Coal has been utilized in its raw state for industrial applications prior to the advent of environmental restrictions and the reduction in supplies of alternative fuels, predominantly from petroleum resources. During the 1930s, Germany led the advances in coal refinement to provide alternate fuel compositions from a raw coal source. These advances in coal refinement centered around the high pressure hyrogenation of coal in the presence of a hydrocarbon solvent. Despite the considerable improvements in such coal liquefaction, the solvent refining of coal remains an expensive process requiring complex flowschemes and apparatus to produce potentially liquid fuels and solid solvent refined coal material (SRC).
Not all industrial applications for coal require that the coal be refined or converted to liquid fuelstocks. Many heavy industry requirements necessitate only the desulfurization, demineralization or deashing of coals in order to make them amenable for combustion for power or heat. In order to render such coals readily combustible in appropriate industrial applications. it is desirable to at least partially refine or depolymerize the complex chemical structure of coal. Such depolymerization occurs when the bonds of a heteroatom in the predominantly carbon structure of coal is broken and is effectively capped with an agent such as hydrogen to prevent repolymerization. Depolymerization does not substantially affect carbon to carbon bonds in the coal molecular structure. Such depolymerized coal is more readily combustible than raw coal for industrial applications. However, the depolymerized coal does not constitute a liquid fuelstock, but rather a solid fuelstock which may be used in a solid, pulverized form referred to as neat coals or used in slurry form comprising a coal-water slurry. In the latter case. the coal is not solubilized, but rather is in suspension with emulsifying agents in a water phase. Alternately, such depolymerized coal could be suspended in an organic phase, such as a coal oil slurry.
In contrast to the refining of raw coal with hydrocarbon solvents, various techniques are known in the prior art for refining coal and more particularly deashing and desulfurizing coal in an aqueous system. In U.S. Pat. No. 4.121,910 a process is set forth wherein a bituminous or lower grade of coal in a finely dispersed solid form is contacted with an aqueous alkaline solution to separate out ash and sulfur components from the coal. The alkaline aqueous solution is made basic with sodium hydroxide or other hydroxides and combinations thereof. The treated coal is separated from the by-products by acidification of the basic reaction medium to precipitate the desired coal product from the dissolved by-product impurities remaining in the aqueous phase.
It is also known to use various quinones as hydrogenation catalysts in the more traditional hydrocarbon solvent liquefaction of coal. In U.S. Pat. No. 4,049,537, a process is set forth wherein a non-hydrogen donor solvent of a hydrocarbon composition is used in the liquefaction of coal wherein quinones are added to the reactor in order to enhance the dissolution of the feed coal to liquid product. The hydrogenation capability of quinones and their theoretical activity in the presence of coal materials and various carbon containing compositions, such as unsaturated carbon structures, is set forth.
Alternate methods for producing quinones are set forth in U.S. Pat. No. 4,369,140 where hydroanthraquinone is produced by a Diels-Alder reaction of naphthoquinone with a diolefin.
Finally, in a defensive publication in the U.S. Pat. Office published on April 22, 1969 in Volume 861 of the Official Gazette page 1020 by Hemminger, it is set forth that traditional solvent refined coal may be extracted using supercritical ammonia.
Additional art which is generally relevant to the process of the present invention includes: U.S. Pat. Nos. 3,700,583, 4,049,536, 4,051,012, 4,085,032, 4,085,033 and 4,092,125.
The present invention comprises a unique implementation of the various aspects of the prior art to provide an unexpected improvement in the depolymerization of solid raw coal to a solid coal product having increased solubility in part in ethylacetate and in part in pyridine. Such coal product has enhanced attributes for use in industrial combustion processes.