Pyrite liquefaction

The Effect of Mineral Matters on the Decomposition Ethers. Recently, the effect of mineral matters of coal on the coal liquefaction has received much attention. It was shown that small amounts of FeS or pyrite are responsible for the hydro-genative liquefaction of coal. Therefore, it is interesting to elucidate the effect of mineral matters of coal on the decomposition rate and products of aromatic ethers, and so three diaryl ethers were thermally treated in the presence of coal ash obtained by low temperature combustion of Illinois No.6 coal at about 200°C with ozone containing oxygen. 

The present authors identified an optimal mixture of solvents for catalytic liquefaction in presence of pyrite. Figure 10 shows the influences of solvent composition (4HF1/Py) on the liquefaction of Morwell coal in an autoclave... 

It is generally appreciated that the mineral matter associated with some coals may act as a catalyst for liquefaction. A common observation is that among bituminous coals from the eastern United States, those with a relatively high mineral matter content also provide relatively high liquefaction yields. Also, addition of coal-derived mineral matter increases the liquefaction yields from those coals with low mineral matter content. The involvement of pyrite in these effects has been fairly well established. The importance of clay and/or other minerals is less well defined. 

Figures 2 and 3 contain yield curves for naphthalene and 1-methylindan as a function of reaction time for tetralin and tetralin plus coal, pyrite, or asphaltene. The asphaltene was a homogenized mixture of several samples isolated from coal liquefaction products during other work in our laboratory (9). This asphaltene sample contained essentially a negligible ash content (<0.1%). Therefore, it contains many organic structures similiar to those found in coal, but unlike coal, its reactions will be free of any complicating factors due to mineral matter. The yields of naphthalene and 1-methylindan are greater in the presence of asphaltene than in its absence, although not quite as high as in the presence of coal. This is additional evidence that these two products arise mainly from reactions associated with the presence of the organic portion of coaly matter. These reactions are quite likely free radical in nature.

These studies have shown that a variety of reactions are promoted when either organic matter from coal or mineral matter from coal, principally pyrite, is heated to liquefaction temperature with tetralin. However, when just pyrrhotite is heated with tetralin, only dehydrogenation is catalyzed. Thus, in order to evaluate the effects of iron sulfides, it is of critical importance to separate their actions as reactants from their actions that are truly catalytic in nature. 

The strategies used in studies of high temperature reactions of metals have been brought to bear on some of the problems associated with the direct liquefaction of coaL Many coals contain sulfur, combined in both organic and inorganic forms, in excess of amounts allowable under current combustion standards. In some coals much of the sulfur is in the form of pyrite, Fe 2> which may, paradoxically, serve as a catalyst or the precursor of a catalyst for the liquefaction process. The information available for the Fe-S-O-H system has been assembled in an attempt to provide a framework for interpreting experimental results, and to facilitate the planning of further experim ents. 

Phase Diagrams. The phase diagrams shown in Figures 2A-2E display the stability regions of iron, the iron oxides, pyrite and the pyrrhotites, and will assist in interpreting the significance of the form of pyrrhotite observed in coal liquefaction experiments. 

If the reactor zones were superimposed on Figure 6 or 7, and the comers were to be linked up through the diagram, it seems relatively clear that one or another of the pyrrhotites would be the principal iron-containing reaction product of pyrite throughout the coal liquefaction range of temperatures and reaction conditions. 

Although SRC-II was basically a thermal liquefaction process, it was most successful using bituminous coals with a high native pyrite content. Iron sulfides are well known to have catalytic properties for coal liquefaction. Recycling part of the ash-minerals-containing bottoms had two beneficial effects (1) it increased the pyrite concentration in the reactor feed, and (2) it increased the residence time for heavy components, thus giving them more time to hydrocrack to distillate products. A block flow diagram of the SRC-II process is shown in Fig. 19.19. 

Coal cleaning, which involves the separation of some of the ash from the coal prior to liquefaction, can yield several benefits. Primarily, it reduces the load on the solid-liquid separator, thereby reducing the amount of organic material rejected with the ash. Other benefits include the reduction of wear on plant components and better utilization of reactor volume. However, removal of mineral matter prior to reaction may eliminate beneficial catalytic effects that coal minerals, particularly iron pyrite, provide. 

NEDOL [New Energy Development Organization Liquefaction] A coal liquefaction process in development in Japan by the New Energy and Industrial Technology Development Organization (NEDO), Tokyo. Crushed coal is mixed with a pyrite catalyst and slurried in a hydrogenated heavy oil. Liquefaction takes place at 450°C, 170 bar. The overall oil yield is 59%. The used solvent is hydrogenated and recycled. Piloted in Kashima, Japan, in 1997 to 1998. Two Chinese companies were licensed to build test units in 2006. 

Coal ash is not always a deleterious material for a process. In coal liquefaction, it has been observed that the rate is increased in the presence of pyrite. In gasification, the rate is increased in the presence of alkalies. There is limited data available on the effects of materials on combustion. Although interest in synthetic fuels from coal is quite limited at present, there is an interest in developing the technical capability to permit the production of more premium fuel types from less desirable ones. The conversion of solid coal to liquid fuels has been a very demanding process in terms of the pressures and, to some extent, the temperatures that have been used. Catalysts have been required in all cases. The catalysts have been poisoned by the sulfur and other species in the mineral matter. As a result, catalyst costs and replacement rates can be quite high. A cheap, naturally occurring catalyst that came with the coal would be of significant interest. Pyrite seems to be such a material. 

Liquefaction. Montano et al. [ ] have investigated the transformation of pyrite to pyrrhotite in coal liquefaction environments. They conducted in situ Mossbauer spectroscopy measurements on coals maintained at 1.24 MPa nitrogen pressure and observed changes in the isomer shift at approximately 300°C that signalled the beginning of the transformation of pyrite to pyrrhotite. The transformation accelerated between 300 and 400°C, and from 20 to 80 percent of the pyrite in four different coals was transformed after one hour at 440°C. From examination of both the in situ spectra and the spectra of cooled residues, they concluded that the pyrrhotite underwent covalent bonding to the coal molecules, causing a catalytic effect on coal liquefaction. 

The specific role of pyrite (FeS2) as a catalyst has been under investigation since pyrite was identified as the most active inherent mineral for coal liquefaction. Under liquefaction conditions, FeS2 is transformed into a nonstoichiometric iron sulfide, Fei-x (0 X 0.125). Thomas et al. (15) studied the kinetics of this decomposition under coal liquefaction conditions, and concluded that the catalytic activity of FeS2 is associated with radical initiation resulting from the... 

Stohl and Granoff (18) investigated the effects of pyrite particle sizes, pyrite defects and surface areas on coal liquefaction. They observed no effect due to surface area and concluded that the observed particle size effect was due to diffusional limitations in the transformation of pyrite to pyrrhotite. 

Pyrite has been shown to catalyze the hydrogenation of quinoline to tetrahydroquinoline (THQ) at 325°C and a 30 minute residence time (19). It has been known that THQ is a good hydrogen donor solvent for coal liquefaction (13). In experiments with Kentucky coal and quinoline, it was found that pyrite was required to maintain a sufficient concentration of THQ and prevent retrogressive reactions (19). It appears, therefore, that pyrite catalyzes the in situ regeneration of hydrogen donors, and allows more efficient hydrogen uptake from the gas phase to the solvent at lower temperatures than would be possible in the absence of pyrite. 

Mineral matter has been known to enhance the conversion of coal to liquid products (1,2,3). Addition of pyrite, pyrrhotite, and liquefaction residues ( ) to coal has been shown to affect the coal conversion yields and the viscosity of the products (5.). Of all the minerals present in coal, pyrite (and marcasite) are the most important for coal utilization, especially in direct coal liquefaction (1,5). However, one has to remember that under coal liquefaction conditions pyrite rapidly transforms to a nonstoichiometric iron sulfide Fe S(0 x 0.125). It is noted that the sulfur formed as a result of the decomposition of pyrite is able to extract hydrogen from poor donor solvents. The stoichiometry of the pyrrhotite formed from FeSp depends strongly on the partial pressure of H S. 

The fate of pyrite in coal has been the subject of a number of publications, particularly in the area of liquefaction, where pyrite or its products are thought to play an important catalytic role (2). In a previous publication (3) it was reported that the decomposition of pyrite to pyrrhotite occurred in the temperature range 500-550°C for a run-of-mine(ROM) Prince coal. This was within the range of 440-580°C reported by other workers for the decomposition of pyrite in coal (4,5). The current work extends the previous study to three washed coals and includes some preliminary work on magnetic separation. 

The NiMo catalyst supported on nanoporous CB was compared with the commercial NiMo/Al203 catalyst and synthetic pyrite during the two-stage liquefaction of several coals.In this study the eifect of the tetralin/coal ratio on the yield of oil was the focus of attention. As expected, the yield of oil decreased with the decreasing tetralin/coal ratio. However, in every case, the NiMo/CB catalyst was the most active. Thus, even in the absence of tetralin, the yield of oil reached 52 and 64% after the first and second stage, respectively. Moreover, the 373 to 573 K fraction was the largest in the oil product obtained using the NiMo/CB catalyst. 

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