Energy & Fuels 1990, 4 , 456-463
456
Terpenoid Biomarkers in Argonne Premium Coal Samples and Their Role during Coalification R. Hayatsu,* R. L. McBeth, P. H. Neill,? Y. Xia,t and R. E. Winans Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 Received April 1 1 , 1990. Revised Manuscript Received July 2, 1990
It has been found that major portions of solvent-extractable hydrocarbons released from the low-rank Argonne Premium Coal Samples are terpenoid biomarkers. These hydrocarbons are considered to be important intermediates in the transformation from the naturally occurring terpenoids to aromatic hydrocarbons commonly found in higher rank coals. Recent physical and chemical studies show that phenolic oxygen groups in lignin are eliminated during coalification. The present study suggests one possible mechanism of how phenolic structures are altered. Terpenoid biomarkers may be acting as hydrogen donors and promote the alteration of phenolic structures to aromatic hydrocarbon structures in early stages of coalification. Model experiments show that elimination of phenolic oxygen proceeds by thermal catalytic hydrogen-transfer reactions in the presence of biomarkers and clay minerals.
Introduction Terpenoid hydrocarbons, one of the major groups of biomarkers,172have been widely found in the geosphere. The study of terpenoid biomarkers found in solvent extracts and pyrolyzates of low-rank coals3-" has provided useful information not only on the origin of coal but also on the diagenetic and catagenetic transformation reactions that occur during coalification and maturation. As suggested by several l a b ~ r a t o r i e s ~ J ~including -'~ O U ~ Sthe , ~ transformation ,~ of naturally occurring terpenoids to partially aromatized terpenoid hydrocarbons and finally to aromatic hydrocarbons involves a rather systematic and sequential series of reaction processes such as defunctionalization, isomerization, rearrangement, aromatization, and carbon-carbon bond cleavage. Among these, aromatization is one of the main chemical reactions that occurs during coalification. Indeed, as coalification progresses, terpenoid biomarkers found in low-rank coals greatly decrease while there is an increase in the thermally more stable nonsubstituted and methylated aromatic hydrocarbons that are widespread constituents of higher rank coals. These changes may reflect the increasing thermal maturation of organic macromolecules in coals. Recently, NMR,16-18p y r o l y s i ~ , land ~ * ~oxidation ~ studies21s22have shown that phenolic structures found in lignin are transformed into aromatic hydrocarbon structures during coalification. The process is considered to involve the following reactions: demethylation of methoxyls, demethoxylation, cleavage of aryl alkyl ethers, elimination of phenolic OH groups, transalkylation, and condensation. Such natural transformations occur by microbial (early stages of diagenesis) and geochemical processes. However,
'Permanent address: Helene Curtis, Chicago, IL 60639.
* Permanent address: Department of Chemistry, Tsinghua Univ-
ersity, Beijing, China.
0881-0624/90/2504-0456$02.50/0
little is known of the reaction mechanisms for the transformation of phenolic structures. Our preliminary studyn phenolic structures are altered to benzene and other aromatic hydrocarbon structures by catalytic hydrogentransfer reactions in the presence of hydrogen donors and (1).Philp, R.P. Fossil Fuel Biomarkers: Applications and Spectra; Elsevier: New York, 1985. (2)Tissot, B. P.;Welte, D. H. Petroleum Formation and Occurrence; Surineer-Verlae: New York. 1984:DD 93-130. (4)Hayatsu, R.;Bot1 E.Org. Geochem. 1987,11,245-250. (5)Chaffee, A. L.; Johns, R. B. Geochim. Cosmochim. Acta 1983,47. 2141-2155. (6)Chaffee,A.L.; Strachan, M. G.; Johns, R. B. Geochim. Cosmochim. Acta 1984,48,2037-2043. (7)Gallegos, E. J. J . Chromatogr. Sci. 1981,19,156-160. (8)Chang, H.-C. K.;Nishioka, M.; Bartle, K. D.; Wise, S. A.; Bayona, J. M.: Markides. K. E.: Lee. M. L. Fuel 1988. 67. 45-57. (9)Hazai, I.; Alexander, G.; Szekely, T. Fuel 1989,68, 49-54. (10)Wang, T. G.;Simoneit, B. R. T. Fuel 1990,69,12-20. (11)Li, M.; Johns, R. B. Org. Geochem. 1990,15,109-121. (12)Tan, Y. L.; Heit, M. Geochim. Cosmochim. Acta 1981, 45, 2267-2279. (13)Simoneit, B. R.T.; Grimalt, J. 0.;Wang, T. G.; Cox, R. E. Org. Geochem. 1986,10, 877-889. (14)Villar, H. J.; Puttmann, W.; Wolf, M. Org. Geochem. 1988,13, 1011-1021. (15)Wakeham, S. G.;Schaffner, Ch.; Giger, W. Geochim. Cosmochim. Acta 1980,44,415-429. (16)Botto, R. E. Energy Fuels 1987,1,228-230. (17)Hatcher, P. G. Energy Fuels 1988,2, 40-58. Related papers
published previously by the author and co-workers are cited in this reference. (18)Bates, A. L.; Hatcher, P. G. Org. Geochem. 1989,14,609-617. (19)Hatcher, P. G.;Lerch, H. E.; Kotra, R. K.; Verheyen, T. V. Fuel
1988,67,1069-1075. (20)Stout, S. A.;Boon, J.; Spackmann, W. Geochim. Cosmochim. Acta 1988,52,405-414. (21)Hayatsu, R.;Botto, R. E.; Scott, R. G.; McBeth, R. L.; Winans, R.E.Fuel 1986,65,821-826. (22)Hayatsu, R.;Botto, R. E.; McBeth, R. L.; Scott, R. G.; Winans, R. E. Prepr. Pap.-Am. Chem. SOC..Diu. Fuel Chem. 1988. 33(3). 107-112.
0 1990 American Chemical Society
Energy & Fuels, Vol. 4, No. 5, 1990 457
Terpenoid Biomarkers in Argonne P r e m i u m Coal S a m p l e s
number APCS no. 1 APCS no. 2 APCS no. 3 APCS no. 4 APCS no. 5 APCS no. 6 APCS no. 7 APCS no. 8
Table I. Argonne Premium Coal Samples and Compositions (in wt % ) coal rank C H 0 med vol bitum 85.50 4.70 7.51 Upper Freeport subbituminous Wyodak-Anderson 75.01 5.35 18.02 high vol bitum 77.67 5.00 13.51 Illinois No. 6 high vol bitum 83.20 5.32 8.83 Pittsburgh No. 8 low vol bitum 91.05 4.44 2.47 Pocahontas No. 3 high vol bitum Blind Canyon 80.69 5.76 11.58 high vol bitum 82.58 5.25 9.83 Lewiston-Stockton lignite 72.94 4.83 20.34 Beulah-Zap
clay m i n e r a l catalysts. T e r p e n o i d biomarkers m a y a c t as one of the hydrogen d o n o r g r o u p s and p r o m o t e the elimination of phenolic oxygen groups in the alteration of lignin t h r o u g h h u m i n i t e and vitrinite coal materials. Indeed, i t is that hydrogen-transfer reactions of terpenoids and s t e r o i d s occur and are due to t h e increase in temperature and c a t a l y t i c activity of the m i n e r a l m a t r i x i n later diagenetic and e a r l y catagenetic stages. Thermal decomposition in dissociation reactions of anisoles b y very low pressure pyrolysis has also been discussed i n In this s t u d y , we isolate and identify t e r p e n o i d biom a r k e r s present in A r g o n n e P r e m i u m Coal S a m p l e s (APCS)a n d demonstrate that phenolic structures in lignin could b e transformed, at least partially in the presence of b i o m a r k e r s , at early stages of coalification. To obtain insight into the transformation mechanisms and processes of phenolic s t r u c t u r e s , abiogenic simulation e x p e r i m e n t s (catalytic hydrogen-transfer reactions) with phenolic compounds/ polymers and lignin in the presence of terpenoid b i o m a r k e r s h a v e been carried out. We h a v e also s t u d i e d h o w terpenoid b i o m a r k e r s used i n the experiments are transformed d u r i n g the reactions.
org S
N
0.74 0.47 2.38 0.89 0.50 0.37 0.65 0.70
1.55 1.12 1.37 1.64 1.33 1.57, 1.56 1.15
COAL
Bz-MeOH ( 3 1 )
1
I RES.
EXT.
HCI-HF Bz-MeOH ( 3 1 )
Bz-Et20 (1 : I )
2% NaOH aq. sol
I 7
,
Aq. Sol
2% HCI Bz-Et20
Org. Sol
lnsol (H-2)
(A-2)
Experimental Section Samples. Eight APCS (no. 1-no. 8) were used in this study (see Table I). The detailed analytical data of these coals have been recently published.26 Extraction. The extraction procedure, which was carried out under nitrogen atmosphere, is shown in Figure 1. Each coal sample (as received, -100 mesh, 30 g) was heated with benzenemethanol (3:1,250 mL) a t reflux (24 h) and then with CHCl, (250 mL, 24 h). Both extracts were combined and then separated into neutral (N-1) and acidic fractions with 2% NaOH aqueous solution. An acidic fraction was isolated after the alkaline solution was acidified. The acidic fraction was further divided into nonpolar solvent soluble fraction (A-l), which can be analyzed by GC/MS, and a polar solvent soluble fraction (H-1;high molecular weight humic-like material). T o obtain more extractable material, the extracted coal was treated three times with HCl-HF (1:l) by stirring at room temperature for 24 h. The HCl-HF solution was diluted with water and filtered all insoluble residue was extracted with benzene-methanol (3:l). The extractable material was divided into three fractions (N-2, A-2, H-2) as described above. A summary of solvent extracts from eight Argonne Premium Coal Samples is shown in Table 11. C h r o m a t o g r a p h i c Separation. T o obtain a concentrated fraction of hydrocarbons (n-alkane, terpenoid hydrocarbon, aromatic hydrocarbon), each neutral fraction (N-1 N-2) from a coal sample was chromatographed. For example, 0.5 g of a neutral fraction was dissolved in 150 mL of n-hexane-benzene (1:l) (a small amount of material was not soluble) and passed
+
(23) Hussler, G.; Connan, J.; Albrecht, P. A. Org. Geochem. 1984,6, 39-49. (24) Brassell, S. C.; McEvoy, J.; Hoffmann, C. F.; Lamb, N. A.; Peakman, T. M.; Maxwell, J. R Org. Geochem. 1984, I , 11-23. (25) Suryan, M. M.; Kafafi, S.A.; Stein, S. E. J. Am. Chem. SOC. 1989, 11 1, 1423-1429. (26) Vorres, K. S. Users Handbook for the Argonne Premium Coal Sample Program; Argonne National Laboratory: Argonne, IL, Oct 1, 1989. Elemental compositions of all APCS are also seen on outside back cover of recent preprints of the Fuel Chemistry Division, ACS.
F i g u r e 1. Extraction and isolation procedures of neutral and acidic fractions from a n APCS coal. Table 11. Summary of Solvent Extracts re1 abund of fractions sepd from total extracts sample total neutral acidic humic(A-1 + like' (H-1 (APCS) extracts,b (N-1 + no. % C" wt % N-2) A-2) + H-2) 8 2 3 6 7 4 1 5
72.9 75.0 71.7 80.7 82.6 83.2 85.5 91.0
6.4 12.4 8.6 9.8 5.2 5.0 0.7 0.4
32.7 35.6 57.6 38.0 80.5 79.2 89.9 89.2
38.5 25.4 22.2 36.5 5.2 4.3 3.1d 4.0d
28.8 39.0 20.2 25.5 14.3 16.5 7.0d 6.Bd
Total amounts of a On a dry mineral free basis (see ref 26). N-1, N-2, A-1, A-2, H-1, and H-2 fractions; wt % was calculated from each coal sample, on a dry mineral free basis. 'Humic-like fractions are soluble in aqueous alkaline solution and methanol but not for nonpolar solvents. Characterization of these fractions has not been carried out, because of very small amounts. through a column containing alumina grade 1 (24 cm X 2 cm i.d.1. The column was eluted with the same solvent (500 mL) and then n-hexanebenzene 1:2 (600 mL). The two fractions were combined and evaporated. Results obtained from the neutral fractions of eight coal samples are shown in Table 111. Each acidic fraction (A-1 + A-2) was methylated with diazomethane. The methylated sample was dissolved in CHCl, (a small amount of material was not dissolved) and analyzed by GC/MS. Characterization of humic-like fractions has not been carried out yet. T h e r m a l C a t a l y t i c H y d r o g e n - T r a n s f e r Reactions. Transfer reactions were carried out with phenolic and lignin samples in the presence of hydrogen donors. Phenolic samples,
Hayatsu et al.
458 Energy & Fuels, Vol. 4, No. 5, 1990 Chart I
4@l&ll& 4 4 & & +p V
I
, VI
XIVb XIVC
VI I
A hydrocarbon group was obtained through column chromatography of a neutral fraction extracted from each coal sample (see Experimental Section). Relative abundances were estimated from GC analyses. Wt % was determined from a hydrocarbon fraction obtained from each coal sample, on a dry mineral free basis. 'THB, terpenoid hydrocarbon biomarker; AH, aromatic hydrocarbon; nd, not detected.
*
4,4'-dihydroxybiphenyl,4,4-dimethoxybiphenyl,poly(4-methoxy-d, styrene) and softwood ligninz1were used. Dehydroabietic acid
fl
IX
-2H -CH,
Table 111. Relative Abundances of Terpenoid Hydrocarbon Biomarkers, Alkanes, and Aromatic Hydrocarbons in Hydrocarbon Fractionsa relative abundancesn sample (APCS) sesquino. wt %* alkane THB di-THB tri-THB AH 8 1.7 a 8 53 17 14 10 2 12 49 13 16 3.6 3 5.5 9 7.5 4 74 3.5 9 6 3.2 26 9 23 33 7 3 3 1 3 90 3.4 4 3 2 1 90 4 2.7 99 99
I
VI I I
,,
16,
k02H
dehydroabietic acid (from pine tree resin) and A2-allobetulene(from Australian brown coal4) were obtained respectively after purification by column chromatography and were used as hydrogen donors. A mixture of terpenoid biomarkers isolated from APCS no. 8 was also used as a hydrogen donor. A phenolic sample (0.3 g), a hydrogen donor (0.5 g), and K-10 montmorillonite clayz7 (1.5 g) were ground together and then placed in a 25 X 2 cm i.d. glass tube. For lignin-donor experiments, 1 g of lignin, a hydrogen donor (0.5 g), and K-10 (5 g) were used. After evacuation, 0.5 atm. of argon was added and the tube was sealed and then heated a t 150 "C for 1month (see Table IV). After the reaction, the mixture was (27) Acid Activated Clay (Aldrich Chemical Co.); for review of this catalysis, see: Laszlo, P. Science 1987, 235, 1473-1477.
extracted with refluxing benzene-methanol(3:l) and then CHC13. T o understand the role of hydrogen donors for the transformation, two experiments were carried out under identical condition but in the absence of terpenoid biomarkers. In general, phenolic groups are strongly absorbed on the surface of clay minerals. Therefore, it is necessary to treat the reaction mixture with 6 N HCl (reflux for 6 h) before extraction with organic solvent. The solvent-insoluble residue was treated with concentrated HCl-HF (1:l)a t room temperature to remove the clay. Two Steps: Alkaline Hydrolysis-Oxidation. This method has been previously reported in Each sample (0.4-0.5 g) was hydrolyzed with 12% NaOH aqueous solution in an autoclave at 180 "C for 4 h. The air in the autoclave was replaced by nitrogen. Each alkaline hydrolyzed fraction was oxidized with alkaline silver oxide a t 80 "C for 10 h. The yields of oxidation products are shown in Table VI. The silver oxide oxidation is known not to destroy phenolic rings. C h a r a c t e r i z a t i o n a n d Identification. Hydrocarbons obtained from the coals and the catalytic hydrogen-transfer reaction products were analyzed by GC/MS and/or solid-probe highresolution MS. All mass spectra were obtained with either Kratos MS25/DS55 or Hewlett-Packard 5970B/MSD. Solid-probe data were obtained in a precise mass measurement mode. GC separations were made by using a 60 m x 0.25 mm bonded OV-1701 fused-silica column or DB-5 (30 m X 0.25 mm) temperature programmed from 50 to 580 "C a t 8 "C/min and then isothermal for 20 min. a. Terpenoid Hydrocarbon B i o m a r k e r s a n d Aromatic Hydrocarbons. These compounds structures were assigned or identified by comparing GC retention behavior and mass spectrometric fragmentation patterns with authentic standards or with published data.% Biomarkers, where standards of published data were not available, were tentatively assigned on the basis of mass spectral interpretation. In Chart I, structures of biomarkers are shown. Some of them have several isomers depending on the position of alkyl groups, location of double bonds, stereoconfiguration, and conformation, and such biomarkers represent only carbon skeletal structures. Cadalene (111) and retene (IX) are alkyl derivatives of naphthalene and phenanthrene, respectively; however, they are considered to be biomarkers because the carbon skeletons of the original terpenoids are preserved. (28) (a) McLafferty, F. WT;Stauffer,D. B. The WileylNBS Registry Mass Spectral Data; Wiley: New York, 1989; Vol. 1-7. (b) Livsey, A.; Douglas, A. G.;Connan, J. Org. Geochem. 1984,6,73-81. (c) Richardson, J. S.; Miller, D. E. Anal. Chem. 1982,54,765-768. (d) Greiner, A. Ch.; Spoyckerelle, C.; Albrecht, P.; Ourisson, G . J . Chem. Res., Miniprint 1977,3829-3871. (e) Chaffee, A. L.; Fookes, C. J. R. Org. Ceochem. 1988, 12, 261-271.'See also refs 1, 5, 6, 8-10, and 12.
of
Terpenoid Biomarkers in Argonne Premium Coal Samples
Energy & Fuels, Vol. 4, No. 5, 1990 459
Table IV. Terpenoid Biomarkers Detected in t h e Hydrocarbon Fractions of Four APCS APCS no.a,b compound composition structure 8 2 + tetramethyldecalins + bicyclic alkanes + tetramethyltetralins C14H20 C15H22 I calamenene + C15H22 I1 tetrahydrocadalene + C15H18 I11 cadalene C4-naphthalene C14H16 + C5-naphthalene C15H18 + CZOH36 IV pimarane + C2OH36 V abietane + C1sHzs VI dehydroabietin + C20H30 VI1 dehydroabietane C,-tetrahydrophenanthrenes C18H22 unknown CZOH28 + C19H24 VI11 simonellite + C3-phenanthrenes C17H16 + unknown CZlHZ8 C3-phenanthrenes C17H16 unknown C22H30 + C18Hl8 IX retene C20H24 X dimethyloctahydrochrysene unknown Cl8Hl8 + trimethyloctahydrochrysenes C21H26 + C27H36 XI diaromatic 8,14-secotriterpenoids + C27H32 XIIa triaromatic 8,14-~ecotriterpenoids C2SH34 XIIb triaromatic 8J4-secotriterpenoids C26H36 XIIIa D-ring monoaromatic triterpenoids c27H4C XIIIb D-ring monoaromatic triterpenoids + C28H42 XIVa A-ring monoaromatic triterpenoids C28H40 XIVb A-ring monoaromatic triterpenoids C27H38 XIVC A-ring monoaromatic triterpenoids + xv C27H36 A,B-ring diaromatic triterpenoids + C26H30 XVI A,B,C-ring triaromatic triterpenoids A,B,C,D-ring tetraaromatic triterpenoids C25H24
+
6
3
+ +
+
+
+ +
+
+ +
+ +
+
+ +
+
+
+ +
+ +
+ +
+ + + + + +
+
a
Number in parentheses (no. 8 coal) refers to the GC peak number in Figure 3.
+, identified, including tentative identification.
Qp
b. Terpenoid Acids. Diterpenoid acids (biomarkers) isolated from acidic fractions of low-rank coals were analyzed as their methyl esters by GCMS. c. a - A l k a n e s and Aliphatic Acid M e t h y l Esters. These compounds were conveniently identified by the use of m/z 57 and 71 (for alkanes) and 74 (for esters) mass fragmentograms followed by full mass spectral analysis.
Results and Discussion In general, n-alkanes were minor components in the low-rank premium coals. In higher rank coals, there were very little or no alkanes. Analyses of hydrocarbon fractions of subbituminous and lignite coals indicated the predominance of odd-numbered n-alkanes (C16 to C3*,maximum at C2,). A slight odd-carbon preference was observed for Illinois No. 6 and Blind Canyon bituminous coals (ranging from C16 to C31). I t is interesting to note that while isoprenoid and other branched alkanes were very minor components in the fractions of subbituminous and lignite coals, pristane was the most abundant alkane for Illinois No. 6 and Blind Canyon bituminous coal samples. Fatty Acids. Acidic fractions (A-1 and A-2) of both subbituminous and lignite coals were shown to consist mainly of even-numbered long-chain fatty acids ranging from CP2to C3,, (maximum at C%). It was also found that even-numbered fatty acids in the acidic fraction of Illinois No. 6 and Blind Canyon bituminous coals were present in very small amounts. Little or no fatty acids were detected in higher rank coals. Baset et alez9analyzed extractable
/
II -Alkanes.
(29) Baset, Z. H.; Pancirov, R. J.; Ashe, T. R. Adu. Org. Geochem. Douglas, A. G.,Maxwell, J. R., Eds. Pergamon: New York, 1980; pp
610-630.
& I;I;'
A
I
I
I
15
20
25
30
35
40
45
Time(minutes)
Figure 2. GC/MS analysis of a hydrocarbon fraction obtained from the subbituminous coal (APCS no. 2). Structures of several compounds are shown as examples. For other identified compounds, see Table 111.
fatty acids and n-alkanes obtained from Wyodak coal (corresponding to APCS no. 2 subbituminous coal), and the results were very similar to these found in this study. Terpenoid Hydrocarbons. As shown in Table 11, terpenoid hydrocarbons were major components in hydrocarbon fractions of subbituminous, Blind Canyon bituminous, and lignite coals. Tricyclic diterpenoid hydrocarbons were found to be the most abundant biomarkers in subbituminous and lignite coals (Table 11; Figures 2 and 3). On the other hand, sesqui- and triterpenoid hydro-
Hayatsu et al.
460 Energy & Fuels, Vol. 4 , No. 5, 1990 m n
f I
300
'
"
'
'
I
'
600
'
/11 I f8*
'"I.,j
'"I J&
40
m/z
1
'
900
1200
Scan Figure 3. GC/MS analysis of a hydrocarbon fraction obtained from the lignite (APCSno. 8). For identification, see Table 111. Minor components are not numbered in this figure.
carbons were detected as significant components in Utah bituminous coal. These three terpenoid biomarker groups were very minor components in Illinois No. 6, LewistonStockton, and Pittsburgh coals and were not detected in Upper Freeport medium-volatile and Pochahontas lowvolatile bituminous coals. Sesquiterpenoids. It is most likely that sesquiterpenoids detected were derived mainly from the naturally occurring cadinene group by aromatization and partial saturation. We have identified calamenene, tetrahydrocadalene, and cadalene, which have the cadinane skeleton (e.g., peaks 2,3, and 4 in Figure 3) structure. Mass spectra of these three compounds are shown in Figure 4. We also detected a total of seven bicyclic alkene isomers, C15H26, in subbituminous, Blind Canyon bituminous, and lignite coals (e.g., in Figure 2, several peaks before tetrahydrocadalene appeared; in Figure 3, peak 1 and small peaks between peaks 1 and 3). The GC retention behavior and mass spectra indicated that they are bicyclic hydrocarbons (Clo)with one double bond and alkyl groups (five carbons). Several investigatorslOsBhave previously found the C15H2, molecules in low-rank coals and have identified them as bicyclic sesquiterpenoids; however, the structure assignments for each molecule were not made. We infer that three of the isomers detected have cadinane structure with one double bond from the interpretation of mass spoectra of cadinane' and a cadinane-type hydrocarbons with two double bonds.30 For example, the mass spectrum of one of the isomers shows m/z 163 (100),107 (631,206 M+ (471, 93 (35). The other four isomers have been tentatively assigned as bicyclic alkenes with five alkyl carbon atoms that have eudesmane- or drimenane-type s t r ~ c t u r e . ~ One - ~ l of four isomers indicates the m / z 191 (M - 15) is the base peak in the spectrum [ m / z191 (loo), 95 (56), 81 (42), 109 (40), 206 M+ (27)]. We have been seen a different type of spectrum for the other isomer: that is, m/z 123 is the most intense peak, but m / z 191 is a less intense peak [m/z 191 (32)]. Such a difference is probably due to configurational effects as shown and described by Richardson et a1.= and Alexander et al.31 Diterpenoids. Saturated and aromatized diterpenoid hydrocarbons identified are transformed products from naturally occurring abietane (V) and pimarane (IV)groups. Many of them have the abietane skeleton (see Figure 2). Indeed, we have also identified dehydroabietic acid as the methyl ester in acidic fractions (A-1 and A-2) of subbituminous and lignite coals. Dehydroabietic acid is a transformed product from abietic acid and is a precursor of (30) Albaiges, J.; Grimalt, J. 0.;Bayona, J. M.; Risebrouch, B.; de Lappe, B.; Walker, W. Org. Geochem. 1984,6, 237-248. (31) Alexander, R.; Kagi, R.; Noble, R. J . Chem. SOC,Chem. Commun. 1983, 226-228.
40
80
10
100
110
140
180
180
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140
180
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.
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Figure 4. Mass spectra of (top) cadalene, (middle)tetrahydrocadalene, and (bottom) calamenene identified in hydrocarbon fractions of lower rank APCS. dehydroabietin and retene. Relatively large amounts of pimarane were tentatively identified in the three coals (Table IV and Figure 3, peak 7). The mass spectrum was nearly identical with that of the published oneBb[m/z 247 (loo), 163 (97), 95 (96), 123 (95), 191 (75), 276 M+ (56), 261 (35)]. We have also tentatively identified an isomer of pimarane between peaks 7 and 8 (very small peak, not numbered in Figure 3). The spectrum gave values and relative intensities of m / z 123 (loo), 95 (95), 163 (85), 247 (771, 191 (60), 276 (48), 261 (30). It is known that a member of pimarane group, pimaradiene, rearranges to abietadiene from which are derived abietic acid and its congeners. Diterpenoid hydrocarbons were major components in the hydrocarbon fractions of subbituminous and lignite but were minor for Illinois No. 6 and Blind Canyon bituminous coals. In the other coals, the presence of these hydrocarbons was negligible. Triterpenoids. Aromatized triterpenoids were identified in appreciable amounts in the three coals (subbituminous, Blind Canyon bituminous, lignite). Among them, Blind Canyon bituminous coal contains more of this group than the other coals, They are tetracyclic terpenoids (X), 8,14-secoterpenoids (XI, XII), and pentacyclic (XIII-XVI) terpenoids with a five- or six-membered E ring which substituted with methyl, ethyl, or geminal methyl groups. At least eight monoaromatictriterpenoids were detected in the hydrocarbon fraction of lignite coal (Figure 3, peaks 24-31). Three of them are D-ring aromatic compounds with a five-membered E ring (XIIa,b),which were believed to be derived from hopane or lupane groups. A possible transformation pathway of these compounds has been propased in which the aromatization starts with ring D and continues through ring A.2sd The other five compounds are A-ring monoaromatic compounds with six-membered E ring (0-amyrin and a-amyrin types). However, we are
Terpenoid Biomarkers in Argonne Premium Coal Samples run
Energy & Fuels, Vol. 4, No. 5, 1990 461
Table V. Thermal Catalytic Hydrogen-Transfer Reaction' reactant hvdroeen donorb extractable maior Droducts (% vield)' 4,4'-dihydroxybiphenyl none 4-hydroxybiphenyl (28), phenol (16) A 4,4'-dihydroxybiphenyl biphenyl (36), 4-hydroxybiphenyl (12) 4-cyclohexylphenol (7) biphenyl (31), 4-hydroxybiphenyl (13) B 4,4'-dihydroxybiphenyl 4-cyclohexylphenol (7), phenol (7) A biphenyl (27), 4-hydroxybiphenyl (17) 4,4'-dimethoxybiphenyl methylbiphenyl (lo), 4-hydroxymethylbiphenyl (5) B po1y(4-methoxy-d3-styrene)' (Me)z-3-CD3-benzene(18) (Me)l-2-CD3-styrenedimer (29) softwood lignin none f softwood lignin A f C softwood lignin f
insoluble residued
'Reaction conditions 150 OC for 1 month in the presence of K-10 montmorillonite. bAfter the reaction, hydrogen donor A produced naphthalenes, partially aromatized triterpenoids, aromatic 8,14-~ecotriterpenoids,and picenes as major transformed products; B produced tetrahydroretene, retene, and phenanthrenes; C produced a complicated mixture which was derived from terpenoids used. A, A2-allobetulene; B, dehydroabietic acid; C, a mixture of biomarkers isolated from no. 8 coal (see Table 111). Number in parentheses represents yield determined by GC/MS. Calculation was made from starting reactant. Only major GC peaks were determined, because there are many other peaks that are due to transformed products from hydrogen donor($ dInsoluble residue obtained from the reactions of biphenyls or styrenes are polymerized material; the residue from lignin represents the yields of transformed lignins. eThis polymer was prepared from methylation of poly(4-hydroxystyrene) with dimethyl-d6 sulfate. 'Degradation products from lignin, in general, are highly volatile, small molecules such as COz, H20, and C1-3 or C, alkanes, alcohols, and carbonyl compounds. GC shows that major solvent extractable compounds are transformed products from terpenoids (runs 7 and 8).
not excluding the possibility that some of the A-ring monoaromatic compounds have hopane type skeletal structures. Compounds CBH42 (XIVa) show the most intense peak at m / z 145 in the mass spectra. On the other hand, unsaturated analogue compounds CzaHlo (XIVb) and CnHB (XIVc) show two intense peaks at m/z 145 and 158 in the spectra. These A-ring monoaromatic triterpenoids have been previously identified in extracts of brown coalsg and have recently had their chemical structures confirmed by syntheses.32 Other triterpenoid hydrocarbon groups (octahydrochrysenes, aromatic 8,14-secotriterpenoids di-, tri- and tetraaromatic triterpenoids) have been found in the premium coals (see Table IV); however, these hydrocarbons were very minor components in the Illinois No. 6, Lewiston-Stockton, and Pittsburgh coals. Thermal Catalytic Hydrogen-TransferReaction. In our previous thermal catalytic reactions (absence of hydrogen donors) of lignin models indicated that ether linkages in lignin structures (benzyl aryl type ethers; 0-0-4, a-0-4, and 7-0-4 linkages) were labile and readily cleaved with accompanying intra- or intermolecular rearrangements. Demethylation from methoxy groups also occurred. In the present work as shown in Table V, it is found that elimination of phenolic oxygen readily occurs in the presence of a hydrogen donor such as terpenoid biomarkers, which have been found in low-rank coals. In general, to remove each phenolic OH group, two atoms of hydrogen were required. One atom of hydrogen replaces the OH group on aromatic nucleus with the other hydrogen atom forming water with the OH group. For example, a dihydroxybenzene undergoes catalytic hydrogen transfer with a hydroaromatic compound such as tetralin, acting as a hydrogen donor, in the presence of a catalyst. During the reaction tetralin is aromatized and two phenolic OH groups of benzene are removed if hydrogen derived from tetralin was efficiently used. However, since transformation (aromatization) of terpenoid biomarkers does not proceed via the same pathway, their hydrogen-transfer reactions are not as simple as the example described above. Pentacyclic triterpenoid group (32) Wolff, G. A,; Trendel, J. M.; Albrecht, P. Tetrahedron 1989,45, 6721-6728. (33) Winans, R. E.; Hayatsu, R.; Squires, T. G.; Carrado, K. A.; Botto, R. E. Prepr. Pap-Am. Chem. SOC.,Diu.Fuel Chem. 1990,35(2),423-429. (34) Carrado, K. A.; Hayatsu, R.; Botto, R. E.; Winans, R. E. Clays Clay Miner. 1990, 38,250-256.
(e.g., A2-allobetulene, run 2 in Table V) is known to undergo at least three different pathways during successive aromati~ation.~*6J~J~J5 In run 8, a mixture of terpenoid biomarkers isolated from no. 8 lignite was used as a hydrogen donor for alteration of lignin phenolic structures. The GC/MS shows that the mixture contains at least 30 sesqui-, di-, and triterpenoids (Table IV). Aromatizations of these terpenoids are expected to undergo highly diverse pathways with accompanying dealkylation, isomerization, rearrangement, etc. Indeed, our previous study showed that catalytic transformation of pure A2-allobetuleneyielded more than 70 aromatic and hydroaromatic hydrocarbon^.^ Therefore, it is not possible to consider how much hydrogen could be eliminated from terpenoid biomarkers and how much of the eliminated hydrogen could be used for alteration of phenolic structures. In run 2 or 3 (Table V), it is shown that elimination of phenolic OH groups of 4,4'-dihydroxybiphenyl is promoted in the presence of a hydrogen donor. On the other hand, run 1 (absence of a hydrogen donor) shows that polymerization and/or condensation reactions of 4,4'-dihydroxybiphenyl were more favorable than elimination of phenolic OH. Indeed, the yield of insoluble residue (polymeric material of phenol) from run 1is 2.5-3 times higher than those of runs 2 and 3. In the case of methoxy substituents (runs 4 and 5), four atoms of hydrogen were required: for cleavage of ether linkages at initial stages and then elimination of phenolic OH formed with the cleavage. Also, demethoxylation might have occurred with elimination of methanol. The reaction of poly(4-methoxy-d3-styrene) (run 5) yielded methylated and d3-methylated benzenes and styrene dimers as major products. This indicated that the reaction proceeds by demethylation/demethoxylation and cracking of polystyrene carbon chains. Finally, both alkylation and elimination of oxygen functional groups occurred. In run 8, lignin (1 g) and a mixture of terpenoid biomarkers (C in Table V, 0.46 g) was heated in the presence of clay catalyst. Insoluble residue (transformed lignin, 0.59 g) and organic solvent extractable material (0.32 g) were obtained. The GC/MS indicates that the solvent-soluble fraction consists mainly of various transformed terpenoids such as naphthalenes, phenanthrenes, chrysenes, picenes, and hydroaromatic hydrocarbons. Some of the phenolic compounds, which were released from the degradation of
462 Energy & Fuels, Vol. 4,No. 5, 1990
sample ligninC product from run 6 product from run 8 product from run 7
Hayatsu 'et al.
Table VI. Summary of the Silver Oxide Oxidation Products elemental relative abundance,b % composn per yield," 3,4-(OH),-BZ4-OH-BzOH-Bz100 carbons wt% COOHd COOH (COOH)2-se B z - ( C O O H ) , ~ ~ ClOoH108033 61.7 64.8 13.3 8.4 2.d C100H95030 54.5 31.8 16.2 27.7 10.3 ClOoHBsO25 48.3 7.3 19.8 28.8 28.6 C100H87026 g
others 11.5 14.0 15.5
Solvent-extractable free acids; calculated from starting sample. All oxidation products were methylated with diazomethane for GCMS analysis. Relative abundances were calculated from GC data. Bz-COOH, benzenecarboxylic acid; others, compounds other than phenolic and benzenecarboxylic acids, including unidentified compounds. The data, including oxidation, were obtained from ref 22. Including, 3,4-dihydroxy-1,5-benzenecarboxylicacids. e Including methyl and dimethyl derivatives. IGenerally, lignin does not contain benzene rings. It is considered that some aromatic structures, which produce benzenecarboxylic acids by oxidation, are formed during isolation of lignin from wood. NO oxidation is made.
lignin, were seen in the chromatogram. To understand the alteration of lignin phenolic structures, the insoluble residue was characterized by using two-step depolymerization of alkaline hydrolysis followed by silver oxide oxidation. To compare the oxidation products from run 8, lignin and transformed lignin (run 6, absence of terpenoid biomarkers) were also hydrolyzed and oxidized. The oxidation products are summarized in Table VI. The major oxidation product from lignin is 3-methoxy-4-hydroxybenzoic acid. This result is in good agreement with the softwood lignin modeP5 and other oxidation studies.36 On the other hand, the GC/MS analysis of the oxidation products from run 8 indicated that the concentration of 3-methoxy-4-hydroxybenzoic acid is much lower than that of the same acid which is lignin's major product. The major products are monohydroxybenzenepolycarboxylic acids and benzenecarboxylic acids. These acids are very minor products in the oxidation of lignin. Results of the oxidation (run 6) also showed that some phenolic OH groups are reduced when lignin was heated in the presence of K-10clay catalysts but in the absence of hydrogen donors. This had been previously found by NMR16g37and o ~ i d a t i o n ~studies ~ p ~ ~ of * ~synthetic ~ coals prepared from lignin. Presumably hydroaromatic structures, which may be acting as hydrogen donors, are formed in transformed lignin during the reaction. However, as shown in Table VI, the concentration of total phenolic acids from run 6 is higher than that of total phenolic acids from run 8. Furthermore, the oxidation of run 8 produced benzenecarboxylic acids in much higher yields than those in the oxidation of run 6. These results suggest that elimination of phenolic OH groups in lignin could significantlybe promoted by thermal catalytic transfer reactions in the presence of hydrogen donors such as terpenoid biomarkers. It is found that clay catalysts such as K-10montmorillonite clay have an important role in the transformation of phenolic material. If catalyst(s) is(are) not present, the transformation reaction does not proceed. Some polymerization only occurs. The products obtained from lignin reactions have been studied in detail by spectrometric and chemical degradation methods, and their results will be reported elsewhere. Role of Terpenoid Biomarkers during Coalification. In 1978 we proposed3a hypothetical reaction pathway for the transformation of diterpenoid to phenanthrene, the relative abundance of which has been shown to increase with increasing rank from lignite to anthracite. It is be(35) Sakakibara, A. Wood Sci. Technol. 1980. 14, 89-100. (36) Morohoshi, N.; Glasser, W. G. Wood Sci. Technol. 1979, 13, 165-178. (37) Hayatsu, R.; McBeth, R. L.; Scott, R. G.; Botto, R. E.; Winans, R. E. Org Geochem. 1984, 6,463-471.
lieved that a variety of polynuclear aromatic hydrocarbons (PAH) found in coals and other geological material were derived at least partially from the transformation of terpenoids and other natural products during the maturation.2*4v6J2'5Indeed, the present study showed that terpenoid biomarkers are major components in the hydrocarbon fractions of lignite, subbituminous, and Blind Canyon bituminous coals. On the other hand, hydrocarbon fractions in higher rank coals (e.g., Illinois No. 6, Lewiston-Stockton, and Pittsburgh) consist mainly of PAHs. For example, at least 22 naphthalenes and 14 phenanthrenes were identified in relatively large amounts in the hydrocarbon fraction of Illinois No. 6 coal. In addition, other polynuclear aromatic hydrocarbons such as chrysenes and picenes were also found in lesser amounts. Thermal catalytic reaction of terpenoid biomarkers isolated from low-rank coals (e.g., run 8 in Table V) yielded transformed terpenoids that are qualitatively similar to those found in Illinois No. 6 coal. Puttmann and co-workers have p r o p o ~ e d ' ~that ?~~ 1,2,5-trimethylnaphthalene, 1,2,7-trimethylnaphthalene, and 1,2,5,6-tetramethylnaphthalene found in coals are derived from pentacyclic triterpenoids via aromatic 8,14secotriterpenoids (e.g., structures XI and XI1 in Chart I). Bicyclic sesquiterpenoids are also known to transform into methylated naphthalenes. Our oxidative21!nand pyrolytic1.3 studies of the premium coals show that the low-rank coals, which contain terpenoid biomarkers in solvent extracts, produce large amounts of phenolic compounds and benzenes. Since benzene rings are not present in the structure of lignin, it is clear that phenolic oxygen is removed during coalification. With increasing rank, the biomarkers decrease significantlywhile aromatic hydrocarbons become the most abundant extractable compounds. Macromolecular materials of the higher rank coal yield only minor amounts of phenolic compounds in the oxidative and pyrolytic experiments. The present study suggests one possible mechanism and process for the alteration of phenolic structures at the early stages of coalification. The alteration is probably promoted by thermal catalytic hydrogen-transfer reactions in the presence of clay and hydrogen donors such as terpenoid biomarkers. Some low-rank coals contain relatively large amounts of terpenoid biomarkers. We have previously isolated pentacyclic triterpenoid biomarkers from a Victorian brown coal (pale lithotype); the yield was 1.26 g from 30 g of the dried coal.4 However, terpenoid biomarkers are generally minor components in coals; therefore, we may also have to consider other possible hydrogen donors (e.g, hydroaromatic compounds) for the alteration of phenolic structures. Resinite macerals are polymers of terpenoids that undergo successive aromatization during coalification. For
Energy & Fuels 1990,4,463-466 example, APCS no. 6 coal used in this study is known to be rich in r e ~ i n i t e . Perhaps ~~ such resinite is acting as a hydrogen donor. Botto16 has suggested formation of hydroaromatic structures such as dihydrofurans during coalification of lignin. Indeed, NMR and oxidation studiesa of synthetic coals (prepared from lignin and activated clay a t 150 OC for 2 and 4 months) suggest that phenolic oxygen groups are partially removed. Presumably, hydroaromatic structures are formed in transformed lignin molecules. Recently, Dong and OuchiqOdemonstrated that long alkyl chain aromatic structures in coal macromolecules are formed from lignin and lipids by thermal catalytic reactions in the presence of clay. Hydroaromatic structures are also shown to be formed from the long-chain alkylaromatic groups by cyclization. (38)Puttmann, W.; Villar, H. Geochim Cosmochim. Acta 1987,51, 3023-3029. (39)Pierce, B.C.; Stanton, R. W.; Cecil, C. B. Open-File Report 89634;Department of the Interior, US.Geological Survey, 1989. (40)Dong, J.-Z.; Ouchi, K. Fuel 1989,68,1354-1357.
463
There may also be reaction mechanisms and processes for elucidation of the alteration of phenolic structures other than hydrogen-transfer reactions proposed by us. It is apparent that more study is needed to reveal how benzene rings (major aromatic units in low-rank are formed at the expense of lignin-derived phenols during coalification. Acknowledgment. We are grateful to Robert G. Scott and Paul Melnicoff, for the GC/MS analyses. The elemental analysis was provided by Steven Newman of the Argonne Analytical Chemistry Laboratory. This work was performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, US.Department of Energy, under Contract No. W-31-109-ENG-38. Registry No. 4,4'-Dihydroxybiphenyl,92-88-6;4,4'-dimethoxybiphenyl, 2132-80-1; poly(4-methoxystyrene),24936-44-5; dehydroabietic acid, 1740-19-8;A2-allobetulene,2652-05-3;lignin, 9005-53-2. (41)Winans, R. E.;Hayatsu, R.; McBeth, R. L.; Scott, R. G.; Botto, R. E. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1988, 33(1), 407-414.
Pretreatments of Solid Coals for Their Beneficiation and Structural Analyses Kinya Sakanishi, Akihisa Takayama, Tomoko Hieida, and Isao Mochida* Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816, Japan Received April 5, 1990. Revised Manuscript Received July 10, 1990 Three (Pittsburgh, Wyodak, and Beulah-Zap) of the eight Argonne Premium Coals were pretreated and analyzed by solid-state CP/MAS 13CNMR and IR spectroscopies, to elucidate the influence of coal rank and the effects of pretreatments such as deashing, solvent extraction, and heat treatment in the presence of a hydrogen donor. The line width of solid-state NMR was improved by the deashing pretreatment with 1 N HCl/methanol, especially in the aromatic and oxygenated carbon regions regardless of the coals. IR absorption of carboxyl groups (ca. 1700 cm-') appeared for Wyodak and 'Beulah-Zap coals after the deashing pretreatment. The line width of solid-state NMR was much better for the extracts than that of the corresponding residue when the coals were extracted with the mixed solvent of CS2/N-methylpyrrolidinone (50/50 vol %). The heat treatment at 450 "C for 10 min using octahydroanthracene (8HAn) increased aromatic carbons with decreasing aliphatic carbons, and the resolution of solid-state NMR for the HI-THFS (hexane insoluble-THF soluble) fraction was much improved by removing the THF-insoluble fraction in which inorganic and unreacted organic materials were concentrated. These results suggest the usefulness of pretreatments such as deashing, solvent extraction, and heat treatment for the characterization and beneficiation of coals.
Introduction CP-MAS/ 13CNMR spectroscopy with high-power proton decoupling has been applied for analyzing the carbon functional group distributions in solid carbonaceous materials such as coals, petroleum residues, and coal tar pitches, increasing its importance in the characterization techniques for the structural understandings of solid fuels during the past decade.'-1° However, the quantitative (1)Zilm, K. W.; Pugmire, R. J.; Larter, S. R.; Allan, J.; Grant, D. M. Fuel 1981,60,717-722. (2)Maciel, G.E.; Sullivan, M. J.: Petrakis, L.; Grandv, D. W. Fuel 1982,61,411-414. (3)Russel. N. J.: Wilson. M. A.: Puemire. R. J.: Grant. D. M. Fuel 1983,62,601-605. (4)Furimsky, E.;Ripmeester, J. Fuel Process. Technol. 1983, 7, 191-202. (5)VanderHart, D.L.;Retcofsky, H. L. Fuel 1976,55,202-207.
reliability still places in question the general utility of the CP-MAS measurements, because a significant fraction of the carbon atoms are invisible to solid-state 13C NMR analysis regardless of the pulse excitation sequence (6)Sullivan, M. J.; Maciel, G. E. Anal. Chem. 1982,54, 1615-1620. (7)Vassallo, A. M.; Wilson, M. A.; Collin, P.; Oades, J. M.; Waters, A. G.;Malcolm, R. L. Anal. Chem. 1987,59,558-564. (8)Hagaman, E. W.; Chambers, R. R.; Woody, M. C. Anal. Chem. 1986,58,387-395. (9)Vassallo, A. M.: Wilson, M. A.; Edwards, J. H. Fuel 1987,66, 622-629. (10)Wilson, M. A.; Pugmire, R. J.; Karas, J.; Alemany, L. B.; Woolfenden, W. R.; Grant, D. M.; Given, P. Anal. Chem. 1984,56,933-943. (11)Solum, M. S.;Pugmire, R. J.; Grant, D. M. Energy Fuels 1989, 3,187-193. (12)Opella, S.J.;Frey, M. H. J. Am. Chem. SOC. 1979,101,5854-5860. (13)Murphy, P. D.; Cassady, T. J.; Gerstein, B. C. Fuel 1982,61, 1233-1238.
0887-0624190/25O4-0463$02.50/0 0 1990 American Chemical Society
