Microwave Synthesis And Characterization Of High-purity SAPO-5 Molecular Sieves

The new family of silicoaluminophosphate SAPO-n molecular sieves with ion-exchange capacity and somewhat adjustable acidity, consist of some 6-12-ring one-dimensional microporous framework structure. Therefore, SAPO-n molecular sieves can be used as adsorbents for separation and purification of molecular species, catalysts or catalyst supports, and as ion-exchange agents. It has attracted more and more interests known to date. The present work investigates the effect of various synthetic conditions on the synthesis of SAPO-5 molecular sieves under the microwave irradiation compared with conventional hydrothermal method on the basis of previous work, and also characterizes the obtained molecular sieves samples by XRD and SEM techniques. The results show that impure SAPO-5 samples along with SAPO-34 crystals, which is difficult to be removed, are always formed under the conventional hydrothermal method. However, it is easy to obtain the high-purity SAPO-5 molecular sieves under the microwave irradiation. At the same time, the present work also discusses the crystallization mechanism of molecular sieves in both synthesis processes.1. Based on the effects of the raw materials composition, pH value, crystallization temperature and time on the synhesis of SAPO-5, the process parameters have been investigated in details and optimized. And at the same time, the difference of synthetic parameters has been studied between conventional hydrothermal and microwave synthesis of SAPO-5. It is proved that the synthetic parameters in microwave irradiation are different from those of conventional method, however, some results in conventional method is helpful to the application of microwave irradiation in the synthesis of SAPO-5.2. It is found that microwave irradiation is able to prevent SAPO-34 crystals to be produced in the crystallization of SAPO-5, and SAPO-5 samples with a high-purity and high-crystallinity can be obtained under microwave irradiation. All evidences show that microwave irradiation is more advantageous in the rapid synthesis of pure SAPO-5 molecular sieves.3. Due to the uniform and high performance inter-heating, the microwave irradiation can lead to uniform heating of the synthesis mixture in a short time, and speed the sprout of a great deal of crystal nucleus, therefore increase the crystallization...