PhD Oral Qualifying Examination : Microporous polymer membranes for organic solvent nanofiltration

Speaker Xu Qisong (Supervisor: A/Prof Jiang Jianwen)

Host artment of Chemical and Biomolecular Engineering

Date/Time 02 Mar - 02 Mar, 3.00PM

Venue E5-02-32 , Faculty of Engineering, National University of Singapore


Chemical separations account for 40-70% of capital and operating costs in chemical production. Existing separation technologies such as distillation are energy-intensive. As an alternative, membrane separation has been proven to be more energy-efficient and easier to operate. While membrane filtration in aqueous systems is well-established, its application in organic media has been on the rise recently. In particular, organic solvent nanofiltration (OSN) shows great potential for the molecular separation of high value solutes from organic solvents. Microporous polymer membranes are drawing considerable attention owing to their ease of processing and capability for molecular discrimination. From a molecular perspective, this thesis aims to explore OSN through microporous polymer membranes toward their rational design and optimization for high-performance OSN.

In the first study, a computational characterization of ultrathin amorphous polymer films in liquids is proposed. The integration of molecular simulations and defined characteristic lengths allows the analysis of dynamic and equilibrium properties of these systems. The polymer of intrinsic microporosity (PIM-1), a notable example of microporous polymers, is investigated. Molecular simulations of PIM-1 swelling in liquids reveal simultaneous solvent occupation of free volume and dilation of polymer matrix. With defined characteristic lengths, swelling process has been validated against a predictive model. In addition, gravimetric swelling degree of PIM-1 in solvents and their correlation with solubility parameters are in good agreement with experimental findings. Detailed analyses on the equilibrium structures of swollen PIM-1 offer further molecular insights.

In the second study, molecular simulations are performed for the permeation through PIM-1 by a series of organic solvents such as acetone, acetonitrile, ethanol and methanol. Solvent permeabilities obtained are in good agreement with experimental data, thereby validating the simulation results. The permeabilities are found to correlate well with combined solvent property and comparable to those of existing polyamide nanofilms. Subsequently, molecular simulations of OSN on the rejections of hesperetin solute from organic solvents are investigated. While the solute rejection is 100%, the solvent fluxes and permeabilities decrease. For all solvents, the adsorption of hesperetin on PIM-1 is unraveled to caused solute rejection. In the case of acetone, solvent permeability is the highest due to high polymer swelling and hesperetin solubility. This simulation study illustrates the performance of PIM-1 for OSN that is a manifestation of molecular interactions among solute, solvent and membrane.

In the future work, various functionalized PIM-1 will be investigated to further optimize OSN performance; moreover, other microporous polymeric membranes will be explored and designed for solute enrichment and solvent recovery, which are relevant to the pharmaceutical and petrochemical industries. Microporous polymer network may also be explored to separate other chemical mixtures.