Preparation And Gas Separation Of Siiicatite-1Membranes

Zeolites are crystalline structures that have uniform, molecular-sized pores.These inorganic structures have been used extensively as catalysts and adsorbents.More recently, continuous polycrystalline zeolite layers have been deposited onporous supports and used as zeolite membranes. Suzuki reported the first zeolitemembranes in1987. Since then, significant progress has been made to improve thequality of zeolite membranes and widen their range of applications. Today, more than14zeolite structures, including MFI, LTA, MOR, FAU, CHA, MEL, AFI, FER, BEA,GIS, ANA, DON, OFF, and ATN have been prepared as membranes. With growingconsumption of fossil fuels, gigatons of carbon dioxide are emitted into theatmosphere every year. Carbon dioxide is the main component of greenhouse gases,and would trigger severe global climate change if it accumulated to a high level in thelong run. To alleviate CO₂accumulation it is important to separate and recycle carbondioxide before it is released in to air. Currently, several types of zeolite membranesare used for the separation of CO₂from other gases, such as MFI, LTA, FAU, DDR.The MFI structure is most commonly used in zeolite membranes because of its poresize and ease of preparation, and this structure includes silicalite-1and ZSM-5.Silicalite-1is made up of pure silica, and ZSM-5has Al substituted for some of the Siatoms.Zeolite membranes can be synthesized on a variety of supports. The supports canbe made of any of the available materials such as amorphous silica, silicon wafers,glass, stainless-steel-net, porous ceramics, porous α-Al₂O₃, γ-Al₂O₃. In order to obtain a better separation performance, zeolite membrane should be preferably made of purezeolite crystals with uniform and small particle size. Several preparation methods arereported for the synthesis of zeolite membranes, In-situ hydrothermal synthesismethod, Secondary growth method, Microwave synthesis, Continuous flow synthesismethod, pulsed laser ablation method and so on.A new method for quick fabrication of continuous and compact silicalite-1（Si-MFI）membrane on stainless steel net was developed. The method consists of pre-treatmentof substrate of stainless steel net with silica solution containing polyethylene oxide（PEO） polymer and a secondary growth process. The continuous and compact Si-MFImembranes were obtained within12h under hydrothermal conditions. The membranewas further characterized by scanning electron microscopy （SEM） and X-raydiffraction （XRD） analyses. SEM analyses showed that the membrane was continuousand highly compact. XRD analyses suggested that the micro-crystals embedded in themembrane were well crystallized. The permeance and separation performance of theSi-MFI membrane were examined with a gas-separation setup combining a gaschromatography. The results showed that the Si-MFI membrane had an excellentpermeance and separation performance for CO₂and N₂.The influence of the synthesis parameters, such as the molecular weight of PEO,the type of template, and the modification or not of the substrate, on the quality of theSi-MFI membrane supported by stainless-steel-net was also investigated.