Acid extraction to a hydrophobic ionic liquid: the role of added tributylphosphate investigated by experiments and simulations

Abstract

We have studied the extraction of four HA acids (HNO(3), HReO(4), HClO(4), HCl) to a hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)amide (BMI(+) Tf(2)N(-)) at room temperature, in a wide range of acidic concentrations in water. The effect of tributylphosphate (TBP) as co-solvent is investigated. According to experimental observations, water dragging to the IL phase increases with added TBP and/or acids. Acid extraction is found to be weak, however, for the four acids except for concentrated HNO(3) (>3 M). Molecular dynamics simulations on model biphasic systems show that TBP is not surface active, but well dissolved in the IL. They also reveal the importance of HA acid model (either totally or half dissociated) and of the TBP content on acid extraction to the IL. Furthermore, they show that "the proton" can be extracted by TBP (H(3)O(+)(TBP)(3)"complex") without its A(-) conjugated base, via a cation transfer mechanism (BMI(+) transfer to water). Experiments and simulations show that TBP plays an important role in the mutual solubility between water and ionic liquid, by different amounts, depending on the HA acid. On the other hand, both approaches indicate that a HTf(2)N containing aqueous solution completely mixes with the [BMI][Tf(2)N] IL that contains the same Tf(2)N(-) anion.

Homogeneous Liquid–Liquid Extraction of Rare Earths with the Betaine—Betainium Bis(trifluoromethylsulfonyl)imide Ionic Liquid System

“…A possible explanation for this observation is the increase in ionic strength by addition of chloride ions, which results in a lower solubility of the ionic liquid in water (salting-out effect) [31,54]. An increasing water miscibility between water and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide by adding HTf 2 N has been observed as well by Gaillard et al [55]. They also found an increasing water miscibility when HCl was added, which is opposite from what has been observed here for the addition of HCl to [Hbet][Tf 2 N].…”

Modulating the Solubilities of Ionic Liquid Components in Aqueous–Ionic Liquid Biphasic Systems: A Q‐NMR Investigation

“…Experimental results by Gaillard et al [49] have already evidenced that aqueous solutions containing large amounts of perchloric acid (in the molar range, from 0.5 to 6 m), when contacted with [C 1 C 4 im][Tf 2 N], behave somewhat differently from others containing nitric, hydrochloric, and perrhenic acids.…”

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

“…[32] In our previous work, [29] our model was built on the assumption that the concentrationso fb oth [Tf 2 N À ]a nd [C 4 mim + ]i ons, which intervene in the two extraction equilibria shown in Equations (3) and (4), N À ]v ariations are strongly dependento nb othT BP and nitric acid concentrations, and that the RTIL cation and anion behave in adifferent way.W e, thus, need to take this fact into accounti no ur new model.Considering the intricate ion exchanges in such biphasic systems, [31,33] we limit ourselves to an empiricalm athematicald escription of the concentration data, by use of ad hoc analytical expressions between [HNO 3 ] = 0a nd 7 m as Equations (7) and (8):…”

“…Indeed,[ C n mim][Tf 2 N] has as light, but not negligible, solubility in water compared with organic molecular solvents. [30] During liquid-liquide xtraction, the presence of am ineral acid in the aqueous phase results in as ignificant increase of the aqueouss olubility of the IL;t his solubility is not only dependent on the nature and concentration of the acid, [31,32] buta lso on the RTIL structure. [33] It has also been shown that the introductiono fv ariousn eutral organophosphorus extractantsi nto the IL phase significantly increases the solubility of [C 5 mim][Tf 2 N] in 1 m HNO 3 .…”