Gas-phase catalysis of coal fast pyrolysis volatiles over acid, base and acid-base composite catalysts and the catalysts coking behavior

Abstract

The gas-phase catalytic upgrading of coal rapid pyrolysis volatiles is a promising strategy for achieving high-value utilization. The catalytic reforming characteristics of coal rapid pyrolysis volatiles over solid base catalyst (calcium aluminate, AlCa), acid catalyst (HZSM-5, Z5), and acid-base composite catalyst (AlCa-Z5) were investigated using a falling bed reactor. The composition and properties of coke deposits on various catalysts were systematically compared and evaluated using NH₄/CO₂-TPD, XPS, Raman spectroscopy, and temperature programmed oxidation (TPO). The findings indicate that AlCa and Z5 markedly increased olefins and aromatics in tar, respectively, and the AlCa-Z5 elevated olefins, aromatics and phenols to over 70 %. The coke mainly deposited on strongly basic and acidic sites, predominantly blocking the 2–6, 1–2, and 0–6 nm pore channels of the AlCa, Z5, and AlCa-Z5 catalysts, respectively. AlCa formed less catalytic coke than the Z5 (48.76 vs. 60.09 %), although the coke graphitization and particle size were greater owing to its exceptional dehydrogenation properties. Specifically, the graphitization and particle size of coke formed on AlCa-Z5 were remarkably reduced. The oxidative weight loss temperature of thermal coke is around 450 °C, while the catalytic coke on AlCa reaches up to 720 °C, over 100 °C higher than that of Z5. The CC/C-C structures (>80 %) dominate in coke, exhibiting more O-CO on AlCa and more C-O on Z5. The research results support the advancement and industrialization of coal hierarchical pyrolysis gas-phase catalytic cracking technology.