以低温固相碱熔活化高岭土为原料合成ZSM-5分子筛

以天然矿物高岭土为主要硅铝原料,经低温固相碱熔活化后,在常规水热条件下合成ZSM-5分子筛,考察m(高岭土)∶m(氢氧化钠)、碱熔温度及碱熔时间等因素对高岭土活化效果的影响。采用XRF、XRD、FT-IR和N2-吸脱附等对不同样品进行表征。结果表明,在m(高岭土)∶m(氢氧化钠)=1∶1.5、碱熔温度250℃和碱熔时间30 min条件下,可以实现高岭土完全活化。该活化方式不仅降低了活化温度,且能在极短时间内提高高岭土活性。以最适宜低温固相碱熔活化条件下所得活性硅铝物质为主要原料,硅溶胶为外加硅源,采用水热法合成高相对结晶度的纯相ZSM-5分子筛。与工业ZSM-5分子筛相比,合成ZSM-5分子筛具有更大的比表面积和孔容。

Synthesis of ZSM-5 zeolite from kaolin activated by low temperature alkali fusion

ZSM-5 zeolite was synthesized through conventional hydrothermal method using natural mineral kaolin activated by low temperature alkali fusion as main silica source and aluminum source.Effects of kaolin/NaOH mass ratio,alkali fusion temperature and alkali fusion time on kaolin activation were investigated.The samples were characterized by XRF, XRD, FT-IR and N₂ adsorption-desorption.Results showed that kaolin could be completely activated when mass ratio of kaolin to sodium hydroxide was 1:1.5,temperature of alkali fusion was 250 ℃ and time of alkali fusion was 30 min.The activation method not only greatly reduces activation temperature, but also improves activity of kaolin in a very short period of time.Pure ZSM-5 zeolite with relatively high crystallinity is synthesized by hydrothermal method using active silica-alumina material obtained under the optimal condition of alkali treatment and extra additional silica sol as raw material.Compared with commercial ZSM-5 zeolite,as-synthesized ZSM-5 zeolite sample has larger specific surface area and pore volume.