In-situ catalytic upgrading of Hami coal pyrolysis volatiles over acid-modified kaolin. (1st January 2023)

• Record Type: Journal Article
• Authors: Hou, Yujie; Bai, Zongqing; Lu, Hao; Feng, Zhihao; Zhang, Tingting; Jia, Yuxing; Guo, Zhenxing; Kong, Lingxue; Bai, Jin; Li, Wen
• Is Part Of: Fuel. Volume 331:Part 1(2023)
• Publication Date: 2023-01-01
• Subjects: Acid-modified kaolin -- Coal pyrolysis -- Catalytic upgrading -- Light tar -- Aromatics; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.125660
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Low-cost kaolin with modification can significantly upgrade coal pyrolysis volatiles. Calcination and HCl treatment affect kaolin structure and upgrading performance. AMK800 shows the best performance on the production of light tar and aromatics. Tar quality is determined by BAS amount and pore structure of AMKs together. Abstract: Low-cost kaolin was modified by calcination at different temperatures, followed by HCl leaching, and used as catalyst for in-situ upgrading of Hami coal pyrolysis volatiles in a fixed-bed reactor. The catalyst characteristics, pyrolysis product distributions and tar properties were investigated by multiple methods to understand the relationship between catalyst properties and tar quality. The results indicated that calcination of kaolin promoted the formation of amorphous metakaolin, then the HCl leaching removed most metakaolin framework Al, leading to the production of abundant micro-/mesopores and acid sites. As the rising calcination temperature, the specific surface area and pore volume of acid-modified kaolin (AMK) showed a trend of increasing and then decreasing, and the Brønsted acid sites (BAS) displayed an increasing trend. Compared to non-catalytic pyrolysis, the high specific surface area and certain acid sites of AMKs enhanced the light tar fraction from 37.81 wt% to 43.00–48.45 wt%, and the relative content of aromatics in tar increased from 9.76% to 16.65–22.11%, with monocyclic aromatics, naphthalenes and polycyclic aromatics increasing to 3.5–4.2, 1.2–1.8 and 2.1–3.3 times higher, respectively. AMKs also reduced the content of element O in tar by 17.92–31.54% by promoting the deoxygenation reaction. The tar upgrading performance was determined by the BAS amount and the pore structure of AMKs together. Among all AMKs, AMK800 (calcined at 800 °C and treated by HCl) exhibited the optimum performance for heavy tar conversion, aromatics generation and oxygen removal due to its highest specific surface area and the maximum BAS except AMK900. The acid-modified kaolin has the potential to be an inexpensive and efficient catalyst for future practical applications of upgrading coal pyrolysis tar.