Synthesis And Characterization Of Lanthanum Silicoaluminophosphate Molecular Sieve

Porous crystalline silicoaluminophosphate molecular sieves possess three-dimensional framework structure of tetrahedral units AlO4, PO4 and SiO4, and ion-exchange properties and acidity. In this dissertation, Lanthanum is used to substitute part of Phosphorus or Aluminium in the framework and enter into the tetrahedron structure unit of oxygen negative ion for obtaining a kind of heteroatom molecular sieve with acidity. LaSAPO molecular sieve expands the realms of synthesis and application of molecular sieve materials, which can be used as sorbent of separating and purifying molecular species, catalyst or catalyst's carrier and ions exchanger etc. The main studies of this dissertation are summarized as follows:1. The effect of using template amounts, starting pH value of reaction system, crystalloid temperature and time, stirring speed, the SiO2/Al2O3 ratio and adding seed on synthesis of LaSAPO molecular sieve were systematically investigated. The experiment results show that a new type of pure lanthanum silicoaluminophosphate molecular sieve (LaSAPO) with higher crytal degree was synthesized by hydrothermal synthesis in TMAOH-Al2O3-P2O5-SiO2-La2(CO3)3-H2O-CTAB system. the optimal conditions are as follows: n(TMAOH)∶n(Al2O3)∶n(P2O5)∶n(SiO2)∶n(CTAB)∶n(La2O3)∶n(H2O)=3.83∶1.0∶1.0∶0.6∶0.35∶0.4∶335(mol ratio), crystallization is at 170℃for 36 hours, stirring speed is 780 rpm and the pH is 6.0~7.0. In the process of molecular sieve synthesis the formation of LaSAPO molecular sieve was effectively promoted and crystal degree was increased by adding seed before or behind stilling.2. The LaSAPO sample was characterized by XRD, FTIR, XRF, DTA-TG, TEM and so on, and the results shows that pure LaSAPO molecular sieve with better heat stability was obtained.3. The LaSAPO sample was used as esterification of acetic acid and butanol to investigate its catalytic activity The result shows LaSAPO molecular sieve possess better catalytic activity and the percent conversion of acetic acid is up to 84.52%.