Synthesis Of Fe-SAPO-34 Membranes And Their Applications For CO₂/CH₄ Separation

As a type of silicoaluminophosphate microporous zeolite,SAPO-34 has the chabazite structure with pore diameter of 0.38 nm.Due to its well defined pore structure,medium acid strength,and satisfactory thermal,mechanical and chemical stability,SAPO-34 crystals have been widely used in catalysis,especially the catalytic process of methanol to olefins?MTO?.SAPO-34 membranes have shown the application potential in CO₂/CH₄ separation due to both molecular sieving and competitive adsorption.The isomorphous substitution of metal heteroatoms into framework can change the pore size and adsorption properties of molecular sieves,resulting in the variation of separation performances for the corresponding membrane.In this thesis,we will focus on the synthesis of Fe-SAPO-34 molecular sieves and membranes.Fe-SAPO-34 crystals were synthesized by traditional heating.The influence of both Fe/Al ratio of synthesis solution and temperature were studied in detail.Scanning electron microscopy?SEM?,fourier transform infrared spectroscopy?FT-IR?and ultraviolet visible spectroscopy?UV-Vis?were used to characterize Fe-SAPO-34molecular sieves.It was found that under the Fe/Al ratio of 0.01,Fe-SAPO-34crystals were regular cubic and highly crystallographic.The crystallization temperature had significant effects on the morphology and framework structure of the molecular sieves.The pure Fe-SAPO-34 molecular sieves with good morphology could be obtained at 220°C for 24 h.The effects of synthesis conditions including the Fe/Al ratio in the secondary synthesis solution,crystallization time and temperature were investigated to manufacture perfect Fe-SAPO-34 membranes.When the Fe/Al ratio was 0.01,the Fe-SAPO-34 crystals were closely cross-linked into membranes.Continuous and dense Fe-SAPO-34 membranes were obtained at 220°C by traditional heating for 36h.Finally,the as-synthesized SAPO-34 membranes and Fe-SAPO-34 membranes were used to separate CO₂/CH₄ gas mixture.Compared with SAPO-34 membranes,the CO₂/CH₄ selectivities of Fe-SAPO-34 membranes were higher,while the CO₂permeaces were lowered.The CO₂/CH₄ separation performance of SAPO-34membranes prepared by microwave irradiation was much better compared with those synthesized by traditional heating.