Catalytic cracking of gasoline and diesel to produce olefins is crucial for the high-value utilization of surplus fuels. This process typically employs zeolite catalysts. In order to reveal the effects of zeolite type and acidic properties on the catalytic cracking performance for the diesel model compound dodecane, SAPO-34, ZSM-5-38 (SiO2/Al2O3 ratio of 38, the same below), ZSM-5-85, ZSM-5-200 and USY were taken as research subjects. These zeolites were characterized by X-ray diffraction, scanning electron microscope, N2 physical adsorption, NH3-temperature programmed desorption and pyridine adsorption Fourier-transform infrared spectroscopy, and their catalytic cracking performance was systematically evaluated on a fixed-bed reactor. Results indicated that the zeolite type was the primary determinant of dodecane conversion and product distribution. SAPO-34, with a 0.38 nm pore size, exhibited low catalytic activity, achieving a dodecane conversion of 24.33% and nearly zero BTX aromatics yield. Although SAPO-34 showed high light olefins selectivity, severe coking occurred on its external surface. In contrast, ZSM-5-38, with a moderate pore size and acid amounts, demonstrated excellent catalytic activity, achieving nearly 100% dodecane conversion. Its liquid products were predominantly BTX aromatics, with the relatively highest light olefins yield of 18.40% and minimal coke yield of 0.18% among the three different zeolites. USY, featuring the largest pore size, also fully converted dodecane but primarily produced light alkanes and coke. Secondly, based on the identified zeolite type, adjusting the acidic properties could further refine product distribution. Experimental data indicated that the number of acid sites in ZSM-5, especially the Brønsted acid sites, decreased as the SiO2/Al2O3 ratio increased. Among ZSM-5 with different acidic properties, ZSM-5-200 showed superior catalytic cracking performance for dodecane, achieving a total gas product yield nearing 65% and a conversion of 97.79%. Additionally, the yields of ethylene, propylene and butene rose to 11.11%, 20.33% and 10.49% respectively, while maintaining a low coke yield of 0.43%. Finally, based on the above findings, the reaction pathway and regulation mechanism of dodecane catalytic cracking were proposed, including cracking, hydrogen transfer, oligomerization, aromatization and coking. The zeolite type and its acidic properties significantly influenced the conversion and product distribution by modulating the relative strength of these reactions. This study elucidates the structure-activity relationship between zeolite type, acidic properties and catalytic performance, enhances the understanding of catalytic reaction mechanisms and guides the optimization of gasoline and diesel catalytic cracking processes toward olefins production.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |