Sulfation-acidified HZSM-5 catalyst for in-situ catalytic conversion of lignite pyrolysis volatiles to light aromatics

This study elucidated the effects of crystalline structure and acidity of sulfation-acidified HZSM-5 (HZ5) catalyst on the reaction routes and light aromatics (LAs) distribution during catalytic fast pyrolysis (CFP) of Shengli lignite. HZ5 modified by (NH4)2SO4 (AS), (NH4)2S2O8 (APS), and H2SO4 (HS) were applied to conduct CFP of lignite in a drop tube quartz reactor at 600 °C. The results indicated that the yield of LAs, especially monocyclic aromatics, increased considerably as the increase of pore size and midstrength acid sites (the decrease of non-shape selective acid sites) caused by sulfation-acidification modification. Among all the modified catalysts, 0.5AS-550 (modified with 0.5 mol/L AS and calcined at 550 °C) showed a better prospect than APS and HS modification in promoting the formation of LAs (the maximum yield of 28.8 mg/g). Meanwhile, the elimination of non-shape selective acid sites and regeneration of mesoporous reduced coke yield by 0.6% compared to HZ5. In addition, the possible reaction routes and catalytic mechanism over sulfation-acidified HZ5 catalysts were proposed to describe the formation of LAs.