Clean liquid fuels from direct coal liquefaction: chemistry, catalysis, technological status and challenges

TLDR

Increased demand for liquid transportation fuels and dwindling oil reserves have renewed interest in coal‑to‑liquids technologies, with large recoverable coal reserves offering a potential reduction in oil dependence. This review surveys coal structure, chemistry, and catalysis in direct liquefaction, discusses its historical development and current status, and outlines key challenges and future research directions. Direct coal liquefaction converts solid coal (H/C ≈ 0.8) to liquid fuels (H/C ≈ 2) by adding hydrogen at high temperature and pressure, with or without catalysts.

Abstract

Increased demand for liquid transportation fuels coupled with gradual depletion of oil reserves and volatile petroleum prices have recently renewed interest in coal-to-liquids (CTL) technologies. Large recoverable global coal reserves can provide liquid fuels and significantly reduce dependence on oil imports. Direct coal liquefaction (DCL) converts solid coal (H/C ratio ≈ 0.8) to liquid fuels (H/C ratio ≈ 2) by adding hydrogen at high temperature and pressures in the presence or absence of catalyst. This review provides a comprehensive literature survey of the coal structure, chemistry and catalysis involved in direct liquefaction of coal. This report also touches briefly on the historical development and current status of DCL technologies. Key issues, challenges involved in DCL process and directions for the future research are also addressed.