owxL2509/84 s3.00 + .xl ?wgamoo Press Ltd.

SOLVENT EXTRACTION OF AROMATICS FROM MIDDLE DISTILLATES

EQUILIBRIA PREDICTION METHOD BY GROUP CONTRIBUTION

MAIZAR RAHMAN Oil and Gas Technology Development Center “LEMIGAS”. PO Box 39/JKT, JL, Jakarta (Selatan),

Indonesia

and

PAUL MIKITENKO* and LIONEL ASSELINEAU Institut Fran@ du P&ok, 4, Avenue du Bois P&u, 92, Rueil Malmaison, France

(Receiued 7 July 1983; accepted 3 January 1984)

Abstract-This work describes a method of calculating liquid-liquid aromatics extraction of a middle distillate. The group contribution models of the ASOG and UNIFAC type are investigated. Four vapour liquid equilibrium (VLE), two solid-liquid equilibrium (SLE), three binary and six ternary liquid-liquid equilibrium (LLE) have been measured. The parameters of the models are based mainly on the data of the systems having l&20 carbon number. VLE, SLE, and infinite dilution activity coefficient data (17-2459c) have been used for calculating interaction parameters between hydrocarbon groups and LLE data (ZO-8O’C) for interaction parameters of dimethylformamide-hydrocarbon groups. Middle distillate representation is based on mass spectrometric and gas chromatographic analysis and on limited data of middle distillate-DMF liquid-liquid equilibrium. It is shown that the performance of ASOG and UNIFAC models are sufliciently valid in representation of data base and in extraction calculations. Considering the predictive character and the rapidity of its application this method can be useful in the preliminary study of extraction processes.

INTBODUCCION

Until now, the design and simulation of solvent extraction processes for medium petroleum fractions have been done mostly by fully empirical methods which often require long and costly experimental work. The major problems in the mathematical sim- ulation of the processes for such fractions are the complexity of the mixtures, the scarcity of basic data and the very limited availability of suitable thermo- dynamic models.

This paper describes a method for calculating liquid-liquid extraction of aromatics from middle distillates. Group contribution models of the ASOG and UNIFAC type are investigated. The parameters of these models are based mainly on the data of the systems having a carbon number of l&20, i.e. those normally encountered in middle distillates. More- over, two models, one detailed and one simplified, based for a good part on analyses by mass spec- trometry and chromatographic methods, have been proposed to represent a gas-oil fraction (24&35O”C). These models have been associated with thermo- dynamic models and applied to extraction calcu- lation.

EXPEBlMENTATION FOR BASIC DATA

Four binary vapor-liquid equilibria (VLE), two binary solid-liquid equilibria (SLE), three binary and six ternary liquid-liquid equilibria (LLE) were mea- sured. VLE data were obtained by the IFP Cottrell

pump type ebulliometer[2]. The temperature and pressure of the mixture were measured at fixed com- position.

SLE data were measured by the sealed-tube method which is similar to the one described by McLaughlin and Zainal[3]. For the LLE data, di- methyformamide (DMF) WBS chosen as the solvent due to its better selectivity toward polyaromatics, particularly in a mixture with other solvents[rl]. LLE data between hydrocarbon and DMF were measured by a thermostatic cell. The phase compositions were determined by chromatography. The ternary LLE systems were correlated by NRTL. The overall mean absolute deviation between experimental and calcu- lated LLE compositions is 0.4mole%. The complete results of this experimental work are available elsewhere [l].

GROUP CONTRIBUTION MODELS,

UNIFACANDASOGTYPE

In the UNIFAC or ASOG models, the activity coeflkients are given by a combinatorial term and a residual term:

lny,=lny,C+ln~iR (1)

a detailed description of these models is given by Fredenslund et a1.[5] for UNIFAC and Kojima-Tochigi[6] for ASOG.

1543

1544 MAIZAR RAHMAN et al

In this work for UNIFAC, we use the modified combinatorial term given by Kikic ef al. [7j written as

ln yc = (ln oi/xi + 1 - 0$x,)

- 1/2ZqXln &/e, -I- 1 - &/ej) (2)

where Z = coordination number = LO; q, = area parameter; xi = mole fraction; 0, = area fraction = 4&iPjxflji qhi = vollmle fraction = V&ZjV+, and wi - modified volume fraction - V~~‘/YZjV~~‘x,, where V, is a volume parameter. Subscript i denotes that the parameter is for component i.

In UNIFAC, the residual term is introduced as a temperature dependent interaction parameter, writ- ten as:

a,,,, = A, + B,,#- - 273.15). (3)

For ASOG, we used the mod&d combinatorial term, given by Rogers and Vera[8], written as:

In yc = In wi/xi + 1 - wJx, (4)

where xi = mole fraction; oi = x~VC~~~/~,:,X,VC~/~; VC, is the critical volume of compound i, calculated by using Lydersen’s method (9) with subscript i standing for component i. For the residual term, we used the same formulation as the one described by Kojima- Tochigi[6], where the group interaction parameter is already temperature dependent:

a, = exp (WQ, + n,/T). (5)

Since parameter +, = exp( - a,,,JT) of UNIFAC is similar to a,, of ASOG, the formalism of the residual term of UNIFAC and ASOG used here is similar and has the same number of interaction parameters.

GROUP DRMNITION

UNIFAC hydrocarbon groups CH2, ACH, ACCH, described in [5] are used here. To characterize the fused ring hydrocarbon we introduce the new groups ACC (relating to condensed aromatics) and CHNA (relating to condensed naphtbenics). To char- acterize the thiopbenic compounds, the new group STH is incorporated. Dimethylformamide is consid-

ered as one group. The characteristics of these new groups are given in Table 1.

To facilitate the comparison of the two models, for

ASOG we use the same groups as used in UNIFAC.

CALCULATION OF GROUP

JNTERACl’lON P-

The basic data for the group interaction parame- ters estimation consist of the data obtained in this work and those from the literature (Table 2).

Almost all of the interaction parameters between hydrocarbon groups and between STH-hydrocarbon groups were estimated from VLE, SLE and y ” data

in the 17-245°C temperature range. The interaction parameters between DMF and other groups as well as between the pairs CHJSTH, CHNA/STH and ACC/STH were calculated from LLE data (2CrSO”C).

The parameters were estimated by minimizing the objective function. For VLE, SLE and y m data, the objective function used is:

F - F F [In y,(EXp) - In yXMODEL)$ (5)

y,(EXP) were mostly generated from VLE data using the NRTL model and from SLE data, using the following equation [28]:

y,=iexpk(g- l)] (6)

where T = temperature of the system; R = the gas constant; T,,,, and Ah/, are respectively melting point and heat of fusion of pure substance i, xi = mole fraction of component i in the liquid solution.

LLE data are treated separately by using the objective function in terms of activity:

i= 1,2,.. . N (components); j = 1,2, . . . M (tie lines); I = 1,2, . . . L (data sets); ajj, = yij,xiji yi,, = activity coefficient of i calculated by the model. I and II, reference of phases.

To minimize the objective function, we used the Nelder-Mead search method [5, 341.

Table 1. Volume and surface area parameters of groups

Group

XC

CHNA

STH

DW

Rk 'k

0.3125 0.084

0.4344 0.190

0.7119 0.520

3.086 2.736

Sample group assignment

I methyt naphchalene : 7 ACH, 2 ACC, I ACCH3

Decalin : 2 CH NA, 8 CH2NA1)

Benzothiopheoe : 6 AC”, 2 ACC, I STH

DimeehyLformamide : 1 DMF I

" CH2NA group represents the noncondensed naphthenic Sroup (with Rk = 0.4344 and Qk = 0.520) considered

as the subSroup of CH2.

Solvent extraction of aromatics from middle distillates 1545

REPIUBENTATION OF DATA BASE Average residuals for N total points. Table 3 gives the UNIFAC and ASOG group

interaction parameters obtained. To distinguish these parameters from existing ones, we designate them as (14)

UNIFAC 10-20 and ASOG 10-20 (lo-20 indicates the carbon number range for which this variant may where I is the reference system and N = Z Mk be better suited). Table 4 gives the numerical values of these average

In an attempt to quantify the difference between residuals. It may be seen that, compared to existing the experimental (indicated by EXP) and the calcu- parameters, the new parameters represent the VLE lated (indicated by MODEL) values, the following and y Do data better. This improvement is mainly due average residual terms (for N total points of each to the estimation of new parameters by the direct fit data type) are defined: of the data base to the models and the introduction

of the new groups. VLE data However, the representation of SLE data is not

isobaric system: improved and is even worse, particularly for ASOG 10-20.

n - i 2 1 (T(EXP) - T( MODEL)) 1 in “C. The average residual for binary LLE data is 0.3

(8) (ASOG 10-20) and 0.4 (UNIFAC 10-20) mole %. It I was observed that the introduction of temperature-

dependent interaction parameters carried out in this Isothermal system: work improved the representation of these systems.

The average residuals for ternary LLE data are 2.2

P=_!_$j~~xlOOin%. (9) (ASOG l&20) and 2.0 (UNIFAC 10-20) mole%. Compared to the representation by NRTL, these last two values are about five times worse. Figure 1 shows experimental points and calculated binodals of the

For isobaric or isothermal systems ternary systems as well as the experimental points and calculated values of the solute distribution ratio. It

dy, = ; i [y,(JZXP) - yXMODEL)I can be seen, however, that when the solute content in

in mole %_ (10) the m&ate is less than 10 mole % (the usual wncen- 1 tration range in an industrial extraction of aromatics

from a middle distillate) the solute distribution ratios T. P are respectively temperature, pressure; yt is are calculated better by both models. vapor phase composition of component i.

PREDICI’ION OF MULTICOMFONENT

SLE data LIQUID-LIQUID FXJUILIBRIA

Five equilibrium data points including eight com-

- Ax, = f 2 Ix,(EXP) - x,(MODEL)( in mole %.

ponents were measured and are described in [I]. The

(11) components of the system are the same as those of the I ternary LLE experiment. Figures 2(a) and 2(b) show

that, compared to the observed values, the predicted xi is liquid-phase composition of component i. results given by UNIFAC 10-20 are generally good.

ASOG 10-20 gives a similar quality of prediction. It y” data can be noted that the nature of prediction is similar

for ternary as well as multicomponent systems, i.e. prediction is better at 35°C and for the equilibrium having low solute concentrations.

MODELING OF MIDDLEDISTILLATE

EXTRACITON

LLE data A mass spectrometric analysis of a middle distillate For a system I: (gas-oil range) is given in Table 5. The carbon-

number distribution of each type of aromatic (mass spectrometric analyses) as well as that of normal paraffins (chromatographic analyses) is given in Ta- ble 6.

- &,,JMODEL)[ in mole a,&. (13) Two types of gas-oil representations were exam- ined for prediction calculations, designated as de-

i=l, 2,... n,, n, = number of tie lines, j = 1, 2 (bi- tailed and simplified gas-oil models. In the first, the nary) or 1, 2, 3 (ternary), number of components, k=1,2=referenceofphases;M,=2xjxn,.

gas-oil is considered JO be composed of 72 com- ponents: 64 aromatics as given in Table 6; n-hep-

Tabl

e 2.

Bas

ic d

ata

for

para

met

er e

stim

atio

n fo

r th

e m

odel

A H

sys

L Ulll

1.2.

3 tr

imct

hyl

benz

ene

- n

deca

ne

buy1

be

nzen

e -

n ci

cosa

nc

hcpt

yl

hcnz

cnc

- n

hexo

decn

nc

bury

1 be

nzcn

c -

n hc

xade

canc

prop

yl

benz

ene

- n

hexo

deca

nc

tulu

cnc

- n

hcxn

dccn

no

tibcn

ryl

- n

hexa

deca

ne

phcn

onth

rene

-

n ho

xndc

cone

phcn

anth

rcnc

-

n he

xade

cane

noph

thal

ene

- n

tetr

adec

Jne

naph

thal

ene

- n

dodc

cane

naph

thill

enc

- n

dodc

canc

phcn

anth

rcne

-

n de

cane

phen

anth

rene

-

n do

deca

ne

phcn

nnth

rcne

-

n he

xade

cane

naph

thal

ene

- n

hexn

deca

ne

phen

anth

rene

-

buty

l be

nzen

e

phcn

nnth

rene

-

prop

yl

benz

ene

phcn

anth

rcne

-

I m

ethy

l na

phth

alen

e

TY

PC

VLE

SLE

VLE

VLE

VLE

VLE

VLE

VLI

:

-r- 2

-fz9

S

LE

SLE

SLE

Y” 2

Y_ 2

Tabl

e 2.

(C

od)

tram

dc

calin

e -

n de

cant

V

LE

56-9

1 17

15

trans

dc

calin

e -

1,2,

3 tri

awth

yl-b

enze

ne

VLE

I1

0 an

d lb

0 2b

IO

C

tra

n~

doca

line

- be

nzen

e V

LC

27-6

6 13

th

is

wor

k

dcca

line

- be

nzen

e Y

” 2 25

I

2h

tetra

lin

- ci

s de

calin

vu

98

-108

9

lb

cl

phcn

anth

rene

-

trans

de

calin

SL

I: 64

-92

b 21

naph

thal

cne

- de

calin

SL

C

IO-4

8 5

22

thio

phen

c -

benz

ene

SLE

55

nnl.l

61

22

17,

16

1:

thio

phcn

c -

tolu

cnc

SLE

86

;~nd

105

7

19

n ha

xade

cane

-

D?f

f LL

E 35

I,,

61

1 4

rhis

vi

lrk

1?

n tc

tradc

cane

-

‘DM

F LL

E 35

Jl

ld

80

2 II

G

(tran

s l

cis)

de

calin

-

DW

LL

E 35

to

55

2

this

w

rk

n hc

xodc

cnnc

-

octy

l be

nzen

e -

DM

F LL

E 35

an

d 80

II

I%

n hc

xade

xane

-

Tetra

lin

- D

?IF

LLE

35

rrlld

80

9 II

n he

xade

cane

-

I m

ethy

l nn

phth

alen

c -

DW

LL

E 35

nn

d 80

II

II

II

n hc

xadc

cane

-

phcn

anth

rcnc

-

Dkf

F LL

1:

35

illlll

MO

II

II

n he

xade

cane

-

ethy

l be

nzen

e -

DEW

LL

E 20

4

27

n he

xade

cane

-

I I d

iphe

nyl

etha

ne

- D

HF

LLE

20

4 I7

n hc

x~df

cane

-

bcnz

o~hi

ophc

nc

- D

EIF

LLE

35

.1

11<1

HO

9

this

w

rk

1 (tr

ans

+ ci

s)

Dec

alin

-

bcnz

othi

ophe

na

- D

XF

LLE

35

nnd

55

a II

Tab

le 3

. UN

IFAC

10

-20

and

AS

OG

l&

20

grou

p i

nte

ract

ion

par

amet

ers

--

_ ___

_-

nsoc

IO-

20

h I:

, .

Imsl

z

"kl

'"1 k

I'~,

, K

'Ilk

' K

rrt*

atcd

- rl

.821

9 I)

.611

1 24

9.tm

ltl

- 13

7.36

68

- 0.

6208

0.

7971

) 17

G.GS

iX

- 23

1.32

51

A

- 0.

0715

0.

7228

14

3.15

06

- 25

4.3X

lY

- 2.

1477

. 2.

6069

b5

2.80

70

- 2F

8.4t

177

- I.

0034

1.

9723

51

1.93

76

87.6

728

1%

- 0.

5439

-

0.12

79

64.9

575

-199

9,YS

?h

UN

IYA

C IO

-20

. -

II.9

781

- 0.

0142

i 0.

1988

- 92

.755

6

- 34

.689

8

- 0.

0242

2.34

11

7.37

13

0.08

22

- 0.

1973

- 0.

1348

cll,/

cHtu

0.

0 0.

0

---l-

- 0.0

0.0

8.38

05

3073

.240

1

-I---

2.

9741

67

.032

0

7162

3.40

13

- 71

4.93

9 -

443.

3231

0.

9404

0.0

0.0

0.0

0.0

- 6.

1050

0.

055:

! -

512.

5657

IO

.453

9 (~

0.31

54

0.21

79

- 76

.807

2:

92.5

116

--

- 8.

5658

-

0.01

58

- 13

5.99

05.

j58.

0296

u

5.92

32 1

- 17

3.13

48

ACll

/STH

10

1.98

74

100.

4142

0.

0 0.

0

ACCl

12/S

TlI

17bb

.469

6 17

26.9

511

0.0

0.0

I I

I 4

CH2/

DHF

448.

5146

-

39.3

629

- 1.

5884

-

0.20

91

- 0.

1054

1

1.19

45 1

11

6.14

32 1

- 64

5.95

4 1

F

93.2

216

1 -

2.64

70 1

O.

Bl62

1.

6746

-

2.94

89

- 34

9.79

69

583.

3034

1

C

0.38

63

- 0.

654

22.1

648

138.

4911

1.33

39 -

21.9

358

447.

8053

-

259.

Lbll

II

0.00

49

0.00

07

- 10

4.67

83

- 8.

5347

0.01

72

58.9

759

- 98

.653

6 -

- -2

258.

5746

2.43

4 -

46.0

245

- 89

5.43

52

-391

5.99

89

I 0.

0 0.

0 -1

6266

.874

-2

656.

1942

0.0

0.0

-307

17.4

87

-804

35.2

1 i

- 34

.764

1

- 13

1.42

21

330.

7022

- 80

.638

2 0.

0834

1481

.794

9 9.

8007

121.

7394

-

0.47

53

0.03

26

- to

.563

2

I.12

13 I

STH/

DMF

STH/

CI12

STII

/CII

NA

STll

/ACC

- 21

3.58

81

- 4.

2423

7478

8.31

62

45t3

1.88

95

253.

0073

215.

3484

2956

5.5)

41

- 20

4.07

82

0.22

26

0.37

71

0.40

47

- 1.

0546

0.0

0.0

0.0

0.0

Solvent extraction of aromatics from middle distillates

Table 4. UNIFAC and ASOG residuals for the systems in the basic data

1549

ax, ma1 x

Infinite dilution activity coefficient

A?. z

Binary LLE

x%, LwlX

Ternary LLE

YiF* rnol z

Existing parameters This project

ASOG:’ uNIp*(y:::

1.92 1.31

5.3 L.0

2.92 3.45

2.90 2.49

40. 31.

ASOG IO-20 "NIFAC IO-2c

:: parameters for the interaction between groups CHZ, CyH, ArCH [ref. 6).

:::: parameters for the intuaction between groups CH2. ACH, ACCH2 (ref. 5).

Table 5. Characteristics of the gas-oil used in the experiments, boiling range: 24O-350°C; density at 20°C; 0.8373

N’

I

2

3

4

5

6

7

8

9

II

12

l- - -

Compound type

Saturates - paraffins (n+iso)

- noncondensed naphthenes

- condensed naphthenes

- alkyl benzenes, C,H2n_6

- indans and Tetralins, C,H2n_B

- indenes. CnH2n_,0

Gj.romatics

- naphthalenes, CnIi2n_12

- aceeaphtheees and diphenyls, CDR2n_,4

- acenaphthylenes and fluorenes, C,H2n_,6

Triaromeries

- ph6nanthrenes and anthrscenen, CIIl$_,B

Sulfur compounds

- benzothiophenes. CnH2n_IOS

- dibenrethiophenes, CnE12n_,6S

Mass %

73.51

04.26

18.2L

II.01

10.79 9.03 16

4.51 16

1.25 16

8.71

5.42

2.44

0.85

15

15

lb

0.61

0.61 16

2.30

1.67

0.71

14::

14::

17

17

17

: estimated from pa-ail boiling range.

Tabl

e 6.

Car

bon

mem

ber

dist

ribut

ion

of th

e hy

droc

arbo

ns i

n th

e ga

soil

used

in th

e ex

perim

ents

(mas

s %

I

Car

bon

1

nu

mbe

r n

P

araf

fin

s (A

lkyl

be

nze

nes

)

12

0.0

0.38

3.4

0.00

17

.03

0.00

0.

00

0.0

13

1.50

5.

30

IO.5

5 7.

55

I 20

.55

9.21

I

4.58

I

o.uo

14

’ 17

.44

14.6

8 15

.44

17.5

0 14

.46

21.0

0 8.

58

0.00

I5

19.2

2 17

.78

14.3

4 17

.43

I 14

.17

22.7

5 1

29.1

6 1

27.1

16

16.5

4 15

.26

13.3

3 16

.93

9.36

22

.21

26.9

1 21

.5

17

16.2

4 14

.78

12.2

5 14

.72

1 7.

74

I IO

.84

16.4

2 1

16.1

I8

14.0

3

19

10.4

0

20

4.63

21

0.00

12.5

2 II

.46

10.8

7

9.69

10

.88

7.19

6.20

5.

40

5.21

3.41

2.

95

2.60

6.59

6.

47

4.92

9.

0

5.20

4.

37

4.94

14

.0

2.63

I.

58

2.17

1.

6

2.38

1.

57

2.29

1.

6

Solvent extraction of aromatics from middle distillates 1551

‘2E ,’ .

-30

‘2E 20

se

0 10

xf X2.w 5

10 20 30

%E .30

20

/’

10

./T-T ,

XZR

IO 20 30 4p

Fig. 1. Ternary liquid-liquid equilibria (mol Oh). Experimental points: 0 2oDc; l 35OC; 0 5S°C, A 80°C. Calculated curves: -- UNIFAC l&20, i ASOG lc20, E - extract (solvent rich phase), R - raffinate

(hydrocarbon rich phase), Ax - average residual of each system (cqn (13)).

1552 MAIUR RAHMAN et al.

.M

‘2E .

-ID

SE 20

5.

m-

XZE

lo-

30

7.0

. I? XZE . 20.

. 10 .

I IO-

IO 20 X2R x1 , _

Fig. 1. (Conrd) Ternary liquid-liquid equilibria (mol%). Experimental points: 0 ZO’C; l 35%: 0 55%; A WC. Calculated ourveB: -- UNIFAC 10-20, - ASOG 10-20. E _ extract (solvent rich phase), R -

raffinate (hydrocarbon rich phase), 4x - average residual of each system (eqn ( 13)).

Solvent extraction of aromatics from middle distillates 1553

Tabl

e 7.

U

NIF

AC

10

-20

pred

ictio

n fo

r on

e-st

age

gas-

oil

extra

ctio

n, u

sing

det

aile

d ga

s-oi

l m

odel

r - t

Ten

per

ntu

re/s

olve

nt

to

feed

ra

tio

35/i

.03

3512

.71

I 80

/1.9

0 60

/3.

I I

(‘C/m

ass

ratio

)

Com

posi

tion,

w

eigh

t Z,

DFtF

Para

ffin

5

Aon

cand

ensr

d na

phth

enes

Con

dens

ed

naph

then

cs

Alk

yl

bent

enes

Tetr

al

ins

lnde

nes

Nap

htha

lene

s

Ace

naph

then

es

Ace

naph

thyl

enes

Ph&

mnt

hren

cs

Ilcnz

othi

aphm

es

Dib

cnzo

thio

phcn

cs

::

I-

t

, r

j R

T

-i T

R

E

R I

f R

r:

EXP

CALC

EX

P CA

LC

EXP

CA

LC

05.7

08

.7

4.8

3.9

90.

I 92

.2

15.

t 13

.4

6.9

6.7

5.2

5.4

16.7

16

.8

0.0

8.3

1.2

2.7

20.9

21

.4

9.8

9.:

4.7

3.2

2.0

2.9

4.2

6.1

3.7

3.7

5h.7

21.5

12.1

6.1

2.5

0.5 I.6

0.G

0.1

0.

I

0.2

0.0

;

12.

I 17

.7

17.7

!1 .o

9.

0 8.

9

2.2

6.4

7.1

6.5

17.0

17

.6

3.3

P.l

8.6

0.8

2.5

2.7

2.0

16.1

17

.2

0.9

8.3

-7 .a

0.3

38

2.6

0..

2 2.

1 2.

t

0.7

4.3

5.1

q.2

3.7

2.6

ES

P

CA

LC

EXQ

CALC

lb.

I 14

.7

77.0

81

.8

50.3

51

.9

38.6

32

.9

23.7

20

.7

17.8

14

.5

13.2

11

.5

9.7

10.3

6.5

6.5

11.8

12

.7

2.7

3.2

5.b

b.5

0.4

0.8

I .l

I .8

2.0

2.5

7.9

9.8

0.8

1.t

3.2

b.5

0.2

0.4

1.5

I .5

n.

I 0.

2 0.

9 I

.2

0.0

0.9

1.3

2.9

cl.

I 0.

3 0.

9 I

.4

EXt’

15.0

51.0

22.1

15.2

5.3 I.9

0.0 1.2

0.0

0.1

0.0

0.0

0.0

L

t

L

I L T I

CA

LC

t3.7

t

56.6

i-

21.3

II.3 5.

5

2.7

0.7 1.8

0.8

0.3

0.2

0.7

0.2

L

EXP

CA

LC

EXP

CA

LC

81 .

o 84

.3

65.1

3b

.6

17.5

15

.9

10.5

IO

.8

10.3

11

.7

L.?

5.0

0.7

1.7

b.I

8% I

2.4

3.7

0.9

I.3

0.6

0.9

0.7

1.5

0.6

I.1

“L

T 6.

0 I L

51.0

22.3

10.4

7.4

3.7

0.1 2.7

0.9

0.2

0.2

0.4

0.

I

4.5

48.7

19.9

I I

.a

1.9

4.0 t .o

3.1 I .4

0.5

0.3 I.1

0.3

:: C

ompo

sitio

n of

so

lven

t fr

ee

phas

es

R =

R

affin

atc

; E

= E

xtra

ct

Tabl

e 8.

pre

dict

ion

of g

as-o

il ex

tract

ion.

Com

paris

on b

etw

een

deta

iled

and

sim

plifi

ed g

as-o

il m

odel

s

Car

oil

lnod

el

Det

aile

d S

impl

ifie

d A

ccu

racy

Th

erm

odyn

amic

m

odel

U

NIF

AC

IO

-20

IJN

IFA

C I

O-2

0 A

SO

G

IO-2

0 of

an

alys

es::

xi

B

E

h

E

E

E

H

DM

P

1.3

3.3

1.3

2.9

I .3

4.

0 0.

3 0.

3

solv

ent

free

ph

ases

Psr

af

f in

s I.

8 4.

0 1.

8 3.

1 1.

6 3.

5 1.

30

0.5

Non

con

den

sed

kph

then

es

1.7

1.3

1.5

I .4

1.2

2.9

1.70

0.

45

Cond

enie

d n

aph

then

es

1.5

0.5

I .a

0.

4 I.

7 0.

6 I

.40

0.25

Alk

yl

ben

aen

es

0.3

0.8

0.2

I .o

0.

3 I

.3

0.44

0.

35

Tet

rali

ns

0.6

0.6

0.6

0.9

0.6

0.9

0.14

0.

17

Inde

nes

0.

4 0.

9 0.

4 0.

8 0.

4 I

.o

0.20

0.

38

Nsp

hth

alen

es

0.5

I .4

0.

5 1.

3 0.

3 2.

1 0.

29

0.88

Ace

nap

hth

enes

0.

5 0.

9 0.

3 0.

9 0.

3 1.

3 0.

28

0.68

Ace

nap

hth

ylaa

es

0.2

0.8

0.1

0.4

0.1

0.4

0.18

0.

24

Ph

enan

thre

nes

0.

1 0.

2 0.

1 0.

2 0.

1 0.

4 0.

14

0.15

Ben

zoth

ioph

enes

0.

7 1.

5 0.

7 I.

1 0.

8 I.

6 0.

4 0.

4

Dib

enzo

thio

phen

es

0.2

0.5

0.2

0.5

0.2

0.6

0.1

0.1

--i-

4 A

i -

i lX

i(E

XP

) -

Xi

i;

(CA

LC

)I

, m

a88 .Z

::

Ref

. 32

. 33

i -

R

(raf

fin

ate)

or

E

(e

xtra

ct)

1556 MAIZAR RAHMAN et al.

Table 9. Yields of one stage extraction* (simplified gas-oil model)

T - 35’13,

I .03 2.71 I

CALC . CALC . EXP. EXP.

UNIFAC IO-20 ASOG IO-20 UNIFAC IO-20 ASOG 10-20

SaCUrateS 5.4 5.4 3.7 13.2 10.6 8.8

Monoaromatics 29.5 24.3 22.6 56.6 416.7 44.2

Diaromatics 66.5 53.6 54.6 94.7 76.6 77.4

Polyaromatics 75.1 63.0 69.5 100.0 81.4 86.7

Sulfur compounds 54.3 51.3 31.4 98.4 74.5 74.5

T = BO’C

Solvent/feed mass ratio

:: Weight X on fe

48.6

67.8

78.5 80.0

50. I

1.90

tadecane representing the paraffins;? undecylcyclo- hexane representing the alkylmononaphthenics;t hep-

tyl Decalin representing the alkyldinaphthenics;t four benzothiophenes having 10, 12, 14 and 16 carbon numbers$ and ethyldihenzothiophenes$.

In the simplified model, the gas-oil is considered to be composed by 12 components, respectively 12 principal types of hydrocarbons determined by the analyses given in Table 5. The carbon numbers of these “components” are taken to IX equal to the average carbon numbers determined.

Lacking the precise structure of the aromatics found in gas-oil we had to define the appropriate molecular structures to which the ASOG 10-20 aad UNIFAC 10-20 models are sensitive, particularly the number of alkyl substitution in the aromatic ring (the number of ACCHs group) ia the molecule. Limited LLE data for the middle distillate-DMF system are sufficient for this determination[l]. In our case, the structures which best represented the experimental aromatics distribution ratio were: (i) for the alkyl aromatics, the sort ofmolecular structure having only single alkyl substitution in the aromatic ring; and (ii) for the naphthenoaromatic compounds, no alkyl substitution in the aromatic ring (could be in naph- tenic ring).

tThe carbon number of these Compounds is 17, equal to the average Carbon number of saturated hydrocarbons as given by the analyses.

STbese compounds represent the tbiophentcs, and their composition and carbon numbers are estimated from the analysis of four TRP fractions of the gas-oil investigated.

3.11

CALC. EXP.

UNIFAC IO-20 ASOC 10-20

71.9 50.3 42.5

76.3 76.6 71.5

78.1 87.1 66.3

71.2 86.1 85.0

39.5 83.4 82.8

ItIBUL’I-S AND DISCIJSSION The results of the prediction with the detailed

gas-oil model are compared with the experimental data in Table 7. To simplify the presentation, the results are regrouped in 12 principal hydrocarbon types. The agreement between calculated and experi- mental values is relatively good, particularly at 35 “C. This nature of prediction is similar to that of the representation of ternary in the basic data.

Table 8 compares the results of prediction using different gas-oil models and two thermodynamic models. It is clear that the simplified gas-oil model gives results comparable to these obtained with the detailed model (columns 2, 3 and 4, 5). There is therefore no point in using the detailed model.

Further, columns 4, 5 and 6, 7 of Table 8 indicate that the performances of the UNIFAC 10-20 and ASOG 10-20 models are equivalent on the whole. Since ASOG 10-20 consumes less computer time, due to its simpler formulation, this model might be more advantageous to use.

To consider the equality of the modeling of the extraction, the average residuals obtained by ASOG 10-20 are compared with the precision of the anal- yses. Columns 6, 8 aad 7, 9 show that the rafhnate compositions are predicted better than the extract compositions. This caa be explained by the fact that the smallest error in calculated extract composition is considerably amplified by solvent elimination. On the whole, the residuals calculated by the models are higher than the precision of the analyses. Table 9 shows, in more condensed form, the experimental and predicted values of extraction yields. It can be

Tabl

e 10

. The

e-st

age

cros

s cur

caat

ext

ract

ion

(35”

C, s

olve

nt/fe

ed m

ass

ratio

s at

lst

, 2n

d an

d 3r

d st

ages

ar

e re

spec

tivel

y I.0

1, 1

.14 a

nd 1

.31,

the

feed

at

2nd

and

3rd

stag

es is

the

raE

hate

of

prec

edin

g st

age)

ca

lcul

ated

vaI

ucs,

usi

ng s

impl

ified

gas

A

mod

el

Sat

ura

ted

hyd

roca

rbon

a 92

.0

89.1

U

maa

rom

4tic

s 7.

3 9.

2

Dia

rom

atic

s 0.

7 1.

3

Tri

arom

atic

s 0.

0 0.

0

Su

lfu

r co

mpo

un

ds

0.0

0.4

DN

F

Ref

ined

ga

s-oi

l yi

elds

, w

eigh

t X

on

fe

ed

Pd

stage

raff

inate

com

posi

tion

w

eig

ht

I

EXP

.

b.7

66.1

I- CA

LC

.

UN

IFA

C

IO-2

0

3.5

72.1

ASCI

I3

IO-2

0

89.0

9.4

1.2

0.0

0.4

3.5

74.6

r t t

Aro

mat

ics

reco

vere

d by

ex

trac

ts

wei

ght

% o

n

inta

ke

EX

P .

67.7

96.7

99.9

90.2

--

CALC

.

UN

IFA

C

IO-2

0 AS

OG

IO

-20

55.4

89.2

95. I

86.7

52.6

90.6

97.8

86.

I

-___

1558 MAIZAR RAHMAN ef al.

seen that the difference between experimental and [lo] Gmehling J., Onken V. and Arlt W., Vupor Liquid predicted value is nearly always positive. This implies Equilibrium Data Colleciion. DECHEMA Chemistry that a predictive calculation with these models nearly Data Series, DECHEMA, Frankfurt.

always gives conservative results for aromatics but [i 11 Messow V. and Engel I., Z. Phys. C&m. Leipzig 1977

optimistic for saturated hydrocarbons. 25q4) 798.

[12] McMakin L. E. Jr., Ph. D. Thesis, The University of Three-stage cross current extraction was also stud- Texas 1969.

ied, and the complete results are given in [I]. Table (131 Houser H. F. and Van Winkle M., Ind. &gng Chem. 10 shows the results of tbe calculations using the 1958 2(l) 12.

models described above. It may be seen that the [14] Lyvers H. T. and Van Winkle M., Znd. Engng Chem.

deviations in the prediction results from experimental 1958 3(l) 60.

[15] Struck R. T. and Kinney C. R., Ind. Engng C&m. 1950 values are of the same magnitude as those in one- 42(l) 77.

stage prediction. The fact that the stage effect does [16] Lagrange G., Laurence G. and Dannois R., Chim.

not practically degrade the accuracy of prediction Anal. 1971 53(2) 107.

proves the validity of the model for multistage extrac- [17] Kudryavtseva L., Viit H. and Eizen O., Eesri NSY

Tend. Akad. Toim.. Keem-Geol. 1971 20 292. tion’ calculations.

Finally, it must be admitted that this method is not totally perfect. Considering the predictive character and the rapidity of its application, it can at least be useful in preliminary studies of solvent extraction processes on middle distillates.

Acknowledgement~e of the authors Maizar Rahman, wishes to thank the Indonesian Government for a grant.

[l] Rahman M., Docteur lngenieur Thesis, ENSPM-IFP, 1983, Editions Technip, 27 rue Ginoux, 75737 Paris Cedex 15, France.

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863. [4] Faid M. K., Docteur lngenieur Thesis, Universitt Pierre

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[.5] Fredenslund An., Gmehling J. and Rasmussen P., Vapor-Liquid Equilibria Using UNZFAC. Elsevier, Am- sterdam 1977.

[6] Kojima K. and Tochigi K., Prediction of Vapor Liquid Equilibria by the ASOG Method. Elsevier, Amsterdam 1979.

[7l Kikic I., Alessi P., Rasmussen P. and Fredenslund Aa., Con. J. Chem. Engng 1980 58 253.

[S] Rogers W. G. and Vera J. H., Proc. 301h Con. Chem. Engng Co& pp. 777-783. Edmonton 1980.

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Prik!. Khim. (Leningrad) 1974 47 2087. [ZO] Zarah B. V., Luks K. D. and Kohn J. P., AZChE Symp.

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J. P.. J. Chem. Enpnp Data 1976 21(2) 220. [22] Step& H. and St&&n T., Solubiiitids~f Znorgrmic Md

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1968 13(4) 527. [25] Turek E. A., Arnold D. W., Greenkom R A. and

Kwang-Chu-Chao, Znd. Engng Chem. Fundls 1979 18(4) 426.

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