Study On Preparation Of Twodimensional Nanomaterials/Polymer Hybrid Membrane And Pervaperation Performance For Aromatics/Aliphatics Separation

The separation of aromatic/aliphatic mixtures is an important but challenging process in petrochemical industry.Traditional separation technologies,such as rectification,extraction and adsorption usually require a high energy consumption and complex operation processes,because of the similar physicochemical properties of aromatics and aliphatic.Pervaporation is considered as the most promsing alternative technique due to its efficiency,energy conservation,eco-friendliness,and facile scale-up.Based on the solution-diffusion mechanism,the separation performance in a pervaporation process were mostly depended on the membrane.Therefore,it is crucial to develop a membrane with high selectivity and permeabilityfor the aromatic molecules.In this paper,layered double hydroxides（Co-Al LDH）and covalent organic frameworks（TpPa-2）,which have affinity to aromatic and similar layered stacking structure,were utilized as the functional materials to fabricate hybrid membrane.The hybrid membranes were successfully constructed on the Al₂O₃ ceramic substrate and showed great protentials for the pervaporation of aromatic/aliphatic mixtures.Firstly,an aromatic-permselective CoAl-LDH/W3000 nanohybrid membrane was fabricated by solution blending method.The morphology and structure of the resulting membranes were characterized by scanning electron microscope（SEM）,powder X-ray diffraction（XRD）and Fourier transform infrared spectrometer（FTIR）.The CoAl-LDH/W3000 membranes were used for the pervaporation of toluene/n-heptane mixtures.When the concentration of W3000 was 10 wt.%,the loading of CoAl-LDH was 0.75 wt.%,the stirring time was 2 h,the immersing time was 30 min,the toluene content in feed solution was 50 wt.%and the feed temperature was 40 ^oC,the permeate flux and the separation factor could reach 107.5 g/（m²·h）and 3.92,respectively.Owing to the p-πconjugation between Co²⁺and aromatic molecules,the flux of the hybrid membrane were almost doubled while its separation factor was similar to the W3000membrane.Secondly,TpPa-2 was introduced for the preparation of aromatic-permselective pervaporation membranes.An additional wet grinding step were employed to improve the dispersity of TpPa-2 nanoparticles in PEBAX polymeric matrix.SEM,XRD and TGA were used to characterize the morphologies and structures of the TpPa-2 particles and TpPa-2/Pebax membranes.The effects of Pebax concentration,TpPa-2 loading feed composition,and operating temperature on membrane performances were investigated.The optimized TpPa-2/Pebax membranes could perform a separation factor of 3.2 and a permeate flux of 1324 g/（m²·h）.The results indicated that the added TpPa-2 materials could improve the flux greatly due to its porosity and aromatic rings in the molecules,where its flux is 11.8 times higher than the pure polymer membrane’s flux.