Relationships Between the Organic Structure of Vitrinite and Selected

7 Relationships Between the Organic Structure of Vitrinite and Selected Parameters of Coalification as Indicated by Fourier Transform IR Spectra 1

DEBORAH W. KUEHN , ALAN DAVIS, and PAUL C. PAINTER

Downloaded by UNIV OF AUCKLAND on March 27, 2017 | http://pubs.acs.org Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch007

College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, PA 16802

Q u a n t i t a t i v e data f o r the organic f u n c t i o n a l groups in 24 vitrinite concentrates were obtained by FTIR a n a l y s i s of samples c o l l e c t e d from the Lower Kittanning coal seam i n western Pennsylvania and eastern Ohio. Absorption areas f o r aliphatic and aromatic CH groups were determined and compared t o s e l e c t e d parameters of coalification i n b i v a r i a t e and principal components a n a l y s e s . A l i p h a t i c C H and CH groups d i s p l a y e d a slight p o s i t i v e increase w i t h i n c r e a s i n g coalification and v a r i e d dependently w i t h calorific value and moisture content. A l i p h a t i c C H groups decreased with an increase i n coalification and components a n a l y s i s revealed partial dependent relationships with volatile matter, carbon content, and r e f l e c t a n c e . Aromatic bands at 884, 815, 8 0 1 , and 750 c m - 1 r e p r e s e n t i n g 1, 2 , 3 , and 4 adjacent hydrogens, r e s p e c t i v e l y , and total aromatic content all showed strong p o s i t i v e c o r r e l a t i o n s with i n c r e a s i n g coalification. P r i n c i p a l components a n a l y s i s r e vealed interdependent r e l a t i o n s h i p s and similar patterns of v a r i a t i o n among these bands. The a r o matic bands at 864, 834, and 785 cm e x h i b i t e d differing patterns of v a r i a t i o n and it is suggested that t h e y , in fact, may not be aromatic i n nature. 3

2

-1

V a r i a t i o n s i n organic s t r u c t u r e of v i t r i n i t e concentrates were determined with F o u r i e r transform i n f r a r e d spectroscopy (FTIR). FTIR i s a r e l a t i v e l y new method f o r o b t a i n i n g q u a n t i t a t i v e data from the organic c o n s t i t u e n t s of coal and provides s p e c t r a of greater q u a l i t y than conventional i n f r a r e d spectrometers. The system employs an o n - l i n e minicomputer which enables the user to analyze data and perform a v a r i e t y of mathematical m a n i p u l a t i o n s . Current address: Department of Geosciences, University of Tennessee at Chattanooga, Chattanooga, T N 37402 1

0097-6156/ 84/ 0252-0099S06.00/ 0 © 1984 American Chemical Society

Winans and Crelling; Chemistry and Characterization of Coal Macerals ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

COAL MACERALS


100

The o b j e c t i v e s of t h i s study were (1) t o reveal trends be tween s e l e c t e d regions of the i n f r a r e d spectrum and accepted i n d i c a t o r s of c o a l i f i c a t i o n ; (2) t o determine the nature and degree of interdependency among these data using s t a t i s t i c a l a n a l y s e s ; and (3) to evaluate the usefulness of FTIR data i n measuring degree of coalification. Twenty-four v i t r i n i t e concentrates were obtained from samples of the Lower K i t t a n n i n g coal seam i n western Pennsylvania and eastern Ohio by hand p i c k i n g the b r i g h t bands i n the c o a l . A l o c a t i o n map of sample s i t e s with t h e i r designated i d e n t i f i c a t i o n numbers i s given i n Figure 1. The Lower K i t t a n n i n g seam i s w e l l s u i t e d f o r t h i s study because i t i s known t o d i s p l a y a broad range of c o a l i f i c a t i o n (high v o l a t i l e Β to low v o l a t i l e bituminous). Some chamical and o p t i c a l parameters of c o a l i f i c a t i o n are reported in Table I f o r the v i t r i n i t e c o n c e n t r a t e s . T o t a l v i t r i n i t e con tent i s included as an i n d i c a t i o n of sample p u r i t y . Equipment FTIR analyses were performed on a D i g i l a b FTS 15/B spectrophotom e t e r having a s p e c t r a l range of 10,000 - 10 cm" . The system i s c a l i b r a t e d a u t o m a t i c a l l y with a helium-neon l a s e r and i s accurate to 0.2 cm" . The o n - l i n e computer system i s a 16 bit/word m i n i computer c o n t a i n i n g 32 Κ words of memory. Disk storage of 256 Κ words contains the system programs, user programs, and i n f r a r e d d a t a , among o t h e r s . 1

1

Sample Preparation Pressed d i s k s were prepared from a mixture c o n t a i n i n g 300.0 mg of potassium bromide and 1.2 mg of c o a l . T h i s mixture was ground in a v i b r a t i n g m i l l f o r 30 sec and placed i n a d e s i c c a t o r f o r 24 h. A f t e r d r y i n g , the mixture was pressed under vacuum f o r 1 min using 9000 kg of l o a d . Potassium bromide was s e l e c t e d as the binder because i t does not have s p e c i f i c absorption bands i n the m i d - i n f r a r e d region although i t does absorb water r e a d i l y . Water masks the OH ab s o r p t i o n at 3400 cm" , making i n t e r p r e t a t i o n of t h i s region difficult. U t i l i z i n g such small weights of coal (1.2 mg) i n each d i s k can permit r e l a t i v e l y large sampling e r r o r s . Previous e x p e r i ments on the r e p r o d u c i b i l i t y of such small samples have revealed n o n s i g n i f i c a n t e r r o r s over the s p e c t r a l regions under i n v e s t i g a t i o n . The average standard e r r o r was found to be Î 3 % . 1

Procedure V i t r i n i t e concentrates were analyzed i n the m i d - i n f r a r e d region between 3800 and 450 c n r using a s p e c t r a l r e s o l u t i o n of 2 c m " . Four hundred scans were co-added f o r each sample and a r a t i o was 1


1


Figure 1. Sample s i t e s of v i t r i n i t e concentrates from the Lower K i t t a n n i n g seam.



Total V i t r i n i t e (mmf) Vol %

98.4 98.1 99.0 98.4 99.0 98.8 98.8 97.8 98.0 94.2 97.6 89.3 98.4 98.8 95.5 98.6 98.8 96.5 97.8 99.2 96.1 96.8 96.2 97.4

ID #

16 18 20 30 33 36 39 48 49 50 52 54 56 58 59 60 62 65 67 68 69 70 71 72

Table I.

86.6 85.8 85.4 84.6 83.0 84.3 85.1 88.8 88.3 90.1 91.3 89.8 89.4 83.7 83.3 80.2 84.7 82.2 83.2 87.0 85.2 87.3 85.5 88.7

C (dmmf)

5.6 5.6 6.0 5.2 5.3 5.3 5.7 5.4 5.3 5.2 4.8 4.7 5.3 5.3 5.6 5.3 5.5 5.3 5.6 5.5 5.2 5.6 5.6 5.6

H (dmmf)

Volatile Matter (dmmf) 33.3 37.6 40.7 35.5 39.4 34.9 40.7 29.8 26.4 24.2 21.8 18.5 30.7 40.7 42.0 37.7 36.4 37.8 41.4 38.0 28.9 36.8 33.6 25.9

Moisture (mmf) 2.1 2.1 2.2 3.1 2.1 2.6 1.8 1.0 0.9 0.8 1.0 1.8 1.2 7.4 4.1 7.1 3.7 6.7 5.4 1.6 1.1 2.2 2.4 1.3

Chemical and P é t r o g r a p h i e Data f o r V i t r i n i t e

15085 14883 15194 14407 14674 14405 15127 15628 15643 15846 15854 15378 15738 13675 14208 12932 14357 13407 13891 15441 15595 15278 14780 15703

Calorific Value (mmmf)

Concentrates


1.03 0.87 0.83 0.89 0.87 0.96 0.83 1.19 1.34 1.43 1.50 1.71 1.14 0.55 0.60 0.60 0.80 0.64 0.57 0.92 1.26 0.89 1.03 1.31

Reflectance in O i l , %

7. KUEHN ET AL.

Vitrinite and Coalification:

FTIR

103

Spectra

taken to 400 scans of the atmosphere w i t h i n the sample chamber. This step removed the e f f e c t s of any water vapor which was not e l i m i n a t e d by the normal purge of the sample chamber with dry a i r . Several computer programs were employed on the D i g i l a b s y s tem f o r the adjustment of s p e c t r a . In order to e l i m i n a t e e f f e c t s due to v a r i a t i o n i n sample weights, a l l spectra were normalized to 1 mg using appropriate s c a l i n g f a c t o r s . A l s o , a program f o r s p e c t r a l s u b t r a c t i o n was used to remove mineral c a l c i t e which appears as a small shoulder on the 864 crrr band i n the aromatic o u t - o f - p l a n e bending region [1). Other techniques used to obtain q u a n t i t a t i v e data were d e r i v a t i v e spectroscopy, i n t e g r a t i o n , and l e a s t - s q u a r e s curve f i t t i n g . A t y p i c a l i n f r a r e d spectrum of a v i t r i n i t e concentrate i s presented i n Figure 2 . Three regions of t h i s spectrum are of i n t e r e s t here: aromatic s t r e t c h i n g between 3100 and 3000 cm" , a l i p h a t i c s t r e t c h i n g between 3000 and 2750 cm" , and aromatic o u t - o f - p l a n e bending between 900 and 700 c m - . Q u a n t i t a t i v e data were obtained f o r these regions both by i n t e g r a t i o n and l e a s t squares curve f i t t i n g . I n t e g r a t i o n i s a method f o r determining the area under a s e l e c t e d region of the spectrum. I t can provide data very q u i c k l y ; however, i t cannot provide data from the i n d i v i d u a l absorption bands found w i t h i n a r e g i o n . Least-squares curve f i t t i n g i s a method which r e s o l v e s a region i n t o component bands. In a l e a s t - s q u a r e s a n a l y s i s , parameters are s e l e c t e d so t h a t the d i f f e r e n c e s between observed data and data c a l c u l a t e d from a model are minimized ( 2 ) . F i r s t , the number of major component bands i s ascertained By t a k i n g the second d e r i v a t i v e of the spectrum. D e r i v a t i v e spectroscopy enhances very weak s h o u l ders i n spectra so long as the peaks are separated by more than h a l f t h e i r h a l f w i d t h . D e t a i l s of t h i s technique, as a p p l i e d to these s p e c t r a l r e g i o n s , are reported elsewhere ( 1 , 3 , 4 ) . Weak absorption i n the aromatic s t r e t c h i n g region does not permit the use of d e r i v a t i v e spectroscopy, so i n d i v i d u a l component bands were not o b t a i n e d . Second, a s u i t a b l e mathematical f u n c t i o n f o r c h a r a c t e r i z i n g the observed band shapes i s chosen. Maddams (ji) r e c e n t l y has reviewed methods f o r curve f i t t i n g and suggested employing a Lorentzian band shape. Other workers have used products or sums of Gaussian and Lorentzian curves ( 6 , 7 ) . Solomon, et al_. (8) used Gaussian band shapes, e x c l u s i v e l y . Our method was adopted from Jones, et a l . {9) who obtained t h e i r best r e s u l t s using a sum of Gaussian and"Torentzian f u n c t i o n s . In t h i s study, curve f i t t i n g was performed on the a l i p h a t i c s t r e t c h i n g region (using f i v e component bands) and the aromatic o u t - o f - p l a n e bending region (using seven component bands). Table II l i s t s the peak l o c a t i o n s and assigned f u n c t i o n a l groups f o r both of these r e g i o n s . The peak l o c a t i o n s were not held constant f o r a l l samples so t h a t the wavenumbers reported i n Table II represent average v a l u e s . When curve f i t t i n g was completed, areas f o r the component bands were c a l c u l a t e d by i n t e g r a t i o n .


1

1

1

1


COAL M A C E R A L S


OH groups, water

τ — ι — ' — ' — ι — I — ι — ι — τ — f — ι — ι — ι — ι — ι — ι — ι — ι — i — i — ι ι ' — r — ι — f — ι — ι — ι ι—r'T 3600 3200 2800 2400 2000 1600 1200 800 Wave Numbers (cm- ) 1

Figure 2 .

FTIR spectrum of a v i t r i n i t e

concentrate.


7. KUEHN ET AL.

Table I I .

Vitrinite and Coalification: FTIR

Spectra

105

Band Assignments f o r the A l i p h a t i c S t r e t c h i n g and Aromatic Out-of-plane Bending Regions

Region

Peak P o s i t i o n (cm- )

Assignment

1


Aliphatic Stretching

Aromatic Out-of-plane Bending

2956 2923 2891 2864 2853 884 864 834 815 801 785 750

CH3 groups (asymmetric s t r e t c h ) Composite of CH3 & CH (asymmetric s t r e t c h ) CH groups CH3 groups (symmetric s t r e t c h ) CH2 groups (symmetric s t r e t c h ) 2

1 Adjacent Hydrogen 1 Adjacent Hydrogen Possible a l i p h a t i c rocking & secondary aromatic o u t - o f plane bending modes 2 Adjacent Hydrogens 3 Adjacent Hydrogens P o s s i b l e i s o l a t e d and 2 adjacent CH2 u n i t s 4 Adjacent Hydrogens

R e s u l t s and Discussion Q u a n t i t a t i v e FTIR data were combined with chemical and p é t r o graphie data f o r the 24 v i t r i n i t e concentrates and subjected to b i v a r i a t e and m u l t i v a r i a t e s t a t i s t i c a l analyses i n order to i d e n t i f y the e f f e c t s of c o a l i f i c a t i o n on the a l i p h a t i c and aromatic f u n c t i o n a l groups. B i v a r i a t e A n a l y s i s . C o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d f o r every p o s s i b l e p a i r of v a r i a b l e s in order to determine the nature and degree of l i n e a r interdependence between them. The c o r r e l a t i o n c o e f f i c i e n t (r) ranges from +1 to - 1 , with the end members i n d i c a t i n g a complete l i n e a r dependence and a zero i n d i c a t i n g complete independence. A p o s i t i v e value f o r r i n d i c a t e s a d i r e c t r e l a t i o n s h i p e x i s t s between a given p a i r of v a r i a b l e s and a negat i v e value s i g n i f i e s an inverse r e l a t i o n s h i p . The s i g n i f i c a n c e of each r value was determined by comparison to t a b l e d values (10). At the 95% confidence l e v e l , a c o r r e l a t i o n c o e f f i c i e n t must exceed 0.404 to be s i g n i f i c a n t based on a sample set of t w e n t y - f o u r . Anything l e s s than 0.404 i s n o n s i g n i f i c a n t , meaning i t can be explained by random e r r o r . Data obtained both by i n t e g r a t i o n and l e a s t - s q u a r e s curve f i t t i n g are compared in order to reveal p o s s i b l e d i f f e r e n c e s i n the q u a l i t y of data produced. I n t e g r a t i o n over a s p e c t r a l region takes only the time needed to input the i n f o r m a t i o n , whereas curve f i t t i n g may take 30 min to r e s o l v e the component bands be-


COAL MACERALS


106

f o r e i n t e g r a t i o n can be performed. T h e r e f o r e , curve f i t t i n g should improve the r e s u l t s to j u s t i f y i t s use. Table III l i s t s c o r r e l a t i o n c o e f f i c i e n t s f o r both methods with s e l e c t e d parame t e r s of c o a l i f i c a t i o n . T o t a l area by curve f i t t i n g i s obtained by adding the i n t e g r a t e d areas of the component bands. There i s l i t t l e d i f f e r e n c e in c o r r e l a t i o n c o e f f i c i e n t s f o r t o t a l a l i p h a t i c CH; some c o r r e l a t i o n s are higher f o r area by curve f i t t i n g , some are lower. A l l but the c o r r e l a t i o n s with moisture and c a l o r i f i c value are n o n s i g n i f i c a n t . Therefore, curve f i t t i n g does not appear to improve the data f o r t o t a l area of a l i p h a t i c CH groups. The remaining s i g n i f i c a n t c o r r e l a t i o n s are low and suggest only a s l i g h t increase in a l i p h a t i c content as c o a l i f i c a t i o n i n c r e a s e s . Areas determined by i n t e g r a t i o n both before and a f t e r curve f i t t i n g produce s i g n i f i c a n t c o r r e l a t i o n s with parameters of c o a l i f i c a t i o n f o r the aromatic o u t - o f - p l a n e bending r e g i o n . However, c o r r e l a t i o n c o e f f i c i e n t s f o r the area obtained a f t e r curve f i t t i n g are c o n s i s t e n t l y h i g h e r . Only f i v e of the seven bands reported i n Table II f o r t h i s region are included i n the t o t a l area by curve f i t t i n g because two bands do not appear to be aromatic i n nature. Bands representing both i s o l a t e d and two adjacent CH u n i t s were reported at 834 and 785 cm" by D r u s h e l , et aT. (11) and supported by P a i n t e r , et a l . ( 1 2 ) . These must Be i n c l u d e d , however, in the t o t a l area o ï ï t a i n ê ï ï by i n t e g r a t i o n and probably account f o r the lower c o r r e l a t i o n s using t h i s method alone. A l s o included i n Table III i s the integrated area f o r the aromatic s t r e t c h i n g r e g i o n . This region e x h i b i t s some of the highest c o r r e l a t i o n s with parameters of c o a l i f i c a t i o n and appears to be a s l i g h t l y b e t t e r i n d i c a t o r of degree of c o a l i f i c a t i o n than the aromatic o u t - o f - p l a n e bending r e g i o n . A comparision of the two methods f o r o b t a i n i n g data f o r t o t a l aromatic CH r e v e a l s t h a t l e a s t - s q u a r e s curve f i t t i n g i s j u s t i f i e d f o r the aromatic o u t - o f - p l a n e bending r e g i o n , producing higher c o r r e l a t i o n c o e f f i c i e n t s than i n t e g r a t i o n a l o n e . However, the highest c o r r e l a t i o n s are obtained f o r the aromatic s t r e t c h i n g region by i n t e g r a t i o n , which suggests that t h i s region should be used f o r determining aromatic CH content. Although l e a s t - s q u a r e s curve f i t t i n g may not be a u s e f u l method i n determining t o t a l area of a given s p e c t r a l r e g i o n , i t does supply information on component bands not o b t a i n a b l e by i n t e g r a t i o n a l o n e . Areas f o r the component bands i n the a l i p h a t i c s t r e t c h i n g and aromatic o u t - o f - p l a n e bending regions are compared to the same parameters of c o a l i f i c a t i o n and presented as a c o r r e l a t i o n matrix i n Table IV. No one parameter shows the best overa l l c o r r e l a t i o n s with a l l bands. C a l o r i f i c value gives the best c o r r e l a t i o n s f o r f i v e c a s e s , v i t r i n i t e r e f l e c t a n c e and elemental carbon each f o r t h r e e , and v o l a t i l e matter f o r one. The c o r r e l a t i o n c o e f f i c i e n t s f o r the a l i p h a t i c bands at 2956 and 2864 cm" , both of which belong to CH3 groups, are j n e x p l a i n ably d i f f e r e n t . The asymmetric CH3 s t r e t c h at 2956 cm" produces 1

2

1

1



Integration

Aromatic S t r e t c h i n g Region

Integration Least-squares Curve Fitting

Aromatic Out-of-plane Bending Region

Integration Least-squares Curve Fitting

-0.728

-0.749

0.903

0.888

-0.675

-0.501

0.274

0.867

-0.489

Moisture (mmf)

0.203

Carbon (dmmf)

-0.932

-0.800

-0.683

0.185

0.266

Volatile Matter (dmmf)

0.821

0.830

0.783

0.528

0.475

Calorific Value ( b t u / l b , mmmf)

0.965

0.868

0.743

0.019

-0.056


C o r r e l a t i o n s Between Methods of Determining T o t a l Areas of A l i p h a t i c and Aromatic Regions and Parameters of C o a l i f i c a t i o n

A l i p h a t i c S t r e t c h i n g Region

Table I I I .



Volatile Matter -0.421 -0.176 -0.123 0.323 0.837 0.185 -0.877 -0.516 0.124 -0.738 -0.862 -0.502 -0.837 -0.800

Moisture (mmf) -0.817 -0.748 -0.733 -0.346 0.436 -0.501 -0.620 -0.697 -0.218 -0.716 -0.691 -0.574 -0.765 -0.749

Carbon (dmmf) 0.659 0.549 0.560 0.146 -0.555 0.274 0.846 0.732 0.244 0.847 0.877 0.667 0.909 0.903

2956 2923 2891 2864 2853 T o t a l A l i p h a t i c Area 884 864 834 815 801 785 750 T o t a l Aromatic Area

0.849 0.782 0.768 0.377 -0.445 0.528 0.709 0.734 0.225 0.790 0.769 0.639 0.849 0.830

Calorific Value ( b t u / l b , mmmf)

0.585 0.374 0.321 -0.149 -0.771 0.019 0.904 0.604 -0.024 0.797 0.914 0.589 0.911 0.868


C o r r e l a t i o n Matrix f o r Areas of FTIR Absorption Bands and Parameters of C o a l i f i c a t i o n

Areas (dmmf) (Band L o c a t i o n , cm-1)

Table IV.


7.

KUEHN ET AL.

Vitrinite and Coalification:

FTIR

Spectra

109

s i g n i f i c a n t and higher c o r r e l a t i o n s compared to the symmetric CH3 s t r e t c h at 2864 cm" whose c o r r e l a t i o n s are n o n s i g n i f i c a n t . This suggests that the assignment f o r the band at 2864 cm" should be re-examined. As shown i n Figure 3 , area of the 2956 cm" band increases as c o a l i f i c a t i o n ( c a l o r i f i c value) i n c r e a s e s . A c a l c u l a t e d r value of 72% means t h a t c o a l i f i c a t i o n expressed by c a l o r i f i c value e x p l a i n s 72% of the v a r i a b i l i t y observed i n a l i phatic CH3 groups. A s i m i l a r d i r e c t r e l a t i o n s h i p i s found between the area at 2891 c m (assigned to lone CH groups) and c a l o r i f i c v a l u e . F i n a l l y , the symmetric CH s t r e t c h at 2853 cm- shows the only i n d i r e c t r e l a t i o n s h i p with i n c r e a s i n g c o a l i f i c a t i o n (Figure 4) with an r of 70% ( v o l a t i l e matter i s highest f o r low l e v e l s of c o a l i f i c a t i o n ) . C o r r e l a t i o n c o e f f i c i e n t s f o r the composite of CH and CH3 s t r e t c h at 2923 cm" suggest t h a t the c o n t r i b u t i o n of CH i s only minor. Not only are the values c l o s e r to those f o r asymmetric CH3 s t r e t c h but, more important, they are p o s i t i v e . If the cont r i b u t i o n s of CH and CHo to the 2923 cm" band were n e a r l y e q u a l , i t would seem l i k e l y t h a t t h e i r opposing trends would cancel and no s i g n i f i c a n t c o r r e l a t i o n s would be observed f o r t h i s band. T o t a l a l i p h a t i c area has a p o s i t i v e c o r r e l a t i o n w i t h c o a l i f i c a t i o n f o r moisture and c a l o r i f i c v a l u e ; however, the c o r r e l a t i o n s are weak. The highest r value obtained i s only 28%. The reason f o r the low c o r r e l a t i o n s i s the inverse r e l a t i o n s h i p with i n c r e a s i n g c o a l i f i c a t i o n shown by CH groups at 2853 c m - . If the trend had been p o s i t i v e , the c o r r e l a t i o n s f o r t o t a l area p r o bably would have been h i g h e r . The aromatic o u t - o f - p l a n e bending region has c o n s i s t e n t l y higher c o r r e l a t i o n s with parameters of c o a l i f i c a t i o n than the a l i p h a t i c region and a l l of them vary d i r e c t l y w i t h i n c r e a s i n g c o a l i f i c a t i o n . Figures 5 and 6 show examples of trends f o r the bands at 884 and 750 c m - having r values of 82% and 83%, r e s p e c t i v e l y . The data suggest t h a t any one of the aromatic bands would appear to work e q u a l l y w e l l i n expressing the degree of c o a l i f i c a t i o n of the c o a l . Since t h e i r trends show the same patterns with c o a l i f i c a t i o n , i t i s not s u r p r i s i n g t h a t the t o t a l aromatic area a l s o shows high p o s i t i v e c o r r e l a t i o n s with i n creasing c o a l i f i c a t i o n . Some workers have reported t h a t under i n c r e a s i n g c o a l i f i c a t i o n the degree of s u b s t i t u t i o n w i t h i n aromatic u n i t s decreases, meaning t h a t more hydrogens are attached to the aromatic nucleus (13-15). This f i n d i n g a l s o i s suggested here. Although the band at 884 cm" assigned to one adjacent hydrogen shows the same p o s i t i v e c o r r e l a t i o n with c o a l i f i c a t i o n as the band at 750 c n r a s signed to four adjacent hydrogens, the slopes of the l i n e s i n Figures 5 and 6 are d i f f e r e n t . The slope f o r area at 884 cm" versus r e f l e c t a n c e i s 145.4, whereas f o r 750 cm" i t i s 2 0 4 . 5 . T h e r e f o r e , the i n t e n s i t y of the 750 cm" band increases at a greater r a t e than the band at 884 cm- as c o a l i f i c a t i o n i n c r e a s e s . 1

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COAL MACERALS

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CM

Relationships Between the Organic Structure of Vitrinite and Selected

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