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Studying the application of lignin for the fabrication of high-performance membranes
- Author / Creator
- Shamaei, Laleh
Lignin is one of the most plentiful natural polymer on the earth, produced on a large scale as the waste of pulp and paper industries. The inherent properties of lignin, such as nontoxicity, cost-efficiency, and biocompatibility, make it suitable for the green modification of bulk and surface characteristics of membranes to mitigate the fouling phenomenon. Fouling is the major drawback to the widespread application of membrane technology for wastewater treatment. Among multiple approaches that have been employed to minimize membrane fouling, enhancing the surface hydrophilicity of membranes is found to be indispensable. Herein, an industrial waste derivative of lignin, sulfonated kraft lignin (SKL), was used as a hydrophilic modifier for the synthesis of microfiltration (MF), ultrafiltration (UF), and thin-film composite (TFC) forward osmosis (FO) membranes with improved antifouling and permeation performance.
In the first stage, SKL was used as a bulk modifier to synthesize antifouling polyethersulfone (PES) UF membranes using the phase inversion technique. Different SKL concentrations (1-3 wt%) were employed to tune the physicochemical properties of PES membranes. The fabricated membranes were employed to treat the steam-assisted gravity drainage (SAGD) produced water. The SKL-modified membrane containing the highest SKL additive content (3 wt%) provided the maximum flux recovery ratio of 98.2% compared to the 52.2% flux recovery ratio of the pristine PES membrane. The enhanced antifouling property of the SKL-modified membranes was primarily ascribed to their improved hydrophilicity and more negative surface charge. By adding 3 wt% SKL, the underwater oil contact angle increased by 14°, and the surface charge of the membrane became 3 times more negative under the operating pH (>8) of SAGD produced water, confirming the results of the antifouling tests. The water flux increased significantly from 25.3 LMH/psi (L m-2 hr-1 psi-1) for the pristine membrane to 68.6 LMH/psi for 3 wt% SKL-blended membrane, while the rejection of the organic matter slightly decreased from 61.7% to 56.1%.
In the second stage of this research, hydrophilic SKL was coated on the surface of PES membranes by layer-by-layer (LbL) assembly technique using SKL as a polyanion and poly (diallyldimethylammonium chloride) (pDAC) as a polycation. The effect of the polyelectrolyte concentrations (0.1-2 wt%) and the number of polyelectrolyte bilayers (1, 2, and 3) were investigated to fabricate UF membranes with improved antifouling property. The membrane made by 3 pDAC/SKL bilayers and 2 wt% concentration of the individual polyelectrolyte solution possessed the highest antifouling performance against the n-hexadecane-in-water emulsion as synthetic oily wastewater. This membrane exhibited a low total flux decline ratio (DRt) of 23.1% and a high flux recovery ratio of 93.8% compared to 44.2% DRt and 75.9% flux recovery ratio of the pristine membrane. The improved antifouling propensities of the LbL-assembled membrane could be related to the significantly higher underwater oleophobicity of this membrane (oil contact angle of 157°) compared to the pristine membrane (oil contact angle of 109°).
In the last stage, SKL was used as a hydrophilic modifier for the fabrication of TFC FO polyamide membranes with enhanced permeation performance and antifouling propensities. TFC membranes were fabricated by interfacial polymerization reaction between m-phenylenediamine (MPD) and trimesoyl chloride (TMC). The effect of SKL concentration was examined by dispersing different contents of SKL (1, 3, and 6 wt.%) in MPD-aqueous solution. The SKL-embedded membranes provided higher water flux and lower specific solute flux compared to the pristine TFC membrane. The membrane, modified with the highest content of SKL, possessed 33.5 LMH water flux when tested in FO setup using 2 M NaCl solution as draw solution and deionized water as feed solution. The antifouling property of the membranes was tested for the filtration of SAGD boiler feed water. The DRt of the TFC membranes decreased from 36.5% for the pristine membrane to 21.9% for the 6 wt% SKL membrane. The enhanced antifouling performance of the SKL-modified membranes was attributed to their improved hydrophilicity. The water-in-air contact angle decreased from 88.7° for the pristine TFC membrane to 70.6° for the TFC membrane modified with 6 wt% SKL.
The present study created wealth from waste, sulfonated kraft lignin, and showed the tremendous potential of lignin for green and value-added applications. This work opens up a new paradigm to develop high-performance membranes using industrial waste lignin.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
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