Sapropelic Coals Research Articles

Hydrocarbon generation from deltaic and intermontane fluviodeltaic coal and coaly shale from the Tertiary of Texas and Carboniferous of Nova Scotia

Selected samples of coal and coaly shale from southeastern Texas (depositional environment: deltaic; Age: Paleocene-Eocene; R o: 0.25–0.75%) and Nova Scotia (depositional environment: intermontane swamp, delta and lacustrine; Age: Carboniferous-Westphalian A-D; R o: 0.67–0.70%) were analyzed by fluorescence microscopy, Rock-Eval pyrolysis, NMR, anhydrous pyrolysis (temperature programed and flash) and hydrous pyrolysis to evaluate the hydrocarbon potential and hydrocarbon types. Based on maceral assemblages, palynofacies and hydrocarbon potential, these coal and coaly shale samples are classified as humic, mixinitic (mixed), and sapropelic compared to humic and sapropelic as defined by Stach et al. ( Coal Petrology. Gebruder Borntraeger, Berlin, 1982). Mixinitic (or mixed) coal and coaly shale containing mainly humodetrinite and lipodetrinite generated more than 10% pyrolysate (expelled oil + oil in wash fraction + remaining coal extract) and show a bimodal n-alkane distribution (derived from cutinite, suberinite and alginite). Pyrolysis of humotelinite/humocollinite-rich and liptinite-poor humic coals generated low amounts (<10%) of pyrolysates, mainly consisting of low molecular weight hydrocarbons. A modified model of oil-prone and non-oil-prone coal types, related to depositional environments, is proposed. A new concept of primary migration is proposed: the humodetrinite-liptodetrinite network of mixinitic (or mixed) and sapropelic coal (excluding exsudatinite) acts as a migration pathway for liquid hydrocarbons which migrate as a hydrocarbon phase. According to pyrolysis, NMR, organic petrography and the primary migration concept, mixinitic (or mixed) coal or coaly shale are considered as likely source rocks for liquid hydrocarbons within deltaic and intermontane basins.

Peculiarities in methanol action during liquefaction of different coal type

The peculiarities in methanol action during liquefaction of coals having different origin and rank were investigated. When liquefying sapropelic coals, the action of methanol does not differ from that of toluene. In the case of humic coals, methylation of aromatic fragments takes place and methylated liquid products are produced. The degree of alkylation increases with decrease in coal rank. The alkylation of model coal substances and some polyaromatic hydrocarbons was small. It was concluded that during coal liquefaction, reactive coal intermediates are subjected to alkylation.

A progress report on the Alpern Coal Classification

The Alpern Coal Classification has already been largely utilized and successfully applied, both to Laurasian (North Atlantic) and Gondwana coals. It was accepted on basic principles by the International Committee for Coal Petrology, and, as the official contribution of France, it has been recently also partly adopted by the Economic Commission for Europe of the United Nations in Geneva (1988). This paper deals with the improvement of the previous versions of the classification, mainly by introducing new statistical data in order to establish more accurately proposed rank limits. A ternary division for RANK is maintained with the categories: low-rank coal or lignite (instead of brown coal because high-rank lignites may be black not brown), medium-rank coal or bituminous coal, and high-rank coal or anthracite. The prefixes hypo-, meso- and meta-, are used for rank subdivision, thus avoiding non-coherent previous prefixes such as sub-(bituminous) and semi-(anthracite). The selected rank parameters are: moisture holding capacity (ash free) and calorific value (moist, ash free) for lignites, mean random reflectance for bituminous coals and anthracites. Correlations for bed moisture (ash free) and calorific value (dry, ash free) are given for lignites. Correlations for volatile-matter content, mean maximum vitrinite-reflectance, and hydrogen content are also given for bituminous coals and anthracites. TYPE is determined from maceral data and is divided into: vitric (vitrinite (V) > 60%), fusic [V < 60%; inertinite (I) > liptinite (L), and liptic (V) < 60%; L >. I). The ash content and the washability potential at 10% ash level are used to determine GRADE (or FACIES) and allow the distinction between transportable clean coals and non-washable coals. The run-of-mine ash content (dry basis) permits the division between: coal, middlings, and shale. If the type is liptic, the subdivisions “sapropelic coals” and “oil shales” are used. These are not washable but are solid fuels with a positive energy potential. If the coals to be classified are clean (or washed) the vertical axis becomes free and can be used, for example, for swelling properties in bituminous coals. The system has been recently computerized and allows for data to be displayed effectively for all relevant fields of application. Computer-output examples are presented for coals from a Euramerican and a Gondwana basin.

Properties of high-rank coals and dispersed organic matter of associated rocks in the Donets Basin (U.S.S.R.)

High-rank organic matter (OM) (from Ess coal stage to meta-anthracite) of different concentrations has been studied by means of coal petrography and coal chemistry. Sixty polished surfaces (blocks and from kerogen concentrates), as well as 30 samples from mines in the southwestern Donets Basin, where the Middle Carboniferous (Mississippian) high-rank coals occur, were analyzed. Major emphasis has been laid on establishing the optical features and petrographic composition of coals and dispersed organic matter (MOD) in different facies, from terrigenous alluvial to marine limestones. The influence of tectonic structures and mineralization on the properties of coal matter were also taken into account. A general evolutionary trend of OM of different concentration is observed on the basis of changes in the optical features and chemical properties. At high ranks, there is a distinct change in vitrinite reflectance and anisotropy at R 0max of about 2% and carbon content of 90% (C daf). The next, less distinct jump in coalification takes place during the transition from the anthracite to metaanthracite rank at R 0max Vt = 6% and C daf = 96%. In most cases, vitrinite reflectance and anisotropy in coals are higher than those of MOD from nearby locations. The lowest values of R 0max and anisotropy are recorded in OM of limestones. At all stages in the metamorphic series there are differences in the elemental composition and real density values between coals and MOD. MOD displays features of elevated primary oxidation as compared to coals. It would be reasonable to subdivide anthracites proceeding on the basis of the elemental composition of coals and MOD, using atomic percent values. Despite the convergence of the optical features of various macerals in the course of coalification, and owing to irregular changes in the maximum and minimum R 0 values at high metamorphic grades, one can draw a reliable distinction between fragmentary homogeneous and structural plant remains, among them spores and algae. No appreciable changes are recorded in the size of liptinite macerals in anthracites as compared to less metamorphosed coals. The alteration products of higher and lower plants are slightly different in their chemical characteristics at anthracitic rank. Sapropelic coals have a lower amount of hydrogen as compared with humic coals. The presence of pyrite in coals results in local (microscopic) changes in R 0max and R 0min of vitrinite and a decrease of its bireflectance value. In tectonically dislocated areas, there is no appreciable increase in OM reflectance. However, in these areas anisotropy quite frequently does increase. The data obtained can be of great significance in working out the classification of coals in the more advanced stages of the coalification series, defining the nature of organic inclusions in host rocks, and in accomplishing studies on black shale metal-bearing complexes, which contain carbonaceous matter of anthracitic and meta-anthracitic rank.

Paleoenvironmental controls on vertebrate-bearing abandoned channels in the Upper Carboniferous

A paleoenvironmental study of the vertebrate-bearing sapropelic coal that underlies the Upper Freeport coal (Westphalian D, Upper Carboniferous) at Linton, Ohio, identifies a hierarchy of physical and chemical controls that influenced the formation of this deposit. Surface and subsurface data from previous work and field study of extensive exposures show that the fossiliferous cannel occurs at the bottom of an approximately 15 m deep abandoned river meander within a sandstone-dominated multistorey sediment body. Storeys of this sediment body fine upward and consist of varying proportions of sandstones and siltstones within lateral accretion beds that are interpreted as point-bar deposits. Associated channel fills are generally organic rich and composed of coals, such as the Linton cannel, or carbonaceous mudstones. Maximum observed channel depth is approximately 18 m, and the maximum thickness of the multistorey sediment body reaches nearly 40 m. The sandstone-dominated sediment body that contains the Linton cannel trends northwestwardly and contrasts with mudstone-dominated, coarsening-upward sequences that were deposited contemporaneously in adjoining areas. This lithic pattern suggests that fluvial activity was restricted to a persistent topographic low that may have resulted from movement along the Transylvania Fault Zone a previously documented basement-controlled feature. Rapid subsidence on the southern side of this structure confined the fluvial system and favored the preservation of deposits within the meander belt, including the fossil-bearing sapropelic channel fill at Linton. The low inorganic content and oxbow-like outline of the Linton fossil deposit and its lateral relationship to other storeys in the multistorey channel sequence indicate that the abandoned meander was closed rapidly by neck cutoff and, in the absence of clastic influx, filled by sapropelic peat. Remains of aquatic to terrestrial animals that lived in or near the oxbow lake slowly rotted in this scavenger-free anaerobic setting. Because of the substantial depth of the original meander and a lack of coarse-grained fill materials, a prolonged period of sapropelic filling insured the preservation of an abundant and diverse autochthonous vertebrate assemblage. Most Westphalian tetrapod deposits represent sapropelic peats and muds and share some of the taphonomic attributes of the Linton deposit. The high degree of autochthony evidenced by Westphalian vertebrate accumulations indicates that taphonomic controls of low-lying peat-forming alluvial and delta plain systems differ significantly from those of well-drained alluvial valley settings.

Petrography and Taphonomic Significance of the Vertebrate-Bearing Cannel Coal of Linton, Ohio (Westphalian D, Upper Carboniferous)

ABSTRACT Petrographic study of a vertebrate-bearing cannel coal which underlies the Upper Freeport coal (late Westphalian D, Upper Carboniferous) in the area of Linton, Ohio, provides information on the depositional conditions represented by fossiliferous sapropelic coals. Samples of the cannel obtained from an approximately 10-km-long curvilinear area were prepared as polished blocks and point counted in reflected light. The cannel typically consists of over 50 percent very finely grained, micrinite-rich groundmass; approximately 25 percent exinite and 10 percent pyrite; and varying amounts of vitrinite and inertinite. Sporinite is the most abundant exinite, but no alginite occurs; euhedra and framboids are the most common forms of pyrite; and vitrinite is poorly preserved and virtually struc ureless. Vertebrate scales, teeth, and bones preserved in the cannel show no significant mineralogic alteration. These petrographic findings agree with results from an investigation of the physical paleoenvironment of the Linton deposit, and together these data sets indicate that the vertebrate-bearing cannel represents a freshwater sapropelic peat that formed within abandoned segments of a fluviodeltaic channel. In the absence of clastic influx, macerated plant debris and resistant spores accumulated in the bottom of the channel, and decay of these organic-rich sediments led to anaerobic conditions in which sulfate-reducing bacteria thrived. Vertebrate remains introduced from the overlying oxygenated waters were not subjected to scavenging in this anoxic, nonacidic setting but slowly rotted, leaving skeletal parts intact.

Chemical characteristics of liptinite macerals in humic and sapropelic coals

According to previous studies alginite does not occur in humic coals. However, in coals from the Saar District, F.R. Germany, alginite was identified by fluorescencemicroscopy. In addition, high amounts of an undeterminable liptinite maceral were found and tentatively explained as an alteration product of alginite. Therefore, organic geochemical methods were used to characterize and identify this unknown liptinite maceral. Organic geochemical parameters such as CPI, pristane/phytane ratio and methylphenanthrene index, show not only a dependence from coal rank but also yield additional information about the type of organic matter input and the depositional environment of the coals. A series of coals of different origins around 0.8% vitrinite reflectance were investigated, to determine how far the geochemical parameters reflect change in facies. The samples included cannel, boghead and resinite-rich coals, as well as isolated durain bands. With increasing amounts of alginite in the coal, the CPI, pristane/phytane- and C 4-naphthalene/phenanthrene ratios of the extracts decrease. As illustrated by two representatives samples, some resinite- and sporinite-rich coals show a primarily naphthalene derived aromatic composition, whereas some alginite-rich coals of the same rank show phenanthrene and its derivatives to be dominant. With respect to technological properties most coals from the Saar District correspond with a higher rank than indicated by reflectance measurements. Those coals in general show lower values of the aforementioned ratios in comparison with Ruhr coals of similar vitrinite reflectance values.

Gallium porphyrins in bituminous coal

Metalloporphyrins are minor constituents in crude oil and its relatives1 but their presence in coal is not clearly established. This is surprising as such complexes are thought to arise from chlorophyll, and coal is largely of plant origin. Although coal samples were among the earliest examined in this context2,3, most later workers1,4 followed Treibs5 in mainly considering crude oils, asphaltenes and shales. Weigelt and Noack2 presented early evidence for chlorophyll derivatives in fossilised leaves from brown coal, while Treibs3 found trace amounts of metal-free porphyrins in various coals. Uspenskii and Gorskaja6 confirmed the latter finding, but observed that the porphyrin content of sapropelic coals such as cannel coal was much higher than that of hard coals. Metalloporphyrins in fossil plant material are important because they provide information on the geochemical transformations of chlorophyll. Moreover, metal complexes with organic ligands (such as the metalloporphyrins) are of particular interest in contemporary coal chemistry because they are probably extracted by the organic solvent in the conditions used in certain coal liquefaction processes, and hence may modify the activity of catalysts used in subsequent chemical reactions with the coal extract. We report here the isolation of a metalloporphyrin fraction from a British bituminous coal, and show that the principal metal present in the isolated material is gallium.

Studies on artificial coal. 1. Caking power and chloroform extracts

The hydrothermal treatment of wood, cork, peat and lignite is recognized as a method of preparing artificial coal (AC). Excepting cork, the other substances give non-caking AC in neutral medium and caking AC in alkaline medium. Cork produces caking AC even in neutral medium. The concept of the relation between the caking power of natural coals and the chloroform-extraction yield of the corresponding preheated coals was primarily used in the present investigation on AC. Besides the usual procedure of preparing AC, we also employed a modified method in which the hot tarry vapours were vented before the autoclave was allowed to cool overnight. The principal conclusions drawn are: 1. (1) The roles of the neutrality or alkalinity of the medium and the starting material on the cakeability of AC were confirmed. 2. (2) Irrespective of the starting material, chloroform-extraction yield (fairly exhaustive cold and also soxhlet extraction) of the AC's was high, ranging from 11.6 to 60.4% daf, the lower values for the non-caking AC and the higher for the caking AC. The difference between the extract yields by cold and soxhlet extraction was about 5%. 3. (3) The venting of the hot tarry vapours did not influence the caking properties of AC appreciably. 4. (4) The venting of the tarry vapours led to a lower yield, VM and chloroform-extraction yield of AC in general. But the lowering in the yield of AC and also in the chloroform-extraction yield was higher than the lowering in the VM. Therefore the tarry vapours appeared to undergo some condensation reactions during cooling overnight. 5. (5) In all cases the preheating of AC caused a progressive fall in the yield of chloroform extract. In this respect non-caking AC behaved like non-caking natural coal and caking AC behaved like a long-flame coal made caking by mild hydrogenation. No similarity of any AC was observed either with an exinite-concentrate of exinite-rich bituminous coal or with a sapropelic coal, both of which showed pronounced maxima in the temperature plots of chloroform-extract yields from preheated samples. 6. (6) The role of volatility of chloroform extracts (indirectly deduced from VM tests on the various coal samples) in determining the caking properties of coal appeared more clearly in this investigation: the caking properties will be poor unless sufficient residue derived from the extract remains at the VM-test temperature.

Thermal decomposition of a blackband ironstone. I. Overall mass and energy balances

AbstractA sample of blackband ironstone containing 31% iron and approx. 26% sapropelic coal was calcined in a small fixed‐bed under reducing conditions to give a solid residue, aqueous and tarry distillates and an inflammable gas. By observing weight‐loss and gas composition as a function of temperature, reaction was found to occur in two stages, the first (200–600°) involving decomposition of ferrous carbonate and coal, and the second (700–900°) further pyrolysis of the organic residue. From analyses and heats of combustion of the products, mass and energy balances have been set up, and an estimate of the heat of decomposition obtained.