Gustavo Capannelli

Preparation and characterization of novel porous PVDF-ZrO2 composite membranes☆

Poly(vinylidene) fluoride (PVDF)-ZrO2 composite membranes were prepared by casting and immersion into a water bath of ternary suspensions obtained by adding additional amounts of ZrO2 particles to PVDF solutions. Methods to obtain an intimate dispersion of the inorganic particles in the PVDF solutions were developed. A large variety of supported and unsupported membranes were prepared by varying some of the preparative parameters such as: the PVDF solvent (N-methyl-2-pyrrolidone or triethylphosphate), the total concentration and the PVDF/ ZrO2 ratio in the ternary dispersion. Membranes were also cast from a binary solution of PVDF and solvent for comparison purposes. All the obtained membranes were characterized by scanning electron microscope observations and ultrafiltration tests. The effect of the above-mentioned preparative parameters on the structure, flux and dextran retention properties of the membranes is discussed.

Treatment and reuse of textile effluents based on new ultrafiltration and other membrane technologies

Different membrane processes were experimented on at pilot scale to verify the possibility of reusing textile wastewater. The pilot plant used sand filtration and ultrafiltration (UF) as pre-treatments for a membrane process of nanofiltration (NF) or reverse osmosis (RO). UF was obtained by the installation of an innovative module designed on flat membranes operating under vacuum; the configuration of the NF and RO membranes was spiral wound. The efficiency of the various treatments in removing pollutants from textile wastewater from an activated sludge plant was tested on the reduced scale to optimize the industrial plant design. The UF module tested works at low operating pressure (that involves low energy costs) and guarantees a constant permeate (feed of the next membrane process of NF or RO). The RO permeate can be reused in the dyeing processes as demonstrated by many yarn dyeing tests on the industrial scale. NF does not reach the retention behaviour of RO (total hardness removal of 75% and >90% for NF and RO, respectively). Nevertheless, a change in the freshwater treatment (at present an ion-exchange resin softening) downstream from the use of process water in the factory would decrease the secondary effluent salinity, so the design of the advanced purification industrial plant could reasonably foresee a NF treatment instead of RO, allowing a reduction of the costs.

Preparation and properties of novel organic–inorganic porous membranes

This paper deals with the preparation and characterization of novel organic–inorganic composite membranes formed by fine silica particles uniformly dispersed in the porous matrix of poly(vinylidene fluoride). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments, burst pressure tests and scanning electron microscope (SEM) observations. Spectroscopic (FTIR-ATR, FT-Raman) and calorimetric (DSC) measurements were also carried out in order to investigate interactions between membrane components. Supported membranes were finally prepared and their ultrafiltration performance was compared with that of unsupported ones.

ULTRAFILTRATION MEMBRANES - CHARACTERIZATION METHODS

Abstract The experimental data obtained by application of two different techniques for measuring the porosity of asymmetric ultrafiltration membranes are reported. The measurements were carried out keeping the membranes in conditions similar to those utilized in most ultrafiltration processes. The techniques used were: (a) cut-off evaluation by means of proteins of known molecular weight; (b) pore distribution measurement by means of the so-called “bubble pressure” method. It has been verified that use of these methods supplies information on the structure of asymmetric membranes and also on the influence of the operative parameters. p]Limitations for the reliability of above techniques were taken into account, namely in connection with chemical properties of the membrane and experimental conditions. From the above considerations it is inferred that all techniques must be uniform in order to compare experimental data from different laboratories.

High performance ultrafiltration membranes cast from LiCl doped solutions

Abstract This paper deals with the preparation and properties of ultrafiltration polyvinylidene fluoride based membranes obtained by casting and gelation of ternary solutions of polyvinylidene fluoride, solvent and LiCl as an appropriate inorganic salt additive. The membranes were tested in a laboratory scale pilot plant. Flux and rejection were evaluated as functions of the type of solvent and the amount of inorganic salt added. The influence of these latter variables on the morphology and mechanical properties of the membranes was also investigated. The role of LiCl on the properties and the mechanism of membrane formation is discussed.

Casting and performance of polyvinylidene fluoride based membranes

Abstract The investigation of factors governing membrane preparation is of paramount importance in order to understand the formation of the membrane and its behaviour under test conditions. A large amount of fundamental work on membrane formation has been carried out on cellulose acetate membranes, but less information is available for other polymers. The purpose of the present work is to provide a better understanding of the parameters governing the formation of polyvinylidene fluoride membranes. The parameters controlling the casting process have been investigated in some detail.

Membrane morphology and transport properties

Abstract By changing properly the preparation conditions, it is possible starting from the same polymer to obtain asymmetric membranes with different morphology and U.F. performances. The SEM cross-section give us information about the overall structure. Unfortunately these results are not enough, as the membranes properties mainly depend from the thin dense skin layer poorly resolved with the SEM technique. On the other hand, rejection and fluxes investigated with the conventional U.F. pilot units only supply an indirect information about skin layer properties. With the purpose to improve the knowledge on this topics, we have developed an automatic porosimeter based on the combined bubble pressure and solvent permeability method in order to obtain the pore number and radius distribution of the membrane in wet conditions. Despite some problems related to the absolute values we have obtained some interesting results both for new and used membranes.

SURFACE CHARACTERIZATION OF CERAMIC MEMBRANES BY ATOMIC FORCE MICROSCOPY

Abstract Atomic force microscopy (AFM) has been used to investigate the surface of ultrafiltration and microfiltration ceramic membranes. The AFM has been shown to resolve the feature of the γ-Al 2 O 3 selective skin layer of ultrafiltration membranes providing information on both the size and shape of the γ-Al 2 O 3 particles as well as the surface roughness of the skin. When applied to study α-Al 2 O 3 microfiltration membranes the AFM has been shown to yield results very similar to those obtained by conventional scanning electron microscopy.

Ultrafiltration of hydrosoluble polymers. : Effect of operating conditions on the performance of the membrane

Abstract Two sulfonated polyvinylidene fluoride membranes of different porosity, prepared by the casting and gelation technique, were tested in an ultrafiltration laboratory-scale pilot plant with hydrosoluble polymer feed solutions. Polyethyleneglycols and dextrans of different average molecular weight were used as solutes for the feed solutions. Flux and rejection of the membranes were determined as functions of operating conditions (pressure, temperature and recirculation rate). The effect of properties of feed solutions (solute, concentration and molecular weight) on the performance of the membranes was also investigated.

Porosity and protein adsorption of four polymeric microfiltration membranes

Abstract Four different microfiltration (MF) membranes were analysed with respect to porosity and protein adsorption. Liquid displacement porosity (LDP) and adsorption of 14 C-labelled β-lactoglobulin were used as characterization methods. LDP showed a clear pore size distribution for all membranes analysed, with maximally 10% of the pores having at least 90% of the permeability. The protein adsorption came to equilibrium within 30 minutes, giving decreased permeabilities for all membranes. The permeability loss could not be modelled as a simple membrane pore restriction, but the protein load corresponded to a monolayer of protein adsorbed on and in the membranes.