Synthesis Of Zeolite Beta In The Presence Of TEA~+ Template

In this paper,the hydrothermal synthesis of zeolite Beta was conducted with tetraethylammonium(TEA⁺) template,and the characterization of samples were done by XRD,XRF,SEM,TEM,TG-DTA and IR.First,the synthesis of nano-size zeolite Beta was studied with tetraethylammonium bromide(TEABr) cheap template,colloidal silica and pseudo-boehmite raw materials.By optimizing the gel-preparation process,aging and crystallization temperatures and so on,the crystallization of nano-size zeolite Beta was successful,and the time needed was shortened from 3 days to 2 days.On the basis of this,the synthesis of zeolite Beta with different SiO₂/Al₂O₃ ratio was attempted.By replacing pseudo-boehmite with NaAlO₂ as aluminum source,nano-size Beta zeolite having SiO₂/Al₂O₃ ratio of 15 to 60 were obtained.Results show that,in the low end of the SiO₂/Al₂O₃ ratio mordenite was a major impurity crystal phase; however,in the high end of the SiO₂/Al₂O₃ ratio ZSM-5 accounted for the major impurity.To facilitate the filtration separation of zeolite Beta from its mother liquor,several agents were added to the mixture of zeolite and its mother liquor.Results show that the addition of hydrochloric acid,ammonium chloride,ammonium nitrate,and citric acid increased the filtration separation efficiency.In the cases of using hydrochloric acid,ammonium chloride and ammonium nitrate as aids,Na-Beta was transformed into NH₄-Beta or H-Beta during filtration,which would simplify the preparation of Beta zeolitic catalyst.The synthesis technology of large crystal zeolite Beta was also studied using tetraethylammonium hydroxide(TEAOH) template,fumed silica,NaAlO₂,and ammonium fluoride as raw materials.Results show that,in the presence of F^-,zeolite Beta of 15×20μm crystals was obtained in pure silica form.However,the high viscosity and poor fluidity of the initial gel would deny its synthesis in scale-up vessel.Research indicated that the addition of some agents like alcohols,amines and surfactants into the prepared gel was helpful for improving the viscosity and fluidity of the initial gel.Among them ethanol,polyacrylamide and tween-20 showed additional merit in adjusting the size and dispersion of Beta zeolite crystals.