Indian Journal of Chemistry Vol. 3SA, November 1999, pp. 111 6- 11 22

Viscosity and density of ternary mixtures of di-(2-ethylhexyl)phosphoric acid (D EHPA)-benzene-toluene

N Swain! & V Chakravortty* Department of Chemistry, Utkal Uni vers ity, Vani Vih ar, Bhubaneswar 751 004, Indi a

and S K Singh & D Panda

Regional Research Laboratory, Bhubaneswar 751 01 3, India

Received 14 May 1999; revised 8 September 1999

Vi scositi es and densities of the ternary liquid mixtures of di (2-ethylhexyl) phosphoric acid + benzene + toluene have been measured at 30,35,40 and 45 "C. The mixture viscos ity, 11 "" is fitted to a Redlich-Kister-type equation which includes the contribution of each constituent binary system along wi th a ternary contribution term. The non-idealities reflected in mix ture viscosi ties are ex­pressed and discussed in terms of excess viscositi es whi ch are negative over the entire range of mole fraction. Negative values of xcess viscosity, 11 E, and the nonlinear va ri ation of viscosity and density with change of composition indicate molecul ar interacti on between

the polar ex tractant and non-polar diluents.

Di- (2-ethyl hexyl) phosphoric acid is one of the most widely used and characterized ex tractants in the atomic energy industry. It is highly effective extractant for the ex traction of uranium , vanadium, beryllium, yttrium, cobalt, zinc, rare earths and other valuable metals. Ex­traction of europium(III), americium(III) and curium(III) has been carried out us ing DEHPA as one of the extractants in our laboratory!. The extraction effici ency improves with the addition of suitable organic diluents and modifiers2-9• To study the solvent extraction of lan­thanides and actinides using binary mixtures as diluents, it is necessary to have the appropri ate density and vis­cosity data. In continuation of earlier work7

-9 on vi scos­

ity and density of liquid mixtures, the present paper re­ports the viscosities and densities for the ternary mix­tures of DEHPA + benzene + toluene in the temperature range 30 to 45 °C. Studies on variation of properties I ike viscosity, density and excess properties are likely to throw light on molecular environment and molecular interac­tion which may be correlated with the extraction effi ­ciency of DEHPA in the binary mixture of diluents.

Materials and Methods Benzene (BDH) and toluene (BDH) were of analyti­

cal reagent grade and were obtained from E. Merck (In-

t Coll ege of Basic Sciences & Humanities, QUAT, Bhubaneswar-751 003, India

dia) (purity greater than 98 mol. %). Benzene and to lu­ene were purified by the method of fractional di still a­tion lo

. The metal extractant , di (2-ethyl hexy l) phospho­ric acid was of practical grade obtained from Fluka Chemie AG with density 1.026 x 103 kg nr3 at 20 °C. In the present investigation the density va lue was measured to be 1.024 x 103 kg m-3 at 20 °C which is in good agree­ment with the value specified by the manufacturer. The purity of benzene and toluene was checked by compar­ing their viscos ity and density with those reported in lit­erature ll

-13 and also with values reported in our earlier

work7•8• The viscosities and densities of pure compo­nents at different temperatures are presented in Table I . However, the viscosities and dens ities of DEHPA at dif­ferent temperatures are not available in literature. The values presented in Table 1 are the experimental va lues determined by us.

Ternary mixtures of DEHPA, benzene and to luene were prepared by volume. Sixteen mix tures were pre­pared . Densities and viscosities of the solutions were measured at four different temperatures, viz. 30, 35 , 40 and 45 °C. The increment in temperature was kept regu­lar at 5 °C with a view to ensuring measurable effects of temperature change on experimental observations . The

highest temperature level was restricted to 45 °C ± 0 .1 °C in order to avoid errors due to evaporation losses dur-

'-,.

~

SWAIN e/ al.: VISCOSITY & DENSITY STUDIES OF TERNARY MIXTURES 111 7

Table I - Density (p) and viscosity (11) for DEHPA, benzene and toluene at different temperatures

Pure component T/ "C I O" p / kg m" 11 / mPa.s

DEHPA 20 1.024 (exptl. ) 1.026'

30 1.010 186.92 1 35 1.008 148.745 40 1.005 112.462 45 1.003 96.204

Benzene 25 0.876 0.647 (0.874)" (0.645)h (0.874/ (0.643)'

30 0.866 0.630 35 0.862 0.604 40 0.859 0.59 8 45 0.856 0.553

Toluene 25 0.863 0.554 (0.862)" (0.552)"

30 0.857 0.523 35 0.854 0.499 40 0.851 0.478 45 0.848 0.458

*Specified by the manufacturer, Fluka Chemie AG " Reference - II h Reference - 12 "Reference - I 3

ing the measurements7.14

. The densities were measured by a bicapillary pycnometer calibrated with deionized doubly distilled water (density = 0.996 x 103 kg m-3 at 30

0C) . The accuracy of density measurement was ± 0.2 %. Viscosity of the solutions was measured by a thor­oughly cleaned, dried and calibrated Ostwald viscom­eterl5 . The viscometer was kept in a thermostatic water bath and the temperature variation was maintained within ± 0.1 dc. The time of flow was determined after equili­brating the viscometer with the bath temperature. The

accuracy of viscosity measurements was within ± 0.1 %. The same procedure was followed for the measurement of viscosities of constituent binary mixtures of DEHPA(l )+benzene(2), DEHPA(I )+toluene(3) and benzene(2)+toluene(3) .

Results and Discussion The viscosity and density data for the ternary mix­

tures DEHPA( I) + benzene(2) + toluene(3) at 30, 35,40

80 r-----------------------~

70

eo

50

& 40 ~

30

20

10

~ 30 DC • 35 DC o 40 DC • 45 DC

/ I / " /. ,/

/ ! ~/ / i f

/0./ /! / ,/ /

/ /. !

/ () !

/

I I I i

i / I~ t/ I/U // ~/ Q/

/~/t ~. / , v

;/ ."

O~~~~-L~~~~ 0.032 0.132 0.232 0.332 0.432 0.532 0.632 0.732

X DEHPA

Fig. 1- Plot of mixture viscosity, 11m against mole frac ti on of DEHPA, XOEHPA at 30, 35, 40 and 45 "C

and 45 °C over the entire range of mole fraction have been presented in Table '2. Table 3 shows the viscosity data for the constituent binary mixtures DEHPA( I) + benzene(2" DEHPA( I) + toluene(3) and benzene(2) + toluene(3).

From the viscosity data for the ternary mixtures of DEHPA( 1) + benzene(2) + toluene(3) the excess viscosi­ties have been calculated using Eq. (I )1,14.16

11E = 11 - LX n m ,'I, ... ( I)

where 11m is the mixture viscosity, Xi is the mole fraction

of component i, and 11i is the viscosity of pure i. The ternary results were fitted in Eq. 2, which includes

the contribution of each binary constituent as calcu­lated by a three-parameter Redlich- Kister-type equation along with a ternary contribution term.

3 3

11 m = L Xj ll j + L XjxJ[AjJ. + B j;(x-x) + C(x-xY l + xxx A . •

~ J I IJ J I I J k. IJk

i i 'F- j ... (2)

The constants A ., B.. and C. were determined by least-I) I) I) ' -

111 8 INDI AN J CHEM, SEC. A, NOVEMBER 1999

Table 2 - Experi mental densities (p,,) , experimental viscosi ties (11,) and excess vi scositi es (Il E) for the ternary mi xtures of DEHPA ( I) + benzene (2) + toluene (3) at different temperatures

XI Xz X TI"C 1 O-Jp../kg m-J 11 ImPa_s ll E/mPa_s J '" 0.032 0.526 0.442 30 0.878 0.683 -5.86 1

35 0.876 0.630 -4 .669 40 0.873 0.595 -3.530 45 0.869 0.560 -3.0 12

0.068 0.5 11 0.420 30 0.890 0.887 -12. 365 35 0.888 0.8 19 -9.8 14 40 0.886 0.780 -7 .374 45 0.882 0.726 -6.29 1

0.098 0.490 0.412 30 0.900 1.119 -17.723 35 0.898 1.023 -14.056 40 0.895 0.965 -10.546 45 0.893 0.900 -8.988

0. 117 0.479 0.405 30 0.908 1.354 -2 1.029 35 0.905 1.23 1 -16.664 40 0.902 1.148 -12.490 45 0.899 1.076 -10.630

0.142 0.465 0.394 30 0.9 15 1.667 -25.375 35 0.913 1.520 -20.079 40 0.910 1.41 0 -15.026 45 0.906 1.309 -12.790

0. 176 0.446 0. 378 30 0.920 1.971 -3 1.406 35 0.9 18 1.820 -24.8 17 40 0.9 15 1.677 -18.564 45 0.9 11 1.548 -15 .804

0.204 0.430 0.366 30 0.926 2.720 -35.874 35 0.924 2.485 -28 .30 1 40 0.92 1 2.259 -2 1.11 5 45 0.919 2.057 -17.974

0.238 0.413 0.350 30 0.934 3.474 -41.456 35 0.932 3.159 -32.666 40 0.930 2.844 -24. 336 45 0.927 2.572 -20.713

0.276 0.394 0.330 30 0.943 4.923 -47 .088 35 0.940 4.357 -37 .099 40 0.938 4.034 -27.399 45 0.936 3.540 -23.38 1

0.3 17 0.367 0.317 30 0.950 6.381 -53 .270 35 0.948 5.549 -41 .983 40 0.946 5.229 -30.792 45 0.942 4.507 -26.338

0.363 0.345 0.292 30 0.959 9.964 -58.258 35 0.956 8.602 -45 .747 40 0.954 7.493 -33.677 45 0.951 6.689 -28.558 .. . (contd)

'""

SWAIN et al.: VISCOSITY & DENSITY STUDIES OF TERNARY MIXTURES

Table 2 - Experimental densities (Pn), experimental viscosities (11) and excess viscosities (l1E) for the ternary mixtures

of DEHPA (I) + benzene (2) + toluene (3) at different temperatures

XI x2 x) TI"C I O-Jp,,/kg m-J

0.425 0.311 0.264 30 0.966 35 0.965 40 0.961 45 0.959

0.483 0.283 0.233 30 0.974 35 0.972 40 0.969 45 0.966

0.554 0.243 0.203 30 0.980 35 0.979 40 0.975 45 0.973

0.635 0.200 0.165 30 0.988 35 0.985 40 0.983 45 0.981

0.740 0.142 0.117 30 0.997 35 0.995 40 0.991 45 0.989

squares method for the binary constituent using the bi-

nary results. 1.000

The constants Ajj' Bjj' Cjj and Ajjk * of Eq. 2 were de­termined by least-squares method for each temperature and the values are listed in Table 4. The parameters were used as input in Eq. 2 for calculating root mean square deviations as listed in Table 4. 0.950

The molecules of DEHPA, one of the components forming the ternary mixtures are polar and show non-ideal behaviours in mixtures. DEHPA is an acidic ex- Q.E

tractant which can deprotonate to form an anion.

o o II II

0.900

0.850

11 ImPa.s m

13.556 11.665 9.761 8.877

21.040 17.860 14.802 13.030 28.538 24.059 19.855 17.187

51.358 42.819 34.194 29.428

74.174 61.585 48.542 41.674

(contd ... )

llE/mPa.s

-66.219 -51.871 -38.348 -32.303

-69.543 -54.271 -39.798 -33.700 -75.275 -58.594 -42.691 -36.337

-67.549 -51.837 -37.418 -31.848

-64.298 -48 .630 -34.821 -29.649

~ 30 DC a 35 DC o 40 DC • 45 DC

1119

This hydrophobic anion can chelate a cation from an aqueous phase in solvent extraction, the chelate being soluble in the organic phase. In the present system DEHPA has been treated with the organic aromatic diluents benzene/toluene for lowering its viscosity. The change in viscosity with change in mole-fraction of DEHPA are shown in Table 2. The observed values of

llm(Exptl) increase with mole fraction of DEHPA

<l.032 0.132 0.232 0.332 0.432 0.532 0.632 0.732

X DEHPA

Fig. 2- Plot of mixture viscosity, Pm against mole fraction ofDEHPA, XDEHPA at 30, 35, 40 and 45 "C

1120 INDIAN J CHEM, SEC. A, NOVEMBER 1999

Tab le 3 - Experimental viscosities (11,,) for the const ituent binary mi xtures DEHPA( I ') + benzene(2) , DEHPA( I) + toluene(3) and benzene(2) + toluene(3) at di fferent temperatures .

30"

DEHPA ( I) + Benzene (2)

XI x2

0.000 1.000 0.630 0.0 12 0.918 1.315 0.180 0.820 2.898 0.364 0,635 12.786 0.60 1 0.399 38.227 0.799 0,201 96.725 0.901 0,100 142,629 1.000 0.000 186.921

DEHPA ( I) + Toluene (3)

x I x .l

0.000 1.000 0.523 0. 100 0.900 1. 275 0.200 0.800 2.340 0.405 0.595 10.524 0.600 0.400 3 1.764 0.800 0.20 1 92.668 0.900 0,10 1 126.264 1.000 0,000 186.921

Benzene (2) + Toluene (3)

x2 X3

0.000 1.000 0,523 0.1 01 0.899 0.530 0,200 0,800 0.539 0.400 0,600 0.551 0,601 0.402 0.563 0.800 0.200 0,576 0.900 0.100 0.587 1.000 0.000 0.630

(Fig, I). The values of density also show a similar trend (Fig. 2). The nonlinear variation of these parameter with the change of composit ion of mixtures indicates the pres­ence of molecular interaction 6

.7

.18

.

The non-idealities as reflected in mixture viscosities are expressed in terms of excess viscosity given by Eg.

I. Fig. 3 shows the plot of ll E versus xDE;HPA (mole frac­

tion of DEHPA) . Negative va lues ofllE are the conse­quence of lower viscosity contribution of non specific

11 I mPa.s at T = '"

35 " 40 " 45 "C

0.604 0,598 0.553 1.243 1.151 1.072 2,594 2.348 2.12 1 11.032 9,5 14 8.388 32,177 26.792 22.7 18 71.060 6 1.832 48.844 102,328 85.882 68.467 148,745 112.462 96.204

0.499 0.478 0.458 1.196 1.103 1.047 2.099 1.934 1,803 8.858 8.043 7.147 25.862 21.88 I 19.1 84 73.275 58.037 49.8 11 102.679 82.924 68.794 148,745 112.462 96,204

0.499 0.478 0.458 0.507 0.483 0.464 0,518 0.49 1 0.47 1 0.532 0.505 0.484 0.54 1 0.5 17 0.500 0.556 0.529 0.5 17 0,564 0.550 0.531 0.604 0.598 0.553

interactions in non-ideal mixtures HI.l o. The high nega­

tive values of l1 E show that DEHPA interacts strongly

with unl ike molecu les of di luents6 . The minimum value

of ll E indicates the maximum dispersion of unlike mo l­

ecules6•19• The negative values ofllE also indicate com­

plex formation between the component liquids of the mixture solutionS which is in good agreement with the work of Fort and Moore2

, Piotrowska20 and Kaulgud2 1.

The negative values of ll E and the nOll-linear varia-

"

w t:'"

System

DEHPA( I) + Benzene(2)

DEHPA( I) + Toluene(3)

Benzene(2) + Toluene(3)

DEHPA ( I) + Benzene(2) + To luene (3)

SWAIN et 01.: VISCOSITY & DENSITY STUDIES OF TERNARY MIXTURES

Table 4 - Values of binary polynomial constants A;J' B;j' C;; and additional te rnary co nstan t A; jk * used in Eq 2 and roo t mean square (rms) deviations at different temperatures

Parameter 30 " 35 " 40 "

AI 2 - 134.38 -106.82 -74.39

BI 2 41.20 52.24 20.90 C I2 8.53 -22. 19 -2.02

rms deviatioll'1f 0.1622 0.0985 0.0606

AI] - 149.80 - 11 8.78 -87.13

BI) 67.39 52.22 29 .8 1 C ll - 4.74 -0.2429 12.07

rms deviation'1f 0.0462 0.0817 0.1 956

A2J -0.0376 -0.028 1 -0.0534

BB 0.0777 0.0746 0.0896

C2) -0.0796 -0.0722 -0.0993 rills de viatioll'1f 0.0043 0.0046 0.0025

A12) * 2 10.94 141.05 99.53

rl"l1s deviatioll'1f 0.11 74 0.1592 0.0732

11 21

45 "C

-66.24 30.48

-1 3.18 0.0652

-73.23 27.67

3.43 0.0739

-0.0285 0.0286

-0.023 1 0.0008

78. 17

0.1228

I f the constituents of the binary sys tems are interchanged [e.g. the binary DEHPA( I) + benzene(2) is changed to benzene( I ) + DEHPA(2)]. then the values of A'j and C;j remain the same. The value of B;j also remains the same but its sign changes.

0

·10

·20

·30

·40

·50

·eo

·70

·eo

'1f rms devi ation = [2: d;2/n] 112, where n is the number of observations and d = [(ll" Ptl -ll '''k)/lle'PII].

[!;

a 0

•

'"', .... --. . -~ . • 0

II

30°C 35°C 40 °C 45 °c

• .....• ~" ,. . 0

tI /'

.'

/

tion of viscosity and density with change of composi­tion in the present system confirm molecular interac­tion between the polar extractant and the non-polar diluents.

Acknowledgment The authors are grateful to the authorities of Orissa

University of Agriculture and Technology (O.U.A.T.), Bhubaneswar, India and Regional Research Laboratory, Bhubaneswar, India. Thanks are also due to Mr. Sunil Mohanty of Regional Research Laboratory , Bhubaneswar, India for hi s cooperation during the ex­perimental work.

Reference I . Mi shra S, Chakravortty V & Murli M S, Indian J Chem, 34 A

(1995) 843. 2 . Fort R J & Moore H, Trans Faraday Soc, 61 (1965) 2 102

0,032 0.132 0.232 0.332 0.432 0.532 0.e32 0.732 3. Prasad N, Singh R, Prakash 0 & Prakash S, Indian J pure

appl Phys, 14 ( 1976) 37 1

XOEHPA 4. De A K, Khopkar S M & Chalmers R A, Solvel1l extraction of metals (Van Nostrand-Reinhold, London) , 1970.

Fig. 3- Plot of mixture viscosity, ll E against mole fraction of DEHPA, XDEHPA at 30, 35, 40 and 45 "C

5. Rout B K , Dash S K , Chakrovortty V & Swain B B , ./ pure appl Ultrasonic, 18 ( 1996) 125

6. Rout B K, Dash S K Chakrovortty V & Behera D, Indian J Technology, 3 1 (1993) 745 .

1122 INDIAN J CHEM, SEC. A, NOVEMBER 1999

7. Swain N & Chakravortty V, Indian J Chem, 35 A ( 1996) 395. 14. Singh R P , Sinha C P, Das J C & Ghosh P, J Chem Eng Data,

8. Swain N, Panda D, Singh S K & Chakravortty V, J Chem Eng 35 (1990) 93.

Data , 42(1997) 1235. 15. Das K C, Panda D & Singh S K, Phys Chem Liq , 32 ( 1996)

9. Swain N, Panda D, Singh S K & Chakravortty V, J Chem Ellg 123.

Data, 44 (1999) 32 16. Singh R P, Sinha C P , Das J C & Ghosh P, J Chenl En g Data, 10. Weissberger A, (Editor), Techniques of orgall ic chemistry, or- 34 ( 1989) 335

ganic soLvents, Vol. VII (Wiley Interscience, New york) 1959. 17. Redlich 0 & Kister A T, Ind Eng Chem, 40 (1948) 345

II. Dean J A, (Editor), Lange's hand book of chemistry , 12th edn (Mcgraw Hill-Kogakusha , New york), 1979. 18. Rout B K & Chakravortty V, Indian J Chem , 33A ( 1994) 303

12. McCabe W L & Smith J C, (Editors) , Unit operation of chemi- 19. Joshi S S, Aminabhavi T M & Balandgi R H, J Chelll Ellg cal Engineering, 2nd edn (Mc Graw Hill , New york) 1970. Data , 35 (1990) 185.

13. Rout B K, Mishra N C & Chakravortty V, Indian J chem Tech-20. Piotrowska A, Rocz Chern, 39 (1965) 437 .

nology, 1 (1994) 347. 21. Kaulgud M V, Z phys Chem, 36 (1963) 437