A Comparative Study of Exinite, Vitrinite, and Micrinite

20 A Comparative Study of Exinite, Vitrinite, and Micrinite

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H. TSCHAMLER* and E. DE RUITER Union Carbide

European

Research Associates,

S.A., Brussels 18,

Belgium

An exinite, vitrinite, and micrinite of the same rank were investigated. From elementary analysis alone it follows that their structures must be different. Combining the results from IR and PSR measurements, the hydrogen distribution, the aliphatic group distribution, and possible intervals for the aromaticity are derived. Exinite possesses the biggest aliphatic position with the highest relative amount of CH groups, and micrinite possesses the 2

smallest aliphatic position with the lowest relative amount of CH groups. From x-ray measurements 2

and hydrogen distribution, limits for the aromatic cluster size are derived; exinite has the smallest clusters, micrinite the largest. Finally, the presence of nonaromatic rings is demonstrated, of which at least a part should be hydroaromatic or alicyclic.

por several years the structural features of a vitrinite ( 8 3 . 9 % C ) have been intensively studied. T h e two macérais, exinite and micrinite, which accompany the above mentioned vitrinite in the dull coal were also examined. Separating the three macérais from the d u l l coal was difficult. T h e petrographical purity of the exinite is 8 6 % and that of the micrinite 9 4 % . F o r both macérais, vitrinite is the main " i m p u r i t y . " Since the vitrinite has a petrographical purity of 9 9 % , it is not difficult to calculate the values for the pure exinite and pure micrinite from the experimental data on the highly enriched maceral fractions. A l l values reported i n the tables are corrected ones. Table I summarizes the results of elementary analysis (maf ) and the percentage of volatile matter. The reported values fully agree with those found b y other investigators (2, 8) on exinites, vitrinites, and micrinites of the same rank. T h e atomic H / C * Present address: Kupkagassc 6, Vienna VIII, Austria.

332

In Coal Science; Given, P.; Advances in Chemistry; American Chemical Society: Washington, DC, 1966.

20.

TSCHAMLER AND Table I.

Exinite, Vitrinite, Micrinite

333

Analytical Data (maf) for an Exinite, Vitrinite, and Micrinite

Sample Exinite Vitrinite Micrinite


DE RUÏÏER

Volatile Matter

%C

66.7 35.2 22.9

84.1 83.9 85.7

Elementary Analysis (maf) %H %0 %N 7.0 5.5 3.9

6.3 8.0 8.0

1

1.3 1.4 1.2

%S(Diff)

H/C

1.3 1.2 1.2

0.991 0.780 0.542

ratio (last column i n Table I) remarkably decreases from exinite over vitrinite to micrinite, mainly o w i n g to the large decrease i n hydrogen content. F r o m a structural point of view this fact can be explained by ( 1 ) a considerable difference i n the number of aliphatic groups whereby the mean aromatic cluster size remains the same for a l l three samples, ( 2 ) a considerable difference i n the mean aromatic cluster size, the number of aliphatic groups being constant, or ( 3 ) a combination of these two extreme cases. F i n a l l y , from the volatile matter Car

(%V)

and the carbon content ( % C ) the aromaticity /« ( =

) can be

estimated ( 1 0 ) : _ f

n

1200(100—

~

% V )

1240(%C)

(

1

)

It is, however, known that the /« values from Equation 1 must be regarded as being too l o w because not only the aliphatic part but also small aromatic systems are split off during determination of the volatile matter (11). Furthermore, these /· values make sense only as long as the % V is not too high. This method is, therefore, limited to the vitrinite (/ 1, the term 1/m can be neglected, so that _ R

C a , ( 2 - H / C )

Car

-

(5a)

Ύ

O n the other hand, an /« value can be derived from Equation 5 which corresponds to the limiting case, that R . = 0, or i n other words R = R a r : n

r

C „ ( 2 - H / C )

'" ^ < R

a r >

=

2(R. —1/m) + C a ,

(

P

5

b

)

E a c h true /· value which is smaller than / < R = K . , r > requires the presence of nonaromatic rings. F o r the three macérais under investigation there is no doubt that 1/m = 0 can be used. T h e values i n Table V I I show that 12 nonaromatic rings should be present for nine mean structural units i n the case of exinite, 10 in the case of vitrinite, and 16 i n the case of micrinite. Since all / < R - - R n n r > values are higher than the highest ones obtained from the aliphatic group distribution (see Table I V ) , all samples must contain nonaromatic rings even if the most probable fa values e

e

Table VII. Sample

Mean Number of Nonaromatic Rings, Rnar per Structural Unit and fo(K=K:.r>of an Exinite, Vitrinite, and Micrinite Car

Rar

Exinite 13.25 ± 2.45 2.83 ± 0.63 Vitrinite 15.50 ± 2.50 3.42 ± 0.66 Micrinite 19.25 i t 3.05 4.39 ± 0.79

fa

R

Rnar

fa(R Rar)

0.62 0.77 0.89

4.05 ±: 0.75 4.53 ± 0.73 6.14 ± 0.97

1.32 ± 0.12 1.11 i t 0.07 1.75 ± 0.18

0.71 ± 0.01 0.85 :£ 0.01 1.00 ± 0.01


COAL SCIENCE


338

(column 4 i n Table V I I ) are not the true values. If the true /· values are some what higher, the R » . r values w i l l be somewhat lower than those reported i n Table V I I , column β, and vice-versa. T h e nonaromatic rings can be either only alicyclic (hydroaromatic) or only heterocyclic, but it is also possible that both types are present simultane ously. T h e heterocyclic rings may contain N , S, and/or "nonreactive" oxygen. If it is assumed that all N , S, and nonreactive oxygen is present i n heterocyclic form, these heteroatoms can b u i l d at most 0.8 heterocyclic rings per mean structural unit. T h e m i n i m u m number of alicyclic rings is then given b y R.KmiD) = R n . r — 0.8, whereas the maximum number of alicyclic rings is reached if R hatero 0, and therefore R . = R n . r . If tetra-substituted ali phatic carbon atoms are excluded, only CH2 and C H groups can form alicyclic rings. T h e mean number of CH2 and C H groups per structural unit can be calculated from the aliphatic group distribution and d , w h i c h follows from C . r and /-. If it is assumed to a first approximation that mainly five- and sixmembered rings w i t h at least two and at most four alicyclic carbon atoms are present, C . i equals 2 R . u m m ) and C«ncyeiic equals 4 R.i CnUcfrHmin) CaHrfcl(max)

8.13 ± 1.50 4.63 :± 0.75 2.39 ± 0.37

Table IX.

6.85 ± 1.26 3.32 zt 0.54 1.54 ± 0.24

0.40 0.24 0.77

1.44 1.18 1.93

0.80 0.48 1.30

5.76 3.86 1.78

Maximum and Minimum Portion of Alicyclic Carbon Atoms of C i and Cot for an Exinite, Vitrinite, and Micrinite n

Sample

(Calic*cl/Cal)min (Catir rl/Cat)max V

Exinite Vitrinite Micrinite

0.12 0.12 0.64

0.60 0.72 0.64

(C*Uc9cl/C)min 0.05 0.03 0.07

(Calieyct 0.23 0.17 0.07

F r o m the values of columns 3, 7, and 8 i n Table V I I I together w i t h C t o t per structural unit, the results summarized i n Table I X can be obtained. T h e range of C . n c y d / C (columns 4 and 5, Table I X ) is particularly important be cause C . n c y c i / C follows also directly from dehydrogenation reactions. T h e results of column 3 i n Table I X show that i n all three macérais more than half of the aliphatic carbon atoms may be present i n alicyclic or/and hydroaromatic rings. T h e micrinite has no range but only one value because even 2 R . i ( . i is bigger than the smallest value for (CH2 + C H ) . There is no doubt that i n the case of the micrinite even small errors i n the values of the n )


20.

TSCHAMLER AND DE RUITER

structural

parameters

( C a l l c y c l / C a l ) m l n and

would

339

Exinite, Vitrinite, Micrinite

allow

only

a

small

difference

between

( C a 1 leyc I / C a I ) m a i .

F i n a l l y , the alicyclic fraction of Η · ι should be discussed. This structural parameter can be calculated f r o m :


»£. H a l leyel

it 7^

Η . Ileyel

H a . leyel

Calleyel

C

Η

Η •1

Calleyel

C

Η

Η..

_

,

is known. This ratio corresponds to:

Calleyel Hallcycl

( H c H ) a 11 eye 1 -f*

( H c H ) a l leyel

?

C a l leyel

and w i t h

2 (CH2)

al Icycl +

C a l leyel

( C C H ) . I leyel H . lleyel • lleyel

C a l leyel

C a l leyel —

(Ccnijaieiyei

—

Hallcycl

2Callcycl

Calleyel

( C c H ) al leyel

7

II

1

:

L»alleyel

If

then (2)

Callcycl(maz)

A Comparative Study of Exinite, Vitrinite, and Micrinite

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