New insights into the structure of membrane fouling by biomolecules using comparison with isotherms and ATR-FTIR local quantification.

The objective of this paper was to propose a deepened analyze of a microfiltration membrane fouling by two biomolecules: a protein (Bovine Serum Albumin) and a peptide (Glutathione). In addition to an analysis of flux decline, the mass of biomolecules accumulated on the membrane during filtration was quantified and compared to adsorption experiments, using Fourier Transform Infra Red spectroscopy in Attenuated Total Reflection mode (ATR-FTIR). It was demonstrated that the same quantity of accumulated biomolecules on the apparent membrane area can generate totally different flux declines because of different fouling mechanisms. On the one hand, Glutathione can adsorb in the whole porous media of the membrane, penetrating through the pores, modifying the hydrophilicity at low concentrations and generating pore constriction at high concentrations. On the other hand, BSA organize a dense irreversible fouling in the first minutes of filtration containing a quantity equivalent to more than 45 monolayers, leading to pore blocking and pore constriction. This structure is resistant to rinsing and NaOH cleaning. Then a reversible fouling, containing a quantity equivalent to more than 90 monolayers is settled. The above structure can be removed with an intensive water rinsing and corresponds to a rather porous cake leading to a low resistance to water permeation, whereas the intermediate structure can only be removed with chemical cleaning and has a higher impact on water permeation. The original approach detailed in this paper allowed to go deeper in the understanding of the membrane fouling by soft matter, not detailed in previous papers.

Filterability of exopolysaccharides solutions from the red microalga Porphyridium cruentum by tangential filtration on a polymeric membrane.

The red microalga Porphyridium cruentum is exploited industrially for its exopolysaccharides (EPS) and pigments production. EPS produced by P. cruentum are partially released and dissolved into the surrounding environment, they can be recovered from the culture medium after removing the cells. This paper presents a parametric study of the ultrafiltration of EPS solutions on organic membrane. The EPS solutions were produced in conditions representative of an industrial production. They were filtered at lab-scale on a flat, PES 50 kDa MWCO membrane in a complete recirculation mode of permeate and retentate. Permeate flux-transmembrane pressure (TMP) curves were established up to the limiting flux for the filtration of solutions with various values of concentration in EPS (0.10-1.06 kg GlcEq m-3), fluid tangential velocity (0.3-1.2 m s-1) and temperature (20°C and 40°C). The reversible and irreversible parts of fouling were evaluated for each experiment and the critical flux was determined for an intermediate EPS concentration (0.16 kg GlcEq m-3). The results showed that EPS solutions had a strong fouling capacity. When filtering the lowest concentrated solution (0.10 kg GlcEq m-3) with moderate fouling conditions, the overall fouling resistance was approximately half of the membrane and the share of irreversible/reversible fouling was 88% and 12%. However, the part of reversible fouling becomes predominant when approaching the limiting flux. Permeate fluxes which were obtained allow to estimate that a VRR of approximately 10 could be obtained when concentrating EPS solutions using PES membranes in flat or tubular modules but not in spiral-wound.

Coupling Rhodium-Catalyzed Hydroformylation of 10-Undecenitrile with Organic Solvent Nanofiltration: Toluene Solution versus Solvent-Free Processes.

Intensification of the rhodium-catalyzed hydroformylation process to produce 12-oxo-dodecanenitrile from biosourced 10-undecenitrile was performed by coupling the reaction with organic solvent nanofiltration (OSN) for the recycling of the expensive Rh catalyst and the ligands. Four phosphorus-based ligands were compared with respect to their catalytic performance and rejection in OSN. Biphephos showed the best compromise and up to 3 reaction-OSN cycles were performed in toluene. A good recycling of the catalytic system was evidenced arising from the OSN (up to 88 % rejection). In order to develop a greener process, a similar approach was achieved in bulk (i. e. solvent-free medium), thus proving the catalyst recycling feasibility but also that the optimal OSN conditions are not the same as for toluene. Finally, integration of OSN in the overall production process is discussed, aiming at the proposal of a hybrid separation process involving a combination of OSN and distillation for an energy-efficient separation step.

Degradation of poly(ether sulfone)/polyvinylpyrrolidone membranes by sodium hypochlorite: insight from advanced electrokinetic characterizations.

Poly(ether sulfone) (PES)/polyvinylpyrrolidone (PVP) membranes are widely used in various industrial fields such as drinking water production and in the dairy industry. However, the use of oxidants to sanitize the processing equipment is known to impair the integrity and lifespan of polymer membranes. In this work we showed how thorough electrokinetic measurements can provide essential information regarding the mechanism of degradation of PES/PVP membranes by sodium hypochlorite. Tangential streaming current measurements were performed with ultrafiltration and nanofiltration PES/PVP membranes for various aging times. The electrokinetic characterization of membranes was complemented by FTIR-ATR spectroscopy. Results confirmed that sodium hypochlorite induces the degradation of both PES and PVP. This latter is easily oxidized by sodium hypochlorite, which leads to an increase in the negative charge density of the membrane due to the formation of carboxylic acid groups. The PVP was also found to be partly released from the membrane with aging time. Thanks to the advanced electrokinetic characterization implemented in this work it was possible for the first time to demonstrate that two different mechanisms are involved in the degradation of PES. Phenol groups were first formed as a result of the oxidation of PES aromatic rings by substitution of hydrogen by hydroxyl radicals. For more severe aging conditions, this membrane degradation mechanism was followed by the formation of sulfonic acid functions, thus indicating a second degradation process through scission of PES chains.

Interest of the Precatalyst Design for Olefin Metathesis Operating in a Discontinuous Nanofiltration Membrane Reactor.

This study aimed at evaluating the impact of the structure of several new olefin metathesis homogeneous catalysts on the performances of a membrane reactor running in a discontinuous mode and equipped with a nanofiltration membrane that was stable in toluene. A set of tailor-made ruthenium-based precatalysts were prepared with a first objective of enhancing the retention of the precatalyst, that is the stable source of the active catalyst, by organic solvent nanofiltration using a commercial polyimide membrane (Starmem 122). These prototype precatalysts were designed taking into account both the molecular weight and the physicochemical characteristics allowing up to 99.6 % retention of the precatalyst in toluene. The new precatalysts were then engaged in a model ring-closing metathesis reaction in the membrane reactor. Results, expressed as the precatalyst apparent turnover number, showed significant differences according to the selected precatalyst, underlining that the membrane reactor advantages and limitations were closely linked to the intrinsic activity of the catalyst. In addition to the retention of the precatalyst by the membrane, a major parameter was the percentage of the precatalyst really activated during the first load of the substrate since that controls the residual amount of precatalyst to be engaged in the following reaction cycle. The main consequence was the proposal of different running modes consisting of a cascade of synthesis in batch mode and separation by the membrane or a membrane reactor process.

Recovery of enlarged olefin metathesis catalysts by nanofiltration in an eco-friendly solvent.

This study was aimed at integrating a green separation process without phase change, namely nanofiltration, with olefin metathesis to recover the homogeneous catalyst. As the commercially available Hoveyda II catalyst was not sufficiently retained by the membrane, a set of homogeneous ruthenium-based catalysts were prepared to enhance the recovery of the catalyst by solvent-resistant commercial membranes made of polyimide (Starmem 228). The molecular weights of the catalysts were gradually increased from 627 to 2195 g mol(-1), and recovery was found to increase from around 70 % to 90 % both in toluene and dimethyl carbonate. The most retained catalyst was then engaged in a series of model ring-closing metathesis reactions associated to a final nanofiltration step to recover and recycle the catalyst. Up to five cycles could be performed before a deterioration in the performance of the process was observed.

Small molecular ion adsorption on proteins and DNAs revealed by separation techniques.

Ion binding is a term that assumes that the ion is included in the solvation sphere characterising the biomolecule. The binding forces are not clearly stated except for electrostatic attraction; weak forces (hydrogen bonds and Van der Waals forces) are likely involved. Many publications have dealt with ion binding to proteins and the consequences over the past 10 years, but only a few studies were performed using high-performance liquid chromatography (HPLC: ion exchange, reversed phase without the well-identified immobilised metal affinity chromatography) and capillary zone electrophoresis (CZE). This review focuses on the binding of proteins and DNAs mainly to the oxyanions (phosphate, borate, citrate) and amines used as buffers for both the HPLC eluent and the background electrolyte of CZE. Such specific ion adsorption on biomolecules is evidenced by physico-chemical characteristics such as the mobility or retention volume, closely associated with the net charge, which differ from the expected or experimental data obtained under the conditions of an indifferent electrolyte. It is shown that ion binding to proteins is a key parameter in the electrostatic repulsion between the free protein and a fouled membrane in the ultrafiltration separation of a protein mixture.