Chemistry and Characterization of Coal Macerals - ACS Publications

2 Premaceral Contents of Peats Correlated with Proximate and Ultimate Analyses 1

A. D. COHEN and M. J. ANDRΕJKO

Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch002

Earth and Space Sciences Division, MS D462, Los Alamos National Laboratory, Los Alamos, NM 87545

P r o p o r t i o n s o f premacerals and b o t a n i c a l c o n s t i t u ents composing s e l e c t e d peat samples from Minnesota, Maine, North C a r o l i n a , and Georgia were determined by m i c r o s c o p i c a n a l y s i s o f o r i e n t e d microtome t h i n s e c t i o n s . These r e s u l t s were compared w i t h p r o x i mate and u l t i m a t e analyses o f the same samples. Peats w i t h the h i g h e s t p r o p o r t i o n s o f b i r e f r i n g e n t premacerals tended to have the h i g h e s t volatile matter (and H, O, and Ν c o n t e n t s ) . Peats w i t h a dominance o f premacerals i n the light y e l l o w t o red range tended to be higher in volatile matter (and lower in f i x e d carbon) than those w i t h a significant component o f brown t o black i n g r e d i e n t s (preinertinites). V o l a t i l e matter a l s o tended t o i n c r e a s e as root content increased and to decrease as stem content i n c r e a s e d . On the other hand, BTU tended t o c o r r e l a t e more w i t h ash content than w i t h premaceral composition.

In a number o f p u b l i c a t i o n s , peat types have been d e f i n e d p e t r o g r a p h i c a l l y by t h e i r b o t a n i c a l and "premaceral compositions (1-4). "Premacerals" are the o r g a n i c components i n the peats which, due t o t h e i r c o l o r , o p a c i t y , shape, and f l u o r e s c e n c e , can be p r o j e c t e d as the probable p r o g e n i t o r s o f p a r t i c u l a r c o r r e s ponding macérais i n c o a l s . Although the pétrographie c h a r a c t e r i z a t i o n o f peats c o n s t i t u t e s an important " f i r s t s t e p " i n understanding the o r i g i n and i n p r e d i c t i n g the general composition o f the r e s u l t a n t c o a l s , i t i s important t h a t premaceral types and amounts i n peats be c o r r e l a t e d w i t h v a r i o u s c o a l - q u a l i t y t e s t s (such as "proximate" and " u l t i m a t e " a n a l y s e s ) . With these r e s u l t s i t then becomes p o s s i b l e t o develop a s e r i e s of models 11

'Current address: Department of Geology, Washington State University, Pullman, WA 99164-2812

0097-6156/ 84/ 0252-0021 $06.00/0 © 1984 American Chemical Society

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

COAL MACERALS


22

with which to p r e d i c t more p r e c i s e l y the chemical and p h y s i c a l composition of the r e s u l t i n g t h e o r e t i c a l c o a l s . These p r e d i c t i v e c h a r a c t e r i z a t i o n s can be a p p l i e d not only to the projected seam-wide v a r i a b i l i t y i n c o a l q u a l i t y f o r c o a l s produced i n s i m i l a r d e p o s i t i o n a l s e t t i n g s as that of the s t u d i e d peats, but a l s o to the p r e d i c t i o n of the v a r i a t i o n s i n i n d u s t r i a l p r o p e r t i e s of the peats themselves, such as f o r g a s i f i c a t i o n , l i q u i f a c t i o n , s o i l c o n d i t i o n i n g , organic chemical production and so f o r t h . I t i s f o r these reasons that we have i n i t i a t e d t h i s c o r r e l a t i v e study of peat petrography and peat i n d u s t r i a l - c h e m i c a l ( c o a l q u a l i t y ) p r o p e r t i e s . Note that the information reported h e r e i n represents p r e l i m i n a r y r e s u l t s based on a l i m i t e d number of d i f f e r e n t types of peats that were analyzed f o r only a few " c o a l q u a l i t y t e s t s " ( i . e . , proximate a n a l y s i s , u l t i m a t e a n a l y s i s , and BTU c o n t e n t ) . Future s t u d i e s w i l l i n v o l v e measurement of other pétrographie parameters and i n c l u d e other i n d u s t r i a l analyses (such as, gas and l i q u i d y i e l d s , p h y s i c a l p r o p e r t i e s , organic chemical y i e l d s , and so f o r t h ) . Objectives The 1. 2.

3.

o b j e c t i v e s of t h i s study are t o : Determine the v a r i a t i o n s i n premaceral types and proportions w i t h i n a wide v a r i e t y of peat types. C o r r e l a t e premaceral contents with corresponding proximate ( f i x e d carbon, moisture, ash, v o l a t i l e m a t t e r ) , u l t i m a t e (C, Η, 0, N, S) and heating value (3TU) analyses. P r e d i c t the probable v a r i a t i o n s i n the proximate and u l t i m a t e makeup and BTU l e v e l s f o r c o a l s which formed i n s i m i l a r v e g e t a t i o n a l and d e p o s i t i o n a l s e t t i n g s to those of the peats studied i n t h i s p r o j e c t .

Methods C a r e f u l l y extracted samples of peat were slowly dehydrated i n a s e r i e s of a l c o h o l s o l u t i o n s and then embedded i n p a r a f f i n . A f t e r embedding, t h i n - s e c t i o n s (15 microns i n t h i c k n e s s ) were cut from these samples with a s l i d i n g microtome and mounted i n Canada Balsam. D e t a i l s of the procedure f o r the embedding and s e c t i o n ing of peats have p r e v i o u s l y been described by Cohen.(2,3). Premaceral i d e n t i f i c a t i o n was made i n t r a n s m i t t e d white l i g h t , i n p o l a r i z e d l i g h t ( b i r e f r i n g e n c e ) and blue l i g h t f l u o r e s cence. Premaceral proportions were determined by area p o i n t counting at 200 X. Proximate and u l t i m a t e analyses and BTU were obtained from commercial t e s t i n g l a b o r a t o r i e s and a l s o from the Department of Energy's Energy Technology Center at Grand Forks, North Dakota.


2.

C O H E N A N D A N D R Ε J KO

Premaceral Contents of Peats

23


Results and D i s c u s s i o n B o t a n i c a l Composition. F i g u r e 1a shows the r e l a t i v e abundances of p l a n t groups observed i n microtome s e c t i o n s o f the peats. Note t h a t these peats v a r i e d c o n s i d e r a b l y i n t h e i r b o t a n i c a l compositions. The Minnesota peat c o n s i s t e d predominantly o f Sphagnum (peat moss) d e b r i s w i t h some grasses and c o n i f e r s . The Maine peat was composed mostly o f a l g a l m a t e r i a l w i t h some Sphagnum and Nymphaea (water l i l y ) d e b r i s . The North C a r o l i n a peat was dominated by bay t r e e (Magnolia, Persea, Gordonia) and gum t r e e (Nyssa) d e b r i s ; w h i l e the Georgia Nymphaea peat con s i s t e d predominantly o f Nymphaea d e b r i s . Figure 1b shows the abundance o f p l a n t organs comprising the peat. Again the d i f f e r e n c e s between peat types are pronounced. The Minnesota peat i s dominated by r o o t s but w i t h l e s s e r but equal amounts o f stem and l e a f d e b r i s . On the other hand, t h e Maine peat has the highest c o n c e n t r a t i o n o f l e a v e s ; the North C a r o l i n a peat has the highest wood content (stems) and lowest l e a f content, w h i l e the Georgia (Nymphaea) peat has the h i g h e s t p r o p o r t i o n of r o o t s . Premaceral Types and P r o p o r t i o n s . One s i m p l i f i e d but u s e f u l means o f d i s p l a y i n g pétrographie composition o f peats i n t h i n s e c t i o n i s by graphing the area percentages o f i n g r e d i e n t s o f d i f f e r e n t c o l o r s . F i g u r e 2 shows such a point-count f o r four r e p r e s e n t a t i v e types o f peat from t h i s study. Note t h a t the Minnesota Sphagnum and Georgia Nymphaea peats have approximately the same range o f c o l o r s (peaking between l i g h t - y e l l o w and l i g h t brown) but t h a t the Maine peat peaked i n the c l e a r t o l i g h t y e l l o w range w h i l e t h a t o f the North C a r o l i n a peat had peaks i n the l i g h t - y e l l o w t o red-brown range and a l s o i n the dark-brown and b l a c k c a t e g o r i e s . The Georgia Nymphaea and Minnesota Sphagnum peats tended t o have the highest p r e v i t r i n i t e s w h i l e the North C a r o l i n a and Georgia Taxodium peat (not shown) had the highest prephlobaphenites (and p r e c o r p o c o l l i n i t e s ) and a l s o the h i g h e s t p r e i n e r t i n i t e s ( p r e m i c r i n i t e s , p r e f u s i n i t e s , and p r e s c l e r o t i n i t e s ) . F i g u r e s 3 and 4 give the area percentages o f biréfringent premacerals found i n the samples s t u d i e d . Since b i r e f r i n g e n c e has been equated w i t h c e l l u l o s e content, i t might t h e r e f o r e be expected t h a t b i r e f r i n g e n c e would decrease w i t h depth i n a deposit as a r e s u l t o f c e l l u l o s e decomposition. However, as can be seen i n Figure 3 ( r e p r e s e n t i n g two cores from the Okefenokee Swamp o f G e o r g i a ) , b i r e f r i n g e n c e may i n c r e a s e or decrease w i t h depth depending on successions o f peat types and moisture c o n d i t i o n s d u r i n g i n i t i a l d e p o s i t i o n . F i g u r e 4 shows t h a t Georgia Nymphaea and Minnesota Sphagnum peats have the h i g h e s t proport i o n s o f biréfringent c o n s t i t u e n t s . The c o n c e n t r a t i o n o f f l u o r e s c e n t premacerals tended t o c o r r e l a t e s l i g h t l y w i t h the p r o p o r t i o n o f biréfringent premacerals.



COAL

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< ω

2 5 ζ en

MACERALS

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MINN

N.CAR.

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Figure 1a. R e l a t i v e p r o p o r t i o n s o f p l a n t types i d e n t i f i e d from microtome s e c t i o n s o f peats from Minnesota, Maine, North C a r o l i n a , and Georgia (A = abundant, C = common, Ρ = present, R = r a r e , and 0 = absent).

55

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a-

.ο

MINN

MAINE

N.CAR.

GEORGIA

Figure 1b. R e l a t i v e abundances of p l a n t organs i d e n t i f i e d from microtome s e c t i o n s of peats from the same samples as i n Figure 1a.


2.

COHEN AND ANDREJKO

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F i g u r e 2. C o l o r o f a l l i n g r e d i e n t s i n t h e f o u r p e a t t y p e s as d e t e r m i n e d by a r e a p o i n t c o u n t s o f m i c r o t o m e s e c t i o n s . ( A v e r a g e o f t h r e e samples from e a c h a r e a )


COAL MACERALS


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Figure 3 . Percentage o f biréfringent o r g a n i c s compared w i t h peat types i n two cores from the Okefenokee Swamp.




COHEN AND AN DR E J KO

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Figure 4. Percentage o f biréfringent o r g a n i c s i n each o f 3 samples o f peat from Minnesota, Maine, North C a r o l i n a , and Georgia.


COAL MACERALS

28


However, d i f f e r e n t p l a n t types were found t o produce d i f f e r e n t f l u o r e s c e n t c o l o r s and i n t e n s i t i e s . Furthermore, n a t u r a l " s t a i n i n g " ( i . e . , darkening or c o l o r i n g by n a t u r a l impregnation or chemical a l t e r a t i o n ) o f c e l l w a l l s tended t o e f f e c t b i r e f r i n g e n c e and f l u o r e s c e n c e i n very d i f f e r e n t ways ( F i g u r e s 5 and 6 ) . N a t u r a l s t a i n i n g tended t o c o r r e l a t e s t r o n g l y w i t h b i r e f r i n g e n c e ( i . e . , the darker the s t a i n i n g the l e s s the b i r e f r i n g e n c e ) , but d i d not c o r r e l a t e w e l l w i t h o v e r a l l f l u o r e s c e n c e p r o p e r t i e s . For example, some t i s s u e s t h a t were h i g h l y s t a i n e d tended t o have higher f l u o r e s c e n c e i n t e n s i t i e s than those t h a t were unstained (Figure 6 ) . Proximate and U l t i m a t e Analyses and BTU. F i g u r e 7 shows the r e s u l t s o f proximate and u l t i m a t e analyses and BTU measurement. Note that the peat from North C a r o l i n a (a l o w e r - c o a s t a l - p l a i n , woody, dark, more i n e r t i n i t e - r i c h sample) had the h i g h e s t f i x e d carbon, elemental carbon and s u l f u r content. Woody Taxodium peats from Georgia (not shown) and South C a r o l i n a (not shown) were s i m i l a r i n c h a r a c t e r t o the North C a r o l i n a samples. The Georgia Nymphaea peats, which had the h i g h e s t p r e v i t r i n i t e s , can be seen t o have the h i g h e s t oxygen, hydrogen, and v o l a t i l e matter contents. Note that BTU values tended t o c o r r e l a t e more s t r o n g l y w i t h ash contents than w i t h maceral c o n t e n t s . Summary and Conclusions P r e l i m i n a r y c o r r e l a t i o n s o f pétrographie c h a r a c t e r i s t i c s o f peats ( i . e . , peat types, premaceral p r o p o r t i o n s , and premaceral types) w i t h p r o x i m a t e and u l t i m a t e a n a l y s e s s u g g e s t t h e f o l l o w i n g trends: 1. Peats w i t h the h i g h e s t p r o p o r t i o n s o f biréfringent macérais tend t o have the h i g h e s t v o l a t i l e matter (and H and 0 contents). 2. Fluorescence o f macérais, on the other hand, seems t o c o r r e l a t e only s l i g h t l y w i t h proximate and u l t i m a t e analyses. 3. Higher p r e v i t r i n i t e contents (determined by c o l o r ) tend t o c o r r e l a t e w i t h higher v o l a t i l e matter c o n t e n t s . 4. Peats with higher p r e i n e r t i n i t e s , prephlobaphenites (and p r e c o r p o c o l l i n i t e s ) , .and p r e s c l e r o t i n i t e s have the h i g h e s t f i x e d carbon. 5. BTU c o r r e l a t e s s t r o n g l y w i t h ash content and o n l y s l i g h t l y w i t h maceral content. Acknowledgments This work was funded i n p a r t by Grant #EAR-79-26382 from the N a t i o n a l Science Foundation and i n p a r t by funding from the O f f i c e o f B a s i c Energy Sciences o f the Department o f Energy.



2.

C O H E N A N D A N DR EJ KO


Figure 5a. Photomicrograph o f a microtome s e c t i o n o f peat i n transmitted l i g h t . Note that the c e l l w a l l s i n the upper l e f t h a l f o f the f i g u r e (even though f i l l e d w i t h reddish-brown t a n n i f e r o u s m a t e r i a l ) are not as d a r k l y s t a i n e d as the c e l l s i n the lower r i g h t h a l f o f the f i g u r e . Scale bar equals 100 microns.

Figure 5b. Same view as 5a except under c r o s s - p o l a r i z e d l i g h t t o show biréfringent i n g r e d i e n t s . The l e s s s t a i n e d w a l l s are the most biréfringent.


29


COAL MACERALS

Figure 6a. Photomicrograph of a microtome s e c t i o n o f peat showing a cross s e c t i o n o f a n a t u r a l l y s t a i n e d Woodwardia v i r g i n i c a (chain fern) r o o t l e t ( t r a n s m i t t e d l i g h t ) . Scale bar equals 250 microns.

Figure 6b. A s i m i l a r view as i n F i g . 6a o f a s l i g h t l y l a r g e r root o f Woodwardia but observed under blue l i g h t f l u o r e s c e n c e . Note that ( i n c o n t r a s t t o b i r e f r i n g e n c e ) the more d a r k l y s t a i n e d t i s s u e s tend here t o be more h i g h l y fluorescent.



2. COHEN AND AN DR EJ KO

Ultimate


OXYGEN Τ CARBON 70605040? 30? 20 % lo ot MIMANCGAMIMANCGA

Analyses

HYDROGEN

s

MOISTURE

SULFUR

NITROGEN

m esd

Ml MA NC GA Ml MA NC GA Ml MA NC GA

Proximate

70 60 50 40 30 r 20* 10

31

Analyses

MAT.

VOL.

FIXED C

ASH

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Heating Value

10.000

8 8,000;?

5

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Figure 7. Proximate and u l t i m a t e analyses o f samples from Minnesota (MI), Maine (MA), North C a r o l i n a (NC), and Georgia (GA).


COAL MACERALS

32

Literature Cited 1. 2. 3.


4.

Cohen, A. D. Ph.D. T h e s i s , Pennsylvania State U n i v e r s i t y , 1968. Cohen, A. D.; Spackman, W. Geol. Soc. Am. Bull. 1972, 83, 129-142. Cohen, A. D. T e s t i n g o f Peats and Organic Soils, STP 820, Am. Soc. f o r T e s t i n g and M a t e r i a l s , P h i l a d e l p h i a , PA, 21-36, 1982. Corvinus, D. Α.; Cohen, A. D. Compt. Rendu. IX I n t e r . Carb. Congress, In Press.

RECEIVED January 6, 1984


Chemistry and Characterization of Coal Macerals - ACS Publications

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