Exxon donor solvent process (EDS) is a coal liquefaction process developed by Exxon Research and Engineering Company, starting in 1966. The process converts solid

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

directly to liquid

synthetic fuel Synthetic fuel or synfuel is a liquid fuel, or sometimes Fuel gas, gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by ...

s which could be used as a substitute for

petroleum products Petroleum products are materials derived from crude oil (petroleum) as it is processed in oil refineries. Unlike petrochemicals, which are a collection of well-defined usually pure organic compounds, petroleum products are complex mixtures. Most ...

. The process does not involve an intermediate step of

coal gasification In industrial chemistry, coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen (), carbon dioxide (), methane (), and water vapour ()—from coal and water, air and/or oxygen. H ...

. Exxon operated a pilot plant in Texas from 1980 until 1982.

History

Exxon started to develop this process in 1966 and the development process continued until 1976. By 1975, the process was used in 1/2-tons per day pilot plant. In 1977, preparations to build the demonstration-scale 250-tons per day plant in

Baytown, Texas Baytown is a city in the U.S. state of Texas, within Harris County, Texas, Harris and Chambers County, Texas, Chambers counties. Located in the Greater Houston, Houston–The Woodlands–Sugar Land metropolitan statistical area, it lies on the nor ...

. The plant was opened in April 1980. The plant was built by Carter Oil, an affiliate of Exxon Corporation later renamed Exxon Coal, U.S.A. The plant was financed by the

United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...

and by the private investors Carter Oil,

Electric Power Research Institute EPRI, is an American independent, nonprofit organization that conducts research and development related to the generation, delivery, and use of electricity to help address challenges in the energy industry, including reliability, efficiency, affo ...

, Japan Coal Liquefaction Development Company, Phillips Coal Company, ARCO Coal Company, Ruhrkohle and

Agip Agip S.p.A., acronym for Azienda generale italiana petroli, was an Italian automotive gasoline, Diesel fuel, diesel, Liquefied petroleum gas, LPG, lubricants, fuel oil, and bitumen retailer established in 1926 and Subsidiary company, subsidiary ...

. The plant was closed and dismantled in 1982. Originally Exxon planned to open its first commercial scale plant in 1997; however, this plan was abandoned.

Process

The Exxon donor solvent process is a non-catalytic processing of solvent-slurried coal in a high-pressure

liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of t ...

reactor. Coal is cleaned, crushed and fed to the slurry dryer, where water is removed. The dry crushed coal is slurried with the hydrogen donor recycle solvent. The coal slurry is treated with hydrogen and heated in a liquefaction slurry furnace. The liquefaction occurs at and . The process produces gas and liquids. After separation of gas from liquids and remaining solids, the gas is cooled to separate vaporized

naptha Naphtha (, recorded as less common or nonstandard in all dictionaries: ) is a flammable liquid hydrocarbon mixture. Generally, it is a fraction of crude oil, but it can also be produced from natural-gas condensates, petroleum distillates, and ...

, and scrubbed to remove

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

hydrogen gas Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest and most abundant chemical element in the universe, constituting about 75% of all normal matter. Under standard conditions, hydrogen is a gas of diatomi ...

, and

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

. The remaining gas is treated with hydrogen, and reused in the liquefaction reactor. Liquids, remaining solids, and condensate from the process gas are treated in

fractionator Fractionation is a separation process in which a certain quantity of a mixture (of gasses, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which t ...

s for separating naptha, a spent solvent, and vacuum gas oil. Naptha is processed into different hydrocarbon products while spent solvent hydrogenated before reusing in the slurry drier. By this process from of dry, high volatile coal can be produced more than of a synthetic fuel. Initially, the process was focused to be used for

bituminous coal Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the coal seam, ...

s but it was tested also for lower grade coals, such as

lignite Lignite (derived from Latin ''lignum'' meaning 'wood'), often referred to as brown coal, is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% and is considered the lowest ...

. Pilot testings show that lignite was harder to process than

s and it resulted a lower oil yield.

References

{{Reflist ExxonMobil Coal technology Synthetic fuel technologies Industrial processes