Date of Graduation

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Xianghong Qian

Committee Member

Ranil Wickramasinghe

Second Committee Member

Paul Millett

Third Committee Member

Jamie Hestekin

Fourth Committee Member

Mathias Ulbricht

Keywords

Applied sciences, anti-fouling, Concentration polarization, Membrane, Micro-mixing, Nanofiltration, Separation

Abstract

Nanofiltration (NF) is a relatively new membrane separation process mainly used for removing low molecular weight species from aqueous and non-aqueous solutions. NF membranes suffer from concentration polarization leading to membrane fouling thus compromised membrane performance. Magnetically responsive nanofiltration (NF) membranes functionalized with superparamagnetic nanoparticles (SPNs) attached to the chain ends of grafted polymer nanolayers have been shown to be effective in breaking concentration polarization at the membrane-liquid interface under an appropriate external oscillating magnetic field. Under an oscillating magnetic field, the movement of the polymer chains acts as micro-mixer leading to the suppression of concentration polarization and improved filtration performance. NF270 is one of the most commonly used NF membranes for removing low molecular weight species and di- and trivalent ions from the feed solutions. In this dissertation, the effects of grafted polymer chain length and chain density on NF performance were investigated. Feed solutions containing salts (NaCl, CaCl2, MgSO4, 10mM pH=7 sodium phosphate buffer and (CH3)3N•HCl) at varied concentrations as well as model oily wastewater were used to investigate the performance of these magnetic responsive membranes as anti-fouling self-cleaning membranes. Several commonly used mathematical models for describing NF processes have been adopted to quantify the solvent and solute transport of the functionalized membranes and the effects of micro-mixing on the performance of these NF membranes. Our results demonstrate that there is a significant improvement in both flux and rejection in the presence of an external oscillating magnetic field compared to results without an external field. Moreover, the improvement becomes more evident as the chain length and chain density of grafted polymer increases. An increase in membrane selectivity due to decreased concentration polarization for the functionalized membranes in the presence of an external field has been analyzed using several models. Besides the inorganic and organic salt feed solutions, our functionalized magnetically responsive nanofiltration membranes exhibit anti-fouling capacity towards model oily waste water.

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