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

Abstract 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 (NH 4 ) 2 SO 4 (AS), (NH 4 ) 2 S 2 O 8 (APS), and H 2 SO 4 (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.