Coal, conversion, liquid hydrocarbons

Among the different possibilities for conversion of coal to liquid hydrocarbons, at present only the Fischcr-Tropsch synthesis is performed on a commercial scale. Approximately 2000000 t/a of liquid hydrocarbons are produced at Sasol. Republic of South Africa, and a further increase of production capacity is planned. Due to the present situation in South Africa, which... 

TABLE 27-13 Basic Approaches of Coal Conversion to Liquid Hydrocarbons... 

It is possible to produce some liquid hydrocarbons from most coals during conversion (pyrolysis and hydrogenation/ catalytic and via solvent refining)/ but the yield and hydrogen consumption required to achieve this yield can vary widely from coal to coal. The weight of data in the literature indicate that the liquid hydrocarbons are derived from the so-called reactive maceralS/ i.e. the vitrinites and exinites present (7 8 1 9). Thusf for coals of the same rank the yield of liquids during conversion would be expected to vary with the vitrinite plus exinite contents. This leads to the general question of effect of rank on the response of a vitrinite and on the yield of liquid products and/ in the context of Australian bituminous coals, where semi-fusinite is usually abundant/ of the role of this maceral in conversion. 

Hydrogen donors are, however, not the only important components of solvents in short contact time reactions. We have shown (4,7,16) that condensed aromatic hydrocarbons also promote coal conversion. Figure 18 shows the results of a series of conversions of West Kentucky 9,14 coal in a variety of process-derived solvents, all of which contained only small amounts of hydroaromatic hydrocarbons. The concentration of di- and polyaromatic ring structures were obtained by a liquid chromatographic technique (4c). It is interesting to note that a number of these process-derived solvents were as effective or were more effective than a synthetic solvent which contained 40% tetralin. The balance between the concentration of H-donors and condensed aromatic hydrocarbons may be an important criterion in adjusting solvent effectiveness at short times. 

Because of the massive "unconventional" reserves of liquid hydrocarbons afforded by oil sand bitumens and heavy oils, Canadian interests in coal conversion are generally more likely to centre on gasification than on liquefaction, and to focus on long-term supply of fuel gas (which could in many cases be substituted for oil where coal can not, and thereby reduce projected oil supply shortfalls). 

This paper touches on the chemistry of coal gasification and liquefaction comments on the current status of conversion processes and the influence of coal properties on coal performance in such processes and examines the contributions which coal conversion could make towards attainment of Canadian energy self-sufficiency. Particular attention is directed to a possible role for the medium-btu gas in long-term supply of fuel gas to residential and industrial consumers to linkages between partial conversion and thermal generation of electric energy and to coproduction of certain petrochemicals, fuel gas and liquid hydrocarbons by carbon monoxide hydrogenation. 

Hydrocarbonization, or low-temperature carbonization under hydrogen pressure, is representative of a class of coal conversion processes distinctly different from the slurry hydroliquefaction processes and processes which synthesize liquid fuels from cr 1-derived synthesis gas. Hydrocarbonization technology is reviewed, and major process alternatives and problem areas are discussed. The present status and future prospects for hydrocarbonization are assessed. 

Methane is the simplest, most abundant, and geographically most widely distributed hydrocarbon. It therefore receives constantly increasing attention as an alternate energy source to coal and petroleum from both the world fuels industry and from the science and engineering community to broaden its utility and enhance its transportability by energy-efficient conversion to liquid hydrocarbons and functional chemical raw materials. 

The Fischer-Tropsch process converts synthesis gas into hydrocarbon products. It was extensively used by Germany in the Second World War and developed in South Africa during the Apartheid years. It is now subject to extensive research and development for the conversion of coal into liquid fuels as an alternative to crude oil. The general process flow-sheet is shown in Figure 11.4. 

Coal Liquefaction, Steam is used to produce hydrogen for the liquefaction of coal. In the liquefaction process, coal is crushed, dried, pulverized, and then added to a solvent to produce a slurry. The slurry is heated, usually in the presence of hydrogen to dissolve the coal. The extract is cooled to remove hydrogen, hydrocarbon gases, and hydrogen sulfide. The liquid is then flashed at low pressure to separate condensable vapors from the extract. Mineral matter and organic soHds are separated and used to produce hydrogen for the process. The extract may be desulfurized. The solvent is separated from the products. There are at least six different liquefaction processes (see Coal conversion process, liquefaction Fuels, synthetic-liquid fuels). 

On the other hand, the conversion of natural gas into liquid hydrocarbons is seen as a more attractive alternative, at least in the medium term, since the specific capital expenditure, expressed in capital investment per barrel of distillate produced per calendar day, is significantly lower than when starting from coal. 

The present world rcscr es of natural gas that contains mainly methane are still underutilized due to high cost of transportation. Considerable interest is therefore presently shown in the conversion of methane to transportable liquids and feedstocks in addition to its previous sole use for heating purposes by combustion. One possible new route for the utilization of methane derived from natural gas or other sources for conversion to more valuable higher hydrocarbons is the methylation of aromatic hydrocarbons. This chapter provides a general overview of the work that has been done so far on the use of methane for catalytic methylation of model aromatic compounds and for direct liquefaction of coal for the production of liquid hydrocarbons. The review is especially focused on the use of both acidic and basic zeolites in acid-catalyzed and base-catalyzed methylation reactions, respectively. The base-catalyzed methylation reaction covered in this discussion is mainly the oxidative methylation of toluene to produce ethylbenzene and styrene. This reaction has been found to occur over basic sites incorporated into zeolites by chemical modification or by changing the electronegative charge of the zeolite framework. 

This paper provides a general overview of the recent work that has been done on the use of methane for catalytic methylation of aromatic compounds and for direct liquefaction of coal for the production of liquid hydrocarbons. Such methylation reactions constitute a new route for the utilization of methane derived from natural gas or other sources for conversion to more valuable hydrocarbons. The review focuses on the use of both acidic and basic zeolites in acid-catalyzed and base-catalyzed reactions, respectively. 

When coal is heated in a slurrying vehicle, it is liquefied at 400°C-500°C (750°F-930°F). Though the reaction mechanism involving conversion of coal to oil is very complex, it appears that the interaction of coal with solvent at the initial stage of the reactions plays the vital role to determine the sequential conversion of coal substances—first to a pyridine-soluble solid and thereafter to benzene-soluble liquid hydrocarbons and low-boiling products. Thus the isolation and identification of the products of coal-solvent interactions to yield pyridine-soluble matter may provide information regarding the suitability of the coal for liquefaction. 

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