Pyrolytic and Spectroscopic Studies of the Diagenetic Alteration of

Chapter 4

Pyrolytic and Spectroscopic Studies of the Diagenetic Alteration of Resinites Tatsushi Murae, Shuji Shimokawa, and A. Aihara

Downloaded by EAST CAROLINA UNIV on March 22, 2016 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1995-0617.ch004

Department of Earth and Planetary Science, Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812, Japan

Alteration of the chemical structure of resinites has been investigated by spectroscopic methods, due to the potential value of resinites as geochemical indicators of sedimentary environments. FT-IR and pyrolysis GC-MS data correlate with the reflectance values of coexisting vitrinites for the specimens of resinite collected from different coalfieldsof various degrees of coalification. All specimens are included in Class I (Anderson's classification). FT-IR studies of structural changes in resinites on heating indicated decarboxylation to be the major reaction path for thermal structural alteration. The data obtained indicate that spectroscopic analysis of resinites may afford useful maturation indicators for immature samples.

Coal macérais, of which resinite is an example, are penological components of coals derived from the preserved remains of plant material (/). Most macérais are derived from the remains of various types of plant tissues. Therefore, the molecular compositions of macérais are usually very complicated. However, maturation processes modify the original plant tissues, and diminish differences between the molecular structures of each component in the maceral. The degree of modification of the original structures corresponds to the maturity of the maceral. Therefore, we can use the alteration of physical properties of the macérais as an indicator for maturation degree of the samples. Vitrinite reflectance values are the most widely applied indicator for the determination of maturity of sediment samples containing coaly fragments. Determination of the maturity of sediment samples obtained from environments less mature than the so called "oil window" is very important to understanding of various geological phenomena. However, for low maturity samples, vitrinite

0097-6156/95/0617-0076$12.00/0 © 1995 American Chemical Society

Anderson and Crelling; Amber, Resinite, and Fossil Resins ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


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Diagenetic Alteration of Resinites

reflectance values are very irregular and very difficult to use as a maturation indicator due to the remaining molecular complexity reflecting the source plant tissues. Therefore, the development of maturation indicators for low-maturity samples has been desired. Resinite is derivedfromplant resins and secretions such as waxes, oils, and fats. Since resins are derived from a number of different sources, they can consist of a variety of substances including terpenes, phenols, alcohols, and acids. Their exact composition and mode of occurrence depend upon the type of plantfromwhich they are derived and their mode of deposition. Resinites are yellowish orange to amber color in transmitted light and gray in reflected light. Due to their diverse origins, they exhibit a variety offluorescencecolors an alteration property (2,3). Consequently, it has been claimed that the optical properties of resinites are not a good indicator of thermal maturity (4). However, the chemical components of resinites are remarkably simple compared with those of other macérais. Resinites contain only the compounds exuding naturally from plant tissues. Other macérais are formedfromthe tissues themselves, and hence contain a great variety of chemical components. This fact enables us to classify the resinites on the basis of structural characteristics. Anderson et al. classified them into five classes (Classes I ~ V) (5,6,7). They classified Class I resinites further into three sub groups (Classes la ~ Ic) on the basis of details of their composition. Resinites belonging to Class la are derived from/based on polymers and copolymers of labdanoid diterpenes, having the regular [\S,4aR,5S,8aR] configuration, including communie acids and communol and incorporating significant amounts of succinic acid. Those belonging to Class lb are also derivedfromresins based primarily on polymers and copolymers of labdanoid diterpenes having the regular [IS, 4aR, 5S, 8a#] configuration, including but not limited to communie acid, communol and biformene. Class Ic resinites are derivedfromresins based primarily on polymers and copolymers of labdanoid diterpenes having the enantio [15, 4aS, 5R, 8aS] configuration, including not limited to ozic acid, ozol, and enantio biformenes. Thermal maturation probably modifies the chemical structure of the polymer in resinites. The differences of chemical structure among resinite samples belonging to the same class possibly indicate differences in the degree of maturation. The chemical reactions that alter the structure of the polymer in resinites probably proceed at lower temperature than aromatization reactions. Therefore, it may be possible to use the alteration of the chemical structure of resinites as a diagenesis indicator for the samples whose maturity is too low to be determined by vitrinite reflectance. In order to determine the alteration of the chemical structure of the polymer in resinites, it is necessary to examine resinite samples from different source having different thermal histories. Analyses by elemental analysis, FT-IR (Fourier transform infrared spectroscopy), pyrolysis GC-MS (gas chromatography-mass spectrometry) and CP-MAS C NMR (cross polarization-magic-angle spinning solid-state C nuclear magnetic resonance) are usually effective for characterization of organic polymers. Comparisons between the data obtained using the above methods on resinites, and the reflectance values of vitrinites coexisting with the resinite samples may provide information about the correlation between the structural alteration of 1 3


1 3

78

AMBER, RESINITE, AND FOSSIL RESINS

H/C 1.60" Ube

1.55 _ Kuji*

Ono

strobe

T o k u s u e

1.50Nakama ®Fushun


1.45 ~

decarboxylation

1.40 ~ I

0

I

0.05

I

0.10

!

0.15

0.20

o/c

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8 O/C

Figure 1. Plot of the resinites in a van Krevelen diagram.


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79

resinite and its thermal maturity. Laboratory experiments of the structural alteration of resinite samples by heating also afford a useful information on their thermal maturity.


Resinite Samples Resinites usually coexist with other macérais, although some low maturity resinite samples exist as soft lumps. High maturity resinites are hard, and relatively large pieces are referred to by the name "amber". Table I lists the characteristics of the resinite samples used in this work along with reflectance values of coexisting vitrinites, type of coalfromwhich the resinite was picked out, and the geologic age of the strata containing the coal sample. Most of the samples listed in table I were collected at coal fields in Japan except the Latrobe (Australia) and Fushun (China) resinites. All of the resinites was collected by hand pickingfromcoal samples. Thermal maturity is the multiplied result of maximum temperature with effective heating period. Geological heating mechanisms are very complicated in Japan. Therefore, the geologic age is not always directly proportional with the thermal maturation of the samples. Experimental IR spectra were recorded from KBr pellets using a Perkin Elmer 1600 FT-IR spectrometer. IR spectroscopic examinations of thermal alteration of Latrobe resinite were carried out for a KBr pellet cooled down to room temperature after keeping at each heating temperature for 10 minutes under nitrogen. Pyrolysis GC-MS experiments were carried out using a Hitachi G-5000 gas chromatograph coupled to a JEOL D-300 mass spectrometer and a JAI JHP-2 Curie point pyrolyser (for analysis of low boiling point pyrolysates) or JAI JHP-3S Curie point pyrolyser (for analysis of high boiling point pyrolysates). For analysis of high boiling point pyrolysates, simultaneous pyrolysis methylation procedures were employed in order to methylate acidic products (8). The GC oven was operated from 60 °C to 260 °C with temperature ramp rate of 4 °C/min. An OV-1 chemically bonded fused silica capillary column (25m χ 0.25mm I.D., 1.5μπι dp) was used under helium carrier gas. Each sample was pyrolised at 445 °C and 740 °C. Results and Discussion Elemental Composition of Resinites. The elemental composition of macérais changes according to their degree of maturation. This alteration is well represented using a van Krevelen diagram (9), in which H/C vs. O/C atomic ratios are plotted. Figure 1 shows the plot of resinite samples in a van Krevelen diagram. The H/C atomic ratios of the resinites are much higher than those of vitrinites indicating the presence of highly saturated structures in the resinites. Although the difference of O/C values between the samples is remarkable, the H/C values are almost the same for all samples. Similar tendency of the alteration of elemental composition has been reported for amber and resinite samples from other sources (10). This fact probably



Color

Opaque white yellow Clear yellow -yellow brown Clear yellow ~ yellow brown Clear brown Clear yellow ~ brown Clear yellow brown Clear yellow

Coalfield

Latrobe Ube Fushun Orio Tokusue Nakama Kuii

100 — 10 -5 — 10 —3 —5 — 10

0.40 0.51 0.59 0.60 0.61 0.67 0.69

Coal type

Brown Sub bituminous Sub bituminous High volatile bituminous High volatile bituminous High volatile bituminous High volatile bituminous

Size Vitrinite (mm) reflectance(%)

Table I. Data for Resinite Samples and Coexisting Macérais


Late Oligocène Middle Eocene Eocene Early Oligocène Early Oligocène Early Oligocène Late Cretaceous

Geologic Age

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indicates that decarboxylation is the major chemical reaction during the maturation of the resinite samples provided all of these resinites belongs to Class I of Anderson's classification (5-7). IR Spectra of the Resinites. IR spectra reflect the type of functional groups present in organic molecules very well. The IR spectra of the resinites in Table I are shown in Figure 2. Gross features of the IR spectra of the resinites in Figure 2 resemble each other. This fact indicates the presence of similar functional groups in all samples. This suggests that these resinites have similar chemical structures and are consistent with the spectra of other Class I resinites (5,11,12,13,14). Closely similar IR spectra have been reported for other amber and resinite samples by Grimait et al. (10). The absorptions at ca. 3000 cm" and ca. 1450 cm" are assigned to aliphatic C-H bonds, and these at ca. 3400 cm" and ca. 1700 cm" to carboxyl groups. The broad absorption band at ca. 3400 cm" may contain the signal due to water also. The absorption at ca. 880 cm" in the spectrum of Latrobe resinite can be assigned to exomethylene groups. The absorption intensities of the signals due to the carboxyl and exomethylene groups differ between the samples of differing maturation. Absorption due to exomethylene disappeared in the spectra of the samples of vitrinite reflectance greater than ~ 0.4% (Latrobe resinite). Grimait et al. classified ambers and resinites into two major age groups, irrespective of origin, using the exomethylene IR bands. In the samples of lower maturity the bands are easily recognizable, but are absent in more mature samples (10). Our results indicate that the exomethylene group is modified during the early stages of maturation. This fact is consistent with the NMR observations by Lambert et al. (75). The intensities of absorptions at ca. 1700 cm' due to carboxyl groups decrease according to the incremental increase of the reflectance value of coexisting vitrinites. The decrease of the intensity of carboxyl band probably indicates the occurrence of decarboxylation reactions as suggested by the results of elemental analyses. The relative intensities of the IR absorption at ca. 1700 cm" to the absorption at ca. 1450 cm" are plotted against the reflectance value of coexisting vitrinite in Figure 3. These relative intensities indicate the relative abundance of carboxyl group in the molecules. Figure 3 shows almost linear correlation between the relative intensities of the IR bands and the vitrinite reflectance values. This fact indicates that decarboxylation reaction proceeds mainly during relatively early stages of maturation processes. 1

1

1

1

1

1

1

1

1

Thermal Alteration of IR Spectra. Heating causes structural changes in the organic components of sedimentary samples during maturation processes. The maximum temperature and the effective heating period are the factors that determine the degree of the maturation. In order to estimate the thermal history of a sample from chemical analysis, it is very important to know what kind of structural alteration occurs at what temperature for specific compounds incorporated in the sample. Evaluation of the maturity of relatively immature samples using vitrinite reflectance suffers from a number of difficulties (16). The main factors determining alterations of vitrinite reflectance values are aromatization reactions that proceed at relatively high


82


Aliphatic C-H

C

=

C

H

( Latrobe


Ro=0.40

Ί*ο=0.69

4000

3500 3000 2500 2000

1500

1000

cm-'

Figure 2. IR spectra of the resinites (vitrinite reflectance value of coexisting vitrinites are indicated).



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temperature. Hence it is difficult to use vitrinite reflectance values as thermal indicators for immature samples which have never experienced prolonged high temperatures. Based on the data described in this report, decarboxylation reactions cause the major structural alteration of resinites. These reactions usually proceed at lower temperatures than aromatization reactions. Therefore, the structural alteration of resinites has a potential as a thermal maturity indicator for immature samples. This was confirmed by observation of the alteration of IR spectra of Latrobe resinite in response to laboratory heating experiments as shown in Figure 4. Vassallo et al. have carried out similar experiments using Fushun and Yallourn resinites (77). Hwang and Teerman measured thermal alteration of IR spectra of resinites during pyrolysis for hydrocarbon characterizations (18). Latrobe resinite is the most immature sample among those in Table I. Therefore, that is the most suitable sample for heating experiment. The results of this experiment indicate that isomerization of exomethylene structures occurs at ca. 250 °C and is complete by ca. 300 °C. Decarboxylation reactions begin at ca. 300 °C and are almost complete at ca. 400 °C. Aromatization reaction follows the decarboxylation reaction. The relative intensity of the absorption at 1700 cm" to that of at 1450 cm" decreases linearly following the elevation of heating temperature between 300 °C and 400 °C. This observation may allow us to estimate the highest temperature limit of the thermal history of immature samples containing resinites on the basis of IR spectra. 1

1

Pyrolysis GC-MS of Resinites. Analyses of pyrolysis products give us very useful information about the structure of organic polymers. On pyrolysis using a direct inlet probe of a mass spectrometer, most of the resinites in the Table I afforded a characteristic ion peak at m/z 302 whose exact mass 302.2246 indicates the elemental composition of the ion to be C20H30O2. This elemental composition is compatible with that of communie acid (I) which is a major component of Class la and Class lb resinites (5,6,7). The relative intensity of the ion decreased in the spectra of the more matured samples. This may indicate that the modification of the structure unit of the resinite polymers proceeds according to the incremental increase of thermal maturation. Anderson suggested that loss of monomelic diterpene acids such as abietic acid, which is a common component in recent and immature resinites, as maturation increase is the main possible reason of the above observation (79). Structure elucidation of the products yielded on vacuum pyrolysis experiments of Latrobe resinite is under way in order to confirm that possibility. Distribution pattern of pyrolysis products from a polymer reflects the chemical structure of the polymer. The major components of low boiling pyrolysis products obtained by heating at 740 °C are aromatic hydrocarbons and the distribution patterns of the components resemble each other for all samples (Figure 5). That suggests the presence of similar basic skeletal structure for all samples (consistent with the results obtained by IR spectra). Pyrolysis at such high temperature as 740 °C is accompanied by dehydration reactions to yield aromatic compounds. However, on heating at 445 °C using the same pyrolysis system as above, the resinite samples gave pyrograms that differed significantly. Figure 6 shows the distribution patterns of


84


D

l 7 0 0

(C =0) / D

1 4 5 0

(Aliphatic C - H) -

Ro(%)


Latrobe

1

1

Figure 3. Relative intensity of IR absorption at 1700 cm" to that at 1450 cm" of the resinites vs. the reflectance value of coexisting vitrinites.

the pyrolizates. The major components of low boiling pyrolysis products obtained by heating at 445 °C are aliphatic hydrocarbons and the gross features of the pyrograms divided the samples into three groups. The first group contains the resinite from Latrobe, the second contains the resinitefromUbe and Fushun, and the third contains the resinite from Orio, Tokusue, Nakama, and Kuji. The resinites within each group show similar relative intensity of IR absorption at 1700 cm" to that at 1450 cm* . Therefore, this grouping seems to reflect the differences in diagenetic processes and burial metamorphism. Only pyrolysis products having low boiling point were analyzed in the experiments described in Figures 5 and 6. According to the report by Anderson et al. (5), some of the major pyrolysis products from Class I resinites contain carboxyl group, and the amount of three characteristic bicyclic acids esters (II, III and IV) derived from the A/B ring system of polycommunic acid (V) is maturity dependent. Pyrolysis of the resinites in Table I at 445 °C with tetramethylammonium hydroxide as a methylation reagent gave the methyl ester of the acids II and III (and probably IV) along with other various components as shown in Figures 7a and 7b. Examinations of the pyrolysis products by mass chromatograms indicated that the compounds II and III are the major acid ester products. The mass chromatograms also suggested that the peak corresponding to the compound IV may overlap with that of III as a minor component. Therefore, we evaluated the intensity of the peak assigned to III in Figures 7a and 7b as the accumulated amount of III and IV. Figure 8 shows the plot of the ratio of esters II/(III+IV) against the reflectance value of vitrinite coexisting with the resinite. Although, as a general trend, the ratios of the esters correlate with vitrinite reflectance values, much more examples are necessary in order to use the ratio of the acids as an effective maturity indicator. 1


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85



4.

Aromatic C=C 4000

3500 3000

2500

2000

1500

1000

Figure 4. IR spectra of resinites samples heated to various temperatures. Temperatures and assignments of the major peaks are indicated.




86

Figure 5. Distribution of components yielded on pyrolysis of the resinites at 740 °C. Amounts of structural isomers are summed. The relative amount of each sum is normalized to the highest amount.


MURAE ET AL.



4.

Figure 6. Distribution of components yielded on pyrolysis of the resinites at 445 °C. Amounts of the compounds bearing same carbon numbers are summed. The relative amount of each sum is normalized to the highest amount.


87

88


100

ISO

200

2Ç0

-100

K M

i l i l l l l l i l l l i i l i t tU4±*AU>l


TMAH

Ilt.l

f j ^ J

ι

^6θ^Η

Nakama

3

Ro=0 67

I W ^ X j ^ . . . . . . . . . . . . . . .

-

. - - 11 .

•-

1

Figure 7a Py-GC-MS total ion chromatograms of Nakama, Kuji, and Latrobe resinites.


M U R A E ET AL.



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Figure 7b Py-GC-MS total ion chromatograms of Fushun, Orio, and Tokusue resinites.


89

90


1.2

> +

1.0 Latrobe 0.8


00

Ο

Fushun I Tokusue

0.6 0.4

Ube

Orio

0.2

Nakama Kuji

0 0.4

COOCH

0.6

0.8 (Ro)

3

(Π) Polymer

Polymer

Pyrolysis Π , Ι Π , I V , etc. Methylation Figure 8. Ratio of characteristic bicyclic acids methyl esters [II/(III+IV)] yielded on pyrolysis of the resinites at 445 °C (with simultaneous methylation) vs. reflectance value of coexisting vitrinites.


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Conclusions All of the resinites investigated in this work are included in the Classes I of the Anderson's classification (5,6,7). The relative intensity of IR absorption at 1740 cm" to that at 1450 cm" indicates maturity of the sample. The presence of the IR absorption due to exomethylene indicates that the thermal maturity of the sample is too low to be evaluated by the intensity of carboxyl bands. The ratio of specific components of pyrolysis products of the resinites also works as a maturity indicator for immature samples. Molecular structures of resinites were easily modified irreversibly by heating in short period. Therefore, provided a sample contains resinite, spectroscopic examination of the resinite may be useful for determining the upper temperature limit in thermal history of the sample.

1


1

Literature Cited 1 Killops, S. D.; Killops V. J. An Introduction to Organic Geochemistry; Longman Scientific & Technical: Essex, England, 1993; pp 98-100. 2 Teichmuller, M.; Durand, Β. Int. J. Coal. Geol., 1983, 2, 197-230. 3 Senftle, J. T.; Brown, J. H.; Larter, S. R. Int. J. Coal. Geo., 1987, 7, 105-117. 4 Senftle, J. T.; Landis, C. R.; McLaughlin, R. L. In Organic Geochemistry: Principles and Applications; Engel, M. H.; Macko S. Α., Ed.; Topics in Geobiology 11; Plenum Press: NY, 1993; pp 355-374. 5 Anderson, K. B.; Winans, R. E.; Botto, R. E. Org. Geochem. 1992, 18, 829-841. 6 Anderson, Κ. B.; Botto, R. E. Org. Geochem. 1993, 20, 1027-1038. 7 Anderson, Κ. B. Org. Geochem. 1994, 21, 209-212. 8 Challinor, J. M.; J. Anal. Appl. Pyrol. 1991, 18, 233-244. 9 Van Krevelen, D. W. Coal. Typology-Chemistry-Physics-Constitution; Elsevier Publishing Co: Amsterdam, 1961; 514p. 10 Grimalt, J. O.; Simoneit, B. R. T.; Hatcher, P. G.; Nissenbaum, A. Org. Geochem. 1988, 13, 677-690. 11 Langenheim, J. H. Science 1969, 163, 1157-1169. 12 Anderson, Κ. B.; Johns, R. B. Org. Geochem. 1986, 9, 219-224. 13 Mosini, V.; Cesaro, S. N. Phytochemistry, 1986, 25, 244-245. 14 Beck, C. W. Naturwissenschaften, 1972, 59, 294-298. 15 Lambert, J.B.; Frye, J. S.; Poinar, J. O. Jr. Archaeometry, 1985, 27, 43-51. 16 Whelan, J. K.; Thompson-Rizer, C. L. Organic Geochemistry: Principles and Applications; Engel, M. H.; Macko S. Α., Ed.; Topics in Geobiology 11; Plenum Press: NY, 1993; pp 289-353. 17 Vassallo, A. M.; Liu, Y. L.; Pang, L. S. K.; Wilson, M. A. Fuel 1991, 70, 635639. 18 Hwang, R. J.; Teerman, S. C. Energy Fuels 1988, 2, 170-175. 19 Editorial suggestions. R E C E I V E D August 17, 1995


Pyrolytic and Spectroscopic Studies of the Diagenetic Alteration of

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