Two- and Three-Phase Equilibrium Calculations for Coal Gasification

20 Two- and Three-Phase Equilibrium Calculations for Coal Gasification and Related Processes

Downloaded by STANFORD UNIV GREEN LIBR on October 19, 2012 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch020

D.-Y.

PENG and D. B. ROBINSON

Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6

The gasificiation of coal, shale-oil, or other lower grade hydrocarbon base stocks inevitably leads to the production of process streams which contain a very wide range of paraffinie, naphthenic, aromatic and olefinic hydrocarbons in the presence of associated non-hydrocarbons such as hydrogen, nitrogen, carbon dioxide, hydrogen sulfide and ammonia. These streams are often contacted with water at process conditions which normally lead to either gas - water - rich liquid equilibrium or gas water - rich liquid - hydrocarbon rich liquid equilibrium. The processing conditions and stream compositions which may lead to the formation of these different phases and the distribution of the components between phases are of great importance to the design engineer. For this reason the establishment of reliable procedures for predicting the behavior of these mixtures in the one-, two-, and three-phase regions is a matter of considerable importance. In an earlier paper (1), the authors presented an efficient procedure for predicting the phase behavior of systems exhibiting a water - rich liquid phase, a hydrocarbon - rich liquid phase, and a v a p o r p h a s e . The P e n g - R o b i n s o n e q u a t i o n o f s t a t e (2) was used t o r e p r e s e n t t h e b e h a v i o r o f a l l t h r e e phases. I t has t h e following form: . a(T) v-b " v ( v + b j + b ( v - b )

= KL v

(1)

where a ( T ) = a α a

c

= 0.45724

- j ±

= 1 + K(1-T ^ ) R

2

(2)

0-8412-0569-8/80/47-133-393$05.50/0 © 1980 American Chemical Society

In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

394

THERMODYNAMICS

OF AQUEOUS SYSTEMS

W I T H INDUSTRIAL

κ = 0 . 3 7 4 6 4 + 1.54226ω - 0.26992ω R T

b = 0.07780 For m i x t u r e s


b =

I

x.

APPLICATIONS

2

(3)

c

ψ-± c

b.

(5)

A l t h o u g h t h e c a l c u l a t e d phase c o m p o s i t i o n s f o r t h e h y d r o c a r b o n - r i c h l i q u i d phase and t h e v a p o r phase showed e x c e l l e n t agreement w i t h the e x p e r i m e n t a l d a t a , the c a l c u l a t e d hydrocarbon c o n t e n t s o f t h e aqueous l i q u i d phase was c o n s i s t e n t l y s e v e r a l o r d e r s o f magnitude lower than the r e p o r t e d e x p e r i m e n t a l v a l u e s . I t was s p e c u l a t e d t h a t a d d i t i o n a l t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r s w o u l d be r e q u i r e d t o b r i n g t h e p r e d i c t e d v a l u e s and t h e e x p e r i m e n t a l r e s u l t s i n t o q u a n t i t a t i v e a g r e e m e n t ; n e v e r t h e l e s s , no a t t e m p t was made a t t h a t t i m e t o t r y t o a c c o m p l i s h this. In t h i s s t u d y , i t has been p o s s i b l e t o d e v i s e a p r o c e d u r e w h i c h c a n be used t o g e n e r a t e r e l i a b l e phase c o m p o s i t i o n s f o r b o t h t h e h y d r o c a r b o n - r i c h phase and t h e aqueous phase o v e r a w i d e r a n g e o f t e m p e r a t u r e and p r e s s u r e . Moreover, the c a l c u l a t i o n p r o c e d u r e has been s u c c e s s f u l l y a p p l i e d t o n o n - h y d r o c a r b o n water systems w i t h q u a n t i t a t i v e r e s u l t s . C a l c u l a t i o n Procedure. W i t h t h e e x c e p t i o n o f two s i g n i f i c a n t m o d i f i c a t i o n s , t h e c a l c u l a t i o n p r o c e d u r e used i n t h i s s t u d y was b a s i c a l l y t h e same as t h a t used p r e v i o u s l y . The f i r s t m o d i f i c a t i o n c o n c e r n s t h e use o f E q n . ( 2 ) f o r water. When d e v e l o p i n g t h e o r i g i n a l c o r r e l a t i o n f o r oh and κ as e x p r e s s e d by E q n . ( 2 ) and ( 3 ) , w a t e r was n o t i n c l u d e d as one o f t h e c o m p o n e n t s , and c o n s e q u e n t l y t h e p r e d i c t e d v a p o r p r e s s u r e s f o r w a t e r w e r e n o t as good as e x p e c t e d . Thus i n o r d e r t o c o r r e l a t e t h e v a p o r p r e s s u r e o f w a t e r more a c c u r a t e l y o v e r t h e e n t i r e t e m p e r a t u r e range^ E q n . ( 2 ) was m o d i f i e d f o r t h i s compound a t t e m p e r a t u r e s where T R ^ < 0 . 8 5 as f o l l o w s : h

a

= 1.0085677

+ 0.82154

(I-TJ*)

ν

(6)

K

A t t e m p e r a t u r e s where T >_ 0 . 8 5 , E q n . ( 2 ) s t i l l a p p l i e s . The s e c o n d m o d i f i c a t i o n c o n c e r n s t h e c o r r e l a t i o n o f t h e c o m p o s i t i o n o f t h e aqueous l i q u i d p h a s e . In o r d e r t o a c c o m p l i s h t h i s , a t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r was used f o r t h e aqueous l i q u i d phase and t h e p r e v i o u s t e m p e r a t u r e i n d e p e n d e n t p a r a m e t e r was u s e d f o r t h e non-aqueous l i q u i d phase and t h e v a p o r p h a s e . Thus f o r t h e aqueous - l i q u i d phase E q n . ( 4 ) becomes R

2



20.

PENG AND ROBINSON

Coal Gasification and Related Processes

395

where τ-jj i s a t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r . The i n t r o d u c t i o n o f t h i s p a r a m e t e r f o r each aqueous b i n a r y p a i r means t h a t t h e i n t e r a c t i o n between t h e w a t e r m o l e c u l e and t h e g a s m o l e c u l e i n t h e aqueous l i q u i d phase i s much d i f f e r e n t f r o m t h a t i n t h e nonaqueous p h a s e s . F o r a l l t h e aqueous b i n a r i e s w h i c h have been e x a m i n e d i n t h i s s t u d y , t h e t e m p e r a t u r e d e p e n d e n t i n t e r a c t i o n p a r a m e t e r s t a k e on n e g a t i v e v a l u e s a t a m b i e n t t e m p e r a t u r e and m o n o t o n i c a l l y i n c r e a s e a s t e m p e r a t u r e increases. T h i s i n d i c a t e s t h a t t h e a t t r a c t i o n e n e r g y between t h e w a t e r m o l e c u l a r and t h e o t h e r m o l e c u l e s d e c r e a s e s as t h e temperature i n c r e a s e s . Non-Hydrocarbon - Water

Binaries

Of t h e many p o s s i b l e n o n - h y d r o c a r b o n - w a t e r b i n a r y s y s t e m s w h i c h a r e r e l a t e d t o s u b s t i t u t e gas p r o c e s s e s , t h e d a t a on o n l y t h e w a t e r b i n a r i e s c o n t a i n i n g H S , C 0 , N , and N H were u s e d i n this study. The t r e a t m e n t o f h y d r o g e n , a quantum g a s , i s d i f f e r e n t from t h a t o f t h e o t h e r g a s e s . A separate paper w i l l deal w i t h t h e c o r r e l a t i o n o f t h e d a t a on hydrogen m i x t u r e s . 2

2

2

3

Hydrogen S u l f i d e - Water S y s t e m . The d a t a o f S e l l e c k e t a l . (J3) were used t o e v a l u a t e t h e i n t e r a c t i o n p a r a m e t e r s f o r t h e hydrogen s u l f i d e - water s y s t e m . The d a t a i n c l u d e t h e c o m p o s i t i o n o f b o t h p h a s e s a t t e m p e r a t u r e s f r o m 100°F t o 340°F a n d p r e s s u r e s f r o m 100 t o 5000 p s i a i n t h e c o e x i s t i n g v a p o r and aqueous l i q u i d hydrogen s u l f i d e - r i c h l i q u i d - vapor e q u i l i b r i u m l o c u s . A s i n g l e , c o n s t a n t i n t e r a c t i o n p a r a m e t e r has been d e t e r m i n e d f o r the hydrogen s u l f i d e - r i c h p h a s e s . T h i s d e t e r m i n a t i o n was b a s e d on t h e t h r e e - p h a s e p r e s s u r e - t e m p e r a t u r e l o c u s . While i n v e s t i g a t i n g t h e t h r e e - p h a s e r e g i o n , i t was n o t e d t h a t t h e t h r e e phase l o c u s a n d t h e c o m p o s i t i o n o f t h e h y d r o g e n s u l f i d e - r i c h phase w e r e r a t h e r i n s e n s i t i v e t o t h e t e m p e r a t u r e - d e p e n d e n t aqueous phase i n t e r a c t i o n p a r a m e t e r . Furthermore, the composition o f t h e aqueous phase was r e l a t i v e l y i n d e p e n d e n t o f t h e c o n s t a n t i n t e r a c t i o n parameter. For these reasons, the s o l u b i l i t y o f h y d r o g e n s u l f i d e i n t h e aqueous l i q u i d was c o r r e l a t e d a t t h e same t i m e as t h e p a r a m e t e r was b e i n g d e t e r m i n e d f o r t h e h y d r o g e n s u l f i d e - r i c h phases. The c a l c u l a t e d and e x p e r i m e n t a l g a s e o u s and l i q u i d phase c o m p o s i t i o n s a r e shown i n F i g u r e s 1 a n d 2 r e s p e c t i v e l y . C a r b o n D i o x i d e - Water S y s t e m . The d a t a o f Wiebe and Gaddy (1? §) e x c l u s i v e l y i n t h i s study to determine the i n t e r a c t i o n parameters f o r the carbon d i o x i d e - water b i n a r y system. These d a t a c o v e r t h e t e m p e r a t u r e a n d p r e s s u r e r a n g e f r o m 12°C t o 100°C a n d f r o m 25 atm t o 700 atm r e s p e c t i v e l y . As w i t h t h e H2S - H2O s y s t e m , a c o n s t a n t i n t e r a c t i o n p a r a m e t e r has been o b t a i n e d f o r t h e g a s e o u s phase and t h e c a r b o n d i o x i d e - r i c h w

e

r

e

u

s

e

d



396

THERMODYNAMICS

OF AQUEOUS SYSTEMS

W I T H INDUSTRIAL

APPLICATIONS

4000

0

I 0.80

1 0.85

L 0.90

0.95

1.00

M O L E FRACTION H Y D R O G E N S U L F I D E

Figure 1. Experimental and predicted vapor phase compositions for the hydrogen sulfide-water system (( ) P-R prediction; data from Ref. 3: (Φ) 340°F; (O) 280°F;(0) 220° F; (A) 160°F)



PENG AND ROBINSON


397

M O L E FRACTION H Y D R O G E N S U L F I D E Figure 2. Experimental and predicted aqueous liquid phase compositions for the hydrogen sulfide-water system (( ) P-R prediction; data from Ref. 3: (Φ) 160°F; (A) 220°F; (U> 280 T; Cf) 340°F)


398

T H E R M O D Y N A M I C S OF AQUEOUS SYSTEMS W I T H INDUSTRIAL

APPLICATIONS


l i q u i d phase. A t each t e m p e r a t u r e , t h e s o l u b i l i t y o f carbon d i o x i d e i n w a t e r c a n be c o r r e l a t e d a c c u r a t e l y t h r o u g h t h e w h o l e p r e s s u r e r a n g e u s i n g one i n t e r a c t i o n p a r a m e t e r f o r t h e aqueous phase. The e q u i l i b r i u m aqueous l i q u i d and v a p o r c o m p o s i t i o n s f o r t h i s b i n a r y a t two t e m p e r a t u r e s a r e shown i n F i g . 3 . M a l i n i n ( 7 ) , T o d h e i d e and F r a n c k ( 8 ) a n d T a k e n o u c h i and Kennedy ( 9 ) r e p o r t e d e q u i l i b r i u m d a t a f o r t h i s s y s t e m a t t e m p e r a t u r e s up t o 350°C a n d p r e s s u r e s t o 3500 b a r s . However, t h e v a p o r phase d a t a o f t h e s e a u t h o r s do n o t a l w a y s a g r e e w i t h each o t h e r . The aqueous phase d a t a have been used t o e x t e n d t h e t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r t o 300°C. N i t r o g e n - Water System. The i n t e r a c t i o n p a r a m e t e r s f o r t h e n i t r o g e n - w a t e r s y s t e m have been e v a l u a t e d u s i n g t h e d a t a o f Wiebe and Gaddy ( 1 0 ) , P a r a t e l l a a n d S a g r a m o r a (21), Rigby and P r a u s n i t z ( 1 2 ) a n d 0 ' S u l l i v a n and S m i t h ( 1 3 ) . As w i t h t h e two p r e v i o u s s y s t e m s , o n l y one c o n s t a n t i n t e r a c t i o n p a r a m e t e r was n e c e s s a r y t o c o r r e l a t e t h e v a p o r phase c o m p o s i t i o n w h i l e t h e i n t e r a c t i o n p a r a m e t e r f o r t h e aqueous l i q u i d phase i n c r e a s e d monotonically with temperature. A comparison o f the c a l c u l a t e d and e x p e r i m e n t a l v a p o r phase and aqueous l i q u i d phase c o m p o s i t i o n s i s g i v e n i n T a b l e I. Ammonia - W a t e r S y s t e m . I n t e r a c t i o n parameter f o r the ammonia - w a t e r s y s t e m was o b t a i n e d u s i n g t h e d a t a o f C l i f f o r d and H u n t e r ( 1 4 ) and o f M a c r i s s e t a l . ( 1 5 ) . A s i n g l e - v a l u e d p a r a m e t e r was c a p a b l e o f r e p r e s e n t i n g t h e c o m p o s i t i o n o f t h e l i q u i d phase r e a s o n a b l y w e l l a t a l l t e m p e r a t u r e s , h o w e v e r , t h e c a l c u l a t e d amount o f w a t e r i n t h e v a p o r phase i n t h e v e r y h i g h ammonia c o n c e n t r a t i o n r e g i o n was somewhat l o w e r t h a n t h e d a t a o f C l i f f o r d and H u n t e r and M a c r i s s e t a l . Edwards e t a l . ( 1 6 ) have a p p l i e d a new t h e r m o d y n a m i c c o n s i s t e n c y t e s t t o t h e d a t a o f M a c r i s s e t a l and have c o n c l u d e d t h a t t h e d a t a a p p e a r t o be i n c o n s i s t e n t and t h a t t h e r e p o r t e d w a t e r c o n t e n t o f t h e v a p o r phase i s t o o h i g h . The e x p e r i m e n t a l d a t a and t h e c a l c u l a t e d r e s u l t s a r e g i v e n i n Fig. 4. Hydrocarbon - Water B i n a r i e s The i n t e r a c t i o n p a r a m e t e r s f o r b i n a r y s y s t e m s c o n t a i n i n g w a t e r w i t h m e t h a n e , e t h a n e , p r o p a n e , η-butane, n - p e n t a n e , n - h e x a n e , η - o c t a n e , and benzene have been d e t e r m i n e d u s i n g d a t a from t h e l i t e r a t u r e . The phase b e h a v i o r o f t h e p a r a f f i n - w a t e r s y s t e m s c a n be r e p r e s e n t e d v e r y w e l l u s i n g t h e m o d i f i e d p r o c e d u r e . H o w e v e r , t h e a r o m a t i c - w a t e r s y s t e m c a n n o t be c o r r e l a t e d satisfactorily. P o s s i b l y a d i f f e r e t n type o f m i x i n g r u l e w i l l be r e q u i r e d f o r t h e a r o m a t i c - w a t e r s y s t e m s , a l t h o u g h t h i s has n o t as y e t been e x p l o r e d . Methane - W a t e r S y s t e m . I n t e r a c t i o n p a r a m e t e r s were g e n e r a t e d f o r t h e v a p o r phase and t h e aqueous l i q u i d phase f o r t h e methane -




PENG AND ROBINSON


399


400

TABLE I.

Experimental

APPLICATIONS

and C a l c u l a t e d Aqueous L i q u i d and V a p o r

Phase C o m p o s i t i o n s f o r t h e N i t r o g e n - W a t e r S y s t e m . Pressure, atm.

* 3 x χ 10

y

N

Expt.

Calc.

*

Expt.

Χ 10

3

Calc.

Τ = 25°C


22.20

1.529

1.502

30.50

1.149

1.123

38.19

0.941

0.919

6.260

6.190

3.680

3.640

59.04

2.420

2.410

75.99

1.956

1.952

25

50

0.280

0.278

0.542

0.537

100

1.015

1.004

200

1.812

1.795

300

2.455

2.458

500

3.558

3.555

800

4.909

4.869

1000

5.720

5.604 Τ = 50°C

20.81 25

0.219

0.220

36.93 50

0.436

0.428

100

0.812

0.810

200

1.470

1.470

300

2.034

2.032

500

2.982

2.968

800

4.181

4.084

1000

4.900

4.701


20.

PENG AND ROBINSON

Table

401


I - continued.

Pressure,

atm.

* χ

N

Expt.

3 χ 10 Calc.

y

*

Expt.

Χ 10

3

Calc.

Τ = 75°C 25

0.204

0.203


41.66

10.09

50

0.397

10.12

0.398

60.35

7.21

7.25

88.55

5.23

5.23

100

0.760

0.760

200

1.390

1.395

300

1.936

1.942

500

2.872

2.859

800

4.052

3.948

1000

4.747

4.544 Τ = 100°C

25

0.214

0.206

50

0.415

0.410

56.42

19.94

19.94

78.44

15.03

14.89

12.19

12.09

100

0.792

0.792

100.o9 200

1.462

1.470

300

2.042

500

3.044

3.052

800

4.294

4.223

1000

5.003

4.857

2.060

* Mole

Fraction



402

THERMODYNAMICS

0

OF

0.2

AQUEOUS

0.4

SYSTEMS W I T H INDUSTRIAL

0.6

0.8

APPLICATIONS

10

M O L E FRACTION AMMONIA

Figure 4. Experimental and predicted vapor and liquid phase compositions for the ammonia-water system (( ) P-R prediction; data from Ref. 15: liquid— (A) 300°F; (f) 200°F; (*) 100°F; vapor—(A) 300°F; (V) 200°F; (O) 100°F)



20.

PENG AND ROBINSON


403

w a t e r b i n a r y s y s t e m u s i n g e x p e r i m e n t a l d a t a r e p o r t e d by S u l t a n o v e t a l . (17_, 1 8 ) , O l d s e t a l . ( 1 9 ) , a n d C u l b e r s o n and McKetta ( 2 0 ) . The v a p o r - p h a s e mole f r a c t i o n s o f w a t e r o f O l d s e t a l . ( 1 9 ) can be r e p r e s e n t e d v e r y w e l l u s i n g t h e P e n g - R o b i n s o n e q u a t i o n o f s t a t e i n c o n j u n c t i o n w i t h a constant i n t e r a c t i o n parameter over t h e t e m p e r a t u r e r a n g e f r o m 100°F t o 4 6 0 ° F . The same i n t e r a c t i o n p a r a m e t e r c a n be u s e d t o r e p r o d u c e t h e d a t a o f S u l t a n o v e t a l . (18) up t o 300°C w i t h good r e s u l t s . However, a t h i g h e r t e m p e r a t u r e s t h e c a l c u l a t e d w a t e r c o n t e n t i n t h e v a p o r phase d e v i a t e d somewhat f r o m t h e i r d a t a . The t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r s were d e t e r m i n e d f r o m 7 7 ° F t o 680°F u s i n g t h e d a t a o f C u l b e r s o n a n d McKetta ( 2 0 ) a n d o f S u l t a n o v e t a l . (1_8). This parameter i n c r e a s e s w i t h temperature and appears t o converge t o t h e v a l u e o f t h e c o n s t a n t p a r a m e t e r u s e d f o r t h e v a p o r phase a s t h e c r i t i c a l temperature o f water i s approached. The e x p e r i m e n t a l a n d c a l c u l a t e d r e s u l t s f o r t h i s b i n a r y s y s t e m a t 250°C a r e p r e s e n t e d i n F i g u r e 5 . Ethane - Water System. The d a t a u s e d f o r t h e d e t e r m i n a t i o n o f the i n t e r a c t i o n parameters f o r the ethane - water b i n a r y a r e t h o s e o f C u l b e r s o n and M c K e t t a ( 2 1 ) , C u l b e r s o n e t a l . ( 2 2 ) and Reamer e t a l . (230 · A c o n s t a n t i n t e r a c t i o n p a r a m e t e r was c a p a b l e o f r e p r e s e n t i n g t h e mole f r a c t i o n o f w a t e r i n t h e v a p o r phase w i t h i n e x p e r i m e n t a l u n c e r t a i n t y o v e r t h e t e m p e r a t u r e r a n g e f r o m 100°F t o 4 6 0 ° F . As w i t h t h e methane - w a t e r s y s t e m , t h e t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n parameter i s a l s o a m o n o t o n i c a l l y i n c r e a s i n g f u n c t i o n of temperature. However, a t each s p e c i f i e d t e m p e r a t u r e , t h e i n t e r a c t i o n parameter f o r t h i s system i s n u m e r i c a l l y g r e a t e r than t h a t f o r t h e methane - w a t e r s y s t e m . Although i t i s p o s s i b l e f o r t h i s b i n a r y t o f o r m a t h r e e - p h a s e e q u i l i b r i u m l o c u s , no e x p e r i m e n t a l d a t a on t h i s e f f e c t have been r e p o r t e d . F i g u r e 6 i l l u s t r a t e s t h e c a l c u l a t e d and e x p e r i m e n t a l e q u i l i b r i u m phase c o m p o s i t i o n s a t 220°F f o r t h i s b i n a r y s y s t e m . Propane - Water System. The i n t e r a c t i o n p a r a m e t e r s f o r t h e p r o p a n e - w a t e r s y s t e m were o b t a i n e d o v e r a t e m p e r a t u r e r a n g e f r o m 4 2 ° F t o 310°F u s i n g e x c l u s i v e l y t h e d a t a o f K o b a y a s h i a n d Katz (2^). T h i s i s b e c a u s e among t h e a v a i l a b l e l i t e r a t u r e on t h e phase b e h a v i o r o f t h i s b i n a r y s y s t e m , t h e i r d a t a a p p e a r t o g i v e t h e most e x t e n s i v e i n f o r m a t i o n . A c o n s t a n t i n t e r a c t i o n p a r a m e t e r was o b t a i n e d f o r t h e p r o p a n e - r i c h p h a s e s a t a l l temperatures. The m a g n i t u d e o f t h e t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r f o r t h i s b i n a r y was l e s s t h a n t h a t f o r t h e e t h a n e - w a t e r b i n a r y a t t h e same t e m p e r a t u r e . Azarnoosh and McKetta (25) a l s o presented experimental data f o r the s o l u b i l i t y o f p r o p a n e i n w a t e r o v e r a b o u t t h e same t e m p e r a t u r e r a n g e a s t h a t o f K o b a y a s h i and K a t z b u t a t p r e s s u r e s up t o 500 p s i a o n l y . However, a d i f f e r e n t s e t o f t e m p e r a t u r e - dependent parameters



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Figure 5. Experimental and predicted vapor and liquid phase compositions for methane-water system at 250°C (( ) P-R prediction; (A) (17); (A) (IS))



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M O L E FRACTION Figure 6. Experimental and predicted vapor and liquid phase compositions for the ethane-water system at 220°F (( ; P-R prediction; (A) (21); (O) (23))


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w o u l d be r e q u i r e d t o a c c u r a t e l y c o r r e l a t e t h e i r r e s u l t s . The w a t e r c o n t e n t o f t h e p r o p a n e - r i c h p h a s e s i n t h e aqueous l i q u i d - p r o p a n e l i q u i d - v a p o r r e g i o n a r e i l l u s t r a t e d i n F i g u r e 7. η-Butane - W a t e r S y s t e m . Reamer e t a l . (26) have d e t e r m i n e d t h e c o n c e n t r a t i o n o f w a t e r i n t h e n-butane - w a t e r s y s t e m i n t h e v a p o r and t h e η-butane l i q u i d phases i n t h e t h r e e - p h a s e r e g i o n . Reamer e t a l . (27) have p u b l i s h e d e x p e r i m e n t a l d a t a f o r t h e s o l u b i l i t y o f η-butane i n w a t e r and o f w a t e r i n η-butane i n t h e two-phase r e g i o n c o v e r i n g a t e m p e r a t u r e r a n g e f r o m 100°F t o 460°F and a t p r e s s u r e s up t o 1 0 , 0 0 0 p s i a . L e B r e t o n and M c K e t t a (28) have p r e s e n t e d t h e r e s u l t s o f an e x p e r i m e n t a l s t u d y on t h e s o l u b i l i t y o f η-butane i n w a t e r a t f o u r t e m p e r a t u r e s b u t a t p r e s s u r e s up t o o n l y 1000 p s i a . W h i l e the r e p o r t e d three-phase p r e s s u r e s f r o m t h e s e two s o u r c e s a g r e e v e r y w e l l , t h e d a t a on t h e s o l u b i l i t y o f η-butane i n w a t e r show marked d i f f e r e n c e s . The s o l u b i l i t y v a l u e s p r e s e n t e d by L e B r e t o n and M c K e t t a a r e c o n s i s t e n t l y l o w e r t h a n t h o s e r e p o r t e d by Reamer e t a l . In v i e w o f t h e f a c t t h a t t h e d a t a o f Reamer e t a l . c o v e r e d a much b r o a d e r r a n g e o f b o t h t e m p e r a t u r e and p r e s s u r e , t h e i r d a t a w e r e used f o r d e t e r m i n i n g the i n t e r a c t i o n parameters f o r t h i s system. As w i t h t h e f i r s t t h r e e p a r a f f i n - w a t e r s y s t e m s , o n l y a c o n s t a n t p a r a m e t e r was r e q u i r e d t o c o r r e l a t e t h e h y d r o c a r b o n r i c h phases a l t h o u g h a t e m p e r a t u r e - d e p e n d e n t p a r a m e t e r was n e c e s s a r y t o f i t t h e aqueous - l i q u i d phase d a t a . The e q u i l i b r i u m c o m p o s i t i o n o f t h e n-butane - w a t e r b i n a r y i n the three-phase r e g i o n a r e i l l u s t r a t e d i n F i g u r e 8. n-Pentane - W a t e r S y s t e m . S c h e f f e r (29) has p r e s e n t e d t h e t h r e e - p h a s e l o c u s f o r a m i x t u r e o f i - p e n t a n e and n-pentane o v e r a t e m p e r a t u r e r a n g e f r o m 150°C t o 1 8 7 . 1 ° C . H o w e v e r , no c o m p o s i t i o n a l measurements were r e p o r t e d . N a m i o t and B e i d e r (30) r e p o r t e d t h e s o l u b i l i t y o f n-pentane i n w a t e r a t t h r e e temperatures a l o n g the three-phase l o c u s . I n t e r a c t i o n parameters f o r t h e n-pentane - w a t e r s y s t e m w e r e d e t e r m i n e d u s i n g t h e s e d a t a . n-Hexane - W a t e r S y s t e m . The n-hexane - w a t e r s y s t e m i s t h e l i g h t e s t p a r a f f i n - w a t e r b i n a r y where t h e v a p o r p r e s s u r e l o c u s o f the hydrocarbon i n t e r s e c t s t h a t f o r pure w a t e r . The e x p e r i m e n t a l phase b e h a v i o r d a t a a v a i l a b l e i n t h e l i t e r a t u r e f o r t h i s s y s t e m c o v e r a w i d e r a n g e o f t e m p e r a t u r e and p r e s s u r e . Unfort u n a t e l y t h e s e d a t a do n o t c o r r o b o r a t e each o t h e r and n o t i c e a b l e discrepancies e x i s t . The d a t a o f S c h e f f e r ( 3 1 ) , R e b e r t and Hayworth ( 3 2 ) , and S u l t a n o v and S k r i p k a ( 3 3 j were employed i n d e t e r m i n i n g the i n t e r a c t i o n parameter f o r the hydrocarbon - r i c h phases. A unique value f o r t h i s i n t e r a c t i o n parameter c o u l d not be o b t a i n e d b e c a u s e o f t h e d i s c r e p a n c i e s among t h e d a t a . However, a t e n t a t i v e v a l u e , b a s e d on t h e e x t r a p o l a t i o n o f t h e v a l u e s f o r o t h e r p a r a f f i n - w a t e r i n t e r a c t i o n p a r a m e t e r s , has been a s s i g n e d to the c o n s t a n t i n t e r a c t i o n parameter. The i n t e r a c t i o n p a r a m e t e r s f o r t h e aqueous l i q u i d phase were d e t e r m i n e d u s i n g t h e d a t a o f



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M O L E FRACTION WATER χ 103 Figure 7. Experimental and predicted water content of propane liquid and vapor phases for the propane-water system along the three-phase locus (( ) P-R prediction; data from Ref. 24: (O) vapor; (Φ) liquid)



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K u d c h a d k e r and M c K e t t a (34). Their s o l u b i l i t y data i n the v a p o r - l i q u i d r e g i o n a r e b e l i e v e d t o be i n e r r o r p r o b a b l y due t o t h e i r i n c o r r e c t p r o c e d u r e o f s m o o t h i n g t h e raw d a t a . However, t h e i r d a t a i n t h e l i q u i d - l i q u i d r e g i o n seem t o be a c c e p t a b l e . The d a t a o f R e b e r t and H a y w o r t h ( 3 2 ) were used t o e x t e n d t h e temperature - dependent i n t e r a c t i o n parameters t o temperatures above t h e c r i t i c a l p o i n t o f n - h e x a n e . Other Hydrocarbon - Water Systems. I n t e r a c t i o n parameters w e r e g e n e r a t e d f o r t h e benzene - w a t e r s y s t e m . The d a t a u s e d were t h o s e o f S c h e f f e r (3]_), R e b e r t a n d Kay (35)> and C o n n o l l y (36). As w i t h t h e a l k a n e - w a t e r s y s t e m s , t h e i n t e r a c t i o n p a r a m e t e r s f o r t h e aqueous l i q u i d phase were f o u n d t o be temperature - dependent. However, t h e c o m p o s i t i o n s f o r t h e b e n z e n e - r i c h p h a s e s c o u l d n o t be a c c u r a t e l y r e p r e s e n t e d u s i n g any s i n g l e v a l u e f o r t h e c o n s t a n t i n t e r a c t i o n p a r a m e t e r . The c a l c u l a t e d w a t e r mole f r a c t i o n s i n t h e h y d r o c a r b o n - r i c h p h a s e s were a l w a y s g r e a t e r t h a n t h e e x p e r i m e n t a l v a l u e s as r e p o r t e d by R e b e r t and Kay ( 3 5 ) . The f i n a l v a l u e f o r t h e c o n s t a n t i n t e r a c t i o n p a r a m e t e r was c h o s e n t o f i t t h e t h r e e phase l o c u s o f t h i s system. N e v e r t h e l e s s , the c a l c u l a t e d three-phase c r i t i c a l p o i n t was a b o u t 9°C l o w e r t h a n t h e e x p e r i m e n t a l v a l u e . I n t e r a c t i o n p a r a m e t e r was a l s o g e n e r a t e d f o r t h e h y d r o c a r b o n r i c h phases o f t h e n-octane - water s y s t e m . The d a t a o f K a l a f a t i and P i i r ( 3 7 ) were u s e d . T h e r e were no d a t a a v a i l a b l e f o r t h e w a t e r - r i c h l i q u i d phase f o r t h i s b i n a r y . E x p e r i m e n t a l s o l u b i l i t y d a t a a r e a v a i l a b l e f o r some h i g h e r alkane - water systems ( s e e , f o r example, S k r i p k a e t a l . , (38)). However, these d a t a e i t h e r c o v e r o n l y a v e r y l i m i t e d temperature r a n g e o r c o n t a i n r e s u l t s f o r one phase o n l y . No a t t e m p t h a s been made t o d e t e r m i n e t h e i n t e r a c t i o n p a r a m e t e r s f o r w a t e r - h y d r o c a r b o n s y s t e m s where t h e h y d r o c a r b o n i s l a r g e r t h a n n - o c t a n e . The t e m p e r a t u r e - d e p e n d e n t i n t e r a c t i o n p a r a m e t e r s d e t e r m i n e d f o r s e v e r a l a l k a n e - w a t e r s y s t e m s a r e p l o t t e d i n F i g u r e 9 . The v a l u e s f o r t h e hydrogen s u l f i d e - carbon d i o x i d e - , and n i t r o g e n w a t e r b i n a r i e s a r e g i v e n i n F i g u r e 1 0 . I t c a n be s e e n t h a t a systematic trend e x i s t s f o r these parameters. The i n t e r a c t i o n p a r a m e t e r i n c r e a s e s w i t h t h e s i z e o f t h e m o l e c u l e and f u r t h e r m o r e i t a p p e a r s t o c o n v e r g e r a p i d l y a s t h e c a r b o n number i n c r e a s e s . A t a g i v e n temperature and p r e s s u r e , t h e s o l u b i l i t y o f a l k a n e s i n w a t e r g e n e r a l l y d e c r e a s e s as t h e m o l e c u l a r w e i g h t o f t h e h y d r o carbon i n c r e a s e s . The amount o f n - o c t a n e a n d h e a v i e r h y d r o c a r b o n s d i s s o l v e d i n water streams r e s u l t i n g from s y n t h e t i c gas p r o c e s s e s i s b e l i e v e d t o be i n s i g n i f i c a n t . The c a l c u l a t i o n o f t h e s o l u b i l i t y o f t h e s e compounds i n w a t e r u n d e r t h e s e c o n d i t i o n s by u s i n g e x t r a p o l a t e d values from i n t e r a c t i o n parameters o f l i g h t e r p a r a f f i n - water b i n a r i e s p r o b a b l y w i l l n o t cause l a r g e e r r o r s . Three-Phase L o c i . F i g u r e 11 shows t h e t h r e e - p h a s e l o c i f o r the a l k a n e - water systems. No e x p e r i m e n t a l t h r e e - p h a s e d a t a w e r e a v a i l a b l e i n t h e l i t e r a t u r e f o r the ethane - water b i n a r y .



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Figure 11. Experimental and predicted three-phase loci for selected paraffin-water binary systems (( ) P-R prediction; (V) (24); (·) (21); ( 0 ) (39); (O) (29); (k) (3l);(A)PV;W(3V)


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N e v e r t h e l e s s , a c a l c u l a t e d locus i s i n c l u d e d f o r completeness and t o i n d i c a t e t h e p o s s i b l e r e g i o n o f t h r e e - p h a s e e q u i l i b r i u m . As was m e n t i o n e d e a r l i e r , t h e t h r e e - p h a s e d a t a r e p o r t e d by S c h e f f e r (29) f o r p e n t a n e - w a t e r were f o r a " b i n a r y " composed o f w a t e r ancf a m i x t u r e o f i - p e n t a n e a n d n - p e n t a n e . As shown i n t h e f i g u r e , t h e s e d a t a a r e bounded b y t h e c a l c u l a t e d l o c i o f t h e i - p e n t a n e - w a t e r and n-pentane - w a t e r s y s t e m s . Conclusion. The m i x i n g r u l e f o r u s e w i t h t h e P e n g - R o b i n s o n e q u a t i o n o f s t a t e has been m o d i f i e d t o i n c l u d e t e m p e r a t u r e dependent i n t e r a c t i o n parameters. Both t h e c o n s t a n t and t h e temperature - dependent i n t e r a c t i o n parameters c o v e r i n g a wide r a n g e o f t e m p e r a t u r e s have been d e t e r m i n e d f o r h y d r o c a r b o n w a t e r s y s t e m s i n c l u d i n g methane - w a t e r , e t h a n e - w a t e r , p r o p a n e w a t e r , n-butane - w a t e r , a n d n-hexane - w a t e r a n d n o n - h y d r o c a r b o n water systems i n c l u d i n g hydrogen s u l f i d e - w a t e r , carbon d i o x i d e w a t e r , n i t r o g e n - w a t e r , a n d ammonia - w a t e r . The i n c l u s i o n o f t h e s e t e m p e r a t u r e - d e p e n d e n t p a r a m e t e r s has g r e a t l y i m p r o v e d t h e a c c u r a c y o f p r e d i c t i o n s o f t h r e e - p h a s e a n d two-phase e q u i l i brium f o r systems i n v o l v i n g w a t e r . Acknowledgement. The f i n a n c i a l s u p p o r t r e c e i v e d f r o m t h e N a t i o n a l S c i e n c e a n d E n g i n e e r i n g R e s e a r c h C o u n c i l o f Canada i s sincerely appreciated. Abstract

Two-constant equation of state phase behavior calculations for aqueous mixtures often require the use of temperature dependent binary interaction parameters. The methods used for evaluating these parameters for some of the typical aqueous binary pairs found in coal gasification and related process streams are described. Experimental and predicted phase compositions based on these methods are illustrated for aqueous pairs containing CO , H S, NH , and other gases. 2

2

3

Literature Cited

1. Peng, D.-Y., Robinson, D.B., Can. J. Chem. Eng., 1976, 54, 595. 2. Peng, D.-Y., Robinson, D.B., Ind. Eng. Chem. Fundam., 1976, 15, 59. 3. Selleck, F.T., Carmichael, L.T., Sage, B.H., Ind. Eng. Chem., 1952, 44, 2219. 4. Wiebe, R., Gaddy, V.L., J. Am. Chem. Soc., 1939, 61, 315. 5. Wiebe, R., Gaddy, V.L., J. Am. Chem. Soc., 1940, 62, 815. 6. Wiebe, R., Gaddy, V.L., J. Am. Chem. Soc., 1941, 63, 475. 7. Malinin, S.D., Geokhimiya, 1959,3,235. 8. Todheide, K., Franck, E.U., Ζ. Physik. Chem. (Frankfurt), 1963, 37, 387. 9. Takenouchi, S., Kennedy, G.C., Am. J. Sci., 1964, 262, 1055. 10. Wiebe, R., Gaddy, V.L., Heins, C., J. Am. Chem. Soc., 1933, 55, 947.


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11. 12. 13. 14. 15.

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Two- and Three-Phase Equilibrium Calculations for Coal Gasification

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