Group Isolation of Nickel and Vanadyl Porphyrins from Crude Oil

Chapter 26

Group Isolation of Nickel and Vanadyl Porphyrins from Crude Oil Using Macroporous Silica Gel 1

1

2,3

2

David H. Freeman , Rosalie M. Angeles , Katherine H. Freeman , Thomas C. Hoering , Joseph S. Flynn , Tracie A. Lango1, and C. T. Homonay-Preyer 1,4

1

1

Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742 Geophysical Laboratory, Carnegie Institution of Washington, 2801 Upton Street, Washington, DC 20008 Department of Geology, Wellesley College, Wellesley, MA 02181 U.S. Naval Academy, Annapolis, MD 21412

Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: July 6, 1987 | doi: 10.1021/bk-1987-0344.ch026

2

3

4

An efficient, ten-fold concentration of combined nickel and vanadyl porphyrins in crude o i l is obtained by liquid column chromatography with disposable, macroporous silica gel. The concentrate contains the biomarker metalloporphyrins based on chromatographic and spectral comparisons with etioporphyrin-I standard compounds. The concentrate is free of asphaltene materials that would otherwise cause major chromatographic interference. The procedure, in brief, begins with one gram of crude oil sorbed on top of a column containing 5 grams of 5 0 0 Åpore size s i l i c a gel. The initial elution is with petroleum ether:methylene chloride (97v:3v) to remove saturated and aromatic hydrocarbons. The metalloporphyrins are eluted next with methyl acetate while the remaining asphaltene components are immobilized. In a second step, 100Å silica gel is used to further separate the metalloporphyrins. The method is rapid, simple and reproducible. It is applicable to processing large numbers of samples and i t is economical in its use of solvent and adsorbent. Details on the considerable effort expended on this method development are given. 0097-6156/87/0344-0402$06.25/0 © 1987 American Chemical Society

In Metal Complexes in Fossil Fuels; Filby, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


26.

FREEMAN ET AL.

Group Isolation of Nickel and Vanadyl Porphyrins

403

M u l t i - s t e p s e p a r a t i o n and p u r i f i c a t i o n p r o c e d u r e s a r e needed t o i s o l a t e m e t a l l o p o r p h y r i n pigments from g e o l o g i c a l samples. The many r e p o r t e d p r o c e d u r e s v a r y f r o m m i n i m a l m e t h o d o l o g y p r e c e d i n g mass s p e c t r o m e t r y (1) t o l e n g t h y i s o l a t i o n s o f i n d i v i d u a l compounds f o r X - r a y c r y s t a l l o g r a p h y (2.) , c o m b i n e d m a s s s p e c t r o m e t r i c a n d NMR a n a l y s i s Q ) a n d h i g h r e s o l u t i o n HPLC a n d mass spectrometry (4.) . The g o a l o f t h e p r e s e n t s t u d y i s t o d e v e l o p a r u g g e d and r o b u s t method f o r g r o u p s e p a r a t i o n o f t r a c e s of metalloporphyrins. This includes r e l i a b i l i t y and m i n i m a l m o d i f i c a t i o n when a p p l i e d t o a w i d e r a n g e o f samples. I s o l a t i o n from a g e o l o g i c a l matrix i n v o l v e s d e a l i n g w i t h u n c e r t a i n numbers o f p o r p h y r i n homologues and i s o m e r s , and unbounded numbers o f o t h e r compounds that are a l s o present. Trace enrichment with high r e c o v e r y and m i n i m a l i n t e r f e r e n c e i s needed t o a s s u r e q u a l i t a t i v e and q u a n t i t a t i v e a c c u r a c y (5-7). O p t i m i z a t i o n o f a m u l t i - s t e p s e p a r a t i o n s scheme r e q u i r e s an e x p e r i m e n t a l a p p r o a c h , b u t n o t e x c l u s i v e l y . A proper choice of l i q u i d chromatographic v a r i a b l e s i s e s s e n t i a l , a t l e a s t i n a p r a c t i c a l sense (&). Many s i n g l e step o p t i m i z a t i o n c r i t e r i a are a v a i l a b l e Q ) a l t h o u g h m i x t u r e s c o n t a i n i n g unbounded numbers o f compounds a r e t h e most d i f f i c u l t . Solvent and a d s o r p t i v e r o u t e s t o c h e m i c a l s e l e c t i v i t y have become more a c c e s s i b l e and f a s t e r ( 1 0 ) . In d e a l i n g w i t h h i g h l y c o m p l e x m i x t u r e s , t h e f i r s t s t e p may b e t h e m o s t d i f f i c u l t t o work o u t , and t h e most i m p o r t a n t . E x t e n s i v e e x p e r i m e n t a t i o n was n e e d e d t o a c h i e v e t h e present g o a l , d e t a i l s of which are given below. First, i t was d e m o n s t r a t e d t h a t a m u l t i m o d a l liquid c h r o m a t o g r a p h i c procedure, u s i n g s i l i c a g e l , Sephadex L H - 2 0 a n d C-18 b o n d e d p h a s e a s s u b s t r a t e s c o u l d make t h e desired separation. Thin l a y e r chromatography proved to be a v a l i d m e t h o d f o r r a p i d m e t a l l o p o r p h y r i n s c o u t i n g . Many s o l v e n t s y s t e m s w e r e t r i e d b e f o r e a b a s i s f o r i m p r o v e d e l u a n t c o m p o s i t i o n was f o u n d . Column t e s t i n g s h o w e d t h a t c r u d e o i l f r a c t i o n a t i o n on n a r r o w p o r e s i l i c a gel i s not a p p r o p r i a t e i n the f i r s t step. An o p t i m u m e l u e n t s e q u e n c e was f o u n d o n t h e b a s i s o f t w o d i m e n s i o n a l TLC s c o u t i n g e x p e r i m e n t s . The b r e a k t h r o u g h came w h e n i t was o b s e r v e d t h a t c o n v e n t i o n a l s i l i c a g e l d i d not p r o v i d e the needed r e t e n t i v e c a p a c i t y for the dark asphaltene f r a c t i o n that s e r i o u s l y i n t e r f e r e s w i t h c h r o m a t o g r a p h i c s e p a r a t i o n and a n a l y s i s . A c r i t i c a l t e s t i n g of s i l i c a g e l p o r o s i t y lead to the use o f macroporous s i l i c a g e l . A d u a l o p t i m i z a t i o n o f s o l v e n t a n d a d s o r b e n t was t h u s o b t a i n e d a n d t h e s e p a r a t i o n g o a l was reached. r

Experimental

T e s t o f M u l t i - M o d a l LPLC. The u s e o f n o n - r e d u n d a n t s o r p t i v e modes i s known t o be t h e o r e t i c a l l y w e l l - s u i t e d



404

METAL COMPLEXES IN FOSSIL FUELS

f o r i s o l a t i n g compounds f r o m e x t r e m e l y c o m p l e x m i x t u r e s (10) s u c h a s c r u d e o i l s . A f e a s i b i l i t y s t u d y w a s made u s i n g l o w p r e s s u r e l i q u i d c h r o m a t o g r a p h y (LPLC) t o concentrate themetalloporphyrins, s p e c i f i c a l l y the predominant n i c k e l p o r p h y r i n (NiP)group i n t h e Messel S h a l e o f Germany ( J J J . F r e s h l y p u l v e r i z e d s a m p l e s o f t h e s h a l e were e x t r a c t e d w i t h benzene a n d m e t h a n o l (1:1 volume/volume) s o l u t i o n . One g r a m o f t h e o r g a n i c e x t r a c t remained a f t e r r o t a r y evaporation. The e x t r a c t was (A) e l u t e d s u c c e s s i v e l y w i t h h e x a n e a n d b e n z e n e f r o m a 60cm b y 5 cm p r e p a r a t i v e c h r o m a t o g r a p h i c c o l u m n o f s i l i c a g e l (Grade 62, D a v i s o n C h e m i c a l Co., B a l t i m o r e , MD). C o l l e c t i o n o f t h e r e d p o r p h y r i n band i n t h e b e n z e n e e l u a t e was e s t i m a t e d v i s u a l l y . T h e n , (B) s i m i l a r p r e p a r a t i v e c h r o m a t o g r a p h y w i t h S e p h a d e x LH-20 gel i n 1:1 b e n z e n e a n d m e t h a n o l s o l u t i o n w a s c a r r i e d o u t on t h e c o n c e n t r a t e f r o m s t e p ( A ) . T h e s e t w o s t e p s a r e b a s e d o n p r o c e d u r e s d e s c r i b e d b y B a k e r (12.) · H P L C a p p a r a t u s w a s t h e n u s e d w i t h (C) C-18 b o n d e d phase, Sep-Pak c a r t r i d g e s used as s h o r t , d i s p o s a b l e c h r o m a t o g r a p h i c columns (Waters A s s o c i a t e s , Framingham, MA). A l i n e a r g r a d i e n t was u s e d f r o m 1:1 a c e t o n i t r i l e (MeCN) a n d w a t e r t o p u r e MeCN. The m e t a l l o p o r p h y r i n c o n c e n t r a t e w a s c h r o m a t o g r a p h e d i n a s i m i l a r w a y (D) o n Sep-Pak s i l i c a g e l u s i n g a l i n e a r g r a d i e n t o f hexane t o benzene. The c a r t r i d g e s u s e d i n C a n d D were c o n f i n e d to a t i g h t - f i t t i n g metal holder and t h e i n s e r t i o n o f machined e n d f i t t i n g s reduced t h e dead volume. I n d e p e n d e n t t e s t s showed a t 1 ml/min f l o w r a t e t h a t c o l u m n e f f i c i e n c i e s o f c a . 40 t h e o r e t i c a l p l a t e s c o u l d be a c h i e v e d . The Sep-Pak columns b u r s t o c c a s i o n a l l y , p e r h a p s due t o m i g r a t e d p a r t i c l e s t h a t p l u g g e d t h e e n d frit . E n r i c h m e n t o f t h e N i P g r o u p was m o n i t o r e d b y v i s i b l e absorption spectrophorometry a f t e r each step and i s d e m o n s t r a t e d i n F i g u r e 1 w h e r e i n t h e S o r e t B-band a t 408 nm e m e r g e s f r o m t h e UV a b s o r b i n g b a c k g r o u n d . D e f i n i t i v e , s i n g l e peak i s o l a t i o n o f t h e m e t a l l o p o r p h y r i n s , s h o w n i n F i g u r e 2, w e r e o b t a i n e d b y m o n i t o r i n g t h e e f f l u e n t a t 550nm i n a f l o w spectrophotometer. It i sconcluded that t h euse o f short disposable column c h r o m a t o g r a p h y i n s t e p s C a n d D (See F i g u r e s 1 a n d 2) i s i n d e e d a p p l i c a b l e t o t h e p r o b l e m , g i v e n t h a t the b u l k o f t h e sample m a t r i x , t h e non-analyte group, h a s b e e n p r e v i o u s l y r e m o v e d b y s t e p s A a n d B. T h e A a n d Β s t e p s were c o s t l y i n terms o f t i m e , s o r b e n t a n d carrier liquid. This experiment defined t h e o v e r a l l goal: t o streamline t h e i n i t i a l clean-up procedure and produce a metalloporphyrin concentrate that i s s u i t a b l e for high r e s o l u t i o n chromatographic separation. P r e l i m i n a r y Test o f LP-LSC. S i l i c a g e l i sa versatile and i n e x p e n s i v e a d s o r b e n t t h a t i s a t t r a c t i v e f o r p o t e n t i a l use i n t h e clean-up procedure sought i n t h i s



405


26. FREEMAN ET AL.

350

650 Wavelength

(nm)

F i g u r e 1. Nickel petroporphyrins (NiP) e x t r a c t e d from the M e s s e l s h a l e a r e m o n i t o r e d by s p e c t r o p h o t o m e t r y as they are c o n c e n t r a t e d i n f o u r - s t e p p r e p a r a t i v e column chromatography: e l u t i o n w i t h (A) b e n z e n e o n s i l i c a , a n d (B) b e n z e n e - m e t h a n o l o n L H - 2 0 , (C) w a t e r - M e C N gradient o n S e p - P a k C - 1 8 , a n d (D) h e x a n e - b e n z e n e g r a d i e n t o n S e p Pak s i l i c a .



406


Elution Time (Min)

F i g u r e 2. The C-18 Sep-Pak column, s t e p C o f F i g u r e 1, i s shown w i t h a l i n e a r g r a d i e n t a t l m l / m i n f r o m 1:1 MeCN-water t o p u r e MeCN (10 min) w i t h N i P e l u t i o n a t 20 min. S i m i l a r l y , i n s t e p D a s i l i c a Sep-Pak column, e l u t i o n g r a d i e n t from p u r e hexane t o 1:2 hexane:benzene (9 m i n ) , i s shown. The N i P peak e l u t e s a t 13 min. The f e a s i b i l i t y o f s h o r t column c l e a n - u p p r o c e d u r e s i s demonstrated.



26. FREEMAN ET AL.


work. P r e l i m i n a r y column t e s t s were p e r f o r m e d w i t h s i l i c a g e l i n an attempt t o d e f i n e p r o p e r chromatographic conditions. An g l a s s c o l u m n w i t h a n a d j u s t a b l e b e d o f t h e M i c h e l - M i l l e r d e s i g n (Ace G l a s s Co., V i n e l a n d , N . J . ) was p a c k e d w i t h 1 0 0 g o f W o e l m s i l i c a g e l , 32-63μπι p a r t i c l e s i z e . A carrier gradient was r u n f r o m c y c l o h e x a n e t o d i c h l o r o m e t h a n e w h e r e i n t h e s o l v e n t s t r e n g t h was v a r i e d b y 0.04 p e r c o l u m n v o l u m e (13). N i a n d v a n a d y l p o r p h y r i n c o m p l e x e s , N i P a n d VOP, of e t i o p o r p h y r i n - I (Mid-Century Chemicals, Posen, IL) were u s e d t o m o n i t o r t h e s e p a r a t i o n s . Resolution of the N i P a n d VOP s t a n d a r d s b y t h e m s e l v e s was d e m o n s t r a t e d a s s h o w n i n t h e u p p e r c h r o m a t o g r a m o f F i g u r e 3. A similar t e s t w i t h a 1% l o a d o f N o r t h B e l r i d g e c r u d e o i l ( U n i o n O i l Company, B r e a , C A ) , t h a t h a d b e e n s p i k e d w i t h e q u i v a l e n t amount o f s t a n d a r d s , g a v e much w o r s e r e s u l t s a s s h o w n i n t h e l o w e r c h r o m a t o g r a m o f F i g u r e 3. Here, t h e N i P a n d VOP s e p a r a t i o n s w e r e i n c o m p l e t e a n d irreproducible. The h i g h l y p o l a r a n d d a r k l y p i g m e n t e d asphaltene m a t e r i a l s , sorbed i n i t i a l l y a t t h e head o f the column, b l e d o f f and coated t h e adsorbent, thus changing column c o n d i t i o n s as t h e s e p a r a t i o n proceded. An a d d i t i o n a l c o m p l i c a t i o n was a n t i c i p a t e d b e c a u s e vanadyl m e t a l l o p o r p h y r i n s form strong complexes w i t h L e w i s b a s e s (14) t h a t a r e p o s s i b l e c o m p o n e n t s o f c r u d e oil. Such complex f o r m a t i o n w i l l change t h e i r chromatographic behavior ( l u ) . Therefore, the present work i s n o t c o n f i n e d t o t h e i s o l a t i o n o f a d e f i n i t e c l a s s o f m e t a l l o p o r p h y r i n s , b u t t o a c l a s s t h a t may change i t s c o m p o s i t i o n d u r i n g t h e a n a l y s i s . A p r e l i m i n a r y s t r a t e g y was f o r m u l a t e d f r o m t h e s e experiments. An i n e x p e n s i v e s o r b e n t w i t h p r a c t i c a l mass l o a d i n g f o r adsorbed asphaltenes i s needed. A more d e t a i l e d knowledge o f s o l v e n t s e l e c t i v i t y e f f e c t s i s needed. An u n n e c e s s a r y c o m p l i c a t i o n w o u l d be a v o i d e d b y f i n d i n g conditions that minimize separation behavior of t h e N i P a n d VOP c o m p o n e n t s . Effect of S i l i c a Gel Porosity. I t i s known t h a t m a c r o p o r o s i t y tends t o boost t h e macromolecular sample l o a d c a p a c i t y o f s i l i c a g e l and i t s bonded phase derivatives. The p r e p a r a t i v e s e p a r a t i o n o f p r o t e i n s a n d o t h e r m a c r o m o l e c u l e s c a n be i m p r o v e d on t h i s b a s i s . Because asphaltene c o n t a i n s macromolecular components, t h e e f f e c t o f s i l i c a g e l p o r e s i z e was s t u d i e d u s i n g a s e r i e s o f Matrex s i l i c a g e l samples p r o v i d e d by t h e A m i c o n C o r p o r a t i o n ( D a n v e r s , MA). A t e s t s o l u t i o n was p r e p a r e d c o n s i s t i n g o f 1.00g o f B o s c a n o i l ( P h i l l i p s P e t r o l e u m C o m p a n y , B a r t l e s v i l l e , OK) d i s s o l v e d i n 4 0 m l of petroleum ether and methylene c h l o r i d e s o l u t i o n ( 5 0 : 1 ) . T h e l a t t e r was a d d e d t o r e t a r d d e a s p h a l t e n i n g . The c h r o m a t o g r a p h i c c o l u m n s u s e d i n t h i s w o r k w e r e g l a s s Flex-Columns (Kontes, V i n e l a n d , N J ) . The t e s t s o l u t i o n t u r n e d t h e s i l i c a g e l b l a c k a t the i n l e t end o f t h e column as t h e pigmented components


407


408


were a d s o r b e d . The b l a c k zone was f o u n d t o be c o r r e l a t e d i n s i z e w i t h t h e mass o f o i l sample. The sample l o a d c a p a c i t y , mass o f o i l p e r u n i t mass o f s i l i c a g e l bed t h a t had become d a r k , was t h e r e b y ascertained. P r e l i m i n a r y e x p e r i m e n t s were c a r r i e d out w i t h s i l i c a g e l samples o f 20-45μιη and 35-70μπι p a r t i c l e s i z e s , w i t h 60, 100, 250, 500 and 1000Â a v e r a g e p o r e sizes. The l o a d c a p a c i t y was h i g h e s t f o r t h e 500Â p o r e s i z e and 20-45μπ\ p a r t i c l e s i z e range, and t e n - f o l d h i g h e r t h a n t h a t o b t a i n e d w i t h 60Â and 35-70μπι. With s p e c i f i c regard t o the r e t e n t i o n of the a s p h a l t e n e - l i k e group, t h e e x p e r i m e n t s showed t h a t column l e n g t h can be s h o r t e n e d by p r o p o r t i o n t o l o a d c a p a c i t y f o r t h i s s i m p l e group s e p a r a t i o n . While the p r e s e n t r e s u l t s are s p e c i f i c f o r t h e Boscan r e f e r e n c e o i l , t h e h i g h sample l o a d c a p a c i t y o f t h e 250Â and 500Â m a t e r i a l s f o r t h e a s p h a l t e n e component have been v e r i f i e d i n t h e i n i t i a l a d s o r p t i o n s t e p w i t h s e v e r a l dozen c r u d e o i l s a m p l e s . A more d e t a i l e d i n v e s t i g a t i o n o f t h e e f f e c t o f p o r e s i z e i s b e i n g made ( 1 6 ) . T h i n l a y e r chromatography. 5μg samples o f NiP a n d / o r VOP s t a n d a r d s were s p o t t e d on aluminum b a c k e d s i l i c a g e l s h e e t (Eastman Kodak), 5cmX5cm s q u a r e s , and d e v e l o p e d i n the p r e s e n c e o f s o l v e n t v a p o r . 700μg o f s p i k e d c r u d e o i l ( d i s s o l v e d i n m e t h y l e n e c h l o r i d e ) was s p o t t e d o v e r 5μg s p o t s o f e a c h o f t h e s t a n d a r d s . P h o t o d e g r a d a t i o n was o b s e r v e d a f t e r NiP and VOP s p o t s were e x p o s e d f o r 16 h o u r s t o a 60 watt i n c a n d e s c e n t o r 16 watt f l u o r e s c e n t l i g h t (6 i n c h d i s t a n c e from l i g h t t o s a m p l e ) . A f t e r t h e e x p o s u r e , TLC development showed a new, more d e e p l y c o l o r e d and more h i g h l y r e t a i n e d band. NiP and VOP s t a n d a r d s , f o l l o w i n g TLC development, were a l s o f o u n d t o d a r k e n on s i l i c a a f t e r two weeks o f s t o r a g e a t room t e m p e r a t u r e i n t h e dark. The r e s u l t s showed c e r t a i n l i m i t a t i o n s b u t TLC a p p e a r s t o be v a l i d f o r m e t a l l o p o r p h y r i n s c o u t i n g under r e s t r i c t e d e x p o s u r e t o l i g h t , a i r and c o n t a c t w i t h t h e TLC a d s o r b e n t (17,18). The TLC e l u t i o n window f o r m e t a l l o p o r p h y r i n s has a wide s o l v e n t a c t i v i t y range ( 1 9 ) . Over one h u n d r e d TLC s c o u t i n g t e s t s were c a r r i e d out on t h e s p i k e d c r u d e o i l . S i n g l e and b i n a r y s o l v e n t s o l u t i o n s were u s e d f o r development i n t h e s o l v e n t a c t i v i t y range shown i n F i g u r e 4. The q u a l i t y o f t h e r e s u l t s was u n s a t i s f a c t o r y and m u l t i p l e p r o b l e m s were a p p a r e n t . P r a c t i c a l l y a l l of the i n d i v i d u a l s o l v e n t s a p p e a r e d t o be i n a p p r o p r i a t e . In t o l u e n e , f o r example, NiP and VOP m i g r a t i o n was s a t i s f a c t o r y b u t t h e d a r k a s p h a l t e n e s showed marked forward s t r e a k i n g , or f r o n t i n g . Metalloporphyrin t a i l i n g o c c u r r e d i n a c e t o n i t r i l e (MeCN), l i g h t e r a l c o h o l s and m e t h y l a c e t a t e (MeOAc). In p o l a r s o l v e n t s s u c h a s , MeCN, some o f t h e i n i t i a l sample s p o t o c c a s i o n a l l y f a i l e d t o d i s s o l v e and r e m a i n e d a t t h e origin. In h a l o g e n a t e d h y d r o c a r b o n s o l v e n t , s u c h as


26.


FREEMAN ET AL.

NiP

409

κ Λ" VOP

Porphyrin

Boscan Oil


1g., Spiked

llhlllllllls 1 2 3 4 5 6 7 8 9 10111213141516

718192021 22 2324 25 262728 2930

No. of Bed Volumes

0

10

F i g u r e 3. L i q u i d c h r o m a t o g r a p h y o f N i P a n d VOP s t a n d a r d s , a l o n e a n d i n c r u d e o i l i s s h o w n f o r a 60Â s i l i c a g e l column; s o l v e n t g r a d i e n t from c y c l o h e x a n e t o methylene c h l o r i d e . C h r o m a t o g r a p h y o f 10μg o f i n j e c t e d s t a n d a r d s , m o n i t o r e d a t 405nm, g a v e s a t i s f a c t o r y N i P / V O P separation. This s e l e c t i v i t y i s l o s t i n t h e lower c h r o m a t o g r a m w h e r e 1.Og o f B o s c a n c r u d e o i l , c o n t a i n i n g 0 . 1 % o f e a c h o f N i P a n d VOP s t a n d a r d s , w a s i n j e c t e d .

Rf

0.0

0.1

0.2

0.3

0.4 0.5

Solvent Strength

F i g u r e 4. O v e r o n e h u n d r e d d i f f e r e n t i n d i v i d u a l a n d b i n a r y s o l v e n t c o m p o s i t i o n s were mapped i n T L C experiments. T y p i c a l R f v a l u e s a r e shown i n t h e a b o v e (see r e f 18, p . 2 3 0 ) . The p r e s e n c e o f crude o i l ( n o t shown) c o n s i s t e n t l y i n t e r f e r e d w i t h t h e q u a l i t y o f t h e results.


410



methylene c h l o r i d e , t h e d a r k l y colored a s p h a l t e n e - l i k e components m i g r a t e d a l o n g w i t h t h e m e t a l l o p o r p h y r i n s . S o l v e n t b l e n d i n g was t r i e d . Improved band s h a r p n e s s was o b s e r v e d i n t h e p r e s e n c e o f t h e m o r e v o l a t i l e s o l v e n t s , e s p e c i a l l y m e t h y l e n e c h l o r i d e , MC, and p e t r o l e u m e t h e r , PE, (Baker C h e m i c a l Co., 35-60°C). Two d i m e n s i o n a l T L C s c o u t i n g . This approach gives a c l o s e r p a r a l l e l t o t h e d e s i r e d sequence i n which s a t u r a t e d a n d a t l e a s t some a r o m a t i c h y d r o c a r b o n s a r e e l u t e d before desorbing t h e m e t a l l o p o r p h y r i n group w i t h a stronger solvent. The i n i t i a l TLC d e v e l o p m e n t was d o n e w i t h 3:97 MC:PE. A o n e - m i n u t e p a u s e was made f o r solvent evaporation. T h e T L C p l a t e was t h e n r o t a t e d f o r p e r p e n d i c u l a r development. The s o l v e n t s a r e l i s t e d i n Table I . S i l i c a G e l TLC S c o u t i n g f o r Optimum E l u e n t C o m p o s i t i o n . The r e t e n t i o n a n d s e l e c t i v i t y o f t h e t w o metalloporphyrins s t a n d a r d s , N i P a n d VOP, w e r e a p t t o vary markedly with solvent composition. This i s i l l u s t r a t e d b y t h e T L C x e r o g r a p h s s h o w n i n F i g u r e 5. The c a p a c i t y f a c t o r s , k ( N i P ) a n d k ' ( V O P ) , a n d c o r r e s p o n d i n g VOP/NiP s e l e c t i v i t i e s were c a l c u l a t e d from t h e R f v a l u e s o b t a i n e d i n t h e TLC e x p e r i m e n t s u s i n g t h e w e l l - k n o w n r e l a t i o n s h i p , k' = (1 - R f ) / R f . The s e l e c t i v i t y , alpha, i s d e f i n e d as t h e r a t i o o f two d e s i g n a t e d k' v a l u e s — l a r g e r o v e r s m a l l e r . The o b s e r v e d s e l e c t i v i t y maxima f o r two b i n a r y s o l v e n t s y s t e m s a r e shown i n F i g u r e 6. Selectivity v a r i a t i o n s p r e s e n t two o p t i o n s , species s e p a r a t i o n under c o n d i t i o n s o f h i g h s e l e c t i v i t y and group s e p a r a t i o n s under c o n d i t i o n s o f low s e l e c t i v i t y . In t h e f i r s t stage o f a multi-step s e p a r a t i o n , group s e p a r a t i o n i snormally p r e f e r r e d . The c h a r a c t e r i s t i c s o f t h e N i P a n d VOP s t a n d a r d s were s t u d i e d a l o n e a n d a s s p i k e s added t o a sample o f a Boscan crude o i l ( P h i l l i p s Petroleum Co.), an a s p h a l t e n e - r i c h and m e t a l l o p o r p h y r i n - r i c h o i l used f o r reference purposes. The e f f e c t s o f s o l v e n t composition on t h e m e t a l l o p o r p h y r i n a n d t h e a s p h a l t e n e - l i k e g r o u p s were s t u d i e d . T h r e e o f t h e more h i g h l y d i f f e r e n t i a t e d TLC r e s u l t s are i l l u s t r a t e d i n Figure 7 ( a - c ) . I n F i g u r e 7(a) with toluene-cyclohexane (1:1) i n t e r m e d i a t e r e t e n t i o n o c c u r s but t h e N i P band i sb a d l y t a i l e d . The s t r o n g l y r e t a i n e d , d a r k l y c o l o r e d , a s p h a l t e n e - l i k e m a t r i x shows pronounced forward s t r e a k i n g , o r f r o n t i n g . In Figure 7 ( b ) w i t h T H F - c y c l o h e x a n e (7:3) t h e m e t a l l o p o r p h y r i n s t a n d a r d s a n d t h e dark m a t r i x components appear t o e x h i b i t f r a c t i o n a t i o n o f t h e a s p h a l t e n e - l i k e group which i s not s t r o n g l y r e t a i n e d and which brackets t h e metalloporphyrins. T h i s may b e d u e t o e x c e s s i v e s t r e n g t h o f t h e THF c o m p o n e n t . I n F i g u r e 7(c) with M e C N - m e t h y l e n e c h l o r i d e s o l v e n t s (1:1) t h e a s p h a l t e n e l i k e b a n d was r e t a i n e d w i t h o u t p r e d o m i n a n t f r o n t i n g . 1


26.

FREEMAN ET AL.

Table

I.


Results

of

ID


2D

ε

SOLVENT Pet. Ether (PE) Toluene Methylene Chloride Ethylene Chloride MeCN-MC-PE 1:1:4 1:2:3 1:3:2 1:4:1 2:3:1 2:1:0

and

(Fig. (0) (3) (6) (3) (6) (6)

Scouting

0

0.0 0.29 0.42 0.49 If)

Ν GN GN

R Ν GN G

R Ν GN GN

GN G GN GN G G

GN G GN GN G GR

GN GN GNR GN GNR GNR

GR R GNR GR

GNR GR GNR GR

GR R R GNR

GR R R GNR

0.5

G

A c e t o n i t r i l e (MeCN) Methanol Acetic Anhydride * Dimethylformamide *

0.65 0.95 1 1

G

G

GN

strength parameter values, ε

0

, are

S n y d e r ( H ) . A b o v e , ID a n d 2D, r e f e r t o TLC c r u d e o i l s p i k e d w i t h N i P a n d VOP standards G Ν R *

= = = =

TLC

2D

0.60 0.62 0.63 0.64

solvent

by

in

STPS-,

Methyl Acetate (MeOAc) Dimethylsulfoxide * Morpholine * Nitromethane

The

Tests

411

mainly

:

of Boscan O t h e r not

N i P and VOP G r o u p I s o l a t i o n ( R f > 0. 7) . N o n - t a i l i n g of metalloporphyrins A s p h a l t e n e s t r o n g l y r e t a i n e d (Rf < 0.2). S l o w TLC d e v e l o p m e n t .


412


α = 9.4

α = 1.8

V


• NiP

m Q

c

m

«

oa

i oa

NiP

VOP

. VOP

F i g u r e 5. S i l i c a T L C x e r o g r a p h y s h o w s how t h e a d s o r p t i o n s e l e c t i v i t y f o r N i P a n d VOP s t a n d a r d s v a r i e s f i v e - f o l d a s t h e c y c l o h e x a n e t o m e t h y l e n e c h l o r i d e (MC) s y s t e m i s c h a n g e d f r o m 1:1 ( l e f t ) t o p u r e MC ( r i g h t ) .

10H

10

20

40

30

50

%MC 1.0

MC, Cyclohexane System

• «—

1

MC, MeCN System

7—^^-w,

0.9

0.8

0.2 0.0

0.6 80

• •

0.7

Q VOP • NiP 100

1

1

10

1

1

1

20

Γ

1

30

VOP NiP 1

«

40

%MC

F i g u r e 6. N i P a n d VOP s t a n d a r d s o n s i l i c a g e l T L C g i v e v a r i e d R f a n d s e l e c t i v i t y (a) v a l u e s . While high metal speciation i s obtainable, the minimal metal species s e l e c t i v i t y needed f o r p o r p h y r i n group s e p a r a t i o n i s o b t a i n e d a t l o w a , p r e f e r a b l y on t h eMC-rich s i d e w i t h cyclohexane.


50


26.

FREEMAN ET AL.


•iNIP

Tol:CH (1:1)

1 Oil

VOP

THF:CH (7:3)

413

f NiP

Oil

VOP

MeCN:MC (1:1)

Figure 7. X e r o g r a p h e d s i l i c a TLC s c o u t i n g r e s u l t s a r e s h o w n f o r N i P a n d VOP s p i k e d B o s c a n o i l a t t h e c e n t e r o f e a c h TLC. At l e f t : a s p h a l t e n e components m i g r a t e w i t h marked forward s t r e a k i n g which i s t y p i c a l o f aromatic s o l v e n t systems. Middle: metalloporphyrins migrate together with asphaltenes. Right: t h i s was t h e f i r s t indication of asphaltenes being retained while metalloporphyrins migrate.


414



M e t a l l o p o r p h y r i n m i g r a t i o n w a s o b t a i n e d a t t h e same time. The p o t e n t i a l f o r s e p a r a t i n g t h e m e t a l l o p o r p h y r i n s f r o m t h e a s p h a l t e n e - l i k e g r o u p was i n d i c a t e d f o rt h e f i r s t time by t h i s r e s u l t . The c o l l e c t e d T L C r e s u l t s p r o v i d e d a k e y e v i d e n c e for t h e use o f s i l i c a g e lt o separate metalloporphyrins from t h e asphaltene group i n t e r f e r e n c e s . F u r t h e r , i n F i g u r e 7 (c) i t i s s e e n t h a t N i P a n d VOP a p p r o a c h c o e l u t i o n due t o t h e i r h i g h R f v a l u e s . Other problems were a p p a r e n t i n c l u d i n g m e t a l l o p o r p h y r i n t a i l i n g a n d less than complete r e t e n t i o n o f t h e a s p h a l t e n e - l i k e components. Y e l l o w p i g m e n t e d components were o b s e r v e d with diverse a f f i n i t i e s f o rs i l i c a g e l although t h i s i s not apparent i n t h e x e r o g r a p h i c records. O p t i m i z a t i o n o f TLC S o l v e n t T r i a d . Binary solvent s o l u t i o n s s h o w e d q u a l i f i e d a d v a n t a g e s , n o t a b l y MeCN o r methylene c h l o r i d e combined w i t h a s a t u r a t e d alkane d i l u e n t s u c h a s c y c l o h e x a n e (CH) o r p e t r o l e u m e t h e r (PE). A ternary mixture offered t h ep o t e n t i a l that t h e d i f f e r e n t advantages o f b i n a r y blends might be combined. An o p t i m i z a t i o n s t u d y i s u s u a l l y b a s e d o n t h e r e s o l u t i o n o f a l i m i t e d number o f compounds ( 2 0 ) . We a d a p t e d t h i s t y p e o f a p p r o a c h t o s t u d y t h e TLC o f t h e h i g h l y c o m p l e x m i x t u r e o f N i P a n d VOP s p i k e d c r u d e o i l w i t h t h e MeCNMC-PE s o l v e n t t r i a d . This extends t h e data i n Figure 6 beyond t h e two sets o f b i n a r y mixtures which a r e p a r t o f this triad. These TLC e x p e r i m e n t s g e n e r a t e d o v e r one h u n d r e d qualitative observations. The r e s u l t s were i n f o r m a t i v e , i n g e n e r a l terms f a i r t o good o v e r a l l , b u t no one s o l v e n t b l e n d seemed t o be e x c e l l e n t . A q u a n t i t a t i v e d e s c r i p t i o n o f t h e r e s u l t s w a s made i n o r d e r t o o b t a i n a more p r e c i s e c o m p o s i t e d e s c r i p t i o n o f e a c h TLC r e s u l t . The o b s e r v a t i o n s e t was r e f i n e d b y assigning numerical values t o previously q u a l i t a t i v e criteria. The f o l l o w i n g e v a l u a t i o n c r i t e r i a were d e f i n e d : (a) m i s c i b i l i t y o f s o l v e n t b l e n d s , (b) n o n t a i l i n g o f t h e m e t a l l o p o r p h y r i n s p i k e s , (c) s i m i l a r h i g h Rf v a l u e s f o r t h e m e t a l l o p o r p h y r i n s p i k e s — s i n c e t h a t c o n v e r g e s t o w a r d s u p p r e s e d V O P / N i P s e l e c t i v i t y , (d) n o n f r o n t i n g o f t h e N S O - a s p h a l t e n e b a n d , a n d (e) l a c k o f y e l l o w s u b s t a n c e s t h a t were a p t t o c o - e l u t e w i t h t h e metalloporphyrins. These performance c r i t e r i a d e s i g n a t e d ρ(a) t h r o u g h p ( e ) , w e r e m e a s u r e d o n t w o s c a l e s , 0-1 f o r t h e f i r s t , s o l v e n t m i s c i b i l i t y , a n d 0-3 for t h e others. The s c a l e s a r e b o t h p o s i t i v e ; z e r o i s bad a n d h i g h v a l u e s a r e good. To i l l u s t r a t e , i f t h e porphyrin e x h i b i t e d pronounced t a i l i n g then that r e s u l t was g r a d e d z e r o , p ( c ) = 0 f o r t h a t p a r t i c u l a r s o l v e n t composition. O r , s t r o n g a s p h a l t e n e r e t e n t i o n w i t h no d i s c e r n a b l e f r o n t i n g w o u l d s c o r e t h r e e , ρ ( d ) = 3. T h e s c a l e s have worst case zero v a l u e s , so zero l e v e l performance i n any c r i t e r i o n a t any composition forces a corresponding zero value i n t h e composite product value.


26.


FREEMAN ET AL.

The n u m e r i c a l s c o r e s f o r e a c h o f t h e c r i t e r i a a r e shown i n F i g u r e 8 ( a - e ) f o r e a c h p e r f o r m a n c e c r i t e r i o n and c o m p o s i t i o n c o o r d i n a t e s as d e s i g n a t e d w i t h i n t h e triangular plots. A c o m p o s i t e p e r f o r m a n c e i n d e x , P, was obtained by m u l t i p l y i n g t h e i n d i v i d u a l performance values together a t each solvent composition.


Ρ

=

p(a)p(b)p(c)p(d)p(e)

The c o m p o s i t e p e r f o r m a n c e i n d i c e s r e a c h e d t o 3 6 o u t o f 81 a s a p o s s i b l e maximum. Conveniently, the results g a v e s i n g l e d i g i t i n t e g e r v a l u e s a f t e r d i v i s i o n b y 6. The r e s u l t s a r e s h o w n i n F i g u r e 8 ( f ) . F i g u r e 8 ( f ) s h o w s t h e n u m e r i c a l l y h i g h e s t c o m p o s i t e i n d i c e s (P = 6) t h a t d e n o t e t h e o p t i m a l c a r r i e r c o m p o s i t i o n s b a s e d upon t h e s e one d i m e n s i o n a l TLC e x p e r i m e n t s . These s c o u t i n g e x p e r i m e n t s were c a r r i e d f u r t h e r by testing several intermediate l i q u i d compositions a d j a c e n t t o a l i n e c o n n e c t i n g t h e TLC p e r f o r m a n c e maxima a t Ρ = 6. No i m p r o v e m e n t was o b s e r v e d . B i d i m e n s i o n a l TLC a s a S o l v e n t S c r e e n . I t was r e c o g n i z e d t h a t t h e o n e d i m e n s i o n a l ID TLC e x p e r i m e n t s were n o t s t r i c t l y a n a l o g o u s t o t h e p l a n n e d t w o - s t e p i s o l a t i o n o f t h e m e t a l l o p o r p h y r i n group. A TLC s c o u t i n g s t u d y was c a r r i e d o u t s o a s t o b e m o r e a n a l o g o u s t o a n i n i t i a l d e v e l o p m e n t t o remove t h e s a t u r a t e s g r o u p . A second dimension, o b t a i n e d by p e r p e n d i c u l a r development, was d o n e w i t h v a r i o u s s o l v e n t s b e l i e v e d c a p a b l e o f p r o p e r l y desorbing t h e sought m e t a l l o p o r p h y r i n s . An e s s e n t i a l g o a l was t h a t t h e a s p h a l t e n e - l i k e g r o u p r e m a i n adsorbed. The 2D T L C r e s u l t s s u m m a r i z e d i n T a b l e I c o n f i r m t h e I D T L C f i n d i n g s g i v e n i n F i g u r e 8. The t h r e e o p t i m a l s o l v e n t b l e n d s n o t e d i n t h e MeCN-MC-PE s y s t e m , a s w e l l a s t h r e e new s y s t e m s , g a v e g o o d g r o u p s e p a r a t i o n o f t h e c o m b i n e d N i P a n d VOP s p i k e s f r o m c r u d e o i l . The 2D T L C e x p e r i m e n t s g a v e r e s u l t s t h a t d i f f e r e d s i g n i f i c a n t l y f r o m t h e ID TLC. I n f o u r i n s t a n c e s , a s shown i n T a b l e I , t h e p r e l i m i n a r y r e m o v a l o f t h e s a t u r a t e s g r o u p i m p r o v e d t h e q u a l i t y o f t h e s e c o n d TLC development. T h i s i s apparent from t h e improvement t r e n d i m p l i e d by t h e o v e r a l l r e s u l t s i n Table I . An i m p o r t a n t e x a m p l e o f t h i s o c c u r s w i t h MeOAc ( m e t h y l a c e t a t e ) w h i c h g a v e g r o s s t a i l i n g d u r i n g 1D-TLC o f t h e m e t a l l o p o r p h y r i n standards, alone and i n t h e spiked Boscan. I n 2D-TLC t h i s t a i l i n g e f f e c t d i s a p p e a r e d a n d MeOAc j o i n e d t h e s o l v e n t s d e s i g n a t e d w i t h s u p e r i o r performance. Among t h e s o l v e n t s t e s t e d , t h e l o w b o i l i n g p o i n t a n d l o w v i s c o s i t y o f MeOAc a r e m a r k e d a d v a n t a g e s . It i s concluded that t h e presence o f thesaturated and aromatic hydrocarbons, soon t o be c a l l e d t h e A l f r a c t i o n , i s able t o i n t e r f e r e w i t h t h e subsequent removal of t h e metalloporphyrins. A s t h e s o l v e n t s t r e n g t h (21.) was i n c r e a s e d f u r t h e r ,


415

416


MC 1


1

3 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0

3

1

(a) Miscibility

MeCN

3 3 3 2 3 3 3 2 0 3 3 2 0 0 0 2 2 2 0 0 0 0 0 0 3

3

PE

(b) NiP, VOP Tailing

2 0

0 3

2 3 3 2 2 3 3 0 3 3 2 3 0 3 3 3 3 2 0 2 3 3 2 3 0 0

(c) NiP, VOP Co-Elution

0 1

2

2 1 3 2 2 1 3 3 2 2 0 3 3 2 1 1 2 3 3 2 3 0 1 3

(d) Asphaltene Retention

1

0 0 1 1 1 2 2 1 2 3 1 1 0 2 3 2 2 0 2 3 3 3 3 3 1 3

(e) Yellow Pigment Isolation

0

2:3:1

0

0

1:3:2

\ 0

3 2 ^ 2 6 6 0 2:1:0—6 0 2 3 0 0 0 0 2 0 0 0 0 0 0 0 0 0

(f) Overall Performance

F i g u r e 8. A 2 8 - p o i n t TLC o p t i m i z a t i o n i s c a l c u l a t e d from e s t i m a t e d q u a l i t y o f s e p a r a t i o n b r o k e n down by category. Ο i s bad, 1 i s m i n i m a l and 3 i s maximal, as described i n the text. In (a) MC p r e v e n t s MeCN/PE i m m i s c i b i l i t y w h i l e i n (b) MC c o u n t e r s m e t a l l o p o r p h y r i n tailing. In (c) MeCN b o o s t s N i P and VOP c o - e l u t i o n w h i l e i n (d) i t promotes a s p h a l t e n e r e t e n t i o n . In (e) h i g h l e v e l s o f y e l l o w pigmented contamination, appearing immediately f o l l o w i n g the m e t a l l o p o r p h y r i n spikes, i s seen a t ρ = 0 o r 1 i n o n l y t h r e e l i q u i d c o m p o s i t i o n s . The " b e s t " o v e r a l l p e r f o r m a n c e c o m p o s i t i o n s a r e shown i n ( f ) ; see a l s o t a b l e I .



26.

FREEMAN ET AL.


t h e 2D TLC p e r f o r m a n c e improved and t h e n d e t e r i o r a t e d . One h i g h p o l a r i t y s o l v e n t , d i m e t h y l f o r m a m i d e , q u a l i f i e d as a s u p e r i o r m e t a l l o p o r p h y r i n d e s o r b a n t . (Less b e n e f i c i a l : i t e x h i b i t e d slow TLC development and i t has a high b o i l i n g point.) I t s d i s t i n c t i v e r o l e i n vanadyl p o r p h y r i n e x t r a c t i o n was r e p o r t e d i n t h e work o f S p e n c e r et a l ( 2 2 ) . I t i s l i k e l y t h a t o t h e r a t t r a c t i v e s o l v e n t systems c a n be f o u n d t o s a t i s f y t h e p e r f o r m a n c e c r i t e r i a named so f a r . The 2D TLC r e s u l t s f o r t h e b e s t s o l v e n t s i n T a b l e I show t h a t t h e i s o l a t i o n o f t h e N i P and VOP b i o m a r k e r g r o u p was e v a l u a t e d w i t h r e g a r d t o t h r e e key p r o p e r t i e s : i t was weakly r e t a i n e d , Rf v a l u e s o f 0.7 o r h i g h e r ( c l a s s "G" i n T a b l e I ) , w i t h o u t a p p a r e n t t a i l i n g ( c l a s s "N" i n T a b l e I) and w i t h s t r o n g r e t e n t i o n o f t h e a s p h a l t e n e - l i k e group ( c l a s s " R " ) . B a s e d on TLC, column e l u t i o n o f t h e m e t a l l o p o r p h y r i n g r o u p by t h e b e s t s o l v e n t s a r e d e s i g n a t e d by t h e t r i o o f s a t i s f a c t o r y c r i t e r i a , "GNR" i n T a b l e I . The G a l o n e means t h a t t h e combined b i o m a r k e r s a r e e x p e c t e d t o be c o m p l e t e l y e l u t e d w i t h i n one column volume a f t e r t h e f r o n t o f t h e m e t a l l o p o r p h y r i n band. W i t h f o u r s o l v e n t systems, d e s i g n a t e d w i t h an a s t e r i s k i n T a b l e I, t h e TLC m i g r a t i o n was c o n s p i c u o u s l y s l o w e r . These systems were not c o n s i d e r e d a c c e p t a b l e f o r column a p p l i c a t i o n b a s e d upon p o o r dynamic b e h a v i o r . Desorption of Metalloporphyrins. T e s t s were made o f t h e d e s o r p t i o n o f a d s o r b e d m e t a l l o p o r p h y r i n s from a m a c r o p o r o u s s i l i c a g e l column u s i n g t h e u n s p i k e d B o s c a n reference o i l . I n i t i a l l y t h e o i l was a d s o r b e d from c y c l o h e x a n e w i t h 3% MC as d e s c r i b e d i n t h e e x p e r i m e n t a l section. Then, 1:3:2 MeCN:MC:PE was added as t h e s e c o n d solvent t o desorb the metalloporphyrins. This solvent b l e n d r a n k e d among t h e b e s t b a s e d on t h e TLC t r i a d o p t i m i z a t i o n (see F i g u r e 8) and i t had t h e l e a s t amount of t h e h i g h e r b o i l i n g MeCN s o l v e n t . However, t h e c o l l e c t e d f r a c t i o n s showed t a i l i n g t h a t spanned o v e r e i g h t column volumes. T h i s was measured a t 20% sample l o a d (Boscan r e f e r e n c e o i l ) as shown i n F i g u r e 9. This d e s o r p t i o n c h a r a c t e r i s t i c was c o n s i s t e n t l y p o o r even a t s u b s t a n t i a l l y s m a l l e r sample l o a d s . This f a i l u r e i n r e t r o s p e c t s h o u l d n o t be c o n s i d e r e d t o o s u r p r i s i n g b e c a u s e t h e TLC t e s t s d i d n o t a c t u a l l y t e s t f o r desorption. Comparison was made, a g a i n a t 20% sample l o a d , w i t h MeOAc s o l v e n t f o r m e t a l l o p o r p h y r i n d e s o r p t i o n . These r e s u l t s a r e a l s o shown i n F i g u r e 9. The m e t a l l o p o r p h y r i n d e s o r p t i o n was 95% c o m p l e t e w i t h i n two column v o l u m e s . A l t h o u g h 20% sample mass l o a d i n g may seem u n u s u a l l y h i g h , we have so f a r o n l y r a r e l y o b s e r v e d evidence f o r overload during the i n i t i a l adsorption step. Thus, t h e i n i t i a l m e t a l l o p o r p h y r i n g r o u p i s o l a t i o n i s achieved: strong r e t e n t i o n of the a s p h a l t e n e - l i k e group w h i l e t h e s a t u r a t e s f r a c t i o n i s


417


418

removed, a n d h i g h r e c o v e r y o f t h e desorbed metalloporphyrins while t h e remainder o f t h e asphaltenel i k e group i sn o t desorbed.


Final

Results

and Conclusions

P e t r o p o r p h y r i n s i n Boscan Crude O i l . As t h e r e s u l t o f the e x p e r i m e n t s on macroporpous s i l i c a g e l , a n d two d i m e n s i o n a l TLC a s g i v e n a b o v e , a g r o u p s e p a r a t i o n o f p o r p h y r i n c l a s s e s was d e v i s e d . The f i n a l scheme t h a t was a d o p t e d i s p r e s e n t e d i n F i g u r e 1 0 . T h r e e m a j o r p o r p h y r i n f r a c t i o n s i n t h e Boscan crude o i l and i n other petroleums subsequently studied a r e defined by t h e i r r e l a t i v e b e h a v i o r i n t h i s scheme: B - l t h e l o w p o l a r i t y N i P a n d VOP b i o m a r k e r m o l e c u l e s ; B-2 t h e p o l a r p o r p h y r i n s a n d A-3, a s p h a l t e n e - b o u n d m a t e r i a l . Details o f t h e e x p e r i m e n t a l method c o m p r i s i n g t h i s scheme a r e a s follows. A f i v e g r a m b e d o f M a t r e x s i l i c a g e l (500Â p o r e s , 20-45μπ\ p a r t i c l e s i z e ) was p a c k e d i n a 2.5cm i . d . b y 10 cm F l e x c o l u m n ( K o n t e s , V i n e l a n d , NJ) w i t h a r e s u l t i n g b e d h e i g h t o f a b o u t 3.5 cm. T h e s i l i c a g e l h a d b e e n d r i e d o v e r n i g h t a t 105°C. T h e b e d was e q u i l i b r a t e d w i t h m e t h y l e n e c h l o r i d e a n d t h e n washed w i t h f i v e column volumes o f a h y d r o c a r b o n s o l v e n t ; hexane o r p e t r o l e u m e t h e r gave s i m i l a r r e s u l t s . A one gram sample o f B o s c a n c r u d e o i l w a s a p p l i e d i n 4 0 m l o f c y c l o h e x a n e w i t h 3% added m e t h y l e n e c h l o r i d e . The m e t h y l e n e c h l o r i d e r e t a r d s asphaltene p r e c i p i t a t i o n and promotes e l u t i o n o f yellow non-porphyrins that interfere with spectrophotometry. T h e c o l u m n was t h e n e l u t e d w i t h 5 0 m l of hexane and methylene c h l o r i d e (97:3). M e t a l l o p o r p h y r i n s a r e s i g n i f i c a n t l y more s o l u b l e i n c y c l o h e x a n e t h a n i n p e t r o l e u m e t h e r and, d e p e n d i n g on the c o n d i t i o n o f t h e s i l i c a and t h e asphaltene content, some N i P may b e e l u t e d w i t h t h i s s o l v e n t . I t i s important t o t e s t t h e i n i t i a l hydrocarbon-rich eluant for losses of porphyrins. The s o l v e n t was c h a n g e d t o m e t h y l a c e t a t e t o d e s o r b the metalloporphyrins. A sharply defined asphaltene band remained s t r o n g l y r e t a i n e d w h i l e t h e deeply c o l o r e d m e t a l l o p o r p h y r i n g r o u p s m o v e d t o g e t h e r down t h e w h i t e column. E t h y l a c e t a t e was s u b s e q u e n t l y found t o behave a b o u t t h e same. R e t e n t i o n o f t h e A s p h a l t e n e - l i k e Group. The chromatographic retention o f the asphaltene-like i n t e r f e r e n c e s i s t h e k e y t o t h e s e p a r a t i o n scheme. The adsorption/desorption steps a r ea t least i n part c o n t r o l l e d by s o l u b i l i t y r e l a t e d processes. The A 1 / A 2 / A 3 s o l v e n t s t e p g r a d i e n t ( F i g u r e 10) e x e r t s control t o a s i g n i f i c a n t extent by providing low s o l u b i l i t y o f t h e a s p h a l t e n e - l i k e group i n t h e two i n i t i a l s o l v e n t s where t h e p r e d o m i n a n t a l k a n e a n d t h e n m e t h y l a c e t a t e h a v e t h e common c h a r a c t e r i s t i c t h a t



FREEMAN ET AL.


1

2

3

4

5

6

7

8

1

No. of Column Bed Volumes

2

3

4

5

6

419

7

8

No. of Column Bed Volumes

F i g u r e 9. T h e b i o m a r k e r f r a c t i o n f r o m t h e B o s c a n i s separated from t h e r e t a i n e d asphaltene f r a c t i o n a t high sample l o a d l g o i l / 5 g s i l i c a g e l . The m e t a l l o p o r p h y r i n e l u t i o n i n MeCN-MC-PE i s b a d l y t a i l e d . However, 95% o f the biomarker metalloporphyrins e l u t e d i n methyl acetate s o l v e n t w i t h i n two column volumes. (At l a s t ! )

Boscan Oil - 1.OOg Silica Gel (500A)-5.0g

MC:PE 600mg* (O.Omg)** I Sats, Aromatics

'Mass

"(Mass)

* Whole fraction ** Metalloporphyrin

MeOAc

Toluene:MC:MeOH

200mg (1.6mg) Silica Gel (100A)

40mg (0.2mg)

MC I 100mg (1.2mg) NiP and VOP Biomarkers

|

Asphaltenes

MeOAc 30mg (0.1 mg) Polar Metalloporphyrins

F i g u r e 10. S h o r t column c h r o m a t o g r a p h y w i t h m a c r o p o r o u s s i l i c a provides three i n i t i a l fractions of specified m a s s , w i t h t h e d e s i g n a t e d m e t a l l o p o r p h y r i n m a s s () b a s e d on S o r e t b a n d s p e c t r o p h o t o m e t r y . Various second stage options are available. I n t h e above, s i l i c a g e l separates t h e biomarker metalloporphyrins concentrated t e n - f o l d f o l l o w e d b y a more p o l a r m e t a l l o p o r p h y r i n fraction.



420


asphaltene group i s s t r o n g l y r e t a i n e d and b u t s p a r i n g l y soluble. The a s p h a l t e n e - l i k e g r o u p i s r e t a i n e d d u r i n g t h e i n i t i a l d e s o r p t i o n c o n d i t i o n s : (1) t h e e l u t i o n o f t h e s a t u r a t e d h y d r o c a r b o n s w i t h some a r o m a t i c c o m p o u n d s i n f r a c t i o n A l , a n d (2) d u r i n g t h e d e s o r p t i o n o f t h e m e t a l l o p o r p h y r i n A2 f r a c t i o n . N o t e t h a t t h e A2 f r a c t i o n contains metalloporphyrins concentrated f i v e - f o l d , but A2 i s s t i l l o v e r 9 9 % n o n - p o r p h y r i n i c a s s t a t e d i n F i g u r e 10. The f i n a l d e s o r p t i o n o f t h e A3 a s p h a l t e n e group depends upon a s p h a l t e n e s o l u b i l i t y i n t h e MeOH:Toluene:MC b l e n d . The " a s p h a l t e n e - l i k e " g r o u p A 3 i s d e f i n e d o p e r a t i o n a l l y by t h epresent chromatographic procedure. This appears t o overlap t h e o r i g i n a l Boussingault d e f i n i t i o n made i n 1 8 3 7 ( 2 3 ) i n w h i c h asphaltene s o l u b i l i t y i n turpentine and i n s o l u b i l i t y i n methanol are both s p e c i f i e d . This i sdiscussed i ngreater d e t a i l by B o c k r a t h a n d S c h w e i g h a r d t ( 2 4 ) . The a s p h a l t e n e - l i k e m a t e r i a l , as d e f i n e d by t h e present chromatographic p r o c e d u r e , appears t o be u n l i k e t h e s i m p l e r o p e r a t i o n a l d e f i n i t i o n based on i n s o l u b i l i t y i n a s p e c i f i e d lower a l k a n e s o l v e n t (2ϋ). Alkane p r e c i p i t a t e d asphaltenes normally contain metalloporphyrins while the " a s p h a l t e n e - l i k e " components d e f i n e d h e r e do n o t , e x c e p t p o s s i b l y t o a minor extent. I t i squite possible that the l a t t e r metalloporphyrins a r e chemically d i s t i n c t f r o m t h o s e o b t a i n e d b y e l u t i o n w i t h MeOAc. The e f f e c t o f t h i s o p t i m i z e d s e p a r a t i o n i s a much f a s t e r chromatographic basis f o r s u b - d i v i d i n g t h e crude o i l into a fraction that contains the metalloporphyrin groups which e l u t e e a s i l y , and t h e asphaltene i n t e r f e r e n c e s that a r e s t r o n g l y adsorbed. The m e a s u r e d 1 0 - f o l d r a n g e i n t h e s o r p t i o n c a p a c i t y of s i l i c a g e l , depending upon p o r e s i z e a n d p a r t i c l e s i z e , shows i t s e l f i n t h e f i n d i n g t h a t column h e i g h t s o f o n l y a f e w (3.5) c e n t i m e t e r s w e r e n e e d e d t o c a r r y o u t the present group s e p a r a t i o n s . The o p t i m i z e d asphaltene group s o r p t i o n c a p a c i t y provided by macroporous s i l i c a g e l means t h a t c o r r e s p o n d i n g l y l e s s s i l i c a g e l i s required. Correspondingly smaller quantities of elution solvent and o f e l u t i o n time a r et h e r e s u l t . I t i s n o t e d i n F i g u r e 10 t h a t t h e r e t a i n e d c o l u m n l o a d i s 2 0 0 mg o f A2 a n d 40mg f o r A 3 f r a c t i o n s . This s u g g e s t s t h a t t h e e f f e c t i v e l o a d s h o u l d be r e s t r i c t e d t o t h e a d s o r b e d c o m p o n e n t s : t h i s c o r r e s p o n d s t o 5% b a s e d o n a d s o r b e d mass o f t h e B o s c a n sample p e r mass o f t h e macroporous s i l i c a . This view i s l e s s i n f l a t e d than t h e 20% o f c o l u m n l o a d , s t a t e d e a r l i e r . The l a t t e r i n c l u d e s components t h a t do n o t a d s o r b and, p e r h a p s , s h o u l d n o t be c o u n t e d . The B o s c a n B l m e t a l l o p o r p h y r i n f r a c t i o n i s concentrated approximately t e n - f o l d as i n d i c a t e d i n F i g u r e 10. I n t h e t e s t i n g done s o f a r , m i n o r amounts o f t h e m o r e p o l a r B2 m e t a l l o p o r p h y r i n s h a v e b e e n o b s e r v e d in other crude o i l samples. I n sum, t h e s c h e m e



26.

FREEMAN ET AL.


421

g e n e r a t e s t h e A2 f r a c t i o n a n d t h e B l a n d B2 s u b f r a c t i o n s which appear t o be m e t h o d o l o g i c a l l y r o b u s t . The B l a n d B2 c l a s s i f i c a t i o n s a r e e a s i l y m o d i f i e d t o s e p a r a t e t h e N i P a n d VOP c o m p o n e n t s b y v a r y i n g t h e eluant r a t i o o f methylene c h l o r i d e and alkane diluent. The k e y t o t h i s f l e x i b i l i t y i s t h e p r i o r r e m o v a l o f t h e major i n t e r f e r e n c e s i nt h ei n i t i a l step. This enables more d e f i n i t i v e s u b s e q u e n t i s o l a t i o n s i n s u c c e e d i n g steps. These f a c i l e group s e p a r a t i o n s a r e o b t a i n e d because o f t h e i n t e r f e r e n c e s t h a t have been removed. The m e t h o d d e v e l o p m e n t c o n c l u d e s w i t h t h e finding that i t i s t h e f i r s t separation step that i so f primary importance. I n the present case, m e t a l l o p o r p h y r i n i s o l a t i o n i ss i m p l i f i e d by the i n i t i a l removal o f t h e major i n t e r f e r e n c e . I t i s because o f t h i s t h a t t h e d e f i n e d N i P a n d VOP b i o m a r k e r s c a n b e s e p a r a t e d f r o m e i t h e r t h e A2 o r B l g r o u p s . Acknowledgments

T h i s r e s e a r c h was f u n d e d i n p a r t b y a g r a n t f r o m t h e U.S. D e p a r t m e n t o f E n e r g y . C l i f f o r d Walters and P a t r i c k L. G r i z z l e w i t h t h e Sun E x p l o r a t i o n a n d P r o d u c t i o n Co. p r o v i d e d h e l p f u l g u i d a n c e a n d s u p p o r t . T e c h n i c a l d i s c u s s i o n s a n d s i l i c a g e l samples were h e l p f u l l y p r o v i d e d by the Chromatography Marketing Department o f Amicon C o r p o r a t i o n . Literature Cited 1.

2. 3. 4. 5. 6. 7.

8. 9. 10.

11.

B a k e r , E.W.; Palmer, S.E.; a n d Huang, W.Y., "Init. Rep. Deep Sea Drilling Proj.", National Science F o u n d a t i o n , S u p p l . 1978a, 38-41, pp. 639-647. S.A. Miller, T.W. Hambley and J.C. T a y l o r , A u s t . J . Chem. 1983, 37, 761-66. J.M.E. Q u i r k e , J.K. M a x w e l l , G. E g l i n g t o n , J.K.M S a n d e r s , T e t r a h e d r o n L e t t . , 1980, 21, 2987-2990. P. Sundararaman, A n a l . Chem. 1985, 57, 2204-2206. F. Amore, N a t . B u r . o f S t a n d a r d s Spl. Pub. 244, V o l . 2, 1976, pp. 661-8. ACS Subcommittee on E n v i r o n m e n t a l Analytical C h e m i s t r y , A n a l . Chem. 1980, 52, 2242-2240. G. Wernimont i n "Validation o f t h e Measurement P r o c e s s , " J.R. DeVoe, Ed., ACS SYMPOSIUM SERIES No. 63, A m e r i c a n C h e m i c a l S o c i e t y : W a s h i n g t o n , D.C., 1977, 1-29. V.R. Meyer, J . C h o m a t o g r . 334, 197-209 (1985). H.J.G. D e b e t s , J. Liquid Chromatogr. 8, 2725-2780 (1985). D.H. Freeman In " U l t r a h i g h R e s o l u t i o n Chromatography";ACS SYMPOSIUM SERIES No. 250, A m e r i c a n C h e m i c a l S o c i e t y : Washington, D.C., 1984, pp.77-90. K.H. Freeman, Honors T h e s i s in G e o l o g y , W e l l e s l e y C o l l e g e , W e l l e s l e y , MA 1984.


422 12.

13. 14. 15.


16. 17.

18. 19.

20. 21. 22. 23. 24.

25.

M E T A L COMPLEXES IN FOSSIL FUELS

E.W. Baker In " O r g a n i c G e o c h e m i s t r y " , G. E g l i n g t o n and M.T.J. Murphy, E d s . , S p r i n g e r - V e r l a g , 1969, Chap. 19. L.R. Snyder and D.L. S a u n d e r s , J . Chromatogr. Sci. 1969, 7, 195-207. J . S. Flynn and D. H. Freeman, J . Chromatοgr., 1987, 386 111-121. E.W. Baker, M.S. B r o o k h a r t a n d A.H. C o r w i n , J . Am. Chem. S o c . 1964, 86, 4587-90 To be p u b l i s h e d . J.-H. F u r h o p and K.M. Smith in " P o r p h y r i n s and Metalloporporphyrins," K.M. Smith, Ed., Elsevier, New York, 1975, p.841. S.R. A b b o t t , LC:GC 1986, 4, 522. L. R. Snyder and D.L. Saunders in "Chromatography i n Petroleum Analysis,"Chromatographic Science Series, K.H. Altgelt and T.H. Gouw, M. Dekker, 1979, pp. 215272 . J . L . Glajch and J.J. Kirkland, A n a l . Chem. 1982, 55, 319A-336A. L.R. Snyder, "Principles of Adsorption Chromatography", M. Dekker, New York, 1968, pp.194-5. W.A. S p e n c e r , J . F . G a l o b a r d e s , M.A. Curtis and L.B. R o g e r s , S e p a r a t i o n Sci. and Tech. 1982, 17, 797-819. J.B. B o u s s i n g a u l t , Ann. Chim. Phys. 64, 141 (1837). B.C. B o c k r a t h and F.K. S c h w e i g h a r d t In " C h e m i s t r y o f A s p h a l t e n e s " , ADVANCES IN CHEMISTRY SERIES No. 195, A m e r i c a n C h e m i c a l S o c i e t y , Washington, D.C., 1981, pp.29-39. R.B. Long,

ibid.

pp. 17-27.

R E C E I V E D January 2, 1987


Group Isolation of Nickel and Vanadyl Porphyrins from Crude Oil

Recommend Documents