Sulfur FEEDSTOCKS - COAL CHEMICALS

In recent years, the use of coal as a raw material for the productions of hydrocarbons, liquid transportation fuels, chemical feedstocks and solid fuel is gaining importance. Tliree important processes for the achievement of this goal are (1) direct (2) removal of sulfur from coal by oxydesul-indirect coal liquefaction or the Fischer-All of these processes employ three-phase slurry reactors. In this overview, a present state of the art for the models, scaleup, design and other operational problems associated with these processes are briefly evaluated. 

The search for alternative ways to produce monomers and chemicals from sources other than oil, such as coal, has revived working using Fisher Tropseh technology, which produces in addition to fuels, light olefins, sulfur, phenols, etc. These could he used as feedstocks for petrochemicals as indicated in Chapter 4. 

Gasification technologies offer the potential of clean and efficient energy. The technologies enable the production of synthetic gas from low or negative-value carbon-based feedstocks such as coal, petroleum coke, high sulfur fuel oil, materials that would otherwise be disposed as waste, and biomass. The gas can be used in place of natural gas to generate electricity, or as a basic raw material to produce chemicals and liquid fuels. 

Petroleum became the primary source of hydrocarbons for chemical feedstocks, beginning in about 1850 with the discovery of easily extracted cmde oil in eastern Pennsylvania and in the Ural mountains of Russia. The gases from the primary distillation of cmde oil and the light products from FCC, catalyticfreforming, and hydroprocessing are ideal mixtures of C2 to Cg alkanes that can be used to make many chemicals. Petroleum products are also cleaner than those from coal, producing no ash and less sulfur. 

The importance of sulfur as an industrial chemical is discussed and forecasts of projected sulfur demand in the U.S. are given. Three processes for conversion of coal and oil shale to synthetic fuels are examined in some detail to show how the sulfur in the original feedstock material is recovered as elemental by-product sulfur. Three synthetic fuel scenarios are examined and their potential impact on sulfur availability with current and projected markets to the year 2000 are examined. 

The liquids require a hydrorefining step to stabilize their reactive properties, to reduce the asphaltenes and preasphaltenes, to reduce sulfur, nitrogen, and oxygen, and to make the liquids more distillable. The extent of hydrorefining depends on the end use of liquids—fuel oil or chemical feedstocks. The objective of this work is to evaluate the hydrorefining processibility of ORC flash pyrolysis coal tar as a part of the tar characterization task. Results of the initial phase of catalyst screening tests are reported in this chapter. 

The removal of both mineral matter and sulfur species to very low values would provide premium solid fuels and possibly new chemical feedstocks. Several techniques are being explored to achieve these goals. The mineral matter in a physically cleaned coal can be further reduced by the solubilization of the aluminosilicate minerals. This can technically be accomplished with the use of alkaline and then acid treatments. A variety of studies are under way to define the conditions required for effective removal of the mineral matter and establish the amount of sulfur reduction that can be accomplished. Others involve the use of fine grinding to liberate the coal from the mineral matter. Then an agglomerant is used to separate the coal matter from the aqueous phase containing suspended mineral matter. A new approach uses microwave energy to selectively decompose the clays into species that can be solubilized and removed. Still another technique involves treatment with carbon dioxide to reduce the particle size and permit the liberation of the mineral matter. Over the next few years these will be studied further and it is hoped that coal will become available in a form with less of these interesting, but not entirely desirable mineral species. 

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