5 Azeotropic Distillation Results from Automatic Computer Calculations
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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.
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Computer Output Page 1
to
In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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
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THE USER
2
Computer Output Page k
Computer Output Page 3
Computer Output Page
In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
R
L
C
T
C
T
D(1C> WHEN KNTFL(1>«3
EC
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FORMAT
T
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mP
T U
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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/^OL •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
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In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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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