Hydrogen coals, dependence

A severely weathered bituminous coal from eastern Canada was treated by thermal hydrogenation under various reactor conditions. The coking properties of this coal were found to be restored under appropriate hydrogenation conditions. The semi-coke of the hydrogenated coal exhibited an anisotropic coke structure. The size of the anisotropic domains in the semi-coke was found to depend on reactor temperature and hydrogen pressure during hydrogenation. 

Results and Discussion. In dilute-phase hydrogasification, the composition of the effluent gas is determined by the feed gas rate and composition and the gas yield. The feed gas rate and composition can be selected somewhat freely, but the gas yield depends on many variables, some of which interact. The most prominent variables are coal rate, hydrogen coal ratio, maximum temperature attained by the solids and the vapors, residence times of the solids and the vapors, total pressure, hydrogen partial pressure, particle size and density, gas viscosity, heat... 

Coal hydrogenation to produce motor fuels is not as yet economical, even after allowing credit for various by-product chemicals such as phencd, cresols, xylenols, toluene, xylenes, naphthalene, and liquified hydrocarbon gases. The immediate future of coal hydrogenation probably depends on the recent developments such as those of Union Carbide Chemicals Com-paiQT toward the production of hi yields of chemicals, although a large proportion of these consists of complex structures that are not well-known. 

With these processes, hydrogen can be extracted from all hydrocarbons as well as coal. The cost of hydrogen strongly depends on the cost of the basic material. The quotient of this raw material price and the utilization rate of the production process represents the lower limit for the price of hydrogen. Cost of capital and operating costs have to be considered as well (Fig. 1.3). 

The distribution of liquids produced from coal depends on the character of the coal and on the process conditions and, particularly, on the degree of hydrogen addition to the coal (Aczel et al., 1978 Schiller, 1978 Schwager et al., 1978 Wooton et al., 1978 Whitehurst et al., 1980 Kershaw, 1989c). Nevertheless, it is in this area that mass spectrometry has proved to be extremely useful, providing valuable evidence about the nature of the compound types in coal liquids and their relationship to the original coal (Anderson et al., 1981 Batts and Batts, 1989). 

It has to be noted that all those experiments have been conducted on dry or slightly wet coal samples. Our preliminary tests of coals with high moisture contents revealed that hydrogen emission depends on moisture content and its... 

Originally Bergius felt that coal hydrogenation could not be catalyzed because the large quantities of sulfur present would poison the catalysts. He added luxmasse simply to absorb sulfur from the products although, coincidentally, the combination of iron oxide with titania and alumina was an excellent choice of catalyst. Since his first tests, however, the industrial use of the process has depended on catalysts that were developed more or less empirically. It was soon realized that the processes involved in hydrogenating coal were more complex than the simple reactions described by Sabatier and Ipatieff. Different catalysts such as iron oxide or iron snlfide, probably with traces of other metal oxides, were reqnired. These catalysts could be used in the presence of snUhr and were, in fact, even more active when sulfided. Several studies reported that iron, nickel, cobalt, tin, zinc, and copper chlorides were effective catalysts and claimed that aimnoninm molybdate was particularly active. 

Gasification technologies for the production of high heat-value gas do not all depend entirely on catalytic methanation, that is, the direct addition of hydrogen to coal under pressure to form methane. 

Typical COED syncmde properties are shown in Table 12. The properties of the oil products depend heavily on the severity of hydroprocessing. The degree of severity also markedly affects costs associated with hydrogen production and compression. Syncmdes derived from Western coals have much higher paraffin and lower aromatic content than those produced from Illinois coal. In general, properties of COED products have been found compatible with expected industrial requirements. 

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

Outside the United States, coal pyrolysis is more important as a source of BTX. The proportions are about 70 20 10, but can vary greatiy depending on the coal and on the pyrolysis process used. Product quaUty is not as good as petroleum-derived BTX. This source could become more important again if petroleum costs escalate. Much higher yields of BTX from coal can be obtained by first hydrogenating the coal (22). 

The H-Coal process could operate in one of two modes, depending on the desired product slate. In the "syn-cmde" mode, a fluid-bed coking unit was employed to maximize recovery of distillate from the Hquefaction product (Fig. 7a). When operated in the fuel oil mode (Fig. 7b), no coker was used and the primary product was a coal-derived low sulfur fuel oil. Total hydrogen demand on the process was also reduced in the latter mode of operation. 

Depending on its rank, coal can be dissolved in as little as one minute in the temperature range of 623 to 723 K (662 to S42°F) in suitable solvents, which are assumed to promote thermal cracking of the coal into smaller, more readily dissolved fragments. These fragments may be stabilized through reactions with one another or with hydrogen supplied either by a donor solvent or from a gas phase. 

The low activation energies suggested that the dissolution rate is controlled by counterdiffusion of organic components from the coal surface and dissolved hydrogen from the solvent. Also, the rate of dissolution appeared to depend exponentially on hydrogen partial pressure. 

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