Antonio Comite

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.

Polymeric and ceramic membranes in three-phase catalytic membrane reactors for the hydrogenation of methylenecyclohexane☆

Abstract This work investigates the hydrogenation of methylenecyclohexane using catalytic membrane reactors. Flat polymeric (PVDF) and tubular ceramic (γ-Al2O3) membranes were prepared and the hydrogenation catalyst, palladium, was deposited into their porous structure. Characterisations were carried out on the membrane morphology and on the deposited catalyst. Preliminary data on their reactivity are reported.

Electron microscopy characterization of airborne micro- and nanoparticulate matter

The aim of this work was to offer a state-of-the-art critical survey for characterizing airborne nano- and microparticles by means of electron microscopy (EM) techniques and to highlight advantages and limits of different possible operation modes. Procedures of collection and sample preparation are revisited and improved to analyse airborne particles deposited on filtering membranes by using various sampling methods. Three kinds of electron microscopes are used to this end: scanning electron microscope (SEM), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). Following and extending previous studies, we optimized procedures by varying both the sample collection/preparation and the operational parameters of the microscopes. In particular, we diversified the sampling methods applied, using ad hoc filters as well as common filters for standard gravimetric measures. This approach enabled us to achieve a simple and clean procedure allowing direct SEM or TEM observation of the collected particulate matter.

Catalytic ceramic membrane in a three-phase reactor for the competitive hydrogenation–isomerisation of methylenecyclohexane

Abstract Hydrogenation and oxidation reactions can be carried out in very mild conditions using a three-phase catalytic reactor. The challenge is to overcome the diffusion resistance that affects this type of reactor. The catalytic membrane reactor (CMR), where the membrane is used not only as physical selective barrier but also as a chemical reactor, can be an efficient alternative to more conventional systems in improving the contact among solid catalyst, gas and liquid. The performances of different catalytic membranes were explored in the hydrogenation–isomerisation of methylenecyclohexane, in a temperature range between 288 and 343 K. Comparisons between a classic batch stirred tank and CMR were also carried out. Various characteristics of the reacting system, such as the overall process rate, the effect of temperature, the reaction order with reference to the substrate and the hydrogen and reaction selectivity were studied.

Inorganic membrane reactors for the gas phase partial oxidation of toluene

The gas phase oxidation of toluene was studied as an alternative way to obtain benzaldehyde and benzoic acid. A traditional support (TiO2) and a new mixed Al2O3–TiO2 support for the active catalyst element, vanadium, was used. The oxidation process was investigated by either using a packed bed reactor or inorganic membrane reactors. Vanadium was deposited on the supports (powder or inorganic membranes) through either ion exchange or impregnation from a solution of ammonium metavanadate. The catalysts were characterized in terms of vanadium content and distribution, morphology, specific surface area and porosity. The reaction runs quantified catalytic activity of the catalysts prepared. The effect of the temperature and of the hydrocarbon=oxygen ratio was investigated. Selectivity to intermediate oxygenated products was higher for vanadium supported by Al2O3–TiO2 and when the hydrocarbon to oxygen ratio was higher, the formation of carbon oxides was lowered. Finally inorganic membrane reactors were explored using different reactor configurations (i.e. both the reactants, toluene and oxygen, were flowed inside a inorganic membrane tube with catalytic walls, or were forced through the membrane from the internal side to the outer side).

Wetting of Polypropylene Membranes by Aqueous Solutions in CO2 Absorbing Devices

A polypropylene hollow fiber membrane contactor was utilized to absorb CO2 from a gas stream into an aqueous solution. Three reagents were studied: monoethanolamine, piperazine, and potassium carbonate. Attention was focused on the possible intrusion of absorbent in the membrane pores, which reduces the solute mass-transfer rate. Membrane/liquid interface was thoroughly characterized. The removal efficiency of the reagents contacted with a CO2/N2 stream was assessed. It is shown that potassium carbonate and piperazine could be considered interesting candidates for applications in membrane contactors, as they appear more successful than monoethanolamine in ensuring proper and stable conditions at the membrane/liquid/gas interface.

Numerical simulation of CO2 diffusion and reaction into aqueous solutions of different absorbents

A numerical model comprising a system of partial differential equations was set up to describe the diffusion and reaction of carbon dioxide into aqueous solutions of different absorbents. The solution of the governing equation was a function of the physical and chemical parameters involved, such as Henry constant, diffusion coefficients and reaction rates. Although these parameters have been estimated and reported in literature, uncertainty still exists about their reliability. Comparison between numerical predictions and experimental values from specifically designed experiments shows them to be in good agreement, thus increasing the confidence on the correctness of these parameters, which form then the basis for a proper design of industrial units.

Novel polytetrafluoroethylene tubular membranes for membrane distillation

AbstractThis paper deals with the preparation of novel polytetrafluoroethylene (PTFE) membranes from an aqueous dispersion of fluorinated polymer and a pore forming agent (PFA) sintered onto the outer surface of a porous tubular support. Different membranes were obtained by varying the ratio between PTFE and PFA in the starting dispersion as well as the number of dispersion layers sintered on the support. Membranes were characterized through scanning electron microscopy and gas–liquid displacement porosimetry. Distillation tests of the membrane were carried out on a laboratory scale unit fed with a NaCl solution. The characteristics and performance of the membranes were compared with those of commercial porous PTFE tubulets.

Dehydration of Basil Leaves and Impact of Processing Composition

Abstract Both consumers and the food industry are increasingly interested in aromatic herbs, not only as flavoring agents, but also for their content in biologically active compounds. Sweet basil (Ocimum basilicum L.) is a very important culinary herb and a functional ingredient marketed fresh, dried, or frozen. At present, drying is by far the most widely used basil preservation method, thus ensuring microbiological safety and extending basil shelf-life. Nevertheless, during drying, a series of physical and chemical changes that may have an adverse effect on basil quality may take place. Such alterations include changes in its flavor and appearance, mainly caused by the loss of volatile components and the formation of new compounds. Both these aspects are important quality factors with a deep impact on the consumers’ acceptance of the product. In this chapter the most commonly used drying methods are described and their impact on the sensorial and nutritional properties of this raw material are analyzed.

A pilot system for the characterization of hydrophobic membrane contactor modules to be used in air handling processes

Thermal comfort control in electrical vehicles calls for air conditioning systems with a low energetic demand. The paper describes a pilot system developed in the frame of the “Xeric” EU project in order to study the effect of different operating variables (e.g. desiccant temperature, air velocity) on the performance of hydrophobic membrane based on desiccant air humidification/dehumidification. The overall vapour mass transfer coefficient was estimated in different conditions. By evaluating the membrane mass transfer resistance of the membrane through a modified desiccant inverted cup method, the experimental estimation of the mass transfer resistances in the fluid phases was done. The data obtained through the pilot system are of great interest for the development of air condition systems based on membrane contactors to be used in vehicles cabins.