Volumetric and Thermodynamic Properties of Liquid Mixtures of 2- n -Butoxyethanol with Water

International Journal of Thermophysics, Vol. 19, No. 1, 1998

Volumetric and Thermodynamic Properties of LiquidMixtures of 2-n-Butoxyethanol with Water

P. J. Back,1 R. Malhotra,1 and L. A. Woolf1, 2

1 Atomic and Molecular Physics Laboratories, Research School of Physical Sciences andEngineering, Australian National University, Canberra, ACT 0200, Australia.

2 To whom correspondence should be addressed.

191

0195-928X/00/0700-0191$18.00/0 C 2000 Plenum Publishing Corporation

Received August 22, 1997

p-V-T data for six compositions of 2-n-butoxyethanol (BE) and water havebeen obtained in the form of volume ratios at several temperatures in the range278.15 to 353.13 K at pressures from atmospheric to 347 MPa or higher. One ofthe compositions is in the region where two phases exist at certain temperatures,while two compositions are near the boundary of that region. Densities atatmospheric pressure in a temperature range similar to that for the p-V-T dataare also reported. Isothermal compressibilities, isobaric expansivities, andchanges in the isobaric heat capacity have been calculated from the volumetricdata for pressures up to 300 MPa. The values of normalized volume fluctuationsobtained from the data at 0.1 MPa approach those of water for conditionswhich are close to those for phase separation in this system. Such behavior isnot observed at 100 MPa, where such separation is suppressed.

KEY WORDS: compressibility; expansivities; 2-n-butoxyethanol; heat capacity;p-V-T data; Tait equation; volume fluctuations.

1. INTRODUCTION

Although this system has been studied extensively at pressures close toatmospheric, there are few data for its properties at high pressures. Thiswork was performed principally to provide p-V-T data for the study byMensah-Brown and Wakeham [ 1 ] of the effect of pressure on the thermalconductivity of mixtures of 2-n-butoxyethanol (BE) and water. Accor-dingly, two of the six compositions of the present work were close to but

outside opposite sides of the concentration region at which phase separa-tion occurs [2-4] at atmospheric and higher pressures. Another composi-tion was close to that of the lower consolute mixture and measurements forthis mixture were made at temperatures extending to close to the lowerconsolute temperature at 0.1 MPa. (At 0.1 MPa the two-phase region existsfor a small range of water-rich compositions at temperatures betweenabout 322.3 and 403.3 K.) An extensive series of density measurements at0.1 MPa has been made to assist the interpretation of the results at higherpressures. These data have enabled the effect of pressure and temperatureon volume fluctuations in the system to be determined. An earlier paper[5] reported p-V-T measurements for pure BE.

2. EXPERIMENTAL

The BE was Fluka Chemika HPLC-GC grade material of statedpurity <99.9% mol, which, before use, was fractionally distilled underreduced pressure in an argon atmosphere and then stored under helium.Temperatures were measured relative to IPTS-68 and converted to ITS90;they had an accuracy of +0.01 K and were constant within +0.005 K.Volume ratios k=V p /V 0 . 1 , with Vp and V0.1, the volumes of a fixed massof liquid at pressure p and 0.1 MPa, respectively, were measured with anautomated bellows volumometer described in detail elsewhere [6].

A summary of the pressure measurement system is given in Ref. 7.Densities at atmospheric pressure (0.093 to 0.095 MPa) were measured forsamples taken from the volumometer at the conclusion of the experimentsfor each composition with a reproducibility of +0.005 kg.m - 3 with anAnton Paar Model DMA 602 densimeter calibrated frequently with waterand dry nitrogen [8]. Measurements were also made for a series ofstandard solutions to enable determination of the composition of thevolumometer samples.

3. RESULTS AND DISCUSSION

3.1. Volumetric Data

The experimental pressures, temperatures, and volume ratios are givenin Tables I-VI for each mole fraction, x1, of BE. The molecular weightswhich were used were 0.118767 and 0.0180153 kg.mol for BE and water,respectively. For the system with x1 = 0.04826 the highest temperature usedwas 322.14 K, which is about 0.1 K below the temperature at 0.1 MPa atwhich a phase separation is expected [4], which persists to a temperaturewell above the highest attainable with the present volumometer [6]. The

192 Back, Malhotra, and Woolf

Properties of Mixtures of 2-n-Butoxyethanol with Water 193

Table I. Experimental Pressures, Volume Ratios, k = V p /V 0 . 1 , and Densitiesa at 0.1 MPa for2-Butoxyethanol (1) + Water (2), x1 =0.006934

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T = 278.15 K; p(0.1) = 999.46 kg . m-3

2.5474.9969.839

14.60519.57924.218

0.99890.99780.99570.99370.99160.9897

27.6138.5458.5578.4798.55

119.25

0.98830.98410.97660.96950.96270.9561

138.74158.58177.93198.48223.71248.98

0.95010.94420.93880.93330.92680.9205

273.22298.93324.37348.67366.62

0.91480.90910.90360.89870.8951

T= 288.15 K; p(0.1) = 998.04 kg.m - 3

2.5474.9969.519

14.58519.95523.522

0.99890.99780.99590.99370.99150.9901

26.9737.6457.8978.1797.96

118.42

0.98870.98460.97700.96990.96320.9567

138.58158.24178.10198.24224.32248.48

0.95050.94480.93930.93390.92720.9213

274.01298.46324.18348.82370.04

0.91530.90980.90430.89930.8950

T=298.14 K; p(0.1) =995.61 kg . m-3

2.5474.996

10.15514.53520.05523.011

0.99880.99770.99540.99350.99120.9900

28.0338.6158.6578.6698.93

119.14

0.98790.98380.97630.96920.96240.9559

139.10158.67178.36199.31224.32248.47

0.94980.94410.93860.93310.92670.9208

273.84299.38322.68348.33374.21

0.91480.90910.90410.89890.8938

T=313.14K; p(0.1 ) = 990.28 kg . m-3

2.5474.9969.938

15.45419.42923.547

0.99880.99770.99550.99310.99140.9897

27.5839.0758.7678.5198.56

118.60

0.98800.98340.97590.96890.96200.9556

139.16158.62179.09198.96223.97249.13

0.94930.94360.93780.93250.92610.9200

273.34298.75323.95346.87374.55

0.91430.90850.90310.89850.8930

T= 323.14 K; p(0.1) = 985.76 kg . m-3

2.5474.9969.396

14.53519.40423.646

0.99880.99760.99550.99320.99100.9892

28.2437.8957.9078.6298.43

118.31

0.98720.98320.97540.96780.96100.9544

138.72158.76179.08198.64224.14248.75

0.94800.94210.93630.93100.92440.9183

273.74297.55322.84349.30373.67

0.91240.90700.90150.89600.8912

a Value at 338.13 K measured; values at other temperatures except 278.15 K interpolated fromdata at each temperature given in Table VIII. Value at 278.15 K obtained from extrapolationof the values at the higher temperatures.


Table I. (Continued)

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 338.13 K; p(0.1) = 977.79 kg • m-3

2.5474.9969.56814.86019.55423.571

0.99880.99760.99550.99310.99100.9892

28.0538.7658.7678.8499.26118.94

0.98730.98290.97500.96750.96030.9537

139.14159.10179.23198.62223.70249.24

0.94730.94120.93540.93010.92350.9172

273.95298.77323.71346.31377.89

0.91130.90560.90030.89570.8894

Table II. Experimental Pressures, Volume Ratios, k= Vp/V0 . 1 , and Densitiesa at 0.1 MPafor 2-Butoxyethanol (1) + Water (2), x1 = 0.015965

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 288.15 K; p(0.1) = 997.18 kg . m-3

2.5474.9969.839

14.60519.57924.218

0.99890.99780.99570.99370.99160.9897

27.6138.5458.5578.4798.55

119.25

0.98830.98410.97660.96950.96270.9561

138.74158.58177.93198.48223.71248.98

0.95010.94420.93880.93330.92680.9205

273.22298.93324.37348.67366.62

0.91480.90910.90360.89870.8951

T=298.14 K; p(0.1) = 993.98kg.m-3

2.5474.9969.519

14.58519.95523.522

0.99890.99780.99590.99370.99150.9901

26.9737.6457.8978.1797.96

118.42

0.98870.98460.97700.96990.96320.9567

138.58158.24178.10198.24224.32248.48

0.95050.94480.93930.93390.92720.9213

274.01298.46324.18348.82370.04

0.91530.90980.90430.89930.8950

T= 313.14 K; p(0 .1 ) = 987.48 kg . m-3

2.5474.996

10.15514.53520.05523.011

0.99880.99770.99540.99350.99120.9900

28.0338.6158.6578.6698.93

119.14

0.98790.98380.97630.96920.96240.9559

139.10158.67178.36199.31224.32248.47

0.94980.94410.93860.93310.92670.9208

273.84299.38322.68348.33374.21

0.91480.90910.90410.89890.8938

aValue at 313.14 K measured; values at other temperatures interpolated.


Table II. (Continued)

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 323.14 K; p(0.1) = 982.28 kg.m-3

2.5474.9969.93815.45419.42923.547

0.99880.99770.99550.99310.99140.9897

27.5839.0758.7678.5198.56118.60

0.98800.98340.97590.96890.96200.9556

139.16158.62179.09198.96223.97249.13

0.94930.94360.93780.93250.92610.9200

273.34298.75323.95346.87374.55

0.91430.90850.90310.89850.8930

T= 338.13 K; p(0.1) = 973.47 kg . m-3

2.5474.9969.39614.53519.40423.646

0.99880.99760.99550.99320.99100.9892

28.2437.8957.9078.6298.43118.31

0.98720.98320.97540.96780.96100.9544

138.72158.76179.08198.64224.14248.75

0.94800.94210.93630.93100.92440.9183

273.74297.55322.84349.30373.67

0.91240.90700.90150.89600.8912

T=348.13K; p(0.1) = 967.04 kg . m-3

2.5474.9969.56814.86019.55423.571

0.99880.99760.99550.99310.99100.9892

28.0538.7658.7678.8499.26118.94

0.98730.98290.97500.96750.96030.9537

139.14159.10179.23198.62223.70249.24

0.94730.94120.93540.93010.92350.9172

273.95298.77323.71346.31377.89

0.91130.90560.90030.89570.8894

Table III. Experimental Pressures, Volume Ratios, k= V p /V 0 . 1 , and Densitiesa at 0.1 MPafor 2-Butoxyethanol (1) + Water (2), x1 = 0.048263

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 288.15 K; p(0.1) = 986.97 kg . m-3

2.5474.9969.381

14.83519.15923.199

0.99880.99760.99550.99300.99110.9894

27.9438.3158.5378.5798.09

118.85

0.98740.98310.97540.96820.96160.9549

139.37159.42178.79199.18224.51248.98

0.94870.94300.93770.93240.92610.9203

273.67298.50321.35335.24348.96

0.91470.90930.90460.90190.8992

a Value at 313.14 K measured; values at other temperatures interpolated.


Table III. (Continued)

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 298.14 K; p(0.1) = 981.65 kg.m-3

2.5474.9969.14514.36419.42423.701

0.99870.99760.99560.99320.99090.9890

28.2138.5059.0178.9599.00119.03

0.98710.98280.97480.96760.96070.9543

138.58158.56178.92199.03224.14249.47

0.94830.94250.93690.93170.92540.9193

274.05297.65321.47332.95347.48

0.91370.90860.90360.90130.8985

T = 313.14 K; p(0.1) = 972.92 kg . m-3

2.5474.9969.41015.00019.73523.776

0.99870.99750.99530.99260.99040.9886

27.8538.1157.9077.8197.97118.16

0.98680.98240.97440.96700.96000.9533

138.15158.58178.33199.01223.80248.79

0.94710.94110.93560.93010.92380.9177

274.06298.19323.80349.11373.48

0.91190.90650.90120.89610.8913

T = 322.14 K; p(0.1 ) = 966.92 kg.m-3

2.5474.9969.31715.20219.64923.666

0.99870.99740.99520.99230.99020.9883

28.0238.3159.0578.7696.71117.07

0.98630.98180.97330.96590.95950.9527

138.24159.10178.82199.32224.55249.85

0.94600.93980.93420.92860.92210.9160

273.28299.41323.99346.57379.42

0.91050.90470.89950.89500.8885

Table IV. Experimental Pressures, Volume Ratios, k= V p /V 0 . 1 , and Densitiesa at 0.1 MPafor 2-Butoxyethanol (1) + Water (2), x1= 0.17484

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 288.15 K; p(0.1) = 957.48 kg • m-3

2.5474.9969.716

14.72719.56423.726

0.99860.99730.99480.99220.98980.9878

28.6838.6559.3778.9399.44

119.31

0.98550.98100.97230.96490.95760.9510

138.92158.79179.85199.99225.23249.55

0.94490.93910.93320.92790.92170.9159

274.16299.23323.87347.22367.62

0.91040.90510.90010.89550.8917

aValue at 313.14 K measured; values at other temperatures except 353.13 K interpolated.Value at 353.13 K extrapolated from p(0.1) at lower temperatures.


Table IV. (Continued)

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T=298.14K; p(0.1) = 950.36 kg.m-3

2.5474.9969.67714.72519.47123.969

0.99860.99720.99460.99200.98950.9873

28.6339.4859.2279.0899.27118.81

0.98500.97990.97140.96360.95630.9497

138.74159.22179.07199.85224.80250.00

0.94340.93720.93160.92600.91970.9137

275.32299.53324.23347.53372.99

0.90790.90270.89760.89300.8883

T=313.14K; p(O.l) = 939.14 kg.m-3

2.5474.9969.66014.90519.97924.416

0.99850.99700.99430.99130.98850.9862

29.2939.7459.7279.5299.98120.02

0.98370.97850.96950.96130.95360.9466

139.67160.08179.62200.05225.75250.74

0.94010.93380.92810.92250.91580.9097

275.35301.17324.93346.91371.87

0.90390.89830.89330.88890.8841

T = 323.14 K; p(0.1) = 930.96 kg • m-3

2.5474.9969.80814.61020.10423.746

0.99840.99680.99390.99100.98790.9859

28.0739.4459.4478.4999.24119.53

0.98350.97770.96830.96020.95210.9448

139.65159.54178.87199.08224.38249.97

0.93800.93170.92590.92020.91340.9070

273.59299.79324.64347.17371.39

0.90150.89560.89030.88570.8810

T= 338.13 K; p(0.1) = 918.81 kg.m-3

2.5474.99610.16515.14420.60424.223

0.99820.99660.99320.99000.98670.9845

28.8339.6559.1779.0899.43119.38

0.98190.97600.96630.95740.94910.9416

139.14159.48179.35199.29225.09249.24

0.93460.92790.92180.91600.90890.9027

274.69300.24324.73347.98371.96

0.89660.89070.88540.88050.8758

T= 353.13 K; p(0.1) = 906.36 kg.m-3

2.5474.9969.71214.62019.25423.639

0.99810.99630.99300.98970.98670.9839

30.1739.0458.8478.6798.47119.26

0.98000.97490.96450.95520.94670.9385

139.28159.07179.39199.89224.29248.92

0.93120.92440.91780.91160.90470.8982

275.00300.10325.43360.16385.66

0.89170.88590.88030.87310.8682


Table V. Experimental Pressures, Volume Ratios, k= Vp/V0.1, and Densitiesa at 0.1 MPafor 2-Butoxyethanol (1) + Water (2), x1=0.50247

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T=288.15 K; p(0.1) = 925.01 kg.m - 3

2.5474.9968.948

14.77719.11223.804

0.99840.99690.99440.99100.98850.9859

26.5937.4757.2576.9996.86

116.64

0.98440.97870.96920.96060.95280.9455

136.07156.69176.48197.25221.66247.64

0.93890.93240.92650.92060.91420.9078

273.03296.73318.89338.33350.10

0.90200.89670.89210.88820.8859

T= 298.14 K; p (0 .1) = 917.07 kg . m-3

2.5474.9969.612

14.69220.12524.138

0.99830.99670.99370.99050.98730.9849

26.7336.0356.8276.2895.88

117.37

0.98340.97830.96780.95900.95090.9429

136.35156.73176.14196.51220.50245.92

0.93630.92970.92370.91790.91140.9049

271.14294.34320.00343.17357.39

0.89890.89370.88830.88360.8808

T=313.14 K; p(0.1 ) = 904.65 kg . m-3

2.5474.9969.701

14.46919.22424.092

0.99820.99650.99340.99030.98720.9843

38.6358.5378.8297.61

118.05138.24

0.97580.96530.95570.94760.93950.9322

158.05177.00196.84222.47247.47271.89

0.92540.91940.91340.90620.89960.8936

295.19320.19346.40367.26

0.88830.88280.87740.8732

T= 323.14 K; p(0.1) = 895.70 kg . m-3

2.5474.9969.796

14.27819.75624.335

0.99800.99610.99260.98940.98560.9825

29.5637.4856.0975.7395.67

115.81

0.97920.97430.96370.95390.94490.9367

135.87155.37177.44197.05222.53247.29

0.92930.92250.91540.90950.90230.8957

271.39294.68319.51341.87355.17

0.88970.88420.87870.87390.8712

T= 338.13 K; p(0.1) = 882.55 kg . m-3

2.5474.9969.986

14.56819.73424.230

0.99780.99580.99180.98820.98440.9812

30.0537.4156.5277.1496.87

116.72

0.97720.97240.96100.95020.94090.9324

136.24157.17177.63197.05222.31246.52

0.92480.91710.91020.90410.89670.8901

270.39296.41321.25347.08372.21

0.88400.87770.87200.86640.8613

a Value at 288.15 K measured; values at other temperatures interpolated.


Table V. (Continued)

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 348.13 K; p(0.1) = 873.55 kg.m-3

2.5474.9969.48914.59619.82323.608

0.99770.99560.99180.98760.98350.9807

25.5939.7856.3777.0496.58116.10

0.97930.96950.95940.94820.93870.9300

137.14156.15176.32195.55222.82246.71

0.92150.91430.90720.90100.89270.8861

270.27295.80320.22349.32376.44

0.88000.87380.86820.86190.8565

Table VI. Experimental Pressures, Volume Ratios, k= Vp/V0.1, and Densitiesa at 0.1 MPafor 2-Butoxyethanol (1) + Water (2), x1 = 0.75398

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 288.15 K; p(0.1) = 912.45 kg.m - 3

2.5474.996

10.04614.59719.64223.516

0.99830.99670.99340.99060.98750.9853

27.1436.9756.8176.6496.81

116.67

0.98320.97770.96770.95870.95030.9428

136.14156.60176.16196.73221.04246.73

0.93600.92930.92330.91740.91080.9043

272.40296.77319.01332.61350.21

0.89820.89280.88810.88530.8818

T = 298.14K; p ( 0 . 1 ) = 904.40 kg . m-3

2.5474.9969.496

14.65719.44824.074

0.99820.99640.99330.98980.98670.9838

27.3836.7256.3875.9995.82

117.25

0.98180.97640.96600.95670.94820.9398

136.36156.81176.24196.62220.88246.34

0.93280.92590.91980.91380.90710.9005

271.13294.27319.54334.34349.47

0.89450.88920.88370.88070.8777

T=313.14K; p(0.1) =891.91 kg.m - 3

2.5474.9969.905

14.61719.53323.881

0.99800.99600.99230.98890.98540.9825

26.7436.7156.4276.7195.84

116.90

0.98060.97430.96320.95300.94440.9357

135.64155.48176.69196.78222.71247.69

0.92860.92170.91470.90860.90120.8946

272.45296.51318.35337.32347.92

0.88840.88280.87790.87390.8717

aValue at 288.15 K measured; values at other temperatures interpolated.


compositions x1 = 0.01596 and 0.17484 lie just outside opposite sides ofthe phase boundary at 0.1 MPa for all of the temperatures at whichmeasurements were made. The volume ratios are expected to have anaccuracy of +0.03-0.05% for pressures above 50 MPa, increasing to+ 0.1% at pressures near 0.1 MPa. The k can be represented within theexperimental accuracy by either the modified Tait equation, Eq. (1), or thesecant bulk modulus (SBM), K [ =(p — p 0 . 1 ) / (1 — k)] represented by third-order equations, with the pressure p in MPa:

for which the coefficients are given in Table VII together with the B and Cfor Eq. (1). Equation (1) is particularly suitable for extrapolation of the k,while Eq. (2) is the more accurate representation of them.

Table VI. (Continued)

p(MPa) k

p(MPa) k

p(MPa) k

p(MPa) k

T= 323.14 K; p(0.1) = 882.85 kg . m-3

2.5474.9969.404

14.04019.74623.640

0.99790.99590.99230.98880.98460.9818

30.9537.1258.1677.8096.80

117.40

0.97680.97290.96050.95030.94150.9328

137.18158.30176.52196.25221.55246.06

0.92510.91750.91150.90530.89790.8913

270.53296.62321.56347.22372.57

0.88510.87880.87320.86770.8626

T=338.13 K; p(0.1) = 869.72 kg .m - 3

2.5474.9969.546

14.53819.64724.088

0.99760.99540.99140.98720.98310.9797

26.3437.5760.3076.2895.97

115.83

0.97800.97000.95590.94710.93740.9286

137.19156.30176.78196.24221.33247.93

0.91990.91280.90560.89930.89170.8843

271.72296.75321.34350.70377.54

0.87820.87210.86640.85990.8545

T= 348.13 K; p(0.1) =860.72 kg.m - 3

2.5474.9969.770

14.57719.61224.002

0.99750.99510.99070.98640.98220.9786

27.0340.5357.6277.5496.56

117.27

0.97630.96650.95550.94420.93450.9249

136.16158.27178.26197.16221.73247.67

0.91690.90840.90120.89500.88740.8801

270.78295.23322.95348.37371.92

0.87390.86780.86150.85600.8512


Table VII. Coefficients of the SBM Equation (1) and Tait Equation (2) for 2-Butoxyethanol(1) + Water (2)

T ( K )a0

(MPa) a1

-a2(GPa-1)

a3

(GPa-2)102

(Dk/k)B

(MPa) C102

<Dk/k>

x1 =0.006934

278.15288.15298.14313.14323.14338.13

2116.12204.52266.82282.22232.32181.5

3.55873.46703.36043.44404.23084.0366

1.15330.69380.24300.16134.73402.8051

0.8640.097

-0.718-1.434

6.6932.754

0.0010.0000.0010.0020.0040.001

275.28288.86301.41301.78295.95280.76

0.30240.30490.30950.30690.30330.2957

0.0040.0040.0030.0010.0040.004

x1= 0.015965

288.15298.14313.14323.14338.13348.13

2229.82261.52172.72155.72053.92068.4

4.8424.685.3665.1265.534.944

7.43266.48658.78537.48639.09057.0157

10.0418.419

11.0659.126

11.3199.078

0.0100.0080.0110.0090.0110.010

298.41303.38285.86279.63262.66260.75

0.30170.30320.29210.28980.28290.2845

0.0080.0070.0140.0130.0170.009

x1 =0.048263

288.15298.14313.14322.15

2037.52014.91940.31879

6.2035.9425.9596.063

11.07259.54199.09219.5401

14.48311.89510.46411.079

0.0100.0070.0090.010

237.56233.51225.41217.18

0.25650.25620.25550.2534

0.0190.0190.0230.024

x1= 0.174838

288.15298.14313.14323.14338.13353.13

1804.491742.701626.561541.151425.891335.83

6.13385.95825.89145.98865.92285.8405

8.07907.24216.93697.52257.30227.6226

8.6657.3926.8427.7347.3458.276

0.0060.0040.0030.0050.0050.010

185.44177.87164.88155.89143.31134.78

0.22770.22710.22560.22430.22290.2244

0.0230.0230.0260.0280.0310.026

x1 =0.50247

288.15298.14313.14323.14338.13348.13

1556.681474.421416.531270.421158.811101.39

5.52225.37384.82295,16415.41585.3720

4.95814.14412.68443.02795.29985.7321

4.3632.8881.4160.7084.7435.885

0.0020.0040.0040.0080.0050.007

147.72139.11136.10117. 67109.96104.45

0.21600.21540.22320.21280.21570.2165

0.0140.0170.0050.0250.0210.015

x1= 0.75398

288.15298.14313.14323.14338.13348.13

1474.781359.651233.091176.901060.24994.24

5.22015.57125.60785.33445.37395.5315

3.57635.50405.80304.65285.15296.7450

2.2655.2265.4863.7224.4677.467

0.0040.0030.0030.0030.0050.012

138.12127.64115.60110.1299.0393.63

0.21540.21340.21240.21380.21290.2137

0.0110.0160.0210.0190.0230.017


Table VIII. Density, p(0.1) (kg.m-3), for 2-Butoxyethanol (1) + Water (2) at 0.1 MPaa

X1 p(0.1) x1 p(0.1) x1 p(0.1) x1 p(0.1)

T = 288.15K

00.0010290.0049770.0096850.0148870.0198440.0249460.0302900.049564

999.099998.894998.276997.764997.293996.576995.110993.246986.538

0.0894730.1818280.2532010.3011380.3670680.3980200.4291650.4510910.506773

974.891956.366946.504941.169934.964932.369930.061928.405924.714

0.5471470.5939330.6474690.7015930.7467870.7992550.8456230.8883200.950764

922.300919.769917.090914.625912.734910.711909.081907.693905.795

0.9811080.9835760.9872630.9917180.9958110.9990821

904.930904.874904.775904.603904.516904.423904.412

T = 298.14 K

00.0095800.0160450.019560

997.044995.173993.963992.874

0.0468030.0488060.0550230.168653

982.183981.449979.246951.406

0.1774160.5005540.5460720.447247

949.924917.188914.416920.803

0.6905360.7395150.7907451

907.086904.988902.984896.289

T=313.14K

00.0008670.0051380.0096840.0105810.0157120.016140

992.215991.956990.763989.560989.331987.588987.406

0.0164340.0190120.0298640.0300150.0386310.050930

987.276986.096980.916980.846976.943971.809

0.0607600.0990290.1097250.1236030.1560500.162370

968.050955.935953.042949.615942.648941.413

0.1811330.1959900.3983370.5977120.8147711

937.994935.490912.258899.069889.602883.775

T= 322.14 K

00.0049050.0100660.0157850.0202190.050531

988.484986.869985.213982.863980.584965.990

0.1001940.1532670.1754310.1993580.2987370.380309

948.861936.012931.675927.494913.974905.843

0.3987060.4502610.4988660.5447530.695576

904.264900.219896.828893.961886.226

0.7432630.7990710.9013300.9495411

884.186882.019878.535877.059875.649

T= 338.13 K

00.0099100.0157850.0496520.0496520.1707000.2003140.251227

980.554976.546973.558969.549969.555919.613914.166906.385

0.2512270.2512270.2512270.4448350.4448350.4960840.5446110.693380

906.199906.214906.188886.627886.646882.972879.912872.267

0.693380.7395740.7967140.9003250.9003250.9498311

872.279870.310868.076864.560864.576863.054861.658

00.0030990.0070160.0100400.0140570.0159590.0196781

980.554979.311977.752976.494974.542973.476970.870861.751

T= 348.13 K

00.010037

974.848970.322

0.0158270.196789

967.125906.378

0.4992170.752993

873.765860.760

1 852.730

a Density of water adjusted for local isotopic composition.

3.2. Densities at 0.1 MPa

The densities of the standard solutions at 0.1 MPa used for determi-nation of the composition of the volumometer samples are given inTable VIII. These measurements were made over a sufficient range ofconcentrations to enable an accurate comparison with literature data.The results were compared with the literature data by using the densitiesto obtain excess molar volumes, VmE. These were expressed asVEm/[x1(1-x1)] and plotted against (1 — 2x1). Figure 1 shows the presentdata for VEm/[x1(1-x1)] at the six lowest compositions, excluding x1 =0(see Table VIII), at 298.14 K, with those from Refs. 9, 11, and 12. Figure2 extends the comparison at 298.14 K to the higher compositions for thesame references as in Fig. 1 except Ref. 9, where the data are not available.The values from Roux et al. [10] were not included in the figures becausethey are mostly in close coincidence with either the present results or thoseof the other references. The comparisons were also made at 288.15 K withthe results of Ref. 9 and at 313.14 K with those of Ref. 10. The agreementwith the present data at all temperatures was generally within the com-bined experimental uncertainties, although it is evident from Fig. 1 thatthere is some scatter in the values of Koga et al. [9], and at the lower com-positions their data lie above those from the other sources. At those com-positions the data of Roux et al. [10] (not shown) are closer to those ofthe other data. The densities of the volumometer samples at 0.1 MPa, p0.1,were determined at the temperatures identified in Tables I-VI with a preci-sion of 2 x 10-6/p0.1 and an estimated accuracy of 2 x 10-5/p0.1. These were

Fig. 1. Excess molar volumes for 2-n-butoxyethanol (1) + water at0.1 MPa and 298.14 K for mole fractions x1<0.055. (O) Thiswork; (T) Ref. 11; (S) Ref. 12; ( + ) Ref. 9.



used to determine the corresponding x1 from fits of a Redlich-Kister typefor the standard solutions in Table VIII, although a cubic spline was usedfor the fit because the usual polynomial in (1 — 2x1) did not provide a goodfit. Those x1 were used to calculate the densities given in Tables I-VI at theother experimental temperatures by using a cubic spline fit of a Redlich-Kister type for the VE/[x1(1 -x1)] at those temperatures. At 353.13 K,for x1 = 0.17484 the density was estimated from an extrapolation of a cubicfit of the densities at the lower temperatures. A similar procedure was usedto estimate the density at 278.15 K for x1 = 0.006934. The compositions areestimated to have an accuracy of 0.0001 . x1 .

3.3. Isothermal Compressibilities

Isothermal compressibilities, KT, given in Table IX, were calculatedfrom the coefficients in Table VII for Eq. (2) using the relationship

They have a probable uncertainty of +1-2%. Koga et al. [13] calculatedKT as 0.1 MPa and 298.14 K from speed-of-sound and other measurements;their corresponding value is within the lower bound of our probable uncer-tainty at x1 =0.006934 but smaller by an amount exceeding the combinedmaximum uncertainties at x1 = 0.01596. The isobaric KT for x1 =0.007 and0.01596 initially are less than, and have a similar temperature dependence

Fig. 2. Excess molar volumes for 2-n-butoxyethanol (1) + water at0.1 MPa and 298.14 K for mole fractions x1 > 0.055. Symbols as inthe legend to Fig. 1.


Table IX. Isothermal Compressibilities (KT; MPa - 1) , Molar Volumes (Vm; cm3 .mol - 1) ,Isobaric Expansivities (A;K -1), Volume Fluctuations <(/(DV/V)2>), and Change in Molar

Heat Capacity (DCP; J . m o l - 1 . K - 1 ) in 2-Butoxyethanol (1) + Water (2)

p (MPa)

0.1 20 40 60 100 150 200 250 300

(a) x, = 0.0069337

104KT

vm103A-DCp

<(DV/V) 2 >

T = 278.15K

4.7218.7190.1200.00.0584

4.4718.5490.1570.80.0557

4.2318.3880.1891.50.0532

4.0218.2370.2172.10.0510

3.6617.9590.2643.10.0471

3.2817.6510.3114.10.0430

2.9817.3770.3474.70.0396

2.7217.1320.3745.20.0367

2.5016.9100.3935.50.0342

T=288.15K

104/KT

vm103A-Dcp<(DV/V)2>

4.5318.7460.2030.00.0580

4.3018.5820.2290.90.0555

4.0918.4260.2521.60.0532

3.9018.2800.2722.20.0511

3.5618.0100.3073.30.0473

3.2017.7090.3424.20.0433

2.9117.4410.3694.90.0400

2.6717.1990.3895.40.0371

2.4616.9810.4045.80.0347

T= 298.14 K

104KT

vm103A

-Dcp< ( D V / V ) 2 >

4.4118.7910.2860.00.0582

4.2018.6310.3000.90.0558

4.0018.4790.3141.70.0537

3.8218.3350.3272.30.0516

3.4918.0690.3503.40.0479

3.1517.7720.3744.40.0440

2.8717.5070.3915.20.0407

2.6417.2670.4045.70.0379

2.4517.0490.4156.00.0357

T=313.14K104KT

vm103A

-DcP<(DV/V)2>

4.3818.8930.4100.00.0604

4.1618.7330.4081.00.0579

3.9618.5810.4091.80.0555

3.7818.4380.4102.50.0534

3.4518.1730.4153.60.0495

3.1217.8780.4214.70.0454

2.8417.6140.4255.50.0420

2.6317.3750.4286.10.0394

2.4617.1560.4316.40.0373

T= 323.14 K

104KT

Vm103A-Dcp<(Dv/v) 2 >

4.4818.9790.4920.00.0634

4.2018.8160.4801.00.0600

3.9718.6630.4721.90.0572

3.7718.5190.4665.60.0547

3.4518.2540.4583.80.0507

3.1317.9570.4524.90.0468

2.8717.6900.4475.80.0436

2.6317.4490.4436.30.0405

2.3917.2310.4426.70.0372

T=338.13K

104KT

vm103A

-DCP<(DV/V)2>

4.5819.1340.6160.00.0673

4.3118.9660.5881.10.0638

4.0718.8080.5662.00.0608

3.8518.6590.5492.80.0581

3.5018.3870.5234.10.0535

3.1518.0850.4995.30.0490

2.8817.8150.4816.20.0454

2.6417.5710.4666.80.0423

2.4417.3490.4587.20.0395


Table IX. (Continued)

p(MPa)

0.1 20 40 60 100 150 200 250 300

(b) x1=0.015965

T=288.15K

104kTvm103a-AC,<(Dv/v)2>

4.4819.6690.3160.00.0546

4.1719.5010.3090.80.0512

3.9219.3440.3071.50.0485

3.7019.1970.3092.20.0462

3.3818.9280.3183.40.0428

3.0918.6250.3334.70.0397

2.8518.3500.3485.70.0373

2.6418.1000.3586.60.0349

2.4017.8730.3637.40.0322

T = 298.14K

104KTVm

103a

-Dcp<(DV/V)2>

4.4219.7320.3820.00.0555

4.1319.5650.3730.80.0523

3.8819.4090.3691.60.0496

3.6819.2630.3672.30.0473

3.3618.9950.3693.50.0438

3.0618.6930.3764.90.0406

2.8318.4200.3836.00.0381

2.6218.1710.3896.90.0357

2.4017.9440.3907.70.0332

T=313.14K

104KT

Vm103a-Dcp<(DV/V)2>

4.6019.8620.4820.00.0609

4.2419.6890.4700.90.0566

3.9419.5280.4611.70.0531

3.7119.3800.4542.40.0503

3.3619.1090.4453.80.0462

3.0518.8060.4395.20.0427

2.8318.5310.4366.40.0401

2.6218.2810.4347.40.0377

2.4018.0520.4318.20.0350

T= 323.14 K

104KTVm103a-DCP<(DV/V)2>

4.6419.9680.5480.00.0624

4.2819.7920.5340.90.0581

3.9919.6290.5221.80.0547

3.7619.4780.5122.50.0518

3.4019.2020.4964.00.0475

3.0818.8950.4825.50.0438

2.8418.6180.4716.70.0409

2.6318.3650.4647.70.0384

2.4118.1350.4598.60.0357

T= 338.13 K

104KT

Vm103a

-AC,<(DV/V)2>

4.8720.1480.6480.00.0679

4.4519.9620.6301.00.0626

4.1219.7930.6141.90.0585

3.8519.6360.5992.70.0551

3.4619.3520.5734.30.0503

3.1319.0370.5455.90.0462

2.8818.7530.5247.20.0432

2.6718.4950.5098.30.0405

2.4418.2600.5009.20.0375

T= 348.13 K

104KT

Vm103a-DCp<(DV/V)2>

4.8320.2820.7140.00.0690

4.4620.0950.6951.00.0643

4.1619.9230.6762.00.0604

3.9119.7630.6572.90.0573

3.5319.4720.6244.50.0525

3.1919.1490.5886.10.0482

2.9218.8590.5597.50.0448

2.6818.5970.5398.70.0417

2.4418.3600.5279.70.0384



p (MPa)

0.1 20 40 60 100 150 200 250 300

(c) x1 = 0.048263

T=288.15K

104KT

vm103a

-Dcp( (DV/V) 2 )

4.9123.1500.5020.00.0508

4.4322.9360.4940.80.0463

4.0622.7430.4841.40.0428

3.7722.5660.4742.00.0401

3.3622.2470.4573.10.0362

3.0221.8960.4444.30.0331

2.7721.5820.4385.30.0307

2.5421.2970.4356.10.0286

2.2921.0420.4246.80.0260

T = 298.14 K

104KT

Vm

103a-DCp

<(DV/V) 2 >

4.9623.275

0.5610.00.0528

4.4923.0580.5450.80.0483

4.1222.8610.5301.50.0447

3.8322.680

0.5162.10.0419

3.4122.3550.4953.20.0378

3.0521.9980.4784.50.0343

2.7821.6810.4665.60.0318

2.5521.3930.4576.40.0296

2.3121.1350.4447.10.0271

T=313.14K

104KT

Vm

103a

-Dcp<(DV/V)2>

5.1523.4840.6490.00.0571

4.6423.2570.6200.90.0520

4.2523.0510.5971.60.0480

3.9322.8640.5802.30.0448

3.4722.5290.5533.50.0402

3.0922.1630.5294.80.0364

2.8221.8380.5096.00.0337

2.6021.545

0.4916.90.0314

2.3821.2780.4727.60.0291

T= 322.15 K

104KT

Vm

103a-DCp

<(DV/V)2>

5.3223.630

0.7010.00.0603

4.7723.394

0.6650.90.0546

4.3523.1830.6381.70.0502

4.0122.9900.6182.40.0468

3.5322.6470.5883.60.0418

3.1422.274

0.5605.00.0378

2.8621.942

0.5356.20.0350

2.6321.643

0.5117.20.0326

2.4021.3720.4908.00.0301

(d) x1 = 0.174838

T = 288.15K

104KT

vm103a-Dcp<(DV/V)2>

5.5437.103

0.750.00.0358

4.9336.719

0.710.80.0322

4.4636.377

0.671.40.0294

4.0936.0670.642.00.0272

3.5535.5230.603.00.0239

3.0934.9410.564.10.0212

2.7834.433

0.535.00.0193

2.5333.980

0.515.80.0178

2.3033.5730.496.40.0164



p (MPa)

0.1 20 40 60 100 150 200 250 300

(d) x1 = 0.174838

T= 298.14 K

104KTvm103A-DCp

<(DV/V)2>

5.7337.3810.780.00.0380

5.1136.9810.730.80.0342

4.6136.6240.691.50.0312

4.2236.3030.662.10.0288

3.6435.7390.623.20.0253

3.1635.1390.574.40.0223

2.8334.6180.545.30.0202

2.5734.1550.526.10.0186

2.3333.7400.506.70.0171

T=313.14K

104KT

Vm

103A-DCP

<(DV/V)2>

6.1437.8270.820.00.0423

5.4337.3950.770.90.0378

4.8837.0120.731.60.0343

4.4436.6700.702.30.0315

3.8136.0730.653.40.0275

3.2835.4430.604.70.0241

2.9234.8990.565.70.0218

2.6434.4190.536.50.0200

2.4033.9880.517.20.0184

T= 323.14 K

10V

Vm103A-DCp<(DV/V)2>

6.4838.1590.850.00.0457

5.6937.7020.800.90.0405

5.0737.2990.761.70.0365

4.6036.9410.722.40.0334

3.9236.3210.673.60.0290

3.3635.6690.624.90.0253

2.9935.1090.586.00.0229

2.7034.6140.546.90.0209

2.4434.1720.527.60.0192

T=338.13K

10V

vm103A-DCp<(DV/V) 2>

7.0138.6640.900.00.0510

6.0938.1650.841.00.0449

5.4037.7300.791.80.0402

4.8637.3460.762.60.0366

4.1036.6860.703.90.0314

3.5036.0000.645.30.0273

3.0935.4140.606.50.0245

2.7834.8980.567.40.0224

2.5234.4390.538.10.0205

T= 353.13 K

104KT

Vm

103A-DCP

<(DV/V)2>

7.4839.1950.950.00.0560

6.4638.6570.881.10.0491

5.7038.1910.832.00.0438

5.1237.7810.792.80.0398

4.3037.0810.734.20.0341

3.6636.3550.675.70.0295

3.2235.7370.627.00.0265

2.8935.1960.587.90.0241

2.5834.7190.558.70.0218

Properties of Mixtures of 2-n-Butoxyethanol with Water


p (MPa)

0.1 20 40 60 100 150 200 250 300

(e) x1 = 0.50247

104KT

vm103a-DCp

<(DV/V)2>

6.4273.8800.860.00.0208

5.6972.997

0.811.50.0187

T=288.15K

5.1172.2140.762.60.0169

4.6471.515

0.723.60.0155

3.9470.3040.645.40.0134

3.3569.041

0.587.50.0116

2.9467.968

0.559.20.0104

2.6267.032

0.5210.50.0094

2.3766.201

0.4911.60.0086

T = 298.14K

104KT

vm103a-AC,< ( D V / V ) 2 >

104KT

Vm

103a

-Dcp<(DV/V)2>

104KT

Vm103a-Dcp<(DV/V)2>

104kT

Vm103a-Dcp<(DV/V)2>

104KT

Vm

103a-Dcp<(DV/V)2>

6.7874.519

0.890.00.0225

7.0675.542

0.940.00.0243

7.8776.296

0.970.00.0277

8.6277.432

1.020.00.0313

9.0778.229

1.050.00.0336

5.9973.5810.831.60.0202

6.2874.548

0.871.70.0219

6.8575.190

0.891.80.0245

7.3776.214

0.922.00.0272

7.7176.940

0.952.10.0290

5.3672.753

0.782.80.0182

4.8572.0160.733.80.0167

4.0970.7470.665.70.0143

3.4469.436

0.607.90.0123

T= 313.14 K

5.6573.665

0.813.00.0200

6.0574.229

0.833.20.0219

5.1372.875

0.764.10.0183

T=323.

5.4173.385

0.784.40.0198

4.3471.5140.696.20.0158

14 K

4.4671.960

0.716.50.0167

3.6470.110

0.628.60.0135

3.6870.519

0.649.00.0140

T= 338.13 K

6.4375.1730.863.40.0240

5.7174.269

0.804.70.0216

4.6972.752

0.737.00.0181

3.8871.2200.669.70.0153

T= 348.13 K

6.7075.843

0.883.60.0256

5.9374.894

0.825.00.0229

4.8673.307

0.757.40.0192

4.0271.710

0.6810.20.0162

3.0068.330

0.569.70.0109

3.1568.935

0.5810.50.0119

3.1769.326

0.5911.00.0123

3.3569.949

0.6111.90.0135

3.4670.388

0.6212.50.0142

2.6867.3690.53

11.10.0099

2.7967.921

0.5412.00.0107

2.8368.298

0.5512.60.0111

2.9768.856

0.5613.50.0121

3.0469.257

0.5714.20.0127

2.4366.515

0.5012.20.0091

2.5267.027

0.5113.20.0098

2.5967.382

0.5213.80.0103

2.6567.896

0.5314.90.0110

2.6868.274

0.5415.60.0114

209



p (MPa)

0.1 20 40 60 100 150 200 250 300

(f) x1 = 0.75398

T= 288.15 K

104KT

vm103A-DCp<(DV/v)2>

6.78102.5030.890.00.0158

6.01101.2100.812.20.0142

5.39100.0660.744.00.0129

4.8899.0460.705.60.0118

4.1297.2880.638.50.0101

3.4695.4720.5711.50.0087

3.0193.9450.5314.00.0077

2.6892.6210.4915.90.0069

2.4391.4480.4617.70.0064

T= 298.14

104KTvm103A-DCp<(DV/V)2>

7.35103.4140.920.00.0176

6.40102.0140.832.30.0155

5.66100.7930.774.20.0139

5.0999.7180.725.90.0127

4.2697.8820.659.00.0108

3.5795.9960.5912.20.0092

3.1194.4110.5414.70.0082

2.7693.0380.5016.80.0074

2.4791.8310.4718.60.0067

T=313.14

104KTVm103A

-DCP<(DV/V)2>

8.10104.8620.960.00.0201

6.95103.3090.872.50.0175

6.09101.9750.804.50.0155

5.42100.8110.756.40.0140

4.4898.8480.689.70.0118

3.7396.8540.6113.10.0100

3.2395.1890.5615.90.0088

2.8793.7520.5218.10.0080

2.5692.4910.49

20.00.0072

T= 323.14

10Vvm103A-DCP<(DV/V)2>

8.49105.9370.990.00.0215

7.29104.2930.902.60.0188

6.37102.8820.834.80.0166

5.66101.6540.786.80.0150

4.6599.5930.7010.20.0125

3.8497.5150.6313.80.0106

3.3195.7960.5716.70.0093

2.9394.3190.5319.00.0083

2.6393.0210.50

21.10.0076

T= 338.13

104KTvm103A-DCP<(DV/V)2>

9.42107.535

1.040.00.0246

7.95105.7000.942.80.0212

6.87104.1510.865.20.0185

6.04102.8190.817.30.0165

4.90100.6100.7311.00.0137

4.0298.4080.6514.90.0115

3.4596.5970.5918.00.0100

3.0495.0490.55

20.50.0090

2.7193.6940.52

22.60.0081

T= 348.13 K

104KTVm103A-DCP<DV/V)2>

10.05108.660

1.070.00.0268

8.36106.6990.963.00.0227

7.15105.0640.895.50.0197

6.26103.6680.837.70.0175

5.07101.3650.7511.60.0145

4.1799.0670.6715.70.0122

3.5897.1740.6118.90.0107

3.1395.5600.56

21.50.0095

2.7494.1700.53

23.80.0084


to, those of pure water [14]. The decrease with increase in temperature ofthe KT for the first composition does not persist much above 313.14 K, andfor X1 = 0.01596 the KT have increased to exceed those for water before thattemperature is reached. The isobaric KT for [ acetonitrile (1) +water] [15]and [methanol (1) + water] [14] have KT which remain below those forwater to much higher compositions: 0.1 < x1 < 0.2 for (acetonitrile + water)and 0.25 <x1 <0.35 for (methanol + water).

3.3. Volume Fluctuations

Table IX includes normalized volume fluctuations [16], <(DV/V)2>,defined by Eq. (4)

where Vm is the molar volume, to extend those obtained by Koga andWesth [17] at 0.1 MPa and 298.14 K. The <(DV/V)2> have an estimatederror of +1-2%. The Vm in Table IX were calculated as a function of tem-perature at chosen pressures from the densities at 0.1 MPa and the volume

Fig. 3. Temperature dependence of normalizedvolume fluctuations, <(DV/V)2>, in 2-n-butoxy-ethanol (1) + water at 0.1 MPa. (O) x1 =0.007;(A) x1 =0.016; (S) x1= 0.05; (D) x1 = 0.175;(T) x1 = 0.502; ( + ) water.


ratios from Eq. (2) using the coefficients from Table VII. The <(DV/V)2>for five of the six compositions and those for water calculated from thedata of Easteal and Woolf [ 14] are shown in Fig. 3 at 0.1 MPa. The valueat x1 =0.016 at 298 K is greater than the corresponding value in Ref. 17 byabout 0.0028, an amount which exceeds the combined maximum uncertain-ties and, taken with the other data at that temperature from Table IX,gives no indication of the inflection point which Koga and Westh obtainednear that composition. Figure 3 shows that, as the temperature increases,the <(DV/V)2> for x1 = 0.007, 0.016, and 0.05 increase rapidly and movetoward those for water. At the highest temperature, which is close to thephase boundary for x1 =0.016, the <(DV/V)2> for X1 = = 0.007, 0.016, andwater are virtually coincident. A similar trend appears to be present in thedata for x1 = 0.175, for which the phase boundary is closest at about 358 K.Koga [18] proposed a mixing scheme of three regions for this system witha transition between them which depends on the temperature and composi-tion: region I, x1 < 0.017 at 298 K, where the hydrogen bond network ofwater is enhanced by the BE; region II, 0.017 <x1 < 0.46 at 298 K, typifiedby water-rich and BE-rich clusters; and region III, x1 > 0.46 at 298 K,

Fig. 4. Temperature dependence of normalizedvolume fluctuations, <(DV/V)2>, in 2-n-butoxy-ethanol (1) + water at 100 MPa. Symbols as in thelegend to Fig. 3.

where micelles are significant. The rapid change in <(DV/V)2> for x1 ~0.016 shown in Fig. 3 begins close to the temperature of 298 K identified byKoga [18] as the temperature for transition of this composition from I toII at 0.1 MPa. In contrast, his data indicate that the I-II transition at thesame pressure for x1 .~ 0.007 was near 348 K. Figure 4 shows that themovement of the <(DV/V)2> of the mixtures towards those for water seenin Fig. 3 is not detectable at 100 MPa. The suppression of the phaseseparation [2, 3] before this pressure is reached would be expected fromthe influence of pressure in disrupting the hydrogen bond structure inregion I, and adversely affecting the formation and stability of clusters andmicelles in regions II and III.

3.5. Isobaric Expansivities

Isobaric expansivities, a, also given in Table IX, were calculated byfitting the Vm at a chosen pressure to a quadratic in T and differentiatinganalytically

3.4. Isobaric Molar Heat Capacity, Cp

The effect of pressure on the isobaric molar heat capacity is given by

where Cp (0.1 MPa) is the isobaric molar heat capacity at 0.1 MPa, M isthe molar mass, and p is the density of the liquid at p. The a wereexpressed by a quadratic equation in T to enable analytic differentiation.The error in the DCp is estimated to be +1 J . (mol . K - 1 ) . The change inthe Cp with either temperature or pressure is not very large at low x1 butincreases more rapidly at higher compositions. Apparent molal heatcapacities and molar heat capacities at 0.1 MPa are available [10, 21] forsome of the temperatures and compositions of the data in Table IX.

Properties of Mixtures of 2-n-Bntoxyethanol with Water 213

The a have an estimated error of +2-4%. The values at 0.1 MPa at x1 =0.5025 and 0.7540 for 298.14 and 323.14 K agree within 1% with thoseinterpolated from the data of Onken [19]. A direct comparison with themeasurements of Davies et al. [20] is not possible, as their data are nottrue thermal expansivities.

4. CONCLUSION

The volumetric data have provided values for the normalized volumefluctuations in this system over an extensive range of temperature, pressure,and composition. The magnitude of the fluctuations moves close to thosefor the major component, water, as the phase boundary is approached. Theinflection point in the normalized volume fluctuations at low x1 at 0.1 MPaand 298 K observed by Koga and Westh [15] has not been detected.

ACKNOWLEDGMENT

The authors wish to express their gratitude for the meticulousmeasurements of the densities at atmospheric pressure by Z. J. Derlacki.

REFERENCES

1. H. Mensah-Brown and W. A. Wakeham, Int. J. Thermophys. 16:237 (1995).2. G. Schneider, Z. Phys. Chem. N.F. 37:333 (1963).3. G. M. Schneider, in Water: A Comprehensive Treatise, F. Franks, ed. (Plenum, New York,

1972), p. 381.4. C. M. Ellis, J. Chem. Educ. 44:405 (1967).5. R. Malhotra and L. A. Woolf, J. Chem. Thermodyn. 25:1189 (1993).6. R. Malhotra and L. A. Woolf, Int. J. Thermophys. 14:1021 (1993).7. R. Malhotra and L. A. Woolf, Int. J. Thermophys. 16:901 (1995).8. R. Malhotra and L. A. Woolf, Fluid Phase Equil 94:227 (1994).9. Y. Koga, J. Kristiansen, and A. Hvidt, J. Chem. Thermodyn. 25:31 (1993).

10. G. Roux, G. Perron, and J. E. Desnoyers, J. Solut. Chem. 7:639 (1978).11. M. I. Davis, M. C. Molina, and G. Doheret, Thermochim. Acta 131:153 (1988).12. G. Douheret, A. Pal, and M. I. Davis, J. Chem. Thermodyn. 22:99 (1990).13. Y. Koga, K. Tamura, and S. Murakami, J. Solut. Chem. 24:1125 (1995).14. A. J. Easteal and L. A. Woolf, J. Chem. Thermodyn. 17:49 (1985).15. A. J. Easteal and L. A. Woolf, J. Chem. Thermodyn. 20:693 (1988).16. Y. Koga, J. Phys. Chem. 100:5172 (1996).17. Y. Koga and P. Westh, Bull. Chem. Soc. Japan 69:1505 (1996).18. Y. Koga, J. Phys. Chem. 96:10466 (1992).19. U. Onken, Z. Electrochem. 63:321 (1959).20. J. V. Davies, F. W. Lau, L. T. N. Le, T. T. W. Lai, and Y. Koga, Can. J. Chem. 70:2659

(1992).21. T. Atake and Y. Koga, Natsu Sokutei 21:130 (1994).


Volumetric and Thermodynamic Properties of Liquid Mixtures of 2- n -Butoxyethanol with Water

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