Liquefaction processes, coal

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). 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

W. R. Eppedy and J. W. Taunton, "Exxon Donor Solvent Coal Liquefaction Process Development," paper presented at Coal Dilemma II ACS Meeting, Colorado Spriags, Colo., Feb. 12, 1979. 

W. G. Willson md co-workers, " AppHcation of Liquefaction Process to Low-Rank Coals," paper presented at /0th BiennialEignite Symposium, Grmd Forks, N.D., May 1979. 

Liquefaction. Liquefaction of coal to oil was first accompHshed in 1914. Hydrogen was placed with a paste of coal, heavy oil, and a small amount of iron oxide catalyst at 450° and 20 MPa (200 atm) in stirred autoclaves. This process was developed by the I. G. Earbenindustrie AG to give commercial quaUty gasoline as the principal product. Twelve hydrogenation plants were operated during World War II to make Hquid fuels (see CoAL... 

Direct-Liquefaction Processes Figure 27-8 presents a simph-fied process flow diagram of a typical direct coal liquefaction plant. Specific processes are described in the following paragraphs. 

Owen, J., Liquefaction of coal. In Coal and Modern Coal Processing- An Introduction, ed. G. J. Pitt and G. R. Millward. Academic Press, New York, 1979, pp. 163 181. 

Work has also continued on the solvent-refined coal + hydrocracking concept (the NT.SL, or non-integrat-ed, two-stage liquefaction process), and a pilot plant was operated by Amoco, DOE and the Electric Power Research Institute (EPRI) from 1974 to 1992. 

NIOSH. 1980a. Control technology assessment for coal gasification and liquefaction processes, General Electric Co., Corporate Research and Development Center, Coal Gasification Section, Schenectady, New York. Cincinnati, OH U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Division of Physical Sciences and Engineering. NITS publication no. PB84-181890. 

Perhaps the most important components of reactor solids are those that are generated during processing rather than those that are derived from inert minerals (quartz, clays) and macerals (fu-sinites, etc.) in the feed coal (74). The retention of these formed materials is more difficult to predict from the characteristics of the feed and, hence, control in liquefaction processes. 

Epperly, W. R. (Project Director). "EDS Coal Liquefaction Process Development—Phase IV", Annual Tech. Rept. for July 1978-June 1979 from Exxon Research and Engineering Company to U.S. Department of Energy and Electric Power Research Institute under Contract No. EF-77-A-01-2893, September 1979. 

Coal Characteristics and Their Effects in Liquefaction Process... 

The significance of the above-described work is that in all of the presently developing coal liquefaction processes, the initial step in the conversion is thermal fragmentation of the coal structure to produce very fragile molecules which are highly functional, low in solubility, and extremely reactive toward dehydrogenation and char formation. A more detailed discussion of the chemical nature of these initial products has been presented elsewhere (4). ... 

These observations suggest that new coal liquefaction technology may be possible based on short contact time reactions. The purpose of this and the related papers in this volume by R.H. Heck and W.C. Rovesti is to show some potential advantages for optimized or integrated short contact time liquefaction processes over conventional technology. 

In catalytic coal liquefaction processes, reaction temperatures must be high in order to insure that thermal reactions disrupt the coal structure to the point that the catalyst can act on the products. 

Other Reaction Products. In addition to SRC, gas, light oil, and a filter cake of unreacted coal and inorganic materials are produced in the first step of the short residence time coal liquefaction process. One of the objectives of short residence time coal liquefaction is to minimize the loss of hydrogen to gases and light oil. 

The H2S present in the gas in AC2 represents 22 percent of the sulfur in the coal. The total amount of sulfur released into the gas phase during the first step of this coal liquefaction process is 25 percent of the total sulfur in the as-fed coal. 

Solvent Composition and Recovery. The solvent was defined as the product fraction which is soluble in the hot filtrate and the THF extraction of the filter cake and which boiled between 232 C and 482 C at atmospheric pressure. One of the requirements of a commercial coal liquefaction process is that a least as much solvent be created as is used in the process. In addition, the composition of the solvent must be kept constant if it is to be... 

The present authors studied the solvolytic liquefaction process ( ,7) from chemical viewpoints on the solvents and the coals in previous paper ( 5). The basic idea of this process is that coals can be liquefied under atmospheric pressure when a suitable solvent of high boiling point assures the ability of coal extraction or solvolytic reactivity. The solvent may be hopefully derived from the petroleum asphaltene because of its effective utilization. Fig. 1 of a previous paper (8) may indicate an essential nature of this process. The liquefaction activity of a solvent was revealed to depend not only on its dissolving ability but also on its reactivity for the liquefying reaction according to the nature of the coal. Fusible coals were liquefied at high yield by the aid of aromatic solvents. However, coals which are non-fusible at liquefaction temperature are scarcely... 

In the present study, the liquefaction activities of pyrene, its derivatives, and decacyclene with coals of several ranks are studied to ascertain the previous ideas of liquefaction mechanism and to develop novel liquefaction process under atmospheric pressure. The coals used in the present study are non-fusible or fusible at relatively high temperature, and then gave small liquefaction yield with pyrene of a non-solvoly-tic solvent at 370°C. 

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