Nature of insoluble residues accumulated during hydrogenation of Victorian brown coals

The carbonaceous material and mineral matter in hydrogenation residues from two Victorian brown coals have been characterized. Preliminary data indicate that the mineral and inorganic content of the coal may be related to the formation of different types of carbonaceous solids. The minerals such as quartz, kaolinite and halite appear to be essentially unchanged by hydrogenation, whereas pyrite is reduced to pyrrhotite. Some iron carboxylate also reacts under hydrogenation conditions to form pyrrhotite. The type of carbonate species formed during hydrogenation depends on the distribution of exchangeable cations present in the coal and when high levels of Mg are present in addition to Ca, dolomite is the predominant carbonate phase.     

Effect of sulphur on coal liquefaction in the presence of dispersed iron or molybdenum catalysts

The effects of dispersed catalysts on coal liquefaction under hydrogen pressure were studied using small autoclaves. The catalysts were generated in situ by addition of elemental sulphur plus an oil-soluble carboxylic salt of either iron or molybdenum. Finely divided catalysts of relatively high activity were generated by this method. Residues isolated after liquefaction with added iron carboxylate and sulphur contained pyrrhotite, which is proposed to be the catalytically active species. The prime role of sulphur is to form pyrrhotite in combination with the iron. Addition of sulphur alone did not increase conversion. This method of catalyst preparation seems useful for further scientific study of the relationship between sulphur, metal sulphide catalysts and liquefaction activity.     

Dependence of coal liquefaction behaviour on coal characteristics. 8. Aspects of the phenomenology of the liquefaction of some coal

Steps are now being taken to define in more detail the phenomenology of coal liquefaction and to provide a scientific basis for empirical correlations previously established between liquefaction conversion and basic compositional characteristics of coals. The rates of production of oils, asphaltenes and preaphaltenes have been determined at four temperatures for three coals, two of Carboniferous and one of Creaceousage. Products are formed more slowly from the younger coal (which is of slightly lower rank) than from the others, but oxygen, partly as OH but probably mostly in a type of ether, is lost more rapidly. It is estimated that the maximum content of O as cleavable ether is 7.7 atoms/100 C atoms for the younger coal (from Wyoming) and 4.1 and 5.1 for the other two (from Oklahoma and Ohio, respectively). Until ≈ 50% of the amount present in the Oklahoma coal is lost, the rates of removal of oxygen and organic sulphur are approximately equal; beyond this level, the removal of S is more rapid. The loss of organic sulphur from the Ohio coal is slightly faster. Even so, the data do not support the idea that cleavage of thioethers is more rapid than that of ethers and that this is the basic reason why a high organic sulphur content tends to promote liquefaction. Conversion of the pyrite in the Ohio coal to pyrrhotite occurs considerably more rapidly than the pyrite in the Oklahoma coal. In preliminary experiments, it is shown that a curve-resolving programme allows two aromatic and five aliphatic C-H stretching vibrations to be distinguished in FTIR spectra of the hexane-insoluble products, and the distribution changes with degree of conversion. In particular, there is evidence that new aryl methyl are generated during liquefaction, in agreement with evidence from oxidation studies.     

Pyrite decomposition in fresh Blacksville No. 2 coal: Effect of additives

The Mössbauer effect has been used to study, under liquefaction conditions, the effect of additives (S, FeS₂, Fe₇S₈ and Fe) on the transformation of pyrite in fresh Blacksville No. 2 coal. It was observed that the addition of iron sulphides enhanced the conversion of the inherent pyrite in coal, an effect attributed to a combined cracking activity of the pyrrhotites and H₂S on the less reactive organic covering of some of the inherent coal pyrite. The addition of sulphur produced a higher partial pressure of H₂S; total conversion of pyrite to pyrrhotite was not observed. The stoichiometry of the pyrrhotites present in the residue of the experiment with sulphur showed a smaller atomic percentage of iron than in the experiment without additives, this change in stoichiometry being attributed to the higher partial pressure of H₂S in the reactor. When metallic iron was added, the partial pressure of H₂S in the reactor decreased (iron acts as a scavenger) and troilite was also formed.     

Hydrocracking of diphenylmethaneRoles of H2S, pyrrhotite and pyrite

This study presents the role of H₂S other than H-transfer catalyst in the hydrocracking of diphenylmethane with H₂–H₂S-pyrrhotite. The results indicate that the partial pressure of H₂S controls the conversion of pyrrhotite to FeS and FeS₂, which in turn is closely related to the promotional activity of pyrrhotite on the diphenylmethane conversion. Under higher H₂S overpressures, pyrite bands appear in the Mössbauer spectra providing proof of the reversibility of pyrite decomposition under liquefaction conditions. With lower H₂S pressures, low activity troilite forms from the pyrrhotite. An enhanced activity was observed for a partial pressure of H₂S, sufficient for the maintenance of a high iron deficient surface on the pyrrhotite particles. When the partial pressure was increased too much, the formation of FeS₂ was observed with a slight decrease in activity. FeS did not show as great an activity as the non-stoichiometric pyrrhotite.     

Mössbauer study of transformations of pyrite under conditions of coal liquefaction

The Mössbauer effect is used to study in-situ transformations of pyrite under conditions of coal liquefaction based on Illinois No. 6 coal from St. Clair County. A marked reduction is observed at high temperatures in the isomer shift of the iron sulphides during coal liquefactions. By contrast the pure sulphides do not show such a strong effect in the presence of solvent and hydrogen. This reduction in the isomer shift may result from covalent bonding between the iron on the pyrrhotite surfaces and the coalderived liquid and gases. Marked broadening of the linewidth of Fe_{1 ? x}S occurs above 300 °C in the presence of solvent and hydrogen. The stoichiometries of the pyrrhotites formed in the different runs were determined and a correlation was observed between the total amount of sulphur in the coal and the iron deficiency in Fe_{1 ? x}S. Coal-derived liquids are more active in enhancing pyrite decomposition than tetralin. Both H₂S and Fe_{1 ? x}S seem to be actively involved in the liquefaction process.     

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.     

Hydrocracking of diphenylmethane

This study presents the role of H₂S other than H-transfer catalyst in the hydrocracking of diphenylmethane with H₂–H₂S-pyrrhotite. The results indicate that the partial pressure of H₂S controls the conversion of pyrrhotite to FeS and FeS₂, which in turn is closely related to the promotional activity of pyrrhotite on the diphenylmethane conversion. Under higher H₂S overpressures, pyrite bands appear in the Mössbauer spectra providing proof of the reversibility of pyrite decomposition under liquefaction conditions. With lower H₂S pressures, low activity troilite forms from the pyrrhotite. An enhanced activity was observed for a partial pressure of H₂S, sufficient for the maintenance of a high iron deficient surface on the pyrrhotite particles. When the partial pressure was increased too much, the formation of FeS₂ was observed with a slight decrease in activity. FeS did not show as great an activity as the non-stoichiometric pyrrhotite.     

Study on industrial catalyst for bituminous coal liquefaction

The catalyst activities and the grinding characteristics of natural iron compounds and sulfides were investigated with the aim of preparing an industrial coal liquefaction catalyst for the NEDOL process large-scale plants. From the viewpoint of economy, since these plants are to be located at coal mining sites, it is economical to utilize a natural compound produced in the vicinity of plant site as the catalyst raw material. The coal liquefaction, using an electromagnetic agitation type autoclave, suggested that iron sulfide (pyrite) is the best raw material for the catalyst, because it contains higher iron and sulfur for producing pyrrhotite, an active component under the reacting conditions, and thereby, it needs no pollutant sulfur addition. However, taking into consideration the grinding characteristics, iron sulfide is not thought to have good grinding characteristics in a fine particle zone. Co-pulverization, using iron sulfide and coal, improves the grinding efficiency, the abrasion and the catalyst activities, so that the industrial catalyst preparation can be realized by means of the co-pulverization method.     

依兰煤液化过程中天然矿物催化剂影响的研究

研究了黑龙江依兰煤在加氢液化反应过程中,4种天然含铁矿物的液化催化活性.试验结果表明,黑龙江西林铅锌矿的黄铁矿在依兰煤的加氢液化过程中,催化活性最高,萃取油收率达到68%,蒸馏油收率达到58%.     

Effects of coal cleaning on the short contact time liquefaction of Illinois No. 6 coal

This study was carried out to determine the effect of coal cleaning by oil agglomeration and sink-float methods on yields from short contact time liquefaction of Illinois No. 6 coal. The runs were made in a continuous unit using SRC-II distillates as process solvent. Measured yields included hydrogen (consumption), hydrocarbon gas, distillate oil, SRC (the pyridine-soluble portion of the residue) and insoluble organic matter, the pyridine-insoluble organic residue. The solubility of product SRC in hexane, toluene and pyridine was also determined. The principal finding was that coal cleaning by density methods reduced the yield of IOM obtained in subsequent liquefaction and this is attributed to the removal of inert components from the feed coal. In addition, cleaning which significantly reduced pyrite content of the feed coal also reduced the yield of distillate oil and tended to give a less soluble SRC during liquefaction. Deep cleaning by gravity methods gave the lowest IOM, but reduced pyrite content to the point where distillate oil was consumed rather than produced. Oil agglomeration reduced total ash to 50% of that in the run-of-mine coal, but left the pyrite level in the coal high. The relevance of these results to two-stage liquefaction is discussed.     

Effect of additives on the stoichiometry of iron sulphides formed during liquefaction of a Powhatan No. 5 coal

Transformations of pyrite in a Powhatan No. 5 is studied using Mössbauer spectroscopy. Stoichiometry of the resultant pyrrhotites is shown to be influenced by the H₂S partial pressure in the reactor. Higher H₂S partial pressure yields pyrrhotites with more iron deficiency. Variation in the H₂S partial pressure is achieved through the addition of either pyrite, troilite or pyrrhotite. It is also shown that pyrrhotites having the same average at% Fe may have widely differing vacancy distribution on the Fe sites.     

Behaviour of pyrite during hydrogenation of graphite at atmospheric pressure

The pyrite behaviour during hydrogenation of graphite is investigated. Kinetic experiments were carried out using thermogravimetry. The solid burn up residue was examined by SEM, and by X-Ray and electronic diffraction. The results show how graphite hydrogenation at temperatures lower than 1000 °C can be achieved in the presence of metallic iron obtained from pyrite. Pyrite, or its reduced form pyrrhotite, appears to have no catalytic behaviour during hydrogenation of graphite.     

Mössbauer spectroscopic studies of the mineralogical changes in coal as a function of cleaning,pyrolysis, combustion and coalconversion processes

The mineralogical changes in a Perry County, Illinois coal from the Herrin (No. 6) Member due to cleaning, pyrolysis, combustion, and coal-conversion processes were studied. Mössbauer spectroscopy was used in tandem with X-ray diffraction to follow the changes in the forms of iron originally present in the coal resulting from processing. The chemistry of the pyrite conversion is less complex than expected. Iron does not become uniformly distributed in all possible minerals but tends to form simple products. Pyrrhotites along with spinel and hydrated ferrous sulphates are the primary mineral products found in coat liquefaction and pyrolysis process residues; while mullite, ferrous silicates and the iron oxides (hematite, geothite and magnetite) are the most abundant mineral products found in Lurgi gasification and power plant fly ashes. The detailed distribution of iron, however, is dependent upon conditions in the particular process equipment in which the coal is used and the conversion process in which it is used.     

准东煤燃烧中矿物质转化行为的CCSEM研究

在沉降炉中进行了准东煤的燃烧实验,利用计算机控制扫描电镜技术(computer controlled scanning electron microscopy,CCSEM)研究了煤中矿物质的转化行为。研究表明煤中主要矿物为方解石、高岭石、含铁类物质以及未分类矿物,燃烧后灰中石英、铁的氧化物、白云石的含量急剧增加,未分类矿物和方解石的含量下降。同时对3种重要致渣元素Na、Fe、Ca在燃烧前后的矿物转化行为及颗粒粒径分布进行了详细研究。     

Iron-sulfide crystals in probe deposits

Iron-sulfides were observed in deposits collected on a probe inserted at the top of the furnace of a coal-fired power station in Denmark. The chemical composition of the iron-sulfides is equivalent to pyrrhotite (FeS). The pyrrhotites are present as crystals and, based on the shape of the crystals, it was deduced that they were not deposited but instead grew within the deposit. The presence of unburned char particles within the deposits supports the concept that a reducing environment existed in the deposits. Two processes are proposed for explaining the existence of pyrrhotite crystals within a deposit: (1) impact of low viscous droplets of iron sulfide; and (2) sulfur diffusion. Previous research on the influence of pyrite on slagging focused on the decomposition of pyrite into pyrrhotite and especially on the oxidation stage of this product during impact on the heat transfer surfaces. This research shows that the influence of pyrite and its derivatives is also strongly controlled by the flue gas composition in the deposits.     

Mössbauer study of the thermal decomposition of FeS2 in coal

The Mössbauer effect has been used to study the transformations of FeS₂ in four different coals: IL No. 6, Ky $\text{9}\text{14}$, Blacksville No. 2, and Powhatan No. 5. The transformations of FeS₂ in the coals were studied in an inert atmosphere. It was observed that the pyrrhotites formed from FeS₂ have a considerable reduction in the isomer shift at 440 °C as compared to the values obtained in the absence of coal. This effect is associated with the interaction of the pyrrhotites with the coal constituents at high temperatures. There is also a significant line-broadening at 440 °C. This broadening is due either to vacancy motion in the iron sulphides and/or to motional broadening due to particle motion in the coal-derived liquids. The percentage conversion of pyrite to pyrrhotite depends markedly on time as well as type of coal. The weathering of the coal has a detrimental effect on the rate of conversion of pyrite to pyrrhotite. The ferrous sulphate layers covering the pyrite particles hinder the removal of sulphur from that surface. The major factor affecting the $\text{Fe}\text{S}$ ratio is the total amount of sulphur available for H₂S formation. Partial H₂S pressure is the crucial quantity controlling the stoichiometry of the pyrrhotites. Hence, a high percentage of H₂S in the reactor at high temperature will assure the formation of pyrrhotites with a high number of metal vacancies.     

Catalytic effects of iron compounds and the role of sulfur in coal liquefaction and hydrogenolysis of SRC

Effective iron catalysts in coal liquefaction have been explored. Reduced Fe, Fe(CO)₅, and ferrocene have shown a considerably high catalytic activity in the liquefaction of Yallourn coal at 400°C. Degree of reduction has been shown to be one of the most important factors determining the catalytic activity of the iron catalyst. In the hydrogenolysis of SRC derived from Wandoan coal, water formed in situ has been shown to exhibit a negative effect due to reoxidation of the iron catalyst, but addition of elemental sulfur is greatly effective in preventing such deleterious influence of water. This can be interpreted on the basis of the sulfidation of reduced Fe by elemental sulfur, competing with reoxidation of the iron catalyst by water. In the systems with elemental sulfur, active and oxidation-proof pyrrhotite is formed, and the degree of reduction of the remaining iron oxide is maintained higher than that in the absence of elemental sulfur.     

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.     

Mössbauer investigation of the transformations of the iron minerals in oil shale during retorting

Iron phases in raw and retorted shales have been studied from the TOSCO II, Paraho, and Lawrence Livermore Laboratory (LLL) 125 kg retorting processes by Mössbauer effect spectroscopy. Using the Mössbauer effect, changes in the iron mineralogy during retorting were monitored. Results show that the pyrite fraction in the TOSCO II, and LLL hydrogen run S-9 samples underwent changes during retorting whereas the iron-containing carbonates did not. As in other pyrolysis processes, FeS₂ breakdown is affected by the presence of organic matter. Hydrogen released by the indigenous kerogen acts to reduce pyrite to the magnetic sulphide pyrrhotite. In all of the retorts containing oxygen, carbonate breakdown was observed prior to pyrite oxidation. Free oxygen is introduced to several retorts. The iron minerals within these systems eventually become a mixture of the oxides hematite and magnetite. This study demonstrates that alteration of specific iron minerals during retorting may be controlled by varying the internal retorting conditions.