Article Cite This: J. Chem. Eng. Data 2019, 64, 2710−2717
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Isothermal Vapor−Liquid Equilibrium of the Absorption Working Pairs (HFC-32 + DMETrEG, HFC-32 + NMP) at Temperatures from 293.15 to 343.15 K Yibo Fang,† Zanjun Gao,‡ Kangli Bao,† Jiongliang Huang,† Xiaosheng Ji,† Xiaohong Han,*,† and Guangming Chen†
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†
Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province, Institute of Refrigeration and Cryogenics, Zhejiang University, Hangzhou 310027, China ‡ Aviation Key Laboratory of Science and Technology on Aero Electromechanical System Integration, Nanjing Engineering Institute of Aircraft Systems, Nanjing 211106, China ABSTRACT: The working pairs of HFCs + organic absorption solvents are commonly used in absorption systems. In this work, the vapor−liquid equilibrium (VLE) data of HFC32 + DMETrEG at (293.15−343.15) K and HFC-32 + NMP at (323.15−343.15) K were measured in a dual cycle apparatus. The VLE data were correlated by Antione-type equation, NRTL, and PR + MHV1 + NRTL model, respectively. The predicted VLE data showed a good agreement with the experimental VLE data. NRTL model was recommended to predict the VLE data and characteristic of solution for HFC-32 + DMETrEG and HFC32 + NMP, compared to PR + MHV1 + NRTL model. The comparison of VLE characteristics for five binary mixtures (HFC-32 + DMETrEG, HFC-32 + NMP, HFC-32 + DMF, HFC-32 + DMAC, and HFC-32 + DMEDEG) was carried out. The compared results showed that the system pressures of HFC-32 + DMETrEG and HFC-32 + NMP were lower than other three mixtures, and the negative deviations from Raoult’s law of HFC-32 + DMETrEG and HFC-32 + NMP were larger than the others, which indicated that the two mixtures were more suitable as the working fluids for absorption system.
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evaluated by Kim et al.,4 respectively, and the system with HFC-32 + bmim[PF6] had the highest COP. The properties of working pairs are one of important factors for the performance of absorption system. Therefore, many types of research about the properties of the absorption working pairs were carried out including the vapor−liquid equilibrium (VLE), viscosities, enthalpies, etc. The VLE characteristics of working pairs (HFC-32 + the absorbents) have been investigated.5−11 For example, the VLE data of HFC-32 + DMF,5 HFC-32 + N,N-dimethylacetamide (DMAC),6 and HFC-32 + diethylene glycol dimethyl ether (DMEDEG)6 have been obtained. The VLE data of HFC-32 + DMF at (283.15−363.15) K were measured by Han et al.,5 and the experimental results showed that the HFC-32 + DMF system had a certain negative deviation to the Raoult’s law. The VLE data of three working pairs (HFC-32 + DMAC, HFC-32 + DMEDEG, and HFC-152a + DMEDEG) at (293.15−353.15) K were measured by Li et al., and the data were correlated by NRTL model.6 The investigation on the VLE for the working pairs of HFC-32 + ionic liquids has also been extensively carried out. The VLE data of HFC-32 + [bmim][PF6], and HFC-32 + [bmim][BF4] at (283.15− 348.15) K were measured, and NRTL model was used to
INTRODUCTION
Absorption refrigeration cycle is an effective way in the utilization of waste heat. It has certain advantages in heatdriven refrigeration systems, but there are still some problems such as the low utilization rate of waste heat. The main ways to solve these problems are to build a new and more efficient absorption refrigeration cycle or to find a more suitable working pair, which would be matched with the absorption refrigeration system. Difluoromethane (HFC-32) is an eco-friendly refrigerant (ODP = 0, GWP = 675), and many studies on the application of HFC-32 or its mixtures in refrigeration system have been carried out. For example, Wu et al.1 demonstrated the potential of the ternary mixture 1,1-difluoroethane (HFC-152a) + pentafluoroethane (HFC-125) + HFC-32 in domestic air conditioner. Lee et al.2 found that HFC-32 + HFC-152a had a better system performance than chlorodifluoromethane (HCFC-22) in a water source heat pump. The working pairs with HFC-32 as the refrigerant have been applied into absorption refrigeration system. The working pair 1,1,1,2tetrafluoroethane (HFC-134a) + HFC-32 + N,N-dimethylformamide (DMF) was applied into autocascading absorption refrigeration cycle, and COP reached the maximum when molar ratio of HFC-32 to HFC-134a was about 0.425.3 The cycle performances of HFC-32, HFC-134a, HFC-152a with bmim[PF6] in an absorption refrigeration system were © 2019 American Chemical Society
Received: February 1, 2019 Accepted: May 8, 2019 Published: May 16, 2019 2710
DOI: 10.1021/acs.jced.9b00117 J. Chem. Eng. Data 2019, 64, 2710−2717
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Table 1. Basic Properties for HFC-32, DMETrEG, and NMP12−14
correlate VLE data by Shiflett et al.7 The VLE data of HFC-32 and 19 ionic liquids at (283.15−348.15) K were also measured, respectively, by Shiflett et al.,8 and the experimental results showed that the solubility of HFC-32 in fluorine-containing ionic solution was higher than that in ionic solution without fluorine element. The solubilities of HFC-32 and HFC-152a in [Emim]OTf and [Bmim]OTf were measured by Dong et al.,9 respectively. The experimental results showed that the solubility of HFC-32 in the same ionic solution was higher than that of HFC-152a, and the solubility of HFC-32 in [Bmim]OTf was higher than that in [Emim]OTf. Liu et al.10 measured the solubility of HFC-32, HFC-152a, and HFC-125 in [HMIM][Tf2N]. The experimental results showed that HFC-32 had a second highest solubility in [HMIM][Tf2N]. The solubility of HFC-32 in [P14666][TMPP] was measured by Liu et al.,11 which was lower than that in [EMIM][Tf2N], [HMIM] [Tf2N], and [BMIM][BF6]. It is well-known that organic solvents commonly used in the absorption system mainly include DMAC, DMEDEG, DMF, triethylene glycol dimethyl ether (DMETrEG), and N-methyl2-pyrrolidone (NMP). The VLE data of three organic solvents (DMAC, DMEDEG, and DMF) combined with HFC-32 were available;8,9 however, the VLE data of HFC-32 + DMETrEG and HFC-32 + NMP have not been studied. For evaluating the working pairs (HFC-32 + organic absorption solvents) comprehensively, the isothermal VLE data of HFC-32 + DMETrEG at (293.15−343.15) K HFC-32 + NMP at (323.15−343.15) K were carried out in this work, respectively, and the experimental data were correlated by three models (Antione-type equation, NRTL model, and PR + MHV1 + NRTL model). The comparison of VLE characteristics for three published absorption working pairs (HFC-32 + DMF, HFC-32 + DMAC, and HFC-32+DMEDEG) and the two working pairs (HFC-32 + DMETrEG, and HFC-32 + NMP) in this work was developed and discussed; some working pairs were recommended as promising working fluids to be used in absorption system.
was shown in Table 1. All samples were without any further purification. Experimental Apparatus. The VLE data of HFC-32 + DMETrEG and HFC-32 + NMP were obtained by a dual cycle apparatus, and the flowchart of the experimental apparatus was shown in Figure 1. The dual cycle apparatus was already
Figure 1. Schematic diagram of the experimental apparatus for VLE of absorption working pairs.
introduced in our previous work.15,16 The sample was charged into the equilibrium cell and could be observed through the sight glass. The liquid and vapor phase were cycled in the apparatus by the liquid pump (GAH-T23, Micropump) and vapor pump (self-designed). The bath temperature was measured by the 25 Ω standard platinum resistance thermometer (WZPB-1), which was purchased from Kunming Temperature Instruments Co., Ltd. The measurement uncertainty of temperature was 0.011 K. The vapor pressure was measured by the pressure sensor (PMP4010, Druck), and the full scale was 3.5 MPa with an accuracy of ±0.04%. The composition of sample was analyzed by a gas chromatograph (GC) with flame ionization detector (FID), and the measurement uncertainty of composition was 0.01.
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EXPERIMENTAL SECTION Materials. HFC-32 was supplied by Zhejiang Lantian Environmental Protection Co., Ltd. (FLTCO) with a minimum purity of 99.98%. DMETrEG and NMP were purchased from Aladdin with a minimum purify of 99.0%, and 99.9%, respectively. The basic description of the materials used 2711
DOI: 10.1021/acs.jced.9b00117 J. Chem. Eng. Data 2019, 64, 2710−2717
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Table 2. VLE Data of Binary Mixture HFC-32(1) + DMETrEG(2) at (293.15−343.15) Ka Antione-type
NRTL
PR + MHV1 + NRTL
T/K
x1
pexp/kPa
pcal/kPa
δpb
pcal/kPa
δpb
pcal/kPa
δpb
293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15
0.2204 0.3122 0.4127 0.5307 0.6006 0.6797 0.7731 0.8499 0.9270 0.9830 0.2807 0.5108 0.6316 0.7580 0.8313 0.8544 0.9128 0.9785 0.3395 0.5054 0.6228 0.7624 0.8296 0.8899 0.9777 0.2680 0.4652 0.6454 0.7284 0.7998 0.8859 0.9752 0.2742 0.4837 0.6662 0.7624 0.8503 0.8859 0.9396 0.2602 0.3803 0.5320 0.6720 0.8111 0.8705
175.7 260.4 360.0 482.2 566.0 684.0 861.5 1033.9 1242.1 1404.1 299.3 581.9 779.7 1034.3 1261.7 1340.0 1529.3 1814.3 497.9 783.9 1051.0 1372.5 1641.8 1906.7 2350.1 471.9 873.5 1317.6 1620.8 1931.1 2375.4 2953.4 591.8 1084.6 1684.0 2082.5 2557.0 2738.4 3283.8 665.3 993.7 1474.1 1979.9 2832.9 3211.8
181.0 257.0 355.7 491.1 582.1 697.6 858.4 1020.8 1226.1 1414.2 300.0 603.9 806.5 1070.5 1264.9 1335.5 1540.3 1830.9 470.9 756.2 1000.2 1368.2 1598.3 1852.5 2345.8 462.9 851.8 1309.5 1576.4 1856.8 2294.4 2936.9 587.2 1099.4 1680.6 2087.2 2578.1 2826.6 3278.5 682.5 1010.3 1499.4 2057.6 2834.2 3295.4
−3.04 1.31 1.20 −1.84 −2.84 −1.99 0.36 1.27 1.29 −0.72 −0.24 −3.78 −3.44 −3.50 −0.26 0.34 −0.72 −0.92 5.42 3.53 4.83 0.31 2.65 2.84 0.18 1.91 2.48 0.62 2.74 3.85 3.41 0.56 0.78 −1.36 0.20 −0.23 −0.83 −3.22 0.16 −2.59 −1.67 −1.71 −3.92 −0.05 −2.60
179.7 266.0 364.9 491.9 576.0 684.2 840.5 1008.7 1238.3 1433.3 305.2 606.9 797.9 1052.3 1250.4 1325.0 1548.7 1853.3 479.6 761.6 1009.6 1354.7 1589.7 1861.0 2376.8 458.3 859.9 1308.2 1572.8 1856.2 2317.1 2989.4 576.0 1105.2 1685.6 2093.9 2600.4 2862.0 3362.5 651.7 1001.6 1498.6 2018.5 2863.8 3348.0
2.27 2.16 1.37 2.01 1.77 0.03 −2.44 −2.44 −0.30 2.08 1.99 4.30 2.34 1.74 −0.90 −1.12 1.27 2.15 −3.67 −2.85 −3.94 −1.29 −3.17 −2.40 1.13 −2.87 −1.55 −0.71 −2.96 −3.88 −2.46 1.22 −2.67 1.90 0.10 0.55 1.70 4.51 2.40 −2.05 0.80 1.66 1.95 1.09 4.24
176.5 270.6 371.0 493.8 574.6 680.4 839.8 1018.7 1258.6 1442.7 308.5 609.9 793.4 1049.4 1259.0 1339.0 1576.4 1869.9 486.6 762.7 986.9 1347.2 1595.7 1887.2 2398.7 458.7 861.7 1289.7 1551.4 1845.5 2342.2 3017.9 575.6 1100.8 1652.8 2063.9 2604.5 2893.9 3414.1 649.7 1008.0 1481.9 2018.9 2831.0 3359.3
−0.48 −3.93 −3.06 −2.41 −1.52 0.53 2.52 1.47 −1.33 −2.75 −3.06 −4.82 −1.75 −1.46 0.22 0.07 −3.08 −3.06 2.26 2.70 6.10 1.84 2.81 1.02 −2.07 2.81 1.35 2.12 4.28 4.43 1.40 −2.18 2.74 −1.49 1.85 0.89 −1.86 −5.68 −3.97 2.34 −1.44 −0.53 −1.97 0.07 −4.59
Standard uncertainties: u(T) = 0.011 K, u(x1) = 0.01, u(p)/p = 0.028. bδp (%) = (1 − pcal/pexp) × 100.
a
conditions were = 0.028 for binary mixture of HFC-32 + DMETrEG, and = 0.038 for binary mixture of HFC-32 + NMP, respectively. Experimental Procedure. The experimental procedure mainly contained five steps. (1) A desired amount of absorbent was charged into the equilibrium cell through the inlet at the upper of the cell. Then the apparatus was evacuated. Because of the high boiling point of absorbent, the apparatus could achieve a high vacuum state, and the mass of absorbent nearly did not decrease. (2) The apparatus was charged with a small amount of HFC-32 and evacuated again. This step was repeated three times to eliminate the impurities in the cell. (3)
According to the law of propagation of uncertainty, the combined standard uncertainty of pressure was influenced by the measurement uncertainties of temperature, composition, and vapor pressure in this work. Therefore, the combined standard uncertainty of pressure could be obtained by eq 1: i ∂p yz u Xi zzz z X ∂ k i {
∑ jjjjj 3
uc , p =
i=1
2
(1)
where Xi was the temperature (T), mass fraction (x), and pressure (p), respectively. Eventually, the relative standard uncertainties of pressure uc,p/p in the whole experimental 2712
DOI: 10.1021/acs.jced.9b00117 J. Chem. Eng. Data 2019, 64, 2710−2717
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Table 3. VLE Data of Binary Mixture HFC-32(1) + NMP(2) at (323.15−343.15) Ka Antione-type
NRTL
PR + MHV1 + NRTL
T/K
x1
pexp/kPa
pcal/kPa
δpb
pcal/kPa
δpb
pcal/kPa
δpb
323.15 323.15 323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15
0.2045 0.3548 0.4928 0.578 0.5941 0.691 0.7446 0.2228 0.4061 0.5613 0.5762 0.6398 0.6825 0.7525 0.2236 0.3569 0.5024 0.575 0.6796 0.7481
335.2 659.2 983.6 1299.3 1357.6 1817.2 2105.3 466.2 976.9 1484.9 1560.2 1842.3 2065.6 2502 508.8 914.8 1423 1847.2 2429.8 3056.6
347.0 635.3 1023.5 1324.1 1385.8 1784.7 2021.6 446.6 910.2 1504.5 1571.5 1876.4 2096.8 2481.8 527.2 895.5 1478.6 1846.4 2466.2 2926.0
−3.51 3.63 −4.06 −1.91 −2.07 1.79 3.98 4.19 6.83 −1.32 −0.73 −1.85 −1.51 0.81 −3.62 2.11 −3.90 0.04 −1.50 4.27
339.2 658.2 1029.2 1311.9 1370.6 1767.4 2019.1 443.0 934.8 1499.1 1563.7 1861.3 2085.1 2497.7 515.3 915.1 1477.2 1833.2 2454.4 2962.2
1.19 −0.15 4.64 0.97 0.96 −2.74 −4.09 −4.98 −4.31 0.95 0.23 1.03 0.94 −0.17 1.28 0.04 3.81 −0.76 1.01 −3.09
324.3 634.5 994.4 1280.4 1338.8 1730.8 1977.6 460.4 929.2 1499.7 1564.5 1864.6 2088.6 2495.8 527.6 940.5 1523.7 1886.7 2519.3 3012.8
3.24 3.75 −1.10 1.46 1.39 4.76 6.06 1.25 4.88 −1.00 −0.28 −1.21 −1.11 0.25 −3.70 −2.81 −7.08 −2.14 −3.68 1.43
Standard uncertainties: u(T) = 0.011 K, u(x1) = 0.01, u(p)/p = 0.038. bδp (%) = (1 − pcal/pexp) × 100.
a
The bath temperature was set at 283.15 K, and a desired amount of HFC-32 was charged. The liquid pump and vapor pump were turned on, and it was important to ensure the liquid flow and vapor flow could be observed through the sight glass clearly. (4) After the samples was at the equilibrium state for (1−2) h, the temperature and pressure data were recorded. The composition was measured by GC. The deviation of three consecutive measurements should have been less than 0.003. (5) After the measurements at all temperatures, the apparatus should be evacuated again and the composition of samples should be varied.
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RESULTS AND DISCUSSION The VLE data of HFC-32(1) + DMETrEG(2) in the temperature range (293.15−343.15) K and of HFC-32(1) + NMP(2) in the temperature range (323.15−343.15) K were given in Tables 2 and 3, and Figures 2 and 3. The thermodynamic consistency test was carried out by the area
Figure 3. VLE data of HFC-32(1) + NMP(2) at the temperature range of (323.15−343.15) K.
test, 16 and the experimental data of HFC-32(1) + DMETrEG(2) and HFC-32(1) + NMP(2) could meet the thermodynamic consistency test. Analysis Method. The experimental VLE data were correlated by Antione-type equation, NRTL model, and PR + MHV1 + NRTL model, respectively. Antione-type equation (eq 2) was a successful equation for binary mixture to predict the vapor pressure as the function of temperature and molar fraction.17−19 However, Antione-type equation could only show the characteristic of vapor pressure but was not able to describe the activity coefficient for solution. NRTL model was one of commonly used activity coefficient models but could only describe the characteristic for solution. The excess free energy mixing rules combined with the cubic equation of state and activity coefficient model, such as the PR + MHV1 + NRTL model in this work, could accurately predict the complex mixture at a large pressure range.20,21 Our previous work15,16,19 proved that these three models (Antione-type equation, NRTL model, and PR + MHV1 + NRTL model) all could correlate the experimental data well for the HFCs +
Figure 2. VLE data of HFC-32(1) + DMETrEG(2) at the temperature range of (293.15−343.15) K. 2713
DOI: 10.1021/acs.jced.9b00117 J. Chem. Eng. Data 2019, 64, 2710−2717
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Table 4. Regressed Parameters for Antione-type Equation HFC-32(1) + DMETrEG(2)
HFC-32(1) + NMP(2)
i
Ai
Bi
Ai
Bi
0 1 2 3 R-square ARD(%)a MRD(%)
11.23 6.492 −9.858 6.534
−1.787 −0.09458 1.146 −1.039
9.877 5.943 −5.484 4.288
−1.399 −0.2213 0.9618 −1.180
0.9991 1.85 5.42
0.9981 2.68 6.83
ARD(%) = ∑i=1N|δpi(%)|/N.
a
Table 5. Regressed Parameters for NRTL and PR + MHV1 + NRTL HFC-32(1) + DMETrEG(2)
HFC-32(1) + NMP(2)
parameter
NRTL
PR + MHV1 + NRTL
NRTL
PR + MHV1 + NRTL
α12 a1 a2 b1 b2 ARD(%)a MRD(%)
3.8720 0.4825 −0.3701 −0.0714 −0.0862 2.05 4.51
−0.3109 −0.1467 −0.9923 0.2255 −1.9395 2.32 6.10
1.3683 0.3447 0.3088 5.8673 −1.1553 1.87 4.98
−0.3282 −0.2578 −0.4656 −0.3934 −2.8769 2.63 7.08
ARD(%) = ∑i=1N|δpi(%)|/N.
a
a = 0.457235
(RTc)2 pc
× [1 + (0.37646 + 1.54226ω − 0.26992ω2)(1 − Tr 0.5)]2 (4)
b = 0.077796
RTc pc
(5)
where a was the energy parameter; b was the covolume parameter; Tc was the critical temperature, K; Tr(= T/Tc) was the reduced temperature; pc was the critical pressure, Pa; R was the general gas constant (= 8.314472 J mol−1 K−1); v was the molar volume, m3 mol−1; and ω was the acentric factor. MHV1 Mixing Rule.22 E am 1 ji g = jjjj + bmRT q1 j RT k
Figure 4. Comparison of the VLE data for five working pairs within HFC-32 at 303.15 and 343.15 K.
organic solvents. The expressions of three models were shown
bm =
as follows. Antione-type Equation for Mixture. log(p /kPa) =
i
∑ x ijjjjAi + 3
i=0
k
1000Bi zyz z T /K − 43.15 z{
i
∑ xi i
ai biRT
∑ xibi
(6)
(7)
i
where q1 was the characteristic parameter, and for PR equation, q1= −0.53; gE/(RT) could be calculated by NRTL model; and the subscript m meant the mixture, subscript i meant the ith component. NRTL Model for Binary Mixture.
(2)
ij τ G gE τ12G12 yzz = x1x 2jjj 21 21 + z j RT x 2 + x1G12 zz{ k x1 + x 2G21
where p was the pressure, kPa; T was the temperature, K; x was the molar fraction of HFC-32 in liquid; and Ai and Bi were the Antione parameters. PR Equation of State. RT a p= − v−b v(v + b) + b(v − b)
i bm yzyzz zzzz + zzz b k i {z{
∑ xi lnjjjjj
ln γ1 = (3) 2714
ÅÄÅ Å
ÑÉÑ 2 yz τ12G12 G21 ÑÑÑ zz + Ñ z 2Ñ z (x 2 + x1G12) ÑÑÑ k x1 + x 2G21 { ÑÖ i
Å j x 22ÅÅÅÅτ21jjj j ÅÅ ÅÇ
(8)
(9)
DOI: 10.1021/acs.jced.9b00117 J. Chem. Eng. Data 2019, 64, 2710−2717
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τ12 = a1 + a 2 log(T )
(13)
τ21 = b1 + b2 log(T )
(14)
where γi was the activity coefficient of component i; xi was the mole fractions of component i; and a1, a2, b1, b2, and α12(= α21) were the equation parameters. The objective function (OBF) for Antione-type equation, NRTL model, and PR+MHV1+NRTL model could be expressed as 1 OBF = N
ln γ2 =
ÄÅ ÅÅ
ÉÑ 2 ÑÑ yz G12 τ G ÑÑ 21 21 zz + ÑÑ z 2 z x + x G (x1 + x 2G21) ÑÑÑÑ 1 12 { k 2 Ö
ÅÅ ÅÇ
i
(10)
G12 = exp( −α12τ12)
(11)
G21 = exp( −α21τ21)
(12)
2
(15)
where N was the number of experimental points; pexp was the experimental pressure, kPa; and pcal was the calculated pressure, kPa. By minimizing the OBF, the regressed parameter (Ai and Bi for Antine-type equation, a1, a2, b1, b2, and α12(= α21) for NRTL and PR + MHV1 + NRTL) could be obtained, which were listed in Tables 4 and 5. Correlation Results. As can be seen from Tables 2 and 3, and Figures 2 and 3, the VLE data of HFC-32(1) + DMETrEG(2) and HFC-32(1) + NMP(2) with the measured temperature range were correlated well by the three models (Antione-type equation, NRTL model, and PR + MHV1 + NRTL model). For HFC-32(1) + DMETrEG(2), the average relative deviations of pressure (ARD) for Antione-type equation, NRTL model, and PR + MHV1 + NRTL model were 1.85%, 2.05%, and 2.32%, respectively, and the maximum relative deviations (MRD) for these three models were 5.42%, 4.52%, and 6.10%, respectively. As for HFC-32(1) + NMP(2), the average relative deviations of pressure for Antione-type equation, NRTL model, and PR + MHV1 + NRTL model were 2.68%, 1.87%, and 2.63%, respectively, and the maximum relative deviations for these three models were 6.83%, 4.98%, and 7.08%, respectively. Antione-type equation could predict the system pressures well for HFC-32 + DMETrEG and HFC-32 + NMP, and it was really simple and convenient to use. However, Antionetype equation was empirical and not able to predict the activity coefficient for solution. NRTL and PR + MHV1 + NRTL model could both predict the VLE. The correlated results by NRTL were better than that by PR + MHV1 + NRTL. NRTL model was much easier to use than PR + MHV1 + NRTL; therefore, it was recommended to use NRTL model to predict the VLE for HFC-32 + DMETrEG and HFC-32 + NMP. It should be explained here that the pressures and activity coefficients in figures for this work were both calculated by NRTL model. Comparison for Five Binary Mixtures Containing HFC-32. Han et al.5 and Li et al.6 have investigated the VLE properties of HFC-32 + DMF, HFC-32 + DMAC, and HFC32 + DMEDEG. In this work, the comparison for three working pairs (HFC-32 + DMF, HFC-32 + DMAC, HFC-32 + DMEDEG) and the two working pairs (HFC-32 + DMETrEG, and HFC-32 + NMP) from this work at 303.15, 323.15, and 343.15 K was carried out. Figure 4 shows the responding comparison results of vapor pressures for the five working pairs at 303.15 and 343.15 K. The compared result showed that HFC-32 + DMETrEG had the lowest pressure among five working pairs at the same temperature, and HFC-32 + DMAC had the highest pressure, which meant that the solubility of HFC-32 in DMETrEG was highest and the solubility of HFC-
Figure 5. Comparison of activity coefficient of five working pairs at three temperatures. (a) T = 303.15 K; (b) T = 323.15 K; (c) T = 343.15 K (■ HFC-32(1) + DMF(2); ● HFC-32(1) + DMAC(2); ▲ HFC-32(1) + DMEDEG(2); ▼ HFC-32(1) + DMETrEG(2); ★ HFC-32(1) + NMP(2)).
Å j x12ÅÅÅÅτ12jjj j
ij p − p yz exp cal z zz ∑ jjjjj zz p j z i=1 k exp { N
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Table 6. Molecules of Five Organic Solvents
The comparison of VLE for five working pairs (HFC-32 + DMF, HFC-32 + DMAC, HFC-32 + DMEDEG, HFC-32 + DMETrEG, and HFC-32 + NMP) was investigated. The vapor pressures of HFC-32 + DMETrEG were the lowest, and those of HFC-32 + DMAC were the highest at same temperature. HFC-32 + DMETrEG showed a largest negative deviation from Raoult’s law, HFC-32 + NMP was secondary, and HFC32 + DMAC was the smallest, which suggested that the HFC32 + DMETrEG and HFC-32 + NMP were more suitable than the other three working pairs (HFC-32 + DMF, HFC-32 + DMAC, HFC-32 + DMEDEG) for an absorption system.
32 in DMAC was the lowest. The vapor pressures of HFC-32 + NMP were close to those of HFC-32 + DMETrEG, but at high concentration x1 of HFC-32, the pressures of HFC-32 + NMP were higher than that of HFC-32 + DMF. It meant that the solubility of HFC-32 + NMP at low x1 was as good as that of HFC-32 + DMETrEG, but at high x1, the solubility of HFC32 + NMP became worse than that of HFC-32 + DMF. The vapor pressures of HFC-32 + DMF, HFC-32 + DMAC, and HFC-32 + DMEDEG were similar at low temperature, that is, the solubility of the three working pairs was similar at low temperature. Therefore, for an absorption cycle, HFC-32 + DMETrEG and HFC-32 + NMP were more suitable as the working fluids than the other mixtures. Figure 5 shows the comparison of activity coefficients of the five working pairs at three temperatures (T = 303.15 K, 323.15 K, and 343.15 K). All five working pairs showed a negative deviation from Raoult’s law since their activity coefficients were less than 1. The activity coefficients of HFC-32 + DMF, HFC-32 + DMAC, and HFC-32 + DMEDEG decreased with the increase of temperature. The activity coefficients of HFC32 + DMETrEG almost did not change with the temperature. The HFC-32 + DMETrEG showed a largest negative deviation from Raoult’s law, HFC-32 + NMP was the secondary, and HFC-32 + DMAC was the smallest. It also indicated that the solubility of HFC-32 in DMETrEG was the highest, and that in DMAC was the lowest. Generally, the working fluids of absorption system should have a large negative deviation from Raoult’s law;23,24 therefore, HFC-32 + NMP HFC-32 + DMETrEG were more suitable as the working fluid than the other three working pairs within HFC-32. It was believed that the difference of affinity for the five working pairs was due to the different molecules force. The hydrogen bonds of atom H with atom O, and atom H with atom F, were common between the HFC refrigerants and organic absorbents. Because there were more O atoms in DMETrEG than those in NMP, which was shown in Table 6, the affinity between HFC-32 and DMETrEG was stronger than HFC-32+NMP.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Phone: +86 571 8795 3944. Fax: +86 571 8795 3944. ORCID
Xiaohong Han: 0000-0002-6020-7607 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work has been supported by the Nation Natural Science Foundation of China (No. 51576171) and the fund of the State Key Laboratory of Technologies in Space Cryogenic Propellants.
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CONCLUSIONS
The vapor−liquid equilibrium data of HFC-32 + DMETrEG from 293.15 to 343.15 K and HFC-32 + NMP from 323.15 to 343.15 K were measured in a dual cycle apparatus. Three models (Antione-type equation, NRTL model, and PR + MHV1 + NRTL model) were applied to correlate the VLE data. The predicted VLE data for all three model showed a good agreement with the experimental VLE data. Antione-type equation was convenient to predict the vapor pressure. NRTL model was recommended to predict the VLE data and characteristic of solution for HFC-32 + DMETrEG and HFC-32 + NMP, compared to PR + MHV1 + NRTL model. 2716
DOI: 10.1021/acs.jced.9b00117 J. Chem. Eng. Data 2019, 64, 2710−2717
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