Liquid‐liquid phase split in ionic liquid + toluene mixtures induced by CO₂

Abstract

High pressure carbon dioxide was dissolved in ionic liquid 1 toluene mixtures to obtain the conditions of pressure and composition where a liquid-liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf 2 N] 2 ) anion were selected: 1-hexyl-3-methylimidazolium ([hmim] ). The solubility of CO 2 was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO 2 in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim] IntroductionIonic liquids (ILs) are salts extensively studied in recent years due to their interesting properties, including very low vapor pressure, high thermal stability, and wide liquid range, many of which include temperatures below 373 K.1 Additionally, these compounds have adjustable physical and chemical properties. Given the large number of potential combinations of anion and cation, 2 this confers on them great versatility in being applied in a large number of specific processes. The literature describes multiple applications of ILs in separations; for example, in aqueous biphasic systems 3 for extracting conventional salts, amino acids, polymers, metals, or organic compounds from water; in liquidliquid extractions for obtaining metal ions 4-10 or distributing organic compounds into two immiscible liquid phases [11][12][13][14] ; for CO 2 capture from industrial gas streams 15,16 ; and for separating compounds which form azeotropic mixtures. 17 The attractiveness of ILs in many of these applications coincides with their low volatility; thus, volatile solvents commonly used in separation processes can be replaced, in order to decrease vapor emissions to the environment.CO 2 , a well-known solvent for extraction under supercritical conditions, 18 has been studied in conjunction with ILs. In the first report of this kind, Blanchard et al.19 mixed naphthalene with [bmim] [PF 6 ] and utilized supercritical CO 2 for extracting the dissolved solid from the liquid phase. After the extraction, no IL was detected in the supercritical phase and CO 2 could be easily separated from the naphthalene by depressurization, obtaining a solvent-free solute. Moreover, the same procedure has been used for extracting several organic solids and liquids 20 from the IL phase, demonstrating its general applicability. Following the idea of using high pressure CO 2 , Scurto et al. 21 proposed a new separation involving CO 2 and ILs applying the method depicted in Figure 1. In that work, an organic compound was mixed with an IL, forming a single liquid phase. Then, high pressure CO 2 was added to the system and solubi...

Solubility of CO 2 in [1- n -butylthiolanium][Tf 2 N]+toluene mixtures: liquid–liquid phase split separation and modelling

“…First, the liquid-liquid equilibrium apparatus and method was validated by measuring the solubility of toluene in [hmim] [Tf 2 N] and comparing the results with the literature[51,52]. The results are in agreement with qualitative measurements at room temperature reported in our previous work[27] and in quantitative agreement with the literature values[51,52]. Subsequent measurements of the solubility of toluene in [bthiol] [Tf 2 N] are 0.749 and 0.753 mole fraction at 298.15 and 313.15 K, respectively.…”

“…A new synthetic with material balance apparatus was built to measure CO 2 solubility in liquids, based on a previous apparatus used in our laboratory [12,13,25,27]. A scheme of the new experimental apparatus is shown in figure 2.…”

“…Several works [19][20][21][22][23][24][25][26][27][28] have shown that CO 2 can 'salt-out' water and organic solvents from ILs, by inducing LLV equilibrium. Scurto et al [19] mixed water with different hydrophobic and hydrophilic ILs, inducing a second liquid phase by increasing the pressure of the system and the concentration of CO 2 in the liquid mixture, obtaining LLV equilibrium.…”

Understanding Carbon Dioxide Solubility in Ionic Liquids by Exploring the Link with Liquid Clathrate Formation

“…It has also recently been shown that toluene and CO 2 reduce each other's solubility in ILs. [21] While CO 2 has ag eneral antisolvent effect on solutes dissolved in ILs, [22] the solubility of CO 2 in 1-hexyl-3-methylimidazolium bistriflimide ([C 6 mim][NTf 2 ])-toluene solutions is lower than what was previously observed for solutions of organic liquids in [C 6 mim][NTf 2 ]t hat do not form LCs. This could indicate that CO 2 and aromaticse ngage in something analogous to the "salting out" effect observed in aqueouss olutions, where two solutes reduce the solubility of each other because they restructure the solventi nc ompetitive ways.…”

“…Liquid CO 2 and supercritical CO 2 show the same asymmetric immiscibility with ILs observed with LC‐forming aromatic liquids. It has also recently been shown that toluene and CO 2 reduce each other's solubility in ILs . While CO 2 has a general antisolvent effect on solutes dissolved in ILs, the solubility of CO 2 in 1‐hexyl‐3‐methylimidazolium bistriflimide ([C 6 mim][NTf 2 ])‐toluene solutions is lower than what was previously observed for solutions of organic liquids in [C 6 mim][NTf 2 ] that do not form LCs.…”