Volumetric and viscometric properties of binary and ternary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate, monoethanolamine and water
Graphical abstract
Introduction
In past decades, the capture of carbon dioxide has received increasing attention and accordingly become a hot topic to prevent from greenhouse effect induced mainly by the emission of carbon dioxide [1]. Alcohol amine solvents, such as monoethanolamine (MEA), methyldiethanolamine (MDEA), diethanolamine (DEA), etc., or their mixtures, have been found to have high absorption efficiency for CO2. However, the volatile problem is not negligible in industrial processes [2], [3]. In recent years, the interest in the chemical and industrial application of ionic liquids as green solvents has remarkably increased due to their great advantages over other volatile organic solvents [4], [5], such as those with a wide liquid range, low melting point, high solubility with polar and non-polar substances, and high thermal stability, etc. It has been found that some ionic liquids (ILs), especially the imidazolium-based ionic liquids with the amino group, have high absorption capacity of carbon dioxide [6], and thereby motivate extensive interests of scientists [7]. To be more effective, the mixed solutions of alcohol amine and ionic liquid with higher absorption efficiency, antioxidant activity, lower loss rate of alcohol amines and easy regeneration were adopted [8], [9].
The compound 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) is mutually soluble with monoethanolamine (MEA) at all proportions. However, both [Bmim][BF4] and MEA have higher viscosity, which is not conducive to the two-phase flow and absorption of CO2. Therefore, water is usually added into the {[Bmim][BF4] + MEA} solution to decrease the viscosity of the absorbent [10].
A knowledge of the thermodynamic properties of pure components as well as their mixtures with other compounds is essential for the design, scale up, and optimization of the industrial equipment. At present, a large quantity of studies on the thermodynamic properties of pure ionic liquids has been reported in the literature [11], [12], [13]. However, the studies on the physicochemical properties of ionic liquid and alcohol amine mixed aqueous solutions remain lacking. Zhou et al. [14] calculated the excess molar volume VE and viscosity deviation Δη for binary system {[Bmim][BF4] + H2O}. Taib et al. [15], [16] measured and calculated the densities, refractive indices, and the excess molar volumes of the binary mixtures {[Bmim][BF4] + H2O}, {[Bmim][BF4] + MEA} and the ternary mixture {[Bmim][BF4] + MEA + H2O}. Except for the properties of density and viscosity for the solution, the excess partial molar volume, excess partial molar volume in infinite dilute solution and excess Gibbs energy of activation of viscous flow are also helpful to characterize the molecular structures and interactions between molecules in solution, and they are also important to solve the chemical engineering problems including heat/mass transfer and fluid flow.
The aim of this work is to conduct a systematic study on the volumetric and viscometric properties of the binary and ternary systems of [Bmim][BF4], MEA and H2O. The densities and viscosities of binary and ternary mixtures were measured at temperature T = (293.15–333.15) K, and the volumetric and viscometric properties, such as excess molar volume VE, viscosity deviation Δη, and excess Gibbs energy of activation of viscous flow ΔG∗E for all mixtures, and apparent molar volume, partial molar volume, excess partial molar volume, excess partial molar volume in infinite dilute solution and Grunberg-Nissan interaction parameter G12 [17] for all binary mixtures, were calculated from experimental data. The results are useful in the industrial applications of ionic liquid/alcohol amine aqueous solutions and optimizations of absorption process and equipment.
Section snippets
Materials
1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) was obtained from Henan Lihua Pharmaceutical Co. Ltd, China, and was dried at 333.15 K for at least 12 h under vacuum. The Water content was analysed by Karl Fisher. The monoethanolamine was obtained from Aladdin Chemical Reagent Co. Ltd, China, without further purification before use. And the water (Its conductivity is 1.04 μs·cm−1 at 293.15 K) used in the experiment was obtained from Hangzhou Wahaha Group Co. Ltd, China. The specific
Results and discussion
Table 2 lists the densities and viscosities of the pure components determined in this work. The relative deviation of density or viscosity between experimental and the literature values could be calculated as follows:where Y represents ρ or η, the Yexp and Ylit are the viscosity values of the experiments and the literature, respectively. The comparison of experimental densities with those in the literature is depicted in Fig. 1. It is observed that the relative deviation
Conclusions
The experimental densities and viscosities for the binary {[Bmim][BF4] (x1) + H2O (x2)}, {[Bmim][BF4] (x1) + MEA (x2)}, {MEA (x1) + H2O (x2)} and ternary mixtures {[Bmim][BF4] (x1) + MEA (x2) + H2O (x3)} were measured at T = (293.15–333.15) K. The volumetric and viscometric properties, such as VE, Δη, ΔG∗E for all mixtures, and Vϕ, , , and Grunberg-Nissan interaction parameters G12 for binary mixtures, were deduced from experimental values.
The volumetric properties for {[Bmim][BF4] (x1) + H2O (x2)}
Acknowledgement
The authors are grateful for the financial supports from the National Natural Science Foundation of China (Nos. 21576186, 91434204, and 21306127).
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