(50e) High Performance Dual-Layer Hollow Fiber Membranes for Forward Osmosis Processes

Forward osmosis (FO) is an energy effective technology and has great potentials in a variety of applications such as desalination of seawater, treatment of wastewater, concentration of protein or sugar, dehydration of alcohol, and generation of power. The understanding of this promising technology has been improved with intensive research works carried out worldwide. However, the lack of FO membranes with high water flux and high salt rejection has been a critical factor limiting the real application of this technology in industry.

Ideally, FO membranes should be semi-permeable and hydrophilic, allowing water to permeate through while rejecting other components. For this purpose, we have designed and successfully fabricated nanofiltration-based single-layer hollow fiber membrane from cellulose acetate (CA). However, severe concentration polarization occurs at the lumen side of the fibers because of the highly porous sublayer. The occurrence of concentration polarization has caused drastic reduction in the effective driving force in FO tests and resulted in a water flux much lower than the expected value. The attempt to develop dual-layer hollow fiber membranes is a continuation of the previous work. The objective is to suppress or reduce the negative impact of concentration polarization at the lumen side by varying the sublayer structure and/or chemical properties. The first batch of dual-layer hollow fiber membrane (CA-I) is based on CA, i.e., both of the outer and inner layers formed by CA. Being very thin and dense, the outer layer acts as the semi-permeable barrier for solute separation. The inner layer is highly porous, providing enough mechanical strength as membrane support while creating very little resistance for water permeation. No delamination or interface barrier is observed between the outer and inner layers. In the FO experiments with 0.5?2.0 M MgCl2 draw solutions versus the outer layer, the first batch of CA-based dual-layer hollow fiber membrane shows water fluxes and salt leakages in the range of 12.69?36.75 L m-2 h-1 and 0.16?0.21 g m-2 h-1, respectively. Another two batches of dual-layer hollow fiber membranes (CA-II and CA-III) are under study. The CA-II membrane is fabricated with different porosity or thickness of the support layer and the purpose is to optimizing the sublayer structure. In order to find out whether charge helps to reduce the concentration polarization at the lumen side, the CA-III membrane is fabricated with incorporating different percentages of sulfonated polysulfone into the sublayer. The FO experiments and characterization are being carried out on these two batches of dual-layer hollow fiber membranes and the results will be reported in due time.