Development of Lotus-Root-Like Multi-Bore Hollow Fiber for Direct Contact Membrane Distillation and Vacuum Membrane Distillation

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. A new-generation PVDF multi-bore hollow fiber (MBF) membrane with a lotus root-like geometry was designed and successfully fabricated via the specially designed spinneret and optimized spinning conditions. Various effects of spinning parameters including bore flowrate, dope flowrate and take-up speed were investigated on the membrane macro- and micro-structure, mechanical properties and direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) performance. The tensile strength characterizations have proven the excellent mechanical rigidity and elasticity of MBF membranes. 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 MD performance 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 MD experiment with robust operational conditions. Two different membranes structures are designed for DCMD and VMD processes. Uniform pore size MBF were fabricated for DCMD and highly assymetric MBF with a smaller pore size inner surface was fabricated for VMD. We believe this pioneering work may have profound implication to the development of mechanically durable membranes not only for membrane distillation (MD) but also for other membrane applications. 

Keywords: Multi-bore Hollow Fiber; Lotus root-like structure; Direct Contact Membrane Distillation; Vacuum Membrane Distillation