Propylene and Propane Solubility in Imidazolium, Pyridinium, and Tetralkylammonium Based Ionic Liquids Containing a Silver Salt

Abstract

The gas solubility of propane and propylene in seven ionic liquids, 1-ethyl-3-methyl­imidazolium tetrafluoroborate (EMImBF4), 1-hexyl-3-methyl­imidazolium tetrafluoroborate (HMImBF4), 1-octyl-3-methyl­imidazolium tetrafluoroborate (OMImBF4), 3-methyl­imidazolium nitrate (BMImNO3), 1-butyl-3-methyl­imidazolium bis(trifluoro­methyl­sulfonyl­imide) (BMImTf2N), methyl­trioctyl­ammonium bis(trifluoro­methyl­sulfonyl­imide) (MOOONTf2N), and butyl­trimethyl­ammonium bis(trifluoro­methyl­sulfonyl­imide) (BMMMN Tf2N), is reported. The equilibrium isotherms of both pure gases were measured in the pure ionic liquids and in presence of a silver salt containing the same anion of the ionic liquid in a range of concentration of (0 to 0.77) mol·kgIL –1 at temperatures between (288 and 308) K and pressures ranging from (0 to 700) kPa. Henry’s law constant values for physical solubility as well as the characteristic parameters for chemical solubility such as chemical equilibrium constants and enthalpies of the chemical reactions between silver cations and propylene are reported. Based upon the experimental results, ionic liquids based on imidazolium cations with less and shorter alkyl substituents improve the selective separation of propylene from these mixtures. Regarding to the structure of the anion it was gathered that ionic liquids with the BF4 – anion, combined with the AgBF4 silver salt, provided the best results in terms of olefin capacity and selectivity. In this article we provide valuable data that evidence that the separation of propane/propylene gas mixtures by reactive absorption could represent an efficient alternative to the traditional separation process based on cryogenic distillation and serve for the new process design.

Characterizing Olefin Selectivity and Stability of Silver Salts in Ionic Liquids Using Inverse Gas Chromatography

“…A number of studies have utilized ionic liquids (ILs) as solvents to dissolve silver salts to improve separation performance. 23 − 27 ILs are a class of nonmolecular solvents with melting points lower than 100 °C. 28 ILs possess a number of desirable properties such as negligible vapor pressure that precludes their loss due to evaporation at elevated temperature, excellent thermal stability that extends the temperature range of the separation technique, and structural tunability that provides the capability of imparting desired selectivity toward target compounds.…”

“… 29 − 33 Fallanza and co-workers have evaluated the solubilities of propane and propylene in membrane separations using different combinations of imidazolium, pyridinium, and ammonium-based ILs and silver salts such as silver tetrafluoroborate, silver nitrate, and silver bis[(trifluoromethyl)sulfonyl]imide ([NTf 2 – ]). 23 It was found that anions of the silver salt and structural features of IL solvents strongly affect the olefin capacity and selectivity. Huang and co-workers applied silver-IL complexes, in which the silver(I) ion was a component of the cation, to separate olefin/paraffin mixtures using FTMs.…”

A Perspective of Solutions for Membrane Instabilities in Olefin/Paraffin Separations: A Review

“…133 In this line, Ortiz et al 22,134 developed a material with promising characteristics for the separation of light olefin/paraffin mixtures. Previous to the material choice, a thorough investigation on the most suitable IL to form the IL/silver salt pair was carried out 135,136 . Among several pairs, 1-butyl-3-methylimidazolium tetrafluoroborate/silver tetrafluoroborate (BMImBF 4 /AgBF 4 ) was selected.…”

Liquid silver tris(perfluoroethyl)trifluorophosphate salts as new media for propene/propane separation

“…The addition of silver salts to water or ionic liquids has been shown in the past to drastically enhance both, alkene capacity and selectivity due to the known chemical interaction of the alkene with the silver ion. [6][7][8][9][10][11][12][13][14] Aqueous silver nitrate and silver tetrafluoroborate solutions have been extensively studied and were close to commercialization in absorption/desorption processes. 10,15,16 Yet, both silver salts show tendencies to form explosive silver acetylides or decompose in aqueous environments.…”

“…Consequently, solutions of Ag[NTf 2 ], Ag [NO 3 ], Ag [BF 4 ] and Ag [OTf] in various ionic liquids have also been investigated with respect to their olefin uptake and their application in ene/ane separation processes has been suggested. [11][12][13][14] Dissolution of solid silver salts in an ionic liquid, however, always comes with a decrease in silver concentration and thus decreasing capacity for alkene complexation. Furthermore, an increase in viscosity with increasing silver concentration is generally observed, leading to slower mass transport.…”