Supercritical Fluids - American Chemical Society

Chapter 15

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Supercritical Fluid Extraction and Chromatography of Nonpolar Nonvolatile Coal-Derived Products J. W. Jordan, R. J . Skelton, and L . T. Taylor Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, V A 24061

In recent years supercritical fluid chromatography has gained attention as an alternative technique to high performance liquid chromatography for the separation of nonvolatile or thermally labile compounds, whose analysis with gas chromatography is impossible. The work presented here demonstrates a system that allows supercritical fluid extraction of a high boiling coal-derived material with subsequent direct introduction of a fraction of each extract onto a packed column for analysis via supercritical fluid chromatography. Detection of the eluates included variable wavelength UV and FTIR spectrometry. The coal derived products studied were taken from a bench scale coal liquefaction reactor, in which the same catalyst was used for twenty-five consecutive days. Chemical changes that occur as the catalyst decays were of prime interest. Most significant changes were noted in the aromatic fraction analysis, where a trend towards molecules with higher numbers of condensed rings was observed as the catalyst decayed. I t was s u g g e s t e d i n the l a t e 5 0 ' s t h a t s u p e r c r i t i c a l f l u i d s c o u l d be used as m o b i l e p h a s e s . ( 1 ) S u p e r c r i t i c a l F l u i d Chromatography (SFC) was i n t r o d u c e d i n 1961 when K l e s p e r ( 2 ) d e m o n s t r a t e d the use of a s u p e r c r i t i c a l f l u i d as a m o b i l e p h a s e . These "dense g a s e s " or s u p e r c r i t i c a l f l u i d s have the a b i l i t y t o s o l u b i l i z e n o n v o l a t i l e compounds, and t h u s cause them to m i g r a t e down a column i n p a r t i t i o n chromatography. (_3) T h i s form of chromatography has s e v e r a l advantages t h a t stem from the p h y s i c a l p r o p e r t i e s t h a t are e x h i b i t e d by the m o b i l e phase. In g e n e r a l , d i f f u s i v i t i e s and v i s c o s i t i e s are i n t e r m e d i a t e between t h o s e of a l i q u i d and a g a s , a l l o w i n g more r a p i d a n a l y s i s when compared t o the analogous methods u s i n g a c o n v e n t i o n a l l i q u i d mobile phase. 0097-6156/87/0329-0189$06.00/0 © 1987 American Chemical Society

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

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Many of the same p r o p e r t i e s t h a t make s u p e r c r i t i c a l f l u i d s advantageous i n chromatography a l s o enhance t h e i r a b i l i t y t o e x t r a c t compounds from w i t h i n a sample m a t r i x . ( 4 ) A l s o , s i n c e the s o l u b i l i t y of most compounds i s dependent on the d e n s i t y of t h e supercritical f l u i d , selective extraction is possible.(5) These p r o p e r t i e s a r e w e l l known, and have been e x p l o i t e d i n some c a s e s where the e x t r a c t i o n was f o r m e r l y done w i t h a l i q u i d . In many c a s e s , the q u a l i t y o f e x t r a c t i s h i g h e r , and e x t r a c t i o n s a r e of h i g h e r e f f i c i e n c y than w i t h l i q u i d s . Supercritical fluids, e s p e c i a l l y C 0 , a r e a l s o o f t e n l e s s e x p e n s i v e , l e s s t o x i c and l e s s flammable than t h e i r o r g a n i c l i q u i d phase c o u n t e r p a r t s . 2

W i t h the d e m o n s t r a t i o n of s u p e r c r i t i c a l f l u i d e x t r a c t i o n , an o b v i o u s e x t e n s i o n would be t o e x t r a c t o r d i s s o l v e the compounds of i n t e r e s t i n t o the s u p e r c r i t i c a l f l u i d b e f o r e a n a l y s i s w i t h S F C . ( 6 ) T h i s would be a n a l o g o u s to the c a s e i n HPLC, where t h e m o b i l e phase s o l v e n t i s commonly used f o r d i s s o l v i n g the sample. The work d e s c r i b e d here w i l l employ a system c a p a b l e o f e x t r a c t i n g m a t e r i a l s w i t h a s u p e r c r i t i c a l f l u i d and i n t r o d u c i n g a known volume of t h i s e x t r a c t onto the column f o r a n a l y s i s v i a S F C . D e t e c t i o n of t h e s e p a r a t e d m a t e r i a l s w i l l be by o n - l i n e UV s p e c t r o s c o p y and i n f r a r e d spectrometry. The o p t i m i z e d S F E / S F C system has been used to study selected nonvolatile coal-derived products. The work r e p o r t e d here i n v o l v e d the a l i p h a t i c and a r o m a t i c h y d r o c a r b o n f r a c t i o n s from t h i s residuum m a t e r i a l . R e s i d u a at s e v e r a l times were taken from the r e a c t o r and examined which p r o v i d e d some i n s i g h t i n t o the e f f e c t s of c a t a l y s t decay on the p r o d u c t s p r o d u c e d i n a p i l o t p l a n t operation. Experimental The samples f o r s t u d y were o b t a i n e d from Conoco R e s e a r c h D i v i s i o n i n L i b r a r y , P A , as s o l i d m a t e r i a l s capped under n i t r o g e n g a s . These m a t e r i a l s which were s u b s e q u e n t l y s t o r e d at 5 ° C o r i g i n a t e d from a H y d r o c a r b o n R e s e a r c h I n s t i t u t e bench s c a l e r u n (#227-20) of the C a t a l y t i c Two-Stage L i q u e f a c t i o n process.(2) The s a m p l e s , which a r e d e s i g n a t e d " p r e s s u r e - f i l t e r l i q u i d s , " a r e t h e s o l i d s f r e e p o r t i o n of the major second s t a g e p r o d u c t s t h a t have been " t o p p e d " i n the a t m o s p h e r i c s t i l l , t h e n f i l t e r e d . The p r o c e s s u t i l i z e d a donor s o l v e n t d e r i v e d from p r e v i o u s r u n s and new c a t a l y s t m a t e r i a l . I l l i n o i s 6, B u r n i n g S t a r c o a l was u s e d . The p r o c e s s was r u n f o r 25 consecutive days, with operating c o n d i t i o n s held c o n s t a n t , except f o r the i n i t i a l s t a r t - u p p e r i o d ( i . e . days 1 - 3 ) . Since conditions were c o n s t a n t , any change i n the p r o d u c t s formed, s h o u l d be a f u n c t i o n of c a t a l y s t age. The f i l t e r e d p r o d u c t s were d i s t i l l e d by Conoco i n t o 2 f r a c t i o n s , t h o s e b o i l i n g under 8 5 0 ° F , and t h o s e above. ( A c t u a l f r a c t i o n a t i o n was a t 3 2 0 ° C P o t / 2 7 0 ° C Column/5 T o r r (850°F)). F u r t h e r d e t a i l s of the c o a l l i q u e f a c t i o n p r o c e s s a r e available elsewhere.(7,8) The m a t e r i a l s b o i l i n g above 8 5 0 ° F , were s u b s e q u e n t l y s e p a r a t e d i n t o f o u r f r a c t i o n s by a p r e p a r a t i v e s c a l e c h e m i c a l c l a s s s e p a r a t i o n i n our l a b o r a t o r y . T h i s was done as f o l l o w s : 2 gms of the r e s i d u a l m a t e r i a l were ground and d i s s o l v e d i n t e t r a h y d r o f u r a n (HPLC g r a d e , F i s h e r P r o d u c t s , F a i r l a w n N J ) . Ten grams of 30-40ym s i l i c a gel ("Sepralyte", Analytichem I n t . , Harbor C i t y , C A ) , which was p r e v i o u s l y washed w i t h methanol and d r i e d , was added t o the THF


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191

solution. T h i s s l u r r i e d m a t e r i a l was then r o t a r y e v a p o r a t e d t o dryness. The d r i e d s i l i c a g e l w i t h a d s o r b e d c o a l - d e r i v e d p r o d u c t was p l a c e d a t the t o p o f a g l a s s column which was p r e v i o u s l y s l u r r y - p a c k e d w i t h 40 gms of the same s i l i c a g e l u s i n g h e x a n e . A f i l t e r paper was used t o s e p a r a t e the l a y e r s . The g l a s s column had a d i a m e t e r which a l l o w e d the h e i g h t ( 4 . 5 " ) of the packed p o r t i o n of the column t o e q u a l 3 times i t s d i a m e t e r ( 1 . 5 " ) . The m a t e r i a l s were e l u t e d w i t h t h r e e column volumes each of hexane, t o l u e n e , c h l o r o f o r m and t e t r a h y d r o f u r a n ( c a . 300 mL e a c h ) . The hexane and t o l u e n e f r a c t i o n s were t a k e n t o be s t u d i e d h e r e . Three s e p a r a t i o n s of t h i s t y p e were d o n e , r e p r e s e n t i n g the 1 s t , 14th and 2 5 t h day of the r u n . These a r e samples l a b e l e d 4 4 , 57 and 6 8 , r e s p e c t i v e l y . The f r a c t i o n s were f i l t e r e d w i t h a 5 ym f i l t e r a p p a r a t u s ( M i l l i p o r e , B e d f o r d , MA) t o remove any s i l i c a o r i g i n a t i n g from the p r e p a r a t i v e s c a l e c o l u m n . The f r a c t i o n s were then r o t a r y e v a p o r a t e d t o near d r y n e s s i n t a r e d round bottom f l a s k s . These were s u b s e q u e n t l y d r i e d o v e r n i g h t i n a vacuum oven at 6 0 ° C and weighed. The hexane and t o l u e n e f r a c t i o n s were d i l u t e d t o 5 and 20 mL, r e s p e c t i v e l y , w i t h C C l . Both f r a c t i o n s were t o t a l l y s o l u b l e i n t h i s s o l v e n t as w e l l as i n THF. A n a l y s i s of t h e s e two f r a c t i o n s was p e r f o r m e d by s u p e r c r i t i c a l f l u i d e x t r a c t i o n / c h r o m a t o g r a p h y , u t i l i z i n g the s a m p l i n g p r o c e d u r e s previously described.(6) T h i s was done by e v a p o r a t i n g the s o l v e n t from t h e f r a c t i o n i n the p r e s e n c e o f d r y , washed, i g n i t e d sand which was then used to f i l l the e x t r a c t i o n a p p a r a t u s . Direct i n j e c t i o n of some samples (THF s o l u t i o n ) was a l s o done f o r comparison. E x p e r i m e n t s were c a r r i e d out u s i n g a H e w l e t t P a c k a r d 1082B L i q u i d Chromatograph m o d i f i e d f o r use w i t h s u p e r c r i t i c a l fluids. Columns u t i l i z e d i n c l u d e a H e w l e t t P a c k a r d 15cm χ 4.6mm i . d . C^g column w i t h 5ym p a c k i n g and a Dupont 25cm χ 4.6mm i . d . NH^ column, a l s o w i t h 5ym p a c k i n g . Pure CO^ was used as the m o b i l e phase ( S c o t t S p e c i a l t y G a s e s , P l u m s t e a d s v i l l e , P A ) . A l l on-line e x t r a c t i o n / c h r o m a t o g r a m s u t i l i z e d a 100yL l o o p s i z e . Traditional s a m p l i n g u t i l i z e d a 10yL s y r i n g e and 20yL l o o p . 4

A l l e x p e r i m e n t s u t i l i z e d a v a r i a b l e wavelength UV d e t e c t o r . A n a l y s i s o f the hexane f r a c t i o n was c a r r i e d o u t u s i n g b o t h the UV d e t e c t o r and an o n - l i n e N i c o l e t 6000 F T I R . The FTIR f l o w c e l l i n t e r f a c e has been d e s c r i b e d i n d e t a i l e l s e w h e r e . ( 9 ) T h i s same FTIR was a l s o used t o g a t h e r s t a t i c s p e c t r a on the v a r i o u s f r a c t i o n s , u t i l i z i n g a l i q u i d c e l l w i t h KBr windows. R e s u l t s and D i s c u s s i o n T a b l e I shows the r e s u l t s of the c l a s s s e p a r a t i o n of residuum w i t h a b s o l u t e and p e r c e n t r e c o v e r y f o r each of the f o u r f r a c t i o n s f o r day 1, 14 and 25. In g e n e r a l , the c o n c e n t r a t i o n of the l e s s p o l a r (hexane and t o l u e n e ) f r a c t i o n s d e c r e a s e d o r remained c o n s t a n t w i t h t i m e ; w h i l e , the more p o l a r (CHCl^ and THF) f r a c t i o n s i n c r e a s e d i n percentage. T h i s i s b e s t n o t e d from d a t a f o r days 14 and 2 5 . Data from day 1 a r e somewhat v a r i a n t from t h i s t r e n d . This is probably due to the i n c o n s i s t e n c y i n o p e r a t i n g c o n d i t i o n s t h a t o c c u r r e d d u r i n g the s t a r t - u p p e r i o d . Such a s s u m p t i o n s s h o u l d be viewed c a u t i o u s l y s i n c e t h e p e r c e n t weight r e c o v e r y from day 14 and 25 i s not c o n s t a n t .


192

SUPERCRITICAL FLUIDS The hexane f r a c t i o n s from r u n s 44 and 68 have i d e n t i c a l

tral

spec

i n CCI .

These show a l i p h a t i c C-H (CH- sym s t r = 2872 cm \ -1 -1 -1 asym = 2962 cm ; C H sym s t r * 2853 cm , asym = 2926 cm ) and 2 -± -ι -1 b e n d i n g modes (1470 cm - 1350 cm ) as w e l l as a band at 1600 cm 0

which may be an a r o m a t i c r i n g v i b r a t i o n .

T a b l e I.

No o t h e r

functionalities

R e s u l t s of Residuum C l a s s S e p a r a t i o n *

Fraction

R e s i d 44 (Day 1)

R e s i d 57 (Day 14)

R e s i d 68 (Day 25)

Hexane

0.075 gms. (3.8%)*

0.185 gms. (9.4%)

0.037 gms. (2.1%)

Toluene

1.071 gms. (54.2%)

0.939 gms. (48.0%)

0.857 gms. (48.4%)

CHC1

0.085 gms. (4.3%)

0.082 gms. (4.0%)

0.103 gms. (5.8%)

THF

0.743 gms. (37.6%)

0.755 gms. (38.5%)

0.7 76 gms. (43.8%)

Total Weight Recovered

1.974 gms.

1.958 gms.

1.772 gms.

% Sample Recovered

(98.7%)

(97.8%)

(88.5%)

•Number i n p a r e n t h e s i s e q u a l s p e r c e n t o f r e c o v e r e d m a t e r i a l .

a r e p r e s e n t which c a n be d e t e c t e d . In b o t h c a s e s , t h e amount of CH^ s t r e t c h i n g i s much g r e a t e r than C H s t r e t c h i n g . This indicates that the a l i p h a t i c u n i t s a r e e i t h e r l o n g i n l e n g t h o r a r e i n t h e form of saturated r i n g s . 1

3

The t o l u e n e f r a c t i o n s from d i f f e r e n t t o each o t h e r .

A g a i n , by f a r t h e

days a r e a l s o v e r y

similar

most i n t e n s e modes of absorbance

a r e a l i p h a t i c C-H s t r e t c h i n g and b e n d i n g , however a g r e a t d e a l of a r o m a t i c C-H s t r e t c h i n g between 3000 cm

1

and 3100 cm

1

also exists.

There i s a l s o a v e r y s m a l l amount of a b s o r b a n c e i n the N~H s t r e t c h ing

1

(3740 cm )

and 0-H s t r e t c h i n g

(3610 cm

1

last

two f r a c t i o n s .

1

and 3550 cm )

In g e n e r a l , compounds w i t h t h e s e f u n c t i o n a l i t i e s

regions.

s h o u l d e l u t e i n the

However, v e r y h i n d e r e d f u n c t i o n a l i t i e s


often

JORDAN ET AL.

15.

e l u t e i n the a r o m a t i c f r a c t i o n , i n t h e s e r e g i o n s a r e due CH

2

C-H

than CH^

193

Extraction & Chromatography of Coal-Derived Products

absorbance.

i n sample 68

(day 25)

and

i t i s probable

to these molecules. There

that

absorbances

A g a i n , t h e r e i s more

i s a l s o some i n c r e a s e i n a r o m a t i c

when compared t o sample 44

(day 1 ) .

F u r t h e r s e p a r a t i o n of t h e s e m a t e r i a l s i s needed f o r a b e t t e r u n d e r s t a n d i n g of t h e i r c o m p o s i t i o n . SFC o f Hexane F r a c t i o n s . hexane f r a c t i o n s were a n a l y z e d w i t h an a m i n o - p r o p y l silica

column under moderate d e n s i t y C 0

investigated

2

conditions.

i n c l u d e d cyano, p h e n y l , and C

The

derivatized Other

derivatized

columns

silica.

-LO

No m o d i f i e r s were used

i n any o f t h e s e s e p a r a t i o n s .

the chromatograms a c h i e v e d f o r sample 57 chromatogram was

produced

by m o n i t o r i n g 254

chromatogram by m o n i t o r i n g 280 employed, but no absorbances more i n t e n s e i n a l l c a s e s ( e a r l y peaks d e c r e a s e

(Day

nm.

nm

and

the top

the bottom

D e t e c t i o n at 210

were s e e n .

F i g u r e 1 shows

14) wherein

nm

was

also

L a t e r e l u t i n g peaks a r e

than the e a r l y peaks at 280

nm d e t e c t i o n

i n i n t e n s i t y w h i l e l a t e r peaks a b s o r b more

i n t e n s e l y f o r the same amount i n j e c t e d ) .

T h i s would i n d i c a t e

that

t h e l a t e r e l u t i n g m a t e r i a l s p r o b a b l y have more e x t e n s i v e c o n j u g a t i o n , and

represent molecules

however, v e r y l i t t l e

a r o m a t i c C-H

like

the PAHs.

stretching

There i s ,

i n the s t a t i c

infrared

s p e c t r a of t h e whole f r a c t i o n , a l t h o u g h t h e r e i s the band c e n t e r e d at approximately vibration.

The

explained i f :

1600

cm

which i s a s s o c i a t e d w i t h a r o m a t i c

absence of C-H

(a) t h e r e i s a c o n s i d e r a b l e number of

s u b s t i t u e n t s on the a r o m a t i c n u c l e i or n u c l e u s o r s a t u r a t e d r i n g s a r e f u s e d t o an a r o m a t i c n u c l e u s . number of a l i p h a t i c solubility

ring

a r o m a t i c s t r e t c h i n g c o u l d be

s u b s t i t u e n t s may

aliphatic

(b) many An e x t e n s i v e

have caused i n c r e a s e d

i n hexane, which e n a b l e d t h e s e m a t e r i a l s t o e l u t e

the

from

silica. To g a i n f u r t h e r i n f o r m a t i o n c o n c e r n i n g the hexane f r a c t i o n s , o n - l i n e s u p e r c r i t i c a l f l u i d e x t r a c t i o n / S F C was c o u p l e d w i t h o n - l i n e FTIR d e t e c t i o n . FTIR s h o u l d have an advantage i n t h a t i t i s more s e n s i t i v e t o a l i p h a t i c hydrocarbons than the UV d e t e c t o r . B a s i c a l l y , a f l o w c e l l i s p l a c e d i n the FTIR i n s t r u m e n t and i n f r a r e d s p e c t r a a r e g a t h e r e d i n t h e form of i n t e r f e r o g r a m s c a . e v e r y 0.5 second. The d a t a o b t a i n e d can be used t o c r e a t e a chromatogram, u t i l i z i n g absorbance o v e r the e n t i r e i n f r a r e d spectrum, r a t h e r than a s i n g l e w a v e l e n g t h . T h i s a n a l y s i s was done on samples 44 and 68 ( 1 s t and 25th d a y ) . F i g u r e 2 shows one of t h e s e "chromatograms" (day 25), known as Gram-Schmidt R e c o n s t r u c t i o n s (GSR). One major peak i s seen, which, when compared w i t h the UV c h r o m a t o g r a p h i c t r a c e o b t a i n e d s i m u l t a n e o u s l y , shows maximum IR absorbance w e l l b e f o r e any absorbance i n the UV. A spectrum c o n s i s t i n g of 8 coadded f i l e s taken near the peak maximum r e v e a l s t h a t the o n - l i n e spectrum i s almost e x a c t l y the same as the s t a t i c spectrum of the whole jample. The e x c e p t i o n i s t h e d i s a p p e a r a n c e of the band a t 1600 cm i n the f i l e spectrum. T h i s o b s e r v a t i o n a l o n g w i t h the l a c k o f UV r e s p o n s e i n t h i s e l u t i o n


194


0

1

4

·

·

10

M

14

η

Ι·

90

TIME. MINUTES

F i g u r e 1. SFC s e p a r a t i o n (3 mL/min) o f hexane f r a c t i o n Day 14 (Sample 57) on an a m i n o p r o p y l d e r i v a t i z e d 5 ym s i l i c a column (25 cm χ 4.6 mm, i . d . ) a t 4 0 ° C . M o b i l e phase i s C 0 a t an average p r e s s u r e of 2800 p s i . Top t r a c e c o r r e s p o n d s t o d e t e c t i o n a t 254 nm; bottom t r a c e - 280 nm. 2

Data P o i n t s F i g u r e 2. Gram-Schmidt R e c o n s t r u c t i o n o b t a i n e d from S F E / S F C / F T I R of hexane f r a c t i o n o f Day 25 s a m p l e .


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volume i n d i c a t e s t h a t t h e s e components a r e t o t a l l y a l i p h a t i c i n n a t u r e ; whereas, t h e l a t e r e l u t i n g m a t e r i a l s a r e a r o m a t i c and a r e of i n s u f f i c i e n t c o n c e n t r a t i o n t o be d e t e c t e d by o n - l i n e FTIR detection. A l t h o u g h o n l y one peak i s i n d i c a t e d by the GSR, a c o m p a r i s o n of s p e c t r a o b t a i n e d from the f r o n t of the peak w i t h t h o s e which e l u t e i n the l a t e r h a l f of the peak can be made. When t h i s t e c h n i q u e was a p p l i e d to t h e s e d a t a , i t was found t h a t c e r t a i n changes i n the s p e c t r a were o b s e r v e d . F i g u r e 3 shows the f i r s t 6 s p e c t r a i n the C-H s t r e t c h i n g r e g i o n o b t a i n e d o v e r t h e major peak i n the GSR. Each of t h e s e s p e c t r a r e p r e s e n t 8 coadded f i l e s , r e s u l t i n g i n a time r e s o l u t i o n of about 4 seconds per f i l e . I n f r a r e d s p e c t r a taken from the f r o n t of the peak show the l o w e s t m e t h y l t o methylene r a t i o . As each subsequent f i l e i s r a t i o e d to keep the methylene peak c o n s t a n t , the a b s o r b a n c e s due t o m e t h y l s i n c r e a s e o v e r the w i d t h of the p e a k . Subsequent f i l e s show a l e v e l i n g of t h i s r a t i o . u n f o r t u n a t e l y , a n a l y s i s of the 1 s t and 25th day samples d i d n o t r e v e a l any s i g n i f i c a n t t r e n d s i n the p r o d u c t s . However, i t i s p o s s i b l e t h a t the r e l a t i v e amount of each component p r o d u c e d i s e q u i v a l e n t , but t h a t the t o t a l p r o d u c t i o n s u f f e r s as the c a t a l y s t becomes l e s s e f f e c t i v e . SFC o f T o l u e n e F r a c t i o n s To a i d i n u n d e r s t a n d i n g the components i n the t o l u e n e f r a c t i o n , a l i m i t e d SFC s t u d y of model c o n d e n s e d - r i n g a r o m a t i c systems was performed. Because few f u n c t i o n a l i t i e s a r e IR d e t e c t a b l e i n t h i s f r a c t i o n o t h e r than C-H u n i t s , the t o l u e n e e l u t e d f r a c t i o n of the residuum p r o b a b l y c o n s i s t s p r i m a r i l y of a r o m a t i c r i n g s w i t h s h o r t a l i p h a t i c s u b s t i t u e n t s and/or fused saturated r i n g s . Because of the d i s t i l l a t i o n parameters e m p l o y e d , compounds w i t h 4 o r fewer f u s e d r i n g s s h o u l d have been removed. The t o l u e n e f r a c t i o n s h o u l d , t h e r e f o r e , r e p r e s e n t compounds w i t h a t l e a s t 5 r i n g s . Figure 4 shows a s e p a r a t i o n of s e v e r a l PAH compounds on a 15cm ODS column with a C 0 mobile phase. A l l compounds w i t h t h r e e or g r e a t e r r i n g s are separated to b a s e l i n e r e s o l u t i o n . R e l a t i v e l y high density C0 and a h i g h f l o w r a t e were used to e l u t e l a r g e m o l e c u l e s f a s t e r . These compounds e l u t e l o g a r i t h m i c a l l y w i t h i n c r e a s i n g r i n g numbers which i s e x p e c t e d f o r a homologous s e r i e s w i t h i s o c r a t i c e l u t i o n . 2

2

The t o l u e n e f r a c t i o n s of the residuum samples were s u b j e c t e d t o the same a n a l y s i s c o n d i t i o n s as the PAH model compounds. The chromatogram c o r r e s p o n d i n g t o Day 14 i s shown i n F i g u r e 5. T r a d i t i o n a l o f f - l i n e s a m p l i n g (top) and an o n - l i n e C O . e x t r a c t i o n (bottom) were e m p l o y e d . D e t e c t i o n at 300 nm wavelength was used t o emphasize the l a r g e r PAHs which were e x p e c t e d t o be p r e s e n t . This wavelength was chosen f o r the c h r o m a t o g r a p h i c p r e s e n t a t i o n h e r e ; however, d u r i n g d e v e l o p m e n t , o t h e r wavelengths were u s e d . A t 254 nm, f o r example, the e a r l y e l u t i n g peaks a b s o r b i n t e n s e l y , i n d i c a t i n g t h a t n o n c o n j u g a t e d systems a r e a l s o p r e s e n t . Several i n t e r e s t i n g f e a t u r e s are seen i n t h e s e chromatograms. The l a t e r e l u t i n g peaks become more i n t e n s e at l a t e r r u n - d a y s . T h i s i s most r e a d i l y n o t e d i n the second g r o u p i n g o f peaks i n each chromatogram. The t h i r d g r o u p i n g of p e a k s , which e l u t e where coronene e l u t e s , a r e



196

WAVENUMBERS F i g u r e 3. S t a c k p l o t of C-H s t r e t c h r e g i o n f o r the 7 f i l e s (Nos. 30-36) t a k e n a c r o s s the major GSR peak i n F i g u r e 2.


JORDAN ET AL.


0 1

2

3

4

5

6

7

8

1

9

TIME. MINUTES F i g u r e 4. S e p a r a t i o n of some PAH compounds: ODS column (5 μ ι η ) , pressure: 4200 i n l e t , 3700 o u t l e t . Mobile phase: C 0 a t 3.7 mL/min. Detection: 300 nm, 500 nm r e f e r e n c e . Column: 15cm χ 4.6 mm ODS. 2


198


TIME. MINUTES F i g u r e 5. SFC s e p a r a t i o n (2 mL/min) of t o l u e n e f r a c t i o n o f r e s i d u u m Day 14 comparing o n - l i n e (bottom) and t r a d i t i o n a l (top) s a m p l i n g methods. ODS (5 ym) column (15 cm χ 4 . 6 mm, i . d . ) , 4 0 ° C , C 0 (3800 p s i ) , 300 nm. 2

Ο

Ϊ

2

5

4

S

t

7

·ft' it 12

M

Μ

•

»

22

24

26

T I M E , MINUTES Figure 6. SFC s e p a r a t i o n a f t e r SFE o f t o l u e n e f r a c t i o n o f residuum Day 25 (Sample 6 8 ) : N H column (5 ym, 25 cm χ 4 . 6 mm, i . d . ) , 2 m L / m i n , 4 0 ° C , CO (3200 p s i ) , 300 nm. 2


15. JORDAN ET AL.


199

p r o b a b l y s i x - r i n g compounds. A b r o a d l a t e e l u t i n g peak ( c a . 15 minutes) i s p r o b a b l y a s e v e n - r i n g compound. R e t e n t i o n time f o r t h i s component f i t s t o the p r e v i o u s l y a l l u d e d l o g a r i t h m i c p l o t v e r y well. The second group o f p e a k s , which e l u t e s b e f o r e the s i x - r i n g compounds a r e p o s s i b l y f i v e - r i n g compounds whose r i n g s are o r i e n t e d i n a " s t r e t c h e d " o r i e n t a t i o n , or the e l u t e d m a t e r i a l may be components which c o n t a i n f i v e a r o m a t i c r i n g s and one p a r t i a l l y hydrogenated r i n g . Other d e t e c t o r s , such as d i o d e a r r a y UV and f l u o r e s c e n c e d e t e c t o r s may y i e l d more s e l e c t i v e i n f o r m a t i o n about these s t r u c t u r e s . The i n c r e a s e i n a p p a r e n t c o n c e n t r a t i o n of the l a r g e r a r o m a t i c s as a f u n c t i o n o f time i s p r o b a b l y a d i r e c t r e s u l t of c a t a l y s t fouling. The new c a t a l y s t demonstrated the g r e a t e s t a b i l i t y t o h y d r o g e n a t e t h e fragments formed by t h e r m o l y s i s ; however, t h i s p r o c e s s p r o b a b l y becomes l e s s e f f i c i e n t w i t h t i m e , a l l o w i n g f o r r e f o r m a t i o n o f C - C bonds which r e s u l t s i n h i g h e r a r o m a t i c i t i e s and l a r g e r PAH compounds. The chromatograms g e n e r a t e d w i t h the C column were s p e c i f i c a l l y used t o determine r i n g s i z e . These columns do not show a h i g h d e g r e e of r e s o l u t i o n . An a m i n o p r o p y l column was used a t a somewhat lower d e n s i t y t o s p r e a d the peaks of the t o l u e n e f r a c t i o n out o v e r a l a r g e r p e r i o d of t i m e . Other workers have shown t h i s m a t e r i a l t o s e p a r a t e compounds i n the o r d e r of r i n g number a l s o . F i g u r e 6 shows the chromatogram a c h i e v e d w i t h the f r a c t i o n from Day 25. T h i s was o b t a i n e d w i t h UV 254nm d e t e c t i o n , r a t h e r than 300nm, as l a r g e a r o m a t i c s w i l l not e l u t e i n a r e a s o n a b l e amount of time under t h e s e c o n d i t i o n s . There a r e s t i l l many u n r e s o l v e d p e a k s , which a l l u d e s to the extreme c o m p l e x i t y of the s a m p l e . L a r g e a r o m a t i c m o l e c u l e s have many i s o m e r s , and e x c e l l e n t r e s o l u t i o n of t h e s e w i t h a packed column may be impossible. The o n - l i n e e x t r a c t i o n t e c h n i q u e does not p e r f o r m as w e l l as t r a d i t i o n a l methods f o r the t o l u e n e f r a c t i o n i n c o n t r a s t t o the hexane f r a c t i o n . The l a t e r e l u t i n g peaks are much more i n t e n s e f o r the t r a d i t i o n a l s a m p l i n g i n a l l c a s e s . I t seems t h a t CO f a v o r s t h e lower m o l e c u l a r w e i g h t m o l e c u l e s , even a t h i g h d e n s i t i e s . On l i n e FTIR d e t e c t i o n d i d not y i e l d any new i n f o r m a t i o n f o r the aromatic f r a c t i o n s . H i g h l y a r o m a t i c m a t e r i a l does not a b s o r b infrared radiation greatly. In c o n t r a s t , UV d e t e c t o r s a r e q u i t e s e n s i t i v e and y i e l d s i g n i f i c a n t i n f o r m a t i o n f o r a r o m a t i c compounds. Acknowledgment The f i n a n c i a l a s s i s t a n c e of the Commonwealth of V i r g i n i a Department o f E n e r g y G r a n t DE-FG22-84PC70799 i s g r e a t l y appreciated.

and


200


Literature Cited 1. 2. 3. 4. 5. 6. 7.

8. 9.

Ν. M. Karayannis, Rev. Anal. Chem., 1971, 1, 43. Ε. Klesper, A. H. Corwin, D. A. Turner, J. Org. Chem., 1962, 27, 700. D. R. Gere, Science, 1983, 222, 253. C. Grimmet, Chem. Ind., 1981, 6, 359. E. Stahl, K. W. Quirin, A. Glatz, D. Gerard, G. Rau, Ber. Bunsenges Phys. Chem., 1984, 8, 900. R. J. Skelton, L. T. Taylor, Chromatographia, 1986, 21, 3. A. G. Conolli, J. B. MacArthur, J. B. McLean, "HRI's Two Stage Catalytic Coal Liquefaction Program - A Status Report", presented at the 1984 DOE Direct Liquefaction Contractors' Review Meeting, Albuquerque, NM, October 1984. F. P. Burke, R. A. Winschel, "Recycle Slurry Oil Characterization - Second Annual Report", DOE Contract No. DEAC22-80PC30027, August, 1983. J. W. Jordan, C. C. Johnson and L. T. Taylor, Chromatographia, 1985, 20, 717.

Received July 1, 1986


Supercritical Fluids - American Chemical Society

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