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High pressure solubility of CO2 in non-fluorinated phosphonium-based ionic liquids


Ramdin, Mahinder;




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High pressure solubility of carbon dioxide in three phosphonium-based ionic liquids has been mea-sured experimentally. A synthetic method was used to measure vapor–liquid, vapor–liquid–liquid andliquid–liquid equilibria of carbon dioxide in the ionic liquids trihexyltetradecylphosphonium bromide[thtdp][Br], trihexyltetradecylphosphonium dicyanamide [thtdp][dca] and trihexyltetradecylphospho-nium bis(2,4,4-trime-thylpentyl)phosphinate [thtdp][phos] for a temperature range of 271–363 K andup to 90 MPa. Furthermore, the densities and viscosities of these ILs have been measured in a tem-perature range of 293–363 K. The solubility of carbon dioxide in these ILs is (on mole fraction basis)significantly larger than most of the commonly used fluorinated imidazolium ionic liquids. The latterstatement, however, does not hold for the [Br] and [dca] based IL if the solubility is compared on molality(mole/mass solvent) basis, where the solubility differences among physical ILs tends to vanish indicatinga strong molecular weight effect. The solubility of carbon dioxide in [thtdp][phos], both on mole frac-tion and molality basis, is among the highest compared to all the other physical ILs reported so far inthe literature. The Peng–Robinson equation of state in combination with Wong–Sandler mixing rulesincorporating the NRTL Gibbs excess energy model was applied to represent the experimental data withacceptable accuracy.