Extractive and Azeotropic Distillation - ACS Publications

10 Separation of Water, Methyl Ethyl Ketone, and Tetrahydrofuran Mixtures

Downloaded by MICHIGAN STATE UNIV on September 27, 2013 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch010

HUGH M. LYBARGER and HOWARD L. GREENE Department of Chemical Engineering, The University of Akron, Akron, Ohio 44304

Ternary vapor-liquid equilibrium data for the system water-methyl ethyl ketone-tetrahydrofuran were determined with a vapor recirculating equilibrium still of the type used by Hipkin and Myers. All experimental points were checked for thermodynamic consistency using the test proposed by McDermott and Ellis. Calculated liquid phase activity coefficients were correlated over the range of solvent concentrations using regression analysis. These results indicate a low boiling valley between the binary azeotropes of water-tetrahydrofuran and water-methyl ethyl ketone, but no ternary azeotrope was found. A solvent purification scheme, aided by development of a modified Thiele-Geddes computer program, was designed to separate the ternary mixture into pure components. The resulting system requires use of three ordinary distillation columns and extractive distillation, using dimethylformamide as the solvent.

'^efrahydrofuran

( T H F ) a n d m e t h y l e t h y l k e t o n e ( M E K ) are c o m -

m o n l y u s e d as solvents for h i g h m o l e c u l a r w e i g h t p o l y v i n y l c h l o r i d e resins i n t o p c o a t i n g a n d a d h e s i v e a p p l i c a t i o n s . B l e n d s are u s e d to c o m b i n e the l o w cost o f m e t h y l e t h y l ketone w i t h the h i g h e r s o l v e n c y a n d greater v o l a t i l i t y of t e t r a h y d r o f u r a n .

B e c a u s e of the large a m o u n t of

T H F u s e d , its r e l a t i v e l y h i g h cost, a n d a i r p o l l u t i o n considerations, rec o v e r y is n o r m a l l y necessary. T h e solvent v a p o r m a y b e r e c o v e r e d i n c o m m e r c i a l l y a v a i l a b l e activ a t e d c a r b o n a d s o r p t i o n units.

W h e n the v a p o r - a i r m i x t u r e is passed

t h r o u g h a b e d of a c t i v a t e d c a r b o n , solvent vapors are a d s o r b e d w h i l e the s t r i p p e d a i r passes t h r o u g h . P e r i o d i c regeneration o f the a c t i v a t e d 148

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

10.

LYBARGER

AND

GREENE

Separation

of

149

Mixtures

c a r b o n w i t h l o w pressure steam, h o w e v e r , g e n e r a l l y contaminates t h e solvents w i t h a large a m o u n t o f w a t e r , i n c r e a s i n g greatly t h e difficulty of s u b s e q u e n t separations. T h i s s t u d y w a s u n d e r t a k e n to o b t a i n t h e necessary v a p o r - l i q u i d equilibrium

d a t a a n d to d e t e r m i n e

the distillation requirements

r e c o v e r i n g solvent f o r reuse f r o m t h e s o l v e n t - w a t e r f r o m a d s o r b e r regeneration. d a t a (2, 3)

Previous binary v a p o r - l i q u i d e q u i l i b r i u m

i n d i c a t e d t w o b i n a r y azeotropes

M E K ) a n d a t w o phase region ( w a t e r - M E K ) . Downloaded by MICHIGAN STATE UNIV on September 27, 2013 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch010

for

mixture obtained

(water-THF

and water-

T h e t e r n a r y system w a s

thus e x p e c t e d t o b e h i g h l y n o n i d e a l . Results of this s t u d y h a v e b e e n u s e d to d e s i g n a solvent

recovery

system c a p a b l e of s e p a r a t i n g e a c h solvent i n t o its o r i g i n a l p u r e state. I f s e p a r a t i o n o f t h e T H F - M E K m i x t u r e is unnecessary o r i f p u r i t y r e q u i r e ments are less d e m a n d i n g , t h e p r o p o s e d system c o u l d b e a p p r o p r i a t e l y simplified. Experimental A v a p o r - r e c i r c u l a t i n g e q u i l i b r i u m s t i l l s i m i l a r to t h a t d e s c r i b e d b y H i p k i n a n d M y e r s ( 1 ) w a s u s e d to d e t e r m i n e v a p o r - l i q u i d e q u i l i b r i u m d a t a f o r t h e system, w a t e r - M E K - T H F . I n this s t i l l s h o w n s c h e m a t i c a l l y i n F i g u r e 1, a r e c i r c u l a t i n g v a p o r is c o n t i n u o u s l y c o n t a c t e d w i t h a static l i q u i d sample. T h e v a p o r - l i q u i d system is e n c l o s e d b y a jacket w h e r e

KEY 1 2 3 4 5 β 7 8 9 IΟ II 12 13 14 15 16

Figure 1.

Schematic diagram of the equilibrium

Vacuum Pump Manometer Mtrcury Traps Jacket Condenser Sample Condenser Thermocouples Thermistors Jacket Heater Reboiler Jacket Contactor Body Contactor Throat Contactor Sample Valve Vapor Sample Volve Needle Valves Nitrogen Tank

still


150

EXTRACTIVE AND AZEOTROPIC

T a b l e I.


Run No.

a

ywater.

ΎΜΕΚ,

DISTILLATION

Liquid

YTHF.

Phase

XMEK,

mole fr.

mole fr.

mole fr.

mole fr.

mole fr.

1 3 4 5 6 7 8 910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29"

.288 .217 .256 .257 .275 .236 .199 .226 .297 .244 .226 .234 .267 .314 .250 .247 .121 .103 .230 .163 .248 .311 .269 .244 .215 .181 .206 .262

.181 .289 .177 .209 .388 .223 .102 .178 .478 .216 .058 .162 .327 .299 .182 .174 .039 .278 .619 .123 .477 .599 .291 .304 .040 .350 .284 .284

.532 .494 .566 .534 .337 .541 .699 .596 .225 .540 .717 .604 .407 .387 .568 .580 .841 .619 .152 .714 .275 .090 .440 .452 .746 .474 .510 .453

30 31 32 33 34 35 36 37 38 39 40 41*

.165 .201 .095 .219 .134 .153 .221 .211 .160 .141 .144 .293

.436 .149 .523 .006 .000 .000 .000 .000 .018 .031 .059 .366

.399 .650 .383 .775 .866 .847 .779 .790 .822 .828 .796 .342

42°

.353

.370

.277

43 44"

.197 .318

.071 .447

.732 .235

.561 .486 .866 .506 .377 .460 .322 .697 .375 .508 .585 .869 .379 .507 .507 .438 .071 .043 .110 .118 .184 .281 .438 .289 .296 .501 .169 .594 .862 .093 .189 .034 .596 .091 .121 .424 .661 .131 .093 .113 .502 .892 .469 .914 .177 .518 .862

.166 .237 .039 .181 .399 .211 .124 .092 .486 .194 .046 .037 .342 .267 .169 .181 .062 .409 .787 .197 .607 .665 .287 .374 .051 .279 .409 .208 .064 .587 .213 .678 .005 .000 .000 .000 .000 .029 .048 .092 .315 .064 .383 .058 .103 .368 .101

Two-phase run.


10.

LYBARGER

Activity

AND

GREENE

Separation

of

Mixtures

Coefficients

XTHF

y

water

fMEK

y

THF


.273 .276 .094 .313 .224 .329 .553 .212 .140 .298 .369 .095 .279 .226 .324 .381 .867 .548 .103 .686 .209 .054 .275 .338 .653 .220 .422 .197 .074 .321 .598 .288 .399 .909 .879 .577 .339 .840 .859 .796 .184 .044 .149 .028 .721 .113 .037

Temp. °C.

mole fr. 2.021 1.710 1.343 2.065 2.497 1.925 2.577 1.267 2.608 1.846 1.598 1.088 2.463 2.157 1.876 2.143 7.289 8.396 5.933 5.455 4.274 3.385 2.188 2.994 3.101 1.244 4.588

1.722 1.891 8.008 1.878 1.379 1.612 1.352 3.058 1.353 1.723 2.045 7.152 1.375 1.611 1.661 1.476 1.057 0.980 0.962 0.989 1.050 1.167 1.481 1.186 1.318 1.791 1.060

1.946 1.752 6.582 1.738 1.362 1.587 1.306 2.794 1.421 1.777 2.005 6.462 1.343 1.570 1.706 1.483 1.022 1.041 1.182 1.035 1.136 1.407 1.492 1.242 1.204 1.968 1.173

64.7 65.3 61.6 64.0 67.9 65.8 63.5 64.9 68.8 65.3 63.6 64.2 67.4 67.5 65.5 65.5 62.9 67.4 72.2 64.8 69.6 70.5 67.0 67.1 62.9 67.7 65.7 67.4

5.872 4.179 8.089 1.558 6.745 5.455 2.321 1.375 5.186 6.412 5.343

1.020 1.108 0.966 1.845 0.000 0.000 0.000 0.000 1.054 1.087 1.065

1.099 1.086 1.086 2.038 1.052 1.022 1.465 2.467 1.025 1.010 1.036

68.8 64.7 71.5 63.1 61.4 62.7 62.0 62.7 63.1 63.1 63.5 68.3 68.8

4.738

1.162

1.063

63.1 70.3



152

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

h y d r o c a r b o n v a p o r is m a i n t a i n e d at the b o i l i n g t e m p e r a t u r e of the l i q u i d s a m p l e i n t h e contactor. T h e s t i l l is t h o r o u g h l y i n s u l a t e d so that the l i q u i d a n d v a p o r i n the c o n t a c t o r are m a i n t a i n e d at a d i a b a t i c c o n d i t i o n s . S t a n d a r d i z e d p r o c e d u r e s for o b t a i n i n g e q u i l i b r i u m a n d for s a m p l i n g t h e r e s u l t a n t v a p o r a n d l i q u i d , as o u t l i n e d b y L y b a r g e r ( 7 ) , w e r e f o l l o w e d . A l l v a p o r - l i q u i d e q u i l i b r i u m d a t a w e r e o b t a i n e d at a constant pressure of 730 m m of m e r c u r y w h i c h w a s a c h i e v e d b y a p p l y i n g v a c u u m or n i t r o g e n pressure to the s t i l l ( d e p e n d i n g o n a t m o s p h e r i c pressure) u n t i l the d e s i r e d differential w a s o b t a i n e d . A f t e r the v a p o r was r e c i r c u l a t e d , a constant pressure c o u l d b e m a i n t a i n e d i n the s t i l l w i t h o u t further adjustments. A l l l i q u i d a n d v a p o r samples w e r e a n a l y z e d o n a V a r i a n A e r o g r a p h M o d e l 202-1B t h e r m a l c o n d u c t i v i t y gas c h r o m a t o g r a p h . A 12-foot c o l u m n p a c k e d w i t h P o r a p a k Q , w h i c h g a v e a c l e a n s e p a r a t i o n for water, was u s e d , b u t it c a u s e d the peaks for m e t h y l e t h y l ketone a n d t e t r a h y d r o f u r a n to b e s l i g h t l y m e r g e d . T h e c h r o m a t o g r a p h w a s c a l i b r a t e d u s i n g 11 solvent b l e n d s of k n o w n c o m p o s i t i o n s . A r e a c o r r e c t i o n factors w e r e d e t e r m i n e d f r o m the s t a n d a r d samples, r e l a t i n g w e i g h t f r a c t i o n to a r e a f r a c t i o n . A l l samples w e r e a n a l y z e d t w i c e , a n d the results w e r e a v e r a g e d . C a l i b r a t i o n of the c h r o m a t o g r a p h w i t h k n o w n w a t e r - M E K - T H F samples i n d i c a t e d accurate d e t e r m i n a t i o n to w i t h i n ±0.002-0.005 m o l e f r a c t i o n , d e p e n d i n g o n composition. Results and

Discussion

Vapor—Liquid Equilibrium Data.

F o r t y - f o u r pairs of v a p o r - l i q u i d

e q u i l i b r i u m d a t a w e r e d e t e r m i n e d for the t e r n a r y system; l i q u i d c o m p o sitions i n the s i n g l e a n d two-phase regions w e r e s t u d i e d . Results of these runs are s u m m a r i z e d i n T a b l e

I a l o n g w i t h the l i q u i d phase

activity

coefficients a n d b o i l i n g p o i n t s o b t a i n e d at a pressure of 730 m m of mercury.

Tabulated

compositions

are averages of t w o

analyses for

each

sample. C a l c u l a t e d l i q u i d p h a s e a c t i v i t y coefficients are b a s e d o n R a o u l t ' s and Dalton's laws:

Pi =

Piji

=

tiPiXi

(1)

a s s u m i n g v a p o r phase i d e a l i t y . The

v a p o r — l i q u i d e q u i l i b r i u m d a t a for the single-phase

r u n s are

g r a p h i c a l l y s h o w n i n F i g u r e 2 w h e r e the two-phase r e g i o n at 60 ° C

is

also p l o t t e d to i n d i c a t e the extent of p a r t i a l m i s c i b i l i t y at the b o i l i n g point.

A l i n e connects e a c h p a i r of v a p o r - l i q u i d e q u i l i b r i u m c o m p o s i -

tions. T e m p e r a t u r e results for the v a p o r - l i q u i d e q u i l i b r i u m d a t a i n d i c a t e a l o w b o i l i n g v a l l e y c o n n e c t i n g t h e b i n a r y azeotropes of (66.2

mole

%

M E K , normal boiling point 73.4°C)

and

water—MEK water-THF


10.

L Y B A R G E R

A N D

Separation

G R E E N E

of


Water

0.00 THF

0.10

0.20

0.30

0.40

0.50

153

Mixtures

KEY

0.60

0.70

0.80

030

100 MEK

Figure 2. Ternary vapor-liquid equilibrium data for the one-phase region at 730 mm mercury absolute pressure with the solubility envelope for 60° C

(81.7 m o l e

%

T H F , normal boiling point 64.0°C).

The

dashed line

s h o w n i n F i g u r e 2 indicates the a p p r o x i m a t e l o c a t i o n of this v a l l e y . Results for the two-phase r u n s are p l o t t e d i n F i g u r e 3 a l o n g w i t h the s o l u b i l i t y e n v e l o p e at 60 ° C .

A l t h o u g h the e q u i l i b r i u m s t i l l w a s n o t

d e s i g n e d for two-phase o p e r a t i o n , it was p o s s i b l e to o b t a i n the necessary d a t a for this solvent system since t h e v a p o r i n e q u i l i b r i u m w i t h the t w o phase l i q u i d was a l w a y s single-phase w h e n c o n d e n s e d . S e v e r a l two-phase samples w e r e a n a l y z e d after c o o l i n g h a d o c c u r r e d , a c c o u n t i n g for t h e fact t h a t the ends of the l i q u i d - l i q u i d tielines i n this r e g i o n d o n o t q u i t e e x t e n d to the s o l u b i l i t y c u r v e .

E q u i l i b r i u m vapor compositions

corre-

s p o n d i n g to the l i q u i d c o m p o s i t i o n s are also p l o t t e d i n F i g u r e 3 a n d , except for R u n 42 w h i c h e x p e r i e n c e d

severe b u m p i n g d u r i n g b o i l i n g ,

f a l l a l o n g a n a l m o s t straight l i n e . F o r a t e r n a r y system the c o m p o s i t i o n of v a p o r i n e q u i l i b r i u m w i t h a heterogeneous l i q u i d m i x t u r e c a n b e r e l a t e d to the l i q u i d c o m p o s i t i o n s b y two relationships (5).

F i r s t , the same v a p o r c o m p o s i t i o n w i l l result

f r o m a n y l i q u i d c o m p o s i t i o n o n a g i v e n l i q u i d - l i q u i d tieline. S e c o n d , a


154

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

s m o o t h c u r v e c a n be d r a w n t h r o u g h the v a p o r c o m p o s i t i o n s i n e q u i l i b r i u m w i t h heterogeneous

liquid

c o m p o s i t i o n s . T h i s c u r v e extends

f r o m the v a p o r i n e q u i l i b r i u m w i t h the b i n a r y heterogeneous azeotrope to v a p o r i n e q u i l i b r i u m w i t h the h o m o g e n e o u s l i q u i d w h e r e t h e c o m p o sitions of t h e t w o l i q u i d phases b e c o m e c o i n c i d e n t ( t h e p l a i t p o i n t ) . W i t h these t w o r e l a t i o n s h i p s , one c a n .closely a p p r o x i m a t e t h e c o m p o s i


t i o n o f v a p o r i n e q u i l i b r i u m w i t h a g i v e n t w o - p h a s e l i q u i d f r o m F i g u r e 3.

Wottr

0.00

0.10

0.20

0.30

0.40

0.50

0.70

O60

030

0.90

THF

1.00 MEK

Figure 3. Ternary vapor-liquid equilibrium data for the two-phase region at 730 mm mercury absolute pressure with the solubility envelope for 60° C Thermodynamic and Ellis (6)

Consistency.

T h e test d e v e l o p e d b y M c D e r m o t t

w a s u s e d to d e t e r m i n e t h e t h e r m o d y n a m i c c o n s i s t e n c y of

the v a p o r - l i q u i d e q u i l i b r i u m d a t a . T h i s test i n v o l v e s c a l c u l a t i o n of the deviation, ( D

c d

) , b e t w e e n p a i r s of p o i n t s (c, d)

as d e f i n e d b e l o w :

η D

cd

=

Σ i=l

(x

ic

+ x) id

(log y id

-

log y ) ic


(2)


10.

L Y B A R G E R

Separation

A N D G R E E N E

155

of Mioctures

T h i s d e v i a t i o n is d e r i v e d f r o m t h e i s o t h e r m a l - i s o b a r i c f o r m of t h e G i b b s D u h e m e q u a t i o n a n d c a n b e a p p l i e d to i s o b a r i c e q u i l i b r i u m d a t a b y m i n i m i z i n g t h e c o m p o s i t i o n a n d t e m p e r a t u r e differences b e t w e e n p a i r s of points. T h i s w a s d o n e b y c h o o s i n g d a t a paths t h r o u g h t h e ternary e q u i l i b r i u m d i a g r a m so that differences i n c o m p o s i t i o n a n d t e m p e r a t u r e b e t w e e n pairs o f p o i n t s w e r e m i n i m i z e d . A p o i n t w a s c o n s i d e r e d to b e inconsistent i f i t d e v i a t e d m o r e t h a n 0.02 w i t h b o t h o f its n e i g h b o r s . T h i s d e v i a t i o n w a s chosen since i t a p p r o a c h e d t h e a p p r o x i m a t e l i m i t of t h e d e v i a t i o n c a u s e d b y a n a l y t i c a l i n a c c u r a c y . R u n s 1, 4, 5, 13, 15, 2 3 , 27, a n d 28 w e r e d e t e r m i n e d to b e inconsistent o n this basis. Correlation of Liquid Phase Activity Coefficients. F o r a c t i v i t y c o efficients to b e u s e d i n d i s t i l l a t i o n c a l c u l a t i o n s , t h e y are n o r m a l l y repre sented as a f u n c t i o n o f c o m p o s i t i o n . H e r e a m u l t i p l e regression c o m p u t e r p r o g r a m w a s u s e d to d e t e r m i n e t h e coefficients f o r a n e q u a t i o n o f t h e form lny.i

= α + a&i + a x 0

2

aaXz

2

+

α 7Χ&2

+ a3 X 3 + a X i + 2

4

2

+

a&ix

z

+

a&

2

2

+

(3)

a& x 2

z

w h e r e x x , a n d x a r e t h e l i q u i d m o l e fractions of water, m e t h y l e t h y l ketone, a n d t e t r a h y d r o f u r a n , respectively. l9

2

s

T e r m s w e r e d e l e t e d f r o m t h e regression e q u a t i o n u n t i l a n e q u a t i o n c o n t a i n i n g o n l y terms h a v i n g a confidence l e v e l of greater t h a n 8 0 % to i m p r o v e fit ( i n terms o f s u m o f squares e r r o r ) w a s o b t a i n e d . Coefficients (α/s) f o r t h e r e s u l t i n g s i m p l i f i e d equations a r e s u m m a r i z e d i n T a b l e I I w i t h a n estimate o f fit. Table II.

Regression Analysis Coefficients Used in Equation 3 an

ai

en

a5

-4.5041

2.4778

—

-0.0426

—

2.0063

- 0.1641

-0.0017

—

2.0828

0.1995

a

W a t e r (1) ( R = 0.996) MEK

(2)

( R = 0.983) THF

(3)

( R = 0.997) a

2.2301

All a{'8 not listed above were determined to be zero.

F o r m i x t u r e s c o n t a i n i n g m o r e t h a n 0.95 m o l e f r a c t i o n o f either w a t e r o r M E K , respective a c t i v i t y coefficients f o r w a t e r o r M E K a r e r e c o m m e n d e d to b e chosen as 1.0 rather t h a n t h e v a l u e p r e d i c t e d b y t h e regression equations since insufficient d a t a i n these regions cause a c t i v i t y coefficients to d e v i a t e s o m e w h a t f r o m t h e r e q u i r e d t e r m i n a l v a l u e o f u n i t y .


156

EXTRACTIVE

A N DAZEOTROPIC

DISTILLATION

THF

WATER

f~~®

© IV


20 Plates

WATER

Figure 4.

Feed 5 th

15 Plates

15 Plats»

L/D« 9

Feed 5 th

Feed β*

L/D* 3

L/D»3

1

MEK

Schematic diagram of solvent separation

T e r n a r y Separation B y Distillation.

scheme

T o design a recovery

system,

a s t a r t i n g c o m p o s i t i o n o f 85 m o l e % w a t e r , 7.5 m o l e % t e t r a h y d r o f u r a n , a n d 7.5 m o l e % m e t h y l e t h y l k e t o n e w a s chosen. T h i s assumes 1.5 p o u n d s of steam p e r p o u n d o f solvent are u s e d for r e g e n e r a t i o n a n d a b l e n d o f e q u a l a m o u n t s o f the solvents for t h e p o l y v i n y l c h l o r i d e processing. F i g u r e 2 shows b y t h e r e l a t i v e l e n g t h o f t h e c o n n e c t i n g Unes that i n t h e r e g i o n o f w a t e r - r i c h l i q u i d m i x t u r e s r e c t i f i c a t i o n to p r o d u c e v a p o r s r i c h i n T H F is easily o b t a i n e d . H o w e v e r , the existence o f a m i n i m u m b o i l i n g v a l l e y e x t e n d i n g across the d i a g r a m f r o m the T H F - w a t e r b i n a r y a z e o t r o p e t o t h e M E K - w a t e r b i n a r y azeotrope m a k e s i t i m p o s s i b l e t o r e m o v e a l l w a t e r f r o m the o v e r h e a d b y a single d i s t i l l a t i o n . T h e

best

that c a n b e d o n e i n t h e i n i t i a l d i s t i l l a t i o n is a n o v e r h e a d p r o d u c t i n the l o w b o i l i n g valley a n d a bottom product of substantially pure water. S e v e r a l alternatives exist t o treat f u r t h e r the o v e r h e a d stream. A s e c o n d d i s t i l l a t i o n , u s i n g t h e o v e r h e a d f r o m t h e i n i t i a l d i s t i l l a t i o n as feed, w o u l d y i e l d a n o v e r h e a d close t o the T H F - w a t e r b i n a r y a z e o t r o p e a n d a b o t t o m i n t h e r e g i o n o f the M E K - w a t e r b i n a r y azeotrope.

These

two

streams c o u l d t h e n b e d r i e d b y r e m o v i n g w a t e r p h y s i c a l l y — b y m o l e c u l a r


LYBARGER

10.

AND

Separation

GREENE

of

157

Mixtures

sieve o r c a l c i u m c h l o r i d e treatment, e t c . — t o y i e l d r e l a t i v e l y p u r e T H F and M E K . A s e c o n d alternative, u s i n g o n l y d i s t i l l a t i o n m e t h o d s , is c o n s i d e r e d here. T h i s m e t h o d , s h o w n s c h e m a t i c a l l y i n F i g u r e 4, involves t r e a t m e n t of t h e o v e r h e a d f r o m the first c o l u m n ( c o m p o s i t i o n i n t h e l o w b o i l i n g v a l l e y ) b y a d d i n g to it sufficient d r y T H F to b r i n g t h e n e w f e e d c o m p o s i t i o n across the l o w b o i l i n g v a l l e y . D i s t i l l a t i o n of this n e w f e e d y i e l d s the T H F - w a t e r azeotrope as o v e r h e a d a n d a b o t t o m c o n s i s t i n g of d r y


M E K or an M E K - T H F mixture. T h i s T H F - w a t e r azeotrope may then b e d r i e d b y extractive d i s t i l l a t i o n w i t h d i m e t h y l f o r m a m i d e , as has b e e n p r e v i o u s l y d i s c u s s e d (4).

T h e b o t t o m p r o d u c t , as a n M E K - T H F m i x -

ture, is easily p u r i f i e d b y a n a d d i t i o n a l d i s t i l l a t i o n , b u t w i t h r e g u l a t i o n of f e e d c o m p o s i t i o n i n t h e p r e v i o u s c o l u m n , this stream m a y b e

made

to a p p r o a c h p u r e M E K , e h m i n a t i n g the n e e d for this s u b s e q u e n t d i s t i l l a t i o n . F i n a l l y , a s m a l l c o l u m n u s e d t o separate the solvent, d i m e t h y l f o r m a m i d e ( D M F ) , f r o m the w a t e r is necessary to c o m p l e t e the separat i o n scheme. Multicomponent Computer Methods for Sizing Required Columns. A modified Thiele-Geddes

m e t h o d , p r o g r a m m e d for a n I B M 370-155,

w a s u s e d to p e r f o r m t h e c a l c u l a t i o n s n e e d e d to size e a c h r e q u i r e d c o l u m n . E x p e r i m e n t a l a c t i v i t y coefficient d a t a w e r e u s e d to a l l o w for n o n ideal l i q u i d phase

behavior

while

e n e r g y balances, u s i n g

estimated

e n t h a l p y d a t a , w e r e u s e d to c o r r e c t for non-constant m o l a l overflow. T h e t a M e t h o d w a s u s e d for convergence, a n d a l l p l a t e efficiencies

The were

a s s u m e d to b e 1 0 0 % . ( See R e f e r e n c e 7 for a d d i t i o n a l c a l c u l a t i o n a l details a n d a program listing. ) Table III.

Stream No. Flow Rate (moles/hr) Composition (mole fraction) THF MEK H0 DMF 2

1

2

Column Specifications 3

4

5

100 20.0 80.0 34.3 26.8

.075 .374 .075 .369 .002 .850 .258 .998

6

7

7.5 21.6

.635 .799 .016 .215 .011 .984 .150 .190 —

8

9

10

15.2

5.2

10.0

.999 — —

—

—

.660 .999 .001

.340

—

.001 .999

Column Specification and Flowsheet. A s c h e m a t i c d i a g r a m of

the

solvent s e p a r a t i o n scheme a n d t h e results of the c o m p u t e r analysis for e a c h c o l u m n a r e s h o w n i n F i g u r e 4 a n d T a b l e III, respectively.

Feed

p l a t e locations are g i v e n w i t h respect to the b o t t o m of e a c h c o l u m n . P l a t e


158

EXTRACTIVE AND AZEOTROPIC DISTILLATION


requirements for columns III and IV, which contain dimethylformamide, are based on an extension of a previous design analysis by Shah and Greene (4). Literature Cited 1. "Recovery of THF du Pont Tetrahydrofuran," Ε. I. du Pont de Nemours and Co. (Inc.), Electrochemicals Department, Wilmington. 2. Methyl Ethyl Ketone, Shell Chemical Corporation, Technical Publication SC: 50-2, New York. 3. Shnitko, V. Α., Kogan, V. B., "Liquid-Vapor Equilibrium in the Systems Tetrahydrofuran-Water and Tetrahydrofuran-Ethylene Glycol and a Method for Dehydration of Tetrahydrofuran,"J.Appl. Chem. USSR 4 (6) 1236-1242. 4. Shah, C. S., Greene, H. L., "Vapor-Liquid Equilibrium for the Ternary System Tetrahydrofuran-Water-Dimethylformamide," J. Chem. Eng. Data 15 (3) 408-411. 5. Hala, E., Pick, J., Fried, V., Vilim, O., "Vapor-Liquid Equilibrium," pp. 107-109, Pergamon, 1967. 6. McDermott, C., Ellis, S. R. M., "A Multicomponent Consistency Test," Chem. Eng. Sci. (1965) 20, 293-296. 7. Lybarger, Η. M., "Ternary Vapor-Liquid Equilibrium Data Applied to the Separation of a Mixture of Water, Methyl Ethyl Ketone, and Tetrahydro furan," Thesis, The University of Akron (March 1972). RECEIVED February 14, 1972.


Extractive and Azeotropic Distillation - ACS Publications

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