沸石晶种层形成的影响因素及其对Silicalite-1型沸石膜生长的影响

Factors Affecting the Formation of Zeolite Seed Layers on Different Porous Supports and Effects of Seed Layers on the Growth of Zeolite Membranes

研究了晶种二次成膜法中提拉法晶种涂层形成的主要影响因素,如载体性质、晶种大小和涂层溶剂及晶种层质量对Silicalite-1沸石水热生长成膜的影响。SEM和XRD分析表明,载体的性质、晶种大小及涂层溶剂对晶种层的形成均有很大影响。晶种在平整的小孔径陶瓷载体上易沉积形成连续晶种层,不平整的大孔载体上难以形成连续晶种层。弱极性的乙醇晶种悬浮液有利于晶种粒子的沉积;疏水性的炭载体不宜采用强极性的水作为溶剂进行晶种涂层,而宜在乙醇悬浮液中进行晶种涂层;纳米级小晶粒晶种易形成连续、均匀的晶种层,大晶粒(600nm和2.2μm)晶种不易在大孔载体上沉积。用小晶粒晶种形成的连续晶种层,沸石生长形成的膜质量好。结果表明,沸石膜的质量取决于晶种层的质量。

By using the slip-casting technique, the formation of silicalite-1 seed layers on porous carbon support with 0.5μm pore size and Al2O3 supports with different pore sizes（0.1 μm and 4 μm） were studied. The effects of support property, seed size and solvent on the formation of seed layers were investigated in detail. The growth of silicalite-1 membranes on different seeded supports by hydrothermal synthesis was also evaluated. The SEM and XRD characterizations indicate that a continuous seed layer can be obtained on the smooth support with 0.1μm pore size by using any seed of 100 nm, 600 nm or 2.2 μm in size, whereas, on the coarse supports with either 0.5 μm or 4μm pore size, a continuous seed layer can not be formed by using the above seed sizes and the same seeding time. At a longer contacting time, a seed layer can also be formed by using 100 nm seed on the supports with larger pore size, however, it is not uniform and smooth. For the hydrophobic carbon support, the ethanol seeding suspension, which has weak polarity, favors the formation of a continuous seed layer. The seed layers and membranes grown from the smaller seed are more uniform and continuous and possess smoother surfaces than those from larger seed. The seed layer and respective membrane formed from nanosized seed（100nm） are the most uniform and compact. In this method of zeolite membrane synthesis by seed in twice, the quality of membrane mainly depends on the quality of the seed layer.