多级孔道ZSM-5分子筛的制备及其催化裂解性能

通过直接合成或后改性等方法制备了具有多级孔道结构的ZSM-5分子筛样品，用X-射线衍射(XRD)、扫描电镜(SEM)、N2吸附-脱附、程序升温氨脱附(NH3-TPD)方法对其进行了表征，并在固定床反应器中对其催化裂解性能进行了评价。结果表明：与常规ZSM-5分子筛相比，多级孔道结构的ZSM-5分子筛具有比表面积高、介孔孔体积大、介微孔比率高等优势。在分子筛内引入多级孔道，在正己烷催化裂解反应中目的产物丙烯更易扩散，氢转移反应得到有效抑制，可提高丙烯收率。具有最高介微孔比率的纳米薄层NZSM-5-300样品上，其乙烯选择性为15.8%，丙烯选择性为40.1%，双烯总选择性为55.9%。通过对比发现：介微孔比率高的催化剂，正己烷转化率下降速度减缓，寿命延长。

PREPARATION OF HIERARCHICAL POROUS ZSM-5 ZEOLITE AND ITS CATALYTIC CRACKING PERFORMANCE

Hierarchical porous ZSM-5 zolites were prepared by direct synthesis and post modification and characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption/desorption and temperture-programmed desorption of ammonia (NH3-TPD), respectively. The catalytic cracking performance of the samples was evaluated in a micro fixed-bed reactor. The results indicate that compared with conventional ZSM-5, the hierarchical porous ZSM-5 zeolites have the advantages in higher surface area, mesoporous volume and ratio of meso/micro. The propylene yield is increased because the mesopores are introduced in the modified sieve, which make the product more easily to diffuse and th effectively suppress the hydrogen transfer reaction. Over the nanolayered NZSM-5-300 with the highest ratio of meso/micro, the selectivity of ethylene and reaches 15.8% and 40.1%,respectively. The test results indicate that with increase of meso/micro ratio, the sample exhibits better stability and lower deactivation rate as well as longer.