Characterization of coal maceral concentrates by curie-point pyrolysis mass spectrometry

International Journal of Coal Geology, 4 (1984) 143--171 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

CHARACTERIZATION OF COAL MACERAL CONCENTRATES CURIE-POINT PYROLYSIS MASS SPECTROMETRY

143

BY

HENK L.C. MEUZELAAR 1, ALICE M. HARPER 1, RONALD J. PUGMIRE 2 and JIRINA KARAS 2

Biornaterials Profiling Center, University of Utah, Research Park, Salt Lake City, UT 84108 (U.S.A.) Maceral Separation Laboratory, University of Utah, Research Park, Salt Lake City, UT 84108 (U.S.A.) (Received May 9, 1983; revised and accepted March 6, 1984)

ABSTRACT Meuzelaar, H.L.C., Harper, A.M., Pugmire, R.J. and Karas, J., 1984. Characterization of coal maceral concentrates by Curie-point pyrolysis mass spectrometry. Int. J. Coal Geol., 4: 143--171. A set of 30 maceral concentrates consisting of 5 exinites (sporinites), 14 vitrinites and 11 inertinites (fusinites and semifusinites) was analyzed by Curie-point pyrolysis mass spectrometry in combination with computerized multivariate statistical analysis techniques. Seventeen samples, representing sink/flotation concentrates of 7 different coals, were obtained through the British National Coal Board, whereas the remaining samples represent cesium-chloride density-gradient centrifugation fractions of two different U.S. coals prepared at the University of Utah. It is found that vitrinites, (semi)fusinites and, to some extent, sporinites show qualitatively similar rank-related changes, such as a decrease in dihydroxybenzene signals and an increase in naphthalene signals with increasing rank. In fact, the overall pyrolysis MS patterns of inertinites show a close similarity to those of vitrinites of corresponding carbon content (as obtained from higher rank coals). Notwithstanding these similarities, however, the presence of basic differences in maceral structure is indicated by relatively minor but characteristic peak series in the liptinite (sporinite) as well as inertinite samples. Whereas inertinite spectra show relatively pronounced peak series at the high mass end of the spectrum which can be tentatively identified as representative of polynuclear aromatic compounds, sporinites are characterized by series of branched aliphatic and/or alicyclic potyenic hydrocarbons, possibly representing isoprenoids and related biomarker compounds.

INTRODUCTION M a r k e d d i f f e r e n c e s c a n be o b s e r v e d b e t w e e n t h e p y r o l y s i s m a s s s p e c t r a o f m a j o r m a c e r a l t y p e s s u c h as v i t r i n i t e , f u s i n i t e , s p o r i n i t e a n d a l g i n i t e as r e p o r t e d b y L a r t e r ( 1 9 7 8 ) , V a n G r a a s et al. ( 1 9 7 9 ) , A l l a n a n d L a r t e r ( 1 9 8 1 ) a n d M e u z e l a a r e t al. ( 1 9 8 2 a ) . T h e v i t r i n i t e s e x a m i n e d b y t h e s e a u t h o r s show prominent hydroxyaromatic series, e.g. a l k y l s u b s t i t u t e d p h e n o l s ,

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© 1984 Elsevier Science Publishers B.V.

144 whereas fusinites are dominated by aromatic hydrocarbon series, e.g. alkylsubstituted benzenes and naphthalenes. Alginites appear to lack prominent aromatic signals but show strong aliphatic hydrocarbon series of varying degrees of unsaturation. Somewhat surprisingly, sporinite patterns are remarkably similar to vitrinite patterns, although showing more pronounced contributions from low molecular weight aliphatic hydrocarbons. At first sight there appears to be good overall agreement between these pyrolysis MS results and currently accepted views on the chemical nature of the various coal macerals. However, our study of over 100 Rocky Mountain Province coals (Meuzelaar et al., 1982b) reveals a highly complex relationship between rank, depositional environment (including maceral composition) and geological history (Meuzelaar et al., 1984). In coals with high vitrinite content (> 85%), increase in rank from subbituminous to medium volatile bituminous is accompanied by a rapid decrease in hydroxyaromatic moieties and a concurrent, marked increase in aromatic hydrocarbon series. Thus, in agreement with the Van Krevelen plot (1961), prominent aromatic hydrocarbon series are not only characteristic of fusinites but also of vitrinites of higher rank. With regard to exinite macerals, our study was able to confirm the dominantly aliphatic hydrocarbon nature of alginites as expressed in a boghead coal but provided no further data on sporinites since this maceral is not abundant in coals of Cretaceous age (Teichm~iller and Teichm~iller, 1975). The fact that many questions regarding the nature and composition of vitrinites, fusinites and sporinites were left unanswered prompted us to undertake a systematic study of maceral concentrates by pyrolysis MS. In this we were aided by the availability of a widely studied (Given et at., in press) set of coal maceral concentrates from the British National Coal Board obtained by conventional sink/flotation techniques and some additional maceral fractions of U.S. coals obtained by the new density gradient centrifugation approach (Dyrkacz et al., 1981). The results of this pyrolysis MS study of maceral concentrates will be reported here. EXPERIMENTAL

Sample collection and preparation Seventeen maceral concentrates (6 vitrinites, 7 inertinites and 4 exinites) were obtained from the British National Coal Board where they had been prepared by conventional sink/flotation methods and stored under nitrogen for periods of up to several years. Whereas one inertinite and one exinite (Table I, numbers 16 and 17) were mailed directly to us by NCB, the other NCB macerals were obtained through Dr. Given at Penn State University, who redistributed these samples to different research groups. All petrographic data supplied by NCB were checked independently at Penn State with good correlation being found in most cases (see Table II). Other conventional analytical data are shown in Table I.

Sample

GeUideg ( C o e g n a n t )

Beeston (Peekfield)

A }

A A R } Ra Rb C } C

P } P

9 10 11 12 13 14 15 16

E1 I E2 E3 E4 E5 E6

$S12 t $3 $4

$5 S6 $7

24 25 26 27

28 29 30

[PSOC 2]

[PSOC 858]

D a k o t a (San J u a n River)

VIT VIT INb IN

VIT

VIT VIT

IN a IN

VIT U p p e r E l k h o r n (E. A p p a l a c h ) VIT

EX IN EX VIT

EX VIT IN EX VIT EX VIT IN VIT IN IN VIT IN

V1T IN

Maceral group

[85.1

[85.5

81.5 87.7 82.6 82.2 91.6 87.9 86.6 87.2 86.9 92.1 88.8 93.9 91.9 91.4 92.3 84.3 93.5

%C

5.4

5.6

5.1 3.9 7.4 5.5 3.6 6.9 5.6 7.4 5,4 3.7 5.3 3.5 4.3 4.6 4.2 7.0 2.9

%H

7.8

6.8

10.8 6.9 7,3 9.3 4.1 3.0 4.9 3.6 5.2 3.1 3.6 1.4 3.1 1.9 1.9 4.2 2.7

%0

Ultimate analysisc

1.2

1.5

2.0 1.1 1,1 1.9 0.4 1.1 1.8 1.2 1.8 0.7 1.7 0.5 0.3 1.6 1.1 1.3 0.4

%N

0.6

0.6

0.7 0.4 1.9 1.3 1.2 1.2 1.4 0.7 1.1 0.4 0.7 0.8 0.5 0.6 0.6 1.2 0.5

%S t

4.6

2.1

13.8 6.0 3.8 10.3 2.2 --1.0 2.4 -1.4 0.8 1.3 1.5 1.5 2.7 1.6

Equfl. moist,

29.1

35.4

35.1 21.5 73.7 40.1 18.1 57.8 36.1 66.5 33.2 15.4 29.8 11.8 18.7 16.5 12.9 64.9 9.6

Vol. matter

a p s o c 2 i n e r t i n i t e c o n s i s t s of a p p r o x i m a t e l y e q u a l a m o u n t s of fusirdte, semifusirtite, m a c r i n i t e a n d m i c r i r d t e . b p s o c 858 inertinite consists mainly of semifusinitc. C% C, H, O and N = dry, m i n e r a l m a t t e r free; % S t ( t o t a l sulfur) = dry.

20 21 22 23

18 19

17

Ball&rat ( R o d d y m o o r )

Sflkstone ( A l d w a r k e )

Wheatly Lime (Woolley)

Barnsiey (Markham)

8

}

}

M M M W W

3 4 5 6 7

D u n s i l (Teversal)

Seam ( c o l l i e r y )

T}

2

T

code

1

No.

U l t i m a t e a n d p r o x i m a t e a n a l y s i s v a l u e s of m a c e r a l c o n c e n t r a t e s a n a l y z e d

TABLE I

25.1]

4.5]

0.4 2.9 0.9 1.4 6.0 2.8 1.4 0.3 0.8 5.0 0.5 10.7 1.7 0.8 1.6 1.7 1.2

Mineral matter

1.22 1.44 1.170 1.260 1.288 1.306 1.325 1.375 1.237 1,245 1.259 1.271 1.296 1.327 1.382

i

Density

¢91

VIT

97.1 98 0 0 1 0.3 1.6 0 1.0 2.9 1

Maceral:

vitrinite (PSU) vitrinite (NCB) s p o r i n i t e (PSU) resinite (PSU) liptinite (NCB) fusinite (PSU) s e m i f u s i n i t e (PSU) m a c r i n i t e (PSU) m i c r i n i t e (PSU) i n e r t i n i t e (PSU) i n e r t i n i t e (NCB)

3.1 3 89.5 0.8 88 0 4.0 1.0 1.6 6.6 9

EX 93.6 98 0.7 0 tr. 1.2 1.2 0.4 2.9 5.7 2

VIT

M a r k h a m Main Barnsley

asemifusinite bequal amounts fusinite & semifusinite

5.6 6 0.4 0 tr. 13.1 80.3 0.2 0.4 94.0 93 a

IN

Dunsil Teversal

Seam : Colliery:

8.3 6 0 0 1 68.0 23.7 0 0 91.7 925

IN 0.7 3 86.8 0.3 88 2.6 7.4 1.0 1.2 12.2 9

EX 97.6 96 0.2 0 3 0.4 0.9 0 0.9 2.2 1

VIT

W h e a t l e y Lime Woolley

0.2 3.1 0.8 1.4 5.5 5

95

4.5 0 88.5 1.5

EX

0.2 0.8 0 0.4 1.4 1

I

97.9 98 0.7 0

VIT

Silkstone Aldwarke

43.4 43.0 0 0 86.4 96 a

--

13.3 4 0.3 0

IN

1.5 4.0 0.6 4.3 10.4 3

1

88.7 96 0.8 0.1

VIT

56.0 38.4 0.5 0.5 95.4 97

--

4.6 2 0 0

INa

Ballarat Roddymoor

22.5 59.0 0.9 1.0 83.4 85 a

1

16.6 14 0 0

INb

0.3 6.4 0.2 3.9 10.8 11

0

89.2 89 0 0

VIT

1.9 11.6 0.9 2.0 16.4 66

0

83.6 34 0 0

IN

Gellideg Coegnant

P e t r o g r a p h i c analyses (reflected light) s u p p l i e d b y P e n n s y l v a n i a S t a t e U n i v e r s i t y (PSU) a n d British N a t i o n a l Coal B o a r d (NCB)

T A B L E II

X O5

147 Thirteen maceral concentrates were obtained from Dr. Pugmire's maceral separation laboratory at the University of Utah and were prepared from two U.S. coals (PSOC 2 and PSOC 858) by density gradient centrifugation in cesium chloride. Density gradient profiles for these samples are shown in Fig. 1. All fractions thus prepared were stored under nitrogen for several months. s~

(PSOC 858)

i VITRINITE "~

~

J! ~

/

~

(PSOC 2)

.=

O-

l/i5

120

'125

,130

17~5

, 40

density (g/cm 3)

Fig. 1. Density gradient centrifugation profiles of two US coals (PSOC 2 and PSOC 858) showing the relative yields of density fractions El--E6 and $1--$6 (compare with Table I). Note that PSOC 2 provides sporinite, as well as vitrinite and inertinite (fusinite, semifusinite, macrinite, micrinite) fractions whereas PSOC 858 yields only vitrinite and inertinite (semifusinite) fractions. Further note the higher density of the PSOC 2 vitrinite compared to the PSOC 858 vitrinite. Several days prior to analysis by pyrolysis MS, 4-mg amounts of each sample were suspended in 1 ml of Spectrograde methanol and ground to a fine, uniform suspension. Suspensions were considered satisfactory if noticeable settling of coal particulates did not occur within the first 5 s or so after shaking the suspensions. This corresponds to a particle size of 50 micron or less, as determined by microscopic analysis. All suspensions were stored in sealed vials under nitrogen at - 2 0 ° C until the day of analysis. Curie-point p y r o l y s i s mass s p e c t r o m e t r y

A 5-pl drop of each suspension (20 pg of coal sample) was applied to a ferromagnetic wire with a Curie-point temperature of 610°C and air dried under gentle rotation. Within 60 min after applying the samples to the wires,

148 the coated wires were introduced into the vacuum system of the mass spectrometer and pyrolyzed by high-frequency induction heating (Curiepoint pyrolysis). The Curie-point pyrolysis MS method is described in more detail by Meuzelaar et al. (1984) as well as in Meuzelaar et al. (1982a). Analytical conditions were as follows: equilibrium temperature 610°C, temperature rise time 5 s, total heating time 10 s, electron energy (electron impact ionization source) 12 eV, mass range scanned: 20--260 amu, scanning speed: 1000 amu/s, total scanning time 30 s. Computerized

data processing

The computerized data-analysis procedures used were similar to those described by Harper et al. (in press) and Meuzelaar et al. (1984). In short, these procedures involved spectrum normalization, autoscaling, factor analysis and, finally, plotting of factor scores and factor loadings. In addition, so-called "factor spectra" were calculated and plotted according to a procedure described by Windig et al. (1980). The spectrum normalization procedure was based on the work of Eshuis et al. (1977) and is incorporated into our interactive normalization and bivariate plotting program, NORMA. This normalization method uses replication as a basis of maximizing sample reproducibility during the normalization process. Multivariate analysis was performing using the pattern recognition program ARTHUR (Harper et al., 1977). Autoscaling transforms each peak to equal means of zero and equal variances. If D m x n is the raw data matrix of m samples by n intensities after normalization and D' is the autoscaled data then: D' = (D--D)

o -x

(1)

where D is a m× n matrix with constant columns equal to the measurement means and 0 -1 is a square diagonal matrix of the inverse standard deviation of the measurements. Factor analysis was used to decompose D' into two matrices, a factor score matrix (S) describing the trends within the samples and a factor loading matrix (L) describing the trends of the measurements. In matrix notation: D' = SL

The loading matrix is found through diagonalization of the data correlation matrix and is ordered from highest to lowest eigenvalue. If the resulting eigenvectors in L are orthonormal, the score matrix is simply the projection of D' onto the eigenvectors, i.e.: S = D'L w

(2)

This transform stacks the variable correlations into a set of ordered vectors of decreasing orthogonal information. Viewed this way, the value of the

149 loading on a variable for a particular eigenvector measures that measurement's importance to the projection of the autoscaled data. The factor spectra matrix F is the result of the transform: F= Lo

(3)

It is important not to confuse the interpretation of F with that of the loadings. The intensity of a given peak for a given factor spectrum does not measure its original importance to the transformation of the autoscaled data which produces the factor score matrix, nor is it a "spectrum". However, since all the original information contained in D' for a measurement is spanned by L, the square loading of the ith measurement on the jth eigenvector (lij) is a measure of the proportion of the variance of the ith measurement contained in the j t h vector. Consequently, oi2li~ is the variation of the ith measurement in the direction of the ]th eigenvector in units of the original data. From equations (1) and (2) above: D ' = ( D - - D ) o -1 = S L S = ( D - - D ) [ o -~ L T]

(4) (5)

In other words, the matrix of factor spectra is that matrix which simultaneously transforms the mean scaled data into autoscaled data and projects it into the factor score matrix. The interpretation of the factor spectrum depends on a knowledge of the sources of variance (02) within the individual peaks. For example, if D was a matrix of replicate analyses on a single sample and o was the measurement error associated with the sample, a factor spectrum would look like a spectrum since this error tends to increase with peak height. However, large variance sources such as gross contamination after replication may have small loadings and large factor spectra intensities. Whereas small peaks with important chemistries may become obscured and valuable information about data correlations lost. Consequently, it is important to examine factor loadings in order to arrive at a reliable chemical interpretation of the projection of D' and the factor spectrum to determine which of the peaks in the loading vector have large variations. RESULTS Three pyrolysis mass spectra averaged over all vitrinites, inertinites and exinites (sporinites) respectively are shown in Fig. 2. It should be pointed out that the chemical identities of the major peak series, e.g., "phenols", " d i h y d r o x y b e n z e n e s " , "dienes", "alkenes", "benzenes", etc., as indicated in Figs. 2--6, are primarily based on literature reports regarding pyrolysis experiments with unfractionated coal samples rather than coal macerals (e.g., Van Graas et al., 1979; Philp et al., 1982). Moreover, the authors are aware of the probable presence of m a n y other c o m p o u n d series with similar nominal mass values as the compound series tentatively identified in Figs.

150 2--6. Therefore, most chemical labels should be seen as an attempt to provide a "most probable identity" for the major compound series thought to be represented by a given series of mass peaks. However, in collaboration with Dr. J.W. de Leeuw and co-workers (Technical University of Delft), several of the maceral samples were analyzed by pyrolysis GC/MS in order to help substantiate the chemical identities of major suites of maceral pyrolysis products. The overall pattern of each maceral group in Fig. 2 agrees quite well with the spectra published by other authors (Larter, 1978; Van Graas et al., 1979; Allan and Larter, 1981), with vitrinites showing prominent phenolic series, fusinites being dominated by aromatic hydrocarbon signals and sporinites showing marked alkene peaks. More subtle differences, the significance of which can only be appreciated with the help of computerized data analysis techniques, will be discussed later. In evaluating the relative peak intensities of vitrinite, inertinite and exinite spectra, it should be kept in mind that all intensities were normalized to total ion intensity (with some correction for unwanted influences of strongly varying peaks applied as described by Meuzelaar et al., 1982b). 5.0

34~ I ~6

SPORINITE (averaged spectrum)

Ikenes

_,k

. . . . . . . . . . . . . .

5.0

2 11

v,T ,N,+E

] l

g g 2.

~

I08

,--J~r \ v f . 94"" I

bhl \ I~. ~q~61

(averaged spectrum)

phenols

o 5.0,

INERT[NITE

~i[32

(averaged spect .... )

Ill(S)~--..

HI, I ~ / 2.5

alkyl fragments benzenes

|.jp4 J~....~.;'../~.~..

92 ~o+.

~

.2~__napht~aleoes /!--

I"~.17o __acenaphthenes/biphenyls

IllJlI II I ~"_~-~"~-~I~" +.~I I ~ illdl

{~aphenanthrenes/anthracenes

. 4a

.~i

~g

io¢i

12o

2 140

I6v

I~O

oo ~

.

2L~

.

.

.

.

.

.

.

2,.Q

.

.

.

m/z

Fig. 2. Averaged pyrolysis mass spectra of the three maceral types analyzed. Homologous ion series connected by solid or broken lines. Arrows indicate markedly higher or lower peaks. Chemical identifications are tentative. For conditions see text.

151

The average total ion yields obtained for 20-~g amounts of sample are listed in Table III and show approximate ratios of 12 : 10 : 7 for exinites, vitrinites T A B L E III Average t o t a l ion yields p e r s p e c t r u m for each m a c e r a l g r o u p Maceral g r o u p

i o n c o u n t s × 10 ~ Average

exinites (sporinites) vitrinites inertinites

2.46 2.04 1.41

s.d.

± 0.62 ± 0.46 -+ 0.33

5.0 1 2~3f13"4zs

5 14 11

/~', ," ~

IIII

5.0

Number of samples

jl

281 34 '3°

BARNSLEYVITRINITE (82.2% C)

i,

WHEATLEY LIME VITRINITE (86.6% C)

~ .-~\ //

2.

\\

/

~x

5.0 ~81~2

nlphthalemes

BALLARAT VITRINITE (88.8~o c)

o

31 3

G

5.(]

"

.....

\ \ ~

acena phthenes/bi phenyl s

I

12s[13~| \

o,

// - - -

11 IL.

...

...,,

GELLIDIGVITRINITE

...... J?'TT ....

Fig. 3. Pyrolysis mass s p e c t r a o f f o u r vitrinites d e m o n s t r a t i n g t h e effects o f d i f f e r e n c e s in c o a l i f i c a t i o n stage. N o t e t h e decrease in h y d r o x y a r o m a t i c series a n d s u l f u r c o m p o u n d s a n d t h e c o n c u r r e n t increase in a r o m a t i c h y d r o c a r b o n s w i t h increasing r a n k . T h e fact t h a t t h e b e n z e n e series in Gellideg v i t r i n i t e is m o r e p r o m i n e n t t h a n t h e n a p h t h a l e n e series is p r o b a b l y atypical.

152

and inertinites, respectively. Thus, the relative peak intensities shown in all spectral data plots only reflect the relative abundance of the corresponding ion species; not the absolute ion yield. Four vitrinite samples of different rank (as judged by % carbon content) are compared in Fig. 3. Unsurprisingly, the spectra in Fig. 3 are quite similar to those of vitrinite-rich whole coals of comparable rank and exhibit the same rank-dependent differences. Phenols and dihydroxybenzenes are prominent in the vitrinite of lowest rank with the dihydroxybenzenes disappearing first in higher rank vitrinites concurrent with the expected

5°50]i 0

"

L

.

.

.

.

.

~.2~-;-==,_. 4u

~~I|I3~34 '"Ill

42

6 a~y|fr, ,is

~

BARNSLEY(916 .% FUSINITEc)

hl][

.

.o/

O9

..........TE,.9., dienes

bi phenyl s/acena phtF,enes

--~/_

I82

/196

4

5.0

210

BALLARAT "A" FUSINITE

II Is'

(93.9%C)

3J32'

IBh L

64

p. . . . . . . . . . . . / . . . . . . . . . . .

- .

I

L ........ wI

(wf

w

|w

1211

~

i~

|alJ

m

~

M m/z

Fig. 4. Pyrolysis mass spectra of two fusinite and two semifusinite samples of different coalification stage. Note the overall similarity with vitrinites of equal carbon content (compare with Fig. 3). Further note that although the Dunsil and Barnsley vitrinites are of comparable carbon content (see Table I) the Dunsil inertinite (a semifusinite) has a much lower carbon content than the Barnsley inertinite (a fusinite) with corresponding differences in spectral patterns. The same observation can be made for the two Ballarat inertinites (lower spectrum).

153

increase in naphthalenes and other aromatic hydrocarbon signals. It should be noted that the highest rank vitrinite (Gellideg seam) exhibits a pyrolysis pattern which is at first sight quite similar to that of the fusinite spectrum in Fig. 2. Nevertheless, as will be shown, characteristic differences do remain which help to distinguish fusinite patterns from vitrinite patterns. Four inertinite spectra, representing two fusinite-rich and t w o semifusiniterich maceral concentrates of different rank, are shown in Fig. 4. The semifusinite patterns appear to be more or less intermediate between the vitrinite and fusinite patterns, e.g. with regard to the relative abundance of phenolic series. Both in the semifusinite and in the fusinite patterns the highest rank samples show a lower abundance of phenolic series. Three spectra representing sporinite samples of different rank are shown in Fig. 5. Again, increase in rank appears to be accompanied by a decrease in phenolic series and other heteroatomic compounds and an increase in aromatic hydrocarbons, notably naphthalenes. Although several sporinite spectra, e.g. in Figs. 2 and 5, show a high relative abundance of low molecular weight alkenes compared to vitrinites, this is by no means true in all cases. Nonetheless, other relatively minor yet highly characteristic peak series can be found in all five sporinite samples which distinguish these samples from vitrinites and inertinites, as will be discussed later.

zSl

7H~S

BARNSLEY SPORINITE

(82.6% C)

2,5 phenols

._.- . . . . . .

0

"

.

181,1L

2.5

L. . . . . .

BEESTONSPORINITE

I134 3 42

.~

.

<843 <>

56

IO8 122 70

82

94 . . - ' -

". . . . .

-- ---

• ~;L36 14

156

170 m4

5.0' 28[

~

WHEATLEY LIME SPORINITE

2.5 •

~J~

~

o ~ ""~~ .... .-.-.~

.benzenes

naphthalenes

.........

m/z

Fig. 5. P y r o l y s i s mass spectra o f three sporinite samples o f different carbon c o n t e n t d e m o n s t r a t e the overall similarity w i t h vitrinites and to s o m e e x t e n t fusinites o f c o m parable carbon c o n t e n t (see Figs. 3 and 4).

154

In view of the entirely different origin and preparation methods of the maceral concentrates of the two U.S. coals, several density-gradient fractions of the high-volatile B bituminous coal from the Upper Elkhorn seam in the U.S. Eastern Coal Province (PSOC 2) are shown in Fig. 6. The sporinite, vitrinite, and fusinite fractions of PSOC 2 all bear a close similarity to the corresponding maceral concentrates from the British National Coal Board. The high relative abundance of the HC1 ÷" ion signals at m/z 36/38 in the density gradient centrifugation is apparently due to residual cesium chloride in these fractions. In order to provide a more quantitative representation of the relationships between structural moieties in different maceral concentrates, bivariate plots of selected mass peaks are shown in Figs. 7--13. A scatter plot of m/z 110 vs. m/z 124, believed to represent dihydroxybenzenes and methyldihydroxybenzenes, is shown in Fig. 7. Apart from the close positive correlation between these two mass peaks, a strong negative correlation with rank, as expressed by % carbon content, can be seen.

5°11, •

I

' ~

I

Ill

J

III"I

2.51

\

UPPER ELKHORN SPORINITE

.... I

"~

(fractioo E,. avg ensit ,

d1 . . . .

I jUII

. . . . . . . .

0 -- :-~--,----4

.

.

.

.

.

.

.

.

"~

.

.

.

.

.

.

.

.

.

.

.

.

. - " ' ~ ' --#-' ~

UPPER ELKHORN VITRINITE

( f r a c t i o n E3, avg. density 1.29)

~)

2.5

0

6

•

94 . i

-

.

phenols

I.

~

5.0

~.

L

u °

UPPER ELKHORNINERTINITE (fraction E6, avg. density ].37)

2.5, n 92a

p . h. ~ t~- h"\ \a

l

e

b

i

p

h

~ neses enyl s/acenaphthenes

m/z

Fig. 6. Pyrolysis mass spectra of three cesium chloride density gradient centrifugation fractions of an U p p e r E l k h o r n seam coal (PSOC 2) representing a typical sporinite, vitrinite and inertinite maceral c o n c e n t r a t e fraction respectively. N o t e the overall similarity with the corresponding British maceral c o n c e n t r a t e samples in Figs. 3--5. F u r t h e r n o t e the m a r k e d HCI +" peaks at m/z 36/38 which appear to be due to residual cesium chloride.

155

Surprisingly, all three maceral groups exhibit the same overall rank tendencies with regard to these mass peaks, which brings up the interesting question whether the chemical identity of these peaks is the same in inertinites and sporinites as in vitrinites or whether major contributions from other c o m p o u n d series are present as well. ME

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Fig. 7. Scatter plot of ion intensities at m/z 110 vs. 124, believed to represent dihydroxybenzenes and methyldihydroxybenzenes respectively. Exinites (sporinites), vitrinites and inertinites are represented by circles, squares and triangles respectively. The name code is identified in Table I. Solid black symbols indicate US gradient centrifugation samples.

A negative correlation with rank is also exhibited by the methylphenol and C2-alkylphenol peaks at m/z 108 and 122 respectively, as shown in Fig. 8. In contrast with the dihydroxybenzene signals in Fig. 7, however, the sporinite samples no longer remain in step with the vitrinite and inertinite samples with regard to the relationship between % carbon content and signal intensity. Instead, in Fig. 8 the Beeston and Barnsley seam sporinites, with carbon contents of 84.3 and 82.6% respectively, show relatively low signal intensities compared to the low rank vitrinites as well as the Dunsil seam inertinite. The plot of C2- and C3-alkylnaphthalene peak intensities in Fig. 9 shows a much more complicated pattern. The strong positive correlation with rank observed in our study of whole coals (Meuzelaar et al., 1982b, 1984) still appears to hold true for most maceral samples. However, the Gellideg seam

156 ME3

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Fig. 8. Scatter plot of ion intensities at m/z 108 vs. m/z 122, believed to represent cresols and C2-alkylphenols respectively. For explanation of symbols and codes see Fig. 7 and Table I. Note crude similarity with dihydroxybenzene plot in Fig. 7 but less complete correlation with carbon content due to more pronounced differences between maceral types. 2.7

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vitrinite and inertinite show strongly anomalous values. The spectra of these two macerals reveal the presence of strong alkylbenzene series in combination with relatively low naphthalene signals. The gradual increase in the intensity of the peaks at m/z 156 and 170 in the subsequent density-gradient fractions of both US coals is noteworthy. However, the apparent correlation with density is not quantitative as can be seen from the position of the PSOC 2 exinite as well as, for instance, the position of PSOC 858 fraction 5 (density 1.296) which has lower peak intensities than PSOC 2 fraction 3 (density 1.288). Finally, the lack of a close correlation between the intensities of the C:and C3-alkylsubstituted naphthalenes in the inertinite spectra should be noted. As discussed by Meuzelaar et al. (1984), this might reflect the special thermal histories of these macerals which may well have been exposed to a wide range of elevated temperatures in forest fires (Given and Binder, 1966). Figure 10 shows a plot of m/z 192 vs. m/z 206, believed to represent .86

ARa

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o= % .48

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Fig. 10. Scatter plot of ion intensities at m/z 192 vs. m/z 206 believed to represent methylphenanthrenes (and/or -anthracenes) and C2-alkylphenanthrenes (and/or-anthracenes) respectively. For explanation of symbols and codes see caption Fig. 7 and Table I. Note crude similarity with Fig. 9 but different behavior of Coegnant vitrinite and fusinite. Fig. 9. Scatter plot of ion intensities at m/z 156 vs. m/z 170 believed to represent C=alkylnaphthalenes and C~-alkylnaphthalenes respectively. For explanation of symbols and codes see Fig. 7 and Table I. Note marked positive correlation with density gradient behavior. Further note anomalously low naphthalene intensities of Coegnant vitrinite and inertinite compared to macerals of similar rank.

158

mainly C1- and C2-alkylphenanthrenes and/or -anthracenes respectively. Marked peak intensities at m/z 192 and 206 were also reported to be due to terpenoids, e.g. from alginites, by Winans et al. (1981), using a Py-MS technique at 70 eV electron energy. However, since nearly all high-intensity values at m/z 192 and 206 in Fig. 10 are found among the inertinite samples, polynuclear aromatic moieties are more likely to be responsible than terpenoids. As in Fig. 9, a gradual increase in peak intensities occurs in subsequent density gradient fractions of the two U.S. coals. Moreover, a positive correlation is found with rank which enables a clear separation to be made between samples with known carbon contents above 90% and those below 90%. The C4- and Cs-alkyl fragment ion peaks at m/z 57 and 71 respectively are shown in Fig. 11. Generally, inertinites exhibit the highest alkyl fragment ion values. However, the Beeston inertinite shows unusually low values. Note also the correspondingly low values of the Beeston exinite sample. The cause of this peculiar behavior is unknown. Both Beeston samples show % carbon and hydrogen values which are well within the range of other values listed in Table I. Two mass peak intensities representing sulfur-containing ion species are plotted in Fig. 12. The peak intensity at m/z 64 may be assumed to represent zsRb

¸!--I

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ion i n t e n s i t y )

Fig. 11. Scatter plot of ion intensities at m/z 57 vs. m/z 71 believed to represent C 4alkyl and Cs-alkyl fragment ions respectively. For explanation o f symbols and codes see Fig. 7 and Table I.

159

SO2 +' and/or $2+ and in the analysis of whole coals its intensity was found to correlate positively with pyritic sulfur content, as discussed by Harper et al. (1984b). The peak at m/z 76 should largely represent CS: ÷'. As is evident from Fig. 12, no direct correlation appears to exist with total sulfur content. Interesting is the almost complete absence of a peak at rn/z 64 in all fractions of the two U.S. coals, as well as in all exinite fractions. Also, most inertinites show relatively high peak intensities at m/z 64 and/or 76, with the exception of the Ballarat "B", Silkstone and Dunsil samples, all of which may well consist largely of semifusinite (see Table II). Figure 13 illustrates the large differences in solvent (MeOH) retention between samples. It has been known for a long time (Van Krevelen, 1961) that the amount of MeOH that can be absorbed by a coal increases with rank and indeed a rough correlation with % C appears to be visible in Fig. 13. However, this correlation is far from strong. Although a more detailed numerical analysis of all correlations between Py-MS data and available conventional data is still underway, preliminary findings indicate a marked negative correlation between MeOH absorbtion, as judged from m/z 32 and 31, and % hydrogen (see Fig. 13).

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Fig. 12. Scatter plot o f ion intensities at m/z 64 vs. m/z 76 believed to represent SOs ÷. ( a n d / o r S~ ÷') and CS2 ÷" ions respectively. For e x p l a n a t i o n o f s y m b o l s and c o d e s see Fig. 7 and Table I. N o t e t e n d e n c y o f inertinites to s h o w high values for o n e or b o t h o f these peaks.

160

The foregoing bivariate plots have illustrated the wealth of spectral information available. Since it would be impossible to show all possible combinations of interesting peak pairs, a factor analysis approach was adopted to reduce the large number of mass peaks measured to more manageable proportions. Because of the marked redundance in pyrolysis mass spectra of coal samples (as demonstrated by Meuzelaar et al., 1984) the factor analysis approach is especially well suited for reducing this type of data. A plot of the scores of the first two factors, accounting for 45% and 27% of the total variance in the data respectively, is shown in Fig. 14. In order to obtain an optimal representation of the three maceral categories in the factor i~lot in Fig. 14, both factors were rotated 30 °. Since factors III, IV and V explain not more than 12, 9 and 7% of the total variance respectively, (when normalizing the variance of the first 5 factors to 100%}, only factors I and II will be discussed here. The factor score plot in Fig. 14 shows a clear separation between all three maceral categories with the exception of the Gellideg seam vitrinite which lies in the "inertinite region" of the plot. Within each of the three maceral regions in Fig. 14 there appears to be a rank related trend with

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Fig. 13. Scatter p l o t o f ion intensities at m/z 32 vs. m/z 31 believed to represent CH3OH ÷" and CH~O ÷ signals respectively derived from m e t h a n o l solvent. For e x p l a n a t i o n o f s y m b o l s and c o d e s see Fig. 7 and Table I. N o t e apparent inverse correlation w i t h h y d r o g e n content and t e n d e n c y for differentiation b e t w e e n maceral types.

161

the lower rank macerals occupying the (lower) left side and the macerals of the higher rank plotting on the {upper) right side of each region. Taking into account the relatively low rank of the two U.S. coals {85.5 and 85.1% C d m m f , respectively), the maceral suites derived from these coals by the density gradient centrifugation method appear to have similar characteristics as the corresponding British macerals obtained by the sink/ flotation method. A highly important observation from Fig. 14 is provided by the fact that the pyrolysis mass spectrum of one of the US coal (PSOC 858) plots in between the maceral regions, which indicates that (a) this spectrum may be regarded as a more or less direct sum of the maceral c o m p o n e n t spectra and (b) no major structural alterations were introduced by the density gradient separation procedure. Furthermore, it should be pointed out that Factor I shows a marked positive correlation with the density values of the maceral fractions of the two U.S. coals, with vitrinite fractions occupying an intermediate position between the exinite and fusinite fractions. Also, in Fig. 14, a clear correlation can be observed with atomic H/C ratio's. In order to facilitate interpretation of the underlying chemical tendencies in the factor score plot in Fig. 14, the loadings of these two axes are shown []

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Fig. 14. Plot o f t h e first t w o f a c t o r scores ( a f t e r 30 ° r o t a t i o n ) . F o r e x p l a n a t i o n o f s y m b o l s a n d c o d e s see Fig. 7 a n d T a b l e I. US d e n s i t y g r a d i e n t f r a c t i o n s are c o n n e c t e d b y arrows in o r d e r o f increasing d e n s i t y . N u m e r i c a l values ranging f r o m 0.37 ( B e e s t o n i n e r t i n i t e a) to 1.08 ( B a r n s l e y e x i n i t e ) r e p r e s e n t a t o m i c H/C ratios. N o t e positive c o r r e l a t i o n o f f a c t o r I w i t h d e n s i t y a n d negative c o r r e l a t i o n w i t h H/C ratio.

162

in Fig. 15. Moreover, the factor spectra of both factors are shown in Figs. 16 and 17. The negative component of the first factor spectrum should be characteristic for the exinite region in Fig. 14 and contains a large proportion of odd numbered ion peaks (see Figs. 15 and 16). Although some of these oddnumbered mass signals might fit aromatic nitrogen-containing ion series, e.g. pyrroles (m/z 67), pyridines (m/z 79), indoles (m/z 117) etc., there is no clear correlation with nitrogen content (as linked in Table l). Moreover, all of these odd-numbered peaks are more or less regularly encountered as fragment ions in mass spectra of (cyclic or acyclic) polyenic isoprenoids (Heller and Milne, 1978). In addition to these presumed isoprenoid signals, the negative component of factor spectrum 1 also contains more or less prominent series of phenols, dihydroxybenzenes and possible other hydroxyaromatic series (see Fig. 16). It should be noted however that the loadings of these aromatic series are relatively low compared to the presumed isoprenoid compounds (see Fig. 15).

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Fig. 15. Scatter p l o t o f mass peak loading values on factor I vs. factor II d e m o n s t r a t i n g the presence o f c l o s e l y correlated peak series in the maceral spectra. N o t e the corresp o n d e n c e b e t w e e n the " a r o m a t i c h y d r o c a r b o n " region and the inertinite region in Fig. 14, as well as a similar c o r r e s p o n d e n c e b e t w e e n the " i s o p r e n o i d " (or o t h e r h y d r o c a r b o n ) and e x i n i t e regions. A r r o w s p o i n t to s o m e o f the f e w peaks (m/z 28 and 3 0 ) w h i c h appear to be characteristically high in vitrinites.

163

The positive side of factor spectrum I in Fig. 15b shows peaks characteristic of the inertinite region in Fig. 14. These peak series are dominated by relatively high molecular weight pyrolysis products, thought to represent alkylsubstituted aromatic hydrocarbons (e.g. benzenes, naphthalenes biphenyls/acenaphenes, fluorenes and anthracenes/phenanthrenes). Repre-

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Fig. 16. Factor spectrum representing Factor I in Figs. 14 and 15. N o t e marked simplification o f spectral patterns as compared to Figs. 2--6. Chemical labels are e x a m p l e s o f possible structures o n l y .

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Fig. 17. Factor spectrum representing Factor II in Figs. 14 and 15. N o t e that the positive part s h o w s a more or less characteristic vitrinite pattern whereas the negative part s h o w s the e x p e c t e d c o n t r i b u t i o n s o f more or less characteristic e x i n i t e as well as inertinite fragments.

164

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ion ~ n t e r s ' t ] :

intensities at m/z 39 vs. m/z 1 8 8 believed to represent C3H3 + p o l y e n i c molecular ions respectively. For e x p l a n a t i o n o f 7 and Table I. N o t e that b o t h peaks are m e m b e r s o f the in Fig. 15 and that vitrinites s h o w equally l o w intensities Figs. 16 and 17.

sentatives of some of the peak series with high loading on Factor I are shown in Figs. 18 and 19. Figure 18 provides a scatter plot of m/z 67 vs. m/z 131 representing the main exinite region in Fig. 14. These proposed "isoprenoid" fragment ion peaks appear to be most abundant in exinites and least abundant in inertinites, with vitrinites showing more or less intermediate values. A scatter plot of m/z 208 and 222, two representative peaks for the inertinite region in Fig. 14 and possibly representing C3- and C4-alkyl fluorenes, is shown in Fig. 18. Again the vitrinites occupy an intermediate position between the exinite and fusinite fractions. The factor spectrum of factor II in Fig. 17 shows only a few peak series which correlate positively with the vitrinite region in Fig. 14. Moreover, these apparent phenol and naphthalene series possess relatively low loadings (see Fig. 15). The highest loadings are found for the small molecular fragments at m/z 28 (CO +. and/or C:H4 ÷') and 30 (CH20 ÷" and/or some C2H6+'). A bivariate plot of these two peaks is shown in Fig. 19 and demonstrates an interesting separation between all three maceral categories with m/z 30 exhibiting low values for exinites and m/z 28 showing low values for inertinites. The negative portion of factor 2, as shown in Fig. 15 and Fig. 17b, is very complex since it represents a combination of exinite and inertinite peak series, as can be inferred from the factor score plot in Fig. 14. As a result the factor spectrum in Fig. 17b appears to show a combination of aliphatic and aromatic peak series.

165

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C~

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Rb zS

=

r

Z~ T

g

%

Ak P

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S

R

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Fig, 19. Scatter plot of ion intensities at m/z 208 vs. m/z 222, thought to represent C~- and C 4-alkylfluorenes respectively. For explanation of symbols and codes see Fig. 7 and Table I. Note that both peaks are members of the exinite peak cluster in Fig. 15. Further note the positive correlation with density and the nearly complete separation between the inertinite samples and the other maceral concentrates. DISCUSSION

The observed differences in average total ion signal between the exinite, vitrinite and inertinite maceral groups (approx. ratio's 12 : 10 : 7 respectively; see Table III) are not surprising. Tubing bomb reactor hydroliquefaction studies on several of these macerals by Given (1980) show a similar trend; with exinite conversion yields approximately 4 × higher than inertinite yields and vitrinites providing intermediate yields. Since the pyrolysis conditions in Py-MS are quite different from those in tubing bomb reactor hydroliquefaction experiments, no direct correspondence in absolute or relative yields can be expected. However, Py-MS may be considered as a rapid micropyrolysis in an inert (vacuum) environment and thus may perhaps serve as a model system for liquefaction experiments, as demonstrated by Meuzelaar et al. (1980) and Voorhees et al. (1981). In the present study no close correlation between total ion yield and rank was noted although two of the higher rank samples, e.g. the Gellideg inertinite and vitrinite, produced less than 1 X 10 s ion counts (compare with Table III). Overall, the maceral patterns did correspond quite well with the Py-MS patterns of macerals reported in the literature (Larter, 1978; Van Graas et al., 1979; Allan and Larter, 1981; Meuzelaar et al., 1982a). Moreover, characteristic differences were observed between the exinite (sporinite),

166

vitrinite and inertinite (fusinite and/or semifusinite) groups in spite of the marked heterogeneity with regard to origin, coalification history and sample preparation methods. The fact that some of the differences between maceral groups are expressed in relatively small but abundant ion species such as m/z 28 and 30 (Fig. 20) may indicate the presence of basic structural differences, e.g. involving oxygen-containing functional moieties. Although differences in rank tend to show some overlap with differences in maceral type, especially in the case of vitrinites, semifusinites and fusinites, several characteristic peak series appear to enable a clear discrimination between the three maceral groups regardless of rank. On the other hand, some peak signals, e.g. at m/z 110 and 124 (believed to represent dihydroxybenzenes and methyldihydroxybenzenes, see Fig. 7) and to a lesser extent m/z 156 and 170 (thought to represent C2 and C3 alkylnaphthalenes; see Fig. 9) show a close correlation with rank regardless of maceral type. This explains the usefulness of these (alkyl)dihydroxybenzene and alkylnaphthalene signals for predicting the rank of whole coals, as demonstrated by Meuzelaar et al. (1984). One of the most important new findings of this study is the presence of

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Fig. 20. Scatter p l o t o f ion intensities at m/z 28 vs. m/z 30 believed to represent CO +. ( a n d / o r C2H4 ÷') and CH=O ÷" ( a n d / o r C=H6 ÷'} ions respectively. For e x p l a n a t i o n o f s y m b o l s and c o d e s see Fig. 7 and Table I. N o t e the c o m p l e t e separation b e t w e e n the three maceral t y p e s by these small but abundant ion species, apparently revealing the presence o f basic differences in molecular structure (e.g. functional group c o n t e n t } . Compare also w i t h Fig. 15.

167 characteristic peak series in sporinites which can be tentatively identified as representative of (cyclic or acyclic) polyenic isoprenoid moieties. In contrast with the more or less completely saturated or aromatized isoprenoid skeletons usually found in coal and shale extracts, the putative isoprenoid structures liberated by Curie-point pyrolysis appear to have retained their polyenoid character in spite of burial periods of several hundreds of millions of years. Whether the presumed polyenic isoprenoids represent carotenoid moieties in sporopollenin (Brooks and Shaw, 1971) or perhaps rubber-like components in the spore walls, or else cyclic isoprenoids introduced during microbial degradation processes (Larter, 1978) remains to be determined. A not unexpected finding is the presence of marked HC1 ÷" and CH3C1 ÷" peaks in the vitrinite and exinite fractions of the two US coals, pointing to residual cesium chloride from the gradient centrifugation procedure. It is well known that inorganic salt constituents can exert a marked influence on pyrolysis patterns of organic c o m p o u n d s (Meuzelaar et al., 1982a). Whether residual cesium chloride may have contributed to some of the relatively minor differences observed between the US and UK macerals, e.g. with regard to the differences in sulfur c o m p o u n d s shown in Fig. 12, cannot y e t be determined. The inertinite maceral concentrates examined in this study show characteristic ion series at the high molecular weight end of the spectra. These signals could be tentatively identified as representative of various polynuclear aromatic c o m p o u n d series. Rather surprisingly, most of these peak series show a marked degree of alkylsubstitution, e.g. up to Cs and higher, as is also evident from the high abundance of the alkyl-fragment ion series at m/z 57, 71, 85, etc. in inertinites. Other more or less characteristic inertinite peaks include m/z 64, (SO2 ÷ and/or $2 ÷) and m/z 76 (CS2 ÷') as shown in Fig. 12. As expected, semifusinites show patterns which are somewhat intermediate between those of fusinites and vitrinites. This would seem to support the interpretation of semifusinite as partly charred w o o d tissues as a result of exposure to forest fires (Teichmt:/ller and Teichm//ller, 1975). In contrast to sporinites and fusinites, vitrinites show only a few characteristic peak series, e.g. at m/z 94, 108, 122, 136 (phenols) and at m/z 28 (C~H4 ÷" and/or CO÷'). In other words, most peak series observed in vitrinites are also found in the sporinite and inertinite maceral groups. This could be due to residual contamination of the latter concentrates with vitrinite or, perhaps more likely, to the ubiquitous presence of (poly)phenolic compounds in plant tissues (Given, in press). An important finding of this study is the high degree of similarity between the pyrolysis patterns of British maceral concentrates prepared by the sink flotation technique and the corresponding US maceral fractions obtained by the cesium chloride density gradient centrifugation method. In the factor score plot in Fig. 14, as well as in several bivariate plots (e.g. Figs. 9, 10, 20) the density gradient fractions of the two US coals lie along more or less

168 continuous and parallel tracks, indicating a gradual change in structural characteristics with increasing density. In fact, the first principal c o m p o n e n t in Fig. 14 exhibits a strong positive correlation with density values as well as a negative correlation with H/C ratios. Moreover, the pyrolysis mass spectrum of the original, unfractionated PSOC 858 coal shows a pattern intermediate between that of its various density gradient fractions. This indicates that, at first approximation the pyrolysis mass spectrum of a coal sample can be regarded as the sum of the spectra of individual maceral components. Furthermore, this observation would seem to rule out the occurrence of major structural changes during the density-gradient separation process. An interesting phenomenon is the pronounced difference in the a m o u n t of residual methanol solvent present in the various samples. It is quite well known that the amount of methanol which can be absorbed by coals correlates with rank, especially among higher rank coals (Van Krevelen, 1961). Although a crude correspondence with rank is observed in Fig. 13, a much more direct correlation appears to exist with hydrogen content of the samples. The nature of this negative correlation is as yet unclear. Perhaps, it could be speculated that at higher hydrogen levels the abundance of saturated hydrocarbon groups may prevent the methanol from wetting the internal pore surfaces of the coals, resulting in faster desorption of the methanol in the vacuum system of the mass spectrometer. Finally, it should be mentioned that the Gellideg vitrinite and inertinite maceral concentrates show unusually high concentrations of alkylbenzenes which appear to replace to some extent the alkylnaphthalene series dominating most other high-rank inertinite and vitrinite samples. A somewhat similar behavior is shown by the Beeston inertinite. Whether this anomalous behavior represents differences in biogeochemical origin or coalification history or could be due to weathering phenomena is as yet unclear. As discussed earlier, the Gellideg samples also show conspicuously low total ion yields. Also, as illustrated in Table II, the petrographic analyses of the Gellideg samples at Penn State University show marked discrepancies with the NCB results perhaps indicating a somewhat anomalous morphologic appearance. Nevertheless, our results do not support a reclassification of the Gellideg inertinite as a vitrinite, as suggested by the results of the PSU petrographic analyses. In spite of its unusual characteristics, the Gellideg inertinite consistently clusters with the other inertinite samples rather than with the vitrinites. CONCLUSIONS The spectra of thirty purified liptinites (sporinites), vitrinite and inertinite maceral concentrates examined in this study exhibit characteristic peak patterns which enable a clear distinction between these groups in spite of gross differences in depositional environment, geological age, coalification

169 history, sample preparation techniques and sample storage conditions. The pyrolysis mass spectra of vitrinite, inertinite and sporinite fractions obtained by density gradient centrifugation of two U.S. coals exhibit the same general characteristics as the corresponding maceral concentrates of seven British coals obtained by sink/flotation methods. At first approximation, the pyrolysis mass spectrum of one of the US coals (PSOC 858) appeared to be the sum of the individual c o m p o n e n t spectra, thus ruling out major structural changes during the density gradient separation procedure. Vitrinites, inertinites and sporinites show remarkably similar rank related changes. Some mass peaks, e.g. at m/z 110 and 124 (thought to represent dihydroxybenzenes and methyldihydroxybenzenes respectively) appear to correlate more or less directly with carbon content, irrespective of differences in maceral type. This explains the usefulness of these signals in predicting the rank of whole coals. In general agreement with long-known differences between the methanol absorption capacity of coals of different rank, a negative correlation is found to exist between the intensity of the residual methanol solvent peak in the pyrolysis mass spectra of maceral concentrates and the known H/C ratios of the samples. The spectra of inertinite maceral concentrates show an overall resemblance to the spectra of vitrinite concentrates from higher rank coals. However, inertinite spectra are found to exhibit characteristic peak series at the high mass end of the spectra, thought to represent polynuclear aromatic hydrocarbons, which permit their distinction from vitrinites in nearly all cases. Pyrolysis mass spectra of semifusinite-rich maceral concentrates exhibit patterns which tend to be somewhat intermediate between those of fusinites and vitrinites, which is in agreement with commonly accepted views on the origins of fusinites, semifusinites and vitrinites. All five sporinite samples analyzed exhibit a relatively minor but highly characteristic peak series thought to represent polyenic isoprenoid fragments with a degree of unsaturation more or less similar to that of recent, naturally occurring isoprenoids. The finding that all three maceral groups can be distinguished easily by the relative intensities of the mass peaks at m/z 28 and 30, representing small but highly abundant ion species, suggests the presence of basic structural differences between these maceral groups, e.g. with respect to oxygencontaining functional groups. ACKNOWLEDGEMENTS The authors want to acknowledge the generous contributions of coal samples and coal characterization data by the Penn State Coal Sample Bank (through Dr. Peter H. Given) and the British National Coal Board as well as

170

the invaluable help provided by Dr. Jan de Leeuw and co-workers in checking presumed chemical identities of major series of maceral pyrolysis products by means of Curie-point pyrolysis GC/MS techniques. Furthermore, the authors are indebted to Donna J. Davis, Shelley A. McClennen, Koah-Hsing Wong, David L. Pope, Melinda Van and Veronica Medina for expert technical assistance with sample analysis, data processing and manuscript preparation. The research reported in this publication was supported by Grant Number DE FG22-80PC30242 and DE-FG22-82PC50812 from the Department of Energy and by matching funds for coal research from the State of Utah.

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