(539a) TFC Membranes with Intrinsic Microporosity By Interfacial Polymerization for Organic Solvent Nanofiltration

Many of the conventional separation and purification processes in oil and gas, chemical, and pharmaceutical industries utilise large quantities of organic solvents and entail high energy consumption [1]. Such processes could be totally or partially replaced by membrane technology, with an order of magnitude lower energy consumption. To enable this, membranes need to be both chemically resistant to the solvents involved and provide high flux, in order to process large solvent volumes with a viable area and in a viable timeframe.

Existing state of the art polymeric Organic Solvent Nanofiltration (OSN) membranes are either integrally skinned asymmetric (ISA) or thin film composite (TFC) membranes [2].  However, ISA membranes age as the polymer chains relax towards equilibrium packing, losing permeance. As an alternative, one might consider using polymers of intrinsic microporosity (PIMs), in which equilibrium polymer packing results in significant free volume that will promote permeation. PIMs are a new class of polymers with great potential in separation due to their extremely high porosity. Non-network PIMs are soluble in certain solvents, making them suitable to cast a membrane by phase inversion, or fabricate a TFC membrane via dip-coating.  However, their solubility in a range of solvents restricts their applications in organic solvent nanofiltration. Several efforts to make dip-coated TFC-PIMs membranes solvent resistant have been reported, including photo-crosslinking, blending with other thermally reactive polymers and chemical crosslinking. In this work, we show for the first time the formation of a network PIM-film in situ by interfacial polymerization to develop TFC-PIMs-like membranes for OSN applications.This novel preparation technique represents an advantage compared to conventional TFC-PIMs membranes prepared by coating, where further crosslinking is necessary. Moreover, forming the top layer by IP can produce thinner top layers than when prepared by dip-coating. Solvent stable crosslinked polyimide supports were used for the formation of these TFC-PIMs-like membranes.

To increase permeance we sought to design and control the nanostructure of the top layer in a better way and at a molecular level. This was achieved by incorporating rigid monomers during the IP reaction, resulting in highly porous polymer networks. These TFC-PIMs-like membranes exhibit comparable rejections and a significantly higher permeance for organic solvents, including methanol, acetone, THF, DMF and toluene when compared to commercial ISA OSN membranes and to TFC OSN IP membranes developed previously in our group, eliminating the need for an “activating solvent”. We believe that incorporating rigid monomers into the polymer structure provides higher free volume, which in combination with the polymeric network gives intrinsic microporosity to the top layer, which enables a great improvement of permeance without sacrificing selectivity. Such network TFC-PIMs-like membranes prepared by interfacial polymerization may lead to the next generation of high performance OSN membranes.

[1] G. Szekely, M.F. Jimenez-Solomon, P. Marchetti, J.F. Kim, and A.G. Livingston, “Sustainability assessment of organic solvent nanofiltration: from fabrication to application”, Green Chem., 16(2014) 4440-447.

[2] P. Marchetti, M.F. Jimenez Solomon, G. Szekely, and A.G. Livingston, "Molecular Separation with Organic Solvent Nanofiltration: A Critical Review", Chem. Rev., 114 (21) (2014) 10735-10806.