Article pubs.acs.org/jced
Densities, Viscosities and Excess Properties of Binary Mixtures of 1,1,3,3-Tetramethylguanidinium Lactate + Water at T = (303.15 to 328.15) K Shidong Tian,† Shuhang Ren,† Yucui Hou,‡ Weize Wu,*,† and Wei Peng† †
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China Department of Chemistry, Taiyuan Normal University, Taiyuan 030031, China
‡
S Supporting Information *
ABSTRACT: Densities and viscosities of 1,1,3,3-tetramethylguanidium lactate ([TMG]L) (1) + H2O (2) with different compositions were determined at temperatures from (303.15 to 328.15) K. Densities of [TMG]L (1) + H2O (2) decrease with the increase of temperature. However, when the mole fraction of water is lower than 0.5, the water content does not have an obvious influence on the density of [TMG]L. When the mole fraction of water is greater than 0.5, the densities of [TMG]L (1) + H2O (2) decrease obviously with further increasing the mole fraction of water. Viscosity of [TMG]L decrease dramatically with the increase of temperature and the water content. Excess molar volumes (VE) and viscosity deviations (Δη) of the binary mixtures were calculated by the experimental data and fitted to the Redlich−Kister equation with four parameters. The result shows that the values of VE and Δη for the binary mixtures are negative over the whole composition range and temperatures from (303.15 to 328.15) K. The negative of the excess properties indicates a strong interaction between the ionic liquid and water. The partial molar volumes (V̅ i), excess partial molar volumes (V̅ Ei ), Gibbs energy of activation for viscous flow (ΔG*), and excess Gibbs energy of activation for viscous flow (ΔG*E) of the binary mixtures were also calculated based on the densities and viscosities data. Besides, the Jouyban−Acree model was used to correlate the densities and viscosities of the binary mixtures with respect to the mixture composition and temperature simultaneously.
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[TMG][POBF4], and [TMG][PO2BF4], were also reported.15,16 A series of hydroxyl ammonium ILs such as monoethanolaminium lactate ([MEA]L) were synthesized by Zhang et al., and high SO2 absorption capacities were found in these ILs.17 Other types of ILs such as imidazolium-based,18,19 pyrimidiniumbased,19 ether-functionalized imidazolium-based,20 and caprolactam tetrabutyl ammonium bromide21 ILs were also studied for the removal of SO2. As we know, there is a large amount of water or moisture, such as 8 % to 20 %, in flue gas.22 When ILs are exposed to flue gas with a certain amount of water, they may absorb water from flue gas due to their hydrophilicity. It is reported that [TMG]L absorb not only SO2 but also H2O from flue gas, and interestingly the absorbed water in IL has no influence on the absorption capacity of SO2 and can decrease greatly the viscosity of IL, which is much beneficial to the transportation of the IL system.23 Therefore, ILs with proper amounts of water may be excellent absorbents for the removal of SO2. The physical properties of the IL and water binary mixtures are very important basic data, which are essential for designing the equipment with new absorbents.24,25 As far as
INTRODUCTION Sulfur dioxide (SO2), which is mainly emitted from the burning of fossil fuel, has caused serious environmental pollution. It is well-known that flue gas desulfurization (FGD) is the most efficient way to control the emission of SO2 to date.1−7 Among FGD technologies, wet scrubbing using calcium-based absorbents is the most widely used for the removal of SO2 all over the world. However, there is a large amount of waste such as calcium sulfate produced in these processes. Amines are usually used to trap acidic gases such as SO2 and CO2 efficiently,8−11 but the loss of amines due to their high volatility causes secondary environmental pollution. As a result, recyclable liquid solvents with low volatility and high capacity should be taken into consideration. For their excellent properties,12,13 such as extremely low vapor pressure, tunable structure, and high gas solubility, ionic liquids (ILs) may be promising absorbents for the capture of SO2. Recently, many groups have studied the absorption of SO2 by different kinds of ILs. 1,1,3,3-Tetramethylguanidinium lactate ([TMG]L) is the first task-specific IL used for the absorption of SO2 reported by Han et al.14 They found that [TMG]L had a high capacity even though the content of SO2 was only 8 % by volume. Other ILs based on 1,1,3,3-tetramethylguanidinium, such as [TMG][BF4 ], [TMG][BTA], [TMGB 2 ][BTA], © XXXX American Chemical Society
Received: December 1, 2011 Accepted: May 23, 2013
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dx.doi.org/10.1021/je3009073 | J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Viscosity Measurements. Viscosities of pure chemicals and binary mixtures were determined by gravitational capillary viscometers, which are supplied by Shanghai Shenyi Glass Instrument Co. Ltd. (Shanghai, China), in the same water bath, and the temperature was controlled and measured in the same way as mentioned in the density measurements. In this experiment, we measured the flow time of a given volume of liquid by a digital stopwatch with a precision of 0.01 s. The absolute viscosity (η) was calculated from the viscometer constants, the running time of the liquid, and the density of the liquid. The uncertainty of the viscosity measurement was estimated to be ± 2 %.
we know, [TMG]L is one of the most promising ILs which may be used in practice, and many researches have been done on [TMG]L experimentally or theoretically.14,23,26−31 But few studies26,30,32 report the physical properties of [TMG]L and none on the binary systems of [TMG]L with water. In this paper, densities and viscosities of [TMG]L (1) + H2O (2) were measured at temperatures from (303.15 to 328.15) K and different compositions, and excess molar volumes (VE) and viscosity deviations (Δη) of the binary mixtures were calculated based on the experimental data. The partial molar volumes (V̅ i), excess partial molar volumes (V̅ Ei ), Gibbs energy of activation for viscous flow (ΔG*), and excess Gibbs energy of activation for viscous flow (ΔG*E) of the binary mixtures were also calculated based on the densities and viscosities data. Besides, the Jouyban− Acree model was used to correlate the densities and viscosities of the binary mixtures with respect to the mixture composition and temperature simultaneously.
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RESULTS AND DISCUSSION Table 1 shows the density and viscosity of pure [TMG]L at 318.15 K measured in our work and the available literature data.
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Table 1. Comparison of the Densities, ρ, and Viscosities, η, of [TMG]L at T = 318.15 K and p = 101 kPa with Literature Data
EXPERIMENTAL SECTION Chemicals. N2 with a purity of 99.95 % volume fraction was purchased from Beijing Haipu Gases. 1,1,3,3-Tetramethylguanidine was obtained from Baigui Chemical Company (Shijiazhuang, China), which was distilled before use. The purity was confirmed by gas chromatography, which showed that the mass fraction purity was better than 99 %. Analytical reagent monoethanolamine from Aladdin Chemistry Co. Ltd. (Shanghai, China) with a mass fraction purity of 99.0 % and lactic acid with a mass fraction of 85 % in water were obtained. [TMG]L used in this work was synthesized following a previous literature method.32 After removing large amounts of solvents by a rotary evaporator at 343.15 K, we purified the IL by a nitrogen sweeping method33 (with 10 cm3·min−1 N2 per gram IL at 348.15 K for 12 h) instead of a harsh drying technique. The traditional method usually needs a very long time (such as from 24 h to 48 h) under vacuum and may cause subsidiary reactions. The water content in the IL was determined by Karl Fischer titration, and the mass fraction of water was less than 0.1 % for the IL. The structure of the IL was confirmed by 1H NMR (Bruker AM 600 MHz spectrometer, D2O), which was consistent with the literature (see Figure S1 in the Supporting Information). Water used in this work was deionized, and its conductivity was less than 1.5 μS·cm−1 at 298.15 K. All of the samples were fresh prepared by mass on an analytical balance with an accuracy of 0.1 mg. The uncertainty in the mole fraction of the mixtures was estimated to less than ± 0.0001. The samples were stored in a desiccator to avoid any effect of atmospheric humidity. Density Measurements. Densities of pure chemicals and binary mixtures were determined using pycnometers with volume of 5 cm3, which were calibrated by pure water before the experiment. The densities of pure water were obtained from NIST Chemistry Webbook. A constant temperature water bath which was maintained within ± 0.1 K by using a temperature controller (model A2, Beijing Changliu Scientific Instrument Co. Ltd., China) was used to control the experiment temperature. The temperature was also monitored by a precision mercury thermometer that had a maximum uncertainty of ± 0.05 K. Densities of [TMG]L (1) + H2O (2) were measured at T = (303.15 to 328.15) K at an interval of 5 K. All of the measurements were carried out at least three times, and the average values were the final results. The uncertainty of the density measurement was estimated to be ± 0.0002 g·cm−3.
IL
ref 26
[TMG]L
Ren et al. Wang et al.30 Gao et al.32 this work this work
WH2O/%
ρ/g·cm−3
η/mPa·s
3.15
1.08 1.10 1.07 1.1143 1.1149a
4.18·102
