In situ upgrading of Shengli lignite pyrolysis vapors over metal-loaded HZSM-5 catalyst

- Metal-loaded HZSM-5 was prepared for conversion of lignite to light aromatics.
- The BTEXN formation was enhanced by metal-loaded HZSM-5.
- Oxygen content in pyrolysis tar is remarkably decreased by metal-loaded HZSM-5.
- Ni-loaded HZSM-5 is a potential candidate in catalytic upgrading of pyrolysis oil.

This work is aimed to study in situ upgrading of Shengli lignite pyrolysis vapors over different metal-loaded HZSM-5 in a drop tube reactor. Co/HZSM-5, Mo/HZSM-5 and Ni/HZSM-5 (5.0 wt%) were prepared by wet impregnation and characterized by N2 adsorption-desorption analyzer, X-ray diffraction, transmission electron microscope, Fourier transform infrared spectrometer and temperature programmed desorption of ammonia. The effects of temperature and catalyst on product yields and tar properties were investigated. The results show that the optimal temperature for liquid product was 600 °C and aromatics can be directly produced from solid lignite by catalytic fast pyrolysis over metal-loaded HZSM-5 under such mild condition. Due to the participation of metal and acid sites, the bifunctional metal-loaded HZSM-5 showed comparable catalytic activity for deoxygenation reaction in the valorization of oxygen content below 7.1%. The introduction of metal causes the increase of aromatics and the decrease of organic oxygen species in upgraded tar remarkably. Among the catalysts, Ni/HZSM-5 exhibited the best performance for production of high quality tars with highest aromatics content of 94.2% (area%), which can be used as a potential candidate for catalytic upgrading of pyrolysis oil.