Catalytic pyrolysis of lignin over HZSM-5 catalysts: Effect of various parameters on the production of aromatic hydrocarbon

• Milled wood lignin was pyrolyzed with different Si/Al mole ratio of HZSM-5 catalyst.
• As aromatic hydrocarbon, benzene, toluene, ethylbenzene, and p-xylene were produced.
• The distribution of lignin pyrolysis products was clearly affected by catalyst acidity.
• The effects of pyrolysis temperature, catalyst amount and lignin source were investigated.

The purpose of this study was to investigate (1) the effect of various parameters on catalytic pyrolysis of lignin over HZSM-5 catalysts and (2) the origin of aromatic hydrocarbon (AH) from lignin pyrolysis products. Lignin polymer extracted from poplar wood was pyrolyzed using pyrolysis-GC/MS with HZSM-5 catalysts composed of different Si/Al mole ratios (30–280). Benzene, toluene, ethylbenzene, and p-xylene were produced as the main AH species, and other phenolics as well as fatty acids (FA) were also detected as lignin pyrolysis products. FA was not common lignin pyrolysis products, which might be derived from suberin moieties accumulated together with recovered lignin during lignin separation process. The acidity of HZSM-5 was inversely proportional to Si/Al mole ratio and the yield of AH proportionally increased with increasing catalyst acidity. To trace the origin of AH from lignin pyrolysis products, several lignin model compounds were pyrolyzed with HZSM-5 (Si/Al:30). These results revealed that FA showed the largest contribution to AH production, followed by 4-allylsyringol, coniferaldehyde, and acetoguaiacone. With respect to pyrolysis temperature, AH yield gradually increased with increasing pyrolysis temperature in our investigated range (500–700 °C). In addition, AH yield also increased up to 35.7 mg/g of lignin at a high catalyst to lignin ratio (2:1). Other lignin sources obtained from an industrial pulping/bioethanol plant were also pyrolyzed with HZSM-5 (Si/Al:30) and these results were comparatively studied.