Catalytic upgrading of coal pyrolysis tar over char-based catalysts

Catalytic upgrading of coal pyrolysis tar was investigated in a dual-stage reactor over char and metal-impregnated char (Co-char, Ni-char, Cu-char, Zn-char). The catalytic upgrading caused the lower total tar yield and the higher non-condensable gas yield but the fraction of light tar (boiling point < 360 °C) obviously increased to allow slightly higher total yield of light tar. When the catalytic upgrading was at 600 °C over a layer of char having a mass of 20% of the tested coal, the resulting light tar fraction in the tar increased by 25% in comparison with the coal pyrolysis only at 600 °C. Over the metal-impregnated char, which was 5% of the tested coal in mass, good upgrading effect was obtained at 500 °C. The catalytic tar-upgrading activity decreased in an order of Co-char > Ni-char > Cu-char > Zn-char, and over Ni-char the realized light tar yield and its content in the tar increased by 17.2% and 32.7%, respectively. The upgrading effect also lowered the contents of element N and S in the resulting tar by 45.6% and 43.5%, respectively. NH3-TPD clarified that the order in acidity of the char-based catalysts was the same as for the upgrading activity shown above.