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coal liquefaction
Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. The conversion industry is commonly referred to as "coal conversion" or "Coal To X". "Coal to Liquid Fuels" is commonly called "CTL" or "coal liquefaction", although "liquefaction" is generally used for a non-chemical process of becoming liquid. Today, the share of converted coal used for CTL is less than 50%. It will decrease dramatically in the next years with the development of "coal to chemicals" and "coal to SNG" units, principally in China.
==Direct and indirect processes==
Specific liquefaction technologies generally fall into two categories: direct (DCL) and indirect liquefaction (ICL) processes. Indirect liquefaction processes generally involve gasification of coal to a mixture of carbon monoxide and hydrogen (syngas) and then using a process such as Fischer–Tropsch process to convert the syngas mixture into liquid hydrocarbons.〔(【引用サイトリンク】title=Indirect Liquefaction Processes )〕 By contrast, direct liquefaction processes convert coal into liquids directly, without the intermediate step of gasification, by breaking down its organic structure with application of solvents or catalysts in a high pressure and temperature environment.〔(【引用サイトリンク】title=Direct Liquefaction Processes )〕 Since liquid hydrocarbons generally have a higher hydrogen-carbon molar ratio than coals, either hydrogenation or carbon-rejection processes must be employed in both ICL and DCL technologies.
As coal liquefaction generally is a high-temperature/high-pressure process, it requires a significant energy consumption and, at industrial scales (thousands of barrels/day), multibillion-dollar capital investments. Thus, coal liquefaction is only economically viable at historically high oil prices, and therefore presents a high investment risk.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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