Coal liquefaction catalysis: Iron pyrite and hydrogen sulphide

An unreactive hvC bituminous coal has been hydrogenated in a batch-stirred reactor using pyrite, hydrogen sulphide, and pyrite+hydrogen sulphide as catalysts. The data indicate that H₂S is an active homogeneous catalyst for coal liquefaction, and suggest that pyrite may be acting indirectly as a catalytic agent via H₂S release.     

The effects of iron sulphide surface area variations on coal liquefaction

The purpose of this work was to determine the effects of surface area variations of iron sulphides on coal liquefaction. Several iron sulphides were synthesized including pyrites (FeS₂) with 46.6 wt% Fe, pyrrhotites (Fe_1?xS) with ~ 60 wt% Fe and iron-sulphur compounds of unknown composition. Surface areas of the synthetic pyrites varied from 2 to ? 10 m² g^?1, pyrrhotite surface areas were 6 and 10 m² g^?1, and the surface areas of the iron-sulphur compounds were 40 and 80 m² g^?1. These iron sulphides were tested for catalytic activity in tubing reactor runs with West Virginia Blacksville no. 2 coal and SRC-II heavy distillate. All these sulphides showed catalytic effects as compared to runs with only coal and solvent, although the effects were not as large as those obtained with a cobalt-molybdenum on alumina catalyst. Large differences in surface areas before reactor testing did not cause any significant differences in conversion. The results from an additional series of tubing reactor runs, which was carried out to determine how iron sulphide surface areas change during liquefaction, showed that the surface areas were drastically changed during the two-minute heat-up of the reactor. Robena pyrite with a surface area of 2.0 m² g^?1 and the iron-sulphur compound with a surface area of 80 m² g^?1 yielded iron sulphides with surface areas of 5.2 and 10.8 m² g^?1 after a two-minute heat-up to 425°C and subsequent one-minute quench.     

Coal liquefaction using iron complexes as catalysts

Hydroliquefaction of Japanese Miike and Taiheiyo coals was carried out using various iron complexes as catalysts in tetralin at 375–445 °C. Iron pentacarbonyl (Fe(CO)₅) showed the highest catalytic activity, increasing coal conversion by about 10% at 425 °C under an initial hydrogen pressure of 5 MPa. Amounts of hydrogen transferred to coal increased from 1.4–2.3 wt% of daf coal in the absence of the catalyst to 2.5–4.2 wt% of daf coal in the presence of Fe(CO)₅ at 425 °C.     

Coal liquefaction induced by hydrogen atoms

Reactions between coals and hydrogen atoms were studied using a discharge flow apparatus at temperatures ranging from 403 to 523 K under 133 Pa pressure. Australian brown coal (Yallourn) and Japanese subbituminous coal (Taiheiyo) both yielded liquid hydrocarbons of similar composition. In contrast to conventional coal liquefaction, the present system led to the formation of exhaustively hydrogenated products composed mainly of monocyclic alkanes.     

Coal liquefaction model: microscopic examination of solids from metal halide catalysed coal hydrogenation experiments

Coal undergoes changes during the hydrogenation process which depend on the balance between carbonization and hydrogenation reactions, which in turn depend on various experimental conditions, i.e. hydrogen availability, heating rate etc. If carbonization conditions prevail, semicoke is formed, whereas liquid hydrocarbons are formed under hydrogenation conditions. This model is applicable to hydrogenation reactions carried out under a wide range of experimental conditions.     

Alternative interpretation of coal liquefaction catalysis by pyrite

Many authors have asserted that pyrite is a catalyst for the hydroliquefaction of coal. Catalysis by such a low surface area substance, which is not regenerated, seems doubtful. Evidence is presented suggesting that the H₂S, produced from pyrite decomposition, is responsible for the observed catalytic effects.     

Coal liquefaction using ore catalysts

Ores and ore concentrates containing minerals of Co, Mo, Ni, Fe, and other potentially active metals have been investigated as slurry catalysts for liquefaction of Blacksville mine, Pittsburgh seam, bituminous coal. The tests were conducted batchwise in a stirred autoclave for 30 min at 425°C and 13.79 MPa (2000 psig) hydrogen pressure according to a two-cycle scheme. In the first cycle, the reaction charge consisted of ground coal, catalyst, hydrogen, and SRC-II heavy distillate. The product of the first cycle was hot-filtered, and the liquid product served as a vehicle for the second cycle, which was otherwise run identically to the first. Reaction products from each cycle were analysed to determine conversion of coal, yield of liquids, liquid product viscosity, and group type (preasphaltene, asphaltene, and oil). Mixtures of ores containing iron pyrites and minerals containing other catalytically active transition metals were compared to pyrites alone and to a pulverized supported Co-Mo-alumina catalyst. An ore catalyst containing both Fe and Ni was superior to another that contained an equivalent mass of iron alone. The best ore catalysts tested, in terms of high liquid yields and low product viscosities, were mixtures of pyrites and molybdenum- and cobalt-containing ores. The latter yielded results that approached those obtained with an equivalent mass of cobalt and molybdenum on an alumina support.     

Coal liquefaction by the hydrogen produced from methanol

Methanol was used as an in-situ hydrogen source, following its decomposition over ZnO-Cr₂O₃, for the hydrogenation of coal. The reaction was carried out in a high pressure autoclave at ≈400–440 °C, in the presence of different hydrogenation catalysts. Stabilized nickel, stabilized Co and Ni-Cr-Cu catalysts gave excellent results. The maximum conversion was 100% for pyridine, 94.4% for benzene and 66.2% for straight-chain hexane.     

Coal liquefaction in nitrogen compounds

Model compound studies have shown that 1,2,3,4-tetrahydroquinoline is an exceptionally good coal solvent. In the pure compound, subbituminous coal conversion to THF-soluble products approaches 100% under relatively mild reaction conditions. The effectiveness of tetrahydroquinoline for coal conversion appears to be related to its concentration relative to coal. The unique behaviour of tetrahydroquinoline is ascribed to its being a highly active H-donor; the fact that it is regenerable under reaction conditions by the reaction of hydrogen and quinoline; and that its polarity allows penetration of the coal structure and aids in dispersion of the dissolved coal. It has been found that, during reaction with coal, tetrahydroquinoline and other nitrogen compounds undergo extensive condensation reactions which result in an increase in the nitrogen content of the high boiling and non-distillable liquefaction products.     

煤的直接加氢液化工艺

提出中国搞煤液化的必要性,介绍了煤液化的方法,重点对目前世界上较先进成熟的煤直接液化技术的工艺特点进行了总结和比较,提出了综合利用煤直接和氢液化技术炼油的可行性方案。     

Coal liquefaction in lignin-derived liquids under low severity conditions

It is found that lignin-derived liquids when reacted with coal under mild reaction conditions (375 °C and 2.17 × 10⁶ − 3.55 × 10⁶ N m⁻¹) enhance the rate of coal depolymerization. Up to 30% enhancement in coal conversion rate is achieved using lignin-derived liquids. The influence of time of reaction and temperature on the degree of reaction was investigated. The lignin liquid-assisted coal depolymerization products (liquid) are observed to contain a significant amount of the desirable pentane-soluble fraction. Influence of the time of storage of lignin-derived liquids on coal conversion was also determined. Also reported are data on elemental analyses of the solid and liquid products. The liquid product analyses using n.m.r. and s.e.c. techniques are also presented. Based upon the experimental data collected, it is hypothesized that enhancement in coal depolymerization rate can be explained by a reaction pathway involving intermediates formed from lignin-derived lignin liquids. A mathematical model describing the reaction chemistry has been developed. Computed rate constants are also reported. The analysis indicates that the lignin-derived intermediates are short-lived as compared to the time needed for complete coal depolymerization.     

Effects of catalyst and vehicle in coal liquefaction

Experiments have been carried out, using a semi-batch reactor equipped with a consecutive sampling device, to clarify the effects of catalysts and vehicles in the coal liquefaction process. The results show that a vehicle has a significant effect during preheating, unlike a catalyst which is not effective at this stage. A catalyst is more effective in promoting liquefaction under reaction conditions of 450°C and ≈ 20 MPa than is a vehicle. A vehicle higher in hydrogen donation increases the yield of oil even if a catalyst is present, providing a multiplier effect. In the development of a direct coal liquefaction process, therefore, selection of a vehicle is as important as that of a catalyst.     

Reduction of iron sulphates during coal liquefaction

The transformation of pyrite to pyrrhotite and gypsum to anhydrite is well known during coal liquefaction. Most coals, except extremely fresh ones, contain various iron sulphates resulting from the oxidation of pyrite and marcasite. The reduction of iron sulphates to pyrrhotite during liquefaction is shown with the degree of reduction being temperature dependent. The formation of pyrrhotite from the iron sulphates is important because pyrrhotite is considered to catalyse hydrogénation reactions.     

Catalysis of coal hydroliquefaction by synthetic iron catalysts

The following synthetic iron catalyst precursors were investigated: FeOOH and FeOOH-Al₂O₃ (90:10 wt%) co-precipitated by ammonia, washed and dried either in an oven or by spray-drying, and Fe₂O₃ prepared by flame decomposition of FeCl₃ in the gas phase. These catalyst precursors were sulphided in situ by CS₂ during the hydroliquefaction of a highly volatile bituminous coal. An increasing catalytic activity of the iron sulphide was observed as its particle size decreases down to a very low value (0.05 μm), compared to 2–3 μm and to ? 5 μm. Al₂O₃ did not act as an efficient promoter, even if it gives rise to a decrease of the iron sulphide crystallite size. Diffusional limitations and/or plugging by carbonaceous or mineral solids could result in a low efficiency of the iron sulphide crystallites which lie inside one iron catalyst particle. The above cited flame method, allowing the preparation of pure or doped Fe₂O₃ with particle size even less than 0.05 μm, is worthwhile for further work in coal hydroliquefaction catalysis, where the catalyst acts as Fe_1?xS.     

Pyrite-catalysed coal liquefaction using quinoline/tetrahydroquinoline as an H-donor system

Pyrite catalyses the hydrogénation of the N-containing ring in quinoline (Q) to form the active H-donor, 1,2,3,4-tetrahydroquinoline, (THQ). THQ is shown to dissolve coal readily at 325 °C, a temperature lower than that commonly used in most liquefaction processes. Pyrite is effective for maintaining the H-donor capacity of the solvent by hydrogenating the Q formed after H-donation, thereby providing the high THQ/Q required for sustained operation. Qualitative observations suggest that some source of hydrogen, either molecular or donor, must be present to prevent retrogressive reactions of coal fragments.     

Kinetics and reaction scheme of coal liquefaction over molten tin catalyst

Rates of formation of gases, oils, asphaltenes and preasphaltenes during non-solvent liquefaction of coal over molten tin catalyst have been measured. A probable reaction scheme and the rate constants for the pathways comprising the scheme have been presented. The results show that the catalyst greatly accelerates the conversion of preasphaltenes to asphaltenes. It also accelerates two other reactions, i.e., coal to preasphaltenes and coal to asphaltenes. By contrast, the catalyst does little to promote gasification and formation of oils.     

Organic titanium in coal and the deposition of titanium on direct liquefaction catalysts: An alternative view

Evidence for the presence of soluble organic titanium species in coals and coal-derived materials was sought by the application of dialysis procedures. Dialysates prepared from a heavy direct liquefaction product, an SRC-1, and extracts of the corresponding feed coals contained < 2 ppm titanium. A series of model organic titanium compounds traversed the dialysis membrane at a rate similar to that of the direct liquefaction product. The membrane was also permeable to porphyrinic metals of the type existing in petroleum crudes. These results suggest that mechanisms for the deposition of titanium on coal liquefaction catalysts that do not involve the postulation of significant concentrations of organic titanium species should be considered. A mechanism based upon the deposition of inorganic titanium in microparticulate or colloidal form is consistent with recent findings on the distribution of inorganic titanium in coals, the behaviour of titanium under liquefaction conditions, and the observed deposition on spent catalyst.     

Coal liquefaction solvents: 1. Methods of separation; characterization by chromatography and spectrometry

N.m.r. spectral assignments were carried out for major component identification in liquefaction solvents. Fractionation, n.m.r. and capillary g.c. were applied to analysis of anthracene oils and an SRC middle distillate. Commercial anthracene oils were found to vary widely in composition. Alkane contents ranged from 2–3%, greatly influencing solvent stability, performance and liquefaction yields at 460 °C.     

Coal liquefaction using indene-tetralin and indene-decalin mixtures as solvent

Indene-tetralin and indene-decalin mixtures were used as the solvent for coal liquefaction. The effect of mixing on conversion for Yallourn coal was observed under nitrogen pressure at 400 and 440 °C. Conversion to benzene-soluble material in an indene-decalin mixture (50:50, wt) at 440 °C for 1 h was 73.0% and was only 9% lower than that in 100% tetralin. The reaction of indene with tetralin or decalin may provide the active species for coal dissolution. Simultaneously, coal radicals may be scavenged by indene.     

Coal liquefaction by in-situ hydrogen generation.: 1. Zinc-water-coal reaction

Liquefaction of coal was carried out in a zinc—water—solvent system to give a product with high concentration of pyridine and benzene solubles. In this system the metal reacts with water to produce the corresponding metal oxide and hydrogen. This hydrogen was used for in-situ hydrogenation of coal. The effects of reaction time, temperature, type of solvent, the quantity of metal used and the rank of coal were investigated. The solvent has a very marked effect on the conversion of coal to benzene-soluble materials, especially at short reaction times. A maximum benzene conversion of 96% for Taiheiyo coal was obtained when it was treated at 445 °C for 1 h using wash oil as solvent. With regard to the influence of coal rank it was found that low rank coals were more reactive than high rank coals. The amount of preasphaltene is only slightly influenced by coal rank but depends on the temperature and the type of solvent used.