| Due to its low energy consumption,low capital cost and simplicity,free phase inversion and good separation properties etc.,membrane separation is widely investigated in recent years.High silica MFI zeolite membrane(silicalite-1)posses potential applications for separation ethanol etc.organic solvent aqueous solutions,and other membrane process such as catalytic membrane reactors due to its regular zeolitic pore size,hydrophobicitity and high thermail and chemical stability.In this paper,Silicalite-1 zeolite membranes have been successfully synthesized on theα-Al2O3 supports by secondary thermal synthesis and on stainless steel tubes by the two-stage varying-temperature synthesis,and their properties were characterized by XRD,SEM,EPMA and single gas permeance etc..Finally,Silicalite-1 zeolite membranes are used to separat EtOH/water mixtures.Firstly,the influencing factors of template TPABr and TPAOH,water content,alkalinity content,crystallization time and temperature on the formaion of silicalite-1 zeolite particles were investigated respectively.The as-prepared zeolite crystal were uniformly sized within the range of 0.1～4μm.Using TPABr as template,synthesis solution experiences the gel formation and decomposing process.But TPAOH as template does not experience the process.Secondly,Silicalite-1 zeolite membrane was successfully synthesized on tubularα-Al2O3 support by secondary hydrothermal synthesis with vacuum seeding.The influencing factros of vacuum,seed concentration and seed size on the preparation of silicalite-1 zeolite membrane were investigated.When the size of seed was close to support pores and pressure is 0.06～0.07 MPa,a homodisperse and continues seed layer could be prepared by this method.The gas permeation tests indicate that,at room temperature,the permeance of H2 is 3.25×10-7 mol·m-2·s-1·Pa-1,and idea selectivity of H2/N2 and H2/SF6 are 4.1 and 133.2 respectively. exhibiting a good separation performance.Thirdly,the influencing factros of different structure-directing agents and supports on the morpholigy,thickness and gas separation performance of silicalite-1 zeolite membrane were investigated.Using TPAOH as structure-directing agents,the thickness of the membrane is about 4μm,the permeance of H2 is 9.84×10-7mol·m-2·s-1·Pa-1,and idea selectivity of H2/SF6 is 49;but using TPABr as structure-directing agents,the permeance of H2 is 1.91×10-8 mol·m-2·s-1·Pa-1,and idea selectivities of H2/SF6 is 3.66.The effect of the support characters on the permeance of the zeolite membrane is also very important.At last,the pervaporation separation performances of ethanol from its 5 wt%aqueous solution by using the obtained membranes were examined at 60℃.The affecting factors of structure-directing agent,the support property,Water/Silica ratio on the pervaporation performance were investigated.Using TPAOH as the structure-directing agents,at 60℃,the flux of the EtOH/Water is 0.62 kg·m-2·h-1and idea selectivity is 33.8.Using TPABr as the structure-directing agents,both of the flux and idea selectivity are lower than using TPAOH as the structure-directing agents.
|
PDF Full Text Request