Preparation, Surface Modification Of Silica-based Membranes And Evaluation Of Their Separation Performance For Ethanol-water Mixtures

Based on the application of hydrophobic and hydrophilic membranes during pervaporation membrane separation for bio-ethanol concentration process,the hydrophilic magadiite membrane and hydrophobic silicalite-1 membrane were designed and prepared on porous alumina substrate.The effects of surface modification and chemical vapor deposition functional film on the growth and separation performance of the two kinds of films were investigated.Using the osmotic evaporation membrane separation process,the separation performance of magadiite hydrophilic membrane and silicalite-1 hydrophobic was evaluated by changing the process parameters such as the type,composition and temperature of the material.Through the heterogeneous interface,the magadiite supported film（P-magadiite film）was synthesized by the hydrothermal synthesis of the porous α-A12O3 carrier.The lamellar crystallization of magadiite（P-magadiite film）was synthesized on the porous α-Al₂O₃ carrier by the hydrothermal method,the size is about 5μm,the structure is compact and the crystal is patchy.While the cauliflower-like magadiite was synthesized without the addition of α–Al₂O₃ carrier,with a size of about 15μm.Under the same hydrothermal conditions,the crystal size and grain size of magadiite were changed by the introduction of heterogeneous interface,but the phase composition is still a single phase of magadiite.P-magadiite film has its unique layered structure and abundant hydroxyl groups,it showed good hydrophilicity in the separation of osmotic membrane.The maximum values of permeation flux and separation factor of 75,80,85,90,95 wt.% high concentration ethanol aqueous solution were 2.31 kg·m-2·h-1 and 3.47 respectively.Gas phase deposition PDMS had a hydrophobic modification effect on the P-magadiite film,the maximum value of permeation flux and separation factor of film deposited PDMS at 5,10,15,20,25 wt.% low concentration ethanol aqueous solution was 1.63 kg·m-2·h-1 and 1.55,respectively,which indicated that PDMS completed the transition of the P-magadiite membrane hydrophilic to hydrophobic.In the hydrothermal process of synthesizing silicalite-1 supported membrane,firstly,the polymer film was coated on the surface of the α-A12O3 carrier as the structure directing agent,the types of the guiding film include hydrophilic polymer chitosan,polyvinyl alcohol and hydrophobic corn alcohol soluble protein（zein）and so on,in order to realize the preferential orientation growth of silicalite-1 molecular sieve film crystal.The silicalite-1 membrane modified by PVA,zein and chitosan had an average thickness of 24,31 and 23 μm,and the membranes got thicker as more times the modifiers coated.The nitrogen permeate at 293 K was 9.5×10-9,1.07×10-8 and 9.85×10-9 mol·s-1·m-2·Pa-1.The preferential orientation of the zeolite film is dense and smooth,and showed higher separation factor and lower total permeate flux（α = 3.53,2.33 and 3.17 respectively,J = 1.38,3.02 and 1.55 kg·m-2·h-1 respectively）.The three films showed that α decreased as the temperature and the ethanol concentration increased,while J increased as the temperature and the ethanol concentration increased.The silicalite-1 zeolite membrane by PVA as modifier showed a more stable performance with the increase of temperature and concentration.Silicalite-1 zeolite membranes were synthesized by PVA as a modifier was deposited by the PDMS membrane and carried out osmotic evaporation,it indicated that the separation coefficient increased from 3.53 to 5.17,and the permeate flux decreased from 1.38 to 0.64 kg·m-2·h-1,chemical deposition of PDMS enhances the surface hydrophobicity,it is conducive to the separation and purification of ethanol components.