(142e) Novel Polymeric Hollow Fibers for Pervaporation and Multi-Bore Membranes for Membrane Distillation

Chung, T. S., National University of Singapore
Ong, Y. K., National University of Singapore
Wang, P., National University of Singapore

Pervaporation membranes are often suffered severely due to solvent induced swelling because of the direct contact with the feed. We will review the progress of various polymeric membranes for pervaporation and then propose a novel single-step dual-layer co-extrusion technique called “immiscibility induced phase separation (I2PS)” to fabricate high performance hollow fibers for the dehydration of ethanol. By taking the advantages of phase separation occurring in immiscible dopes made of incompatible polymers, dual-layer hollow fibers can be fabricated by simultaneously extruding immiscible blend dopes through a triple orifice spinneret. A selective layer is formed at the outer surface of the inner layer due to the incompatibility between both inner and outer-layers. As a result, the as-spun hollow fiber membranes consist of a protective layer on top of the selective layer which suppresses the solvent induced swelling during pervaporation. Hence, the flux of the hollow fiber can be enhanced by reducing the selective layer thickness without sacrificing the water/ethanol selectivity. Continuous performance tests demonstrate that the fibers spun from the I2PS process possess stable dehydration performance throughout the monitored period.

Highly constrained by the requirements of high porosity and large pore sizes, traditional single-bore hollow fiber membranes often suffer from easy breakage and performance instability during long-term operations of membrane distillation. We will review the evolution of polymeric membranes for membrane distillation and then propose a new-generation PVDF multi-bore hollow fiber (MBF) membrane with a lotus root-like geometry via novel spinneret designs and optimal spinning conditions. The effects of various spinning parameters will be investigated on the membrane macro- and micro-structure, mechanical properties and direct contact membrane distillation (DCMD) and vacuum MD (VMD) performance. The MBF membranes have excellent mechanical rigidity and elasticity. Even for the MBF membrane with a thin wall of around 40 µm, the maximum load was as high as 2.4 N. Most importantly, the performance of DCMD of the MBF membrane was only slightly lower or even comparable to that of single-bore membranes. In addition, the MBF membranes exhibited superior stability in terms of vapor permeation flux and salt rejection during the continuous DCMD and VMD experiments with robust operational conditions.

We anticipate that these pioneering works may have profound implications to the development of hollow fiber membranes for pervaporation and membrane distillation.