Direct hydroliquefaction of a low rank soft brown coal

The behaviour of the soft brown coal from the Kostolac Mine (Serbia, Yugoslavia) was investigated during hydroliquefaction carried out in a batch reactor by direct catalytic hydrogenation of the pulverized coal (−160 μm) dispersed in tetralin. The effects of temperature (ranging from 365 to 440°C), pressure (13.5 to 15.0 MPa) and residence time (1 to 8 h) on the yield of individual liquefaction products as well as the petrographic composition of the coal residues were closely followed by separation and analysis of the products. These consisted of liquid products soluble in n-heptane (light oils), n-heptane insoluble products (asphaltenes), the solid coal residue and gaseous products. A good reactivity of this soft brown coal was observed. The yield of liquid products varied from 23 to 64 wt.% (based on dry ash-free coal). A total coal conversion of 80 to 86% was achieved. Petrographic composition and optical properties of the solid coal residues were analyzed microscopically in order to establish the character and intensity of the coal changes. The solid residues were found to consist of 12 various grain categories. The low proportions of unreacted or partly reacted coal grains confirmed the good reactivity of the Kostolac soft brown coal in the applied liquefaction process.     

Co-pyrolysis as a method of upgrading some products of coal processing

Co-pyrolysis was investigated as a method of upgrading various products resulting from coal processing. Co-pyrolysis of vacuum residue (VR) with coal extraction products as well as with primary tars from flash pyrolysis leads to a considerably enhanced yield of liquid products. It has been established that superheated steam and increased outgassing rate, favour the yield of liquid products. The proportion of the ingredients in the mixture as well as the quality of the VR also have a definite effect. The excess yield of liquid products in co-pyrolysis of coal extraction products was 8–23 wt%, depending on operating conditions and the composition of the mixture. The flash co-pyrolysis of primary tars yielded a 1.5–15.9 wt% surplus of liquid products depending on the mixture composition. Products originating from co-pyrolysis of these raw materials with VR are characterized by relatively high atomic hydrogen to carbon ratio, usually not less than 1.5 and the total abscence of asphaltenes. Generally, co-pyrolysis of VR with various products of coal processing is comparable with hydrogenation in the light of good yields of liquid products.     

Hydrogenation of liddell vitrinite: Effects of metal halide catalysts in the temperature range 200–480°C

A vitrinite concentrate prepared from the Liddell Seam (high volatile bituminous coal, NSW, Australia) has been hydrogenated in an unstirred 50 cm³, batch autoclave at reaction temperatures between 200 and 480°C in the presence of metal halides (SnCl₁ or ZnCl₁) and/or alumina (α-Al₁O₃). A vehicle was not used. The influence of reaction temperature, metal halide and alumina on the composition of the products was studied by gas chromatography (GC), gel permeation chromatography (gpc), ¹H solution and ¹³C solid-state cross polarization (CP) nuclear magnetic resonance (nmr) spectroscopy and optical microscopy.The metal halides lower the temperature at which softening and agglomeration of vitrinite takes place. The resultant plastic isotropic material forms mesophase at temperatures above 400°C unless an inert diluent, i.e. alumina, is added. The alumina inhibits reactions involved in the formation of mesophase which would otherwise compete with hydrogenation reactions that yield hexane soluble material (oil).Above 400°C carbon monoxide, carbon dioxide and C₁-C₅ alkanes are the principal gaseous products. At lower temperatures, in the presence of alumina, ethylene is formed in the catalysed experiments; the ethylene is converted to ethane at higher temperatures. The structure of the hexane soluble products derived from vitrinite is also temperature dependent. Above 420°C much of the aliphatic component decomposes to yield further quantities of hydrocarbon gases. Tin(II) chloride and zinc chloride produce hexane soluble products of similar molecular composition, which suggests that they operate through a similar mechanism.The addition of alumina to the reaction mixture results in a more aromatic liquid product with shorter aliphatic carbon chains. Whether or not alumina is present, the aromaticity of the solid residues increases with increase in hydrogenation temperature. Thus the increased aromaticity of the liquid products is not caused by the extraction of a greater proportion of aromatic material from the coal with increase in the hydrogenation temperature. It follows that with increase in hydrogenation temperature an increasing proportion of the aliphatic material becomes transformed into aromatic compounds and/or gas.In summary, the results show that over a wide range of temperatures (200–480°C) the structure of the hexane soluble product depends on the thermal stability of the products and the degree of competition from reactions leading to mesophase formation, and not on the nature of the halide catalyst.     

Paramagnetic properties of brown coal from the Kiyaktinskoe deposit before and after mechanical treatment and electron irradiation

Results of a study of the paramagnetic characteristics of brown coal from the Kiyaktinskoe deposit (Kazakhstan) in a native state and after mechanical treatment and electron irradiation are reported. The effects of these actions on changes in the paramagnetic properties of the test coal and on the intensification of a coal hydrogenation process are discussed. It was found that the concentration of free radicals changed only slightly after mechanical treatment in a ball mill at room temperature in an atmosphere of air, whereas the concentration of Fe³⁺ ions noticeably increased. Upon the electron irradiation of coal, the dose dependence of the concentration of free radicals passed through a maximum at a dose of 100 kGy. At the same radiation dose, the yield of a kerosene-gas oil fraction upon the hydrogenation of Kiyaktinskoe coal increased, and the total yield of liquid products increased upon the irradiation of coal and a catalyst (bauxite 094) to a dose of 100 kGy. It was hypothesized that Fe³⁺ ions, which were additionally formed upon coal grinding and irradiation, can serve as an internal catalyst in the course of coal hydrogenation.     

Application of modified iron-containing catalysts and preliminary ozonization of coal from the Shubarkol deposit to the hydrogenation of this coal

The results of the hydrogenation processing of coal from the Shubarkol deposit in the presence of natural bauxites from the Turgai deposit in the Republic of Kazakhstan are reported. With the use of a sample of bauxite containing 23.7% Fe₂O₃ as a catalyst, a higher yield of liquid products (54.2%) was obtained, as compared with those on other bauxite samples (49.5–53.8%). It was established that the modification of catalysts containing iron with elemental sulfur additives (0.75–1.25%) makes it possible to increase the yield of liquid products to 62.3–67.3%. A positive role of the preliminary ozonization of coal, which makes it possible to increase the yield of total liquid products upon hydrogenation by 13.3% in comparison with the yield of liquid products obtained with the use of coal not treated with ozone, was demonstrated.     

Hydrotreating coal-derived liquid distillation fractions. 1. Study of single-stage treated products for transport fuel use

A coal-derived liquid distillate obtained from catalytic hydrogenation of Wandoan coal at Australian Coal Industry Research Laboratories has been fractionated into three main distillation fractions: naphtha, kerosine, and diesel. Compositional properties of each fraction are reported, particularly elemental, ¹H and ¹³C n.m.r. and h.p.l.c. results. Hydrorefining of each fraction was undertaken in a trickle-bed reactor at various conditions using commercial nickel-molybdenum hydrotreating catalysts. The hydrotreated liquid products were assessed for transport fuel use or as feedstocks for further processing.     

Changes in composition of solvent-refined coal with severity of hydrogenation

The effects of mild and severe hydrogenation on the chemical composition of solvent-refined coal (SRC) produced from Wyodak subbituminous coal in the direct coal liquefaction SRC-I process were investigated. The yields of solvent-derived fractions of ‘oils’ and ‘asphaltenes’ increased with increasing severity of hydrogenation at the expense of ‘preasphaltenes’. Further separation of ‘oils’ and ‘asphaltenes’, each into three compound-class fractions, revealed more compositional changes. Concentrations of hydrocarbons, nitrogen compounds and hydroxyl aromatics in ‘oils’ increased with increasing severity of hydrogenation. ‘Asphaltenes’, containing nitrogen compounds and hydroxyl aromatic fractions but almost no hydrocarbons, showed an increase in nitrogen-compound concentration with increasing severity of hydrogenation. Hydroxyl aromatic concentration in ‘asphaltenes’ increased under mild but decreased under severe hydrogenation conditions. High-performance liquid chromatography followed by field-ionization mass spectrometry analysis of the hydrocarbon subfractions revealed a complex picture of structural transformations. Over fifty homologous series of aromatic and hydroaromatic hydrocarbons covering a carbon number range from about C₁₂ to C₅₀ were identified and approximate concentrations obtained. Small amounts of partly aromatized pentacyclic triterpane ‘biomarkers’ and their hydrogenation products were found.     

Conversion of coal into liquid products by hydrogenation and hydropyrolysis processes

The influence of highly dispersed iron-containing catalysts on the process characteristics of the hydrogenation (in tetralin) and hydropyrolysis of B2 brown coal and D and G black coals and the hydropyrolysis of brown coal and polyolefin mixtures was studied. The composition of the resulting liquid products was investigated by a GC-MS technique. It was shown that the use of catalysts significantly increased the degree of coal conversion and the yield of liquid products in all of the test processes. Maximum effects were observed in the presence of mechanochemically activated haematite, which was dispersed in tetralin by ultrasonication.     

Effect of temperature,catalyst and charge gas on the mean chemical structures of the products from hydrogenation of Liddell coal

Liddell coal (New South Wales, Australia) has been hydrogenated at 400, 425 and 450 °C with excess tetralin as vehicle and nitrogen or hydrogen as charge gas for 4 h at reaction temperature. In some experiments a nickel-molybdenum catalyst was used. The structures of the liquid and solid products were investigated by nuclear magnetic resonance spectroscopy, gel permeation chromatography and combustion analysis. Increasing the hydrogenation temperature from 400 to 450 °C decreases the yield of liquid products but increases conversion. At higher temperatures the liquid products are smaller in molecular size and molecular weight and contain a greater proportion of aromatic carbon and hydrogen; the solid residues also contain a greater proportion of aromatic carbon. The changes in variation of yield and structure with temperature are independent of the presence of catalyst under nitrogen and the nature of the charge gas. However, as the reaction system is capable of absorbing more hydrogen than can be supplied by the tetralin, the products from reactions with hydrogen as charge gas contain more hydrogen, some in hydroaromatic groups. Catalyst has little, if any, role in dissolution of the coal when a nitrogen atmosphere is used. When nitrogen is used as charge gas, reactions of coal-derived liquids with the catalyst do not alter the hydrogen, carbon or molecular size distributions in the products. The results show that the changes in composition of the liquid and solid products with increase in hydrogenation temperature are due to pyrolytic reactions and not to increased hydrogenation of aromatic rings.     

‘Solubility parameters’ in coal and coal liquefaction products

‘Solubility parameter’ spectra have been used in polymer research to determine the characteristics of cross-linked polymer systems. Cross-linked systems are not soluble in any solvent. Instead, solvent is imbibed by the cross-linked polymer and causes it to swell. The ‘solubility parameter’ of the solvent which causes maximum swelling is identified as that of the cross-linked material. Coal can be thought of as having some characteristics of a cross-linked system^1,2. That is, when immersed in a solvent with which it interacts, it will swell. In addition, coal contains extractable material. If coal is regarded as a ‘multipolymer’, this extractable matter can be thought of as the uncross-linked portion of the coal. Swelling spectra have been taken for untreated coal and coal from which some extractable matter has been removed, which partly suppresses swelling. This extractable matter can be thought of as similar to the uncross-linked coal molecule. Its structure can therefore be used to model the coal matrix itself, to determine the coal structure without using destructive chemical methods to break the coal apart. Dissolution spectra for both the coal extract and the coal liquefaction products from the PAMCO and Synthoil processes were taken. A set of mixed solvents with effective ‘solubility parameters’ ranging from 14.3 to 47.9 MPa^1/2 (7.0 to 23.4 hildebrands) was used. The behaviours of the coal extract and coal liquid products show striking similarities, leading us to believe that molecules similar to those found in liquefaction products already exist in the virgin coal and that hydrogenation products reflect the properties of the starting material.     

Structure of coal hydrogenation products obtained in the presence of oil and coal paste-forming agents

The structure parameters of hydrogenation products were analyzed in relation to the composition of oil and coal (intrinsic) paste-forming agents used in the process of coal hydrogenation under a low pressure of hydrogen (6–10 MPa). It was found that the structure characteristics of liquefaction products essentially differed at close values of the structure unsaturation parameter δ; this was likely due to a difference in the material composition of solvents (other than aromatic structures).     

Comparison of the chemical structure of coal hydrogenation products,athabasca tar sand bitumen and Green River shale oil

Coal hydrogenation products, Athabasca tar sand bitumen, and Green River shale oil produced by retorting were analyzed by the Brown—Ladner method and the Takeya et al. method on the basis of elemental analysis and ¹H-NMR data, by ¹³C-NMR spectroscopy and by FT-IR spectroscopy. Structural characteristics were compared.The results show that the chemical structure of oils from Green River shale oil and Athabasca tar sand bitumen, and the oils produced in the initial stage of hydrogenation of Taiheiyo coal and Clear Creek, Utah, coal is characterized as monomers consisting of units of one aromatic ring substituted highly with C_3–6 aliphatic chains and heteroatom-containing functional groups. The chemical structure of asphaltenes from Green River shale oil and Athabasca tar sand bitumen is characterized by oligomers consisting of units of 1–2 aromatic rings substituted highly with C_3–5 aliphatic chains and heteroatom-containing functional groups. The chemical structure of asphaltenes from coal hydrogenation is characterized by dimers and/or trimers of unit structures of 2 to 5 condensed aromatic rings, substituted moderately with C_2–5 aliphatic chains and heteroatom-containing functional groups.The close agreement between fa(¹H-NMR) and fa(¹³C-NMR) for Green River shale oil derivatives and Athabasca tar sand derivatives indicates that the assumption of 2 for the atomic H/C ratio of aliphatic structures is reasonable. For coal hydrogenation products, a value of 1.6–1.7 for the H/C ratio of aliphatic structures would be more reasonable.     

Application of Mechanochemical Activation and γ-Radiation to Increase the Reactivity of Coal from the Shubarkol Deposit in Hydrogenation

The results of the mechanochemical activation of coal from the Shubarkol deposit in an impactgrinding mill and under exposure to γ-radiation with an electron beam on a LU-6 electron accelerator are reported. It was established that, upon the hydrogenation of dispersed coal, the yields of both total liquid products and different distillate fractions increased. The maximum yields of liquid products (66.8%) and gasoline (12.8%) and diesel (18.5%) fractions were noted upon the hydrogenation of coal ground for 30 min. It was shown that the irradiation of coal with an electron beam (a dose of 150 kGy) increased its reactivity in the process of hydrogenation and also facilitated the formation of free radicals and changed the compounds of iron that are the constituents of the catalyst based on natural bauxite from the Turgai deposit.     

Rapid pyrolysis and hydropyrolysis of Canadian coals

A range of Canadian coals were subjected to variable heating-rate conditions in a variety of atmospheres. Heating rate was found to have little effect on total weight loss of the coal, but a dramatic effect on the actual composition of products. High heating rates substantially increased the yield of light hydrocarbons. Operation in ≈100 KPa (1 atm) H₂ at high heating rate resulted in 5% conversion to light hydrocarbon gas and liquid products. Operation in ≈10 MPa (100 atm) H₂ at a heating rate of 600 Ks^?1 gave 10% coal conversion to light liquid products (benzene, xylene, toluene).     

Composition and reactivity of coal from the Khoot deposit in Mongolia

The composition and reactivity characteristics of Khoot coal from Mongolia in the processes of pyrolysis, gasification, thermal dissolution, and the production of porous materials were determined. It was established that the coal is characterized by high activity in the reactions of destruction. In the process of semicoking, the yield of liquid tar was as high as 10%. Highly porous activated carbons with specific surface areas to 900 m²/g and high sorption capacities were obtained by the steam activation of carbonizates. To 60.8% liquid products at low gas formation can be obtained from the Khoot coal in the process of thermal dissolution in a hydrogen-donor solvent at 450°C without the use of hydrogen.     

Chemical structure of the high-molecular-weight hydrogenation products of coal from the Zashulanskoe field

The results of experimental studies on the determination of the chemical structure of asphaltenes and preasphaltenes in the liquid products of the hydrogenation of coal from the Zashulanskoe field in the Chita oblast. It was found that, in the preasphaltenes, the value of f _a and the concentrations of oxygen groups (OH, COOH, and C=O) were greater and the concentrations of CH₂ and CH₃ groups were smaller that those in the asphaltenes. The highest concentration of CH₂ groups was found in substances soluble in n-hexane (oils). It is likely that the change in the character of high-molecular-weight hydrogenation products formed from the structural fragments of the organic matter of coal (OMC) largely depended on reaction conditions, namely, the rate of heating and the isothermal exposure time.     

Hydrogenation of coal from transbaikalia deposits in the presence of a recirculating paste-forming agent

Data on the hydrogenation of coal from the Zashulanskoe field in Transbaikalia in three cycles in the presence of a recirculating coal distillate solvent with a boiling point of 300–425°C are reported. It was found that the degrees of conversion of the organic matter of coal (OMC) into liquid and gaseous products reached in the second and third cycles were 85–88%. The yields of liquid products and gases were 81–85 and 6.9–7.4%, respectively, and the consumption of hydrogen was 2.3–2.4%.     

Kinetic relationship of coal hydrogenation,pyrolysis and dissolution

Data are presented concerning the production of gaseous and liquid products from coal. The processes considered include pyrolysis, dissolution in solvent with and without the application of ultrasonic energy, batch hydrogenation, and continuous hydrogenation. The products are compared with respect to both quantity and type. Activation energies are presented and mechanisms discussed. Coal hydrogenation in the presence of an appropriate catalyst shows very great promise as a means of converting coal to liquid and gaseous fuels. Yields of 30% high octane gasoline, 5% diesel oil, 35% high Btu gas, and 30% char, on a weight basis, have been achieved.     

Process effects on the nature of coal liquefaction products

The products obtained by liquefaction of the same coal using four different processes are compared. The processes were dry hydrogenation (hydropyrolysis) in a short residence time semi-continuous reactor and in a rotating autoclave, and supercritical gas extraction using toluene with and without hydrogen assistance using an autoclave and a short residence time reactor. The temperature and pressure were the same for all the experiments and runs were carried out with and without catalysts. The liquid product from the rotating autoclave was more aromatic and contained less polar compounds than the product from the semi-continuous reactor. The asphaltenes from supercritical gas extraction were more aliphatic and of higher molecular weight than those obtained on dry hydrogenation. Solvent breakdown products had a considerable effect on the composition of the oil from supercritical gas extraction, and this breakdown was affected by the time that the solvent was maintained at temperature.     

Changes in vitroplast derived from a high-volatile bituminous coal during tetralin treatment

At an early stage in the hydrogenation of coal using tetralin, a thermoplastic material called vitroplast is formed from vitrinite as one of its primary products. Subsequent changes in the vitroplast depend on the physical and chemical conditions of the coal/solvent mixture: under favourable conditions vitroplast is converted to liquid and gas; otherwise it forms mesophase. Secondary vitroplast is formed, under certain conditions, from previously liquefied material by precipitation or thermal polymerization. In an autoclave, and probably also in a continuous hydrogenation reactor, interconversions between primary and secondary vitroplast, liquid and gaseous products and mesophase take place simultaneously, the overall reaction being the sum of the various reactions.