Method for preparing zeolite CHA membrane

A method for preparing a zeolite CHA membrane, comprising the following steps:

• step (1), coating a seed layer:
• heterogeneous zeolite seeds are dispersed in deionized water to obtain heterogeneous zeolite seed solutions;
• a porous support is preheated at 70-200° C. for 2-5 hours, and then the heterogeneous zeolite seed solutions with different particle sizes or same particle size of zeolite seeds are successively coated on the surface of the porous support and dried at 70-175° C. for 1-10 hours to obtain a heteroseed layer;
• and
• the heterogeneous zeolite seeds are zeolite T, Y or SOD;
• step (2), preparing a synthetic gel:
• the synthetic gel is composed of a silicon source, an aluminum source, a fluorine salt and an alkaline solution;
• the silicon source is silica sol;
• the aluminum source is sodium metaaluminate;
• the fluorine salt is a mixture of sodium fluoride and potassium fluoride, and the molar ratio of sodium fluoride to potassium fluoride is 1:1-5:1;
• the alkaline solution is a mixture of sodium hydroxide and potassium hydroxide;
• a stable SiO2—Na2O—K2O—Al2O3-MF (NaF+KF)—H2O synthetic gel system is formed by adding the aluminum source, the fluorine salt and the silicon source into the alkaline solution, stirring and aging;
• in the synthetic gel, the molar ratios of the components are as follows:
• SiO2/Al2O3=5-30;
• H2O/SiO2=26-70;
• (Na2O+K2O)/SiO2=0.24-2.6;
• Na/K=0.6-10;
• MF/SiO2=0-0.2;
• and
• conditions for preparing the synthetic gel are as follows:
• stirring and aging at 20-40° C. for 12-48 hours;
• step (3), coating a gel layer:
• the synthetic gel obtained in step (2) is used as a coating solution and uniformly coated on the surface of the porous support after the seed layer is coated in step (1);
• step (4), forming a membrane by crystallization:
• the porous support coated with the synthetic gel is loaded into an auetoclave to crystallize and obtain a zeolite CHA membrane;
• the crystallization temperature is 100-180° C., and the crystallization time is 2-24 hours.