ZSM-5分子筛晶粒尺寸对石脑油催化裂解性能的影响

Effect of Crystal Size of ZSM-5 Zeolite on Catalytic Cracking of Naphtha

采用XRD、NH_3-TPD、N_2物理吸附、XRF和SEM等方法对两种ZSM-5分子筛(ZRP和FX分子筛)进行了表征,并在固定床反应器中于600℃下对其催化裂解石脑油的性能进行了评价。表征结果显示,ZRP和FX分子筛均具有ZSM-5分子筛的特征衍射峰,均为单晶条状晶粒,且具有几乎相同的硅铝比和酸量及酸分布,但两者的晶粒尺寸、BET比表面积和微孔比表面积有差异;ZRP分子筛的晶粒粒径为2～3μm,FX分子筛的晶粒粒径小于1μm;FX分子筛的BET比表面积和微孔比表面积大于ZRP分子筛。实验结果表明,ZSM-5分子筛对石脑油的催化裂解能力及乙烯与丙烯的总收率随晶粒尺寸的减小而增大,这与小晶粒分子筛的扩散路程短有关。

Both ZSM-5 zeolites（ZRP and FX） were characterized by means of XRD, NH3-TPD, Nz physical adsorption, XRF and SEM. The catalytic performances of the ZSM-5 zeolites in naphtha cracking were investigated in a fixed-bed reactor at 600 ℃. It was found that both the ZRP zeolite and the FX zeolite possessed ZSM-5 characteristic peaks and bar-shaped single crystal structure. Both of them had nearly same Si/Al ratio, acid amount and acid distribution. However, their different properties were found in the crystal size, the BET specific surface area and the micropore specific surface area. The crystal size of the ZRP zeolite was 2 - 3 μm and that of the FX zeolite was less than 1μm. Both the BET specific surface area and the micropore specific surface area of the FX zeolite were larger than these of the ZRP zeolite. Experiment results showed that the total yield of propylene and ethylene in the naphtha cracking over the ZSM-5 zeolites increased with decrease of their crystal size. The possible reason was the short distance for molecular diffusion. The conclusion was further proved by the performance of a zeolite with small crystal size and less NH3-TPD acid amount.