Vapor–Liquid Equilibrium Measurements of NH3 + H2O + Ionic Liquid

Article pubs.acs.org/jced

Vapor−Liquid Equilibrium Measurements of NH3 + H2O + Ionic Liquid ([Dmim]Cl, [Dmim]BF4, and [Dmim]DMP) Systems Weijia Huang, Guangming Sun, Danxing Zheng,* Li Dong, Xianghong Wu, and Juan Chen College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China ABSTRACT: The isothermal synthesis method is used to investigate the vapor−liquid equilibrium (VLE) data of the ammonia (NH3) + water (H2O) + ionic liquid (IL) ternary system at the temperature of 313.15 K and the pressure of (0 to 0.6) MPa. The 3 ILs are 1,3dimethylimidazolium tetrafluorobrorate ([Dmim]BF4), 1,3-dimethylimidazolium chloride ([Dmim]Cl) and 1,3-dimethylimidazolium dimethyl phosphate ([Dmim]DMP), respectively, and the ratio of mass (rm) of IL/ H2O is 3/4. In addition, the densities of the three binary systems, namely, the H2O + [Dmim]DMP (rm = 1/2, 3/4) at 293.15 K, 313.15 K, and 333.15 K, the H2O + [Dmim]Cl (rm = 3/4) and H2O + [Dmim]DMP (rm = 3/4) at 313.15 K have been measured at atmospheric pressure, respectively. The VLE of the NH3 + H2O + [Dmim]DMP ternary system (rm = 1/2, 3/4) are measured at 293.15 K, 313.15 K, and 333.15 K with the pressures ranging from (0 to 0.6) MPa. Finally, an analytical polynomial equation is used to fit the experimental data.

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crystallization problem.8 Generally, the proportion of the additive in the mixture should be not more than that of NH3, because the additive is just an assistant material to facilitate the separation of NH3 and H2O; however, some researchers did not take notice of that.4,5,9 Ionic liquids (ILs) have unique characteristics, such as ignorable vapor pressure, high heat stability, nontoxicity, and being environmentally friendly.11 Some room temperature ionic liquids are similar to inorganic salt in properties which are helpful in the separation of the NH3 + H2O system. Owing to the diversity of chemical structure, systems including IL are generally superior to those including inorganic salt regarding the corrosivity and crystallization. The main factors influencing the hydrophilicity of ILs are the structure and types of organic cationic, the length of molecular side chains, and the anionic species. For imidazoles ILs, the hydrophilicity of ILs increases with the shortening of the molecular side chain. Furthermore, the smaller the anionic is, the stronger the hydrophilic will be.11−13 On the basis of investigating the dissolving capacity of NH3 within the NH3 + H2O system, highly hygroscopic ILs are chosen as additives in this work, including [Dmim]Cl, [Dmim]BF4, and [Dmim]DMP. According to our previous works,11,21 it is expected that when this kind of IL is added into the NH3 + H2O system, some H2O will be attracted by ILs, weakening the interaction between NH3 and H2O, which is helpful in the removal of NH3 from the water solution. The isothermal synthesis method14 has been adopted to obtain experimental VLE data in this work owing to its

INTRODUCTION As a traditional working fluid, the mixture of NH3 and H2O plays an important role in absorption heat pump cycles, and has been drawing researcher’s attention in many more new applications, for example, modern power generation cycles.1 The NH3 + H2O system possesses perfect characteristics of heat transfer and mass transfer, but some of its thermophysical properties, such as vapor−liquid equilibrium property, should be improved, because the mixture is difficult to separate to pure species, and the separation requires a great amount of heat consumption in a rectification process.2 People found that adding ILs into the NH3 + H2O system could weaken the strong affinity between NH3 and H2O, making it easier to release NH3 from the liquid. Therefore, several new sets of working fluids have been proposed as alternatives in the past decades. Both Mclinden et al.3 and Peters et al.4,5 measured the VLE data of the NH3 + H2O + LiBr system. Cacciola et al.6 measured the VLE data of the NH3 + H2O + KOH system. Daniel et al.7 not only measured the VLE data of the NH3 + H2O + KOH system, but measured that of the NH3 + H2O + NaOH system, which was also researched by Fred et al.8 Simona et al.9 investigated the VLE data of the NH3 + H2O + LiNO3 system. Meanwhile, Vinay et al.2 simulated the VLE behavior of the NH3 + H2O + salt system. The above-mentioned research results show that adding salt is helpful for the removal of the ammonia from the solution. Although much work has been done, there is still much innovation opportunity to improve the performance of the NH3 + H2O + additive ternary systems. One thing that has to be taken into account is that adding LiBr to NH3 + H2O solution will cause a serious corrosion problem and increase the viscosity of solvent.10 Also, adding NaOH or KOH to the NH3 + H2O solution will cause a serious © 2013 American Chemical Society

Received: February 1, 2013 Accepted: April 1, 2013 Published: April 10, 2013 1354

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advantages of good seal performance, without sampling test, short measuring time and simple operation, and it is appropriate for the VLE data measurement under higher pressure.15 The specified experimental conditions of the ternary NH3 + H2O + ILs system (rm = 3/4) were [Dmim]BF4, [Dmim]Cl and [Dmim]DMP at 313.15 K and pressure up to 0.6 MPa. In addition, the densities of H2O + [Dmim]DMP (rm = 1/2, 3/4) at temperatures (293.15, 313.15, and 333.15) K, H2O + [Dmim]Cl (rm = 3/4) and H2O + [Dmim]DMP (rm = 3/4) at 313.15 K binary systems have been measured at atmospheric pressure, respectively. The VLE data of NH3 + H2O + [Dmim]DMP ternary system (rm = 1/2, 3/4) has been investigated at temperatures 293.15 K, 313.15 K, and 333.15 K and pressures up to 0.6 MPa. Then, the experimental vapor pressure data have been correlated with temperature and mole fraction using an analytical polynomial equation.

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EXPERIMENTAL SECTION Materials. NH3 was supplied by Beijing Hengyuantong Gas Limited Company, and its purity is better than 99.999 % in mass fraction. The deionized water was obtained from Beijing University of Chemical Technology. [Dmim]BF4 was supplied by Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences. Its purity is better than 99 % in mass fraction. The molecular formula is C5H9N2BF4, and the molecular weight is 183.97. [Dmim]Cl was prepared and purified in the laboratory according to a method described in the literature,11 and the mass purity was higher than 99.4 % in mass fraction by differential scanning calorimetry (DSC). The molecular formula is C5H12N2Cl and the molecular weight is 132.59. [Dmim]DMP was purchased from Shanghai Chengjie Chemical Co., Ltd. Its purity is not less than 99 % in mass fraction. The molecular formula is C7H15N2O4P and the molecular weight is 222.18. To control the water content, the IL materials used in this work have been treated by means of the vacuum drying for three hours before each measurement. Measurement. The experimental apparatus and procedures adopted in this work were meticulously described in our previous work15 with a few modifications, which were based on the works of Fischer et al.16,17 As illustrated in Figure 1, the system mainly consists of a stainless steel equilibrium cell, of which the volume is VE = 332.89 mL, a NH3 injection system including gas chamber, of which the volume is Vg = 4216.8 mL, a temperature control system and a set of vacuum systems. An isothermal water bath is used to thermostat the equilibrium cell, and a magnetic stirrer is used to accelerate the equilibrium in the cell. The temperature stability of the equilibrium cell and the isothermal water bath is ± 10 mK using a controller designed by Julabo Labortechnik GmbH. The temperature of the gas chamber is measured with PT100 resistance thermometers (273.15 K to 373.15 K) and the measurement error is ± (0.10 + 0.0017|t|) K. The pressure of the equilibrium cell and gas chamber is measured with a PTX7517 pressure sensor (0 MPa to 6 MPa), of which the maximum error is 0.025 % full scope, and was manufactured and calibrated by Ge Druck. The mass of the ILs placed into the equilibrium cell was measured by a Mettler Toledo PL2002IC balance with an error of ± 10−2 g. The density of H2O + [Dmim]DMP binary system was obtained by an Anton Paar DMA 55 digital vibrating-tube densimeter with an error of ± 10−5 g·cm−3.

Figure 1. The isothermal synthetic schematic apparatus diagram: 1, gas chamber; 2, circulation pump; 3, ammonia storage; 4, isothermal water bath; 5, stainless steel buffer; 6, vacuum pump; 7, buret; 8, overhead stirrer; 9, equilibrium cell; 10, temperature controller; 11, magnetic stirrer; 12, ceramic heater band; 13, resistance thermometer; 14, reducing valve; 15, valve.

The experimental uncertainties were assessed as follows: DMA 55 digital vibrating-tube densimeter, 1.041·10−4 g·cm−3; pressure of the equilibrium cell, 8.75·10−4 MPa; pressure of the gas chamber, 8.75·10−4 MPa; volume of the equilibrium cell, 0.075 mL; volume of the gas chamber, 0.204 mL; mass of solvent, 0.007 g; temperature in the equilibrium cell, 0.117 K; temperature in the gas chamber, 0.083 K; buret, 0.029 mL. Apparatus Reliability Validation. To validate the reliability of the above experimental apparatus, the solubilities of NH3 in water were determined at (293.15, 313.15, and 333.15) K, respectively. The results were compared with available data19,20 as shown in Table 1. The maximum absolute Table 1. Comparison of Measured Solubilities for the System NH3 + H2O with Literature Valuesa

a

T/K

lit.

p/MPa

x1,lit.

x1,expt

|x1,expt − x1,lit.|/x1,lit. (%)

293.15

Smolen [19]

313.15

Gillespie [20]

333.15

Gillespie [20]

0.133 0.250 0.537 0.071 0.143 0.501 0.071 0.155 0.301

0.398 0.501 0.700 0.190 0.281 0.498 0.097 0.191 0.283

0.418 0.487 0.702 0.177 0.294 0.501 0.103 0.183 0.277

5.03 2.79 0.29 6.84 4.63 0.60 6.19 4.19 2.12

u(T) = 0.08 K, u(p) = 0.0013 MPa, and u(x) = 0.001.

relative deviations are 5.03 %, 6.84 %, and 6.19 % corresponding to temperature 293.15 K, 313.15 K, and 333.15 K, respectively, and the average absolute relative deviations are correspondingly 2.70 %, 4.02 %, and 4.16 %. It was shown that the data measured in this work were consistent with literature data and indicated that the experimental apparatus was reliable and practicable. 1355

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Figure 2. Flowchart for x1 calculation.

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RESULTS AND DISCUSSION The solubility data x1 (the mole fraction in the entire mixture) is calculated by the method shown in Figure 2. In which, TA and p1A are the initial temperature and pressure of the gas chamber, respectively, TB and p1B are the temperature and pressure of the gas chamber after NH3 injection, respectively, T is the equilibrium temperature of the cell, m3 is the mass of IL, and V2 is the volume of deionized water added to the cell. M3 is the formula weight of ILs. M2 is the formula weight of water, ρ2 denotes the density of water at T0, both of which can be obtained from the literature.18 Vv is the volume of vapor phase in the stainless steel equilibrium cell, Vv = VE − Vmix, Vmix = (m3 + ρ2V2)/ρmix, ρmix stands for the density of the mixture H2O-IL at atmosphere pressure (the values are listed in Table 2) which

[Dmim]BF4 (rm = 3/4), and NH3 + H2O + [Dmim]DMP (rm = 3/4) ternary systems were determined at 313.15 K and at pressures increasing from 0.092 MPa to 0.607 MPa. The experimental results were listed in Table 3 and plotted in Figure 3. Figure 3 illustrates the relationship between the experimental pressures versus the phase equilibrium ratio K1 of NH3 in the ternary systems. The result exhibits that K1,NH3+H2O+[Dmim]BF4 < K1,NH3+H2O < K1,NH3+H2O+[Dmim]Cl < K1,NH3+H2O+[Dmim]DMP under the same pressure. It indicates that the capacity of removing NH3 from water can be improved by means of adding [Dmim]Cl or [Dmim]DMP into NH3 + H2O binary system. The choice of [Dmim]DMP, [Dmim]Cl, or [Dmim]BF4 as additives is reasonable to aid the removal of ammonia from water. In this respect, Figure 3 shows that the effect of adding [Dmim]DMP is superior to adding [Dmim]Cl or [Dmim]BF4, that is, [Dmim]DMP is a relatively optimal option among the three ILs for adjusting the interaction between NH3 and H2O. On consideration of the above results and analyses, we have measured the solubility data of NH3 in the NH3 + H2O + [Dmim]DMP ternary systems (rm = 1/2, 3/4) at temperatures (293.15, 313.15, and 333.15) K and at the pressures up to about 0.6 MPa, as listed in Table 4. For an NH3 + H2O + additive ternary system, the following analytical polynomial equation is applicable to fit the experimental data, which is similar to that proposed by Daniel et al.7,9 except that the description of the mass fraction has been replaced by the mole fraction.

Table 2. Experimental Values of Densities ρmix for the System H2O + IL at Pressure p = 0.1 MPaa T/K 293.15 313.15 333.15

313.15 313.15 a

ρmix/g·cm−3

rm [Dmim]DMP/H2O 1/2 3/4 1/2 3/4 1/2 3/4 [Dmim]Cl/H2O 3/4 [Dmim]BF4/H2O 3/4

1.0864 1.1123 1.0768 1.1041 1.0766 1.1033 1.0961

ln(p/kPa) = A 0 + A1x1 + A 2 x12 + A3x13

1.0984

−3

u(T) = 0.06 K, u(ρmix) = 0.0002 g·cm , and u(ω) = 0.001.

+

was measured by an Anton Paar DMA 55 digital vibrating-tube densimeter, p2 and p1 are the partial pressures of water and ammonia in the vapor phase, respectively. nV1 and nl1 express the amount of substance of ammonia in vapor phase and liquid phase, respectively. nV2 and nl2 are the amount of substance of water in vapor phase and liquid phase, respectively. The Peng−Robinson (PR) equation of state has been selected in the researches of Enick et al.22 and Bombarda et al.23 for the NH3 + H2O system. To the limitation of measurement conditions of temperature and pressure in this work, the PR equation of state has been adopted to regress the experimental data. The uncertainties of solubility were calculated with the method in our previous work,15 and were listed in the data tables. The experimental data for the NH3 + H2O binary system, the NH3 + H2O + [Dmim]Cl (rm = 3/4), NH3 + H2O +

B0 + B1x1 + B2 x12 + B3x13 T /K

2

Ai =

(1)

2

∑ aijx3j ,

Bi =

j=0

∑ bijx3j

with

i = 0, 1, 2, 3

j=0

(2)

In eq 2 the coefficients aij and bij are regressed by the “leastsquares” method upon the experimental data, and the values of aij and bij for NH3 + H2O + [Dmim]DMP ternary system are listed in Table 5. The results of the parameters calculation can be regarded as deviations of the calculated pressure and the experimental pressure for each system. The average deviation Δp can be described as Δp = 1356

1 Np

Np

∑ |pcalc, i i=1

− pexpt , i |

(3)

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Table 3. Experimental (Vapor + Liquid) Equilibrium Data for Temperature T, Pressure p, Liquid−Phase Mole Fraction x, and Gas−Phase Mole Fraction y, for the Systems NH3 (1) + H2O (2) and NH3 (1) + H2O (2) + ILs (3) (rm = 3/4)a T/K

p/MPa

x1

δx1

y1

δy1·104

K1b

δK1

1.189 1.678 1.978 2.180 2.429 2.627

4.818 3.038 2.474 2.231 2.009 1.856

0.168 0.070 0.045 0.032 0.023 0.018

0.903 1.078 1.178 2.680 2.173 2.417

5.245 3.433 2.814 2.458 2.205 2.007

0.188 0.081 0.072 0.042 0.029 0.018

0.933 1.085 1.191 2.667 2.183 2.517

4.034 2.886 2.453 2.197 2.008 1.857

0.138 0.064 0.045 0.037 0.017 0.008

5.880 3.925 3.005 2.578 2.325 2.125

0.321 0.124 0.066 0.045 0.032 0.025

NH3 + H2O

a

313.15 313.15 313.13 313.13 313.16 313.14

0.099 0.218 0.309 0.373 0.473 0.569

0.205 0.325 0.400 0.445 0.494 0.535

313.15 313.17 313.14 313.13 313.15 313.16

0.092 0.201 0.311 0.402 0.506 0.607

0.168 0.281 0.358 0.405 0.454 0.498

313.16 313.14 313.15 313.15 313.13 313.15

0.113 0.199 0.278 0.392 0.477 0.584

0.248 0.334 0.390 0.448 0.486 0.530

313.14 313.13 313.15 313.15 313.16 313.15

0.111 0.206 0.307 0.397 0.481 0.576

0.167 0.252 0.331 0.386 0.428 0.469

0.009 0.985 0.007 0.989 0.007 0.990 0.006 0.991 0.005 0.993 0.005 0.994 NH3 + H2O + [Dmim]Cl 0.010 0.939 0.008 0.974 0.007 0.983 0.006 0.989 0.006 0.991 0.005 0.993 NH3 + H2O + [Dmim]BF4 0.007 0.943 0.006 0.976 0.005 0.985 0.005 0.989 0.004 0.992 0.004 0.994 NH3 + H2O + [Dmim]DMP 0.010 0.980 0.009 0.989 0.008 0.993 0.007 0.994 0.006 0.996 0.006 0.996

83.01 10.44 11.61 18.57 22.05 23.65

u(T) = 0.08 K, u(p) = 0.0013 MPa, and u(x) = u(y) = 0.001. bThe phase equilibrium ratio of species NH3:K1 = y1/x1

Figure 4, and the relative deviations (pcacl − pexpt)/pexpt between the experimental and calculated pressure are shown in Figure 5. It can be found that most of the relative deviations in this work are within ± 5.0 %, which are less than ± 5.0 % and ± 10.0 % in the literatures,7,9 respectively. The maximum absolute value of relative deviation is 6.1 % and the average absolute relative deviation is 2.1 %. Within the temperature and pressure regions studied in this work, it can be seen obviously that the solubility of NH3 consistently increases with the increase of pressure at a given temperature. However, as the addition of [Dmim]DMP, the changing of phase equilibrium ratio is opposite to that of solubility at the same temperature and pressure, the order respectively is x 1,NH3+H2O+[Dm im ]DM P (r m = 3/4) < x1,NH3+H2O+[Dmim]DMP (rm = 1/2) < x1,NH3+ H2O, K1,NH3+H2O < K1,NH3+H2O+[Dmim]DMP (rm = 1/2) < K1,NH3+H2O+[Dmim]DMP (rm = 3/4). Owing to the good hydrophilicity of [Dmim]DMP, it would draw H2O from NH3 when added into the NH3 + H2O system, leading to the escape of some NH3 from the liquid phase to the vapor phase; therefore, the phase equilibrium ratio of NH3 increased. In an absorption cycle with a working fluid NH3 + H2O system, plenty of energy is consumed in a rectification progress to separate ammonia and water. Moderately adding [Dmim]DMP into the NH3 + H2O system will decrease the energy consumption, but the exact appropriate amount of addition that is necessary should be confirmed due to its high production cost. An added IL to the NH3 + H2O system not only participates in the interaction between H2 O and NH 3

Figure 3. The phase equilibrium ratio of species NH3 in the NH3 + H2O binary system and NH3 + H2O + ILs ternary systems: □, NH3 + H2O; ●, NH3 + H2O + [Dmim]BF4; ■, NH3 + H2O + [Dmim]Cl; ▲, NH3 + H2O + [Dmim]DMP.

where pcalc and pexpt denote the calculated pressure and the experimental pressure, respectively, and Np is the number of experimental points. As a result, the average deviation of pressures in this work is 0.006 MPa. Isothermal p−x1 curves calculated with these parameters for each system are compared with experimental data as shown in 1357

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Table 4. Experimental (Vapor + Liquid) Equilibrium Data for Temperature T, Press p, Liquid−Phase Mole Fraction x, and Gas−Phase Mole Fraction y, for the System NH3 (1) + H2O (2) + [Dmim]DMP (3)a T/K

a

p/MPa

x1

293.15 293.13 293.16 293.17 293.18 293.15 313.15 313.15 313.13 313.13 313.16 313.14 333.15 333.16 333.15 333.15 333.15 333.16

0.100 0.195 0.298 0.371 0.474 0.588 0.099 0.218 0.309 0.373 0.473 0.569 0.108 0.212 0.304 0.398 0.485 0.599

0.340 0.450 0.537 0.590 0.660 0.741 0.204 0.325 0.400 0.444 0.493 0.535 0.163 0.246 0.303 0.352 0.392 0.435

293.16 293.13 293.16 293.17 293.18 293.15 313.14 313.15 313.14 313.13 313.16 313.14 333.16 333.17 333.15 333.14 333.15 333.16

0.107 0.216 0.308 0.382 0.481 0.566 0.109 0.215 0.317 0.407 0.493 0.582 0.112 0.230 0.301 0.391 0.500 0.603

0.259 0.405 0.494 0.558 0.640 0.702 0.181 0.280 0.360 0.414 0.461 0.500 0.127 0.216 0.257 0.299 0.344 0.380

293.15 293.17 293.14 293.17 293.12 293.14 313.15 313.13 313.13 313.15 313.16 313.14 333.15 333.17 333.15 333.14 333.15 333.14

0.092 0.195 0.292 0.392 0.486 0.585 0.111 0.206 0.307 0.397 0.481 0.576 0.142 0.233 0.319 0.399 0.491 0.597

0.212 0.340 0.444 0.537 0.616 0.686 0.167 0.252 0.331 0.386 0.428 0.469 0.142 0.197 0.243 0.279 0.315 0.352

δx1

δx3·104

x3

y1

NH3 + H2O 0.008 0 0 0.992 0.007 0 0 0.994 0.006 0 0 0.996 0.005 0 0 0.996 0.004 0 0 0.996 0.002 0 0 0.997 0.009 0 0 0.985 0.007 0 0 0.988 0.007 0 0 0.990 0.006 0 0 0.991 0.005 0 0 0.992 0.004 0 0 0.993 0.010 0 0 0.973 0.008 0 0 0.977 0.007 0 0 0.981 0.006 0 0 0.984 0.006 0 0 0.985 0.005 0 0 0.986 NH3 + H2O + [Dmim]DMP (rm = 1/2) 0.010 0.028 2.704 0.995 0.009 0.024 2.051 0.995 0.008 0.021 1.488 0.996 0.007 0.018 1.171 0.997 0.006 0.016 8.731 0.997 0.005 0.014 6.790 0.997 0.010 0.031 3.495 0.987 0.008 0.027 2.699 0.990 0.007 0.025 2.220 0.992 0.006 0.023 1.891 0.993 0.006 0.021 1.636 0.996 0.005 0.020 1.420 0.997 0.011 0.034 4.120 0.978 0.009 0.031 3.327 0.982 0.008 0.029 2.983 0.983 0.007 0.027 2.657 0.985 0.007 0.026 2.331 0.987 0.006 0.024 2.079 0.988 NH3 + H2O + [Dmim]DMP (rm = 3/4) 0.013 0.044 4.516 0.995 0.011 0.038 3.376 0.996 0.010 0.033 2.533 0.997 0.008 0.029 1.966 0.997 0.007 0.025 1.485 0.997 0.005 0.022 1.122 0.998 0.010 0.047 5.182 0.980 0.009 0.042 4.157 0.990 0.008 0.038 3.371 0.993 0.007 0.035 2.880 0.995 0.006 0.032 2.452 0.996 0.006 0.030 2.154 0.997 0.011 0.049 5.712 0.982 0.009 0.046 5.011 0.983 0.008 0.043 4.444 0.985 0.008 0.041 4.036 0.986 0.007 0.039 3.641 0.988 0.006 0.037 3.261 0.989

δy1·104

K1

δK1

0.558 0.721 0.853 0.932 1.049 1.183 1.189 1.678 1.978 2.180 2.429 2.627 1.976 3.038 3.786 4.444 5.486 5.824

2.913 2.209 1.854 1.687 1.509 1.345 4.818 3.037 2.473 2.230 2.009 1.856 5.959 3.966 3.234 2.790 2.508 2.262

0.071 0.035 0.021 0.015 0.009 0.004 0.168 0.070 0.045 0.031 0.022 0.017 0.380 0.137 0.087 0.056 0.043 0.032

0.505 0.661 0.816 0.916 1.039 1.143 1.002 1.516 1.866 2.126 2.437 2.541 1.591 2.759 3.316 3.877 4.474 4.962

3.849 2.521 2.034 1.785 1.557 1.422 5.442 3.541 2.755 2.397 2.162 1.993 7.708 4.555 3.823 3.295 2.872 2.599

0.114 0.062 0.036 0.025 0.016 0.011 0.251 0.093 0.055 0.038 0.029 0.023 0.660 0.189 0.121 0.081 0.055 0.041

3.697 5.980 7.663 9.328 1.086 1.216 83.01 10.44 11.61 18.57 22.05 23.65 1.848 25.72 32.01 36.84 41.74 46.71

4.704 2.927 2.246 1.856 1.620 1.455 5.880 3.925 3.006 2.578 2.326 2.125 6.909 5.003 4.047 3.535 3.132 2.808

0.218 0.093 0.052 0.033 0.021 0.014 0.321 0.125 0.066 0.046 0.033 0.026 0.510 0.237 0.139 0.097 0.070 0.051

u(T) = 0.08 K and u(p) = 0.0013 MPa, and u(x) = u(y) = 0.001. 1358

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Table 5. Coefficients of eqs 1, 2 for the NH3 + H2O + [Dmim]DMP System coefficient

value

coefficient

value

coefficient

value

coefficient

value

a00 a01 a02 a10 a11 a12

17.59 −44.99 111.7 −2.896 33.55 19.44

a20 a21 a22 a30 a31 a32

−10.07 −196.0 −806.6 21.08 170.2 1430

b00 b01 b02 b10 b11 b12

−4866 14904 429.5 5268 7023 204.6

b20 b21 b22 b30 b31 b32

−1296 3256 94.21 −4618 1486 50.65

Figure 4. Isothermal p−x1 diagram for NH3−H2O and NH3−H2O− [Dmim]DMP. Experimental results: □, NH3−H2O at 293.15 K; ■, NH3−H2O−[Dmim]DMP (rm = 1/2) at 293.15 K; ⊞, NH3−H2O− [Dmim]DMP (rm = 3/4) at 293.15 K; ○, NH3−H2O at 313.15 K; ●, NH3−H2O−[Dmim]DMP (rm = 1/2) at 313.15 K; ⊕, NH3−H2O− [Dmim]DMP (rm = 3/4) at 313.15 K; Δ, NH3−H2O at 333.15 K; ▲, NH3−H2O−[Dmim]DMP (rm = 1/2) at 333.15 K; crossed triangle, NH3−H2O−[Dmim]DMP (rm = 3/4) at 333.15 K; lines, calculated pressure from eqs 1 and 2.

Figure 5. Relative deviation (pcalc − pexpt)/pexpt between the experimental and calculated pressure: □, NH3−H2O at 293.15 K; ■, NH3−H2O−[Dmim]DMP (rm = 1/2) at 313.15 K; ⊞, NH3−H2O− [Dmim]DMP (rm = 3/4) at 333.15 K.

molecules, but also pulls H2O molecules from the vapor phase to the liquid phase, reducing the energy consumption for rectification.

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[Dmim]DMP ternary system as alternative working fluid studied in this work exhibits a promising prospect to improve the performance of the absorption cycle, and has potential to putting relevant research forward. However, the viscosity of an ionic liquid is much higher than that of water, leading to a certain impact on the absorption kinetics of NH3, and thereby the efficiency of the heat pump will be influenced. It has to be taken into account if engineers want to improve heat pump performance.

CONCLUSION The isothermal synthesis method has been used to obtain VLE data for the NH3 + H2O + IL (rm = 3/4, IL: [Dmim]BF4, [Dmim]Cl, and [Dmim]DMP) ternary systems at temperature 313.15 K and pressures up to 0.6 MPa. The results indicate that [Dmim]DMP is more effective than [Dmim]Cl and [Dmim]BF4 as an additive added to the NH3 + H2O system to overcome the problem of high energy consumption in the absorption cycle. In addition, the densities of the H2O + [Dmim]DMP (rm =1/2, 3/4) binary systems have been measured at temperatures (293.15, 313.15, and 333.15) K and at atmospheric pressure. The densities of H2O + [Dmim]Cl (rm = 3/4) and H2O + [Dmim]BF4 (rm = 3/4) binary systems have been measured at 313.15 K and at atmospheric pressure. Then, using [Dmim]DMP as an additive to the NH3 + H2O system, the VLE data of NH3 + H2O + [Dmim]DMP (rm = 1/2, 3/4) ternary systems have been investigated at (293.15, 313.15, and 333.15) K and at pressures up to about 0.6 MPa. The experimental data of vapor pressure have been correlated with temperature and mole fraction with an analytical polynomial equation. Compared with a traditional working fluid NH3 + H2O system, the NH3 + H2O +

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel./Fax: +86-10-6441-6406. Funding

This work was supported by the National Nature Science Foundation of China (No. 50890184, No. 51276010) and the National Basic Research Program of China (No. 2010CB227304). Notes

The authors declare no competing financial interest. 1359

dx.doi.org/10.1021/je400109a | J. Chem. Eng. Data 2013, 58, 1354−1360

Journal of Chemical & Engineering Data

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Article

(21) Li, J.; Zheng, D.; Fan, L. Vapor Pressure Measurement of the Ternary Systems H2O + LiBr + [Dmim]Cl, H2O + LiBr + [Dmim]BF4, H2O + LiCl + [Dmim]Cl, and H2O + LiCl + [Dmim]BF4. J. Chem. Eng. Data 2011, 56, 97−101. (22) Enick, R. M.; Donahey, G. P.; Holsinger, M. Modeling the HighPressure Ammonia−Water System with WATAM and the Peng− Robinson Equation of State for Kalina Cycle Studies. Ind. Eng. Chem. Res. 1998, 37, 1644−1650. (23) Bombarda, P.; Inernizzi, C. M.; Pietra, C. Heat Recovery from Diesel Engines: A Thermodynamic Comparison between Kalina and ORC Cycles. Appl. Therm. Eng. 2010, 30, 212−219.

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dx.doi.org/10.1021/je400109a | J. Chem. Eng. Data 2013, 58, 1354−1360