低模数水玻璃合成ZSM-5分子筛及工艺条件优化

Synthesis of ZSM-5 from Low Modulus Sodium Metasilicate System and Optimization of Process Conditions

以低模数(n=1.03)水玻璃为硅源,通过改良水热合成途径,成功制备出无模板剂ZSM-5分子筛。借助X射线衍射仪(XRD)和扫描电镜(SEM)对ZSM-5分子筛结晶度及晶貌进行表征。在n(硅)/n(铝)为50的情况下,通过考察晶化温度、时间、pH值、水含量、有无搅拌或晶种对ZSM-5分子筛物性的影响,优化合成工艺。结果表明,静置或晶种法得到的ZSM-5分子筛,晶体粒径大且晶貌不规整,不适合用于低模数水玻璃合成ZSM-5体系。ZSM-5沸石最适宜制备工艺为:n(H2O)/n(SiO2)=40,pH=10的合成混合物经室温老化24 h,搅拌状态下,170℃下水热晶化24 h。与商业级ZSM-5相比,低模数水玻璃合成的ZSM-5分子筛在环己烯水合反应中表现出更高的催化活性和选择性。

Template-Free ZSM-5 from low modulus （n = 1.03 ） sodium metasilicate synthesis mixture were successfully synthesized through an improvement hydrothermal synthesis route. The crystallinities and morphologies of the ZSM-5 zeolites were characterized with X-ray diffraction （XRD） and scanning electron microscopy （ SEM）. In the case of silica alumina ratio of 50, the synthesis process was optimized by examining the effect of crystallization temperature, time, pH, water content, stir and seed crystal on the properties of ZSM-5 zeolites. ZSM-5 zeolites with big crystal size, irregular morphology were obtained from static or crystal seed method, the results showed that those two methods were not suitable for synthesis of ZSM-5 system. The suitable synthesis conditions of ZSM-5 zeolite are as follows： pH = 10, n（H20）/n（SiO2） = 40, aged at room temperature for 24 h, hydrothermal crystallization at 170 ~C for 24 h. Compared with the commercial ZSM-5, ZSM-5 zeolites obtained from low modulus sodium metasili- care synthesis mixture exhibited a higher catalytic activity and selectivity in the hydration reaction of cy- elohexene.