High Flux Composite Ultra/Nanofiltration Membrane Based On Polyacrylonitrile (PAN) Nanofibrous Substrates And Cellulose Acetate (CA) Hydrophilic Coatings

Porous supports are. usually obtained by phase inversion technique which mostly generates materials with an asymmetric porous structure. This type of structure poses two limitations to the supports, i.e., relatively low porosity and poor pore-size distribution. Electrospinning is an alternative technique that can be used to prepare a porous support that exhibits a high porosity and an improved pore-size distribution. In this study, we prepared a kind of high flux composite ultra/nanofiltration membrane, which is referred to as CA/PAN composite ultra/nanofiltration membrane, based on PAN nanofibrous substrate and cellulose acetate coating. The preparation and performance of the CA/PAN composite ultra/nanofiltration membrane was investigated in this paper.PAN nanofibrous substrate was prepared by 6wt%, 8wt%, 10wt% PAN solution. Scanning electron microscopy (SEM) was used to examine the surface and cross sectional morphologies of these composite membranes. The PAN nanofibrous substrate was proved to exhibit a high porosity (>85%) and pure water flux (920 L/m~2h·psi), and pure water flux decreased just slightly with the thickness of PAN membranes increased.The hydrophilic CA coating was prepared using sol-gel phase inversion method based on PAN nanofibrous substrate. The effect of exposed time, coagulation bath temperature and heat treatment time during the process of membrane preparation and CA concentration in cast solution on CA/PAN composite ultra/nanofiltration membrane was demonstrated in this paper.As for the CA/PAN composite ultrafiltration membranes (concentration of CA cast solution: 5-15wt%), increasing coagulation bath temperature, heat treatment time or CA concentration in cast solution all made water flux decreased while rejection rate for oil/water emulsion separations increased. CA/PAN composite ultrafiltration membranes with 10wt% CA coating exhibited high water flux (142 L/m~2h) with good organic rejection rate (99%) for oil/water emulsion separation. Compared with CA cast membranes, CA/PAN composite ultrafiltration membranes possessed 5-10 times higher water flux rate and the same rejection rate.There is a most suitable exposed time in preparing CA/PAN composite nanofiltration membrane when CA/PAN composite nanofiltration membrane exhibit highest water flux, while rejection rate for 0.05wt% magnesium solution decreased with exposed time increasing; increasing coagulation bath temperature, heat treatment time or CA concentration in cast solution all made water flux decreased while rejection rate for 0.05wt% magnesium solution separations increased. CA/PAN nanofiltration composite membranes with 25wt% CA coating exhibited relatively good water flux (20.3 L/m~2h) with 65.9% rejection rate when CA concentration is 25wt%.