低硅体系下SAPO-34分子筛的合成

以三乙胺和吗啉为模板剂,考察了硅含量和晶化温度对合成SAPO-34分子筛的影响,研究了低硅条件下SAPO-34分子筛的晶化规律。在n(SiO2)∶n(Al2O3)=0.1的低硅体系中合成出了高结晶度的SAPO-34分子筛,发现将晶化温度从200℃降至170℃更有利于低硅条件下SAPO-34分子筛的合成。根据合成结果初步认为,低硅条件下SAPO-34分子筛的合成可能符合低温成核、高温生长机理,并用分段晶化实验加以证实。实验结果表明,在低硅体系下,先在170℃晶化一段时间再在200℃晶化一段时间(总晶化时间48 h),不仅可获得高结晶度SAPO-34分子筛,且能缩短晶化时间;若将分段晶化温度顺序调换,即先在200℃晶化再在170℃晶化,则无法获得纯相SAPO-34分子筛,说明先低温后高温的分段晶化更有利于低硅体系下纯相SAPO-34分子筛的合成。

Synthesis of SAPO-34 Molecular Sieves from Gels with Low Silicon Concentration

The synthesis of SAPO-34 molecular sieves in a system with low silica content was investigated.It was found that lowering the crystallization temperature from 200 ℃ to 170 ℃ was beneficial to the formation of pure SAPO-34 phase in the low silica system.At 170 ℃,high crystalline SAPO-34 was obtained from the gel with molar ratio of SiO2 to Al2O3 0.1 with triethylamine or morpholine as the template.The synthesis might accord with low-temperature nucleation and high-temperature growth mechanism,which was confirmed by a multistep crystallization,namely first at 170 ℃ for t h and then at 200 ℃ for 48-t h in the low silicon system.The high crystalline SAPO-34 could be synthesized in a short crystallization period.