lle studies on HC sulfolane sys.pdf

8/14/2019 lle studies on HC sulfolane sys.pdf

1/10

Fluid Phase Equilibria, 61 1990) 89-98Elsevier Science Publishers B.V., Amsterdam

89

LIQUID-LIQUID EQUILIBRIUM STUDIES ON HYDROCAR BON(C,,-C,,)-SULFOLANE SYSTEMSASHA MASOHAN, SRIKANT M. NANOTI, KRISHAN G. SHARMA, SOM N. PURLPUSHPA GUPTA and BACHAN S. RAWAT *Indian Institure of Petroleum, Dehra Dun 248 005 India)(Received March 22, 1990; accepted in final form July 4, 1990)

ABSTRACT

Masohan, A., Nanoti, S.M., Sharma, K.G., Puri, S.N., Gupta, P. and Rawat, B.S., 1990.Liquid-liquid equilibrium studies on hydrocarbon (C,,-C,,)-sulfolane systems. FluidPhase Equilibria, 61: 89-98.Equilibrium tie line data have been determined at 60 and 100 o C with sulfolane and five

model hydrocarbon mixtures consisting of butylbenzene-dodecane, hexylbenzene-dodecane,hexylbenzene-cetane, octylbenzene-dodecane and octylbenzene-cetane. The data so ob-tained have been predicted by UNIFAC and correlated by NRTL and UNIQUAC modelequations. The alkylbenzenes used n the study were prepared in the laboratory.

INTRODUCTION

Until now the design and simulation of solvent extraction processes formed ium p etroleum fractions have been done mostly by fully empiricalmetho ds, which often require long and costly experimental work. The majorproblems in the mathem atical simulation of the processes for such fractionsare the complexity of the mixtures, the scarcity of basic data and the verylimited availability of suitable thermod ynam ic models.

Rational design of the processes requires characterization of the complexpetroleum fraction and mode ls for the prediction of their liquid-liquid andvapour-liquid equilibria (LLE and VLE). It has been shown (Meh rotra etal., 1986) that representation of a particular petroleum fraction, e.g. aviationturbine fuel (ATF), by mod el hydrocarbon s, together with the equilibriumpredictions by UN IFAC, forms a sufficiently accurate database for thesimulation mod el. On similar lines, higher petroleum fractions like kerosene

* To whom correspondence should be addressed.

0378-3812/90, 03.50 0 1990 - Elsevier Science Publishers B.V.


2/10

90and gas oil can be represented by models consisting of key components ofrepresentative hydrocarbon types of average carbon numbers (Rahman etal., 1984). Design of extraction columns for systems containing these higherfractions makes it essential to generate equilibrium data on synthetic mix-tures of known hydrocarbons (C,,-C,, range) with newer and industrialsolvents.Various thermodynamic models such as NRTL, UNIQUAC, ASOG andUNIFAC are available for the prediction of liquid-liquid equilibria. Theestimation of the binary NRTL or UNIQUAC parameters also requires theavailability of experimental LLE, VLE or infinite dilution activity coeffi-cient data. Such equilibrium data on higher hydrocarbon components (ClO-C,,) and solvents are not available.

The present paper describes the preparation of C,, C, and C8 alkylatedbenzenes and LLE studies on sulfolane-hydrocarbon systems involving theabove alkylbenzenes and dodecane-cetane, which represent middle distil-lates. The experimental data were predicted by UNIFAC (Magnussen et al.,1981) and correlated by the UNIQUAC (Abrams and Prausnitz, 1975) andNRTL (Renon and Prausnitz, 1968) model equations.EXPERIMENTAL

Synthesis of alkylbenzenesThe butyl-, hexyl- and octyl-benzenes were prepared in the laboratory by

the Friedel-Crafts reaction of benzene with the corresponding olefin (Olah,1964); the latter in turn were prepared by dehydration of butanol, hexanoland octanol respectively (Eley et al., 1966). The final reaction productobtained in the preparation of butyl-, hexyl- or octyl-benzene was subjectedto fractional distillation. The heart cuts representing the isomers of butyl-,hexyl- and octyl-benzene were the 170-175, 213-214 and 235-264C boil-ing fractions, respectively, for which the product yields were maximum.These cuts were taken for the present LLE studies.Purities

Purities of the above three alkylbenzenes were around 99 wt.%, asdetermined by mass spectroscopy. As can be seen from Table 1, the densityand refractive index of isomers of butyj-, hexyl- and octyl-benzenes de-termined experimentally matched fairly well with those reported (Rossini etal., 1953; Egloff, 1946; Hawley, 1971) for the corresponding pure isomers.Dodecane and cetane were obtained from Humphary Chemical Co., Con-necticut, U.S.A. The purities of these two paraffins were better than 99


3/10

TAB

1

Pcpoe

opesua

Po

Deya2oC

E

meavu

Leauevu

sByb

08

3P

h

08

IP

oa

08

Do

07

Ca

07

Soa

12

08

Rnea1

08

Eo1

08

Eo1

07

Hawle1

07

Hawle1

12

Hawle1

Ravin

a2C

E

meavu

14 14 14 14 14 14

Leauevu

14

Rnea1

14

Eo1

14

Eo1

14

Hawle1

14

Hawle1

14

Hawle1

aDeyareavin

vuaea3C


4/10

92

wt.%, as determined by gas chromatography. Sulfolane was obtained fromPhilips Co., U.S.A.Determ ination of liquid-liquid equilibria

Liquid-liquid equilibria were determined at 60 and 100 o C in single stagebatch equilibrium runs carried out in a double-walled mixer-settler of 250ml capacity with a thermometer pocket and a syringe stirrer. The desiredtemperature was maintained to within + 0.05 o C using a thermostatic bath.Varying quantities of aromatic (alkylated benzene) and saturated (dode-cane-cetane) hydrocarbons and sulfolane were taken in the mixer-settlerand the contents were stirred for 15 min for establishment of equilibriumbetween the phases. The phases were allowed to settle for 15 min and thenwithdrawn separately for analysis. Solvent was removed from the raffinatephase by water washing and from the extract phase by azeotropic distillationwith water. This analytical technique has been standardized and reported byRawat and Gulati (1976). The aromatic contents in the solvent free extractand raffinate were determined by gas-liquid chromatography.

For each particular system of alkylated benzene-paraffin-sulfolane, tieline data were obtained using different compositions of aromatic in saturateand keeping the solvent/feed ratio near 2.RESULTS AND DISCUSSION

The experimental LLE data determined at 60 and 100 o C with sulfolaneand model binary hydrocarbon mixtures consisting of butylbenzene-dode-cane, hexylbenzene-dodecane, octylbenzene-dodecane, hexylbenzene-cetane and octylbenzene-cetane are presented in Table 2.

From the ternary LLE data of all the above systems, the binary NRTLand UNIQUAC parameters were estimated using the method of Sorensen(1980). The method starts with minimization of an activity objective func-tion, Fa (eqn. (1)) which does not require qualified guesses of the parame-ters.

Once the convergence is achieved, the search shifts to minimize the con-centration objective function, F, (eqn. (2)), which fits the calculated andexperimental concentrations.

2)


5/10

93

TABLE 2E xperimental L L E data of the systems alk ylbenzene-dodecane/cetane-sulfolaneTemperature Raffinate phase composition extract phase composition(C) (mol ) (mol )

Saturate Aromatic Solvent Satur ate Aromatic SolventOctylbenzene-cetane-sulfolane

60 79.69 14.9380.13 17.8779.59 20.8163.84 33.4960.52 36.1652.25 43.9046.66 50.4430.85 64.0426.35 66.6811.00 83.00

100 80.25 14.0275.92 19.6263.87 31.5866.90 27.67

Octylbenzene-dodecane-sulfolane60 91.15 6.61

77.40 21.1638.03 57.4316.27 76.40

2.80 86.75100 85.93 9.99

63.20 32.2237.20 54.30

2.39 76.95H exylbenzene-cetane-sulfolane

60 79.63 16.8458.17 38.8645.75 52.1931.85 65.5810.88 79.77

100 79.63 16.6058.63 35.0544.17 47.2031.55 58.20

H exylbenzene-dodecane-sulfolane60 87.46 10.65

65.89 30.9458.00 38.9227.98 65.67

9.32 80.732.02 83.81

5.38 0.16 0.44 99.402.00 0.05 0.38 99.574.60 0.07 0.87 99.062.67 0.05 0.88 99.073.32 0.05 1.15 98.803.85 0.08 1.31 98.612.90 0.11 2.11 97.785.11 0.01 2.56 97.436.97 0.00 2.76 97.246.00 0.01 2.96 97.035.73 0.21 0.83 98.964.46 0.21 0.95 98.844.55 0.22 1.79 98.995.43 0.16 2.83 97.01

2.24 0.13 0.36 99.511.44 0.29 0.88 98.834.54 0.18 2.47 97.357.33 0.08 3.38 96.54

10.45 0.00 3.95 96.054.08 0.55 0.58 98.874.58 0.75 2.12 97.138.50 0.50 3.94 95.56

20.66 0.07 9.51 90.42

3.53 0.11 1.42 98.472.97 0.05 2.92 97.032.06 0.05 3.98 95.972.57 0.05 5.67 94.289.35 0.00 8.62 91.383.77 0.17 1.36 98.476.32 0.22 3.58 96.208.63 0.16 5.44 94.40

10.25 0.22 7.70 92.08

1.89 0.24 0.73 99.033.17 0.38 2.32 97.303.08 0.37 3.49 96.146.35 0.22 6.04 93.749.95 0.11 9.44 90.45 .

14.17 0.00 10.61 89.39(continued)


6/10

94TAB LE 2 (continued)Temperature(C)

Raffinate phase compo sition extract phase compo sition(mol%) (mol%)Saturate Aromatic Solvent Saturate Aromatic Solvent

Hexylbenzene-dodecane-sulfolane100 83.47 12.3761.88 32.77

43.23 49.8822.30 65.3013.33 67.82

6.18 64.33Butylbenzene-dodecane-sulfolane

60 88.10 10.2569.00 29.3350.33 46.7639.67 55.9518.80 71.53100 82.07 13.9965.74 30.5451.92 42.1138.97 53.5551.92 42.1138.97 53.55

4.16 0.64 1.65 97.715.35 0.79 4.00 95.216.89 0.65 6.23 93.12

12.40 0.66 10.32 89.0218.85 0.67 14.62 84.7129.49 0.53 21.15 78.32

1.65 0.26 0.89 98.851.67 0.43 4.02 95.552.91 0.29 7.28 92.434.38 0.31 10.22 89.479.67 0.38 17.53 82.093.94 0.79 0.00 99.213.72 0.75 5.42 93.835.97 0.87 8.54 90.597.48 1.05 12.73 86.225.97 0.87 8.54 90.597.48 1.05 12.73 86.22

The model parameters, along with the root-mean-square deviation (RMSD)values, are given in Tables 3 and 4. Experimental LLE data at 60 and 100 o Cwere also predicted by the UNIFAC model, and RMSD values are given inTables 3 and 4. For computation using UNIFAC, the hydrocarbons wererepresented by standard UNIFAC groups (Magnussen et al., 1981) whilesulfolane was considered as one independent group. The hydrocarbon-hy-drocarbon temperature-dependent interaction parameters have been takenfrom Rahman et al. (1984) and the sulfolane-hydrocarbon temperatureindependent parameters were taken from Magnussen et al. (1981).

The RMSD between the experimental and calculated extract and raffinatephase compositions were calculated as [eqn. (3)]

1l/2C C C ( x,J~ - X;jk)2/6Mk iIt is seen that, of all the models, the UNIQUAC model generally correlatesfairly well with the experimental equilibrium data at both 60 and 100 C.The predicted values obtained by UNIFAC also match reasonably well withthe experimental values at 60 o C. However, slightly higher RMSD values at


7/10

95

TABLE 3M odel parameters obtained from ternary L L E data and RM SD values at 60 o CSystem NR TL ( OL 0.2) U N I Q U A C U N I F A C

Ag,,/R Ag,,/R AU ,,/R Au,, /RDodecane-octylbenzene-sulfolane

(1) (2) (3)(l)-(2) - 201.57(l)-(3) 928.03(2)-(3) 376.49RM SD , mol 0.26

Dodecane-hexylbenzenesulfolane(1) (2) (3)

(l)-(2) - 377.69(l)-(3) 858.39(2)-(3) 424.72RM SD , mol 0.25

Dodecane-butylhenzene-sulfolane(1) (2) (3)

(l)-(2) 244.75(l)-(3) 1082.70(2)-(3) 476.91RM SD , mol 0.22

Cetane-hexylbenzene-sulfolane(1) (2) (3)(l)-(2) - 718.89

(l)-(3) 854.56(2)-(3) 452.32RM SD , mol 0.71

Cetane-octylbenzene-sulfolane(1) (2) (3)(l)-(2) - 219.91

(l)-(3) 626.37(2)-(3) 497.21RM SD, mol 0.61

249.261295.20

852.37

414.221321.80

582.09

151.791278.80

312.48

1118.101590.40

574.29

290.921522.10

809.12

- 99.52 150.16353.81 145.46303.75 - 9.32

0.21 0.30

- 11.27 92.86358.58 110.97294.47 - 23.32

0.22 0.51

9.51 - 24.15483.31 44.72231.09 - 13.16

0.18 0.90

205.28 305.89167.82 702.97189.37 37.47

0.56 0.40

- 296.91 723.16391.94 20.85488.01 -45.76

0.57 0.20

100 o C are perhaps due to the limited number of available sulfolane-hydro-carbon parameters at higher temperatures for such systems.The experimental LLE data for a typical kerosene cut (140-240 o C) with

sulfolane at 60 C were predicted using the detailed model suggested byMehrotra et al. (1986). The RMSD value obtained was 0.1404 wt.%. Thiskerosene, when represented by propylbenzene-dodecane andbutylbenzene-dodecane hydrocarbon model mixtures, showed RMSD of


8/10

96TABLE 4Model parameters obtained from ternary LLE data and RMSD values at 100 o CSystem NRTL ((Y= 0.2) UNIQUAC UNIFAC

k, /R Ag,JR WJR AU,,/RDodecane-octylbenzene-sulfolane

(I) (2) (3)(I)-(2) ~ 332.6 2(I)-(3) 786.39(2)-(3) 279.19RMSD, mol% 0.28

Dodecane-hexylbenzene-sulfolane(I) (2) (3)(l)-(2) - 678.5 9

(I)-(3) 866.64(2)-(3) 216.06RMSD, mol% 0.70

Dodecane-butylbenzene-sulfolane(1) (2) (3)(I)-(2) -51.15

(I)-(3) 762.67(2)-(3) 759.88RMSD, mol% 0.57

Cetane-hexylbenzene-sulfolane(1) (2) (3)(I)-(2) 139.85

(I)-(3) 716.33(2)-(3) 404.00RMSD, mol% 0.21Cetane-octylbenzene-sulfo dne

(I) (2) (3)(I)-(2) - 373.7 9(I)-(3) 514.58(2)-(3) 888.87RMSD, mol% 0.41

231.041298.80

819.86

734.551442.80

657.88

-271.171358.30

95.46

- 231.581545.10

580.46

80.461610.40

343.95

_

_

- 63.43 49.09426.16 31.22309.04 - 32.73

0.24 0.87

130.30 126.75351.41 140.55213.00 1.61

0.64 0.16

143.00 - 172.27431.23 29.06375.43 - 105.29

0.58 0.95

379.02 - 256.22442.78 56.79362.85 - 68.75

0.12 0.85

128.40 113.06361.55 44.5 1627.04 - 150.84

0.38 1.08

1.1350 and 2.6767 wt. , respectively. These results suggest that the pro-pylbenzene-d odecane mode l mixture represents this kerosene cut betterthan the butylbenzene-dodecane model.CONCLUSIONS

The experimental tie line data for the alkylated benzene s-cetane/dodecane -sulfolane systems are correlated best by the UN IQU AC mode l.


9/10

9

These data have also been predicted by UN IFAC , and compare well withthe experimental data. Kerosene (140-240 OC) is represented better by thepropylbenzene-dodecane model mixture than by the butylbenzene-dode-cane model mixture.ACKNOWLEDGEMENTS

The authors wish to thank the gas chromatography group for analysingthe extract a nd raffinate phases, the crude evaluation group for carrying outTBP distillation and the ma ss spectroscopy group for determining the purityof the alkylbenzenes used in the experiments.LIST OF SYMBOLS

;activityrequired ratio between the solute (U or L) concentrations inphases I and II at infinite dilution

A *,,, Ag,, NRTL parameters (J mall)M numb er of experimental tie linesP parameter value

constantR gas constant (J mallK-l)Aqj, A&$,UNIQ UAC parameters (J mol-)X, experimentally determined mole fractionGreek letters(Y NRTL non-randomness parametery activity coefficientSuperscript* estimated valuesSubscripts

i componentsj phasesk tie linesI data setsn parametersU upper componentL left component


10/10

98REFERENCESAbrams, D.S. and Prausnitz, J.M., 1975 . Statistical thermodynamics of liquid mixtures: a new

expression for the excess Gibbs energ y of partly or completely miscible systems. A IChE J.,21: 116-128.

Egloff, G., 194 6. Physical Constants of Hydro carbons, Am erican Chem ical Society, Reinhold,New York, Vol. III.Eley, D.D., Pines, H. and Weisz, P.B., 1966 . The Mechanism of Dehydration of Alcohols andAlumina Catalyst. Academic Press, New York, Vol. 16, p. 49.

Hawley, G.G., 1971 . The Condensed Chemical Dictionary, Van Nostrand Reinhold, NewYork, 8th edn.

Magnussen, T., Rasmussen, P. and Fredenslund, Aa., 1981 . UNIFAC parameter table forprediction of liquid-liquid equilibria, Ind. Eng. Chem. Process Des. Dev., 20(2): 331-3 39.

Mehrotra, R., Garg, M.O., Chopra, S.J., Rawat, B. and Khanna, M.K., 1 986. Liquid-liquidphase equilibria for dearomatisation of ATF fraction, Fluid Phase Equilibria, 32: 17-25.

Olah, G.A., 196 4. Advances in Catalysis: Friedel-Crafts and Related Reactions by Others,Interscience, New York , Vol. II, Part 1.

Rahman, M., Mikitenko, P. and Asselineau, L., 1984 . Solvent extraction of aromatics frommiddle distillates: equilibria pred iction method by group contribution, Chem . Eng. Sci.,39(11); 1543-1558.

Rawat, B.S. and Gulati, I.B., 1976 . Liquid-liquid equilibrium studies for separation ofaromatics. J. Appl. Chem. Biotechnol., 26: 425-43 5.

Renon, H. and Prausnitz, J.M., 1968 . Local compositions in thermodynamic excess functionsfor liquid mixtures. AIChE J., 14: 135-14 4.

Rossini, F.D., Pitzer, KS., Arne tt, R.L., Brawn , R.M. and Pimentel, G.C., 1 953 . SelectedValues of Physical and Thermodynamic Properties of Hydrocarbons and Related Com-pounds. API, Carnegie Press, Pittsburgh, PA, U.S.A.

Sorensen, J.M., 198 0. Phase equilibria and separation processes. MAN 8106 . ESTM : Estima-tion of UNIQU AC and NRT L parameters from ternary LL E data. Instituttet forKemiteknik, Lyngby, Denmark.

Documents

lle studies on HC sulfolane sys.pdf