Catalytic fast pyrolysis of herbal medicine wastes over zeolite catalyst for aromatic hydrocarbons production

Abstract

Catalytic pyrolysis is an effective method to upgrade biomass pyrolytic bio-oil. In this study, catalytic fast pyrolysis (CFP) of licorice residue (LR) over ZSM-5 was conducted using pyrolysis–gas chromatography/mass spectrometry. The effects of temperature, Si/Al atomic ratio (SAR) and catalyst to feedstock (C/F) ratio on the formation of aromatic hydrocarbons (AHs) were investigated. The results indicated that ZSM-5 effectively converts oxygenates into AHs. Specifically, benzene, toluene, ethylbenzene, p-xylene and naphthalene (BTEXN) were the dominant components. The pyrolysis temperature and acidity of zeolite exert a greater influence on the formation of BTEXN. The maximum content of BTEXN was 73.45 % at 500 °C and 72.21 % at lower SARs (27 and 36). Coke can be formed and deposited on the zeolite during CFP of LR, which cause the deactivation of catalyst. A higher pyrolysis temperature and C/F ratios inhibits the coke formation, while a higher SAR is beneficial to coke formation. The large oxygenated molecules and aliphatic hydrocarbons (AHCs) was the precursors of coke during catalytic pyrolysis. The coke was tended to disperse on the surface of catalyst at low temperature. However, it was largely deposited in the channels of zeolite catalyst at high temperatures. This study reveals that ZSM-5 is an effective catalyst for the utilization of herbal medicine wastes. The pyrolytic bio-oil has high potential for use in fuels or renewable chemical production.