Process for producing high-purity coal

Claim 2

A process for the production of high-purity coal to reduce or eliminate impurities therein which comprises: (a) digesting the coal in a caustic solution to solubilize at least a portion of said impurities and to react the caustic with other impurities to form acid soluble products; (b) separating the caustic solution and dissolved impurities from the coal; (c) treating the digested coal in a mineral acid other than nitric acid to dissolve said acid soluble products; (d) separating the treated coal from said mineral acid and impurities dissolved therein; (e) thereafter treating the coal with nitric acid to remove metallic sulfide impurities remaining in said coal; and (f) recovering a purified coal from said treatments characterized by having, by weight, respectively not more than 0.1% ash, 0.02% Fe, 0.02% Si, 1.5% total sulfur and 0.1% pyritic sulfur.

Claim 3

The process of claim 1 wherein said coal is screened and ground, when necessary, to a particle size not greater than 28 mesh.

Claim 4

The process of claim 2 wherein said particle size is 80% by weight above 400 mesh.

Claim 5

The process of claim 1 wherein the concentration of said caustic is at least 3% by weight, the ratio of caustic solution to coal is at least 2 parts by weight caustic solution per part by weight coal, the digest time is at least 10 minutes and the digest temperature is at least 120° C.

Claim 6

The process of claim 1 wherein said mineral acid is selected from the group consisting of sulfuric acid and hydrochloric acid, said acid has a concentration of at least 4% by weight, the ratio of acid solution to coal is at least 2 parts by weight acid solution per part of coal, and the treatment is carried out for at least 15 minutes at a temperature of at least 40° C.

Claim 7

The process of claim 1 wherein said nitric acid has a concentration of at least 5% by weight, the ratio of nitric acid solution to coal is at least 4 parts by weight nitric acid per part by weight of coal and the treatment is carried out for at least 30 minutes at a temperature of at least 70° C.

Claim 8

A process for the production of high-purity coal useful for producing high-purity carbon therefrom which comprises: (a) grinding coal to a particle size of from 28 mesh to at least 80% by weight above 400 mesh; (b) digesting the coal in an at least 3% by weight sodium hydroxide solution at a ratio of at least 2 parts by weight sodium hydroxide solution per part by weight coal to solubilize at least a portion of the impurities in the coal and to react with other impurities in the coal to form acid soluble products; (c) separating the digested coal from the sodium hydroxide solution and impurities dissolved therein; (d) treating the digested coal with an at least 4% by weight sulfuric acid solution at a solution to solids ratio of at least 2 parts by weight sulfuric acid solution per part by weight of coal to dissolve at least a portion of acid soluble impurities in the coal; (e) separating the treated coal from the sulfuric acid solution and impurities dissolved therein; (f) treating the coal with an at least 5% by weight nitric acid solution at a solution to solids ratio of at least 4 parts by weight nitric acid solution per part by weight coal; and (g) separating the coal from the nitric acid and impurities dissolved therein; said sodium hydroxide digest, sulfuric acid treatment and nitric acid treatment being carried out at temperatures and time periods sufficient to provide a purified coal having, by weight, not more than 0.1% ash, 0.02% Fe, 0.02% Si, 1.35% total sulfur and 0.1% pyritic sulfur.

Claim 9

A process for the production of high-purity coal useful for producing high-purity carbon therefrom which comprises: (a) grinding coal to a particle size of from 28 mesh to at least 80% by weight above 400 mesh; (b) digesting the coal in an at least 3% by weight sodium hydroxide solution at a ratio of at least 2 parts by weight sodium hydroxide solution per part by weight coal to solubilize at least a portion of the impurities in the coal and to react with other impurities in the coal to form acid soluble products; (c) separating the digested coal from the sodium hydroxide solution and impurities dissolved therein; (d) treating the digested coal with an at least 4% by weight sulfuric acid solution at a solution to solids ratio of at least 2 parts by weight sulfuric acid solution per part by weight of coal to dissolve at least a portion of acid soluble impurities in the coal; (e) separating the treated coal from the sulfuric acid solution and impurities dissolved therein; (f) treating the coal with an at least 5% by weight nitric acid solution at a solution to solids ratio of at least 4 parts by weight nitric acid solution per part by weight coal; and (g) separating the coal from the nitric acid and impurities dissolved therein; said sodium hydroxide digest, sulfuric acid treatment and nitric acid treatment being carried out at temperatures and time periods sufficient to provide a purified coal having, by weight, not more than 0.1% ash, 0.02% Fe, 0.02% Si, 1.35% total sulfur and 0.1% pyritic sulfur.