Extractive and Azeotropic Distillation

5 Azeotropic Distillation Results from Automatic Computer Calculations

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch005

CLINE BLACK, R. A. GOLDING, and D. E. DITSLER Shell Development Co., Emeryville, Calif. 94608

In azeotropic distillation the added component, or entrainer, is taken overhead with one of two or more components being separated in a distillation column. If a second liquid phase forms upon condensing the overhead vapors, the entrainer-rich phase is refluxed or recycled back to the col umn. The other liquid phase is discarded, recycled to some suitable point in the plant, or processed further to recover dissolved components before being discarded. Methods pre sented earlier by one of the authors are applied to calculate two and three phase equilibria required in a computer pro gram for calculating azeotropic distillations. A brief descrip tion of the program is given; a sample output is listed and described. Calculated results for dehydrating aqueous etha nol mixtures are compared for the entrainers, n-pentane, benzene, and diethyl ether. Column flows, heat loads, and stage requirements are lowest for n-pentane. The entrain ers are rated in decreasing order of suitability: n-pentane, benzene, and diethyl ether.

T ^ V i s t r i b u t i o n of c o m p o n e n t s b e t w e e n separable phases is the basis for **** most c o m m o n l y u s e d separation methods. R e g a r d l e s s of the t y p e of s e p a r a t i o n step, its d e s i g n d e p e n d s o n accurate d i s t r i b u t i o n coefficients for the c o m p o n e n t s b e t w e e n the c o n t a c t i n g phases.

T h e s e are g i v e n i n

c o m p o s i t i o n s or m o r e f u n d a m e n t a l properties of the e q u i l i b r i u m phases. In

d i s t i l l a t i o n the c o m p o n e n t s are d i s t r i b u t e d b e t w e e n

v a p o r a n d l i q u i d phases.

separable

T h e d i s t r i b u t i o n coefficients or Κ values are

the ratios o f the v a p o r - l i q u i d c o m p o s i t i o n s i n the e q u i l i b r i u m

phases.

T h e y are expressed as the l i q u i d phase a c t i v i t y coefficients, γ / s , the v a p o r 64 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

BLACK,

GOLDiNG,

Computer

A N D DITSLER

65

Calcufotions

pressures of t h e p u r e c o m p o n e n t s Ρ*° s, t h e t o t a l pressure P, a n d t h e i m p e r f e c t i o n - p r e s s u r e coefficients 0/s, as

T h e r e l a t i v e d i s t r i b u t i o n of c o m p o n e n t s i a n d ; is an = KJKt

-

yiP ° β , / τ Λ * 4

(2)

0

A z e o t r o p i c d i s t i l l a t i o n is a c c o m p l i s h e d b y a d d i n g t o t h e l i q u i d p h a s e a v o l a t i l e t h i r d c o m p o n e n t w h i c h changes t h e v o l a t i l i t y o f o n e of t h e t w o Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch005

c o m p o n e n t s m o r e t h a n t h e other, so t h e c o m p o n e n t s a r e s e p a r a t e d b y d i s t i l l a t i o n . T h e t w o c o m p o n e n t s to b e s e p a r a t e d often are close b o i l i n g c o m p o n e n t s w h i c h d o o r d o n o t azeotrope i n t h e b i n a r y m i x t u r e , b u t sometimes t h e y are c o m p o n e n t s w h i c h d o a z e o t r o p e a l t h o u g h t h e y a r e n o t close b o i l i n g c o m p o n e n t s . T h e a d d e d t h i r d c o m p o n e n t , sometimes c a l l e d the entraîner, m a y f o r m a t e r n a r y azeotrope w i t h the t w o c o m p o n e n t s b e i n g separated. H o w e v e r , i t m u s t b e sufficiently v o l a t i l e f r o m t h e s o l u t i o n so t h a t i t is t a k e n o v e r h e a d w i t h one of the t w o c o m p o n e n t s i n the d i s t i l l a t i o n .

If

the entraîner a n d the c o m p o n e n t t a k e n o v e r h e a d separate i n t o t w o l i q u i d phases w h e n the v a p o r o v e r h e a d is c o n d e n s e d , t h e entraîner p h a s e is refluxed b a c k to the c o l u m n . T h e other phase c a n b e f r a c t i o n a t e d t o r e m o v e the d i s s o l v e d entraîner a n d the r e s i d u a l a m o u n t of the o t h e r c o m p o n e n t before i t is d i s c a r d e d . A l t e r n a t i v e l y , this s e c o n d l i q u i d p h a s e is r e c y c l e d to some a p p r o p r i a t e p l a c e i n t h e m a i n process scheme. A z e o t r o p i c d i s t i l l a t i o n has often b e e n d i s c u s s e d i n recent l i t e r a t u r e ( J , 2, 3 ) .

M e t h o d s for p r o v i d i n g phase e q u i l i b r i a f o r a z e o t r o p i c a n d

extractive d i s t i l l a t i o n h a v e b e e n s t u d i e d extensively ( J , 4, 5, 6, 7,

8,9).

S o m e h a v e d i s c u s s e d the d e s i g n ( J O ) o r c a l c u l a t i o n of a z e o t r o p i c d i s t i l l a tions ( 2 , 3 ) ; others o n l y d i s c u s s e d c h o o s i n g t h e entraîner for a z e o t r o p i c d i s t i l l a t i o n processes

(11).

A n u n d e r s t a n d i n g of the phase e q u i l i b r i a i n v o l v e d is also v i t a l i n c h o o s i n g the entraîner.

T h i s not only depends on k n o w i n g the pure

c o m p o n e n t v a p o r pressures b u t also k n o w i n g n o n i d e a l i t i e s of the c o m ponents i n the l i q u i d a n d v a p o r phases. T h e m e t h o d s u s e d here to g i v e t h e phase e q u i l i b r i a are r e v i e w e d , a n d the A z e o t r o p i c D i s t i l l a t i o n P r o g r a m A D P / A D P L L E is d e s c r i b e d . A p p l i c a t i o n of the p r o g r a m to c a l c u l a t e a n a z e o t r o p i c d i s t i l l a t i o n p r o b l e m is s h o w n a n d d i s c u s s e d , a n d a s a m p l e c o m p u t e r o u t p u t is g i v e n a n d is briefly discussed. F i n a l l y , c a l c u l a t e d a z e o t r o p i c d i s t i l l a t i o n results are c o m p a r e d for d e h y d r a t i n g a q u e o u s e t h a n o l f o r t h e three entrainers, n pentane, benzene, a n d d i e t h y l ether.

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

66

E X T R A C T I V E

Phase

A N D

A Z E O T R O P I C

DISTILLATION

Equilibria

T o c a l c u l a t e p h a s e e q u i l i b r i a s u i t a b l e for m o s t a z e o t r o p i c d i s t i l l a t i o n p r o b l e m s , the m e t h o d s s h o u l d b e a p p l i c a b l e to three-phase e q u i l i b r i a . V a p o r - l i q u i d a n d l i q u i d - l i q u i d e q u i l i b r i a are u s u a l l y r e q u i r e d . A suit a b l e m e t h o d for this p u r p o s e has a l r e a d y b e e n d i s c u s s e d ( 5 ) .

It is a p p l i e d

here to c a l c u l a t e c o m p l e t e l y a l l p h a s e e q u i l i b r i a i n v o l v e d i n the u s u a l a z e o t r o p i c d i s t i l l a t i o n process. F r o m E q u a t i o n s 1 a n d 2, the phase e q u i l i b r i a d e p e n d u p o n k n o w i n g the p u r e c o m p o n e n t v a p o r pressures Pi°,

l i q u i d p h a s e a c t i v i t y coefficients

ji a n d i m p e r f e c t i o n - p r e s s u r e coefficients 0 . T h e c o m p u t e r p r o g r a m w h i c h Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0115.ch005

4

has b e e n d e v e l o p e d uses a n y of f o u r different v a p o r pressure e q u a t i o n s for p r o v i d i n g Ρ °. 4

It uses the m o d i f i e d v a n L a a r E q u a t i o n s ( 5 )

to g i v e

l i q u i d phase a c t i v i t y coefficients a n d a M o d i f i e d v a n d e r W a a l s E q u a t i o n of State (4, 6) to g i v e i m p e r f e c t i o n - p r e s s u r e coefficients 0> 3

6) e 6) s

7) 3

KNTRL < KNTRL (

KNTRL KNTRL
3 7) 3

1 2

4) a 4) a

KNTRL KNTRL
» 2 3)

PRESENT MOT PRESENT

CALCULATION

ACCUMULATOR

ISOTHERMAL

M

UTILITY

PROGRAMMED

C O M P ( 2 ) / C O P ( 3 > *AT10 A S FEEO CARD INPUT )

ACCUMULATOR ACCUMULATOR

MEATER/SUBCOOLER HEATER/SJBCOOLER

A

F!.)S f-TFR

IN T O P S VAPOR IN REFLUX

Λ

TRAY AT SAME T ^ A V 3Y D A T A

SOMTFNT ΞΟΜΤΕΝΤ

ρ Τ

PNTANj.>ETHMOL-VfATE«

Λί-L C O M P O N E N T C0MP C«MP(3)

SET F E E D SET F E E O

SET SET

A

LO D

S Y S T E M 14 S Y S T E M i5 SYSTEM 1 6 S Y S T E M i7 SySyEM 1 8

13

9

SY5TEM SYSTEM SYSTEM

SYSTEM

4 5 6 7 β

SYSTEM SYSTEM

1 2 3

SYSTEM SYSTEM SYSTEM

ADPLLE PROGRAM C O M B I N A T I O N OF A D P / A O P L L E

ADP

AVAILABLE.

SYSTEM OF UTILITY SUBROUTINES! W J T H

(ADP/ADPLLE)

Ternary Azeotropic Distillation Program ( A D P / A D P L L E )

AZEOTROPIC DISTILLATION PROGRAM

CONTROL OPTIONS ARE

1) 3 1) a 1) 8

KNTRL KNTRL KNTRL KNTRL KNTRL

TERNARY

PROGRAM USES A SPECIAL

KNTRL KNTRL KNTRL

THESE

THIS

Table I.


Computer Output Page 1

to


THROUGH

QUANTITIES

A L L COMPONENT

BUILT

INTO

THE

PROGRAM

THE USE OF PPMTR-CAROS.

ARE

PRINT

DATA P

N

NJ

*,0

f,0

3.0 25.0

χ) » 2) -

Ρ(

8

S

B

R

C

C°MP(3)

D

C

FAHRENHEIT MOLE F R A T I 0 N MOLES/HR MOLE F R A CT TION MOLE F R A CΓ I ON

T

FRACT

F^RENHEH

MOLE

MOLFS/HR

T

A

FORM T

FORMAT FORMAT FORMAT FORMAT FORMAT FORMAT FORMAT < I F KNTRL FORMAT FORMAT

Y

MOLF

C

Γ I ON FRA T

FORMAT (IF KNTRL(4)«2> FORMAT FORMAT ION FORMAT I ON C0MPÎ2) FORMAT ION C0MP(3) FORMAT ION 0 M P ( R (D I F KNTRL(5)P2> FORMAT T (IF K N T R L ( 5 ) « 2 ) FORMAT DP (TOP PRESS-AC PRESS) P S H FORMAT HFATER/SUBCOOLER TEMP FAHRENHEIT FORMAT NUM E ° F C C L E S FOR A ° L L E (IF KNTRL(7)«2) FORMAT

8

REFLUX

C0MP(2) C0MPÎ2)

V
»2#3 AND KNTR^(7)sj.) MAX CYCLES(JF KNTRL(l)s2.3 AND KNTR.(7),2> FEED TRAY DISPLACEMENT(ONLY IF KNTRL(Î)=3) MAXIMUM AQP PASSES ALLOWED (IF KNTRL«3>

TMESE

KNTRL ( f t ) * 1 KNTRL < C) s 2

BP

CHANGED BY


THE USER

2

Computer Output Page k

Computer Output Page 3

Computer Output Page


R

L

C

T

C

T

D(1C> WHEN KNTFL(1>«3

EC

L )

U

T

FORMAT

T

R

E

mP

T U

E

A

£15.8

MOLES/MR

T

FOR THIS

CALCULATION

0

(2l)

0(15) 0(16) D(17> 0(18) 0(19) 0(20)

8!»

0( 9 ) 0(1C) 0 ( H ) 0(12)

o( a)

0( 2 ) 0( 3 ) Oi 4 ) D( 5 ) 0( 6 ) 0< 7 )

0 ( 1>

.00000000

0

.24202000*03 .85640000*00 ,11000000*03 .50000000*02 .14000000*00 ,15445000*03 .34999999*01 .80000000*03 ,61999999-06 ,25560000*03 .13850000*00 .15000000*02 .99999999* 5 ,89999999*04 .99990000*00 .00000000 .15445000*03 ,00000000 .00000000 .0

SET FEED A * AT SAME C O M P ( 2 > / C O M P ( 3 > R A T I O S F E E O ACCUMULATOR CALCULATION ISOTHERMAL ( I F KNTRL«2»3) HE ATFR/S.jBCOOL N N Ç T P R E S E N T S T R I P P E R P R E S E N T (PROGRAM C Y C L E S ONCE I F KNTRL*1>«2|3> P R I N T A L L COMPONENT DATA

A P EUSED

COMP(?)

DATA

S E T AS FOLLOWS

C O M B I N A T I O N O F ADP/ADPLLE PROGRAMS SYSTEM 7 3NTAN2-ETHNOL-WATER S £ T cChP(2) ; C M T £ K T I N T O P S VAPOR

BEEN

TEST OF AQP/ADPLLE OPTION KNTRL(1>«3

OPTIONS HAVE

1) 2) 3) 4> b) 6) 7) t)

FOLLOWING

( ( ( < < ( < (

E C

OF

W

w

TERNARY AlEOTROPIC DISTILLATION PROGRAM ( A D P / A D P L L O

VALUE

n FL

T

h OLE FRACT I ON COMP(2) FAHRENHEIT FEEO TEMPERATURE (SUBCOOLED L I Q U I D ) PS I A REB°ILEP PRESSURE PSIA P R E S S U R E DROP P E R TRAY FAHRENHEIT REFLUX TEMPERATURE MOLE F R A C I 3 N ( I F KNTRL(3>«2> REFLUX OMP MOLES/HR R E B I L E P VAPOP MOLF. F R A C T I BOTTOMS COMP(i) MOLE F R A C T I BOTTOMS COMP(3) (IF KNTRL(3)«1) MOLE F R A C T I TOPS VAPOR C0MP(2) (IF KNTRL»2> F E E D TRAY L O C A T I O N MOLE FRACTI ON DISTILLATE COMPtj) MOLE FRACTI DN DISTILLATE C0NP{2) MOLE FRACTI ON DISTILLATE tOMP

l 2

0

WATER WATER WATER

ETHNOL ETHNOL ETHNOL

T

PN AN2

PNTAN2

PNTAN2

A

PNT N2 ETHNOL WATER

F

100.000 200.000 300Ό00 100.000 200.000 300.000 100.000 200.000 300,000

TEMP

TC Κ .470300*03 .516300*03 .647000*03

B

0 C

.13747500-00 •22500000*00 .00000000

9

EPR

,000000 .890000-01 .260000-01

9

VAP BTU/MOL ,ΐ5ΐ5ΐ500+θ5 ,17748900*05 .'20346300*05 .20 37 00+05 ,22573300*05 .23969200*05 .19916000*05 .20649000*05 .21290001*05

C4I CC/GM ,141000*03 ,759000*02 ,247000*02

R?SSURE EQUATIONS ,273160*03 ,525l7o*01 ,228980+03 .000000 ,273160*03 ,404859*01

L I O BTU/ÔL •39682500*04 ,82972500*04 .132756 *Q5 .25061000*04 ,60349000*04 .10365300*05 .12250000*04 .30270000*04 ,48200000*04

PC ATMS ,331000*02 ,631000*02 ,218000*03

7 CLASSES COEFFICIENTS FOR VAPOR .226933*02 ,208645*04 PNTAN2 .816290*01 .162322*04 ETHNOL .208440*02 ,28i740*04 WATER

3

AI J

•475000*01 .475000*01

•oooooo

AMPR

,οοοοοο •oooooo

.0000 .0000 .0000

I J PNTAN2-ETHN0L PNTANs-WATER ETHNOL-WATER

,159785*01

TEMP lOOtOOQ

AJI .82406500-00 •2Q3noooo*oi .39250000-00

.83367725-00 . 77 936* i ,76050000-00

AI J

ciJ

1J PNTAN2-ETHN0L PNTAN2-WATER ETHNOL-WATER

TEMP 87,800 87,800 87.800

CÏJ .15507600-00 .25800000-00 .00000000

.87359000-00 .22125185*01 .40080000-00

.88388000-00 .39480000*01 .74600000-00

AJI

PNTAN2-ETHN0L PNTÂN2-WATER EfHNOt««ATER

.93892120-00 .41365440+01 .72799999-00

AI J

TEMP 75.000 C 75.000 C 75i00Q C

RUN CVCLES - 1

TEMP « 154,430 F

CU .17486900-00 .29700000-00 .00000000

PRESENT

CALCULATION

PRESENT

A JI .92929000-00 .24165000*01 .40700000-00

STRIPPER

NOT

ACCUMULATOR

HEATER/SUBCOOLER

ISOTHERMAL

MODIFICATION OF PROGRAM TO CALCULATE PHASE EQUILIBRIA B* ?R2£f5^?^?βίϊϊ2 COEFFICIENTS USED IN iVLE» PROGRAM, USES MODIFIED VAN L*A* COEFFICIENTS AT 3 TEMPS. CALCULATES THETAS. GAMMAS AND COMPLETE PHASE EQUILIBRIA AT EACH STAGE.

AZEOTROPIC



E

C

0MP(2) C0MP(3) TOTAL VALUE

COMP(l)

C0MP C0MP(3) TOTAL C0MP

COMP(l)

R

T

A

e

S

S )

MOLE

A

WA

2

2

2

2

2

2

0

PRESSURE^ 49.7 0 TE^P« 234.558 VAPOR M/HR LIO M/HR LIQ BTU/M .5139 ,5i41 9921,9861 797.7091 1039,7 54 7421.5674 .0024 .0030 3639.4535 798. ?54 2425 77 ι5 3·4

F R A C T Τ ON

FTMNOL WATER TOTAL

PMTAN2

COMP

KTRAYs 2

T

KTRAYs J PRESSURE* 49.860 TE»lPe 234.74P CONP VAPOR M/MR LlQ M / H R LIQ βΤΙΙ/Μ PN AN2 ,0558 .0559 9944.2387 FTHNOL 799,1022 1C41.U86 7440.7544 WATER .O0 3 .00 e 3647.64i7 TOTAL 799,1602 1041,1773 7747273,7 MOI Ε FRACTION V TER (ENTRAINER FREF BASIS)

w

V
• W12) • VUl> •

2

V< 1 ) V< V( 3 ) V( 4 ) V( 5 ) V( 6 ) V< 7)

VAP BTU/M 18655,6430 23087.8140 20883,2230 18470220,0

MOLES/H MOLEE/WR MOLES/HR OF D(10> ^ H E N KNTPL«3

MOLES/HR MOLES/HP MOLES/HR KOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR

REBOILER PRESSURE* 50.00C TEMPt 234.910 C0*P VAPOR M/HR L.!0 M/WR LIS BTU/M PNTAN2 ,0059 ,0061 9961,3993 FTHNOL 799.992C 1042.0083 7455.5545 WATER .0021 .0026 3653.9526 TOTAL 800.0000 1042,0l70 7768820.1 MOLE FACTION A E * o

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Extractive and Azeotropic Distillation

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