PRODUCTION OF POLYMERIC HOLLOW FIBER ULTRAFILTRATION MEMBRANES

Abstract

A thorough study on ultrafiltration (UF) hollow fiber (HF) membranes produced from polyethersulfone (PES) / polyvinyl pyrrolidone (PVP) / N-methyl-2-pyrrolidone (NMP) solutions was carried out in this work. Effects of spinning solution pretreatments and spinning conditions on hollow fiber membrane physical dimensions, and membrane morphology/performance were investigated and discussed in two parts. The first part concerns hollow fiber membranes produced from Victrex 4800P PES. The effects of storage time and prefiltration of the fiber spinning solution on membrane morphology/performance characteristics have been studied. The viscosity of the fiber spinning solution increased upon storage for a few weeks, and it decreased after the solution was filtered prior to use in fiber production. Storage time and filtration treatment of the fiber spinning solution had significant effects on the morphology of the resulting membranes. Spinning solutions of longer storage time and without filtration pretreatment produced fibers with smaller size pores in the skin layer, and thus higher solute separation capability. The effects of feed flow velocity through the fiber bore on pressure drop in the test fiber bundle, membrane separations for polyethylene glycols (PEG) of various molecular weights and the obtainable mass transfer coefficients under the test conditions have been experimentally determined and discussed. The second part concerns hollow fiber membranes produced from Radel A300 PES. Effects of fiber spinning conditions such as internal coagulant flow rate (WFR) and fiber extrusion pressure (EP) on fiber dimensions and membrane morphology/performance were characterized by membrane flux and PEG separation. Generally, an increase in WFR tends to increase fiber outside diameter (OD) and inside diameter (ID), decrease fiber Wall Thickness, and decrease PEG separation. An increase in EP tends to increase fiber OD and Wall Thickness, decrease fiber ID while PEG separation may decrease or show a maximum depending on other production conditions. All the above results are discussed based on considerations of physical and chemical forces acting on the nascent fiber in the physicochemical events of desolvation, fiber swelling and fiber stretching taking place during fiber production. Results reported in this study offer a firm experimental basis for production of HF membranes for a wide variety of UF applications.