Facile preparation of superhydrophobic PVDF/MWCNTs distillation membranes: Synthesis, characteristics and separation performance

Abstract

In recent years, membrane distillation (MD) has emerged as an effective solution to mitigate the high energy consumption associated with conventional fermentable sugar concentration processes. However, the inherent low mechanical strength of traditional organic membrane surfaces can result in issues related to membrane wetting during long-term MD experiments. In this work, superhydrophobic PVDF/MWCNTs (multi-walled carbon nanotubes) distillation membranes with high mechanical strength were prepared by a combination of templating and co-blending techniques. The process involved peeling the semi-gelation membrane from a sandpaper template, subsequently forming a high aspect ratio microstructure on the membrane surface via tearing and pulling. Additionally, the incorporation of MWCNTs further bolstered the mechanical strength of the membrane. At a peeling time of 90 s and a MWCNTs content of 0.08 wt%, the distillation membrane exhibited an impressive water contact angle of 153.2°, indicating it possess exceptional hydrophobicity while maintaining high mechanical strength. The separation performance of the prepared distillation membranes has been inspected by conducting both experimental analyses and computational fluid dynamics (CFD) modeling of the entire MD process. An appropriate elevation in both feed flow rate and temperature could effectively mitigate the problem of temperature and concentration polarization on the membrane surface. PVDF/MWCNTs distillation membrane demonstrated a modest reduction in permeate flux of about 11.69 % and a stable rejection rate exceeding 99.95 % throughout a 100-hour operational period, and it required only 15 h to concentration of aqueous glucose solution to 100 g/L, significantly enhancing the efficiency of the process. This study also employed a combination of experiments and simulations to optimizes the process conditions guiding the vacuum membrane distillation (VMD) process and could provide guidance for the future application of membrane distillation in the concentration of sugar solutions.