Occurrence of tar-rich coal: review and perspectives

Le résumé fourni par la source

Tar-rich coal, a unique coal type characterised by dual attributes as both a resource and energy carrier, holds significant implications for the development of coal-based hydrocarbon resources and the implementation of carbon neutrality strategies. This study systematically reviews the geological–biochemical processes governing the formation of tar-rich coal, with particular emphasis on the differential organic compositions of coal-forming plants, enrichment mechanisms of active macerals (vitrinite and liptinite) and their environmental controlling factors. Studies have demonstrated that the selective preservation of lignin and lipidic compounds in higher plants since the late Paleozoic has provided critical hydrocarbon precursors for tar-rich coal formation, with angiosperms exhibiting greater lipid contribution potential than gymnosperms. Coal-forming environments regulate active maceral content through gelification intensity, where coal facies developed under deep-water anoxic conditions demonstrate tar yields of 15–20%. Sedimentary system analysis reveals that epicontinental marine and lacustrine environments favour the preservation of hydrogen-rich components, with low-salinity alkaline media promoting sulfide formation and enhancing organic matter preservation efficiency. Molecular-scale investigations indicate that the optimal configuration of aliphatic side chains and bridging bonds in medium- to low-rank coals (Ro ≈ 0.5–1.3%) constitutes the fundamental control of peak tar yields (350–550 °C). A novel ‘coal-based hydrogen production-carbon sequestration’ synergistic development pathway is proposed, coupling hydrogen extraction through in situ pyrolysis technology with CO2 sequestration in the semi-coke layer, whose techno-economic feasibility depends on precise regulation of hydrogen-rich structural spatial distribution and thermal conduction efficiency. This study establishes a new theoretical framework for unconventional hydrocarbon exploration and provides strategic insights for advancing the low-carbon transition of fossil energy systems.

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