Enhancement of fluidity and slurry-phase hydrogenation reactivity of coal-oil slurry by preheating treatment.

• Preheating treatment at suitable temperatures can improve fluidity and SHR of COS. • Influence mechanism of preheating treatment was investigated. • Preheating treatment can change coal's structure by enhancing swelling effect. • Expansion of coal's structure and release of light components are key factors. The effects of preheating treatment at temperatures from 200 to 350 °C on the viscosity–temperature properties and slurry-phase hydrogenation reactivity (SHR) of a coal-oil slurry (COS) prepared from Xinjiang lignite and fluid catalytic cracking slurry were studied. Moreover, the structural changes to the coal after preheating treatment were characterized to reveal the origin of preheating treatment effects. As the preheating temperature increased, the viscosity of COS increased, and the sudden increases in the COS viscosity at 160 °C and 240 °C disappeared, improving the fluidity of COS. Moreover, as the preheating temperature was increased, the SHR of the COS increased with increasing preheating temperature up to 300 °C, but decreased when a temperature of 350 °C was used. Structural characterization of the coal showed that increasing the preheating temperature up to 300 °C enhanced coal swelling, promoting expansion of the coal structure, which in turn increased its average particle size, specific surface area, and porosity. The increased release of light components in the coal, which had relatively high and stable contents of ortho -substituted aromatic rings and methyl and methine groups, was also observed with increasing preheating temperatures of up to 300 °C. The irreversible swelling of the coal induced by preheating treatment was responsible for the improved fluidity and enhanced SHR of the COS. However, the pyrolysis of coal occurring at 350 °C decreased the specific surface area and porosity of coal, causing a reduction in contact between the coal and catalyst sites and decreasing the SHR of COS. [ABSTRACT FROM AUTHOR]