晶种法高效合成低硅铝比LSX型分子筛

High Efficient Seeding Synthesis of LSX Molecular Sieve with Low Si-Al Ratio

分别以工业级的偏铝酸钠和水玻璃为铝源和硅源,氢氧化钠为主要碱源,氢氧化钾为辅助碱源,采用LSX晶种法制备了LSX型分子筛。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线荧光(XRF)、傅里叶变换红外光谱(FTIR)和N2吸附-脱附等表征方式考察了有无晶种、钾钠物质的量之比、晶化条件对合成LSX型分子筛的影响。结果表明,加入LSX晶种不仅能显著缩短晶化时间,提高分子筛的结晶度,还可有效抑制方钠石和A型杂晶的伴生;钾钠比过高或过低均会造成A型或方钠石型杂晶的伴生;直接进行高温晶化会导致亚稳态的LSX型分子筛向热力学稳定相转变;延长老化时间或高温晶化处理降低了产物中的硅铝比;样品的比表面积和N2吸附量随老化时间的延长和高温晶化处理而逐渐下降。

Influencing factors for the synthesis of LSX molecular sieve, such as LSX seed, nK/nNa and crystallization conditions were investigated in detail. The products were characterized by XRD, SEM, XRF, FTIR and N2 adsorption-desorption. The results revealed that the addition of LSX seed could accelerate the rates of crystal nucleation and growth, and inhibit the formation of A type and sodalite zeolites. Furthermore, too high or too low value of nK/nNa in the synthesis gel would obtain A type and sodalite impurities. Crystallization at high temperature directly would lead the conversion of metastable LSX zeolite into more thermodynamically stable zeolite phase. The Si-Al ratio, the surface area and N2 adsorption capacity of the end product decreased with the extending of aging time and the increasing of crystallization temperature.