Effect of potassium on catalytic characteristics of ZSM-5 zeolite in fast pyrolysis of biomass-based furan

The effect of potassium in biomass on the catalytic activity of ZSM-5 zeolite in the fast pyrolysis of biomass was investigated using 2-methylfuran (2-MF) as the typical model compound. The mechanism of action of potassium was explored in detail, along with the physicochemical properties of ZSM-5, including crystallinity, pore structure, and surface acidity. The physicochemical properties of ZSM-5 deteriorated to varying degrees after being tainted with different potassium sources (KOH, K2CO3, KAc, and KCl). Compared with neutral KCl and strong alkali KOH, K2CO3, and KAc, with weaker alkalinity but larger crystal structure, exerted a larger influence on ZSM-5. Changes in ZSM-5 tainted with K2CO3 were the greatest, and crystallinity, surface area, acidity, and the corresponding yields of valuable aromatic hydrocarbons and gas products, all declined significantly, compared with raw ZSM-5. When the amount of K(CO32-) on ZSM-5 was less than 0.5 wt%, only minor (<10 %) changes were observed in crystallinity and surface area, but total acidity decreased by over 30 percent. The conversion of 2-MF was increased using ZSM-5 tainted with less than 0.5 wt% K(CO32-) and less liquid oxygenated compounds and more CO2 were produced. Appropriate total acidity, adjusted by a tiny amount of K2CO3, could promote deoxygenation to CO2. However, the decarbonylation reaction was inhibited, causing a negative effect on monocyclic aromatic hydrocarbons, which was attributed to the large-scale loss of both acidity and physical structure of ZSM-5 caused by more than 1.0 wt% K(CO32-).