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Two-stage liquefaction of Tanito Harum coal (Indonesian sub-bituminous coal) was examined in an autoclave of 50 mL capacity at various temperatures for the first stage and various reaction times for the first and second stages under the hydrogen pressure of 15 MPa, using Fe(10 wt %)Ni(10 wt %) catalyst supported on carbon nanoparticles (Ketjen Black:KB). When the total reaction time in the first and second stages was fixed to 120 min, the best conditions of two-stage liquefaction were at 380 °C for 15 min in the first stage and then at 450 °C for 105 min in the second stage at a hydrogen pressure of 15 MPa, providing the maximum oil yields of 80 and 66 wt % (daf coal base) with or without H-donor solvent, respectively. The results also showed that these conditions produced fewer amounts of hydrocarbon gases and lower sulfur content in the oil. The conversion of H-donor solvent (tetralin) after the liquefaction was much lower (13%) than that of the single-stage liquefaction (21%). In addition, the residue yield was much lower (9%) than that of the single-stage (15%) in the solvent-free liquefaction. It is confirmed that prolonged reaction time in the second stage is more favorable than in the first stage. The effects of the first-stage (low temperature) liquefaction both with and without solvent are discussed to explain the optimum conditions of two-stage liquefaction.

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