Effect of alkanolammonium formates ionic liquids on vapour liquid equilibria of binary systems containing water, methanol, and ethanol

doi:10.1016/j.jct.2012.05.001

The Journal of Chemical Thermodynamics

Volume 53, October 2012, Pages 167-175

https://doi.org/10.1016/j.jct.2012.05.001 Get rights and content

Abstract

Vapour pressures were measured using a quasi-static ebulliometer for the pseudo-binary mixtures of (water + ethanol), (water + methanol), and (methanol + ethanol) containing an alkanolammonium-based ionic liquid (IL), namely, mono-ethanolammonium formate ([HMEA][HCOO]) and di-ethanolammonium formate ([HDEA][HCOO]), respectively, with fixed IL mass fraction of 0.30 and over the temperature ranges of (292.12 to 371.13) K. The vapour pressures of the IL-containing ternary systems were favourably correlated using the NRTL model with an overall average absolute relative deviation (AARD) of 0.0082. Further, the salt effects of [HMEA][HCOO] and [HDEA][HCOO] on isobaric vapour liquid equilibria (VLE) of azeotrope and close boiling mixture, especially for the mixtures of (water + ethanol) and (methanol + ethanol), were investigated and compared with other ILs in terms of the x′–y phase diagrams predicted with the binary NRTL parameters. It is demonstrated that the relative volatilities of ethanol to water and ethanol to methanol are enhanced, and [HMEA][HCOO] might be used as a promising entrainer for the efficient separation of ethanol aqueous solution by special rectification.

Highlights

► Vapour pressures for six ternary systems containing an IL were measured. ► Components studied were water, ethanol, methanol, and alkanolammonium formates. ► The isobaric VLE were predicted using the fitted binary NRTL parameters. ► The ILs studied can generate a promising salt effect on VLE of azeotrope. ► [HMEA][HCOO] might be used as a potential entrainer in extractive distillation.

Introduction

On the context of the perceived strength of the global demand of petroleum and the rapid increase in the price of crude oil, bioethanol is regarded as a prominent substitute or additive of fuel and gasoline, which is commonly produced by the process of biorefinery (e.g., fermentation of sugars) [1], however, the high affinity of ethanol for water and the accompanied by product of methanol turn out to be a problem in its purification. In view of the existence of azeotropic phenomenon for the (water + ethanol) mixture and the low relative volatility between methanol and ethanol, special distillation (e.g., extractive or salt distillation) is generally adopted to facilitate the separation for azeotropes or close boiling mixtures, in which an entrainer (a solvent or salt) is often introduced to increase the relative volatility of one component and make the separation more efficient. Unfortunately, the salt (e.g., calcium chloride, potassium acetate or their solutions with glycol) may precipitate in the tower and build up the plates or pipelines due to the limited salt solubility in the lean water composition range. Therefore, new alternative substitutes need to be explored to facilitate the separation process.

Ionic liquids (ILs), an neoteric class of solvents comprised of neutral and ionic entities, have been proved to be applicable in extractive distillation of some mixtures with close boiling points or azeotropes [2], [3], [4], which can be ascribed to their unique properties, namely, negligible volatility, wide liquid region, lower corrosiveness, and tuneable solvating capacity for polar and non-polar compounds [5]. These properties largely lie in their ionic attributes and strong electrostatic interaction among ionic species as well as short range interaction among organic groups. From the point of view of structure and composition, ILs are generally regarded as a class of transition substances from a typical electrolyte to non-electrolyte, which provide us an opportunity to study the thermodynamics of electrolyte and non-electrolyte solutions in a continuum approach.

A number of ILs reported show a promising salting effect on vapour liquid equilibria (VLE) of the azeotropes, e.g., (water + ethanol) mixture [6], [7], [8], [9], wherein the VLE data are of great importance in understanding the interactions between different ILs and solvents, as well as in developing thermodynamic models, and accordingly guiding the design of a separation process. By far, a great many of VLE data have been reported, however, the vapour pressure data for the IL-containing mixtures are still quite scarce in comparison with the huge amount of IL species. In our group, a series of VLE data have been reported for (water + methanol + ethanol) systems containing an imidazolium- or alkanolammonium-based IL [10], [11], [12], [13], [14]. To our understanding, certain ILs with hydroxyl-substituted ammonium cations are of potential applicability and superior to others in terms of their ability of solvating with polar or nonpolar solvents and hydrogen bonding ability with water and alcohols, and more importantly their ease of production and low cost for industrial applications [15].

In this work, we present a novel kind of alkanolammonium-based ILs, namely, mono-ethanolammonium formate ([HMEA][HCOO]) and di-ethanolammonium formate ([HDEA][HCOO]) that are noteworthy for their ease of production, cheapness, and least corrosive to the steel. We measured the vapour pressures for the IL-containing pseudo-binary mixtures of (water + ethanol), (water + methanol), and (methanol + ethanol), respectively, with fixed IL mass fraction of 0.30 and within the temperature ranges of (292.12 to 371.13) K, and the results were correlated with the nonelectrolyte NRTL model. Further, the salt effects of ILs on VLE of (water + ethanol) and (methanol + ethanol) mixtures, were investigated and compared with other ILs in terms of the predicted results of the x′–y phase diagrams based on the fitted binary NRTL parameters.

Section snippets

Materials

The chemicals used for synthesising ILs [HMEA][HCOO] and [HDEA][HCOO] are monoethanolamine (MEA, w ⩾ 0.990), diethanolamine (DEA, w ⩾ 0.990), and formic acid (aqueous solution, w ⩾ 0.880), all of which are AR grade, purchased from Tianjin FuChen Chemical Reagents Factory, China, and used as received. The solvents of methanol and ethanol were supplied by Beijing Chemical Plant, China, both of which were dried over 48 h with the activated fresh molecular sieves ZMS-4 and degassed ultrasonically prior to

Vapour pressure measurement

Vapour pressure measurements were carried out for six ternary systems using a quasi-static ebulliometer method within the temperature ranges of (292.12 to 371.13) K, wherein the ternary systems are {water (1) + ethanol (2) + IL (3)}, {water (1) + methanol (2) + IL (3)}, and {methanol (1) + ethanol (2) + IL (3)} containing one of two ILs (viz. [HMEA][HCOO] and [HDEA][HCOO]) with differing mass fractions of component 2 (namely, ethanol or methanol, $x_{2}^{'}$ = 0.95, 0.75, 0.50, 0.25, and 0.05, respectively) and fixed

Conclusions

Vapour pressure measurements were conducted using a quasi-static ebulliometer for the pseudo-binary systems of (water + ethanol), (water + methanol), and (methanol + ethanol) containing one IL, namely, [HMEA][HCOO] or [HDEA][HCOO], respectively. The experimental data were correlated using the nonelectrolyte NRTL model. The alkanolammonium formates show a remarkable salt effect on the VLE behaviour of the (water + ethanol) azeoptrope and the close boiling mixture of (methanol + ethanol) as indicated by

Acknowledgements

The authors are grateful to the financial support from National Natural Science Foundation of China (21076005) and Research Fund for the Doctoral Program of Higher Education of China (20090010110001).

References (34)

C.A. Cardona et al.
Bioresour. Technol.
(2007)
A.B. Pereiro et al.
J. Chem. Thermodyn.
(2012)
R. Kato et al.
Fluid Phase Equilib.
(2005)
Y. Ge et al.
J. Chem. Thermodyn.
(2008)
J. Zhao et al.
Fluid Phase Equilib.
(2006)
X. Jiang et al.
J. Chem. Thermodyn.
(2007)
J.F. Wang et al.
Fluid Phase Equilib.
(2007)
C. Shen et al.
J. Chem. Thermodyn.
(2011)
C. Shen et al.
Fluid Phase Equilib.
(2011)
N. Bicak
J. Mol. Liq.
(2005)

Y. Xu et al.

J. Chem. Thermodyn.

(2004)

M. Doker et al.

Fluid Phase Equilib.

(2005)

M. Iglesias et al.

J. Chem. Thermodyn.

(2008)

M. Seiler et al.

AIChE J.

(2004)

D. Zhang et al.

Ind. Eng. Chem. Res.

(2008)

K. Marsh et al.

Korean J. Chem. Eng.

(2002)

J. Zhao et al.

J. Chem. Eng. Data

(2006)

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Effect of alkanolammonium formates ionic liquids on vapour liquid equilibria of binary systems containing water, methanol, and ethanol

Abstract

Introduction

Section snippets

Materials

Vapour pressure measurement

Conclusions

Acknowledgements

Bioresour. Technol.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Mol. Liq.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Thermodyn.

AIChE J.

Ind. Eng. Chem. Res.

Korean J. Chem. Eng.

J. Chem. Eng. Data