微波辐射法合成SAPO-5分子筛中硅铝比对产物结晶度和甲苯吸附性能的影响

采用硅溶胶作硅源, 用微波辐射法在酸性条件下(pH=4.5-5.0)合成了SAPO-5分子筛, 利用X射线衍射(XRD), 傅立叶变换红外光谱(FT-IR), 扫描电镜(SEM)和Brunauer-Emmett-Teller (BET)比表面积分析对样品的结晶度、形貌和比表面等进行表征, 考察了晶化原料硅铝比对分子筛结晶度和晶体颗粒长径比(c/a)的影响, 测定了分子筛对甲苯的吸附性能. 结果显示, 采用微波辐射法合成的SAPO-5分子筛, 在硅铝摩尔比为0.50附近生成产物的结晶度最好, 晶体颗粒的长径比最小(约为1.0). 尽管不同硅铝比条件下得到的样品比表面测定结果变化不大, 但对甲苯的吸附实验显示, 在硅铝比为0.50时样品的吸附速率和饱和吸附量均达到了最大值. 这与表征所得的结晶度和长径比的变化一致, 即结晶度好,长径比小的SAPO-5分子筛具有更好的甲苯吸附性能.

Effects of Si/Al Molar Ratio on the Crystallinity and Toluene Adsorption of SAPO-5 Synthesized under Microwave Radiation

SAPO-5 molecular sieves were synthesized using high pressure microwave radiation and at pH=4.5-5.0. Effects of silica/alumina (Si/Al) molar ratios of the initial reaction sol-gel on the aspect ratio (c/a) of resulting crystal particles and the toluene adsorption capability of the products were investigated. X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area analyses showed that good crystallinity and low crystal aspect ratio were apparent at a Si/Al molar ratio of 0.50. The highest toluene adsorption rate and quantity was obtained at around the same Si/Al molar ratio of 0.50. BET surface areas were approximately constant despite the products were obtained under the reaction conditions of different Si/Al molar ratios. The agreement obtained from the characterization and adsorption indicates that SAPO-5 molecular sieves with high crystallinity and low aspect ratio are valuable for toluene adsorption.