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Article published in the journal Industrial Engineering and Chemistry Research, 49 (2010) 4850-4857

Date : 15/10/2015

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Zoran

Uploaded by : Zoran
Uploaded on : 15/10/2015
Subject : Engineering

Title Liquid-Liquid Equilibrium of Mixtures of Imidazolium-Based Ionic Liquids with Propanediols or Glycerol

Imidazolium ionic liquids with bistriflamide and trifllate anions show very distinct solvent abilities toward 1,2-propanediol,1,3-propanediol, and glycerol: while [C2mim][NTf2] exhibited partial miscibility with all of them, [C2mim][OTf] was always completely miscible, even with glycerol. The presented facts and evidence clearly indicate that this distinction is a likely consequence of quite divergent capabilities of NTf2 and OTf anions to form hydrogen bonds. This study brought two other interesting findings. The first is that, in the solutions of [Cnmim][NTf2] with both propanediols and glycerol, the shorter alkyl chain improved the solubility. [C2mim][NTf2] was even found to be slightly more soluble in 1,2-propandiol than in 1-propanol. Thus, this effect of the ionic liquid alkyl chain length on liquid-liquid equilibrium (LLE) phase behavior is the opposite to that existing in the mixtures of the same ionic liquids with normal alcohols. The other finding is a huge impact of the position of the second hydroxyl group in the studied diols on their phase behavior with both [C2mim][NTf2] and [C10mim][NTf2] ionic liquids. When compared to 1,2-propanediol, 1,3-propanediol showed remarkably lower solubility in both [C2mim][NTf2] and [C10mim][NTf2]. On the other hand, this difference between 1,3- propanediol and glycerol was much less striking, particularly at lower temperatures. The Fourier transform infrared (FTIR) spectroscopic studies showed that, with respect to [C2mim][NTf2], [C2mim][OTf] ionic liquid forms considerably stronger hydrogen bonds with all the investigated alkanols. These results support the aforementioned opinion that the [NTf2] and [OTf] anions have different hydrogen bonding capacities. The results presented herein, besides fundamental importance, also offer application possibilities for the sustainable separation of 1,3-propanediol from glycerol and/or its aqueous solutions, which plays an important role in the microbial production of this diol. The application of the Peng-Robinson cubic equations of state (PR EoS), combined with the Mathias-Klotz-Prausnitz (MKP) mixing rule to model the LLE results (denoted as PRMKP), showed satisfactory correlations in all the studied cases, except in the two mixtures with 1,3-propanediol.

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