| Modification by the low-temperature plasma is one of the most important methods to introduce membrane materials with high performance. Dielectric barrier discharge (DBD) plasma is a novel type of plasma that can be generated under atmospheric pressure, which can easily be scaled up to industrial dimensions. In this work, the DBD graft-filling polymerization technique was develpoed for the surface hydrophilization of polyacrylonitrile (PAN) ultrafiltration (UF) membrane and the fabrication of composite pervaporation membranes with the "pore-filling" structure. The effects of preparation parameters on the separation performance were studied systematically. Also, mass transfer through the composite membrane for aromatics/aliphatics separation was discussed.Atmospheric DBD plasma system in Helium was used to prepare the pervaporation composite membrane with an excellent aromatic selective permeability. Using this method, the macromonomer poly(ethylene glycol) methacrylate (PEO526OHMA) was graft-polymerized onto the top surface and in the pores of the separation layer of the asymmetric PAN UF membrane. Attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR). water contact angle measurements (WCA) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) were used to characterize the morphology and chemical structure of the composite membrane, the "pore-filling" structure of the composite membrane as identified. The influences of preparation parameters (DBD treatment time, input voltage, monomer concentration of grafting) on the degree of grafting (DG) and pervaporation performance of composite membrane were systematically investigated by pervaporation separation of toluene/n-heptane mixtures (the mass ratio is 1:4, 80℃). The results showed that, the atmospheric DBD plasma technique was an effective way to fabricate the composite membrane with high selectivity and permeation flux for the aromatics/aliphatic separation. Especially, when the composite membrane was grafted with PEO526OHMA, under the condition of plasma treatment time was 90 s, input voltage was 70 V and monomer concentration was 0.432 mol/L, the separation factor for toluene was 7.8, the flux was 1.62 kg/m2·h, possessing excellent pervaporation selectivity and permeability.With aromatic/aliphatic mixtures (the mass ratio is 1:1,60℃) as feed, the mass transfer through composite pervaporation membranes fabricated by atmospheric DBD technique was discussed. The results showed that the aromatics selective permeability of composite membrane was affected by both solubility selectivity and diffusion selectivity. For the toluene/n-heptane mixtures, the solubility selectivity of composite membrane for toluene was 2.6, the diffusion selectivity was 1.2, the process of dissolution was the dominant step.Using atmospheric DBD plasma technique, the surface hydrophilization of PAN UF membrane and the enhancement of anti-fouling performance with hydrophilic poly(ethylene glycol) methacrylate as the grafted macromonomers were studied. ATR-FTIR. WCA, SEM were used to characterize the chemical structure of the modified membrane. The influences of DG on the amount of protein adsorption, UF performance and anti-fouling performance were systematically investigated with 1000 mg/L bovine serum albumin (BSA) solution. The results showed that with the increasing of DG, the surface hydrophilicity, both protein retention and anti-fouling performance of PAN membrane were improved significantly. |
