HDZ沸石催化剂上正庚烷和丙烯的转化

CONVERSION OF n-HEPTANE AND PROPENE ON HDZ ZEOLITE CATALYST

研究了正庚烷和丙烯在用水蒸汽和高温焙烧改性的直接法合成的HZSM-5型沸石催化剂上反应活性与产物选择性变化规律。结果表明,随水蒸汽处理和焙烧温度提高,沸石表面酸度和强酸中心数逐渐减少。在400℃以上水蒸汽处理或在650℃以上焙烧,沸石在脱羟基同时伴随骨架铝脱除,晶体孔容减少,孔口尺寸收缩。正庚浣和丙烯的反应活性随处理温度提高而降低,芳烃选择性下降,C_5^+脂肪烃含量增加,目的产物汽油收率提高;沸石形选性增加,p/o值急剧增大。两种不同方法改性的HDZ沸石反应活性和产物选择性有完全相似的变化规律。此外,考察了HDZ沸石失活特征和水蒸汽处理对结炭的影响。

HDZ zeolite(HZSM-5 type zeolite) synthesized in the absence of templates was provided by Nankai University. The effects of steam treatment and calcination at various temperatures on the activity and selectivity for conversion of n-heptane and propene on HDZ zeolite catalysts were studied.The experimental results show that with increasing the temperature of steam treatment or calcination the total surface acidity and number of strnog acid sites on the modified HDZ zeolite decreased. When the temperature of steam treatment exceeds 500℃, XPS results reveal that part of the Al migrates to the outer layer from the bulk of the zeolite, so that the Si/Al ratio in the outer layer decreases, the micropore volume decreases and the channel size of modified zeolite contracts slightly. As a consequence, the catalytic activity of zeolite decreases apparently. It can be seen that with increasing treatment temperature, the concentration of aromatics and C_1-C_4 gaseous hydrocarbons diminishes and simultaneously increasee in C_5^+ aliphatics, that results in increasing the selectivity of gasoline. In the case of calcination treatment the selectivity of products is similar to that obtained with steam treatment.The deactivation of the HDZ zeolite catalyst during the conversion of n-heptane and its coking behavior after steam treatment have also been examined.