Supercritical Fluids - American Chemical Society

Chapter 16

Supercritical Carbon Dioxide Extraction of Lemon Oil 1

Steven J . Coppella and Paul Barton

Downloaded by IOWA STATE UNIV on February 16, 2017 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0329.ch016

Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802

Vapor-liquid-equilibrium was measured for lemon oil and carbon dioxide from 303 to 313 Κ and from 4 to 9 MPa using a nonvisual, constant-volume static cell. Two-phase behavior was verified visually in separate experiments. Phase samples were depressurized into cold traps; carbon dioxide was metered through a wet test meter, and liquids were analyzed by gas chromatography. The Peng-Robinson equation of state reproduced the P-x diagram by modeling the system as a carbon dioxide-limonene binary with a temperature-dependent interaction parameter. Solubilities of oil in the vapor phase were in the range of 1 to 3 wt%. Relative v o l a t i l i t y of limonene to geranial decreased from 2.2 to 1.3 over this solubility range; relative volatility for geranial to β-caryophyllene decreased from 1.5 to 1.1. 6

I n 1 9 8 3 - 1 9 8 4 , A r i z o n a and C a l i f o r n i a p r o d u c e d a n n u a l l y o v e r 1 0 kg of c o l d - p r e s s e d l e m o n o i l . A f t e r b e i n g c o n c e n t r a t e d by d i s t i l l a t i o n o r l i q u i d e x t r a c t i o n , lemon o i l i s used as a f l a v o r i n g a n d / o r f r a g r a n c e a g e n t i n b e v e r a g e s and c o s m e t i c s . However, d i s t i l l a t i o n t h e r m a l l y d e g r a d e s lemon o i l , and e x t r a c t i o n w i t h o r g a n i c s o l v e n t s only p a r t i a l l y reduces thermal degradation (since the s o l v e n t s must be r e c o v e r e d by d i s t i l l a t i o n ) a n d i n t r o d u c e s s o l v e n t c o n t a m i n a t i o n . E x t r a c t i o n with s u p e r c r i t i c a l carbon d i o x i d e near i t s critical p o i n t ( 3 0 4 . 3 Κ, 7 . 3 8 M P a , 0 . 4 6 7 g / c m ) o f f e r s a cheap, n o n t o x i c s o l v e n t t h a t does not i m p a r t f l a v o r s nor t h e r m a l l y degrade the product. S u p e r c r i t i c a l e x t r a c t i o n i s a hybrid unit operation i n the domain between e x t r a c t i v e d i s t i l l a t i o n a n d l i q u i d e x t r a c t i o n . S o l v e n t r e c o v e r y i s a c c o m p l i s h e d by d e p r e s s u r i z a t i o n a t a m b i e n t temperature. 3

y

Current address: Department of Chemical Engineering, University of Delaware, Newark, D E

19716

0097-6156/87/0329-0202$06.00/0 © 1987 American Chemical Society

Squires and Paulaitis; Supercritical Fluids ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

16.

COPPELLA AND BARTON

Carbon Dioxide Extraction of Lemon Oil

203

P r o c e s s e s f o r s u p e r c r i t i c a l e x t r a c t i o n o f o i l s have been d e s c r i b e d i n numerous l i t e r a t u r e r e f e r e n c e s , i n c l u d i n g P a u l a i t i s e t al. ( 1 ) , E l y and Baker ( 2 ) , G e r a r d ( 3 ) , S t a h l et a l . ( 4 ) , and Robey and Sunder ( 5 ) . The l i t e r a t u r e l a c k s d e t a i l e d p h a s e e q u i l i b r i u m d a t a on mul t i component e s s e n t i a l o i l s w i t h s u p e r c r i t i c a l solvents i n the p r o x i m i t y o f the s o l v e n t c r i t i c a l temperature. The p u r p o s e s o f o u r r e s e a r c h were t o e v a l u a t e t h e f e a s i b i l i t y of s u p e r c r i t i c a l c a r b o n d i o x i d e e x t r a c t i o n o f lemon o i l near ambient temperature, generate e q u i l i b r i u m d a t a f o r c a r b o n d i o x i d e w i t h mul t i component e s s e n t i a l o i l c o n s t i t u e n t s , and e v a l u a t e the a b i l i t y of the Peng-Robinson e q u a t i o n of s t a t e (6) t o model t h i s mul t i component s u p e r c r i t i c a l s y s t e m .


C o n c e n t r a t i n g Lemon O i l S t a r o s c i k a n d W i l s o n (7) h a v e a n a l y z e d v a r i o u s l e m o n o i l s a n d i d e n t i f i e d 38 c o m p o u n d s . T h e s e compounds c a n be s u b d i v i d e d i n t o t h r e e major c l a s s i f i c a t i o n s : terpenes ( C h y d r o c a r b o n s ) , oxy f r a c t i o n (oxygenated C - C h y d r o c a r b o n s ) , and s e s q u i t e r p e n e s (C hydrocarbons). Lemon o i l i s u s u a l l y c o n c e n t r a t e d t o remove the t e r p e n e s and s e s q u i t e r p e n e s from the d e s i r e d C - C oxy f r a c t i o n 1

8

0

l 2

1

8

1

5

2

(8). When c o n c e n t r a t i n g t h e l e m o n o i l by m u l t i s t a g e fractional d i s t i l l a t i o n under vacuum, column performance coupled with c o n d e n s e r p r e s s u r e , c o l u m n p r e s s u r e d r o p , r e b o i l e r d e s i g n , a n d mode of o p e r a t i o n ( b a t c h or c o n t i n u o u s ) d i c t a t e s t h e d e g r e e o f t h e r m a l exposure. O v e r h e a d t e m p e r a t u r e s r a n g e f r o m 320 t o 340 K , r e b o i l e r t e m p e r a t u r e s r a n g e f r o m 330 t o 370 K , a n d e x p o s u r e t i m e s o f 1 5 t o 20 h o u r s may b e e x p e c t e d d u r i n g b a t c h d i s t i l l a t i o n . In continuous d i s t i l l a t i o n , exposure times are l o w e r but r e b o i l e r t e m p e r a t u r e s may be h i g h e r . In e x t r a c t i v e d i s t i l l a t i o n w i t h a s u p e r c r i t i c a l s o l v e n t , e x t r a c t i o n r a t h e r t h a n vacuum i s u s e d t o v o l a t i l i z e t h e components i n t o t h e vapor phase. Operating t e m p e r a t u r e s c a n be l o w e r t h a n i n c o n v e n t i o n a l d i s t i l l a t i o n , and the d e s i r e d C - C oxy f r a c t i o n w i l l t h e n h a v e been s u b j e c t e d t o l e s s t h e r m a l d e g r a d a t i o n . Carbon d i o x i d e has a c r i t i c a l t e m p e r a t u r e t h a t meets t h i s g o a l . In order t o make data c o r r e l a t i o n p r a c t i c a b l e i n supercritical carbon dioxide e x t r a c t i o n , i t i s convenient to r e p r e s e n t each major c h e m i c a l c l a s s i f i c a t i o n by a s i n g l e c o m p o u n d . E a c h s e l e c t compound s h o u l d h a v e a v a i l a b l e g o o d v a p o r p r e s s u r e d a t a a n d s h o u l d be a p r e d o m i n a n t c o n s t i t u e n t i n i t s g r o u p w i t h r e g a r d to s t r u c t u r e and c o n c e n t r a t i o n . F o r c o r r e l a t i o n p u r p o s e s , we s e l e c t e d l i m o n e n e , g e r a n i a l , and 3 ~ c a r y o p h y l l e n e . Their structures are shown i n F i g u r e 1. S t a h l et a l . ( £ ) p r e s e n t e d s o l u b i l i t y d a t a f o r l i m o n e n e and c a r y o p h y l l e n e w i t h c a r b o n d i o x i d e ; G e r a r d (3) i n c l u d e d c a r v o n e . Temperatures i n t h e r a n g e o f 279 t o 377 K , a n d p r e s s u r e s i n t h e r a n g e o f 1 . 5 t o 11 MPa w e r e c o v e r e d . Robey and Sunder ( 5 ) p r o v i d e d s o l u b i l i t y and r e l a t i v e v o l a t i l i t y d a t a for carbon dioxide with c o n c e n t r a t e d l e m o n o i l and w i t h l i m o n e n e and c i t r a l (geranial/ n e r a l ) f r o m 323 t o 353 Κ a n d 9 . 4 t o 10.6 M P a . G e r a r d (3) d e s c r i b e d a c o n t i n u o u s m u l t i s t a g e c o l u m n p r o c e s s for c a r b o n d i o x i d e e x t r a c t i o n ( d i s t i l l a t i o n ) of e s s e n t i a l o i l s at 8

l 2


204

SUPERCRITICAL FLUIDS

a m b i e n t t e m p e r a t u r e and 8 MPa, w i t h s o l v e n t r e c o v e r y MPa. R o b e y and S u n d e r ( 5 ) p r o p o s e d a l e m o n o i l w h i c h w o u l d o p e r a t e a t 3 3 3 Κ a n d 1 0 MPa w i t h e q u i v a l e n t t o 1 2 s t a g e s ; s o l v e n t r e c o v e r y would be at MPa.


Experimental

a t 273 Κ and 3 fractionator an e f f i c i e n c y 2 9 3 Κ and 5.5

Section

C o l d - p r e s s e d o i l f r o m A r i z o n a e a r l y d e s e r t lemons was s u p p l i e d by Α. M. T o d d Company, K a l a m a z o o , MI. D e g a s s e d l e m o n o i l and d r y c a r b o n d i o x i d e w e r e charged i n t o the o n e - l i t e r i s o t h e r m a l c o n s t a n t volume c e l l shown i n F i g u r e 2 . A f t e r t h e o p e r a t i n g t e m p e r a t u r e was r e a c h e d , t h e s y s t e m was s t i r r e d f o r one h o u r , t h e n a l l o w e d t o s e t t l e f o r 15 m i n u t e s b e f o r e s a m p l i n g . A c o u p l e of e x p e r i m e n t s were made w i t h l o n g e r m i x i n g a n d s e t t l i n g t i m e s t o c o n f i r m t h a t e q u i l i b r i u m had b e e n r e a c h e d . P a r a l l e l phase visualization e x p e r i m e n t s were c o n d u c t e d i n a s i g h t gauge t o i n s u r e that o p e r a t i o n was i n t h e t w o - p h a s e r e g i o n and t h a t s e t t l i n g t i m e was adequate. E x p e r i m e n t s were performed from 303 t o 313 Κ and from 4 to 9 MPa. A s a m p l e o f t h e e q u i l i b r a t e d l i q u i d phase was removed ( a f t e r p u r g i n g ) by d e p r e s s u r i z a t i o n t h r o u g h a v a l v e and h y p o d e r m i c tubing i n t o a t w o - s t a g e t r a p c o o l e d by d r y i c e - a c e t o n e . A wet t e s t meter measured the carbon d i o x i d e o f f - g a s . A sample of t h e vapor phase was t h e n s i m i l a r l y removed. Purge and sample s i z e s were kept s m a l l t o m i n i m i z e d i s t u r b a n c e s of e q u i l i b r i u m . P r e s s u r e changes i n t h e c e i l were 0 - 0 . 1 MPa d u r i n g s a m p l i n g o f l i q u i d phase and 0 - 1 . 2 MPa d u r i n g s a m p l i n g of vapor phase. Special high-pressure sample v a l v e s w i t h m i c r o l i t e r - s i z e d t r a p s were t r i e d i n an e f f o r t t o reduce p r e s s u r e d i s t u r b a n c e , but r e l i a b i l i t y was i n a d e q u a t e . E s t i m a t e d r e l a t i v e e r r o r s a r e 0.2% f o r t e m p e r a t u r e , 5% f o r p r e s s u r e , H% f o r c a r b o n d i o x i d e mole f r a c t i o n i n t h e l i q u i d phase, and 10% f o r lemon o i l mole f r a c t i o n i n t h e v a p o r p h a s e . Relative e r r o r i s d e f i n e d a s e x p e r i m e n t a l e r r o r d i v i d e d by sample average v a l ue. The r e c o v e r e d lemon o i l samples were a n a l y z e d by gas chromato graphy. A 0 . 5 mm i . d . χ 3 0 m t h i n f i l m ( 0 . 1 ym) S E - 3 0 glass c a p i l l a r y c o l u m n ( S u p e l c o , I n c . , B e l l e f o n t e , PA) was used w i t h a flame i o n i z a t i o n d e t e c t o r . The t e m p e r a t u r e was programmed f r o m 348 to 4 7 3 K. Peak i d e n t i f i c a t i o n was based on i n f o r m a t i o n o f S u p e l c o , Inc., A. M. Todd Company, and S t a r o s c i k and W i l s o n ( 7 ) . Staroscik ( 9 ) p r o v i d e d us w i t h t h e r e s p o n s e v a l u e s used i n h i s work and we assumed t h a t our d e t e c t o r would g i v e p r o p o r t i o n a t e r e s p o n s e s . S t a r o s c i k f o u n d i n h i s work t h a t r e l a t i v e s t a n d a r d d e v i a t i o n s of the r e s p o n s e v a l u e s were g e n e r a l l y l e s s than 3%. Results Lemon o i l - c a r b o n d i o x i d e e q u i l i b r i u m was measured a t 3 0 3 , 3 0 8 , and 313 Κ and i n the p r e s s u r e range of 4 t o 9 MPa. Below 6 MPa, t h e r e was i n s u f f i c i e n t l e m o n o i l i n t h e vapor phase t o o b t a i n good samples f o r a n a l y s i s . Above 9 . 0 MPa at 313 K, above 7 . 8 MPa a t 3 0 8 K, a n d above 7 . 4 MPa a t 303 K, the system e x h i b i t e d a s i n g l e phase. Nine e x p e r i m e n t s p r o v i d e d two-phase, 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


16.

COPPELLA AND BARTON


205

CHD H,C


CH.

LIMDNENE

GERANIAL

F i g u r e 1.

β - CARYDPHYLLENE

Key C o n s t i t u e n t s

i n Lemon O i l .

VACUUM PUMP HEATED PRESSURE GAUGE •IL CHARGE AND DEGASSING VESSEL

SAMPLE OF GAS VAPOR PHASE METER

COLD TRAP

WARMED COg CHARGE TANK

25 Kg BALANCE

THERMOSTATIC HEATER

1.11 - LITER EQUILIBRIUM CELL HASTELLDY C RATING' 34 MPa AT 700 Κ F i g u r e 2.

Vapor-Liquid Equilibrium

Apparatus.




206

s u i t a b l e f o r c o r r e l a t i o n s and f o r g e n e r a t i n g c o e f f i c i e n t s f o r the Peng-Robinson e q u a t i o n . D e t a i l e d e x p e r i m e n t a l data can be f o u n d i n C o p p e l l a (JTj). The r e s u l t s o f an e x p e r i m e n t a t 308 Κ and 6.98 MPa are d e t a i l e d here. T h e l i q u i d p h a s e c o n t a i n e d 48 wt% (74 m o l e %) c a r b o n d i o x i d e and the vapor phase c o n t a i n e d 99.5 wt% (99.8 mole %) carbon d i o x i d e . A gas c h r o m a t o g r a m f o r t h e l e m o n o i l f r o m t h e l i q u i d p h a s e s a m p l e i s shown i n F i g u r e 3. Peak i d e n t i f i c a t i o n , r e t e n t i o n , r e s p o n s e v a l u e , and c o n c e n t r a t i o n a r e g i v e n i n T a b l e I . C o m p o s i t i o n o f the lemon o i l i n t h e vapor phase i s a l s o l i s t e d . Average m o l e c u l a r weight o f l e m o n o i l i s 137.9 i n t h e l i q u i d and 136.4 i n the vapor . The r e l a t i v e v o l a t i l i t y , o r s e l e c t i v i t y f a c t o r , f o r e a c h component i n the presence of carbon d i o x i d e i s a l s o g i v e n i n T a b l e I. R e l a t i v e v o l a t i l i t y i s d e f i n e d as t h e r a t i o o f K - v a l u e f o r component i t o K - v a l u e f o r l i m o n e n e . The K - v a l u e f o r component i i s d e f i n e d as m o l e f r a c t i o n i i n the vapor ( e x t r a c t ) phase t o mole f r a c t i o n i i n the l i q u i d ( r a f f i n a t e ) p h a s e . 3y comparing t h e r e l a t i v e v o l a t i l i t i e s of v a r i o u s c o m p o n e n t s , t h e e a s e o f s e p a r a t i o n between t h e s e components can be d e t e r m i n e d . F o r example, a key terpene-oxy s e p a r a t i o n i n v o l v e s t e r p i n o l e n e w i t h a r e l a t i v e v o l a t i l i t y w i t h r e s p e c t t o l i m o n e n e o f 0.7 and c i t r o n e l l a l with r e l a t i v e v o l a t i l i t y w i t h r e s p e c t t o l i m o n e n e of 0.4. The r e l a t i v e v o l a t i l i t y o f t e r p i n o l e n e t o c i t r o n e l l a l i s then 0.7/0.4 or 2. The s e c o n d cut p o i n t i n the s e p a r a t i o n i s between g e r a n y l a c e t a t e and g - c a r y o p h y l l e n e . T h i s s e p a r a t i o n f a c t o r i s 0.06/0.07 o r 0.9. T h i s i s o p p o s i t e that f o r g e r a n i a l to 3-caryophyllene: 0.2/0.07 or 3. S i n c e t h e r e i s some o v e r l a p i n t h e v o l a t i l i t i e s o f C i 2 oxygenated hydrocarbons and sesquiterpenes, some β - c a r y o p h y l l e n e w i l l be e x t r a c t e d i n t o t h e d e s i r e d C - C oxy product. 8

Solubility

and

l 2

Selectivity

S o l u b i l i t y d i a g r a m s were p r e p a r e d f o r the phases t h a t s e p a r a t e d i n the lemon o i l e x t r a c t i o n s performed i n t h i s s t u d y w i t h carbon dioxide. S u c h d i a g r a m s can s e r v e o n l y as g u i d e s , s i n c e s o l u b i l i t y i s composition-dependent and i s a f u n c t i o n of the amount e x t r a c t e d . The d a t a a r e shown i n F i g u r e s 4, 5, and 6 a t 303, 308, and 313 K, respectively. E x t r a c t i o n s or e x t r a c t i v e d i s t i l l a t i o n s with s u p e r c r i t i c a l s o l v e n t need to be performed a t as h i g h as p o s s i b l e a s o l u b i l i t y o f o i l i n t h e e x t r a c t or vapor phase i n o r d e r t o r e d u c e the s o l v e n t or c a r r i e r gas r e q u i r e m e n t . From our l e m o n o i l - c a r b o n d i o x i d e p h a s e d i a g r a m s , i t appears t h a t the h i g h e s t p r a c t i c a l s o l u b i l i t y l e v e l i s 0.9 mole % (2.8 wt%) e s s e n t i a l o i l . T h i s i s o b t a i n a b l e a t 313 Κ . At lower t e m p e r a t u r e , s e n s i t i v i t y of s o l u b i l i t y to pressure r e q u i r e s t h a t s o l u b i l i t y be lower (e.g., 0.3 mole % a t 308 K ) . At 313 Κ and 8.4 MPa, t h e s l o p e o f e x t r a c t p h a s e s o l u b i l i t y v e r s u s p r e s s u r e i s 0.06 w e i g h t f r a c t i o n o i l / M P a . For a 15-m tall e x t r a c t i o n tower o p e r a t e d at a d e n s i t y o f 0.5 g / c m , t h e p r e s s u r e a t t h e b o t t o m i s h i g h e r t h a n t h a t a t t h e t o p by 0.075 MPa. The s o l u b i l i t y at the bottom w i l l then be 0.15 wt£ h i g h e r at t h e b o t t o m 3



F i g u r e 3.

Gas Chromatogram

of Lemon O i l i n L i q u i d

Phase


Sample.

to ο

208


Table

I.

Lemon O i l V a p o r - L i q u i d

Peak No. Compound ref 1 2

3

0

Weight Relative Response

a t E q u i l i b r i u m i n CO2

Volatility Relative to Mole % Limonene Liquid Vapor ~

—

acetone α-thuj ene a-pinene camphene sabinene 3-pinene J

0.00 0.55 0.58 0.63 0.76

0.75 0.75 0.70 0.74

0.61 2.80 0.09 17.27

0.35 1.68 0.06 13.06

myrcene octanal phellandrenej a-terpinene

0.79 0.86

0.73 1.17

1.87 0.09

1.59 0.07

1.2

0.92

1.19

1.21

1.10

1.1

8 9 10

limonene Ύ-terpinene terpinolene"^ 1 inalool I nonanal

1.00 1.09 1.19

0.75 0.78 0.78

67.14 7.59 0.47

68.22 8.45 0.67

11 12 13 14 15

citronellal terpinenen-4-01 a-terpineol decanal neral

1.40 1.51 1.55 1.60 1.70

1.06 0.92 0.92 0.97 0.96

0.02 0.02 0.06 0.01 0.24

0.04 0.04 0.20 0.08 0.92

16 17 18 19 20

geranial nonyl acetate neryl acetate geranyl acetate 3-caryophyllene

1.80 1.95 2.12 2.18 2.36

0.96 1.24 1.02 1.02 0.78

0.29 0.00 0.03 0.009 0.013

1.45 0.03 0.25 0.15 0.18

0.2

21

t r ans-ot her gam ot ene α-humalene β-bisabolene

2.40 2.53 2.60

0.78 0.71 0.77

0.016 0.00 0.013

0.26 0.05 0.38

0.06

3 4


Retention Relative to Limonene

Analyses

5 6 7

22 23

d e t e n t i o n t i m e f o r limonene averaged 8.7 minutes °Peak a r e a m u l t i p l i e r


1.8 1.7 1.6 1.34

1.3

1.0 0.91 0.7

0.4 0.4 0.3 0.1 0.3

— -

0.1 0.06 0.07

0.03


16.

COPPELLA AND BARTON


0.001

0.01

Mole

fraction lemon oil

0.1

1.0

F i g u r e 4. Phase E q u i l i b r i u m f o r Carbon Dioxide:Lemon O i l at 303 Κ. E x p e r i m e n t a l Two-Phase: 0 - Vapor t - Liquid. Δ - E x p e r i m e n t a l One-Phase. Peng-Robinson e q .

0.001

0.0001

Mole

0.01

0.1

fraction lemon oil

F i g u r e 5. Phase E q u i l i b r i u m f o r Carbon Dioxide:Lemon O i l at 308 Κ. E x p e r i m e n t a l Two-Phase: 0 - Vapor · - Liquid. A - E x p e r i m e n t a l One-Phase. Peng-Robinson e q .

10

I

I

1

1

1

1

Δ

-*

8

CP/' ν / /

-

«

2

/

/ I

-

\

. 0.0001

\\ 1

ι \ 1 0.001

.

1 0.01

1 0.1

1.0

Mole fraction lemon oil

F i g u r e 6. Phase E q u i l i b r i u m f o r Carbon Dioxide:Lemon O i l at 313 Κ. E x p e r i m e n t a l Two-Phase: 0 - Vapor · - Liquid. Λ - E x p e r i m e n t a l One-Phase. - - Peng-Robinson e q .


209



210

( i g n o r i n g composition e f f e c t s ) . At 308 Κ and 7.69 MPa, an i n c r e a s e i n p r e s s u r e of 0.15 MPa causes t h e two-phase s y s t e m t o r e v e r t t o a one-phase system. I t i s i m p e r a t i v e t h a t temperature and p r e s s u r e p r o f i l e s i n t h e s u p e r c r i t i c a l e x t r a c t i o n t o w e r be m a i n t a i n e d accurately. Windows i n t h e tower a r e recommended t o c o n f i r m t h a t o p e r a t i o n remains i n the two-phase domain. The s e l e c t i v i t i es i n t h e s u p e r c r i t i c a l c a r b o n dioxide e x t r a c t i o n o f t e r p e n e s from the oxy f r a c t i o n , and the oxy f r a c t i o n from s e s q u i t e r p e n e s , f o r l e m o n o i l a r e shown i n F i g u r e s 7 and 8, respectively. F i g u r e 7 shows t h e r e l a t i v e v o l a t i l i t y , or s e l e c t i v i t y f a c t o r , o f l i m o n e n e t o g e r a n i a l as a f u n c t i o n o f o i l s o l u b i l i t y i n the vapor phase. O p e r a t i o n o f the e x t r a c t o r at 308 Κ and 1 wtyÊ s o l u b i l i t y (the h i g h e s t p r a c t i c a l l e v e l at t h i s t e m p e r a t u r e ) p r o v i d e s a r e l a t i v e v o l a t i l i t y o f 2. O p e r a t i o n at 313 Κ and 2.8 ut% s o l u b i l i t y p r o v i d e s a r e l a t i v e v o l a t i l i t y o f 1.3The s e l e c t i v i t y f a c t o r s a r e an o r d e r o f magnitude lower than t h e vapor p r e s s u r e r a t i o s at 303 t o 313 K. F i g u r e 8 shows t h e r e l a t i v e v o l a t i l i t y o f g e r a n i a l t o β - c a r y o p h y l l e n e as a f u n c t i o n o f o i l s o l u b i l i t y i n the vapor phase. At 313 Κ and 1 w t j s o l u b i l i t y , r e l a t i v e v o l a t i l i t y i s 1.4. A t 308 Κ and 1 wt56 s o l u b i l i t y , t h e s e c o n s t i t u e n t s a r e i n s e p a r a b l e by s u p e r c r i t i c a l carbon d i o x i d e e x t r a c t i o n . The r a t i o of vapor p r e s s u r e s f o r t h i s p a i r i s i n t h e v i c i n i t y o f 2 ( a t 392 Κ, t h e l o w e s t temperature w i t h vapor p r e s s u r e d a t a ) . Modeling of E q u i l i b r i a The c a r b o n d i o x i d e / l e m o n o i l P-x b e h a v i o r shown i n F i g u r e s 4, 5, and 6 i s t y p i c a l of b i n a r y carbon d i o x i de: h y d r o c a r b o n s y s t e m s , s u c h as t h o s e c o n t a i n i n g h e p t a n e (Im and K u r a t a , V\), decane ( K u l k a r n i et a l . , 1_2), or benzene (Gupta et a l . , 1_3 ). Our l e m o n o i l s a m p l e s c o n t a i n e d i n e x c e s s o f 64 m o l e % limonene; so we modeled our d a t a as a r e d u c e d b i n a r y o f l i m o n e n e a n d c a r b o n d i o x i d e . The Peng-Robinson (6^) e q u a t i o n was u s e d , w i t h c r i t i c a l t e m p e r a t u r e s , c r i t i c a l p r e s s u r e s , and a c e n t r i c f a c t o r s o b t a i n e d f r o m D a u b e r t and D a n n e r (V4 ) , a n d R e i d e t a l . (J5_). For c a r b o n d i o x i d e , ω = 0.225; f o r l i m o n e n e , ω = 0.327, T = 656. 4 Κ, P = 2.75 MPa. I t was n e c e s s a r y t o v a r y the i n t e r a c t i o n parameter w i t h temperature i n order to c o r r e l a t e the data s a t i s f a c t o r i l y . The v a l u e s o f d-| 2 a r e 0.1135 a t 303 K, 0.1129 a t 308 Κ, and 0.1013 a t 313 K. Comparisons of c a l c u l a t e d and e x p e r i m e n t a l r e s u l t s a r e g i v e n i n F i g u r e s 4, 5, and 6. A t t e m p t s t o model the r e l a t i v e v o l a t i l i t i e s of the minor o r g a n i c c o n s t i t u e n t s t o limonene 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 proved u n f r u i t f u l . c

c

Proposed P r o c e s s L e m o n o i l can be c o n c e n t r a t e d by s u p e r c r i t i c a l c a r b o n d i o x i d e e x t r a c t i o n i n t h e t e m p e r a t u r e range o f 308 t o 313 K. Pressure i n t h e e x t r a c t o r w i l l be i n t h e range o f 7.7 t o 8.5 MPa. Solubilities of o i l i n the e x t r a c t or v a p o r p h a s e w i l l r a n g e f r o m 1 t o 3 wt%. S e l e c t i v i t y f a c t o r s n e a r 1.4 w i l l be o b t a i n e d f o r t h e terpene-oxy s p l i t and t h e o x y - s e s q u i t e r p e n e s p l i t . T h e o p e r a t i o n c a n be



COPPELLA AND BARTON


0.2

0.4

Solubility,

0.6

wt

1

2

4

7. oil in v a p o r

F i g u r e 7. Lemon O i l : Car bon D i o x i d e V a p o r - L i q u i d Δ - 303 K, • - 308 Κ, 0 - 313 Κ.

I

1

I

1

I 11

Equilibria

Γ

Ratio o f vapor p r e s s u r e s a t 392 Κ

0.1

0.2

0.4 0.6

1

2

Solubility, wt '/ oil in vapor F i g u r e 8. Lemon O i l : C a r b o n D i o x i d e V a p o r - L i q u i d Δ - 303 Κ, π - 308 Κ, 0 - 313 Κ.

Equilibria




212

performed i n a m u l t i s t a g e extractor with r e f l u x . O p e r a t i o n can be e i t h e r i n t h e b a t c h o r c o n t i n u o u s mode. Solvent recovery is p e r f o r m e d at c o n d i t i o n s s l i g h t l y below the c r i t i c a l p o i n t o f carbon dioxide. F l a s h e v a p o r a t i o n can be used; r e f l u x i n g i n an e n r i c h i n g c o l u m n can be a d d e d t o d e c r e a s e t h e o i l c o n t e n t i n the r e c y c l e d carbon d i o x i d e . R e s i d u a l carbon d i o x i d e i n the product o i l s is removed by f l a s h i n g t o a t m o s p h e r i c p r e s s u r e . S o l u b i l i t y limitations require that the s o l v e n t - t o - o i l feed r a t i o be h i g h ; an economic a n a l y s i s i s needed t o e s t a b l i s h p r o c e s s feasibility. The use of c o s o l v e n t s o r h i g h e r t e m p e r a t u r e s can be u s e d t o i n c r e a s e o i l s o l u b i l i t y and t o d e c r e a s e s o l v e n t - t o - o i l f e e d ratio. These p r o c e s s m o d i f i c a t i o n s , however, cause a d d i t i o n a l thermal degradation. W i t h c o s o l v e n t s , thermal degradation occurs d u r i n g the d i s t i l l a t i o n s t e p needed to remove t h e s e unwanted components (and f l a v o r s ) from the d e s i r e d e x t r a c t .

Literature Cited 1. 2. 3. 4. 5.

6. 7. 8.

9. 10. 11. 12. 13. 14. 15.

Paulaitis, Μ. Ε.; Krukonis, V. J.; Kurnik, R. T.; Reid, R. C. Reviews in Chemical Engineering 1983, 1, 179. Ely, J. F.; Baker, J. Κ. NBS Technical Note 1070 1983. Gerard, D. Chem. Ing. Tech. 1984, 56, 794. Stahl, E.; Quirin, K. W.; Glatz, Α.; Gerard, D.; Rau, G., BBPCAX 1984, 88, 900. Robey, R. J.; Sunder, S. "Application of Supercritical Processing to the Concentration of Citrus Oil Fractions", Annual Meeting of American Institute of Chemical Engineers, San Francisco, 1984. Peng, P. Y.; Robinson, D. B. I.E.C. Fund. 1976, 15, 59. Staroscik, J. Α.; Wilson, Α. Α., J. Agric. Food Chem. 1982, 30, 507, 835. Zeigler, E. "Production, Application and Analysis of Concentrates of Citrus Oils in the Food, Pharmacy, and Perfumery Industries"; VIII International Congress of Essential Oils, Cannes, 1980. Staroscik, J. Α., Sunkist Growers, Inc., Ontario, CA, personal communication, 1984. Coppella, S. J. M.S. Thesis, The Pennsylvania State University, University Park, PA, 1985. Im, U. Κ.; Kurata, F. J. Chem. Eng. Data 1971, 16, 412. Kulkarni, A. A.; Zarah, B. Y.; Luks, K. D.; Kohn, J. P. J. Chem. Eng. Data 1972, 19, 92. Gupta, M. Κ.; L i , Y. H.; Hulsey, B. J.; Robinson, R. L., Jr., J. Chem. Eng. Data 1982, 27, 55. Daubert, T. E.; Danner, R. P., Eds. "Technical Data Book Petroleum Refining", 4th ed.; American Petroleum Institute: Washington, DC, 1983. Reid, R. C.; Prausnitz, J. M.; Sherwood, T. K. "The Properties of Gases and Liquids", 3rd ed.; McGraw-Hill Book Co.: New York, 1977.

RECEIVED August 27, 1986


Supercritical Fluids - American Chemical Society

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