NaA沸石的合成及热稳定性研究

Synthesis of Zeolite NaA and Its Thermal Stability

在常压开放水体系中合成了NaA沸石,探讨了Na2O与SiO2摩尔比、晶化温度和晶化时间对合成NaA沸石纯度的影响,阐述了合成过程中产生杂晶NaX沸石和羟基方钠石的原因,并考察了不同煅烧温度对NaA沸石热稳定性的影响。结果表明:体系中合成NaA沸石的最佳优化条件为:Na2O与SiO2摩尔比为2.0,晶化温度为80℃,晶化时间为10 h,其中Na2O与SiO2摩尔比对产物的骨架类型和纯度影响较晶化温度和时间大。热分析结果表明,NaA沸石经850℃热处理仍能保持骨架结构的稳定,热稳定性较强;在900℃时骨架结构被破坏,相变为霞石。

The zeolite NaA sample were prepared in open water system at atmospheric pressure. The effect of molar ratio of Na2O to SiO2, crystallization temperature and crystallization time on the degree of purity of zeolite NaA were explored, and the reasons of the formation of impure crystal zeolite NaX and hydroxy sodalite were elaborated. In addition, the effect of different calcination temperature on thermal stability of zeolite NaA was investigated. The results showed that the optimum conditions of synthetic zeolite NaA were that the molar ratio of Na2O to SiO2 was 2.0, crystallization temperature was 80 ℃, crystallization time was 10 h. The molar ratio of Na2O to SiO2 had a greater inf luence than crystallization temperature and crystallization time for the skeleton type and degree of purity of the products. The zeolite NaX, zeolite NaA and hydroxy sodalite had a similar skeleton structure and structural energy, which were the reasons of the formation of impure crystal zeolite NaX and hydroxy sodalite during the synthetic process of zeolite NaA. The thermal analysis result showed that the zeolite NaA could maintain the integrity of skeleton type and had good thermal stability at 850 ℃. Phase transition from zeolite NaA to nepheline was occurred at 900 ℃.