Catalytic Upgrading of Hami Coal Pyrolysis Volatiles over Mesoporous Kaolin Prepared by Calcination and Naoh Leaching

Catalytic upgrading of coal pyrolysis volatiles is an effective approach to improve tar quality with its high-value utilization, and the use of inexpensive solid acid catalysts can reduce the cost of industrial applications. In this work, kaolin was chosen as the raw material for modification by calcination (950-1200 degrees C) and NaOH leaching to serve as a catalyst (ACK) for upgrading volatiles from Hami coal pyrolysis. The properties of ACK under different calcination temperatures and the distribution of pyrolysis products were characterized to investigate the relationship between ACK properties and catalytic effect. The addition of ACK significantly improved the tar quality, as demonstrated by an increase in light tar fraction from 40.1 wt% to 46.4-52.8 wt%, a reduction in O/C atomic ratio of 11.4 %-37.6 %, and an increase in aromatics selectivity from 18.3 % to 21.2 %-25.0 %. These improvements were attributed to the varying increases in the specific surface area and acid sites of kaolin, a consequence of the formation of differing amounts and locations of amorphous silica during calcination and subsequent desilication by NaOH. Both the specific surface area and acid sites of ACK showed a tendency to increase and then decrease with rising calcination temperature. The improvements in tar quality were intimately linked to the pore structure and acidity of ACK, with ACK1100 (1100 degrees C calcination followed by NaOH leaching) exhibiting the most promising tar upgrading performance due to its maximum acid sites and a high specific surface area second only to ACK1050.