Oral Defense Examination : Membrane development for organic solvent nanofiltration application

Speaker Mohammad Hossein Davood Abadi Farahani (Supervisor: Prof Neal Chung Tai-Shung)

Host Department of Chemical and Biomolecular Engineering

Date/Time 10 Aug - 10 Aug, 10.00am

Venue E5-03-21 , Faculty of Engineering, National University of Singapore

Synopsis

Organic solvent nanofiltration (OSN is a straightforward yet effective membrane-based molecular separation technology with significant applicability in food, pharmaceutical, and petrochemical industries. This thesis tends to cover different methods for the fabrication and modification of OSN membranes to obtain membranes with enhanced chemical, mechanical and thermal stability, improved permeance and selectivity, and great long-term performance for various applications. High-flux mixed matrix membranes (MMMs) for organic solvent nanofiltration (OSN) were designed using two different functionalized carbon nanotubes (carboxyl- functionalized multi-walled carbon nanotubes (MWCNTs-COOH) and amine-functionalized multi-walled carbon nanotubes (NH2-MWCNTs)) and P84 polyimide with the aid of 1,6-hexanediamine (HDA) as a crosslinker and thermal annealing. The MMMs were fabricated in both flat sheet and hollow fiber configurations.

The crosslinked MMM comprising 0.05 wt.% MWCNTs-COOH exhibited a rejection of 85% to Rose bengal (1017.65 Da) while ethanol permeance was 9.6 LMH/bar at 5 bar.  After thermal annealing at 150°C in a 3/1 EG/PEG400 (weight ratio) solution, the same MMM showed superlative rejections to small dye molecules (almost 100% to Safranin O dye molecules, 350.85 Da) in ethanol solutions. The embedding of hydrophilic NH2-MWCNTs into the P84 matrix not only enhanced membrane's porosity, sorption capacity, and liquid transport but also resulted in an amidation reaction between them. The resultant NH2-MWCNT/P84 MMMs had higher water, ethanol, and isopropanol permeances than the pristine P84 one. The crosslinked MMMs consisting of 2 mg/g of NH2-MWCNTs/P84 showed a rejection of > 98% to eosin Y (MW of 648 g/mol) while pure water, ethanol, and IPA permeances were 16.4, 3.3, and 1.4 LMH/bar at 20 bar, respectively. Moreover, they exhibited a notable rejection of 92.1% to tetracycline, a smaller drug solute with a MW of 444 g/mol, in IPA solutions after thermal annealing at 120°C for 40 min. Interestingly, the annealed MMMs still possessed a higher ethanol flux and solute rejections than the pristine P84 membrane. Besides, they also showed promising OSN performance in 72-h continuous tests.

Using the same materials, robust P84 and NH2-MWCNT/P84 hollow fiber membranes have been designed by adjusting spinning parameters and then crosslinking them by (HDA) to achieve desirable separation performance for OSN. A weak bore fluid, an adequately high dope flow rate and a small air gap length were required to produce the desired hollow fiber membranes. The amidation reaction between the imide groups of P84 and the amine groups of NH2-MWCNTs led to greater mechanical properties and thermal stability as well as higher dope viscosity. Moreover, NH2-MWCNT/P84 hollow fibers exhibited great permeances of 4.31, 2.26, 1.45, and 1.17 LMH/bar for acetone, methanol, ethyl acetate, and ethanol, respectively, while having smaller pore sizes with notable rejections. The crosslinked P84 and NH2-MWCNT/P84 membranes showed extraordinary rejections of 97.2, and 99.8% to methylene blue (320 g/mol), respectively. Also, the newly developed hollow fibers demonstrated great potential for separating tetracycline/IPA, L-α-lecithin/hexane, and BINAP-Ru(II)/methanol solutions, representing their applicability in the pharmaceutical, food, and petrochemical industries.

Finally, Integrally skinned asymmetric PBI membranes were crosslinked using a solution containing trimesoyl chloride (TMC) and environmentally benign 2-methyl tetrahydrofuran (2-MeTHF) for the first time. The X-PBI membrane showed a rejection of 99.6% to remazol brilliant blue R (MW of 627 g/mol) while it had pure acetonitrile, acetone, ethanol, and isopropanol permeances of 40.7, 29.0, 13.8, and 5.8 LMH/bar at 10 bar, respectively. Moreover, the X-PBI membrane exhibited excellent performance during the 2-step filtration of tetracycline. It had rejections of 90.4% and 97.8% in the first and second steps of filtration, respectively. The X-PBI membrane was also able to concentrate solutions containing L-α-lecithin, a food additive with a MW of 758, and hexane. It showed a L-α-lecithin rejection of 92% and a pure hexane permeance of 80.8 LMH/bar at 10 bar. Besides, it demonstrated precise shape-selective functions to separate mixed dyes and stable OSN performance during 96-h continuous tests. The membranes possessed remarkable rejection for separation of solutes in different organic solvents with high permeation of solvents.

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