Densities and Viscosities of 1-Ethyl-3-methylimidazolium n-Alkyl Sulfates

Abstract

Density and viscosity data for four 1-ethyl-3-methylimidazolium-based ionic liquids combined with alkyl sulfate, [C n SO 4 ] À with n = 1, 4, 6, and 8, and hydrogen sulfate, [HSO 4 ] À , anions were measured at atmospheric pressure in the temperature range 283 < T/K < 363. Isobaric thermal expansion coefficients were calculated from the density results. This work studies the effect of increasing the alkyl chain length of the sulfate-based anion on the density, viscosity, and related properties of this family of ionic liquids. The effective volumes of the distinct anions used were calculated from the measured density values, simply by subtracting the effective volume of the cation already available from literature to the molar volume of the ionic liquid. We also evaluated the predictive ability of group contribution methods for density and viscosity. Since large deviations between the predictions and the experimental data occurred for both density and viscosity, new group contribution parameters were proposed. The results clearly show that [HSO 4 ] À cannot be considered part of the [C n SO 4 ] À family. ' INTRODUCTIONIonic liquid (IL) research has boomed due to attractive properties common to several families of ILs, such as wide liquid range, nonflammability, and negligible vapor pressure at ambient conditions. 1À4 The potential development of reliable and economical process designs for industrial applications of ILs depends on the thorough knowledge of their most relevant thermophysical properties such as density, 5À7 viscosity, 8 and heat capacity. 9 Although the literature in this area has grown enormously in the past few years, every day new ILs are being synthesized. A careful analysis of the literature shows that the basic properties have only been measured for a limited number of ILs. The IL Thermo database contains no information regarding the density and viscosity data for the ILs used in this work, namely, [C 2 mim][C n SO 4 ] with n = 1, 4, 6, and 8 and [C 2 mim] [HSO 4 ]. However, for the more common [C 2 mim] [C 2 SO 4 ] several studies have been published.Generally, IL density varies between 0.85 g 3 cm À3 and 1.6 g 3 cm À3 , depending on the choice of both cation and anion; it then decreases as the alkyl side chain grows in a systematic way. 10 The viscosity of room temperature IL ranges from 10 cP to 10 5 cP, which is up to 3 orders of magnitude higher than that of conventional organic solvents. Such high viscosities are known to severely hinder possible industrial applications. Impurities such as water are important, since they dramatically reduce the IL viscosity. 11 Commonly, the increase of the alkyl chain length of the [C n mim] + cation increases the viscosity due to an increase in the van der Waals interaction domains. 8 Although considerable data exist relating to the influence of increasing the alkyl side chain in alkyl-imidazolium based ILs, few systematic studies have appeared on the same effect in the anion. In fact, there are few anions where this effect can be evaluated. One such ...

Thermophysical characterization of N-methyl-2-hydroxyethylammonium carboxilate ionic liquids

“…It can be seen that the differences in the molecular volumes in adjacent ILs are 2.97 nm 3 and this value can be mostly attributed to the inclusion of (-CH 2 ) group by assuming that V=V cation +V anion . In this way, V(-CH 2 )= 2.97 nm 3 which is in good agreement with the value of V(-CH 2 )= 2.80 nm 3 given by Costa et al [64]. Gardas…”

Chitosan and Ionic Liquid Based Solid Polymer Electrolytes: The Anion Alkyl Chain Length Effect

“…The lowest ionic conductivity of 1.51 x 10 -4 S.cm -1 at 25 ºC reports to the chitosan[C 2 mim][C 4 SO 3 ] sample. This sequence was the one expected since the increase of the anion alkyl chain length is associated with an increase of the IL viscosity (18)(19). The increase in viscosity led to a decrease in mobility, which typically tends to be accompanied by a decrease in conductivity.…”

Linking Diffusion–Viscosity Decoupling and Jump Dynamics in a Hydroxyl‐Functionalized Ionic Liquid: Realization of Microheterogeneous Nature of the Medium

“…Figure 1( see also Figure S1) showst hat at any given temperaturet he viscosity of [OH-Emim][FAP] is highert han that of ChemPhysChem 2017, 18,198 -207 www.chemphyschem.org [Emim][FAP],a nd the change in viscosity of these ILs with temperaturec an be well described by Vogel-Tammann-Fulcher relationship. [60] However,t he activation energies of viscousf low of neat [OH-Emim][FAP] and [Emim][FAP] were calculated by plottingl n h versus 1/T to an Arrhenius-type relation [61] ( [18] reported that hydroxyl groups can play as ignificant role in the organization of anionsa round [OH-Emim] + .W hile the acidic hydrogen atom (C2H) of the imidazolium ring in conventional IL is the most probables ite for hydrogen-bonding interactions with anions, [25] the hydroxyl group in [OH-Emim][FAP] providesa na dditional hydrogen-bonding site for cation-anion interionic interactions. Gholamie tal.…”