Influence of Si/Al Ratio of ZSM-5 Zeolite on the Properties of Lignin Pyrolysis Products

The pyrolysis of softwood (SW) kraft lignin in the presence of various H-ZSM-5 zeolites with different SiO 2 /Al 2 O 3 mole ratios from 23/1–280/1 as additives were examined at 600 °C. Nuclear magnetic resonance (NMR), including quantitative 13 C, 31 P NMR, and heteronuclear single-quantum correlation (HSQC)-NMR, and gel permeation chromatography (GPC) were used to characterize various pyrolysis oils. On the basis of the results of the 13 C and 31 P NMR for pyrolysis oils, the use of H-ZSM-5 zeolites during the pyrolysis process caused the near complete decomposition of aliphatic hydroxyl and carboxyl groups. With the exception of carboxylic acid, the H-ZSM-5 zeolite with a relatively higher SiO 2 /Al 2 O 3 mole ratio was more effective at the elimination of methoxyl groups, ether bonds, and aliphatic C–C bonds, and dehydration of aliphatic hydroxyl groups during pyrolysis. However, the H-ZSM-5 zeolite with a very large SiO 2 /Al 2 O 3 mole ratio, such as 280, has only limited effects on the properties of upgraded pyrolysis oil. After the use of zeolite, the pyrolysis oils contain some polyaromatic hydrocarbons, the content of which decreased with an increasing SiO 2 /Al 2 O 3 mole ratio of zeolite. GPC results show that the molecular weight decreased by 8–16% after the use of H-ZSM-5 zeolites.