Preparation And Characterization Of Nano - SAPO - 34 Molecular Sieve

SAPO-34 molecular sieve is widely used in gas separation field due to its special pore structure. Compared with traditional micronstructured SAPO-34 molecular sieve SAPO-34 molecular sieve with small particle size has some advantages such as larger surface area, higher surface energy and shorter channel. Therefore, reducing the grain size is the important way of improving the performance of SAPO-34 molecular sieve. SAPO-34 molecular sieve with small particle size was synthesized by traditional hydrothermal method with TEAOH as organic template agent in this thesis, and the main research results are as follows:1. The main factors of influencing the synthesis of SAPO-34 were examined briefly such as crystallization time, aging time and crystallization temperature. The product were characterized by XRD and SEM.It is concluded that the crystallinity and particle size of SAPO-34 increased at first and then decreased with the extension of crystallization time within a certain range. The crystallinity of SAPO-34 grew firstly and then decreased slightly and its particle size always diminished along with the aging time within a certain range. The crystallinity and particle size of SAPO-34 increased with the rising of crystallization temperature when crystallization temperature increased from 180℃ to 220℃.2. The nanoparticles SAPO-34 was syntheized by controlling initial water content and the influence of water content on the SAPO-34 was further studied. The different ratio of nH2O/Al2O3(80,110,140 and 110) was investigated in the reaction system. The products were characterized by XRD, SEM and FT-IR. In conclusion, the crystallinity of product decreases weakly and its size is greatly reduced with reducing the content of water in the reaction system. When the ratio of nH2o/Al2O3 reduced to 80, the particle size of the product is 100-350 nm.3. The influence of phosphate content in the reaction system on the synthesis of the molecular sieve SAPO-34 was investigated. SAPO-34 nanopartieles are prepared by changing the content of phosphate and the synthesis mechanism of SAPO-34 is explored. In the initial system, the np2O5/Al2O3 value is employed as 1.25,1.50,1.75, 2.00,2.25 and 2.50. The product was characterized by XRD, SEM, FT-IR, XRF and TG-DTG. The crystallinity of the products experiences a trend of first increase and then decrease. In addition, the grain size decreases gradually with the increase of phosphate content in the reaction system. The particle size of SAPO-34 is even less than 300 nm and its crystallinity is quite low with the np2O5/Al2O3 ratio of 2.25. It is illustrated that the phosphoric acid in the reaction system not only provides the source of phosphorus, but also plays the role of adjusting the PH value. It is good to reduce the size of SAPO-34 with increasing the phosphate content within a certain scope. It can be deduced that high phosphoric acid content is unfavourable for Si element into the molecular sieve skeleton. Si entered the SAPO-34 skeleton by SM2 mechanism (a Si separately replaces a P) when the np2O5/Al2O3 was 2.00. Si entered the SAPO-34 skeleton by SM2 mechanism and SM3 mechanism (two Si separately replace a pair of P and Al) when the np2O5/Al2O3 is 1.50 and 1.75.4. The influence of CTAB content in the reaction system on the synthesis of the molecular sieve SAPO-34 was explored. The CTAB concentration in the reaction system (0,0.045mmol/L,0.09 mmol/L,0.135mmol/L,0.18mmol/L) was adopted in the reaction system. The product was characterized by XRD, SEM, FT-IR and TG-DTG. The conclusion is that the product particle size significantly reduces, but the crystallinity greatly decreases at the same time with increasing CTAB content in the reaction system within a certain range. The particle size of product is less than 200 nm, but its crystallinity was extremely low when the concentration of CTAB was 0.045mmol/L. It needed to be further studied how to reduce the particle size of product and ensure its high crystallinity at the same time by using CTAB at the appropriate crystallization time.