Ionothermic Synthesis Of Aluminum Phosphate Molecular Sieves And Their Catalytic Properties

As a new type of energy,biomass energy has been rapidly developed in recent years due to its advantages such as clean and efficient,low mining difficulty,and wide distribution range.In the process of using biomass energy,the most critical link is the development and utilization of platform compounds.5-hydroxymethylfurfural(HMF)as an important platform compound has received a lot of research and attention.The preparation of HMF is mainly obtained through the dehydration of sugars by means of acid catalysis.Molecular sieves have been widely used in the field of acid catalysis in recent years due to their rich and diverse pore types and adjustable acid catalytic centers.Aluminum phosphate molecular sieve AlPO₄-5 is an important member in the field of molecular sieve.Because of its new pore structure and special neutral framework,it has been continuously concerned and studied.At present,many heteroatom-doped MeAPO-5(Me=Mg,Si,Zn,Mn,Co,etc.)molecular sieve,by doping means greatly improved the acidity of the aluminum phosphate molecular sieve framework,but also made it used in more acid catalysis.Most molecular sieves are synthesized by hydrothermal method and solvothermal method.The ionothermal method that has appeared in recent years has good prospects in the field of molecular sieve synthesis due to its advantages of green,safety,and simplicity.At present,most of the research on aluminum phosphate molecular sieve AlPO₄-5 is focused on its crystallization mechanism and heteroatom doping to enhance acidity.There is little research on its undoped acid catalytic performance,especially study in the reaction of dehydration of fructose to HMF is still blank.In this paper,the influence of different factors on the synthesis of aluminum phosphate molecular sieve AlPO₄-5 by ionothermal method and its application in the reaction of fructose acid catalysis are studied.Firstly,the effect of factors such as time,temperature,organic amine,ionic liquid and material ratio on the crystallization of aluminum phosphate molecular sieve AlPO₄-5 were studied by using ionothermal method.Crystallization time can promote the formation of molecular sieves;triethylamine in organic amines has the most obvious effect on the templating agent in the crystallization process of molecular sieves;Ionic liquids with longer alkyl branches and suitable P/Al can promote the crystallization of molecular sieves.For the first time,AlPO₄-5 obtained by ionothermal method was used in the acid catalyzed reaction of dehydration of fructose using ionic liquid as the solvent,and a 90%HMF yield was obtained.Using FTIR,NH₃-TPD,py-FTIR,GC-MS,SEM,BET,CHN analysis and other characterization methods to study the acidity of AlPO₄-5 and the possible mechanism in the catalytic process,found AlPO₄-5 has a weak acid that meets the acid strength required to catalyze the dehydration of fructose,and is beneficial to reduce the occurrence of side reactions in this weak acid environment.AlPO₄-5 exists analogous cation exchange phenomenon that occurs between silicon aluminum molecular sieves and ionic liquids.In addition to the weakening of Br?nsted acid,the interaction between AlPO₄-5 and ILs can also cause the weakening of Lewis acid in the framework of AlPO₄-5.The reaction process of dehydrating fructose in the ionic liquid system to generate HMF was optimized for the first time.The reaction rate in the optimized reaction system can be better controlled,and the pollution of the catalyst during the reaction process is greatly reduced and increased catalyst utilization efficiency by this way.In this paper,the potential acid catalysis performance of the aluminum phosphate molecular sieve AlPO₄-5 itself is discovered,and its acid catalytic ability can be fully exerted in the ionic liquid system,which provides a broader research direction for the research of this molecular sieve catalyst.