UV Induced Membrane Surface Modification: Feasibility of CO2 Capture and Catalytic Nanoparticles Stabilization

Polymer based membranes, with their intrinsic characteristics of low energy requirements, environmental-compatibility, easy control and scale-up, provide an important process approach to industrial applications (e.g. drinking water processes or gas/liquid contactor). With suitable modifications, advanced unique properties can be added to the membrane. Various modification methods such as blending, coating and chemical modifications [1] have been successfully performed during the last decade. However, photo-grafting seems to be more interesting as it offers the possibility to confer new functions without altering membrane bulk properties.

Our objectives are to modify hollow fiber membranes for effective gas separation (like CO₂ capture) and catalytic membrane reactors.

Our approach is to compare two methods of membrane fabrication for both applications. The first one is to graft classical monomers and the second one is to graft room-temperature ionic liquids (RTIL). RTILs have generated more and more attention in recent years due to their attractive properties, including extremely low vapor pressure and tunable structures. In addition, an increasing number of RTILs have demonstrated inherently high CO₂ solubility and selectivity [2] compared to other light gases like H₂, CH₄ and N₂.

We grafted hollow fibers by UV induced polymerization of different monomers (sodium p-styrene sulfonate (NaSS), acrylic acid (AA) and polymerizable room-temperature ionic liquids (PRTILs)). A photo-grafting setup including two industrial UV polychromatic lamps was used for the modification. A complete description was already given in a previous work [3]. Depending on the choice of monomers and experimental conditions, porous or dense grafted layer were obtained on polyethersulfone (PES), polypropylene (PP) and polymethylpentene (PMP) hollow fibers.

Up to now, we produced porous poly(acrylic acid) or poly(p-styrene sulfonate) grafted layer onto PES or PP and dense polymerized ionic liquid grafted layer onto PMP. The porous grafted layer was used to prepare catalytic membrane reactors whereas dense grafted layer was tested for CO₂/N₂ separation. An original combination of CO₂selective RTILs onto PMP hollow fibers gives positive results with a selectivity of 14.

Catalytic membranes were prepared by incorporating, or by creating in situ, metal catalytic nanoparticles (MNP). Due to their high surface energy, nanoparticles tend to aggregate in solution without suitable stabilizing agents. When agglomerates are created, an important loss of reactivity is observed. Thus, various ligands, polymers [4] or ionic liquids were used to stabilize MNP by steric, electrostatic or a combination of both effects [5]. Therefore, metal nanoparticles can be stabilized into grafted layers on hollow fiber membranes. We developed palladium-nanoparticle-incorporated catalytic membranes based on intermatrix synthesis [6]. The system performance was studied for the reduction of p-nitrophenol in p-aminophenol. The conversion rate was nearly 100%. We reasonably expect ionic liquid functionalized membranes with porous surface to share similar properties. The activity of the catalytic membrane is to be compared to that of MNP in suspension.

References

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[2] D. Camper, J. Bara, C. Koval, R. Noble, Bulk-fluid solubility and membrane feasibility of Rmim-based room-temperature ionic liquids, Ind. Eng. Chem. Res. 45 (2006) 6279–6283

[3] Akbari A., Desclaux S., Rouch J.C., Remigy J.C., Application of nanofiltration hollow fibre membranes, developed by photografting, to treatment of anionic dye solutions, J. Membrane Sci. 297 (2007) 243-252

[4] Astruc D., Lu F., Ruiz Aranzaes J., Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis, Angew. Chem. Int. Ed. 44 (2005) 7852-7872

[5] I. Favier, D. Madec, E. Teuma, M. Gómez, Palladium nanoparticles applied in organic synthesis as catalytic precursors, Curr. Org. Chem.15 (2011) 3127-3174

[6] Ruiz P., Muñoz M., Macanás J., Turta C., Prodius D. , Muraviev D.N., Intermatrix synthesis of polymer stabilized inorganic nanocatalyst with maximum accessibility for reactants, Dalton Trans. 39 (2010) 1751-1757