Chemical composition and origin of fossil resins from Utah Wasatch Plateau coal

Fuel Processing Technology, 28 {1991 ) 119-134 119 Elsevier Science Publishers B.V., Amsterdam

Chemical composition and origin of fossil resins from Utah Wasatch Plateau coal

Henk L.C. Meuzelaar, Huaying Huai, Robert Lo and Jacek P. Dworzanski

Center/or Micro Analysis and Reaction Chemistry, University of Utah, 214 EMRL, Salt Lake City, UT 84112 (USA)

(Received April 4th, 1990; accepted in revised form March 12th, 1991 )

A b s t r a c t

In order to arrive at a more detailed chemical description of fossil coal associated resins we need to distinguish between micropetrographic, organic geochemical and process technological definitions, each of which may encompass varying quantities of constituents unrelated to fossil tree resins. New information on composition and origin of Utah Wasatch Plateau coal resins obtained by Curie-point pyrolysis/evaporation in combination with iso-butane chemical ionization mass spectrometry, as presented in this paper, points to the presence of four more or less distinct resin components: ( 1 ) a sesquiterpenoid polymer; (2) sesqui- and triterpenoid monomers and dimers; (3) a suite of triterpenoid alcohols, ketones and acids; and (4) a series of increasingly aromatized hydrocarbons with naphthalene and picene type skeletons. Moreover, a strong similarity is found between the composition of recent dammar resin and fossil Wasatch Plateau coal resins indicating a possible Angiosperm (fam. Dipterocarpaceae) origin of these Upper Cretaceous coal resins. Some of the technological implications of these findings and the consequent need for a more precise chemical definition and nomenclature are discussed.

I N T R O D U C T I O N

Utah Wasatch Plateau field coals from the Upper Cretaceous Blackhawk formation are widely known for their unusually high resin content (typically 5-15 wt.% d.a.f, depending on the definition and analytical methodology used) [1-5]. In fact, resin concentrates prepared from these coals have been commercially available for the past 50 years [ 1 ], in spite of highly fluctuating sup- ply and demand patterns. Unfortunately, confusion remains about the exact chemical composition and structure of commercial coal resin preparations as well as their observed heterogeneity.

Fossil resins derived from tree sap are known to occur in a wide variety of different forms, some of which intimately associated with coal ("resinite") or with fossil wood (e.g., "bombicite"), whereas others occur in more or less dis- crete or even isolated forms, such as ambers (e.g., succinite, allingite, retinel- lite, walchowite, schraufite, burni te) or the relatively young copalites ("hard

0378-3820/91/$03.50 © 1991 Elsevier Science Publishers B.V.

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copa ls" ) m o s t of which a p p e a r to have been bur i ed dur ing the Ho locene period. Al though some p r e c u r s o r t rees are t h o u g h t to have b e c o m e ex t inc t (e.g., the hypo the t i ca l source t ree for Bal t ic a m b e r ( succ in i te ) Pinus succiniferus [6] ), r ecen t t ree res ins are still be ing h a r v e s t e d in severa l d i f fe ren t forms, e.g., as soft copals , kaur i gum, d a m m a r , incense or va r ious ba l sams . Never the less , the i n t e rna t i ona l m a r k e t for these res ins has s h r u n k cons ide rab ly due to inc reased c o m p e t i t i o n f rom the i r syn the t i c c o u n t e r p a r t s [7].

Bes ides the of ten confus ing n o m e n c l a t u r e - - b y the t u rn of the cen tu ry more t h a n 100 d i f fe ren t fossil res ins had been descr ibed [6] - - p r o g r e s s in the field is fu r the r compl i ca t ed by d i f fe rences in def ini t ion, pa r t i cu l a r ly be tween geochemis t s , coal pe t ro logis t s and process engineers , as i l lus t ra ted in Tab le 1. I t is in t e res t ing to no te t h a t the m i c r o p e t r o g r a p h i c def ini te of " r e s in i t e " leaves amp le room for the inclus ion of nea r ly every poss ib le class of chemica l compounds r ang ing f rom s t r a igh t cha in fa ts a n d waxes to highly a r o m a t i z e d a n d / or func t iona l ized coal c o m p o n e n t s .

Organic geochemis ts , on the o the r hand , t e n d to use a r a t he r more l imi ted def in i t ion which e m p h a s i z e s the p re sence of cyclic t e rpeno ids as well as of t e rpeno id alcohols, ke tones , or acids [8]. A careful scan of the organic geo- c h e m i s t r y l i t e ra tu re on coa l -as soc ia ted res ins a n d a m b e r s ind ica tes a p r e d o m - inan t ly (poly) d i t e rpeno id compos i t i on of fossil res ins bel ieved to be der ived

Table 1 Approximate relationship between resin (ite) definitions and the probable presence a of specific compound classes

Compound class Coal resin (ite) definition Synthetic resins

Geochemical Petrographic Technical

Terpenoids Acyclic HCs - 0 0 - Cyclic HCs + + + + Alcohols, ketones and

acids + 0 - - Nonterpenoids Straight chain HCs - 0 0 - Branched aliphatic

HCs - 0 + - Alicyclic HCs - - + + Alcohols and fatty acids - 0 - - Terpenoid + nonterpenoid Aromatic HCs 0 + b _ + Hydroaromatic HCs 0 0 + - Hydroxyaromatics - 0 - +

a_ = low probability, + = high probability, 0 = intermediate probability. b Secondary resinite (exsudatinite).

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from Gymnosperms ("softwoods") as well as from several Angiosperm ("hardwood") families [9]. However, a few fossil resins thought to be derived from the Angiosperm family Dipterocarpaceae, were found to consist primarily of (poly) sesquiterpenoids and triterpenoids. Examples of such resins have been reported to occur in association Southeast Asia Indonesian (e.g. Sumatra [ 10-13 ] ) as well as US Gulf Province [ 14 ] coals. The family Dipterocarpaceae includes many resin producing tree species, e.g., Shorea Hopea and Diptero- carpus. The modern resin product of these trees is well known as dammar (damar) resin, oil or gum and has found widespread application as a low acidity varnish [ 15 ] for fine furniture and art objects.

Process engineers generally favor definitions based on processing characteristics (viz. flotability and hexane solubility) which effectively eliminate most of the terpenoid alcohols, ketones and acids as well as some of the more highly aromatized terpenes but may include many straight chain as well as branched aliphatic hydrocarbon compounds. For comparative purposes, Table 1 also lists various chemical components regularly encountered in synthetic resins. Cer- tainly, one is not likely to see significant straight chain and branched hydrocarbons here. On the other hand, there appears to be an emphasis on aromatic hydrocarbons, or even phenols, which puts many synthetic resins in a rather different chemical class than their fossil counterparts (see Table 1 ).

Summarizing, we conclude that the process engineering definition of fossil coal resins based on flotability and solubility tends to be rather different from both the petrographic and the geochemical definitions. Secondly, the process engineering as well as the petrographic definitions leave room for the inclusion of a broad range of components not necessarily representing fossil tree resins while potentially excluding some important, functionalized resin components.

Aside from the confusion caused by the lack of consensus between the various definitions, any study aimed at elucidating the structure and origin of recent and/or fossil plant resins will have to contend with the notoriously het- erogeneic composition and structure of these materials. As noted by Benemelis [ 1 ] in his discussion of Utah Wasatch Plateau coal resin: "...fossil resin is not a pure compound. It is believed to contain high melting point resin 50%, water 0.5%, low melting point resin 10%, asphalt 35%." In order to investigate the chemical basis for the observed heterogeneity in composition we collected several fossil as well as recent tree resins and applied a range of different chemical characterization methods. These include thermogravimetry (TG/DTG) as well as Curie-point pyrolysis/evaporation in direct combination with gas chromatography and mass spectrometry (Py-GC/MS) . As discussed under Experi- mental, the latter technique employed iso-butane chemical ionization in order to avoid excessive fragmentat ion of labile compounds and very short capillary GC columns in order to facilitate observation of large, relatively nonvolatile molecules. At the same time, this approach enabled us to shed new light on the possible origin of Utah Wasatch Plateau resins, such as found in the Hiawatha

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and Blind Canyon seams of the Upper Cretaceous Blackhawk Formation. A separate paper presenting 13C NMR, micropetrography and Py-GC/MS analysis data on Utah coal resins is being published elsewhere [16].

EXPERIMENTAL

Sample collection

Samples of a sink/float resin and of a hand-picked, dark brown subfraction were prepared by J.D. Miller et al. using methods described elsewhere [2 ]. A sample of bombicite, a white resin obtained from a fossil Gymnosperm log in the open pit Yallourn mine (Victoria, Australia), was provided by K. Anderson and has been characterized by him in a previous publication [17]. Pontianak copal and Indonesian dammar samples were provided by J.C. Crelling. Finally, a virgin Wasatch Plateau (Blind Canyon seam) coal sample ( - 1 0 0 mesh) known to contain 11% resinite, was obtained from the Argonne National Lab- oratory Premium Coal Sample Program [3].

Thermogravimetric analyses

Thermogravimetric (TG/DTG) experiments were performed using a Per- kin Elmer Model 7 system with Model 7700 data system. A 4-6 mg ( - 100 mesh) sample was purged under a 60 ml /min N2 flow for 5 minutes at ambient temperature followed by heating up to 700 °C at 25 ° C/min under the same N2 flOW.

Curie-point evaporation/pyrolysis

A 5-10 mg sample was carefully ground into a fine powder and suspended/ dissolved in 1-2 ml of Spectrograde methanol under mild sonication. Subse- quently, 2 #l aliquots of this solution were coated on ferromagnetic wires (Curie- point temp. 610 ° C ) used in Curie-point pyrolysis experiments and withdrawn into borosilicate glass reaction tubes after air drying. Details of the sample preparation techniques [ 18 ] and of the pyrolysis reactor used [ 19 ] have been described elsewhere. In several experiments (as noted in the text and in the figures) the sample was inserted into the pyrolysis reactor (maintained at 290 °C) and volatile sample components were allowed to evaporate without activating the pyrolysis coil. After the GC/MS signals of the evaporate had been recorded, the residue on the wire was submitted to regular pyrolysis. Pyrolysis conditions: total heating time 4 s; estimated heating rate approx. 1000 ° C/s; Curie-point temp. 610 ° C.

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Gas chromatography~mass spectrometry

A 4 m long, 0.22 mm i.d. fused silica capillary column coated with 0.1/~m of BP-1 (SGE, Austin, TX, USA) was used at a He flow of 4 ml/min (10 psi inlet pressure) and a temperature programming rate of 30 K/min from 40-320 ° C. Total analysis time was 700 s. An HP 5890 gas chromatograph coupled to a Finnigan MAT model 700 Ion Trap Detector, was used in chemical ionization (CI) mode with isobutane reaction gas at a reaction time of 30 ms and an ionization time of 100/~s. The mass range scanned was 100- 650 amu (scanning rate 1 spectrum/s). Transfer line and ion trap manifold were kept at 290°C and 230 ° C, respectively.

RESULTS AND DISCUSSION

Thermogravimetric and gas chromatographic/chemical ionization mass spectrometric analysis data

Two Hiawatha seam resin samples prepared by sink/float preparation followed by handpicking of different color types, as described Yu et al. [2], were analyzed by TG/DTG, as shown in Fig. 1. The two samples correspond to the whole sink/float fraction and to a dark brown, handpicked subfraction, respectively. Microscopically the sink/float sample was found to contain 96% of a green fluorescing resinite type in addition to approx. 4% of a mixture of brown and green/yellow resin varieties, whereas the dark-brown resinite subfraction consisted primarily of yellow fluorescing particles (96%) and only 4% of the green fluorescing resinite. These different fluorescent color types of Wasatch Plateau coal resinite have been described in some detail by Crelling et al. [4]. Furthermore, the dark-brown sample showed small but significant differences in NMR and FTIR spectral patterns as well as a slightly higher density [2]. TG/DTG analyses of both resin samples (Fig. 1 ) produced nearly identical curves with less than 10-15% weight loss below 350°C, Tmax values (temperature of maximum rate of weight loss) in the 450-470°C range and char residues constituting less than 3% at 700 ° C. The Tmax values are almost as high as that of the parent coal (also shown in Fig. 1) thereby confirming the well known high thermal stability of Utah coal resins. Nevertheless, it is noteworthy that the dark-brown resin sample started to decompose thermally at temperatures 10-15 °C below those necessary to decompose the total sink/ float sample.

The Curie-point pyrolysis/evaporation GC/CIMS spectra of both resin samples in Fig. 2 (obtained by summing all spectra, with the exception of the first and last 100 scans, which contained mostly background signals), reveal surprisingly regular, as well as similar, patterns. From our analysis of the data as well as from comparisons with earlier pyrolysis field ionization MS data on

124

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whole coals [20] and on a Utah coal resin concentrate [17], we interpret the three main peak groups in Fig. 2 as representing sesquiterpenoid monomers, dimers, and trimers, respectively, probably in combination with triterpenoid contributions. The short GC column, operating at high linear He flow veloci- ties enables elution detection of the trimer compounds at m/z 613. The avail- ability of low resolution GC profiles (see Fig. 3) facilitates further identifica- tion of ion type.

Comparing the spectrum of the sink/float resin (Fig. 2a) with that of the dark-brown subfraction (Fig. 2b) the latter shows a more intense peak group around m/z 325. From pyrolysis field ionization MS data on a resin-rich Was- atch Plateau coal [20] it is known that prominent "biomarker" signals (i.e., signals representing characteristic biochemical fossils) occur at m/z 324 and m/z 342. The same signals were observed by Lee et al. [21 ] by means of GC/ MS analysis of Blind Canyon coal extracts and identified as partially aromatized triterpenoids with picene type skeletons. Since these biomarkers gener-

125

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ally occur as part of the "thermally extractable bi tumen" [22] fraction, we decided to obtain a "flash evaporation" spectrum at 290°C (the temperature of the pyrolysis chamber), followed by a true pyrolysis spectrum produced by rapidly heating the Curie-point wire to 610 ° C. The results, shown in Figs. 4 (a) and (b), demonstrate that nearly half of the total signal, including the biomarker peak at m/z 325, indeed evolves during the flash evaporation step at 290 o C. Obviously, however, the remainder of the mass spectral pattern of the distillable components is markedly different from that of the pyrolyzate. Whereas the latter shows a remarkably clean oligomer pattern, apparently derived from a relatively pure sesquiterpenoid polymer, the distillate spectrum is dominated by signals in the C2s-C32 and C13--C17 regions, apparently representing low molecular weight (MW) triterpenoids and sesquiterpenoids, respectively. Moreover, use of pyrolytic methylation techniques (not shown here) has established that the peak signals around m/z 425 and 441 consist mainly of oxygen-substituted triterpernoids, e.g., in the form of hydroxylic, carbonylic and/or carboxylic functional groups.

Comparing our data on Utah Wasatch Plateau coal resin with those on fossil (Miocene) Lumapas (Bumen) resin reported by van Aarssen et al. [ 13 ], both

126

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Fig. 3. Low resolution GC/CIMS profiles of (a) sink/float resin and (b) dark-brown subfraction, obtained with a 4-m capillary column. Note rapid evolution of oligomers, including [Cz~H24] + at m/z 613. Selected ion chromatograms are included to highlight sesquiterpenoid oligomer frag- ments (m/z 205 ), aromatized triterpenoid (m/z 325 ) and possible triterpenoic acid (m/z 441. ).

the low molecular weight and the polymeric components appear to have highly similar molecular structures and the nondistillable portions of both resins clearly possess a polymeric structure consisting of sesquiterpenoid subunits. Assuming that the Utah Wasatch Plateau coal resin is chemically closely related to the fossil (Miocene) Bukit Asam (Sumatra) Indonesian coal resin described by Brackman et al. [ 12 ], our finding of a flash distillate subfraction containing all or most of the triterpenoid moieties, appears to conflict with their interpretation of the polymeric component as containing sesquiterpenoid as well as triterpenoid building blocks.

Clearly, our simple two-step heating test reveals a great deal of heterogeneity within a given resin sample as well as between samples. This would appear to support the previously quoted statements concerning the presence of significant quantities of low melting point (low MW!) resin components (viz. the signals in the C 1 3 - - C 1 7 and C2s-C32 regions in Fig. 4a) as well as of "asphalt" (viz. the asphaltenic polynuclear aromatic compounds at m/z 325 and m/z 343 in Fig. 4a) in addition to a high melting point bulk resin component (as indi- cated by the oligomer series in Fig. 4b ). Nevertheless, the amount of asphalt- (or rather asphaltene- ) like materials observed in Fig. 4b appears to represent, at most, a few percent of the total signal in Fig. 4. This is in seemingly poor agreement with the previously quoted [1] ca. 50% of "asphalt" components. First of all, however, some or all of the oxygen-substituted C31-C32 terpenoids should probably be counted among the asphalt-like materials from a process

127

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chemical point of view. Secondly, the biomarkers at m/z 325 and 343 are distributed throughout the entire coal mass and only a small proportion can be expected to separate out with the sink/float resin fraction.

This is demonstrated in Fig. 5, obtained by two-step heating of a typical resin-rich Wasatch Plateau coal from the Blind Canyon seam. The flash evaporation fraction is completely dominated by aromatized terpenoids with five ring, picene-type skeletons, in addition to cadalene (at m/z 199) and a small series of lower, alkyl-substituted naphthalenes. The total signal of thermally extractable "bitumen" in Fig. 5(a) is approximately 20% of that of the coal pyrolyzate in Fig. 5 (b). When estimating the pyrolytic coal tar products in Fig. 5 (b) at approx. 25 wt.% of d.a.f, coal, the thermally extractable bi tumen in Fig. 4(a) would represent approx. 5 wt.% of d.a.f, coal. This is in good agreement with earlier estimates of thermally extractable components in fresh Was- atch Plateau coals [23], as well as with the observed weight loss in the 250- 350°C region in the TG plot of the Blind Canyon coal (Fig. 1 ). In other words, the total amount of asphaltene-like, resin-related products in these coals is probably somewhere in the 3-5 wt.% range. Since this is roughly equal to the

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total yield of resin by sink/float procedures it might be worthwhile to explore the commercial extraction of picene derivatives as possible chemical feed- stocks from Wasatch Plateau coals.

In conclusion, Wasatch Plateau contains at least 4, more or less distinctive, resin-related terpenoid fractions, namely: (1) a polymeric fraction (characterized by oligomeric sesquiterpenoid pyrolysis products); (2) sesqui- and triterpenoid monomers and dimers; (3) oxygen-substituted triterpenoids; and (4) more or less highly aromatized terpenoids (viz. alkylsubstituted picene and naphthalene structures). The latter appear to be distributed throughout the entire coal, probably in the form of cell, void and fissure fillings commonly recognized as "exsudatinite" or "secondary resinite" by micropetrography [24].

Chemical affinities with recent and fossil tree resins

What remains to be established at this point is whether all these terpenoids are indeed directly related to fossil tree resins. For instance, what is the pos-

129

sibility that most of the terpenoids in the C2s-C32 range are of bacterial or algal origin?

A strong case for the fossil tree resin nature of the above discussed terpenoid signals can be made by comparing Fig. 4 with the spectra of recent dammar resin in Fig. 6. Both the flash evaporation spectrum in Fig. 6 (a) and the pyrolyzate spectrum in Fig. 6 (b) show an amazing degree of similarity with the corresponding spectra of Upper Cretaceous coal resin from the Wasatch Pla- teau field in Fig. 4. Similar to the coal resin, most triterpenoids in dammar resin appear to be associated with the flash distillable fraction, whereas the polymeric component appears to consist primarily of sesquiterpenoid subunits. Again this would seem to agree with the results reported by Van Aarssen et al. [13 ] while contradicting [25 ] the sesquiterpenoid/triterpenoid co-polymer structure proposed by Brackman et al. [ 12 ].

Unsurprisingly, the oxygen-containing terpenoid series in the C1G-C17 and C31-C32 range are much more pronounced in the recent tree resin whereas picene-type aromatized biomarker signals are absent. The latter, known to represent catagenetic degradation products from certain C3o terpenoid structures

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Fig. 6. Averaged iso-butane chemical ionization mass spectra of'. (a) flash evaporate at 290 °C and (b) subsequent Curie-point pyrolyzate at m/z 610 C; from a recent dammar resin sample. Note prominent resin acid patterns in (a) and regular sesquiterpenoid polymer building block sequence in (b), Compare with Fig. 4.

130

[25], would not be expected in recent materials. As also noted by other re- searchers [26], polymerization (rather than aromatization) appears to be the dominant diagenetic process for resins. In view of the relatively high rank (hvAb and hvBb) of Wasatch Plateau coal (most well recognized coal resins occur in lignites and subbituminous coals) it is not surprising, however, that catagenetic changes are encountered here as well. In particular, catagenetic dehydro- genation and dealkylation processes appear to be responsible for the observed picene and naphthalene type structures.

At this point, it is tempting to address the question of the purported unique- ness of Wasatch Plateau coal resins [4] with regard to chemical composition and reactivity. Do the mass spectra of most other coal resins and recent tree resins look like Figs. 4 and 6 respectively, or can we expect to encounter different structures? The latter appears to be true. Figure 7 shows a typical brown coal-associated Australian (Yallourn mine) resin, called "bombicite", of Ter- tiary age (Fig. 7a) together with a recent Indonesian (Pontianak) copal. Both spectra are dominated by diterpenoid (C2o) acid signals, presumably of the communic acid and/or agathic acid type [17]. Most resins, fossil or recent,

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131

discussed in the literature appear to fall in the diterpenoid (C2o) acid category with lesser amounts of sesquiterpenoid, sesterterpenoid and triterpenoid components. Nevertheless, Southeast Asia coal resins of Tertiary Age analyzed by Mukhopadyay et al. [ 9 ] and Brackman et al. [ 12 ] and Van Aarssen et al. [ 13 ] show similar C15 (sesquiterpenoid) and C3o (sesquiterpenoid dimer and/or triterpenoid) compounds. Comparable findings were also reported by Senftle et al. [11] who emphasized a tentative link between fossil resin type and palaeobotanical affinities, e.g., Gymnosperms vs. Angiosperms.

Although much more work needs to be done before far ranging generaliza- tions can be made, combination of available literature data on fossil as well as recent plant resins [9] with the observations reported here strongly suggests that the combination of sesquiterpenoid and triterpenoid components found in Wasatch Plateau coal resin is indicative of an Angiosperm (fam. Diptero- carpaceae) origin, whereas the more widely reported (poly) diterpenoid fossil resins are derived from Gymnosperms as well as from selected Angiosperm species. Since Angiosperms are generally assumed to have achieved their first global distribution during the Cretaceous period, the Upper Cretaceous Black- hawk Formation coal resins in Utah may well represent one of the earliest recorded massive deposits of Angiosperm resins in general and Dipterocarp resins in particular. Although the marked similarity between Utah coal resin and recent dammar resin is being interpreted here as an indication of the presence of Dipterocarps in the Upper Cretaceous forests which produced the Hia- watha and Blind Canyon coal seams, it should be pointed out that this con- nection is far from conclusive and needs to be confirmed by further analysis of recent plant resins as well as by palaeobotanical, e.g. palynological, studies. Other Angiosperm families, e.g., Burseraceae [9 ] and Anacardiaceae [27 ], have also been shown to produce sesquiterpenoid and/or triterpenoid rich resins. Moreover, perhaps not all commercially available dammar resin may be exclu- sively obtained from Dipterocarp species.

Relationships between chemical composition and technical properties

Estimated contributions and (relative) technical properties of each of the four recognizable components of high purity, sink-float resin concentrates from Wasatch Plateau coals are listed in Table 2 together with the data sources used while preparing these estimates. It should be pointed out, however, that Table 2 is not intended to provide definitive answers or even firm estimates. Rather the authors want to provide benchmark estimates as targets for a more fo- cussed debate on the inherent relationships between chemical structure and technological properties of Wasatch Plateau coal resins.

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T A B L E 2

Estimated contributions and relative technical properties of the main chemical components of high grade Wasatch Plateau coal resin

Resin Approx. components a content

(Wt.°~o) b

Estimated relative technical properties

melting Solubility Visible Density M W

point color range Hexane Toluene Acetone Pyridine (g/mol)

I SQT 75-90 H igh + + + - - Amber L o w / 1000-2000

polymer medium II S Q T + T T 5 10 Low + + + - - Light Low 350-450

mono- and amber dimers

I I I T T alcohols 5-10 M e d i u m - - + + + + Yellow/ Medium 400-500

and acids brown IV T T + S Q T T 0-5 Low - + + + + + Dark High 150 350

aromatics Medium Brown

References [18,20,26] [1,2] [2,21,27] [2,4] [14] [1,18,26]

aSQT-sesquiterpenoid, T T = triterpenoid. bnonterpenoid components (e.g., waxes) not included.

C O N C L U S I O N S

The bulk component of Wasatch Plateau resins consists of an unusually regular, thermoplastic polymer consisting of sesquiterpenoid (C15H24) repeat units. In addition, Wasatch Plateau coal resins contain approx. 10% of thermally extractable components, which consist of a mixture of C13-C17 and C2s- C32 cyclic terpenoids, partially substituted with oxygen functional groups, as well as of aromatized terpenoids with naphthalene- and picene-type skeletal structures.

Chemically similar structural components (with the exception of the aromatized naphthalene and picene type skeletons) are found in recent dammar resin (Indonesia) pointing to an Angiosperm (fam. Dipterocarpaceae) origin of Wasatch Plateau coal resin. Most other recent as well as fossil coal resins studied thus far appear to be primarily derived from diterpenoic (C20) acid- rich precursors commonly found in gymnosperms as well as in some angiosperms [9].

Tentative relationships can be proposed between each of the four major components and the processing characteristics as well as product properties of Wasatch Plateau coal resin. Flash evaporation at 290 ° C appears to be a simple and rapid method for preparing thermally extractable resin components and for purifying the remaining polymer component. The quantity of aromatized, picene-like terpenoid biomarkers dispersed throughout fresh Wasatch Plateau

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coal is of the same order of magnitude as the total quantity of resin extractable by sink/float procedures, and thus may well be some of economic importance.

ACKNOWLEDGEMENTS

The authors are indebted to Drs. J.D. Miller, R.J. Pugmire, J.C. Crelling and K.B. Anderson for generously providing the various fossil and recent tree resin samples described in this paper, to Dr. L.L. Anderson for making unpublished pyrolysis field ionization mass spectral data available on Wasatch Plateau resin and to Dr. T.I. Eglinton for constructive criticism and advice. The work reported here was supported by DOE grant #UKRF-4-23576-90-10 (Consortium for Fossil Fuel Liquefaction Science ), by the Advanced Combustion Engineer- ing Research Center (funds for this Center are received from the National Science Foundation, the State of Utah, 23 industrial participants and the U.S. Department of Energy) and by matching funds from the State of Utah through the Center of Excellence in Advanced Coal Technology program.

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Chemical composition and origin of fossil resins from Utah Wasatch Plateau coal