Ex-situ catalytic fast pyrolysis of low-rank coal over HZSM-5 and modified Mg/HZSM-5 catalysts

Catalytic effects in fast pyrolysis of low-rank coal and coal tar conversion were investigated in a two-stage fixed-bed reactor over HZSM-5 zeolite and Mg/HZSM-5. Mg/HZSM-5 caused the lower total tar yield and the higher non-condensable gas yield but the fraction of light tar (boiling point below 360 degrees C) increased to allow a slightly higher total yield of light tar. It also exhibited good catalytic activity and increased the species of light tar than HZSM-5 zeolite. The light tar fraction was increased from 45 to 74.6 wt% than without catalyst (66%) at the pyrolysis temperature of 600 degrees C. Ex-situ catalytic fast pyrolysis over Mg/HZSM-5 also lowered the contents of element N and S in the resulting coal tars by 29% and 15% respectively. The corresponding increase in the content of element H and molar ratio of H to C of the resulting coal tars was reported as 17% and 13% respectively. The addition of Mg into HZSM-5 increased the ability of the catalyst for inhibiting coke deposition.