Development of Novel PVDF Membranes with Enhanced Transport using Chitosan for Membrane Distillation and Microfiltration

  • Cynthia Noemi Baeza Elizalde

Student thesis: Master's Thesis

Abstract

Nowadays, membrane separation processes are playing an important role in wastewater treatment and desalination applications. This thesis explored the fabrication of improved PVDF membranes, by the phase inversion method, using chitosan (CS) as a hydrophilic additive for the purpose of flux enhancement and flux stability. CS was blended with PVDF at 0.5, 1.0, 1.5, 2.0 and 2.5 wt. % concentrations using LiCl as an agent to help retain CS in the membrane solution. Membranes were fully characterized to prove the presence of chitosan in them and evaluate its impact; where, changes in porosity, pore size, thickness, mechanical strength, roughness and hydrophilicity were observed. Addition of CS resulted in more porous open structures. In terms of hydrophilicity, although the water contact angle of the virgin membrane (PVDF/LiCl) decreased in a small degree upon the addition of CS, from 1220 to 1150, a more hydrophilic character was observed on the membranes, confirmed by a higher work of adhesion and higher surface free energy. However, the wettability of the membranes was more affected due the increase on the pore size. Microfiltration tests showed that the addition of CS was helpful for the reduction of fouling, by observing a lower flux decline through time; still, membranes with CS concentrations higher than 1.0 %w/w presented significant ruptures after the filtration tests probably due to swelling resulting from high water uptake. Moreover, fabricated PVDF/CS membranes were not appropriate for air gap membrane distillation applications. Despite observing that membranes containing 2.0 and 2.5% CS achieved up to a 200% permeate flux increase, compared to the virgin membrane, all membranes were susceptible to wetting and the salt rejection is severely compromised. Nonetheless, this simple method for fabrication of PVDF/CS membranes shows potential for flux enhancement and fouling mitigation of common PVDF commercial membranes.
Date of AwardMay 2017
Original languageAmerican English

Keywords

  • Membrane Distillation
  • Membrane Separation Processes
  • Wastewater Treatment
  • Desalination Applications
  • Chitosan (CS)
  • PVDF/CS Membranes
  • Microfiltration.

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