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Theme 1 : Membranes

Contact : Jean-Froiçois LAHITTE

The theme’s research includes studying the phenomena occurring during the preparation of membranes (phase inversion, functionalization), or during their implementation (solvent/solute/membrane interactions, ageing), their characterization (X-ray micro-tomography, retention model) and their integration into a process (gas/liquid transfers).

CO2 capture: the membrane solution 

- We have shown that gas-liquid (G/L) membrane contactors made of hollow composites with a dense permeable skin offered suitable solutions for CO2 capture. Intensification factors of 4 and more compared to the best conventional absorption columns were obtained along with stability of operation using model gases (in collaboration with LRGP Nancy).
- The LGC has been looking at the manufacture of hollow fibers, in particular at the conditions required for the continuous deposition of thin layers of polymer at the surface of a hollow fiber. The technology developed won the prize for Innovating Technology for the Environment at the Pollutec Trade Fair 2010 and is the object of a patent (WO 2014020019).

Coating of a catalytic membrane loaded with reactive nanoparticles.

New materials for use in catalytic processes

- The efficiency of catalytic membranes has been demonstrated when metal nanoparticles of 3 to 4 nm are incorporated at the surface of functionalized membranes. The catalytic nanoparticles are immobilized and dispersed in a polymer chemical gel. The increase in the filtration flux limiting the role of diffusion, and the high and localized nanoparticle concentration leads to a 30 000-fold increase in reaction rate compared to the results of a stirred reactor, with conversion levels reaching 100%.

Ageing of membranes: better understanding for better use

- Drinking water production plants using membrane filtration processes report membrane failure issues. We showed that membrane degradation is mainly induced by exposure to sodium hypochlorite, an oxidant broadly used during in-place cleaning. - Correlation of molecular and macroscopic characterizations demonstrated that degradation of PVP (a hydrophilic agent in the material) is responsible for the loss of membrane integrity. Autopsy of membranes that had aged for several years on site supported the observations made in the laboratory: the impact of hypochlorite concentration on the degradation rate dominates that of the exposure time.

Hollow fiber ultrafiltration membrane.

Retention of bacteria during micro-filtration: influence of the medium

- During the removal of bacteria by microfiltration using membranes qualified as “sterilising”, leakage of microorganisms was observed. Our findings confirmed that E. coli, a Gram negative bacterium, is able to change its shape sufficiently to pass through a membrane with pores smaller than the smallest dimension of the bacterium. Moreover, hypotonic conditions were found to increase retention of the bacteria while hypertonic media enhanced their ability to cross the membrane.

Membrane/solution interactions and transfer across membranes

- Depending on the type of membrane or on the transfer regime, it was found that the increase in neutral species transfer across the membrane in the presence of electrolyte is governed either by modification of the structural properties of the membrane (material/electrolyte interaction) or by the modification of the properties of the solute (solute/electrolyte interaction).
- The increase of the transfer of neutral solutes, linked to the presence of electrolyte, was correlated to the hydration of the ions (effects of swelling of the material and reduction of the apparent size of the dehydrated ion).

3D reconstitution of the porous structure of a membrane by X-ray tomography analysis.