Catalytic upgrading of lignite pyrolysis volatiles over modified HY zeolites

Abstract

HY zeolite is modified by hydrothermal and HNO3 treatment and used as the catalyst to upgrade Baiyinghua pyrolysis volatiles on a fixed-bed reactor at 600 °C. The results show that hydrothermal and acid treatment obviously affect zeolite structure and upgrading of pyrolysis volatiles. The dealumination of HY increases with hydrothermal temperature, resulting in the decrease of total surface area and acid amount and the formation of larger pores. However, the content and yield of light tar are enhanced over modified HY, and the cracking of volatiles into gas is retarded. Acid treatment of hydrothermal modified HY at 650 °C removes extra-framework Al, improves surface area and the volatiles cracking. But high acid concentration leads to the destruction of zeolite structure, and is unfavorable to the upgrading. Modified HY by treatment at 650 °C and 0.8 mol/L HNO3 shows the best performance in catalytic volatiles upgrading. About 81.5 wt% light tar content and 61.1% light aromatic hydrocarbons content can be obtained. Especially, the yields of naphthalene and methylnaphthalene are increased by 8.9 and 6.8 times. The content of oxygenated PAHs is reduced by 4.3 times. The improved performance is mainly due to high surface area, large pore diameter and suitable acidity.