17 600-MHz Proton Magnetic Resonance Study of Coal-Derived Liquids
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T. H A R A and N. C. LI Duquesne University, Pittsburgh, PA 15219 K. C. TEWARI and F. K. SCHWEIGHARDT Air Products and Chemicals, Inc., Allentown, PA 18105 1
The newly developed 600 MHz H NMR Spectrometer is used to characterize coal-derived liquids and their chromatographically separated fractions. The d i s t i n c t and well resolved proton resonance lines in both aromatic and a l i p h a t i c regions and IR analysis have been used to identify the major compounds and compound types. Double resonance technique has been applied for the chemical shift identification of donor protons (α-CH , β-CH ) of p a r t i a l l y hydrogenated polynuclear aromatic compounds. An NMR difference technique is applied to determine specific compositional changes in upgraded liquids derived under iden tical process conditions, but from different coal sources. 2
2
1
High resolution proton nuclear magnetic resonance ( H NMR) spectrometry has been used as one of the major spectroscopic tools for chemical characterization of coal-derived materials, since Friedel (1) and Brown et al. (2) reported H NMR spectra of coal-derived asphaltenes and low-temperature vacuum carbon ization products. Based on the quantitative proton distri bution data, structural information for complex mixtures of coal-derived materials has been obtained using the Brown and Ladner equations (3) as well as the modified equations reported elsewhere (4,
5, 6).
A h i g h e r - f i e l d NMR s p e c t r o m e t e r (220 MHz)
was a p p l i e d t o t a r component by B a r t l e e t a l . ( 7 ) . The p r o t o n r e s o n a n c e s i g n a l s o f c o a l - d e r i v e d m a t e r i a l s were d i v i d e d i n t o e l e v e n r a n g e s o f c h e m i c a l s h i f t v a l u e s and t h e s i g n a l s i n e a c h r a n g e were a s s i g n e d t o v a r i o u s t y p e s o f h y d r o g e n by t h e a d d i t i o n o f p u r e compounds. S c h w e i g h a r d t e t a l . used a 250 MHz NMR s p e c t r o m e t e r f o r c h a r a c t e r i z a t i o n and t o q u a n t i f y h y d r o x y l g r o u p s i n c o a l - 1 i q u e f a c t i o n o i l s and a s p h a l t e n e s ( 8 ) . Hydroxyl g r o u p s i n c o a l - d e r i v e d m a t e r i a l s were c o n v e r t e d i n t o t r i m e t h y l s i l y l e t h e r s and p r o t o n s i g n a l s i n m e t h y l g r o u p s a t t a c h e d t o s i l i c o n were m e a s u r e d . The w e l l - r e s o l v e d NMR s p e c t r a e n a b l e d them t o c h a r a c t e r i z e t h e n a t u r e o f t h e o r i g i n a l h y d r o x y l g r o u p s in coal-derived materials.
0097-6156/81/0169-0289$07.50/0 © 1981 American Chemical Society
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
NEW
290
APPROACHES IN
COAL CHEMISTRY
I n t h e p r e s e n t s t u d y , a 600 MHz Ή NMR s p e c t r o m e t e r o p e r a t i n g a t 140.9 Kgauss i s used f o r t h e c h a r a c t e r i z a t i o n o f s o l v e n t - r e f i n e d c o a l l i q u i d p r o d u c t s ( S R C - I I ) and t h e i r c h r o matographically separated subfractions. The a s s i g n m e n t o f w e l l - r e s o l v e d r e s o n a n c e l i n e s becomes s i m p l e r by use o f t h e h i g h e s t m a g n e t i c f i e l d p o s s i b l e t o d a y t o i d e n t i f y m a j o r com pounds and compound t y p e s f o u n d i n c o a l - l i q u i d s . A double r e s o n a n c e t e c h n i q u e has been used f o r c h e m i c a l s h i f t i d e n t i f i c a t i o n o f o r C H and β - 0 Η p r o t o n s a t t a c h e d t o a r o m a t i c r i n g structures. An NMR d i f f e r e n c e s p e c t r o s c o p i c t e c h n i q u e i s u s e d on a p a i r o f c o a l - l i q u i d samples t o d e t e r m i n e c o m p o s i t i o n a l change between them. Such q u i c k and d i r e c t c h a r a c t e r i z a t i o n w i t h o u t f r a c t i o n a t i o n may h e l p t o a s s e s s t h e s l i g h t v a r i a t i o n of process parameters i n c o a l - l i q u e f a c t i o n processes. 2
2
Experimental A l i q u i d s o l v e n t - r e f i n e d c o a l p r o d u c t ( S R C - I I ) was made f r o m W e s t e r n K e n t u c k y b i t u m i n o u s c o a l a t t h e F o r t L e w i s SRC p i l o t p l a n t , h a v i n g an i n i t i a l b o i l i n g p o i n t o f 453 Κ and an end b o i l i n g p o i n t o f 665 K. The c o a l - l i q u i d p r o d u c t was f r a c t i o n a t e d u s i n g i o n - e x c h a n g e and s i l i c a - g e l c h r o m a t o g r a p h y ( 9 , 22, 1 J ) . A m b e r l i t e I R A - 9 0 4 and A m b e r l y s t A - 1 5 were used as a n i o n and c a t i o n - e x c h a n g e r e s i n s , r e s p e c t i v e l y . A c t i v a t i o n of t h e r e s i n s and s i l i c a - g e l was p e r f o r m e d by t h e method d e s c r i b e d by J e w e l l e t a l . ( 9 ) . The r a t i o s o f t h e c o a l - l i q u i d t o t h e i o n - e x c h a n g e r e s i n s and s i l i c a - g e l were 1:5 and 1:150 by w e i g h t , respectively. The S R C - I I m i d d l e d i s t i l l a t e s , b o i l i n g p o i n t r a n g e o f 4 5 0 - 5 6 5 K, used were f r o m t h r e e d i f f e r e n t c o a l s ( I l l i n o i s No. 6, W e s t e r n K e n t u c k y 9/14 and P i t t s b u r g h Seam) d e r i v e d under t h e same p r o c e s s c o n d i t i o n s , namely h y d r o g e n p r e s s u r e 13.8 MPa, r e a c t o r t e m p e r a t u r e 730 K, and a r e s i d e n c e time of 1 hr. , The 600 MHz H NMR s p e c t r o m e t e r w h i c h o p e r a t e s a t a mag n e t i c f i e l d 140.9 k g a u s s has been d e v e l o p e d by B o t h n e r - B y and Dadok a t C a r n e g i e - M e l l o n U n i v e r s i t y ( 2 2 ) · The r e s o l u t i o n d e t e r m i n e d by h a l f - h e i g h t w i d t h o f e t h a n o l t r i p l e t was 0.41 H z , and s i g n a l t o n o i s e r a t i o f o r a s i n g l e s c a n was b e t t e r t h a n 500:1. T e t r a m e t h y l s i l a n e was used as a l o c k s i g n a l as w e l l as f o r an i n t e r n a l s t a n d a r d . Each s p e c t r u m r e c o r d e d was t h e r e s u l t o f 1 0 - 1 0 0 t i m e - a v e r a g e s c a n s i n CDC1- s o l u t i o n s . The d i f f e r e n c e s p e c t r u m between t h e two S R C - I I m i d d l e d i s t i l l a t e s was o b t a i n e d f r o m t h e i n d i v i d u a l p r o t o n s p e c t r u m r e c o r d e d u n d e r t h e same c o n c e n t r a t i o n ( 3 8 . 2 g/1 i n C D C l g ) and o p e r a t i o n a l conditions. I n f r a r e d s p e c t r a were r e c o r d e d i n c a r b o n t e t r a c h l o r i d e i n 5 mm KBr l i q u i d c e l l s o r as a t h i n f i l m between NaCl p l a t e s on a Beckman I R - 2 0 i n f r a r e d s p e c t r o m e t e r . The n u m b e r - a v e r a g e m o l e c u l a r w e i g h t s were d e t e r m i n e d by v a p o r p r e s s u r e osmometry i n m e t h y l e n e c h l o r i d e s o l u t i o n s ( 3 - 8 g/1) ( 2 3 ) .
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
17.
HARA
Results
E T
and
AL.
600-MHz
Proton
Magnetic
Resonance
291
Discussion
The S R C - I I l i q u i d , b o i l i n g r a n g e o f 4 5 3 - 6 6 5 K, was f r a c t i o n a t e d by s o l v e n t e x t r a c t i o n b a s e d on i t s s o l u b i l i t y i n n-pentane. The p e n t a n e - s o l u b l e o i l f r a c t i o n ( A ) 9 9 . 3 % o f S R C - I I , was f u r t h e r f r a c t i o n a t e d by s e q u e n t i a l t r e a t m e n t w i t h a n i o n - e x c h a n g e r e s i n , c a t i o n - e x c h a n g e r e s i n and s i l i c a - g e l c o l u m n , as i l l u s t r a t e d i n F i g u r e 1. Weight p e r c e n t y i e l d s of t h e f r a c t i o n s , r e l a t i v e t o A a r e i n c l u d e d i n F i g u r e 1. A f t e r treatment of F r a c t i o n A w i t h anion-exchange resin, the n o n - r e a c t i v e p o r t i o n , a c i d - f r e e f r a c t i o n ( B ) , d i d not e x h i b i t a b s o r p t i o n s c h a r a c t e r i s t i c o f e i t h e r p h e n o l i c OH o r a c i d i c NH s t r e t c h i n g a p p r o x i m a t e l y a t 3,600 and 3,480 cm , respectively. T h i s i n d i c a t e s t h a t compounds c o n t a i n i n g n o t o n l y p h e n o l i c OH g r o u p b u t a l s o a c i d i c NH g r o u p c a n be removed by t h e r e a c t i o n w i t h a n i o n - e x c h a n g e r e s i n , as has been s u g g e s t e d by S c h e p p e l e e t a l . ( 1 0 ) . 600 MHz NMR s p e c t r a o f t h e F r a c t i o n s A and Β a r e shown i n F i g u r e 2. Removal o f t h e a c i d i c f r a c t i o n from A r e s u l t s i n a complete d i s a p p e a r a n c e o f a r o m a t i c p r o t o n s i g n a l s i n t h e r a n g e 6 . 4 2 - 6 . 7 7 ppm. I t i s known t h a t a r o m a t i c p r o t o n s show u p f i e l d s h i f t when e l e c t r o n - d o n a t i n g g r o u p s s u c h as h y d r o x y g r o u p a r e a t t a c h e d t o t h e same r i n g structure. I t i s i n t e r e s t i n g t o note t h a t a l i p h a t i c protons i n t h e r a n g e o f 2 . 2 0 - 2 . 4 0 ppm a s s i g n e d t o - C H ~ p r o t o n s d i r e c t l y a t t a c h e d t o mono-aromatic r i n g s t r u c t u r e (T4), a l s o decreased d r a s t i c a l l y a f t e r t h e removal o f a c i d i c f r a c t i o n s . A c i d i c and b a s i c f r a c t i o n s a d s o r b e d on t h e r e s i n s were r e c o v e r e d by s e q u e n t i a l e l u t i o n w i t h d i f f e r e n t s o l v e n t s y s t e m s , as shown i n F i g u r e 1. Elemental a n a l y s i s , molecular-weight, and e m p i r i c a l f o r m u l a o f F r a c t i o n A and f o u r m a j o r f r a c t i o n s ( C , D, Ε and G ) , a r e summarized i n T a b l e 1. The r e s u l t s i n d i c a t e t h a t a c i d i c f r a c t i o n s , p a r t i c u l a r l y A c i d - I I ( D ) , have l o w e r m o l e c u l a r w e i g h t s and n e u t r a l f r a c t i o n ( E ) c o n t a i n s no s i g n i f i c a n t amount o f h e t e r o a t o m s p e r m o l e c u l e . On an a v e r a g e , A c i d - I I has one oxygen atom and no n i t r o g e n p e r m o l e c u l e . B a s e - I I (G) has one n i t r o g e n atom and n e g l i g i b l e amount o f o x y g e n i n an a v e r a g e m o l e c u l e . I t s h o u l d be n o t e d t h a t A c i d - I ( C ) c o n t a i n s o x y g e n and n i t r o g e n f u n c t i o n a l i t i e s and t h a t t o t a l number o f o x y g e n and n i t r o g e n atoms i n an a v e r a g e m o l e c u l e i s c l o s e t o one. The r e s u l t s may s u g g e s t t h a t a c i d i c f r a c t i o n ( C ) i s a m i x t u r e o f o x y g e n - c o n t a i n i n g and n i t r o g e n - c o n t a i n i n g compounds. The r e s u l t s on t h e h e t e r o a t o m f u n c t i o n a l i t i e s i n T a b l e 1 a r e w e l l s u p p o r t e d by s o l u t i o n i n f r a r e d s p e c t r a o f t h e f r a c t i o n s shown i n F i g u r e 3. Table 2 l i s t s the percent d i s t r i b u t i o n o f h e t e r o a t o m s among t h e f r a c t i o n s , c a l c u l a t e d f r o m t h e d a t a i n T a b l e 1. We f i n d 80% o f t h e t o t a l o x y g e n l o c a t e d i n two a c i d i c f r a c t i o n s (C and D ) , and 49% o f t h e t o t a l n i t r o g e n a r e i n B a s e - I I (G) i n s p i t e o f i t s l o w c o n t e n t ( 6 . 6 % ) . Sulfur i s d i s t r i b u t e d more e v e n l y among t h e f r a c t i o n s , b u t h i g h e r i n n e u t r a l f r a c t i o n ( E ) and l o w e r i n a c i d i c F r a c t i o n s C and D.
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
BASE-II G
(6.6%)
LOSS
(2.4%)
3
2
MeOH (CH ) CHNH
^6 6
Figure 1.
(1.4%)
BASEL F
2
Η
5
1 2
H
"~C5 12
6
H
ACID-II,D (15.0%)
(46.4%)
(8.1%)
Chromatographic fractionation of SRC-II
AROMATIC-!, Κ
CHC1
(9.0%)
C - 1,H
3
2
2
LOSS (2.0%)
(2.6%)
2
AROMATIC-II
MeOH
(2.1%)
3
LOSS (2.1%)
MeOH (CH ) CHNH
ACID-MI (2.3%)
|"mF/HC0 H |
C — 2, I
j MeOH/C0
(99.3% OF SRC II)
[CATION-EXCHANGE RESIN A - 15
C6 6
ACID-I,C (11.1%)
6
C H
SATURATES, J
SILICA GEL
l
(59.1%)
NEUTRAL, Ε
CATION-EXCHANGE RESIN A — 15
n-C H
(69.5%)
ACID-FREE, Β
n - C c5" H 12 ANION-EXCHANGE RESIN IRA -904
PENTANE - SOLUBLE OIL OF SRC II, A
2
H
GO
g
ο χ m
ι
Ο X m
>
m
2
VO
17.
HARA
E T
600-MHz
AL.
-ι
Proton
Magnetic
293
Resonance
r A.
5.0
7.5
2.5 PPM
7.5
B.
2.5
5.0 PPM
Figure 2.
600-MHz NMR
spectra of Fractions A and B
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
294
NEW
APPROACHES IN COAL CHEMISTRY
Table 1 Elemental A n a l y s i s , Molecular Weight, E m p i r i c a l Formulaof t h e Major F r a c t i o n s of SRC-II
Fraction
A
Mol. Wt.* Elemental Analysis:
C H 0** Ν S
C Acid-I 156
D Acid-II 128
G Base-I] 182
161
Ε Neutral 180
86.09 8.48 3.99 1.15 0.29
89.96 8.95 0.61 0.10 0.38
80.57 8.25 8.91 2.17 0.10
77.32 7.60 14.66 0.32
m
00
17.
HARA
E T
AL.
600-MHz
Proton
Magnetic
Resonance
oo
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
300
NEW APPROACHES IN COAL CHEMISTRY
Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
17.
HARA
E T
600-MHz
AL.
Proton
Magnetic
301
Resonance
Table 2 Percent D i s t r i b u t i o n of
Heteroatoms
Y i e l d , Wt.% ( R e l a t i v e t o A) E Fraction
C
Neutral 59.1
D
G
Acid-I
Acid-II
Base-Il
11.1
15.0
6.6
D i s t r i b u t i o n of Heteroatoms
Others
8.2
(wt.%)
Heteroatom 0
9
25
55
2
9
N
5
21
4
49
21
S
78-80
3-4
