Synthesis Of MFI Zeolite And Template Removal Via Low-temperature Plasma

With high hydrothermal and mechanical stabilities,well-defined pore structures and high specific surface area,MFI-type zeolites can be made into membranes to separate various gas or liquid mixtures.As for the synthesis of zeolites or zeolite membranes,organic templates,acting as structure-directing agents?SDA?,must be removed to open channels in zeolites.While the progress of template removal trends to influence the crystal skeleton structure and the compactness of zeolite membranes,it is of great significance to develop mild and efficient methods to remove the SDA within the zeolite channels.In this work,small-sized silicalite-1 and Fe-silicalite-1 particles as seed crystals,tetrapropylammonium hydroxide?TPAOH?as SDA,continuous silicalite-1 and Fe-silicalite-1 membranes were prepared on?-Al₂O₃ substrates.Low-frequency,high-voltage plasmas was applied in the removal of the SDA in zeolite particles and membranes.According to experimental results,the SDA in the zeolite particles cannot be decomposed directly under plasmas.When zeolites were calcined at 300°C for 20 h followed by plasma treatment,the SDA can be effectively removed without decreasing zeolite crystallinity.Then the two-step method,coupling by low-temperature calcination and plasma treatment,was proposed for removal of the template from zeolite membranes.Due to the increased crystal thickness with extended diffusion paths,the calcination temperature needs to be raised to 350°C to decompose the SDA,leading to the clearance of the residual organic matter.The plasma treatment had no significant impact on surface water contact angle,which means that the zeolite membrane can retain a high hydrophobicity.The detemplated zeolite membranes were applied to separate ethanol/water mixture by pervaporation and the results indicated good density and separation property.