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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.
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]
Coal liquefaction emits more carbon dioxide than liquid fuel production from crude oil. Mixing in biomass and using carbon capture and storage (CCS) would emit slightly less than the oil process but at a high cost. [101] State owned China Energy Investment runs a coal liquefaction plant and plans to build 2 more. [102]
Coal tar and coal tar sludges are frequently denser than water and are present in the environment as a dense non-aqueous phase liquid. In the UK, a number of former gasworks sites have been redeveloped for residential and other uses (including the Millennium Dome), being seen as prime developable land within the confines of city boundaries.
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.
One of the main methods of direct conversion of coal to liquids by hydrogenation process is the Bergius process. [33] In this process, coal is liquefied by heating in the presence of hydrogen gas (hydrogenation). Dry coal is mixed with heavy oil recycled from the process. Catalysts are typically added to the mixture.
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 ...
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.