Role in coal liquefaction

In recent years, it has been realized that mineral matter plays an important role in coal liquefaction (9-11), similar to the role of the added catalyst in the Bergius process. Several experimental techniques have been used to study the effects of minerals on coal liquefaction and to identify the specific catalytic phase (12). Most studies (12-14) strongly imply that the iron sulfides are the roost active species, and the other minerals appear to have little effect on enhancement of liquid yield or quality. 

An Isotopic Study of the Role of a Donor Solvent in Coal Liquefaction... 

Fundamental studies of coal liquefaction have shown that the structure of solvent molecules can determine the nature of liquid yields that result at any particular set of reaction conditions. One approach to understanding coal liquefaction chemistry is to use well-defined solvents or to study reactions of solvents with pure compounds which may represent bond-types that are likely present in coal [1,2]. It is postulated that one of the major routes in coal liquefaction is initiation by thermal activation to form free radicals which abstract hydrogen from any readily available source. The solvent may, therefore, function as a direct source of hydrogen (donor), indirect source of hydrogen (hydrogen-transfer agent), or may directly react with the coal (adduction). The actual role of solvent thus becomes a significant parameter. 

The difficult task of examining the role of catalysis in coal liquefaction has been taken on by Mochida and Sakanishi. They show the catalytic requirements in various stages of coal conversion and the many complex interactions of the catalyst with coal constituents. They also point out directions for future catalysis research needed for more economical coal liquefaction, a commendable feature for processes requiring a long lead time. 

In coal liquefaction, highly dispersed, disposable, catalysts are needed because maximal contact between coal and catalysts is essential. It is assumed that one of the roles of the coal liquefaction catalyst is to assist in the rehydrogenation of the donor solvent (e.g. tetralin) by facilitating the hydrogen transfer from the gas phase.36,37... 

Derbyshire, F. J., Role of Catalysis in Coal Liquefaction Research and Development, Energy and Fuels, 3, 273-277 (1989). 

Characterization of the stable radicals present in coals, pyrolyzed coals, and liquefaction and other coal conversion products is a necessary first step toward elucidating the role of radicals in coal liquefaction. Electron... 

Because of the importance of coal as a major source of energy and the environmental hazards involved in its use, considerable research has become necessary in order to understand fully the different compounds appearing in the coal and their transformation during processing and to know how those compounds contribute to the pollution of the environment, i.e., acidity of water streams near the coal mines and pollution by power plants. Some positive properties can be associated with the mineral matter in coal. For example, recently several researchers have shown that the mineral matter in the coal may play an important role in the liquefaction process (i). Of all the minerals in the coal, the iron-bearing minerals seem... 

There are reports in which coal rank has been correlated with the extent of the catalytic Uqnefaction under batch conditions. Thus, while several of the correlations are questionable, there does appear to be a maximum with high-volatile C bituminous coal. However, the ability of coal to undergo liquefaction appears to correlate much more closely with maceral content than with coal rank. For example, vitrinite (Chapter 4) has been found to play a significant role in the liquefaction of coal and an almost linear relationship has been reported to exist between the percent conversion to liquid products and the vitrinite content. 

In preceding sections, fundamental coal chemistry, liquefaction mechanisms, solvent and catalyst characteristics were summarized briefly. In the following three sections, the roles and improvements in solvents and catalysts in multistage liquefaction processes are reviewed in more detail on the basis of recent progress in this area. 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

Apart from the need to fractionate residuum-containing fossil fuels for the measurement and prediction of thermophysical properties, other important problems could be resolved better through the study of residuum pseudocomponents. Two examples in the area of coal liquefaction are the role of... 

While many studies indicate that pyrrhotites are probably involved in the liquefaction process, the exact mechanism by which pyrrhotite catalyzes the conversion of coal to oil is not clear. Based on the works of Thomas et al. (1 ) and Derbyshire et al., (13) one can suggest that a possible role of pyrrhotite is as a hydrogenation catalyst. However, more work is necessary on the surface properties of the pyrrhotites and the interaction with model compounds before a definite catalytic mechanism can be proposed. 

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. 

Drs. Seehra and Ibrahim summarize recent advances in the important analytical tool of electron spin resonance, particularly as it is used in the direct catalytic liquefaction of coal. This tool is especially important because it can now be used in situ. There is some question about the role of free radicals in direct liquefaction, and the authors explore this subject. 

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