M. Persin

Rejection of mineral salts on a gamma alumina nanofiltration membrane application to environmental process

Abstract Nanofiltration of salt solutions through an alumina membrane prepared by a sol gel process was investigated: rejections depend on the charge of the ions and decrease in the order: (divalent cation, monoanion) > (monocation, monoanion) or (dication, dianion) > (monocation, dianion). The surface charge of the membrane in the investigated solutions was shown to be positive over a very large pH range. The rejection of ionic species can be rationalised by taking into account the low pore diameters of the membrane and its surface charge: as in the case of organic nanofiltration membranes, the rejection mechanism depends on the relative ratio of the coulombic, dielectric and hydration interactions between the membrane material and the ionic species. The use of nanofiltration through the alumina nanofiltration membrane for denitration of water is also presented.

Methanol removal from organic mixtures by pervaporation using polypyrrole membranes

Abstract Conducting polymer composite membranes with a separation layer of polypyrrole doped with hexafluorophosphate (PF6−) and p-toluenesulfonate (CH3C6H4SO3−), were examined for the removal of methanol from organic solvents (toluene, IPA, MTBE and acetonitrile) by pervaporation. In all the cases, both membranes displayed preferential permeation of methanol. Selectivities and permeation rates as functions of methanol content were studied. The highest selectivity to methanol over toluene, accompanying an acceptable methanol flux, was obtained with the membrane doped by PF6−.

Salt filtration on gamma alumina nanofiltration membranes fired at two different temperatures

The performance towards filtration of different salts of two gamma alumina nanofiltration membranes, fired at 450°C and 650°C, were compared in terms of flux and rejection. The phenomenological parameters (reflection coefficient σ and overall solute permeability P) were determined for some salts.

Treatment of nickel containing industrial effluents with a hybrid process comprising of polymer complexation–ultrafiltration–electrolysis

A process was studied at the laboratory level and on a pre-industrial pilot for pollutant removal from industrial waste waters containing nickel cations. Five successive steps are involved: (1) complexation of the metal by means of polymeric ligands; (2) ultrafiltration of the complex, which produced a purified effluent and a concentrated metal complex solution; (3) decomplexation by acidification; (4) ultrafiltration of the concentrate after acidification allowing the recycling of the complexing agent; (5) electrolysis of the concentrated nickel solution (filtrate). A polycarboxylate and a polyethylenimine were investigated as complexing agents in a laboratory pilot, which lead to high rejection of nickel, even in the presence of salts such as NaCl or NaNO3. The decomplexation of polyethylenimine appeared to be too slow to be of practical interest for industrial use. The performances of several different membranes with polycarboxylate–nickel complexes were compared in a pre-industrial pilot and the operating parameters (temperature, pressures, liquid rate) were optimised. Starting from nickel at 60 mg l−1, volume concentration factors up to 20 were shown to be of practical interest. Acidification and diafiltration of the concentrate afforded Ni(II) solutions which could be easily electrolysed while the complexing agent could be recycled to the beginning of the process.

Grafting γ alumina microporous membranes by organosilanes:: Characterisation by pervaporation

Abstract γ alumina microporous membranes, produced from a sol–gel process, were grafted by means of chloro-, methoxy- or ethoxy-organosilanes. The grafting conditions were first tested on γ alumina powders which were characterised by means of thermogravimetric analysis and nitrogen adsorption. The membrane material was studied by means of infrared spectrometry, nitrogen adsorption and nitrogen permeation. The performances of grafted and ungrafted membranes were examined for the separation by pervaporation of binary mixtures such as water/ethanol, cyclohexane/toluene, ethanol/cyclohexane and methylethylketone/cyclohexane.

GAMMA ALUMINA NANOFILTRATION MEMBRANE APPLICATION TO THE REJECTION OF METALLIC CATIONS

Abstract A gamma alumina nanofiltration membrane, prepared by a sol-gel process, exhibits interesting properties for the filtration of metallic complexes. Experimental rejection and fluxes depend on the pH of the solution. Comparison of the distribution diagrams of the species in solution as a function of pH, established for several metallic complexes using equilibrium constants, shows that rejections and fluxes are affected by the size and the charge of the complex. High rejection ( > 95%) can be reached if the molecular weight of the complex is higher than 400. For positively charged complexes, the flux of the permeate is almost independent of the pH of the solution, whereas for negatively charged ones, the flux increases with increasing pH.

Electrochemical preparation of polypyrrole membranes and their application in ethanol-cyclohexane separation by pervaporation

Abstract Polypyrrole films were deposited on stainless steel meshes by anodic electropolymerization of pyrrole dissolved in acetonitrile. Established on the electrochemical and morphological studies on the growth of polypyrrole film, both the oxidized, with PF6− as counter-ion, and neutral polypyrrole membranes were obtained. The performances of these membranes towards ethanol-cyclohexane separation by pervaporation were investigated. Results indicate preferentian permeation of ethanol and clearly show a feasibilily of exploiting conducting polymers in the pervaporation process.

Influence of membrane-solution interface on the selectivity of SnO2 ultrafiltration membranes

Abstract SnO 2 supported membranes, presenting 3.0 nm average pore size, have been produced by sol casting on alumina tubular substrate using aqueous colloidal suspensions prepared by sol-gel route. The selectivity and flux throughout SnO 2 membrane were analyzed by permeation experiments, using a laboratory tangential filtration pilot equipped with a monotubular membrane. To evaluate the effect of the surface charge at the membrane–solution interface, aqueous salt solutions (NaCl, Na 2 SO 4 , CaCl 2 and CaSO 4 ) of different ionic strength have been filtered and the results correlated with the values of ζ potential measured at several pH. The results show that the retention coefficient is dependent on the electrolyte present in aqueous solution decreasing as: (dication, monoanion)>(monocation, monoanion)≈(monocation, dianion)>(dication, dianion). The surface charge and the cation adsorption capacity play a determinant role in these selectivity sequences.

Correlation between selectivity and surface charge in cobalt spinel ultrafiltration membrane

In the case of ceramic membranes with pore diameters lower than 10 nm, it was shown that the electrostatic interactions between charged particles and membrane surface charge is an important parameter for explaining the membrane selectivity. So, we have conducted several studies about cobalt spinel membranes (CoAl 2 O 4 ) fired at 450 and 600°C. The pore size is about 4.3 and 5.1 nm, respectively. Firstly, studies of electrophoretic mobility and surface charge measurements were performed on powder and streaming potential determination was measured on membranes. Secondly, we have measured the rejection rate and we have determined the selectivity of salt solutions with different ionic strengths. A correlation between all the results has been established.

Nanopore size growth and ultrafiltration performance of SnO2 ceramic membranes prepared by sol-gel route

Supported ceramic membranes have been produced by the sol-casting procedure from aqueous colloidal suspensions prepared by the sol-gel route. Coatings on a tubular alumina support have been successfully performed leading to crack free layers. Samples have been sintered at 400, 500 and 600°C, and the effect of heating treatment on the nanostructure and on the ultrafiltration properties are analyzed. The characterization has been done by high resolution scanning electron microscopy, nitrogen adsorption-desorption isotherms, water permeation and cut-off determination using polyethylene glycol standard solutions. The micrographs have revealed that grains and pore size increase with the temperature, whereas their shape remains invariant. This results is in agreements with N2 adsorption-desorption analyses, which have revealed that the mean pore size diameter increases from 4 to 10 nm as the sintering temperature increases from 400 to 600°C, while the total porosity remains constant. Furthermore, the tortuosity, calculated from water permeability, is essentially invariant with the sintering temperatures. The membranes cut-off, determined with a retention rate equal to 95%, are 3500, 6500 and 9000 g·mol−1 for 400, 500 and 600°C, respectively, showing that the permeation properties of SnO2 ultrafiltration membranes can easily be controlled by sintering condition.