后处理改性对HZSM-5沸石丁烯裂解性能的影响

摘要

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).%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）。