Measurement and Correlation of Isothermal Vapor–Liquid Equilibrium

Article pubs.acs.org/jced

Measurement and Correlation of Isothermal Vapor−Liquid Equilibrium of Fluoroethane + N,N‑Dimethylacetamide, Fluoroethane + N‑Methyl-2-pyrrolidone, and 1,1,1,2Tetrafluoroethane + N,N‑Dimethylacetamide Systems Xuye Jing, Rulei Deng, and Danxing Zheng* College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China ABSTRACT: The isothermal vapor−liquid equilibrium (VLE) data of fluoroethane (R161) + N,N-dimethylacetamide (DMAC), R161 + Nmethyl-2-pyrrolidone (NMP), and 1,1,1,2-tetrafluoroethane (R134a) + DMAC were measured in a temperature range from (293.15 to 353.15) K, and the five-parameter nonrandom two-liquid (NRTL) model was selected to correlate the obtained VLE data. According to the order of R161 + DMAC, R161 + NMP, and R134a + DMAC, the mean relative deviations of the pressure between the experimental and calculated values are 1.16 %, 1.39 %, and 1.13 %, and the maximum deviations of that are 3.30 %, 3.59 %, and 3.14 %. The experimental results show that all of the binary systems have very good affinity, and especially the affinity of the system R161 + DMAC is the best. Additionally, the three binary systems exhibit negative deviations from Raoult’s law, and the order of the negative deviation degree from strong to weak is arranged as R161 + DMAC > R161 + NMP > R134a + DMAC.

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(DMETEG), N-methyl ε-caprolactam (MCL), dimethyl-ethylene urea (DMEU),16 and N,N-dimethylacetamide (DMAC),17 have been investigated. Moreover, R134a + DMAC could give a significant improvement in the performance in half effect absorption refrigeration cycle,18 and Muthu et al. presented the experimental studies on the absorption refrigeration system using R134a + DMAC.19 The above studies show that R134a is not only a good working fluid for organic Rankine cycle, but also an interesting refrigerant in absorption heat pumps. Therefore, R134a and its suitable organic absorbent are a potential working pair for absorption power/cooling cogeneration cycles. Zehioua et al. measured the isothermal vapor−liquid equilibrium (VLE) data of R134a + dimethylformamide (DMF),20 dimethylether diethylene glycol (DMEDEG), and dimethylether triethylene glycol (DMETrEG).21 Then Han et al. measured the solution of R134a in DMF in a wider temperature range.22 Lopez et al.23 presented the experimental solubility of R134a in DMETrEG and dimethylether tetraethylene glycol (DMETEG) at a 101.33 kPa partial pressure of gas and a range of temperatures between 258.15 K and 298.15 K. Coronas et al.24 reported the VLE data of R134a + DMETrEG from 283.15 K to 353.15 K. Unfortunately, the VLE data of R134a + DMAC are absent.

INTRODUCTION Many bottom cycles have been exploited to recovery midlow grade heat, and the absorption power/cooling cogeneration cycle is one kind of effective bottom cycle. Since the year 2000, Goswami et al.,1 Zheng et al.,2 Zhang et al.,3 Liu et al.,4 and some other scholars5−9 respectively proposed various cycle configurations for power/cooling cogeneration, but it is should be noted that almost all the researchers were limited to choosing ammonia−water as the working pair. Actually, the working pair has a very important effect on the cycle performance. Therefore, exploring a new working pair plays an important role in the development of absorption power/ cooling cogeneration cycles. Power and cooling are simultaneously generated by the absorption cogeneration cycle, and the working pair could be selected by properly combining the working fluids for an organic Rankine cycle and that for an absorption refrigeration cycles. As an important member of the hydrofluorocarnons (HFCs) family, 1,1,1,2-tetrafluoroethane (R134a) has been studied by many researchers. R134a is an important candidate working fluid for organic Rankine cycle. Many researchers assessed the performance of organic Rankine cycle using R134a as the working fluid.10−15 Especially, Tchanche et al. investigated 20 fluids for solar organic Rankine cycle and reported that R134a appeared to be the most suitable.15 On the other hand, R134a is considered to be used in absorption heat pumps to replace chlorofluorocarbons. For example, the possibilities of using R134a as a refrigerant in the combination with many organic absorbents, such as dimethylether tetraethylene glycol © 2013 American Chemical Society

Received: August 29, 2013 Accepted: October 10, 2013 Published: October 22, 2013 3289

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Among the numerous HFCs, fluoroethane (R161) has excellent environmental characteristics. For example, R161 has zero ozone depletion potential, a global warming potential of 12, and a lifespan of 3 years in atmosphere.25 Moreover, R161 has excellent cycle performance. Theoretical and experimental cycle performances of R410A, difluoromethane (R32) and HFC-161 were respectively compared, and the results show that the performance of R161 is quite higher than that of R32 and R410A.26 The mixture of R161 is considered as a promising alternative refrigerant to R502,27 R407C,28 and R410A.28 Han et al. measured the VLE data of R161 + pentafluoroethane (R125),29 Wang et al. presented the VLE data of R161 + 1,1,1,2,3,3,3-heptafluoroproane (HFC-227ea),25 and Dong et al. reported the VLE data of R161 + R134a.30 Meanwhile, HFCs are an important category for working fluid candidates of organic Rankine cycle, and many thermophysical properties of R161 indicated that it can be used in organic Rankine cycle.31−33 R161 and its suitable organic absorbent are also a potential working pair for an absorption power/cooling cogeneration cycle. The common organic solvents used in absorption heat conversion cycles include DMAC, NMP, and so forth,34 and there are no experimental solubility data of R161 in the common organic solvents DMAC and NMP. In this study, the isothermal VLE data of R161 + DMAC, R161 + NMP, and R134a + DMAC were measured with a temperature range from 303.15 K to 353.15 K, and the fiveparameter nonrandom two-liquid (NRTL) model was selected to correlate the obtained VLE data. The experimental and calculated activity coefficients of the three binary systems were used to discuss the deviations of the three binary systems from an ideal solution.

in the equilibrium cell could be accelerated to reach and were then well-maintained. The temperature controller (LC-6) purchased from Julabo was used to detect and control the temperatures of the equilibrium cell and the isothermal water bath. The pressure transducer (PTX7533) supplied by Druck was used to measure the pressure in the equilibrium cell. The gas chromatography (GC-2014) was supplied by Shimadzu; the six-way valve (VACLO) was used to control the sampling injection volume to the gas chromatograph, and the set injection volume was 5 μL. For these three test systems, it is worth noting that the uncertainties on the measurement of temperature, pressure, and composition have been calculated in detail by Meng et al.,37 and the uncertainties are respectively within 0.072 K, 0.6 kPa, and 0.015. The equilibrium cell was processed using stainless steel, and its volume is about 160 cm3. The vacuum pump (CHLF220LDWSC) and refrigerator (Cool-ECS-50) were respectively supplied by Alcatel and Eyela. The vacuum pump had two functions: one was to remove the stranded gas in the equilibrium cell, and the other was to provide the required negative pressure during the experiment. The refrigerator was used to provide the required low experimental temperature. The experimental procedures are described as follows: (1) The vacuum pump was used to evacuate the equilibrium cell and make sure the absolute pressure of the system was less than 3 kPa. Then at the room temperature, it was ensured that the absolute pressure value was no more than 5 kPa for 24 h to confirm the airtightness of the equilibrium cell. (2) About 60 mL DMAC or NMP was added to the equilibrium cell. (3) The temperature controller was used to control the isothermal water bath at the required experiment temperature. Then the circulating micropump was opened and the desired amount R161 or R134a slowly added. (4) When the experiment pressure and temperature were maintained at the required values for more than half an hour, the equilibrium pressure and temperature were recorded, the six-way valve rotated to inject the sample to the online gas chromatography, and the result of the sample composition analysis recorded. (5) The experimental temperature was changed and the above steps repeated. Apparatus Reliability Validation. To validate the reliability of the experiment apparatus, the VLE data of R134a + DMF at 303.15 K and 313.15 K were measured first. The measurement results and the published data22 are listed in Table 2. The symbols pexp and plit respectively denote the pressures of experiment and literature, and x1,exp and x1,lit respectively indicate the liquid mole fraction of R134a of the experiment and literature. Then the literature data were processed with interpolation method to compare with the experiment data, and the average and maximum relative deviations of x1 are 2.67 % and 1.58 %, respectively. Therefore, the experiment apparatus in this work is reliable.

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EXPERIMENTAL METHODS Materials. The materials used in this experiment are listed in Table 1. R161 (C2H5F, CAS registry no. 353-36-6) and Table 1. Materials chemical name

source

mass fraction purify

CAS no.

R161 R134a DMAC NMP DMF

Zhejiang Lantian DuPont Aldrich Aldrich Aldrich

0.9970 0.9990 0.9990 0.9990 0.9990

353-36-6 811-97-2 127-19-5 872-50-4 68-12-2

R134a (C2H2F4, CAS registry no. 811-97-2) were supplied by Zhejiang Lantian Environmental Protection Co., Ltd. and DuPont Co., Ltd., respectively. DMAC (C4H9NO, CAS registry no. 127-19-5), NMP (C5H9NO, CAS registry no. 872-50-4), and DMF (C3H7NO, CAS registry no. 68-12-2) were purchased from Sigma-Aldrich Co., Ltd.. The purity of R161 is more than 99.7 % in mass fraction, and the purities of the other mentioned experiment materials are more than 99.9 % in mass fraction. Experimental Apparatus and Procedures. The diagram of the phase equilibrium apparatus used in this work is schematically shown in Figure 1, and the apparatus was achieved by slightly retrofitting our reported apparatus,35−39 adding a circulating micropump. The effect of the micropump is to circulate the liquid phase of the measured system to the vapor phase of that, and all of the pipeline and values in the circulation loop have been winded with thermal insulation materials. Therefore, the phase equilibrium of the binary system

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COMPUTATIONAL METHODS Vetere reported that the NRTL model is a good predictive tool for vapor−liquid equilibria of nonideality systems.40 Furthermore, many researchers have chosen the NRTL model to correlate the VLE data of HFCs + absorbents.22,24,37,38,41 Therefore, the five-parameter NRTL model was selected to correlate the VLE data of R161 + DMAC, R161 + NMP, and R134a + DMAC. 3290

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Figure 1. Schematic diagram of the VLE experimental apparatus. 1, gas cylinder; 2, gas storage tank; 3, liquid injector; 4, circulating micropump; 5, isothermal water bath; 6, equilibrium cell; 7, refrigerator; 8, temperature controller; 9, six-way valve; 10, cushion tank; 11, vacuum pump; 12, gas chromatography; 13, computer; 14, pressure monitor; 15, five-way valve.

Table 2. Vapor−Liquid Equilibrium Data of R134a + DMFa: x1,exp (Experimental Data) and x1,lit (Literature Data)22 item

303.15 K

pexp/kPa x1,exp plit/kPa x1,lit a

155.6 0.2388 155.8 0.2352

260.2 0.3950 258.9 0.3836

313.15 K 408.5 0.6026 410.8 0.5994

485.8 0.6970 485.8 0.6929

214.5 0.2551 201.6 0.2343

341.6 0.4037 332.2 0.3828

471.5 0.5354 471.6 0.5263

611.2 0.6941 614.1 0.6925

Standard uncertainties u are u(p) = 0.6 kPa, u(T) = 0.072 K, and u(x) = 0.015.

where x1 and y1 are the liquid and vapor mole fractions of species 1, T and p are the system equilibrium temperature and pressure, ps1 denotes the saturated vapor pressure of species 1, VL1 is the mole volume of the saturated liquid of species 1, and the term exp[VL1 (p − ps1)/RT] is the Poynting factor. The values ps1 and VL1 for species 1 at different temperatures can be calculated by REFPROP,31 which are shown in Table 3. Under

The chosen NRTL model can be written as follows: ⎡

ln γ1 =

⎤ ⎞2 G21 G12τ12 ⎥ ⎟ + 2⎥ (x 2 + x1G12) ⎦ ⎝ x1 + x 2G21 ⎠ ⎛

x 22⎢τ21⎜ ⎢⎣

(1)

where G12 and G21 are defined as

G12 = exp( −ατ12)

(2)

G21 = exp( −ατ21)

(3)

Table 3. Saturated Vapor Pressure and Liquid Molar Volume Data for R161 and R134a Obtained from REFPROP31 R161

where the parameters τ12 and τ21 are defined as a + b12 ln(T ) τ12 = 12 RT

(4)

a 21 + b21 ln(T ) RT

(5)

τ21 =

In eqs 1 to 5, γ1 is the activity coefficient of species 1, x1 and x2 are the liquid mole fraction of species 1 and 2, R is the gas constant, and α, a12, b12, a21, and b21 are the five parameters of the NRTL model. For the binary system, the VLE data can be obtained using the following equation ⎡ V L(p − p s ) ⎤ 1 1 ⎥ y1p = γ1x1p1s exp⎢ RT ⎥⎦ ⎢⎣

R134a

T/K

ps1/kPa

VL1 /m3·kmol−1

ps1/kPa

VL1 /m3·kmol−1

293.15 303.15 313.15 323.15 333.15 343.15 353.15

805.6 1058.6 1366.2 1735.7 2175.1 2693.8 3304.1

0.06598 0.06768 0.06962 0.07187 0.07458 0.07798 0.08263

571.7 770.2 1016.6 1317.9 1681.8 2116.8 2633.2

0.08327 0.08592 0.08898 0.09256 0.09691 0.10242 0.10992

the operation experiment conditions, the volatility of the absorbents DMAC and NMP can be negligible,20,22,37,38,41 and the value of y1 can be assumed as 1. So the sampling line of the vapor phase in experimental setup given in Figure 1 was closed in this experiment.

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For the selected NRTL model, the values of the five parameters can be regressed through minimizing the following objective function:

7), the parameter values in the NRTL model of each system were obtained, which are listed in Table 4. Then the VLE data were calculated, which along with the experimental data at seven temperature levels from (293.15 to 353.15) K for R161 + DMAC, R161 + NMP, and R134a + DMAC are respectively shown in Tables 5 to 7. The relative pressure deviations between the experimental and the calculated values are listed in Tables 5 to 7 and also described in Figure 2. According to the order of R161 + DMAC, R161 + NMP, and R134a + DMAC, the mean relative deviations of the pressure are 1.16 %, 1.39 %, and 1.13 %, and the maximum deviations of that are 3.30 %, 3.59 %, and 3.14 %. It is therefore appropriate to choose the NRTL model to correlate the experimental VLE data in this work. The p−T−x diagrams of R161 + DMAC, R161 + NMP, and R134a + DMAC are respectively plotted in Figures 3 to 5. In each figure, the symbols represent the experimental data, and the solid lines denote the calculated data, which were computed by the NRTL model with the parameters shown in Table 4. At a given temperature, the variation trends between p and x1 in Figures 3 to 5 are approximately the same, namely, that when the mole fraction x1 increases, the equilibrium pressure p monotonously increases. Figures 3 to 5 also describe the relative pressure deviations of the experimental data from the

N

OF =

∑ (pexp − pcal )i2

(7)

i=1

where N is the number of the experimental data, and pexp and pcal are the experimental pressure and the calculated pressure.

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RESULTS AND DISCUSSION By correlating the experimental VLE data of each binary system using eqs 1 to 6 and then minimizing the objective function (eq Table 4. Parameters of the NRTL Model values parameters

R161 (1) + DMAC (2)

R161 (1) + NMP (2)

R134a (1) + DMAC (2)

α a12 b12 a21 b21

5.935 8668 −250.2 2321 −4208

6.509 1344 −1398 1824 −3329

15.79 2738 −2441 6394 −1171

Table 5. Experimental and Calculated VLE Data for R161 (1) + DMAC (2)a T/K

x1

pexp/kPa

pcal/kPa

δp/%b

T/K

x1

pexp/kPa

pcal/kPa

δp/%b

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.2234 0.3730 0.4955 0.6100 0.6652 0.7759 0.8584 0.9064 0.1783 0.2977 0.4058 0.4901 0.5983 0.6652 0.8161 0.9078 0.1652 0.2737 0.3952 0.5107 0.5770 0.6704 0.7937 0.8760 0.9368 0.1657 0.2837 0.4600 0.5200 0.6468 0.7265 0.8098

140.2 241.6 333.2 418.1 468.1 567.5 660.2 713.0 138.7 234.2 331.5 405.1 510.8 584.6 774.1 909.0 159.0 263.5 390.2 512.4 591.5 720.0 892.0 1039.0 1185.0 189.2 328.1 550.4 631.4 818.3 950.0 1113.0

139.4 238.7 325.8 414.4 460.5 562.6 649.3 704.1 138.3 234.8 326.2 401.4 505.2 575.4 762.1 906.7 158.0 265.2 390.3 517.0 594.7 714.1 902.0 1063.3 1212.6 193.5 335.7 559.8 641.1 827.9 962.7 1130.9

0.60 1.21 2.23 0.90 1.63 0.86 1.64 1.24 0.32 0.24 1.59 0.91 1.09 1.57 1.55 0.25 0.65 0.64 0.04 0.90 0.54 0.83 1.12 2.34 2.33 2.28 2.30 1.70 1.53 1.18 1.34 1.61

323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

0.8820 0.9381 0.1638 0.2793 0.3776 0.5564 0.6537 0.7419 0.7980 0.8625 0.9066 0.9542 0.1547 0.3008 0.4892 0.5620 0.6454 0.6970 0.7700 0.8269 0.8786 0.9134 0.9711 0.1786 0.2920 0.4620 0.5810 0.6642 0.7320 0.7820 0.8472 0.9050

1312.8 1502.7 234.5 405.2 554.3 845.1 1040.3 1198.1 1325.4 1528.4 1702.3 1965.3 267.2 518.4 860.1 1024.5 1198.1 1265.0 1470.0 1667.0 1879.0 2060.0 2446.0 364.2 590.1 952.1 1230.5 1447.0 1630.2 1810.5 2084.3 2460.3

1318.0 1509.6 231.3 399.0 546.2 832.8 1007.4 1189.0 1325.3 1518.5 1689.7 1932.3 261.9 516.1 861.8 1005.1 1181.6 1300.8 1491.6 1671.0 1877.7 2057.8 2482.1 360.9 595.7 962.2 1237.9 1448.9 1641.1 1802.9 2060.7 2379.1

0.40 0.46 1.36 1.54 1.46 1.46 3.16 0.76 0.01 0.64 0.74 1.68 1.99 0.45 0.19 1.89 1.38 2.83 1.47 0.24 0.07 0.11 1.48 0.90 0.95 1.06 0.60 0.13 0.67 0.42 1.13 3.30

Standard uncertainties u are u(p) = 0.6 kPa, u(T) = 0.072 K, and u(x) = 0.015. bRelative deviation of the pressure (δp): δp/% = (|pexp − pcal|/pexp)· 100.

a

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Table 6. Experimental and Calculated VLE Data for R161 (1) + NMP (2)a T/K

x1

pexp/kPa

pcal/kPa

δp/%b

T/K

x1

pexp/kPa

pcal/kPa

δp/%b

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15

0.1320 0.2433 0.3367 0.4469 0.6171 0.7150 0.8014 0.8830 0.9440 0.1380 0.2285 0.3247 0.4263 0.5272 0.6160 0.7088 0.8084 0.8770 0.9312 0.1249 0.1917 0.2818 0.3920 0.4655 0.6010 0.7000 0.7871 0.9172 0.9669 0.1453 0.2025 0.3140 0.4442 0.5500

84.4 155.8 221.5 298.1 430.5 510.4 606.5 669.4 735.9 108.6 182.1 264.5 355.1 446.5 532.1 634.2 761.6 849.5 930.4 125.1 194.8 291.5 412.8 491.4 648.9 789.4 910.0 1150.8 1287.6 178.3 250.4 391.7 565.4 715.3

82.0 153.3 215.1 291.4 419.9 503.4 586.1 674.7 746.6 108.7 181.8 261.8 349.7 441.9 529.1 629.8 754.7 856.5 948.2 122.7 189.6 281.6 398.0 479.0 638.9 770.6 904.9 1168.7 1295.6 176.4 247.2 388.0 559.7 708.2

2.82 1.61 2.88 2.26 2.45 1.38 3.36 0.80 1.45 0.09 0.14 1.03 1.53 1.03 0.56 0.70 0.91 0.83 1.91 1.92 2.69 3.40 3.59 2.53 1.53 2.39 0.56 1.55 0.62 1.07 1.28 0.94 1.01 0.99

323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

0.6581 0.7490 0.8561 0.9190 0.9628 0.1367 0.1969 0.3117 0.4913 0.5704 0.6735 0.8093 0.8604 0.9067 0.9517 0.1523 0.2317 0.3464 0.4577 0.5620 0.6618 0.7750 0.8660 0.9412 0.1394 0.2187 0.3024 0.3966 0.4881 0.5891 0.6730 0.8240 0.9145

885.7 1043.0 1270.5 1461.7 1602.4 207.8 298.6 466.1 748.2 880.3 1083.6 1398.9 1536.7 1700.4 1910.6 274.0 413.9 624.3 835.4 1056.1 1275.3 1585.1 1915.3 2312.2 302.7 466.8 649.8 853.4 1067.5 1334.1 1596.0 2112.3 2610.5

874.6 1034.8 1272.1 1458.7 1617.1 202.4 293.0 469.2 759.5 896.9 1092.3 1406.9 1560.8 1733.3 1945.1 273.0 418.0 632.2 848.0 1062.2 1285.6 1583.2 1901.1 2297.9 299.7 472.9 658.6 872.8 1088.3 1339.9 1567.4 2075.9 2556.4

1.26 0.78 0.13 0.21 0.92 2.61 1.89 0.67 1.51 1.88 0.80 0.57 1.57 1.93 1.81 0.37 0.98 1.26 1.51 0.57 0.80 0.12 0.74 0.62 1.00 1.31 1.35 2.27 1.95 0.43 1.79 1.72 2.07

Standard uncertainties u are u(p) = 0.6 kPa, u(T) = 0.072 K, and u(x) = 0.015. bRelative deviation of the pressure (δp): δp/% = (|pexp − pcal|/pexp)· 100.

a

calculated values, and the calculated data are basically consistent with the experimental data. From Tables 5 to 7 and Figures 3 to 5, it can be found that the systems R161 + DMAC, R161 + NMP, and R134a + DMAC all have very good affinity, and especially the affinity between R161 + DMAC is the best in the three systems. The activity coefficient of an ideal solution which obeys Raoult’s law equals to 1, and the deviation from Raoult’s law for a real solution can be measured by its activity coefficient. The γ−x diagrams of the three binary systems at two temperatures 313.15 K and 343.15 K are shown in Figure 6, in which γ1 and x1 respectively are the activity coefficient and mole fraction of species 1, and the symbols represent the experimental data and the lines denote the calculated data. In Figure 6, the activity coefficients are always less than the value 1, which shows that all of the three binary systems exhibit negative deviations from Raoult’s law, and the order of the negative deviation degree from strong to weak is arranged as R161 + DMAC > R161 + NMP > R134a + DMAC. Moreover, for each binary system, the activity coefficient decreases when the temperature increases, which means that the degree of the negative deviation from Raoult’s law becomes stronger with the increase of the temperature. Similarly, it is concluded that the degree of the

negative deviation becomes weaker with the increase of mole fraction x1. Many published works37,38 explained the negative deviation differences based on the molecular structure and hydrogen bond. Using this analysis method, we try to explain why R161 + DMAC system has a negative value higher than the other systems. DMAC has a chain-like molecular structure, while NMP has a ring-like molecular structure. The molecular structure of NMP has a stronger steric hindrance effect, and the intermolecular hydrogen bond between R161 and NMP is weaker than that between R161 and DMAC. Therefore R161 + DMAC has a higher negative deviation than R161 + NMP. In molecular structure of R134a, one C atom has three F atoms, and the other C atom has two H atoms and one F atom. The F and H atoms belong to different C atoms are easy to form intramolecular hydrogen bonding, which could decrease the solubility in a polar solvent.42 The number of intramolecular hydrogen bonding in R161 is less than that in R134a, and R161 + DMAC has a higher negative deviation than R134a + DMAC.

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CONCLUSIONS In this work, the VLE data of the binary systems R161 + DMAC, R161 + NMP, and R134a + DMAC at seven 3293

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Table 7. Experimental and Calculated VLE Data for R134a (1) + DMAC (2)a T/K

x1

pexp/kPa

pcal/kPa

δp/%b

T/K

x1

pexp/kPa

pcal/kPa

δp/%b

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15

0.1359 0.2215 0.3190 0.4340 0.5344 0.5848 0.7087 0.7660 0.8573 0.9528 0.1560 0.2702 0.4506 0.5605 0.6256 0.6929 0.7643 0.8058 0.8550 0.9354 0.1737 0.2421 0.3850 0.5208 0.6558 0.7398 0.7842 0.8540 0.9548 0.1436 0.2451 0.4141

68.6 112.4 165.4 229.6 284.8 313.9 382.6 417.3 473.6 532.6 104.5 193.5 324.9 405.7 454.3 507.6 562.3 595.6 635.2 703.1 158.7 223.6 359.4 492.6 623.7 708.7 756.6 835.7 952.4 168.5 291.5 495.7

70.3 115.1 166.7 228.8 284.3 312.8 385.3 420.3 478.5 541.6 107.5 187.4 316.5 397.9 447.6 500.5 559.1 594.4 637.9 712.5 156.4 218.6 350.7 479.8 614.2 702.6 751.7 833.2 961.5 165.8 284.2 485.1

2.43 2.39 0.82 0.37 0.17 0.34 0.71 0.72 1.03 1.69 2.92 3.14 2.57 1.92 1.47 1.39 0.57 0.19 0.43 1.33 1.48 2.22 2.41 2.59 1.53 0.86 0.65 0.30 0.96 1.59 2.50 2.14

323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

0.5720 0.6700 0.7312 0.8180 0.9145 0.1029 0.2304 0.3495 0.4843 0.6472 0.7540 0.8202 0.9099 0.1200 0.2376 0.3930 0.4688 0.5410 0.6310 0.7050 0.8180 0.9040 0.1200 0.2440 0.4050 0.4925 0.5780 0.6530 0.7440 0.8390 0.9127

687.7 804.3 887.4 1008.6 1162.3 154.8 342.6 514.2 718.3 978.5 1157.6 1275.1 1460.3 224.7 439.6 721.5 871.3 1008.5 1180.5 1340.5 1601.6 1845.6 274.6 549.0 915.6 1120.7 1342.6 1534.6 1773.9 2053.6 2300.4

679.6 806.3 889.4 1015.0 1172.0 150.1 337.8 515.5 721.2 981.0 1164.4 1287.9 1476.5 219.8 437.3 729.0 874.2 1014.9 1195.6 1350.7 1608.1 1835.8 271.5 554.0 925.8 1132.0 1338.2 1525.0 1764.1 2040.5 2293.1

1.17 0.25 0.22 0.64 0.83 3.01 1.39 0.25 0.40 0.25 0.59 1.00 1.11 2.16 0.53 1.03 0.33 0.63 1.28 0.76 0.40 0.53 1.11 0.91 1.11 1.01 0.33 0.62 0.55 0.64 0.32

Standard uncertainties u are u(p) = 0.6 kPa, u(T) = 0.072 K and u(x) = 0.015. bRelative deviation of the pressure (δp): δp/% = (|pexp − pcal|/pexp)· 100.

a

Figure 2. Relative deviations of the pressure for the three binary systems at temperatures from (293.15 to 353.15) K: ●, R161 (1) + DMAC (2); ▲, R161 (1) + NMP (2); ■, R134a (1) + DMAC (2).

Figure 3. Isothermal VLE data for R161 (1) + DMAC (2): ■, 293.15 K; □, 303.15 K; ●, 313.15 K; ○, 323.15 K; ▲, 333.15 K; △, 343.15 K; ★, 353.15 K; solid lines, calculated results using the NRTL model.

temperature levels from 293.15 K to 353.15 K were obtained. Then the five-parameter NRTL model was chosen to correlate the experimental VLE data. According to the order of R161 + DMAC, R161 + NMP, and R134a + DMAC, the mean relative deviations of the pressure between the experimental and the calculated values are 1.16 %, 1.39 %, and 1.13 %, and the maximum deviations of that are 3.30 %, 3.59 %, and 3.14 %. It

was appropriate to choose the NRTL model to correlate the experimental VLE data in this work. The VLE data show that the systems R161 + DMAC, R161 + NMP, and R134a + DMAC all have very good affinity, and especially the affinity of the system R161 + DMAC is the best. By observing the experimental and calculated activity coefficients, it is found that all three binary systems exhibit negative deviations from Raoult’s law, and the order of the 3294

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systems could be considered as a potential working pair for absorption power/cooling cogeneration cycles.

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AUTHOR INFORMATION

Corresponding Author

*E-mail address: [email protected]. Tel.: +86 10 64416406. Fax: +86 10 64416406. Funding

The support provided by the National Natural Science Foundation of China (no. 51276010) and the National Basic Research Program of China (no. 2010CB227304) for the completion of the present work is gratefully acknowledged. Notes

The authors declare no competing financial interest.

Figure 4. Isothermal VLE data for R161 (1) + NMP (2): ■, 293.15 K; □, 303.15 K; ●, 313.15 K; ○, 323.15 K; ▲, 333.15 K; △, 343.15 K; ★, 353.15 K; solid lines, calculated results using the NRTL model.

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REFERENCES

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Figure 5. Isothermal VLE data for R134a (1) + DMAC (2): ■, 293.15 K; □, 303.15 K; ●, 313.15 K; ○, 323.15 K; ▲, 333.15 K; △, 343.15 K; ★, 353.15 K; solid lines, calculated results using the NRTL model.

Figure 6. Activity coefficient of species 1 in absorbent as a function of mole fraction at T = 313.15 K and T = 343.15 K: ●, R161 (1) + DMAC (2); ▲, R161 (1) + NMP (2); ■, R134a (1) + DMAC (2);  , 313.15 K; - - -, 343.15 K. Symbols: experimental data; lines: calculated results using the NRTL model.

negative deviation degree from strong to weak is arranged as R161 + DMAC > R161 + NMP > R134a + DMAC. The reason that the R161 + DMAC system has a higher negative value than other systems was explained based on the molecular structure and hydrogen bond. Moreover, for each binary system, the degree of the negative deviation from Raoult’s law becomes stronger with the increase of the temperature, and that becomes weaker with the increase of mole fraction x1. The three binary 3295

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