Study On Ionothermal Synthesis Of Extra-large-pore Germanosilicate Molecular Sieve

Extra-large-pore molecular sieves have broad application prospects in the fields of catalysis,adsorption and separation with bulky molecules,and related researches have received great attention from the both scientific and industrial communities.Germanosilicate molecular sieves are likely to form extra-large-pore structures,however,having problems of high synthetic cost and poor structural stability resulted from the high Ge content in their framework.Ionothermal approach is an emerging molecular sieve synthesis method,which has mild synthesis environment and unique template effect,and shows potential advantages in the synthesis of new extra-large-pore molecular sieves.In this thesis,ionothermal synthesis of germanosilicate extra-large-pore molecular sieve has been studied,achieving the main results as follows:.Organic base assisted ionothermal method was invented for the synthesis of germanosilicate molecular sieve.In 1-ethyl/butyl-3-methyl-imidazolium and 1-benzyl-3-methyl-imidazolium ionic liquids,germanosilicate molecular sieves with STW and IRR structures were synthesized respectively.It was found that the ionic liquid cations acted as template during the crystallization of molecular sieve,and their structures have remarkable effect on molecular sieve phase selectivity.Ionic liquids could form supermolecules through π-πinteraction to direct the formation of extra-large-pore structures;organic base promoted the crystallization of germanosilicate molecular sieves by changing alkalinity of the ionothermal system.There was template competition between organic base and ionic liquid cation,and the high concentration of organic base was detrimental to the ionic liquid taking the role of template.Extra-large-pore germanosilicate molecular sieve with ITT structure was successfully synthesized in several imidazolium ionic liquid with different lengths of alkyl chain.It was found that all these ionic liquids were intact in the pore structure of ITT molecular sieve acting as template.The structure of ionic liquid had distinct influence on the Si/Ge ratio of ITT molecular sieve.Of them,ionic liquid with hexyl chain exhibited the highest initial gel Si/Ge ratio 5.7 for crystallization,producting ITT structure with Si/Ge ratio of 7.8,which was much higher than the reported value of 2 in the literature.ITT structure extra-large-pore germanosilicate molecular sieves isomorphously substituted with boron,aluminum,titanium heteroatoms were prepared in 1-hexyl-3-methyl imidazolium ionic liquid.It was found that the addition of heteroatoms has little influence on the product structure selectivity and high concentration of heteroatoms was not conducive to the crystallization of ITT structure.Aluminum was more likely to be substituted into the framework than boron,with the benefic effect for the crystallization of ITT structure.At Al/T=0.1,the synthesized ITT molecular sieve had the highest higher catalytic activity in propylene oligomerization catalytic reaction,producting mainly dimer(C6)and trimer(C9)of propylene with selectivity of 50%and 20%,respectively.