1. Field of the Invention
A need exists to develop a process for producing an upgraded solid material which is solid and/or semi-solid at room temperature from coal and which is capable of later being combined with a liquid for further uses, such as, for example, as fuel. Since coal reserves represent one of the largest sources of energy supply in the world, much attention has been directed to devising and developing processes for conversion and/or upgrading coal. The term "conversion", as employed herein, includes processes wherein a solid carbonaceous material, essentially hydrocarbon in nature, such as, for example, coal, as defined herein, is changed, in accordance with the process defined and claimed herein, physically and/or chemically, to another distinct specie, such as, for example, the change that occurs as a result of the hydrogenation of coal to a liquid. The term "upgrading" includes processes wherein treatment of the solid carbonaceous material, for example, coal, results in a product having enhanced physical and/or chemical properties, such as, for example, where some of the solid carbonaceous material is not liquified during processing but has a lower ash content and is lower in sulfur and nitrogen and/or where the liquid or solid obtained is lower in sulfur and nitrogen content. Attempts to provide an effective process for upgrading coal have not been generally successful because of the difficulty of incorporation, cost and amount of hydrogen required to convert coal to an upgraded material. Further, when coal, whether ash-containing or deashed, is treated with a catalyst, the result is rapid catalyst aging and a decrease in activity because of excessive coking and/or plugging. Additionally, where a solid and/or semi-solid material at room temperature can be obtained, such product cannot later be readily combined with a liquid for further use, i.e., it is usually burned as solid fuel.
The present invention overcomes these problems by providing a process for upgrading coal which comprises the step of: (1) subjecting a slurry composed of coal and a solvent containing donatable hydrogen, together with hydrogen, to catalyst-free hydrogenation conditions in a first hydrogenation zone to form an intermediate coal-solvent slurry; (2) deashing said intermediate coal-solvent slurry to form a coal solvent solution; (3) subjecting said coal-solvent solution to catalytic hydrogenation conditions in a second hydrogenation zone to obtain a product that can be separated at ambient pressure into (a) a first liquid fraction boiling at a temperature in the range of about 100 to about 375.degree. C., (b) a second liquid fraction boiling above said first liquid fraction at a temperature in the range of about 200.degree. to about 525.degree. C. and (c) a solid and/or semi-solid material; and then (4) recycling at least a portion of said second liquid fraction to said first hydrogenation zone.
2. Description of the Prior Art
U.S. Pat. No. 3,932,266 to Sze et al discloses a method of effecting hydrogen addition to coal in two stages, with ash being separated between stages, to produce a synthetic crude. The synthetic crude is produced from coal by initially hydrogenating coal in the presence of a solvent and a hydrolique-faction catalyst. The liquid product containing insoluble material from the initial hydrogenation is then deashed using a "liquid promoter", and the essentially ash-free liquid coal product is then subjected to a second hydrogenation in the presence of a catalyst wherein sufficient hydrogen is added to provide a synthetic crude (column 1, lines 28 to 58; column 10, lines 24 to 31; and claim 1). In marked contrast to the present invention, the Sze process consumes greater quantities of hydrogen, does not provide a solvent containing donatable hydrogen for use in the initial hydrogenation and results in rapid catalyst aging in the first hydrogenation.