L. Cot

Preparation of a γ-alumina nanofiltration membrane

Abstract The colloidal way of the sol-gel process was used for elaborating nanofiltration ceramic membrane. Boehmite, precipitated in situ, was used as a precursor. The evolution of the sol as a function of the concentration was precised with the help of turbidity, viscosity and colloidal particle size measurements. No binder was added in the sol before coating which was performed by slip-casting. The gel layer was sintered using a “flash” firing treatment. The membrane was characterized by scanning electron microscopy, nitrogen adsorption-desorption and cut-off determination. The pore diameters were ∼ 1 nm.

The sol-gel approach to prepare candidate microporous inorganic membranes for membrane reactors

Abstract In catalytic membrane reactors, the membrane can play a multiple role such as promotion of an integrated catalytic reaction but also partitioning of the reactants and separation of the products. For these applications permselective membranes may be used that can work at high temperature (gas or liquid phase), in organic solvents or in contact with biomass. One type of possible membranes are the ceramic membranes which exhibit a connected microporosity. This kind of membrane can at present be made using the latest developments in sol-gel processing. We used this process to prepare various microporous ceramic membranes in aqueous media: ZrO2, Al2O3, LaOCl; and in organic media: SiO2, ZrO2. Attention has been paid to the microstructure of these membranes in order to identify the main parameters governing the evolution of these membrane materials during their preparation. The main feature of these membranes is the presence of non-aggregated nanosized particles after calcination. A peptization reaction and/or a chemical modification of the precursors has been shown to be of prime interest in the control of the precursor reactivity and in limiting the condensation rate so as to avoid inhomogeneous and rough products. Non-aggregated ceramic particles down to 4 nm in size can thus be obtained and result in microporous membrane formation.

Synthesis and characterization of microporous zirconia powders: Application in nanofilters and nanofiltration characteristics

Abstract Mineral nanofiltration membranes are not commercially available because it is difficult to generate connected micropores in an inorganic material. Recent advances in sol-gel chemistry can be applied for the preparation of mineral oxide particles allowing the formation of a microporous structure after sintering. Zirconia has been chosen as a membrane material because of its chemical and thermal stabilities. Initially powders were synthesized and characterized to determine the optimal synthesis conditions for application in the preparation of membranes. Magnesium oxide stabilized zirconia (13 mol.%) demonstrated high surface areas leading to elevated surface charge densities. Crack-free coating could be deposited on ceramic multichannel substrates. The development of these membranes has permitted both model solute rejections in the nanofiltration range (73.2% B 12 vitamin and 54.5% saccharose), high water permeability (12.31/h m 2 bar) and high fluxes with a 19-channel configuration. The high surface charge density of the membrane material ensured a large divalent anion rejection (66.3% sulfates) and a low rejection of monovalent anions (31.5% chlorides).

Silica membranes by the sol―gel process

Abstract The sol-gel process allows the preparation of thin microporous layers. This technique has been used to prepare silica membranes with controlled thickness (from 2 to 10 μm) and pore diameters (from 6 to 20 nm). The preparation conditions are described and the marked influence of the drying conditions on the final properties of the membranes is pointed out. The filtration performance of the membrane reveals an important interaction with aqueous media.

Preparation and characterization of colloidal solution derived crystallized titania powder

Abstract In this work the influence of the type of the titanium alkoxide and the type and concentration of the peptizing agent on the powder crystallization is pointed out. Anatase or rutile phases are directly precipitated from the sol during ageing in case of the use of hydrochloric or nitric acid as peptizing agent. If tetraethylammonium hydroxide is used the sol is very stable and an amorphous powder is only obtained after drying at 100°C. The sols and obtained powders were characterized. Dans ce travail nous avons etudie l’influence de la concentration et de la nature de l’agent peptisant ainsi que celle de l’alkoxyde de titane sur la cristallisation de la poudre. En utilisant les acides nitrique et chlorhydrique comme agents peptisants, on obtient une poudre cristallisee sous la forme anatase ou rutile. Si on utilise l’hydroxyde de tetraethylammonium le sol obtenu est tres stable, la poudre recuperee apres sechage a 100°C est amorphe. Les sols et les poudres obtenues sont caracterises.

Hafnia ceramic nanofiltration membranes. Part I: Preparation and characterization

Abstract We have used a sol–gel process as an efficient method for the preparation of hafnia nanofiltration membranes. A stable colloidal sol was obtained after hydrolysis of an alkoxide and peptization of the hydrous oxide precipitate. After the drying of the sol, the hafnia powder was characterized using several methods, such as X-ray diffraction, dilatometry, thermal analysis, electrophoretic, and BET measurements. The hafnia membrane was obtained by coating the colloidal sol on a mesoporous ceramic support, followed by a drying and sintering of the gelled layer. The membrane was characterized by SEM and nitrogen adsorption–desorption to determine the pore size. The filtration properties of a hafnia membrane sintered at 450°C were determined using water permeability and rejection of solutions containing sucrose, polyethylene glycols of different molecular weights (400, 600, 1000) and salt solutions. This membrane is characterized by a MWCO of 420xa0Da and pore size near 1xa0nm.

A microporous zirconia membrane prepared by the sol—gel process from zirconyl oxalate

Abstract We have prepared a xirconia membrane by the sol—gel process, that is potentially active in the low-ultrafiltration or high-nanofiltration range. The precursor is a dried gel available as a powder, which leads to a sol when added to water. Coatings of tubular ceramic supports by slip-casting have been successfully performed. Characterization was made by scanning electron microscopy, nitrogen adsorption—desorption and filtration of dextran. This zirconia membrane has pores of ∼4 nm diameter and also retention properties for dextran molecules of molecular weight higher than 10,000 daltons.

Effect of boric acid addition in colloidal sol-gel derived SiC precursors

Abstract Sol-gel derived precursors are known to be suitable for the formation of submicron and homogeneous SiC powders. From colloidal silica and saccharose, we obtained SiC powders whose grain size is 100nm in diameter and which are easily sinterable with boron containing additives. Furthermore, we have pointed out that boric acid added in the original colloidal sols permits to increase considerably the carbothermal reduction yield and the powder crystallinity.

Performance of stabilized zirconia nanofilters under dynamic conditions

The nanofiltration performance of stabilized zirconia nanofilters was tested under dynamic conditions in an electrolytic solution. Interaction between nanostructured materials and solutes may modify the rejection properties of such membranes in the dynamic range of the experiments. Optimal filtration performance can only be realized by a proper understanding of these interactions. At high pressures, a decrease in electrolyte rejection is observed and the membranes show a reduction in hydraulic permeability. Two approaches (one thermodynamic and the other electrokinetic) are considered to explain these phenomena, i.e. the concentration polarization model and the electroviscosity model. A combination of these two approaches is successfully developed to explain the observed nanofilter behaviour at high pressures in the case of electrolytes. Further investigations were performed using an uncharged solute (vitamin B12) in an electrolyte buffer. Although a reduction in permeability was observed at high pressures, there was no important decrease in vitamin B12 rejection because the optimal transmembrane pressure (where the rejection reaches a maximum) was above the pressure range studied experimentally or did not allow the rejection reducing effects of the concentration polarization layer to be observed more clearly.

Potassium titanyl phosphate membranes : surface properties and application to ionic solution filtration

The relationship between the surface charge of potassium titanyl phosphate (KTP), studied on powder suspensions, and filtration properties of KTP nanofiltration membranes was studied. An experimental investigation of KTP powder characterization in different electrolytic solutions is presented: electrophoretic measurements show that the colloid particles are negatively charged whatever the solution pH, although they present a point of zero charge about 7.8. The selectivity of the membrane depends on the charge and size of ions. The interactions between the membrane and charged species have to be taken into account to explain the transfer through the membrane. With salts having the same cation, the rejection is higher for divalent anions than for monovalent anions. The best rejection rate is observed for applied pressure lower than 7 bar.