Separation of coal macerals

The conditions necessary for efficient, small-scale separation of coal macerals are investigated. The method developed takes advantage of known density differences of the various macerais, but unlike most separations, an isopycnic density gradient centrifugation (DGC) technique is used to isolate pure macerals. The technique consists of grinding the coal in a fluid energy mill to ≈ 3 μm average particle size, separating macerals in an aqueous CsCI density gradient, and analysing the products for maceral composition as a function of density. Excellent separations can be achieved in a single run if the coal is first demineralized and then well dispersed with a wetting agent. Sink-float separations also benefit substantially from the addition of a surfactant. The density gradient centrifugation technique is limited more by inability to liberate macerals from each other on comminution than by any inherent errors in the gradient technique itself. Resolution of pure macerals using the DGC technique is much better than would be obtained from sink-float techniques. Data for three coals of differing constitution are presented.     

Photoacoustic microscopy of coal macerals

Photoacoustic microscopy, in which laser-light energy absorbed by coal macerals is converted into thermal energy, has recently emerged as an in-situ technique for coal maceral characterization. By employing two possible detection modes, different thermal properties can be measured and correlated with the material properties of the coal macerals. For the piezoelectric detection method, the photoacoustic signal is proportional to $\text{aB}\text{pc}$, where a is the coefficient of thermal expansion, B is the bulk modulus, p is the mass density, and c is the specific heat capacity of the maceral. The second method employs a gas microphone where the photoacoustic signal is proportional to $\text{l}\text{√Kpc}$, where K is the thermal conductivity. Photoacoustic data gathered by both methods on vitrinite and pseudovitrinite macerals from Appalachian basin coals agree with values predicted from known values of a, B, p and c. Data indicate that the thermal-elastic and thermal-conductance properties vary in a systematic manner from low- to high-rank coals. Throughout the entire rank range up to 92% carbon, vitrinite exhibits a significantly different photoacoustic response than pseudovitrinite. The photoacoustic measurements reflect the chemical composition and molecular structure of the individual coal macerals.     

Infrared spectra of coal macerals separated from Bulgarian lignites

The infrared spectra of the macerals resinite, humoresinite, textinite, ulminite, semifusinite and fusinite, separated from Bulgarian lignites, are discussed. Quantitative increment analysis is used. It has been established that the contents of the functional groups in the liptinite and huminite maceral groups are different, but the aromaticities are quite similar. The spectral characters and complexity are due to the different amount of lignincellulose tissue and resinite which entirely or partially fills the cell lumens of the wood. The infrared spectra of the inertinite maceral group have a simple pattern. In the semifusinite the absorption bands recorded are attributed to the low degree of oxidation and the large resinite content, respectively. The strong absorption of the fusinite is influenced by the higher content of condensed aromatic and hydroaromatic ring structures. The investigations indicate that the fusinite was formed during thermal destruction of the wood tissue, which proceeded at a high speed.     

Behaviour of huminite macerals from Victorian brown coal in tetralin in autoclaves at temperatures of 300–380 °C

The behaviour of various huminite macerals and submacerals in a hydrogen-donor solvent, tetralin, at high temperature under hydrogen pressure was investigated. Small granular samples of three Victorian brown coals of different lithotype were treated with tetralin in two types of autoclave, at temperatures of 300–380 °C and under pressures of 5 or 10 MPa. The residual materials were investigated microscopically. This tetralin treatment caused huminite macerals and submacerals derived from highly gelified cellular material to become plastic even at temperatures as low as 340 °C, whereas it had no such effect on those derived from ungelified material. This relation between the degree of gelification and the tendency to become plastic during tetralin treatment in an autoclave is very similar to that found for vitrinite macerals and submacerals from bituminous coals.     

Scanning electron microscopy of coal macerals

Individual macerals separated from some United Kingdom coals of Carboniferous age and bituminous rank were examined by scanning electron microscopy. In each case a specific morphology characteristic of the macerals studied could be recognized. Collinite (a member of the vitrinite maceral group) was recognizable in all samples by its angular shape and characteristic fracture patterns, the particles (30–200 μm) frequently showing striated or laminated surfaces. Sporinite particles had no well defined shape and were associated with more detrital material than were the other macerals studied. This detritus was shown by conventional light microscopy to be the maceral micrinite. Fusinite was remarkable in having a ‘chunky’ needle form, with lengths of up to 200 μm.     

High-resolution density variations of coal macerals

A number of coals have been separated into their maceral components by density gradient centrifugation. Each maceral group exhibits a distribution of densities. In general, exinite distributions do not overlap with those of vitrinite. However, vitrinite density distributions overlap significantly with inertinite distributions. This behaviour places inherent limits on the ability to completely separate macerais using density measurements alone. The density distribution of vitrinites and probably exinites has been found to narrow as rank increases.     

Development of laser micropyrolysis of coal macerals

The use of the focused output of a laser to pyrolyse coal selectively on a microscopic scale enables the in-situ study of individual macerals. Laser heating coupled with mass spectrometric detection of the pyrolysis products has indicated that the composition of the pyrolysis products consists mostly of alkyl substituted one and two ring species with unsaturated aliphatic fragments resulting from the breakdown of hydroaromatic structures in the coal.     

Electron spin resonance of isolated coal macerals

The g-value, linewidth, lineshapes, carbon radical densities and microwave saturation response have been measured for over 50 exinite, vitrinite, and inertinite maceral samples of coals varying in rank from subbituminous type C to anthracite. The process of maceral isolation has also been examined by comparing carbon radical properties of the starting coal with those of intermediates in the separation procedure: after comminution, demineralization and centrifugation. The g-values, linewidths and lineshapes appear unaltered by the separation steps, while there is some decrease in carbon radical density upon comminution and an increase upon demineralization. Carbon radical g-values fall with increasing coal rank for both vitrinites and exinites, a change associated with loss of oxygen at higher rank. Linewidths generally increase with rank for both vitrinites and exinites, but are extremely narrow (≈1G) for some inertinites, suggesting exchange narrowing between radicals. Radical densities and the ability to absorb microwave radiation increase with coal rank for exinites and vitrinites, reflecting stronger inter-radical interactions at higher radical densities.     

Relationship of coal extraction with free radicals and coal macerals

Extraction and de-ashing of coals with N-methyl pyrrolidone (NMP) under mild conditions has been reported recently. In this work, we have studied about a dozen American coals, along with some of their residues and extracts after treatment with NMP using in situ ESR (Electron Spin Resonance) spectroscopy of free radicals. At room temperature, N-₈ (number of free radials/g) decreases whereas the percentage extraction increases with atomic H/C of coals. Also N₈ for extract (residue) is lower (higher) than that for coals, ESR spectra of the extract exhibits only the single broad component and the weighted average of N₈ for the extract and the residue nearly equals that of the parent coal. These results have led to the hypothesis that the treatment with NMP is an extraction process in which exinites and to a lesser degree vitrinites are favored, whereas the inertinites are nearly rejected by NMP.     

Behaviour of elements and minerals during preparation and combustion of the Pernik coal,Bulgaria

The chemical and mineral composition, including major (Al, Ca, Fe, K, Mg, S, Si, Ti), minor (Na, P) and trace (Br, Cl, Co, Cr, Cu, Li, Mn, Ni, Pb, Rb, Sr, Zn) elements and different minerals, of the Pernik subbituminous coals and their preparation and combustion solid waste products were studied. Feed coals, upgraded coals (high-grade and low-grade coals) and their waste products, namely coal slimes and host rocks generated from the Pernik coal preparation plant, as well as combustion waste products such as bottom ashes, fly ashes and lagooned ashes resulted from the Republica coal-fired thermoelectric power station were characterized. The occurrence and behaviour (partitioning, volatilization, condensation, capture and retention) of the above-mentioned elements and various minerals during coal preparation and combustion are described. The results indicate some technological problems and possible environmental pollution of the air, water, soil and vegetation with certain elements in the areas surrounding both thermoelectric power station and coal preparation plant.     

Liquid products of the hydropyrolysis of brown coal form the Lena basin

Liquid hydrocarbon products were obtained by the hydropyrolysis of brown coal from a deposit in the northern Lena basin on an iron-containing catalyst. The individual and group compositions of gasoline and diesel fractions were determined with the use of capillary chromatography and chromatography-mass spectrometry. The gasoline fraction with a boiling point to 180°C was characterized by a high octane number; it mainly contained monocyclic aromatic hydrocarbons and normal alkanes. The diesel fraction mainly consisted of bi- and tricyclic aromatic hydrocarbons and C₁₃–C₁₉ n-alkanes.     

Hydrogenation of the inertinite macerals of Bayswater coal

Yields of products from the hydrogenation of the inertinite and vitrinite+exinite macerals of the Bayswater (New South Wales, Australia) coal in a batch autoclave were investigated. Samples were hydrogenated for 1 h at 400 and 450 °C with tetralin as vehicle, hydrogen as charge gas and no added catalyst. The results show that the inertinite macerals contributed significantly to the liquid hydrogenation products, in particular to the oil yield obtained at 450 °C.     

Sorbent production from low-ash brown coal

The process for the production of a sorbent upon the carbonization of low-ash brown coal in a fluidized bed in a temperature range of 700–850°C was studied. The dependences of the main characteristics of the sorbent on temperature and the fraction of processed coal were found. The characteristics of the lignite sorbent obtained by the TERMOKOKS-KS technology are presented.     

Chemical structure of coal macerals in Balmer 10 coal and fusinite from Illinois coal as indicated by reductive alkylation

A Canadian Cretaceous coking coal from the Balmer 10 seam, Fernie, British Columbia, was separated by sink-and-float methods into vitrinite and a semifusinite-rich fraction. A portion of the vitrinite fraction was oxidized in air at 100 °C for 72 h to destroy the coking properties. The fresh vitrinite, oxidized vitrinite, and semifusinite of the Balmer coal, and the fusinite from Illinois coal, were each subjected to the reductive alkylation procedure of Sternberg, to cleave the ether linkages and octylate the products. The oxygen functional groups before and after ether cleavage were determined, as were the extractabilities by benzene of the octylated products. Thus the molecular weights of the benzenesoluble fractions of the octylated cleavage products were: fresh vitrinite 1930, oxidized vitrinite 1830, and fusinite 1490. The molecular-weight distribution of the octylated cleavage products was estimated by volatility analysis, which demonstrated the presence of much lower-molecular-weight material. Dilatation analysis of fresh and oxidized vitrinite showed that after cleavage of the ether linkages with potassium in tetrahydrofuran, the two could be brought to the same state. The dilatation behaviour of semifusinite after cleavage of the ether links and octylation showed only contraction, whereas the oxidized vitrinite treated in a similar manner exhibited a large dilatation.     

神木煤显微组分热解半焦CO_2活化特性研究

通过对神木煤显微组分不同温度下（500℃,700℃）热解得到的半焦和半焦CO2活化特性进行研究,发现富惰质组半焦比表面积和孔隙结构明显优于富镜质组半焦;热解半焦均存在较宽泛的中孔、大孔,从500℃到700℃,富镜质组半焦生成的微孔多于富惰质组半焦。在实验条件下,500℃和700℃的半焦CO2活化性能均是富镜质组〉原煤〉富惰质组。热解从500℃提高到700℃,富镜质组半焦的CO2反应活性明显提高。惰质组的结构疏松,在活化过程中容易造成孔壁塌陷,形成大孔,从而导致富惰质组半焦比表面积减小。     

Interpretation of the chemical composition of bituminous coal macerals

Various methods of identifying and classifying macerals are evaluated on the basis of literature references and our own experimental results. Comparison of the diagrams $\text{H}\text{C}$ vs $\text{O}\text{C}$, atomic $\text{C}\text{H}$ ratio vs weight percentage of carbon, and atomic $\text{C}\text{H}$ ratio vs atomic percentage of carbon demonstrates the advantages of the characterization of maceral composition by means of the atomic carbon percentage, which is a function of the content of all five organogenic elements that enter into the composition of the combustible matter of caustobioliths. Illustration by means of maceral analyses from the same seam, of results from pyridine extraction, and of humic acid composition further confirms this view.     

Carbon-13 CP/MAS spectroscopy of coal macerals

¹³C n.m.r. spectra of kerogen concentrates isolated from several different subbituminous to high-volatile bituminous coal macerals have been obtained by a combined cross polarization/magic-angle spinning technique. The samples comprise three vitrinites, two sporinites, two alginites and one fusinite, all of Upper Paleozoic age. It is shown that this technique can be used to differentiate the maceral types by providing characteristic spectral fingerprints. Aromaticities decrease in the order fusinite vitrinite sporinite alginite, as expected with the rank range studied. Furthermore, fine spectral details provide general information on the nature and distribution of discrete structural moieties and their variations with both type and rank.     

Some compounds separated from depolymerized brown coal

The petroleum ether-soluble fraction of the methylated depolymerized product was fractionated by liquid and gas chromatography and the chemical formulae of nine crystalline substances that were isolated were determined completely or partially. Another two compounds (Figure 6, peaks 18, 23, 0.42%) were also separated and their structure was approximately determined. Seven other peaks (4.11%) were also identified as similar to fractions from liquid chromatography already discussed. Because of over lapping yields in Table 1 and text, the total characterized was only 4.8% of the depoly merized coal, and the total separated about 6.0% (Table 1). From these compounds, suggestions are made for the course of the depolymerization process and for the structure of the coal.