煤系高岭土合成NaA分子筛及其机理分析

Synthesis of NaA zeolite from kaolin and its crystallization mechanism

以煅烧煤系高岭土为原料,采用氢氧化钠溶液水热合成制备NaA分子筛。以NaA分子筛晶体的生长过程为基础,利用XRD、SEM对NaA分子筛晶体生长规律进行表征,并对其结晶机理进行了分析。结果表明,煤系高岭土制备NaA分子筛的最佳工艺条件是:煅烧温度为725℃;配料比m(Na2O)/m(SiO2)为3,m(H2O)/m(Na2O)为40;胶化条件为70℃×2 h;晶化条件为100℃×6 h。所制NaA分子筛的钙离子交换量为316.55 g CaCO3/g。在NaA分子筛的碱液合成过程中,在晶化条件下,凝胶固相中的硅铝酸根骨架解聚重排晶化成沸石晶体骨架。

NaA zeolite was successfully synthesized with hydrothermal method from calcined kaolin used as sources for both silica and alumina.The growth of NaA zeolite was studied by XRD and SEM,and the crystallization process of NaA zeolite in the hydrothermal reaction system was ana-lyzed.The optimal synthesis conditions were found to be as follows： m（Na2O）/m（SiO2）=3;m（H2O）/m（Na2O）=40;the calcining temperature is 730 ℃;the temperature and time in the gel formation stage are 70 ℃ and 3 h;and the temperature and time in the crystallization stage are 100 ℃ and 6 h,respectively.Kaolin is suggested to be a feasible and economical raw material for practical industrial production of NaA zeolite.