The Synthesis Of N-tetralky Quaternary Ammonium Salt And The Preparation Of AEI Molecular Sieve

ZSM-5 and SAPO-34 molecular sieves were widely used in the process of MTO/MTP. The novel AEI molecular sieve can overcome their defects and improve propylene selectivity.The work of this paper are the synthesis and separation of N-tetraalkyl quaternary ammonium salt which was the structure-directing agent of molecular sieve and the preparation of AEI molecular sieve.2,6-dimethylpiperidine was chosen as raw material which was alkylated and quaternized in the synthesis of N-tetraalkyl quaternary ammonium salt, and recrystallization was selected as the method in the separation of this salt. In the process of synthesis, ethyl bromide was chosen as alkylating agent and quaternizing ammonium, methanol as solvent, at reflux temperature for a certain constant time. In the process of separation, diethyl ether was added into the product solution, which the product was precipitated, then filtration and dring. The optimum conditions in the process of the synthesis were:n (2,6-dimethyl piperidine):n (dibromoethane):n (methanol)= 1:5:3, the reaction temperature 45?,the reaction time 5 days; In the process of the separation, V (product solution):V (ether solution)= 1: 2-3.Filtration at normal temperature and pressure vacuum filtration, and drying at 50 ?. In such conditions, the N-tetraalkyl quaternary ammonium salt yield was 70.47%.The method of AEI molecular sieve preparation was hydrothermal synthesis wet gel and dry gel conversion, which include the hydrolysis of silicon source, gels, crystallization. In the process of the hydrolysis of silicon source, the hydrolysis rate was influenced by the material ratio; in the process of gel preparation, it was influenced by the material ratio and feeding method and alkali metal cation.Two structure-directing agents were used in preparation of AEI molecular sieve. DEDMPBr was chosen as the structure-directing agent, then the TEOS as silica source, aluminum nitrate as the aluminum source, ammonium fluoride as a fluorine source; while TEAOH was slected as a structure-directing agent, then the TEOS as silica source, aluminum nitrate as the aluminum source, hydrofluoric acid was a fluorine source. Molecular sieve can be prepared through two methods and two structure-directing agents in different material ratio.