Behaviour of butyl ether as entrainer for the extractive distillation of the azeotropic mixture propanone+diisopropyl ether. Isobaric VLE data of the azeotropic components with the entrainer

Behaviour of butyl ether as entrainer for the extractive distillation of the azeotropic mixture propanone+diisopropyl ether. Isobaric VLE data of the azeotropic components with the entrainer

Fluid Phase Equilibria 156 Ž1999. 89–99 Behaviour of butyl ether as entrainer for the extractive distillation of the azeotropic mixture propanoneq di...

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Fluid Phase Equilibria 156 Ž1999. 89–99

Behaviour of butyl ether as entrainer for the extractive distillation of the azeotropic mixture propanoneq diisopropyl ether. Isobaric VLE data of the azeotropic components with the entrainer Jose´ M. Resa ) , Cristina Gonzalez, ´ Miguel A. Betolaza, Aitor Ruiz Departamento de Ingenierıa UniÕersidad del Paıs ´ Quımica, ´ ´ Vasco, Apartado 450, 01006 Vitoria, Spain

Abstract The behaviour of butyl ether as entrainer in extractive distillation for the rupture of the propanoneq diisopropyl ether azeotropic mixture is investigated. The vapor–liquid equilibrium of each component with butyl ether has been carried out at 101.3 kPa in order to check the absence of azeotropes. Neither system showed an azeotrope. Thermodynamic consistency of the experimental data was good. The activity coefficients were correlated by means of the van Laar, Wilson, NRTL and UNIQUAC equations. UNIFAC prediction has been also used. As a final part, an experiment of extractive distillation was carried out and a composition of 0.990 in mole fraction of acetone, 0.001 of diisopropyl ether and 0.009 of butyl ether resulted in the head of the column. In conclusion, butyl ether is an excellent solvent for the rupture of the studied azeotropic mixture. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Experiments; Data; Activity coefficient; Density; Mixtures; Extractive distillation

1. Introduction In the manufacture of acetone by catalytic dehydrogenation of isopropanol, it is relatively easy to separate the acetone from the mixture obtained by rectification. However, some reactions may take place, such as the dehydration of isopropanol to form diisopropyl ether which, together with acetone, forms an azeotrope with a minimum boiling point, containing 61% weight of acetone w1x. Therefore, it is not possible to produce pure acetone by rectification due to the presence of such an azeotrope. The extractive distillation method is used to separate compounds of similar boiling points or those compounds which form azeotropes, by using an additional agent to alter the relative volatility. In this

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Corresponding author. Tel.: q34-945-183030; fax: q34-945-130756; e-mail: [email protected]

0378-3812r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 8 1 2 Ž 9 9 . 0 0 0 3 4 - 5

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way, it is possible to obtain one pure compound at the top of the column and the other, together with the solvent mixture at the bottom, which may be separated easily in a secondary distillation column, due to its high solvent boiling point. The work we now present required a previous selection of possible solvents, which has been done by the Scheibel’s criterion w2x, and suggests in principle, to select them from the compounds of a same homologous series. The solvents selected were checked by the UNIFAC prediction to avoid the presence of binary azeotropes. We chose 3-pentanone w3x, propyl ether w4x and butyl vinyl ether w5x which had been used previously in some former work and in the present research we show the results obtained by using butyl ether. We have measured the vapor–liquid equilibria at 101.3 kPa of propanoneq butyl ether and diisopropyl ether q butyl ether systems. Data for these systems cannot be found in the literature. A check of the patent literature shows that butyl ether is not covered as an extractive distillation agent. 2. Experimental Fluka supplied propanone Ž 99.8 q mol%. and butyl ether Ž 99.5 q mol%. . Analytical grade diisopropyl ether ŽFluka. was purified by distillation in a laboratory column. The purity of the materials was checked by gas–liquid chromatography Ž GLC. and was better than 99.5 mol%. The ˚ from products were degassed using ultrasound and dried on molecular sieves Ž type pore diameter 3 A Fluka. before use. Densities, refractive indexes and boiling points of the pure substances are given in Table 1 and compared with literature values w6x. Measurements were made in an all-glass vapor recirculation-type equilibrium still, similar to the apparatus of Ref. w7x. In this work we have used an apparatus manufactured by Fritz Ž Normag, Germany. described by Rock ¨ and Sieg w8x. The details of the still and its operations were described in a previous paper w9x. The equilibrium temperature was measured with a platinum 100 resistance thermometer with an accuracy of "0.1 K. The pressure was maintained constant with a digital manometer regulator Normag with an accuracy of "0.1 kPa. Refractive indexes were measured with a Mettler Toledo RE50 refractometer. Condensed vapour phase and liquid phase compositions of propanoneq butyl ether and diisopropyl ether q butyl ether systems were determined by densitometry using an Anton Paar vibrating tube densimeter DMA-58, with an accuracy of "0.00001 g cmy3, that was previously calibrated at atmospheric pressure with doubly distilled water and dry air. The temperature of the densimeter was maintained at T s 298.15 K by means a semiconductor Peltier element with a precision of cell sensor

Table 1 Physical properties of pure compounds

r Žkg my3 . Propanone Diisopropyl ether Butyl ether

nD

Obs

Literature w6x

784.71 718.12 763.92

785.47 718.2 764.1

T b ŽK.

Obs

Literature w6x

Obs

Literature w6x

1.3562 1.3651 1.3968

1.35596 1.36550 1.3968

328.8 341.0 413.4

329.23 341.66 413.44

Densities, refractive indexes at 298.15 K, and normal boiling points.

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Table 2 Densities of propanone Ž1.qbutyl ether Ž2. and diisopropyl ether Ž1.qbutyl ether Ž2. mixtures as a function of the mole fraction Ž x 1 . of propanone or diisopropyl ether at 298.15 K

r Žkg my3 .

x1

r Žkg my3 .

x1

r Žkg my3 .

Propanone (1)q butyl ether (2) 0.000 763.92 0.062 764.18 0.091 764.20 0.199 764.69 0.303 765.40

0.404 0.498 0.624 0.697 0.794

766.30 767.53 769.63 771.33 774.17

0.901 0.940 1.000

778.69 780.80 784.71

Diisopropyl ether (1)q butyl ether (2) 0.000 763.92 0.046 762.58 0.051 762.43 0.109 760.30 0.205 756.92

0.312 0.415 0.496 0.605 0.693

752.71 748.39 744.86 739.76 735.47

0.804 0.887 0.929 1.000

729.63 725.03 722.43 718.12

x1

of "0.01 K. Pattern curves density vs. mole fraction were used to calculate the compositions of the vapor and liquid phases. All samples were prepared by weighing with a Salter electronic balance Žmodel ER-182A, accuracy "0.0001 g.. The uncertainty of comparison measurements was estimated to be "0.001 mole fraction. Table 2 shows the density-composition values. The apparatus used for the extractive distillation process, the details and its operations were described in a previous paper w4x. 3. Results and discussion The activity coefficients g i of the components were calculated from: yi f i P gi s x i Pi0

Ž1.

where x i and yi are the liquid and vapor mole fractions in equilibrium, f i is the fugacity coefficient, P is the total pressure and Pi0 is the vapor pressure of pure component i. These vapor pressures were calculated from the Antoine equation, Bi log Ž PrkPa. s A i y Ž2. Ž TrK . q Ci and the constants A i , Bi and Ci , are reported in Table 3. Table 3 Antoine coefficients, Eq. Ž2. w6x Compound

Ai

Bi

Ci

Propanone Diisopropyl ether Butyl ether

6.25478 5.97678 5.930185

1216.689 1143.073 1302.768

y42.875 y53.810 y81.481

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Table 4 Vapor–liquid equilibrium data at 101.3 kPa for the propanone Ž1.qbutyl ether Ž2. and diisopropyl ether Ž1.qbutyl ether Ž2. systems x1

y1

Propanone (1)q butyl ether (2) 0.000 0.000 0.056 0.610 0.137 0.788 0.245 0.891 0.270 0.902 0.340 0.925 0.424 0.943 0.511 0.953 0.616 0.970 0.677 0.974 0.734 0.977 0.790 0.980 0.848 0.984 0.891 0.988 0.942 0.994 0.995 0.999 1.000 1.000

T ŽK.

g1

f1

g2

f2

413.4 385.2 368.9 354.5 352.3 347.5 343.4 340.1 337.2 335.8 334.5 333.4 332.3 331.3 330.1 328.9 328.8

2.163 1.712 1.604 1.569 1.472 1.370 1.266 1.172 1.120 1.081 1.044 1.013 1.000 0.991 0.982

0.994 0.982 0.978 0.974 0.973 0.972 0.971 0.970 0.969 0.968 0.968 0.967 0.967 0.967 0.966 0.966 0.966

0.899 0.928 0.938 0.953 0.982 1.017 1.140 1.054 1.157 1.319 1.528 1.778 1.949 1.938 3.969

0.948 0.938 0.931 0.923 0.921 0.918 0.915 0.912 0.910 0.909 0.908 0.907 0.906 0.905 0.904 0.903 0.903

0.798 0.818 0.823 0.838 0.898 0.911 0.914 0.920 0.916 0.926 0.937 0.941 0.940 0.946

0.982 0.978 0.975 0.973 0.969 0.966 0.965 0.963 0.963 0.961 0.960 0.959 0.958 0.957 0.956 0.953

0.958 0.984 0.991 1.064 0.984 1.012 1.032 1.034 1.041 1.079 1.080 1.048 1.031 1.168

0.949 0.945 0.942 0.940 0.934 0.931 0.928 0.926 0.925 0.922 0.921 0.919 0.917 0.915 0.913 0.907

Diisopropyl ether (1)q butyl ether (2) 0.000 0.000 413.4 0.049 0.213 406.2 0.100 0.381 398.8 0.148 0.501 393.2 0.272 0.695 380.4 0.341 0.795 373.9 0.395 0.834 369.5 0.440 0.860 366.4 0.477 0.880 364.0 0.540 0.906 360.7 0.583 0.920 358.1 0.631 0.936 355.5 0.699 0.955 352.5 0.755 0.967 350.3 0.812 0.974 347.9 1.000 1.000 341.0

Experimental liquid-phase mole fraction Ž x 1 .; experimental vapor-phase mole fraction Ž y 1 .; experimental boiling temperature ŽT ., activity coefficients Žg 1 and g 2 . and fugacity coefficients Ž f 1 and f 2 . at 101.3 kPa.

The fugacity coefficients for the binary mixture, f 1 and f 2 , were calculated by the expressions, P ln f 1 s B11 q y 22 d 12 . Ž3. Ž RT P ln f 2 s Ž4. Ž B q y12d 12 . RT 22

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Fig. 1. x 1 y y 1 diagram for propanone Ž1.qbutyl ether Ž2.: Ž`. experimental data at 101.3 kPa; Ž-. Wilson equation; Ž — — — . UNIFAC prediction.

where P is the total pressure and T the experimental temperature of each point equilibrium, y 1 and y 2 are the vapor mole fractions of compounds 1 and 2, B11 and B22 represent the virial coefficient for a pure compound, and d 12 s 2 B12 y B11 y B22 , where B12 is the cross-section virial coefficient. Pitzer’s correlation for the second virial coefficient was extended by Reid et al. w10x for mixtures to calculate B12 by, B12 s

RTc 12 Pc 12

Ž B 0 q w12 B 1 .

Ž5.

where B 0 and B 1 are functions which depend exclusively on reduced temperature and they can be represented satisfactorily by the following equations, B 0 s 0.083 y 0.422rTr1.6

Ž6.

B 1 s 0.139 y 0.172rTr4.2 .

Ž7.

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Fig. 2. x 1 y y 1 diagram for diisopropyl ether Ž1.qbutyl ether Ž2.: Ž`. experimental data at 101.3 kPa; Ž-. Wilson equation; Ž — — — . UNIFAC prediction.

The rules of mixing proposed by Prausnitz for the calculation of v 12 , Tc12 and Pc12 are,

v 12 s

v1 qv2 2

Ž8.

where v 1 and v 2 are the acentric factors Tc12 s Ž Tc1Tc 2 .

0.5

Ž9.

where Tc1 and Tc2 are the critical temperatures. Pc12 s

Zc12 RTc12 Vc12

Ž 10.

where Zc12 is calculated by, Zc12 s

Zc1 q Zc 2 2

Ž 11.

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Zc1 and Zc2 are the critical compressibility factors. Vc12 is defined by the expression Vc12 s

ž

Vc11r3 q Vc1r3 2 2

3

/

Ž 12.

where Vc1 and Vc2 are the critical molar volumes of compounds 1 and 2. The vapor–liquid equilibrium data for the two systems have been obtained at 101.3 kPa and are presented in Table 4 with an accuracy in the mole fractions of "0.001. The x 1 y y 1 diagrams are shown in Figs. 1 and 2. The activity coefficients were correlated with van Laar w11x, Wilson w12x, NRTL w13x and UNIQUAC w14x equations. To determine the constants of each model, the ‘VLE calc’ method suggested by Gess et al. w15x has been used. Estimation of the parameters for the equation was based on the iterative solution, using the maximum likelihood regression of the objective function Q i w16x with the activity coefficients obtained from the consistency test as experimental values, N

Qi s

Ý is1

ž

gexp y gcalcd gexp

2

/

Ž 13.

where gexp are the activity coefficients calculated from experimental data and gcalcd are the coefficients calculated with the y and T of correlations. The parameters along with the average deviation in T Ž DT ., the average deviation in y Ž D y . are listed in Table 5. The UNIFAC method w17x was also used for obtaining the predictions. The results of the prediction are plotted in Figs. 1 and 2. The thermodynamic consistency of the experimental data was checked by means of the modified Dechema test w18x, where the fugacity coefficients are calculated by the method of Hayden and

Table 5 Correlation parameters for activity coefficients and average deviation for studied systems Equation Propanone (1)q Butyl ether (2) van Laar a Wilsonb NRTLc Ž a 12 s 0.91. UNIQUAC d

A12

A 21

DT ŽK.

D y1

0.7444 2706.16 3194.34 y179.66

1.3494 1201.17 1523.73 1473.79

0.46 0.52 0.33 0.62

0.0067 0.0081 0.0054 0.0088

Diisopropyl ether (1)q Butyl ether (2) van Laar a 63.8988 Wilsonb y1468.27 NRTLc Ž a 12 s 0.31. y319.37 UNIQUAC d 403.95

y0.0046 2395.74 274.19 y370.82

0.24 0.18 0.24 0.24

0.0103 0.0092 0.0090 0.0091

a

van Laar’s constants Ždimensionless.. Wilson’s interaction parameters ŽJ moly1 .. c NRTL’s interaction parameters ŽJ moly1 .. d UNIQUAC’s interaction parameters ŽJ moly1 .. b

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Table 6 Results of the thermodynamic consistency test System

Dy

A

B

D

Propanone Ž1.qbutyl ether Ž2. Diisopropyl ether Ž1.qbutyl ether Ž2.

0.0043 0.0081

0.9714 y0.0792

1.4018 y0.0001

0.7595 y0.0072

O’Connel w19x, and activity coefficients were calculated using the following form of the four-suffix Margules equation, g ErRT s x 1 x 2 Ax 2 q Bx 1 y Dx 1 x 2

Ž 14.

with the corresponding activity coefficients, ln g 1 s x 22 A q 2 Ž B y A y D . x 1 q 3 Dx 12

Ž 15.

ln g 2 s x 12 B q 2 Ž A y B y D . x 2 q 3 Dx 22 .

Ž 16.

Estimated parameters A, B, and D were obtained using the error-in-variables regression maximum likelihood technique. The constraint equation for the regression was, FsPy

ž

x 1g 1 ) f 10

f1

q

x 2 g 2 ) f 20

f2

/

.

Ž 17.

Here the asterisk Ž). denotes a calculated or predicted value. The experimental value has no asterisk; f 10 and f 20 are the standard state fugacities. The errors in the prediction of y 1 were calculated. Predicted y 1 ) values were obtained using equation, y1 ) s

x 1g 1 ) f 10

f1 P )

.

Ž 18.

An average deviation were calculated as, n

Ý Average deviations

Dy

is1

n

.

Ž 19.

Here D y s y 1 y y 1 ) and n s number of experimental data points. A system must have an average deviation less than 0.01 to satisfy the consistency test. The two systems included in this work have passed the consistency test. In Table 6 are listed the obtained values for A, B and D of Eqs. Ž15. and Ž16..

Table 7 Results of the constants of the Margules test System

Margules constant

Propanoneqbutyl ether Diisopropyl etherqbutyl ether

0.9683 0.1908

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Table 8 Results of extractive distillation experiment of system propanoneqdiisopropyl ether with butyl ether as solvent Sample number

Time Žmin.

Mole fraction propanone

Mole fraction diisopropyl ether

Mole fraction butyl ether

Mole fraction propanone without solvent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

30 50 70 90 110 130 150 170 190 210 230 250 270 290 300

0.903 0.901 0.902 0.926 0.924 0.939 0.952 0.953 0.958 0.970 0.968 0.971 0.986 0.983 0.990

0.092 0.083 0.078 0.059 0.056 0.033 0.021 0.019 0.014 0.011 0.007 0.004 0.004 0.001 0.001

0.005 0.015 0.019 0.014 0.021 0.028 0.027 0.027 0.028 0.021 0.025 0.025 0.009 0.016 0.009

0.908 0.916 0.920 0.940 0.943 0.966 0.978 0.980 0.986 0.989 0.993 0.996 0.996 0.999 0.999

We also carried out the Margules Constant Test using the program of Gess et al. w15x. The Margules Constant Test can be used to indicate the ideality of a system. Systems which yield a Margules constant whose absolute value is less than 0.60 can be considered ideal, while those which yield an absolute value greater than 0.60 can be considered non-ideal. This criterion for classification, however, is not rigorous. Table 7 shows the values of this constant. As shown in Figs. 1 and 2, the azeotrope has been completely displaced, and then the butyl ether can be taken as an agent for the extractive distillation. In the same way, the experiment of extractive distillation at a laboratory scale gives a composition of 0.99 mole fraction of acetone at the head of the column. Table 8 shows the results obtained. As a conclusion, butyl ether is an excellent solvent for the rupture of the studied azeotropic mixture. Also, in view of the equilibrium diagrams, the number of necessary plates for the separation is very small, so the economy of the process is very acceptable.

4. List of symbols A A12 , A 21 Ai B Bi B11

parameter in Eqs. Ž 14. – Ž 16. parameters correlation in Table 5 coefficient in Eq. Ž2. parameter in Eqs. Ž 14. – Ž 16. coefficient in Eq. Ž2. virial coefficient for the pure compound 1

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B22 B12 B0 B1 Ci D f 10 f 20 F gE n nD P Pi0 P) Pc12 R T Tc1 Tc2 Tc12 Q Tr Vc1 Vc2 Vc12 x y Zc1 Zc2 Zc12

virial coefficient for the pure compound 2 cross-section virial coefficient, Eq. Ž5. function of reduced temperature, Eq. Ž6. function of reduced temperature, Eq. Ž7. coefficient in Eq. Ž2. parameter in Eqs. Ž 14. – Ž 16. liquid fugacity of compound 1 in the standard state liquid fugacity of compound 2 in the standard state objective function in Eq. Ž17. excess molar Gibbs energy number of experimental points refractive index experimental total pressure vapor pressure at temperature T of compound i predicted value pressure defined value in Eq. Ž10. universal gas constant Kelvin temperature Kelvin critical temperature of compound 1 Kelvin critical temperature of compound 2 defined value in Eq. Ž9. objective function in Eq. Ž13. Kelvin reduced temperature critical molar volume of compound 1 critical molar volume of compound 2 defined value in Eq. Ž12. liquid-phase mole fraction vapor-phase mole fraction critical compressibility factor of compound 1 critical compressibility factor of compound 2 defined value in Eq. Ž11.

Greek letters f fugacity coefficient g activity coefficient r density at temperature T d 12 parameter in Eqs. Ž 3. and Ž 4. v acentric factor

Acknowledgements The authors are grateful to the University of Basque Country for financial support of this work ŽProject UPV 069.123-EA156r97..

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