Direct Coal Liquefaction Technologies and Catalytic Processes

Direct coal liquefaction (DCL) converts solid coal into liquid hydrocarbons by hydrogenation at elevated pressure and temperature. Unlike indirect routes that first gasify coal to syngas and then synthesize liquids, DCL cleaves macromolecular bonds within the coal matrix in a single integrated operation, offering higher oil yields and complex product distributions. Two principal configurations are employed: single-stage processes that combine thermal dissolution and hydrogenation in one reactor, and two-stage schemes that use an initial thermal or catalytic pretreatment followed by a dedicated hydrogenation step. Transition-metal catalysts—commonly iron, cobalt, nickel and molybdenum—facilitate bond cleavage and hydrogen transfer, often in tandem with hydrogen-donor solvents that supply mobile hydrogen atoms and stabilise free radicals. Recent progress has centred on nanoscale catalyst synthesis to improve dispersion, solvent selection and blending to enhance hydrogen solubility, and kinetic modelling to optimise reactor performance. Co-processing coal with biomass or petroleum fractions has emerged as a route to lower costs and emissions. Key challenges include catalyst deactivation, solvent recovery, reactor design and integration of carbon management. Nevertheless, DCL technologies remain strategically important for regions with abundant coal reserves, offering pathways to liquid fuels and chemical precursors while diversifying energy supplies.

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Direct Coal Liquefaction Technologies and Catalytic Processes publication trend

The graph below shows the total number of articles in direct coal liquefaction technologies and catalytic processes across all publications each year (not limited to Nature Index journals).

Technical terms

Direct coal liquefaction (DCL): Conversion of solid coal into liquid hydrocarbons via high-pressure hydrogenation.

Hydrogen-donor solvent: Organic liquid that donates hydrogen atoms to coal radicals, promoting bond cleavage and stabilising intermediates.

Asphaltene: Heavy, high-molecular-weight fraction in liquefaction products, insoluble in light alkanes and prone to forming tars.

Kinetic model: Mathematical representation of reaction rates and mechanisms during coal liquefaction.

Nanocatalyst: Catalyst composed of nanoparticles, offering high surface area and enhanced reactivity for hydrogenation.

References

1. Theoretical analysis of hydrogen solubility in direct coal liquefaction solvents. International Journal of Coal Science & Technology (2024).
2. Theoretical Study on the Mechanism of Hydrogen Donation and Transfer for Hydrogen-Donor Solvents during Direct Coal Liquefaction. Catalysts (2018).
3. Reaction Engineering of Direct Coal Liquefaction. Energies (2009).
4. Room-Temperature Solid-State Preparation of CoFe2O4@Coal Composites and Their Catalytic Performance in Direct Coal Liquefaction. Catalysts (2020).
5. Co-liquefaction Behaviour of Elbistan Lignite and Olive Bagasse. IOP Conference Series Earth and Environmental Science (2016).
6. Investigation of the co-processing technology of crude oil and coal and its deployment. Polish Journal of Chemical Technology (2022).
7. A Study on the Hydro-Liquefaction Kinetics of Shengli Lignite during the Heating-Up and Isothermal Stages under Mild Conditions. Energies (2024).