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.

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

Coal liquefaction and catalysis

Research and development of catalysts and their performances for coal liquefaction are reviewed, enphasizing the contribution of recent 20 years from Japan. A variety of iron based catalysts were extensively examined to define the pyrrhotite as the active species produced in the liquefaction process. Synthetic pyrite, synthesized hydroxy ferric oxide, finely ground pyrite and limonite have been applied in the process development of coal liquefaction. Iron impregnation onto coal particles using waste water was examined also in a continuous-flow reactor. Finer particles were found to reduce significantly the amount of the catalyst to obtain the same oil yield. Usefulness of such catalysts is proved in the continuous operation of a large scale pilot plant. Iron, iron–nickel, and iron–molybdenum sulfides were found to be active catalysts when they are supported on nano-particles of carbon. Catalysts for recovery and repeated use and for selective aromatic ring opening are under current research.

Progresses of coal liquefaction catalysts in Japan

Publisher Summary Coal liquefaction that can provide liquid fuels at the price of current petroleum (not cost but price) is one of the most important technologies that needs to be developed. The catalyst and control of its operating conditions are still key to technology for advanced coal liquefaction. The creative design of catalyst materials and reaction schemes is an important and challenging goal. Multistage coal liquefaction is proposed in the chapter that consist of the following stages: (1) coal pretreatment, (2) coal dissolution, (3) catalytic hydrocracking, and (4) catalytic upgrading and solvent regeneration. Solid/liquid separation is important at all stages and depends on the extent of coal cleaning during pretreatment, depolymerization of coal macromolecules at the dissolution stage, and catalyst durability through the catalytic process. Hence, the catalysts and catalyses of coal liquefaction are reviewed in the chapter.

Catalysis in Coal Liquefaction

The role of carbon black/coal-tar pitch interactions in the early stage of carbonization

On the chemical effects on catalysts in the direct liquefaction of coal

Catalytic hydroliquefaction of coal: about the methodology in batch experiments

The effect ofa nonporous ultrafine iron oxide precursor, prepared by a flame method, was evaluated in the hydroliquefaction of a bituminous coal in tetralin (350, 400, 430 °C) on a laboratory scale, and compared to that of other aerosols (silica, alumina, SnO 2 , MoO 3 , NiMo/Al 2 O 3 ). The precursors were sulfided with S during heating, according to a previously established conditions set. Methods of evaluating catalytic activity in hydroliquefaction runs based on extraction yields are strongly dependent on the experimental conditions. Special emphasis has been given here in the application of two alternative parameters bred on electron spin resonance (ESR) data, and on the ratio of hydrogen consumption from the gas to that from the solvent (H gas /H solv )

M. Oberson

Papers

On the chemical effects on catalysts in the direct liquefaction of coal

Catalytic hydroliquefaction of coal: about the methodology in batch experiments

Evaluation of the effect of a nonporous ultrafine iron catalyst on the hydroliquefaction of a highly volatile bituminous coal

Effect of various catalysts on the chemical structure of oils and asphaltenes obtained from the hydroliquefaction of a highly volatile bituminous coal

Structural changes of highly volatile bituminous coal after catalytic hydrogenation at 350 °C, as revealed by 13C CP/MAS n.m.r. and FT-i.r.