Vapor–Liquid Equilibrium of Ionic Liquid 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium Acetate and Its Mixtures with Water

Abstract

Ionic liquids have the potential to be used for extracting valuable chemicals from raw materials. These processes often involve water, and after extraction, the water or other chemicals must be removed from the ionic liquid, so it can be reused. To help in designing such processes, we present data on the vapor–liquid equilibrium of the system containing protic ionic liquid 7-methyl-1,5,7-triazabicyclo[4.4.0]­dec-5-enium acetate, water, acetic acid, and 7-methyl-1,5,7-triazabicyclo[4.4.0]­dec-5-ene. Earlier studies have only focused on mixtures of water and an ionic liquid with a stoichiometric ratio of the ions. Here, we also investigated mixtures containing an excess of the acid or base component because in real systems with protic ionic liquids, the amount of acid and base in the mixture can vary. We modeled the data using both the ePC-SAFT and NRTL models, and we compared the performance of different modeling strategies. We also experimentally determined the vapor composition for a few of the samples, but none of the modeling strategies tested could accurately predict the concentration of the acid and base components in the vapor phase.

Densities, Viscosities, and Thermal Conductivities of the Ionic Liquid 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium Acetate and Its Mixtures with Water

“…However, when water is present this is not observed, and the sample with excess acetic acid had a lower density than that with an equimolar ratio of acid and base. This is similar to the behavior observed with the vapor-liquid equilibrium data [12]. It has also been shown that protic ionic liquids, such as mTBD acetate, exhibit a reactive azeotrope (or possibly a complex) at a composition where there is an excess of acid, and the higher density at the composition where x acid equals 0.6 and x water is 0 may be due to the same intermolecular interactions that cause the azeotrope [9,10,23].…”

“…To our knowledge, no other articles have investigated how changes in the acid-to-base ratio affect the density of the overall solution. This article is a continuation of our earlier research, which presented data on the vapor-liquid equilibrium of the same system [12].…”

“…The mass was recorded before and after degassing, and this loss was subtracted from the water content of the sample. This was done because vapor-liquid equilibrium measurements showed that the vapor phase consists almost entirely of water [12].…”

“…The ePC-SAFT equation of state was used to model the density of this system [24,25]. The model was described in detail previously, which showed its performance for the vapor-liquid equilibrium (VLE) of this system [12]. 5 components were included in the model: water, mTBD, acetic acid, the mTBDH + ion, and the acetate ion.…”

“…By including mTBD and acetic acid as components and including the reaction in the model, it is possible to also model compositions where there is an excess of the acid or base. Some of the parameters could be fit to literature data, but the remainder were optimized using the experimental density data along with the VLE data [12].…”