Claudio Fabiani

Gas Separation in a Membrane Unit: Experimental Results and Theoretical Predictions

Abstract A laboratory membrane separation unit was assembled by using composite hollow fibers. It was tested in an automated apparatus for gas separation measurements. The performances of the system were measured for CH4/CO2 mixtures as functions of temperature, pressure, stage cut, feed gas composition, and flow regime. The results were analyzed on the basis of a predictive mathematical model of the process. A good fitting of the data was obtained in most cases except at high pressure, probably as a consequence of structural changes of the active layer of the fibers under pressurization.

Non-isothermal potential of phospholipid bilayer films Influence of cholesterol and macrocyclic carrier effects

The effect of cholesterol on the ion selective behavior of phoshpolipid (phosphatidylcholine or phosphatidylethanolamine) bilayer films is studied through the measurement of the membrane non-isothermal potential. It is shown how the mixed phosphatidylcholine-cholesterol membrane can be either cation of anion permselective according to the film composition (cationic behavior is met in the 0--10% cholesterol composition range while anionic selectivity appears in the 20--50% range). On the contrary, mixed phosphatidylethanolamine-cholesterol membranes show the absence of ionic selectivity already met with pure phosphatidylethanolamine films. The presence of a cationic carrier as Dibenzo-18-crown-6 in the film transforms all the studied films (cationic, anionic and no selective bilayers) into ideally cationic selective membranes. These results are discussed on the basis of the current ideas on the charge distribution through the bilayer membranes. Moreover, the role of the permeating ions as potential determining species is stressed.

Strontium Separation with Ultrafiltration Membranes from Dilute Aqueous Solutions

Abstract The separation of Sr2+ from dilute and trace solutions of low activity by means of hollow fiber Amicon ultrafiltration membranes is studied. The cation is absorbed on colloidal particles of titanium oxide formed directly in solution, and the colloidal dispersion is filtrated. The method has been studied under several different operative conditions (pH, Ti/Sr ratio, the presence of interfering ions, colloid formation time) with the aim of determining the optimum conditions to develop a separation process.

Non-isothermal potential of phospholipid bilayer films.

The thermal electrical potential generated in isochemical conditions by a temperature gradient at the two sides of lipid bilayer leaflets is measured. The experimental results agree rather well with the theoretical predictions. The cephaline (from sheep brain) bilayer behaves like a film with zero charge while the phosphatidylcholine (from egg yolk) film performs like a charged membrane. The results presented suggest that the measurement of electrical thermal potential is an interesting method to investigate the electrical behaviour of bilayer membranes.

Performance of a hollow fibre membrane unit in oxygen-enriched air production

Abstract The performance of a pilot test for biogas upgrading has been tested under different process conditions to produce oxygen-enriched air for aqueous media application. The selectivity of the polysulfone hollow fibres for N 2 O 2 permeation allows the production of an oxygen-enriched air stream in the 30–50% range and an inert gas (nitrogen between 82–98%) by operating the pilot unit at different stage-cut values in a single pass mode. Membrane area requirements for a medium size plant of 100 Nm3 h−1 are discussed according to a simple perfect mixing model for gas permeation.

Nafion membrane potential in non-isothermal systems

Abstract The electrical potential difference of non-isothermal Nafion membrane cells has been studied in presence of CsCl, KCl, and NaCl as electrolytes. The thermal electrical potential appears to be rather well described by means of already available equations based on non-equilibrium thermodynamic theories.

Cation and anion responses of zwitterion phospholipid bilayers

Abstract The electrochemical behavior of zwitterion phospholipid bilayers as determined with the help of membrane potential data, is examined. The synthetic DL-β,γ-dipalmitoyl-α-phosphatidylcoline bilayer shows at 30°C nernstian and sub-nernstian anion responses which depend on the cation present in the electrolytes (LiCl, NaCl, KCl, CsCl, CaCl2, CeCl3), and in some cases on the concentration of the solutions considered. On the other hand, nernstian cation responses have been observed in non-isothermal membrane-potential measurements performed on the same lipidic films. These experimental results are explained on the assumption that, from a potentiometric viewpoint the phospholipid membrane behaves as a neutral carrier membrane electrode. Accordingly, the form of the potential equations, and then the anion response of the bilayer, follows from the chemistry of the phospholipid molecules.

402 - Lecithin-cholesterol-cation interactions in mixed lipid cholesterol liposomes

Abstract Electrophoretic mobilities of mixed phosphatidylcholine-cholesterol liposomes formed in KCl solution show a ξ potential minimum at a lecithin-cholesterol 2 : 1 molar ratio. This minimum does not depend on the electrolyte concentration. Shielding of the lipidic negative charged phosphoric group with complexing cations (Ca2+, Ce3+) prevents the occurrence of the electrophoretic minimum. It is suggested that a specific 2 : 1 phospholipid-cholesterol association can be responsible for the observed behavior.

Recovery by Ultrafiltration of a Commercial Enzyme for Cellulose Hydrolysis

Abstract An enzymatic process of cellulose hydrolysis based mainly on the use of membrane techniques is under study. The proposed flow sheet assumes that during cellulose hydrolysis the enzyme is continuously separated from glucose and cellobiose and is recycled in the cellulose reaction vessel by membrane ultrafiltration. The ultrafiltration of Celluclast enzyme by Novo is performed in a DDS column module assembled with flat polysulfone membranes. Membrane polarization effects are studied in the 0.1–5% w/v enzyme concentration range under varying pressures up to 600 kPa. A partial loss of enzymatic activity is observed as a consequence of the ultrafiltration and membrane washing operations.

Gas permeability of wet cation exchange membranes

Abstract The permeation of CO2 across a Nafion cation exchange membrane in different hydrated forms is studied. The water solvent linked to the ion exchanging sites of the charged membranes forms a liquid supported membrane in which the transport of the polar gas is enhanced. This effect is still higher when the dry membrane is swollen in a Li2CO3 solution which increases the carbonate/bicarbonate anion concentration in the wet membranes and reduced the effectiveness of the Donnan co-ion exclusion from the membrane phase.