晶化条件对HZSM-5分子筛合成收率和性能的影响

摘要

In SiO2-Al2 O3-TPABr-NH3 · H2 O-H2 O system,the effects of hydrothermal crystallization time and temperatures,and raw material amounts on the yields and properties of as-synthesized HZSM-5 molecular sieve were investigated. The results showed that the yield and relative crystallinity of as-synthesized samples were 10. 1% and 99. 8%,respectively,under the condition as follows:n( SiO2 ): n( Al2 O3 )=100, n(TPABr):n(SiO2)=0.1,n(NH3):n(SiO2)=1. 5,n(H2O):n(SiO2)=22,seed crystal amount 4%, crystallization temperature 180 ℃ and crystallization time 72 h. The corresponding theoretical yield was 11 . 4%,and the ratio of the yield of as-synthesized samples to the theoretical yield was 0 . 89 . As n(SiO2):n(Al2O3)of the raw material enhanced from 50 to 400,the yield and crystallinity of the as-synthesized samples remained more than 8. 9% and 82. 8%,respectively,and the ratio of as-synthesized sample yield to the theoretical yield was 0 . 76 -0 . 89 . The acid amount of the as-synthesized samples decreased gradually with the increase of n( SiO2 ): n( Al2 O3 )of the raw material. The as-synthesized HZSM-5 molecular sieve with BET surface area of 405 m2 ·g-1 exhibited good acid catalytic activity for methanol-to-olefins reaction. At the set condition,methanol conversion,the selectivity to propylene and C2=-C4= light olefins were 100%,39. 27% and 62. 01%,respectively,using HZSM-5 molecular sieve catalyst prepared with the raw material of n(SiO2):n(Al2O3)=250.%考察了SiO2-Al2 O3-TPABr-NH3·H2 O-H2 O体系晶化时间、晶化温度和原料用量等对合成HZSM-5性能的影响。当n（ SiO2）：n（ Al2 O3）=100、n（ TPABr）：n（ SiO2）=0.1、n（ NH3）：n（SiO2）=1.5、n（H2O）：n（SiO2）=22和晶种添加质量分数为4%时，180℃静态晶化72 h，合成收率与相对结晶度分别为10.1%和99.8%，对应理论收率为11.4%，合成收率与理论收率比为0.89。当投料n（SiO2）：n（Al2O3）从50增加到400，合成收率与结晶度分别超过8.9%和82.8%，合成收率与理论收率比为0.76～0.89；样品酸量随着n（ SiO2）：n（ Al2 O3）的增加逐渐减小，比表面积为405 m2·g-1，合成样品HZSM-5对甲醇制烯烃反应具有良好的酸催化活性。设定反应条件，采用投料n（ SiO2）：n（ Al2 O3）=250的样品，甲醇转化率、丙烯选择性和C2=～C4=选择性分别为100%、39.27%和62.01%。