Effect of different acid-leached USY zeolites on in-situ catalytic upgrading of lignite tar

摘要

In this work, USY zeolites obtained by hydrothermal pretreatment were leached by nitric acid (HNO3), hydrochloric acid (HCl) and oxalic acid (H2C2O4), respectively, and used as catalysts to upgrade in-situ lignite tar into light aromatics. The results showed that the acid leaching with HNO3 and HCl removed extra-framework Al of USY, resulting in the decrease of total acid sites but the increase of ratio Bronsted/Lewis acid sites and mesopores volume, which improved catalytic performance and facilitated mass transfer in the reaction. The H2C2O4 leaching dissolved framework Al of USY, leading to a dramatic reduction of acid sites. USY-HCl and USY-HNO3 catalysts exhibited a good performance in the improvement of light aromatics and light tar (boiling point < 360 degrees C). The promotion of light aromatics, especially the naphthalene homologs, was obvious. The total yields of naphthalene and methylnaphthalene were increased by 7.6 and 6.7 times compared with non-upgrading tar. Light tar contents were also increased by about 47.7% in comparison with non-upgrading tar. This work provides a novel method to upgrade the in-situ lignite tar and generate more light aromatics by optimizing the physicochemical properties of USY zeolites.