Isothermal vapor-liquid equilibria for 2-propanol + octane and 2-propanol + 2,2,4-trimethylpentane at 348.15 K

ELSEVIER

Fluid Phase Equilibria 125 (1996) 79-87

Isothermal vapor-liquid equilibria for 2-propanol + octane and 2-propanol + 2,2,4-trimethylpentane at 348.15 K Toshihiko Hiaki *, Tomoya Tsuji, Masaru Hongo Department of Industrial Chemistry, College of Industrial Technology, Nihon University, 1-2-1 Izumi-cho, Narashino. Chiba

275, Japan

Abstract Isothermal vapor-liquid equilibria were measured for 2-propanol + octane and 2-propanol + 2,2,4trimethylpentane at 348.15 K. The measurements were made in a Rogalski-Malanowski-type still with circulation of both vapor and liquid phases. Both binary isothermal systems form a maximum pressure azeotrope. The azeotropic data are xt(AZ)= 0.882 mole fraction and P(AZ)= 78.20 kPa for 2-propanol (l)+octane (2) and x~(AZ)=0.637 mole fraction and P(AZ)=96.24 kPa for 2-propanol (l)+2,2,4trimethyipentane (2). The experimental data were checked for thermodynamic consistency by using three conventional tests. The activity coefficients of both systems were best correlated with the non-random two-liquid (NRTL) equation. Keywords: Experimental;Equilibria; Azeotrope; Consistencytest

I. Introduction Vapor-liquid equilibrium (VLE) data are required for engineering purposes, such as in the design and operation of separation processes. Recovery of solvents using extraction is carried out by distillation. Therefore, it is important to make accurate measurements of VLE in order to separate alcohols from aqueous hydrocarbon solutions. In the present study, two isothermal VLE were measured for 2-propanol + octane and 2-propanol + 2,2,4-trimethylpentane at 348.15 K using an apparatus with computer control of the temperature and the measurement of total pressure. For determination of VLE, a still with circulation of both vapor and liquid phases was employed. The isothermal VLE for the the 2-propanol + octane system is not available in the literature. For the 2-propanol + 2,2,4-trimethylpentane system, one set of VLE data at 318.10 K (Neau et al., 1973) and one set of x - P data at 298.15 K (Heintz et al., 1986) are

• Corresponding author. 0378-3812/96/$15.00 Copyright © 1996 Elsevier Science B.V. All fights reserved. PII S 0 3 7 8 - 3 8 1 2 ( 9 6 ) 0 3 0 7 8 - 6

80

T. Hmki et aL / Fluid Phase Equilibria 125 (1996) 79-87

reported in the literature. However, the literature data of Neau et al. is not consistent according to the results of a thermodynamic consistency test by Gmehling and Onken, 1977. Therefore, new reliable data are required for these systems.

2. Experimental 2.1. Apparatus A modified Rogalski-Malanowski still (Rogalski and Malanowski, 1980), which was developed in the previous study (Hiaki et al., 1992) with a provision for vapor and liquid re-circulation, was used for the determination of vapor-liquid equilibrium values. The modification concerns the withdrawal of the liquid sample and prevents its contamination with the vapor condensate sample. The still is made of Pyrex glass and has a total capacity of about 100 cm 3. The isothermal VLE measurement apparatus and the associated computer, as described in our previous work (Hiaki et al., 1994), was used for the measurements. The ebulliometer was used for the determination of the total pressure. The performance of the ebulliometer was checked with the normal boiling points of several pure components in the temperature range from 309 to 518 K. The platinum resistance thermometers placed in both the equilibrium still and the ebulliometer were linked with a GP-IB bus, enabling temperature measurement and its control, and proper adjustment of the system pressure.

2.2. Operation procedure The sample was introduced into the VLE still and water was placed in the ebulliometer for the determination of vapor pressure. After establishing a steady state in both the sample and water at atmospheric pressure, the sample temperature was maintained at the desired temperature by adjusting the pressure using the computer in conjunction with four solenoid valves and a vacuum pump. This method for isothermal vapor-liquid equilibria measurements consists of a continuous measurement of equilibrium pressure and control of the temperature in the still. The continuous analysis, generated as a variable resistance and voltage using a computer, is convenient for the rapid determination of the steady state and accurate equilibrium pressure.

2.3. Materials and auxiliary equipment The 2-propanol, octane and 2,2,4-trimethylpentane used in this work were special grade reagents, supplied by Wako Pure Chem. Co. (Japan). 2-Propanol was used after its minute water content was removed with molecular sieves of pore diameter of 0.3 nm. A gas-chromatographic analysis on all three materials indicated that each had a purity of at least 99.9 tool%. The physical properties of the compounds are listed in Table 1 along with the literature values. Normal boiling points were measured by an ebulliometer with a capacity of about 70 cm 3. Density values were determined using a vibrating tube density meter (Shibayama Kagaku SS-D-200-Exp. Type, Japan). Density was measured with an accuracy of -t- 1.0xl0-5(g cm-3).

81

T. Hiaki et al. / Fluid Phase Equilibria 125 (1996) 79-87

Table 1 Normal boiling points and densities of pure components at 298.15 K Component

Boiling p o i n t / K

2-Propanol Octane 2,2,4-Trimethylpentane

Density/g cm- 3

This work

Literature a

This work

Literature a

370.26 398.80 372.40

370.301 398.823 372.388

0.78086 0.69868 0.68764

0.78126 0.69862 0.68781

a Riddick et al., 1986.

The temperature was measured with a calibrated platinum resistance thermometer (Pt 100W) with an accuracy of 0.03 K. A standard resistance thermometer (Chino Co. model R800-2, Japan), which is based on IPTS-90, was used for this calibration. The vapor pressure of the sample was determined by the measurement of the boiling point of water on the basis of vapor pressure data of water (Wagner and Pruss, 1987). From the accuracy of the temperature, the relative error in the values of the experimental vapor pressure is estimated to be 0.08 kPa. The equilibrium composition of the samples was determined using a gas chromatograph (GL Sciences model GC-380, Japan) equipped with a flame ionization detector. The column was 3 m in length and 0.4 cm in diameter, filled with PEG-20M (10% polyethylene glycol on chromosorb W-AW 60/80). The relationship between the peak area and composition was determined from the analysis of samples of known composition. The accuracy of the liquid and vapor composition measurements is estimated to be 0.002 mole fraction.

3. Results and discussion

The activity coefficients Yi were calculated from ~PiPYi =

yiPSxidpSexp[ vi( P - PiS)/RT]

(1)

where th~ and ~bs, the fugacity coefficients of component i in the mixture and pure vapor, respectively, were evaluated by using the second virial coefficients obtained by the Hayden-O'Connell method (Hayden and O'Connell, 1975). The vapor pressures of the pure components, p S, were obtained using the Antoine equation constants (Boublik et al., 1984), which are shown in Table 2. The liquid molar volumes v i were calculated from the Rackett equation as modified by Spencer and Danner, 1972.

Table 2 Antoine constants of the components a Component

A

B

C

2-Propanol Octane 2,2,4-Trimethylpentane

6.86634 6.04394 5.92751

1360.183 i 351.938 1252.340

- 75.557 - 64.030 - 53.060

a l o g P ( k P a ) ~ A - B / [ T ( K ) + C].

82

T. Hiaki et aL / Fluid Phase Equilibria 125 (1996) 79-87

Table 3 Isothermal vapor-liquid equilibrium data, vapor pressure, P, liquid phase, x I, and vapor phase, Yl, mole fractions, and activity coefficient, ~'i, for 2-propanol (I) + octane (2) and 2-propanol (l) + 2,2,4-trimethylpentane (2) at 348. !5 K P /kPa

xI

2-Propanol(1) + octane(2) 19.30 0 39.39 0.0366 49.73 0.0707 55.89 O. 1107 63.32 O. 1894 66.66 0.2652 68.43 0.3105 69.40 0.3336 70.70 0.3747 72.81 0.4469 74.85 0.5646 75.50 0.6272 76.32 0.6795 77.23 0.7421 77.80 0.7948 78.16 0.8519 78.19 0.8832 77.58 0.9537 75.37 1.0000 2-Propanol(1) + 2,2,4-trimethylpentane(2) 48.42 0 74.05 0.0584 79.87 0.0869 85.73 O.1579 91.95 0.2877 93.81 0.3611 95.18 0.4457 95.78 0.5120 96.16 0.6012 96.23 0.6270 96.25 0.6489 96.14 0.6868 95.62 0.7271 95.23 0.7564 94.60 0.7828 92.74 0.8434 92.17 0.8567 91.49 0.8671 88.60 0.9090 82.21 0.9677 75.38 1.0000

Yl

Yt

Y2

0 0.5247 0.6326 0.6788 0.7258 0.7427 0.7553 0.7590 0.7668 0.7797 0.7949 0.8060 0.8162 0.8291 0.8450 0.8664 0.8825 0.9351 1.0000

7.6531 5.9973 4.6055 3.2486 2.4957 2.2232 2.1080 1.9305 1.6930 1.4031 1.2912 1.2194 I. 1471 1.0991 1.0559 1.0375 1.0100

0.9944 1.0017 1.0262 1.0860 !. 1822 1.2295 1.2703 1.3342 1.4667 1.7831 1.9876 2.2148 2.5910 2.9777 3.5780 3.9964 5.5503

0 0.3770 0.4256 0.4868 0.5424 0.5611 0.5798 0.5990 0.6278 0.6334 0.6388 0.6466 0.6681 0.6768 0.6920 0.7274 0.7371 0.7482 0.7917 0.8942 1.0000

6.4306 5.2468 3.5304 2.3064 1.9370 1.6435 1.4860 1.3304 1.2877 1.2548 I. 1985 I. 1630 I. 1278 I. 1066 1.0583 1.0492 1.0446 1.0214 1.0070

.0017 .0248 .0640 .2012 .3101 .4670 .6010 .8280 1.9268 2.0178 2.2116 2.3744 2.5813 2.7437 3.3112 3.4711 3.5618 4.1831 5.6031

83

T. Hiaki et al. / Fluid Phase Equilibria 125 (I 996) 79-87

2.5

I

(a)

(b)

1

80

0 •

2.0

InTi InTz

60

1.5 _= 1.0

eL 20

0 •

0 0.0

P-x] P-Yl

i 0.5

0.5

0.0 0.0

1.0

Mole Fraction 2-Propanol

0.5

1.0

Liquid Mole Fraction 2-Propanol

Fig. 1. Pressure-composition and activity coefficient-liquid composition diagram for 2-propanol ( ! ) + octane (2) system at 348.15 K: ( 0 , 0 ) this work; ( ) NRTL equation.

The VLE data for the 2-propanol ( 1) + octane (2) system at 348.15 K are reported in Table 3 along with the activity coefficients calculated using Eq. (1). The experimental data are shown graphically in Fig. 1. The VLE data for the 2-propanol (1) + 2,2,4-trimethylpentane (2) system at 348.15 K are also reported in Table 3. The experimental VLE together with the literature data of Neau et al. (1973) at 318.10 K are shown graphically in Fig. 2.

120

(a)

,

I

2.5

(b)

I

A A

lnTl

• •

InTz

0

100

2.0

80 1.5 60

0 A P-x]

M

1.0 40 0.5

20 0 0.0

0.5 Mole Fraction 2-Propanol

1.0

0.0 0.0

0.5

1.0

Liquid Mole Fraction 2-Propanol

Fig. 2. Pressure-composition and activity coefficient-liquid composition diagram for 2-propanol (1)+ 2,2,4-trimethylpentane (2) system at 348.15 K: ( 0 , 0 ) this work; ( ) NRTL equation; ( • , A ) at 318.10 K, Neau et al., 1973.

T. Hiaki et a l . / Fluid Phase Equilibria 125 (1996) 79-87

84

3.1. Azeotropic point Both binary isothermal systems form a maximum pressure azeotrope. The azeotropic points were determined on the basis of the experimental VLE data using the following three plots

Apy/APx= [ P - (P,Y, + P2 Y 2 ) ] / [ P - (P,x, + P2x2)] vs. x, XI --

(2)

Yl VS. XI

(3)

vs. x I

(4)

~P --

Oxj

aP The condition of an azeotropic point (x~ - y ~ = 0 and

= 0) are sufficiently well defined by i3x~ Eq. (3) and Eq. (4). For the accurate determination of the azeotropic composition, Eq. (2), A Py/A Px = l at the azeotropic point was employed. The azeotropic points were determined on the basis of the experimental VLE data, yielding xl(AZ) = 0.882 mole fraction and P(AZ) = 78.20 kPa for 2-propanol (1) + octane (2), and xl(AZ) = 0.637 mole fraction and P(AZ) -- 96.24 kPa for 2-propanol (1) + 2,2,4-trimethylpentane (2).

3.2. Thermodynamic consistency test The experimental data were tested for thermodynamic consistency by using the point test of Fredenslund et al., 1977 and Van Ness et al., 1973, and the area test of Herington, 1951 and Redlich and Kister, 1948, as described by Gmehling and Onken, 1977. In addition, the data were checked by the Kojima method (Kojima et al., 1990), which permits the overall check of the data by combining three tests, namely the point test, the area test and the infinite dilution test. The results of the consistency tests for the VLE of 2-propanol ( 1 ) + o c t a n e (2) and 2-propanol ( 1 ) + 2 , 2 , 4 trimethylpentane (2) are shown in Table 4. The results from the three consistency tests indicate that the VLE data for both systems are thermodynamically consistent.

Table 4 The results of the consistency tests for the VLE of 2-propanol (1) + octane (2) and 2-propanol (1) + 2,2,4-trimethylpentane (2) at 348.15 K Test Criterion of consistency 2-Propanol(I) + octane(2) 2-Propanol(1)+ 2,2,4(character. + ) trimethylpentane(2) Method 1 a.b Method 2 ¢.d Method 3 e

Ay < 0.01 D < 10% [Point test] [Area test] [Infinite dilution test]

8<5 A< 3 1~< 30 12 < 30

0.004(+) 4.0 ( + ) 4.0 ( + ) 2.1 ( + ) 13.0( + ) 1.3( + )

0.005 (+) 3.6 ( + ) 2.7 ( + ) 2.4 ( + ) 6.2 ( + ) 1.7 ( + )

a Fredenslund et al., 1977. b Van Ness et al., 1973. c Herington, 1951. d Redlich and Kister, 1948. ¢ Kojima et al., 1990

T. Hiaki et al./ Fluid Phase Equilibria 125 (1996) 79-87

85

3.3. Correlation The activity coefficients were correlated with the Wilson (Wilson, 1964), modified Wilson (Tsuboka and Katayama, 1975), non-random two-liquid (NRTL) (Renon and Prausnitz, 1968) and UNIQUAC (Abrams and Prausnitz, 1975) equations. The parameters in each of these equations were obtained using the Marquardt method (Marquardt, 1963). For the NRTL equation, ct was also used as a fitting parameter. The sum of the squares of the relative deviations in the pressure and vapor composition was minimized during optimization of the parameters. The objective function used was as follows N

Fobj = )-". [(Pobs--Pca,c)2+(y,.obs--Y~.calc)2]

(5)

k=l

For the 2-propanol (1) + octane (2) system, the NRTL equation yielded the lowest mean deviations

Table 5 Parameters and deviations between calculated and experimental vapor phase mole fractions, A Yl, and vapor pressures, A p, of four activity coefficient equations for the 2-propanol ( l ) + o c t a n e (2) and 2-propanol ( 1 ) + 2,2,4-trimethylpentane (2) at 348.15 K Equation

Parameters

Deviation Average

Maximum

AyI

AP/kPa

A y~

AP/kPa

6807.51 965.33 6494.76 -74.80 3942.11 4908.36 0.563 -968.85 3744.51

0.005

0.64

0.015

1.19

0.006

0.85

0.022

1.57

0.004

0.23

0.009

0.60

0.011

1.71

0.043

2.96

6822.54 580.65 6742.05 - 503.05 3677.93 5047.51 0.587 -989.68 3734.44

0.010

0.50

0.020

1.48

0.011

0.60

0.022

1.66

0.005

0.19

0.012

0.89

0.017

1.17

0.031

2.98

2-Propanol(1) + octane(2) system Wilson

Ai2Ai2 -Al2 -AI2g~2 gl2 a ul2 ul2 -

Modified Wilson NRTL

UNIQUAC

All A22 A~l A22 g II g22 utl u22

2-Propanol(1) + 2,2,4-trimethylpentane(2) system Wilson

Ai2 Aj2 Ai2 Al2 -gl2 gt2at ul2 u~2 -

Modified Wilson NRTL

UNIQUAC

Al~ A22 Alj A22 gti g22 u~l u22

N

Wilson, Modified Wilson, NRTL, and UNIQUAC parameters are given in J mol N

= Y ' . K P o ~ - PcaJc)l/N, N -

number of data points.

I . A y t - - ~ - J ( Y t . o b s - Yt.ca,c)l/N, A P

86

T. Hiaki et al. / Fluid Phase Equilibria 125 (1996) 79-87

between the experimental and calculated pressures, 0.23 kPa, and vapor compositions, 0.004 mole fraction. The parameters of the four activity coefficient equations for this system are shown in Table 5. The average and maximum absolute deviations between the experimental and calculated values are also reported in the table. The results for the 2-propanol ( 1 ) + 2,2,4-trimethylpentane (2) system were also best correlated using the NRTL equation. Absolute average deviations of 0.005 in mole fraction and 0.19 kPa in pressure were observed. The parameter values and the average and maximum absolute deviations using the four activity coefficient equations are shown in Table 5. The calculated results of the NRTL equation are shown by solid lines in Fig. 1 and Fig. 2.

4. List of symbols A

lOOlfll n ( T J T 2 ) d x l + fo ledxll

A' B' D gE

area above the x-axis area below the x-axis of ln(Tl/Y2) vs. x l 100l A' - B'I/( A' + B ' ) / % excess Gibbs free energy/J m o l - l

Ii 12

lO0[({gE/RT )X~X2 }x - 0 - I n ( y ~ / Y 2 ) x , - o ] / l n ( Y j Y 2 ) ~ , - o l / % lO0[({( gE/RT)x~ x2}~2.o ] - In( T~/'y2)~:o]/In( y~/'y2)~:o / %

m

number of data points total pressure/kPa component vapor pressure/kPa molar gas constant, R = 8.3144 J mol - ~ K equilibrium temperature/K molar v o l u m e / m 3 mol-i volume of mixing mole fraction in liquid phase mole fraction in vapor phase

P

Pi R T u uM x

Y

0

4.1. Greek letters 8

100 ~ kt(gE/RT)dx~ - In(TI/T2) - e l / m j=l

( - v M/RT)(d p / d x I ) T P

activity coefficient d e n s i t y / k g m -3

4.2. Subscripts i, j, 1,2

components

4.3. Superscripts S

pure component

T. Hiaki et a l . / Fluid Phase Equilibria 125 (I 996) 79-87

87

References D.S. Abrams and J.M. Prausnitz, Statistical thermodynamics of liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems, AIChE J., 21 (1975) 116-128. T. Boublik, V. Fried and E. Hala, The Vapor Pressures of Pure Substances, 2nd. edn., Elsevier, Amsterdam, 1984. A. Fredenslund, J. Gmehling and O. Rasmussen, Vapor-Liquid Equilibria Using UNIFAC, Elsevier, Amsterdam, 1977. J. Gmehling and U. Onken, Vapor-Liquid Equilibrium Data Collection, Chemistry Data Series, DECHEMA, Frankfurt am Main, 1977. J.G. Hayden and J.P. O'Connell, A generalized method for predicting second virial coefficients, Ind. Eng. Chem. Process Des. Dev., 14 (1075) 209-216. A. Heintz, E. Dolch and R.N. Lichtenthaler, New experimental VLE-data for alkanol/alkane mixtures and their description by an extended real association (ERAS) model, Fluid Phase Equilibria, 27 (1986) 61-79. E.F.G. Herington, Tests for consistency of experimental isobaric vapor liquid equilibrium data, J. Inst. Petrol., 37 (1951) 457-470. T. Hiaki, K. Yamato and K. Kojima, Vapor-liquid equilibria of 2,3-dimethylbutane + methanol or ethanol at 101.3 kPa, J. Chem. Eng. Data, 37 (1992) 203-206. T. Hiaki, K. Takahashi, T. Tsuji, M. Hongo and K. Kojima, Vapor-liquid equilibria of ethanol + 2,2,4-trimethylpentane at 333.15 K and l-propanol + 2,2,4-trimethylpentane at 343.15 K, J. Chem. Eng. Data, 39 (1994) 605-607. K. Kojima, H.M. Moon and K. Ochi, Thermodynamic consistency test of vapor-liquid equilibrium data: methanol-water, benzene-cyclohexane, and ethyl methyl ketone-water, Fluid Phase Equilibria, 56 (1990) 269-284. D.W. Marquardt, An algorithm for least-squares estimation of nonlinear parameters, J. Soc. lndust. Appl. Math., I I (1963) 431-441. E. Neau, C. Blanc and D. Bares, Excess thermodynamic functions of the 2-propanol - isooctane binary system, J. Chim. Phys. Physicochim. Biol., 70 (1973) 843-849. O. Redlich and A.T. Kister, Algebraic representation of thermodynamic properties and classification of solutions, Ind. Eng. Chem., 40 (1948) 345-348. H. Renon and J.M. Prausnitz, Local compositions in thermodynamic excess functions for liquid mixtures, AIChE J., 14 (1968) 135-144. J.A. Riddick, W.B. Bunger and T.K. Sakano, Organic Solvents Physical Properties and Methods of Purification, 4th. edn., John Wiley and Sons, New York, 1986. M. Rogalski and S. Malanowski, Ebulliometers modified for the accurate determination of vapor-liquid equilibrium, Fluid Phase Equilibria, 5 (1980) 97-112. C.F. Spencer and R.P. Danner, Improved equation for prediction of saturated liquid density, J. Chem. Eng. Data, 17 (1972) 236-241. T. Tsuboka and T. Katayama, Modified Wilson equation for vapor-liquid and liquid-liquid equilibria, J. Chem. Eng. Jpn., 8 (1975) 181-187. H.C. Van Ness, S.M. Byer and R.E. Gibbs, Vapor-liquid equilibrium: Part I. An appraisal of data reduction methods, AIChE J., 19 (1973) 238-244. W. Wagner and A. Pruss, International equations for the saturation properties of ordinary water substance. Revised according to the international temperature scale of 1990, J. Phys. Chem. Ref. Data, 22 (1987) 783-787. G.M. Wilson, G.M., Vapor liquid equilibrium. XI. A new expression for the excess free energy of mixing, J. Am. Chem. Sot., 86 (1964) 127-130.