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Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "coal to X" or "carbon to X", where X can be many different hydrocarbon-based products.
There is a residue of unreactive tarry compounds mixed with ash from the coal and catalyst. To minimise the loss of carbon in the residue stream, it is necessary to have a low-ash feed. Typically the coal should be <10% ash by weight. The hydrogen required for the process can be also produced from coal or the residue by steam reforming.
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 directly to liquid synthetic fuels which could be used as a substitute for petroleum products. The process does not involve an intermediate step of coal gasification. Exxon ...
As an example of the latter, a "major commercial application of liquefaction is the liquefaction of air to allow separation of the constituents, such as oxygen, nitrogen, and the noble gases." [4] Another is the conversion of solid coal into a liquid form usable as a substitute for liquid fuels. [5]
A number of two-stage direct liquefaction processes have been developed. After the 1980s only the Catalytic Two-stage Liquefaction Process, modified from the H-Coal Process; the Liquid Solvent Extraction Process by British Coal; and the Brown Coal Liquefaction Process of Japan have been developed. [36]
The Fischer–Tropsch process is an important reaction in both coal liquefaction and gas to liquids technology for producing liquid hydrocarbons. [1] In the usual implementation, carbon monoxide and hydrogen, the feedstocks for FT, are produced from coal, natural gas, or biomass in a process known as gasification.
In the Karrick process, 1 short ton of coal yields up to 1 barrel of oils and coal tars (12% by weight), and produces 3,000 cubic feet (85 m 3) of rich coal gas and 1,500 pounds (680 kg) of solid smokeless char or semi-coke (for one metric ton, 0.175 m 3 of oils and coal tars, 95 m 3 of gas, and 750 kg of semi-coke).
3C (as Coal) + O 2 + H 2 O → H 2 + 3CO. If the refiner wants to produce gasoline, the syngas is routed into a Fischer–Tropsch reaction. This is known as indirect coal liquefaction. If hydrogen is the desired end-product, however, the syngas is fed into the water gas shift reaction, where more hydrogen is liberated: CO + H 2 O → CO 2 + H 2