The Ionothermal Synthesis And Characterization Of Aluminophosphate Molecular Sieves

Molecular sieve porous materials play an important part in many applications such as catalysis and separation in modern industry.Traditionally,molecular sieves are synthesized mainly by hydrothermal or solvothermal systems.In those systems,the reactants were placed in a sealed autoclave and heated to 100-200℃resulting in an autogenous pressure.Recently, a novel green method,ionothermal synthesis has been developed for preparing aluminophosphates molecular sieves using ionic liquids as both solvent and structure-directing agent.The extremely low vapor pressure of ionic liquid allows the reactions taking place at near ambient pressure at high temperature eliminating the safety concerns.In addition,the feasibility of recycling use of ionic liquids can make the industrial process more attractive.Therefore,it is expected that this new method can be developed to more widely industrial fields in the future.In this text,a series of imidazolium-based and hydroxyl ammonium ionic liquids have been synthesized.Hydroxyl ammonium ionic liquids are firstly used in the ionothermal systems.Pure and transition metal containing microporous aluminophosphate molecular sieves with different structures were synthesized using these ionic liquids as both solvent and structure-directing agent.The influences of synthesis conditions such as the ratio of raw materials(P₂O₅/Alz 2O₃ ratio,HF/Al₂O₃ radio etc.),crystallization temperature and time,the variety of ionic liquids on the crystallinity and characteristics of materials were systematically investigated,also the recycling use of ionic liquids.Our studies confirm that the novel ionothermal approach is a simple and safe process to synthesize various microporous molecular sieves.Firstly,a series of ionic liquids have been synthesized,including imidazolium-based and hydroxyl ammonium ionic liquids.A common two-steps path to imidazolium-based ionic liquid and a one-step path of neutralization to hydroxyl ammonium ionic liquid have been raised according to synthesis process.Secondly,Pure and transition metal(Co,Fe) containing microporous aluminophosphate molecular sieves were synthesized using a series of ionic liquids including 1-ethyl-3-methylimidazolium bromide([Emim]Br),1-butyl-3-methylimidazolium bromide ([Bmim]Br) and 1-butyl-3-methylimidazolium tetrafluoroborate([Bmim][BF₄]).XRD and FT-IR indicated that all the resulting microporous materials were with SOD structure. Aluminum(gallium) phosphates with quartz and LTA structures were synthesized ionothermally in[Emim]Br system.Aluminophosphate molecular sieves with four structures(AEL,AIPO₄-14A,AFI and GIS) were synthesized ionothermally in hydroxyl ammonium ionic liquid systems including HEA,HEL and THEAL.The results showed that:In imidazolium-based ionic liquid systems,the optimum synthesis conditions were at lower concentration of orthophosphoric acid and higher temperature in the range of 170-190℃for 3-5 days.The content of H₃PO₄ and HF can adjust pH value of the systems.In hydroxyl ammonium ionic liquid systems,different structures of molecular sieves were obtained in different ionic liquids.In THEAL ionic liquid system,AFI and GIS strctures were produced,and the reaction temperature is a key factor in the conversion of two structures.