Sustainable and HIgh Performance MEmbranes via iNTerfacial complexation (SHIPMENT)

Introduction

Membrane technology is a very sustainable approach to separation, as it requires much less energy than conventional separation approaches. However, the sustainable image of membranes becomes substantially tarnished when you realize that nearly all membranes are prepared using large quantities of toxic and unsustainable aprotic solvents (NMP, DMF, etc.).

Need for Sustainable Approaches

To secure the future of membrane technology, it becomes critical to develop more sustainable approaches to membrane fabrication. An Aqueous Phase Separation (APS) technique has recently been proposed by the PI as a green and sustainable alternative to the currently dominant non-solvent induced phase separation (NIPS) process.[1–4]

Aqueous Phase Separation Technique

APS utilizes polyelectrolytes such as:

• poly(sodium 4-styrenesulfonate) (PSS)
• poly(diallyldimethylammonium chloride) (PDADMAC)
• poly(allyl amine hydrochloride) (PAH)
• polyethyleneimine (PEI)

This technique allows for the production of sustainable polyelectrolyte complex (PEC) membranes in a completely water-based process. The structure and morphology of these APS membranes can easily be controlled to produce excellent separation properties.

Performance Challenges

Although APS membranes show high solute retentions, the water permeability is much lower than NIPS membranes currently utilized for the same application. This originates from the fact that the separation is performed by the same material that gives the membrane its mechanical strength and porosity.

As a result:

• The water permeability is compromised when utilizing dense and mechanically strong membranes.
• Mechanical properties are poor when more swollen materials are used that provide high water permeability.

The lower water permeability of the existing APS membranes is now the major obstacle preventing their commercial production and large-scale industrial acceptance.

Proposed Solution

Herein, we propose a modification of the APS procedure by employing Interfacial Complexation (IC) during the phase inversion step to produce composite membranes that ultimately lead to the required high performances.