Preparation And Properties Of ZIF-67/PEBA And MFI Zeolite Membranes For Separation Of Ethyl Acetate/Water Mixtures

Ethyl acetate is an important industrial solvent and the discharge of wastewater containing ethyl acetate is unavoidable in the manufacturing process.It is rather difficult to recover ethyl acetate from aqueous solutions by the traditional separation method because of the azeotrope formed and high energy consumption.Pervaporation has applicaiton potential for the recovery of ethyl acetate from aqueous solution and the development of membrane materials with good separation performance is a key to realize industrialization.Therefore,the preparation and properties of filling modified PEBA polymeric membrane and inorganic zeolite membrane were studied in this work for the ethyl acetate/water mixtures.ZIF-67 was filled into poly?ether-block-amide??PEBA?to prepare ZIF-67/PEBA hybrid membranes.The morphology of the particles and the membranes surface and cross-section were observed using SEM.The hydrophobicity of hybrid membranes was investigated by contact angle analyzer.The chemical structure of hybrid membranes was analyzed by FTIR.The crystalline structures of the ZIF-67 particles and hybrid membranes were confirmed by XRD.The thermal stability of hybrid membranes was investigated by TGA.The swelling degree of hybrid membranes in ethyl acetate aqueous solutions at different concentrations was investigated by the equilibrium swelling experiments.The effects of the ZIF-67 content,feed concentration and temperature on the separation performances for ethyl acetate/water mixtures through the hybrid membranes were investigated through the pervaporation experiments.MFI-type zeolite membranes were prepared by secondary growth on Al₂O₃support,in which TEOS was selected as a silicon source and TPAOH was used as a templates agent.The crystal and chemical structure of Silicalite-1 nanoseeds were analyzed by XRD and FTIR respectively.The morphology of Silicalite-1nanoseeds and MFI-type zeolite membranes were observed by SEM.The contents of Si and Al elements in MFI-type zeolite membrane materials were analyzed by EDS.The effects of the amount of deposited nanoseeds,feed concentration and temperature on separation performance of MFI-type zeolite membrane for ethyl acetate/water mixtures were investigated through the pervaporation experiments.The results showed that there were no interfacial voids between ZIF-67particles and PEBA matrix.The particles appeared aggregation as ZIF-67loading reached 7.5?wt%.With increasing of ZIF-67 loading,the water contact angles of hybrid membranes were enhanced and the hydrophobicity of membranes were increased.There was only physical interaction between ZIF-67and PEBA matrix.The thermal stability of hybrid membranes remained unchanged with increasing of ZIF-67 loading.The swelling degrees of ZIF-67/PEBA hybrid membranes were enhanced with increasing ethyl acetate concentration and the hybrid membranes had selective adsorption capacity for ethyl acetate.With increasing of ZIF-67 loading,the separation factor first increased followed by decrease while the total flux decreased initially and then increased.The maximum separation factor of 64 was obtained at 5?wt%ZIF-67loading and it increased by 77%comparing with the pristine PEBA membrane.The effects of feed concentration and temperature on hybrid membranes performance were investigated with the 5?wt%ZIF-67/PEBA hybrid membrane.With increasing of feed concentration,the total flux and the separation factor increased simultaneously at 30?.The total flux and the separation factor increased with increasing temperature at feed concentration of 4 wt%.The maximum total flux of ZIF-67/PEBA hybrid membrane was 2299 g·m^-2·h^-1 and the maximum separation factor was 122.The MFI-type zeolite membranes by vacuum seeding method were flat and dense.The membranes by dip coating method had more gaps between the crystals.All MFI-type zeolite crystals were randomly oriented.The MFI-type zeolite materials had high Si/Al ratio.With increasing the seed crystals amount,the total flux decreased while the separation factor increased.The effects of feed concentration and temperature on separation performances were investigated using the MFI-type zeolite membrane with 2 g·m^-2 deposition amounts of seed crystals.With increasing feed concentration,the total flux decreased while the separation factor increased at 30?.The total flux and the separation factor increased with increasing temperature at the feed concentration of 4 wt%.The maximum total flux was 821 g·m^-2·h^-1 and the maximum separation factor was172.The comprehensive comparison results showed that the MFI-type zeolite membrane had the higher separation selectivity while ZIF-67/PEBA hybrid membrane had the higher permeation flux.This study provided necessary basic data and theoretical basis for the development and industrialization of membrane materials for pervaporation separation for ethyl acetate aqueous solution.