后处理改性对HZSM-5沸石丁烯裂解性能的影响

采用不同后处理手段(碱处理、水汽处理以及碱处理-水汽处理)对HZSM-5沸石的孔结构和酸性质进行了调变,并对其丁烯裂解性能进行了研究。运用N₂吸脱附、扫描电镜(SEM)、X射线衍射(XRD)以及吡啶吸附红外(Py-IR)对后处理改性前后的沸石样品的物理化学性质进行了表征。碱处理后HZSM-5的质子酸量增加,在5～20 nm处具有分布较宽的介孔,其反应活性升高,丙烯选择性下降,但失活速率没有加快。单独水汽处理在2～4 nm处产生介孔,但介孔体积较小。碱处理-水汽处理在2～4和5～20 nm处具有双分布介孔,前者分布较集中,后者分布较宽。单独水汽处理和碱处理-水汽处理的样品可以提高HZSM-5的丙烯选择性,主要归功于酸量的降低;反应2.5 h后具有较稳定的丙烯收率(高碱浓度处理-水汽处理的样品除外)。

Effects of post treatment of HZSM-5 zeolites on catalytic cracking of butene

The structure and acidity of HZSM-5 zeolites were modified using different post treatment methods: alkaline treatment, steam treatment, and alkaline-steaming treatment. The catalytic performances of modified zeolites were tested in 1-butene catalytic cracking. Their physicochemical properties were characterized by N₂ adsorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy with pyridine adsorption (Py-IR). The acidities of zeolites increased after the alkaline treatment, and as a result, the activity of butene cracking increased and the selectivity of propylene decreased. However, the deactivation rate of alkaline-treated zeolites had no significant change. There was a pronounced development of mesopores (5-20 nm) with a broad pore-size distribution in alkaline-treated ZSM-5 zeolites. Mesopores (2-4 nm) with a narrow distribution is observed after steaming treatment, while the mesopore volume is low. Zeolites after alkaline-and steaming-treatment showed two kinds of mesopore distributions, 2-4 nm (narrow) and 5-20 nm (broad). Due to the decrease of Brønsted acidic sites, the selectivity of propylene increased over ZSM-5 zeolites with any of the post treatments; a relatively stable propylene yield was obtained after the reaction of 2.5 h (except for zeolites treated with high concentration of alkaline followed by steaming treatment).