Production and Characterization of Synthetic Diesel Fuel from Coal via Fischer–Tropsch Indirect Liquefaction

Abstract

This study investigates the production of synthetic diesel fuel from coal through indirect liquefaction using Fischer–Tropsch synthesis. A series of experiments was performed, starting with coal gasification in a vertical reactor at 1270°C and 22 bar to produce synthesis gas containing approximately 51.4% of carbon monoxide and 43.7% of hydrogen. After purification, the synthesis gas underwent catalytic conversion in a high-pressure reactor using a cobalt–zirconia catalyst. Under baseline conditions of 227°C and 25 bar, the average liquid product yield was 12.6 kg over 6 hours, with the diesel and kerosene fractions of 57.4% and 31.2%, respectively. Increasing the pressure to 30 bar enhanced the diesel fraction to 61.8% and improved the total liquid yield by 7.5%. The resulting synthetic diesel exhibited superior properties compared to petroleum-derived fuel, including a cetane number of 72, sulfur content below 2 mg/kg, and aromatic hydrocarbons limited to 3.2%. Stability tests conducted over 180 days confirmed excellent oxidation resistance. These findings demonstrate that indirect coal liquefaction can deliver high-quality diesel fuel with significant potential to reduce environmental impacts and enhance energy security. The cobalt–zirconia catalyst was prepared in-house as a bulk CoO–ZrO₂ granulate and pre-reduced in situ before synthesis. Under 225–230 °C and 25–30 bar, the system consistently delivered 57.4–61.8 wt% diesel within the liquid products with stable operation. The process configuration is compatible with pre-combustion CO₂ capture units, providing a clear pathway for integrating CCS in future scale-up.