Fernando Vigo

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.

The Performance of a Rotating Module in Oily Emulsions Ultrafiltration

Abstract The rotating ultrafiltration module has been applied to concentrated oily emulsions with the aim of checking its practical features. The ultrafiltration yield has been measured as a function of pressure, tangential speed, temperature, oil concentration, and hydrodynamic conditions. An energy consumption evaluation has been performed and a comparison with tubular modules tried. The importance of turbulence promoters and the influence of the radial geometry of the module has been outlined by means of simulation tests with a transparent model system.

Poly(vinyl chloride) ultrafiltration membranes modified by high frequency discharge treatment

Abstract Asymmetric ultrafiltration membranes were prepared by the phase inversion technique from solutions of poly(vinyl chloride) in dimethylformamide. The membranes thus prepared were submitted to high frequency discharge treatment. The change in performance was measured in an ultrafiltration loop with dextran solutions and oily emulsions. The effect of high frequency discharge on membrane characteristics was studied as function of discharge time, power and pressure, and of the type of gas employed. The chemical species produced on the membrane surface and its change in structure were examined by infrared spectroscopy and scanning electron microscopy.

Asymmetric polivinylidenfluoride (pvdf) radiation grafted membranes: preparation and performance in reverse osmosis application

Abstract A new type of reverse osmosis membrane has been synthesized. Membranes were prepared starting from asymmetric PVDF films, obtained by the casting and gelation technique and modified by radiochemical grafting and sulphonation. These membranes were tested in an RO laboratory plant and their performances were determined as a function of preparative parameters. The influences of evaporation time and temperature grafting and solvents were investigated. These membranes exhibit permeabilities as high as 2000 l/m2d and sodium chloride rejections up to 70%.

Influence of the Vorticity at the Membrane Surface on the Performances of the Ultrafiltration Rotating Module

Abstract The performances of a rotating module during the ultrafiltration of oily emulsions have been studied and correlated with the vorticity at the membrane surface. Thus, a fully transparent module has been assembled and the size and shape of the vortices observed as functions of the rotational speed and the clearance of the annular gap around the membrane. The influence of the roughness and profile of the inner wall of the module has also been investigated. Photographs of the vortices have been correlated to the actual performances of a steel module. Evidence has been found relating the permeate flux and the size of the vortices.

Amphoteric membrane preparation and their application to saline water hyperfiltration

Abstract A new type of amphoteric membranes can be synthesized by means of radiochemical grafting followed by selective chemical reactions. Thus polyetrafluoroethylene films were grafted with styrene/4-vinyl pyridine mixtures, and then reacted with chlorosulphonic acid and methyliodide to obtain membranes containing both-SO-3 and-N—CH+3 groups. Such membranes were tested in a RO plant and their performances with brackish water checked.

Mechanical, chemical and bacterial resistance of modified polyvinylidene fluoride membranes suitable for ultrafiltration of oily emulsions☆

Abstract The ultrafiltration membranes prepared at the Institute of Industrial Chemistry of the University of Genoa and, at the present time, developed in a tubular form by ANIC S.p.A. for ultrafiltration of oily emulsions, are made from modified polyvinylidene fluoride. The base polymer shows very good resistance to chemical and bacterial attack and the membranes prepared from it should presumably have the same properties. In order to verify the above assumption, the membranes were stored for one year in the presence of the following agents: water, wool scouring waste water, acids, alkali, calcium chloride sodium hypochlorite and sodium bisulfite at concentrations ranging from a few grams to more than one hundred grams per liter. Every month the membranes were washed and tested. The results show that, in most cases, after an initial decline of about 30% during the first three months of storage, the permeate flux for these membranes becomes constant with values corresponding to more than 7000 liters per square meter per day. Among the chemicals used, only concentrated solutions of sodium hydroxide and sodium hypochlorite affect the performance of the membranes. The membranes were also submitted to bacterial attack tests in order to check their suitability for processes involving ultrafiltration of organic media such as wool scouring wastes or sewage. The bursting strength of the membranes was also checked as a function of their storage in the presence of all the above agents. No change was noticed except for those immersed in sodium hydroxide solutions. It can therefore be inferred that the membranes exhibit substantially the same resistance properties as the parent polyvinylidene fluoride.

The Vibrating Ultrafiltration Module. Performance in the 50–1000 Hz Frequency Range

Abstract The effect of mechanical vibrations on the ultrafiltration of oily emulsions was studied in the 50–1000 Hz range. A cylindrical vibrating module was assembled and coupled with an electrodynamic exciter, controlled by a computerized system. The ultrafiltration experiments were run with a 20% cutting oil/water emulsion at different working conditions. The experimental data demonstrated that both vibration amplitude and frequency are effective in enhancing membrane performance. The influence of the frequency is more marked. Energy consumption was evaluated, and simple equations were proposed in order to predict both performances and energy requirements.

Ultrafiltration membranes obtained by poly(acrylonitrile) grafted onto poly(vinylchloride)

Abstract Acrylonitrile (AN) has been grafted onto Polyvinylchloride (PVC) dissolved in Dimethylformamide (DMF) by means of gamma rays from a Co60 source. The grafting yield has been studied as a function of irradiation dose and initial AN/PVC ratio in the solution. The ratio PAN/PVC has been evaluated both in the grafted copolymer and its fractions by infrared spectroscopy. Ultrafiltration membranes have been prepared from the grafted PVC and its fractions, using the phase inversion technique. The UF performances have been studied as a function of PAN grafted %. The results show that both water flux and rejection increase with the grafting. Electron microscopy has also been employed to investigate the membrane structure.

Phase transitions in nuclei and chromatin

Changes in the volume of rat liver nuclei have been monitored as a function of modifications in ionic environment (from 0 to 20 mM), temperature (from 4 to 37°C) and pH (from 1 to 8). An abrupt reduction of nuclear volume occurred with increasing ion concentration, this contraction being more pronounced with bivalent (either Ca2+ or Mg2+) than with monovalent (either Na+ or K+) cations. The lowering of pH produced a similar effect. Parallel changes in chromatin structure took place at the same time as phase-like transitions. Atomic absorption spectroscopy allowed determination of free and nuclei-bound ions, pointing to the presence of a sizeable number of free binding sites for chromatin-DNA even within intact nuclei. DNA-phosphate sites appear to be neutralized by ions strictly according to the size of the electric charge and polyelectrolyte theory. Partial digestion (by micrococcal nuclease) or simple breaks (by chemical carcinogens) of the chromatin-DNA fiber caused respectively elimination or reduction of the abrupt volume changes in the intact nuclei. The apparent role of chromatin structure versus nuclear matrix in determining the shape and volume of intact nuclei is briefly discussed.