Coal-Derived Carbons

Eor shifting coal-derived gas, conventional iron—chromium catalysts can be used. Because coal gas has a significantly higher concentration of carbon monoxide than is found in gas streams in conventional refineries, the catalyst must be able to withstand high thermal loads. However, potential catalyst poisons such as phenol and other hydrocarbons are not a concern in entrained-bed gasifiers. 

The authors wish to thank 1. C. Lewis and the UCAR Carbon Company for their assistance in the preparation and characterization of the coal-derived graphites. This work was partially funded by a grant from the U. S. Department of F.nergy DE-FG02-91NP00159. This support is gratefully acknowledged. 

Seehra, M. S., and Pavlovic, A. S., X-ray diffraction, thermal expansion, electrical conductivity, and optical microscopy studies of coal-derived graphites. Carbon, 1993, 31, 557 564. 

In addition to knowing the total MTC solubility, it was important to determine the amount of methanol or other solvent retained by the MTC. This quantity, the incorporation ratio (R, gm incorporated organic material/gm coal-derived organic material), was determined by a carbon balance on the reaction. By assuming that any solvent retained in the dried MTC is pyridine-soluble, and subtracting it from the total dissolved material, the minimum solubility of the coal-derived material may be calculated. This quantity, the corrected solubility, is an indicator of the true solubilizing effect on the coal by the particular run conditions. ... 

Traditionally, iron-based catalysts have been used for FT synthesis when the syngas is coal derived, because of their activity in both FTS and WGS reactions. Complex mixtures of straight-chain paraffins, olefins, and oxygenate (in substantial proportions) compounds are known to be formed during iron-based FTS. Olefin selectivity of iron catalysts is typically greater than 50% of the hydrocarbon products at low carbon numbers, and more than 60% of the produced olefins are a-olefins.13 For iron-based catalysts, the olefin selectivity decreases asymptotically with increasing carbon number. 

Only a limited number of coal-derived pitches were examined by H NMR because of their low solubility in solvents commonly used m conventional proton magnetic resonance. Table 12 reports the distribution of hydrogen for three of the pitches. Unlike coal-tar pitches, which typically have over 85% of the hydrogen bonded to aromatic carbon, the materials listed in Table 12 are characterized by a high content of aliphatic hydrogen. 

Figure 4.2 presents a simplified flow diagram of the ENCOAL Liquid from Coal (LFC) process. The process upgrades low-rank coals to two fuels, Process-Derived Coal (PDF ) and Coal-Derived Liquid (CDL ). Coal is first crushed and screened to about 50 mm by 3 mm and conveyed to a rotary grate dryer, where it is heated and dried by a hot gas stream under controlled conditions. The gas temperature and solids residence time are controlled so that the moisture content of the coal is reduced but pyrolysis reactions are not initiated. Under the drier operating conditions most of the coal moisture content is released however, releases of methane, carbon dioxide, and monoxide are minimal. The dried coal is then transferred to a pyrolysis reactor, where hot recycled gas heats the coal to about 540°C. The solids residence time... 

Like natural gas, the producer gas from coal is a clean fuel. Additionally, it is a rich source of chemicals. Coal-derived gas can also be recombined into liquid fuels, including high-grade transportation fuels, and a range of petrochemicals that serve as feedstock workhorses in the chemicals and refining industries. In contrast to conventional combustion, carbon dioxide exits a coal gasifier in a concentrated stream rather than diluted in a high volume of flue gas. This allows the carbon dioxide to be captured more effectively and then used... 

The primary product is fuel-grade, coal-derived gas which is similar to natural gas. The basic gasification process can also be applied to other carbon-based feedstocks such as biomass or municipal waste. 

ERC, "Effects of Coal-Derived Trace Species on the Performance of Molten Carbonate Fuel Cells," topical report prepared for U.S. DOE/METC, DOE/MC/25009-T26, October 1991. 

D.M. Rastler, C. Keeler, C.V. Chang, "Demonstration of a Carbonate on Coal Derived Gas," Report 15, in An EPRI/GRI Fuel Cell Workshop on Technology Research and Development. Stonehart Associates, Madison, CT, 1993. 

The addition of H2O and CO2 to the fuel gas modifies the equilibrium gas composition so that the formation of CH4 is not favored. Carbon deposition can be reduced by increasing the partial pressure of H2O in the gas stream. The measurements (20) on 10 cm x 10 cm cells at 650°C using simulated gasified coal GF-1 (38% H2/56% CO/6% CO2) at 10 atm showed that only a small amount of CH4 is formed. At open circuit, 1.4 vol% CH4 (dry gas basis) was detected, and at fuel utilizations of 50 to 85%, 1.2 to 0.5% CH4 was measured. The experiments with a high CO fuel gas (GF-1) at 10 atmospheres and humidified at 163°C showed no indication of carbon deposition in a subscale MCFC. These studies indicated that CH4 formation and carbon deposition at the anodes in an MCFC operating on coal-derived fuels can be controlled, and under these conditions, the side reactions would have little influence on power plant efficiency. 

D. Rastler, EPRI, G. Devore, Destec Engineering, R. Castle, Haldor Topsoe, C. Chi, ERC, "Demonstration of a Carbonate Fuel Cell Stack on Coal-Derived Gas," in Fuel Cell Seminar. "Effects of Coal-Derived Trace Species on the Performance of Molten Carbonate Fuel Cells," Topical Report prepared by Energy Research Corporation for US DOE/METC, DOE/MC/25009-T26, October, 1991. 

Methanol can also be produced from syngas with hydrogen and carbon monoxide in a 2 1 ratio. Coal-derived methanol typically has low sulfur and other impurities. Syngas from coal can be reformed by reacting with water to produce hydrogen. Ammonium sulfate from coal tar by pyrolysis can be converted to ammonia. The humus substances can be recovered from brown coal by alkali extraction. 

Data from tests at 250,275,300, and 325 C were used to calculate pseudo-first order rate constants for the formation of H2S. These data are expressed on a standard Arriienius plot (Fig. 2) for which the linear least squares coefficient of determination, r, is 0.98. The apparent activation energy calculated from the slope is 28.5 kcal/mol. This result is in excellent agreement with the recent work of Abotsi, who studied the performance of carbon-supported hydrodesulfurization catalysts (10). Using Ambersorb XE-348 carbon lo ed with sulfided ammonium molybdate (3% Mo loading) prepared by the same procedure reported here, Abotsi hydrotreated a coal-derived recycle solvent The apparent activation energy for... 

Both reactions act to reduce hydrogen bonding within the coal structure which may have a direct positive impact on liquefaction reactivity. More indirectly, these reactions lower the concentration of OH species in coal-derived products and hence, reduce the extent of retrogressive condensation via ether bridge formation. Reducing production of THF-insoluble condensation products increases the net THF-soluble coal conversion observed during the liquefaction experiment. None of the spectra from coals pretreated with alkyl alcohols and HCl showed any significant evidence of alkylation at carbon sites in the coal. 

The enormous importance of carbon in such diverse fields as inorganic and organic chemistry and biology is well known however, only the aspects of carbon relevant to catalysis will be described here. The main topics we are concerned with are porous activated carbons, carbon black as catalyst supports and forms of coking. Carbon is also currently used as storage for natural gas and to clean up radioactive contamination. Carbon is available at low cost and a vast literature exists on its uses. Coal-derived carbon is made from biomass, wood or fossil plants and its microstructure differs from carbon made from industrial coke. Activated carbons are synthesized by thermal activation or by chemical activation to provide desirable properties like high surface area. 

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