梯度孔结构空心ZSM-5分子筛构筑与催化裂解性能

Construction and Catalytic Cracking Performance of Hollow ZSM-5 WithGradient Pore Structures

合成内部富硅表面富铝的母体ZSM-5分子筛,采用不同浓度的氢氧化钠溶液处理制备了晶体壳层厚度分别为80、40、20和10 nm的空心介孔ZSM-5分子筛;通过X射线光电子能谱(XPS)、X射线衍射光谱(XRD)、透射电镜(TEM)、扫描电镜(SEM)、氨气程序升温脱附(NH3-TPD)、吡啶红外吸附(Py-FTIR)、N_(2)吸附-脱附曲线等对ZSM-5分子筛样品进行物化表征;并以正辛烷和十氢萘作为模型化合物,在反应温度550和600℃、进料速率0.8 g/min、进料时间150 s、剂/油质量比0.25条件下考察不同分子筛催化烃类裂解反应性能的差异。结果表明,催化裂解反应中,壳层厚度为20 nm的空心介孔分子筛(HZ5-AT3)具有更高原料转化率和低碳烯烃收率,这归因于微孔-介孔-大孔梯度孔分布的空心介孔分子筛可同时提供丰富的酸中心和多方位的扩散路径,提高了分子筛活性中心的可接近性,进而促进了大分子烃类的裂解反应。

The Al-rich external and Si-rich external ZSM-5 zeolite was synthesized as parent zeolite.The hollow mesoporous ZSM-5 zeolites with the shell thickness of 80,40,20 and 10 nm were prepared using different concentrations of sodium hydroxide solutions for treatment.ZSM-5 zeolite samples were physicochemically characterized by means of XPS,XRD,TEM,SEM,NH 3-TPD,Py-FTIR and N_(2) physical adsorption-desorption curves.Moreover,the catalytic performances of ZSM-5 zeolites in hydrocarbons cracking were investigated under the following conditions:the reaction temperature of 550 and 600℃,feed injection rate of 0.8 g/min,feed injection time of 150 s,and catalyst/oil mass ratio of 0.25.The results show that in the catalytic cracking reaction,HZ5-AT3 hollow zeolite with a shell thickness of 20 nm exhibits higher conversion rate and light olefin yield.This is attributed to the fact that the hollow mesoporous zeolite with a gradient distribution of micro-,meso-and macro-pores can provide rich acid centers and multi-directional diffusion paths,thus improving the accessibility of active centers,and promoting the cracking of large molecule hydrocarbons.