaned with acetone and methanol.…”

“…With increasing temperature, δ 2 gradually decreases, which is consistent with the reported results for some ILs. 17,26,45 The regression equation and correlation coefficient relation is δ 2 = − 0.0164T + 28.2641 (R 2 = 0.9850) using the slope and δ 2 = − 0.0255T + 31.8468 (R 2 = 0.9971) using the intercept.…”