Effect of Mixing and Other Operating Parameters in Sol-Gel Processes

In this work the effect of mixing on a sol-gel process is quantitatively investigated. Titanium dioxide synthesis from titanium tetra-isopropoxide is used as a test reaction. Solutions of titanium alkoxide in isopropyl alcohol and water in isopropyl alcohol are mixed in a special mixing device (i.e., vortex reactor) at different mixing rates, and the effect of mixing is quantified and compared with the effect of the other relevant operating parameters, namely the water to alkoxide, acid to alkoxide ratios, and alkoxide initial concentration. Dynamic light scattering, specific surface area measurement through nitrogen adsorption, X-ray diffraction, and field emission scanning electron microscopy are employed to determine particle size distribution, morphology, and crystallite size of the different particulate products (i.e., sols, gels, powders) obtained before and after thermal treatments under different synthesis conditions. A factorial design is used to plan the experimental campaign and results show that the role of mixing cannot be neglected. Moreover results show that mixing can be actively used to control the final product characteristics and must be taken into account when a process is transferred from the laboratory to the industrial scale. Eventually a scale-up criterion based on our previous work will be discussed

Nanocomposite MFI-alumina and FAU-alumina Membranes: Synthesis, Characterization and Application to Paraffin Separation and CO2 Capture

Rouleau, L. Pirngruber, G. Guillou, F. Barrere-Tricca, C. Omegna, A. Valtchev, V. Pera-Titus, M. Miachon, S. Dalmon, J. A.International audienceIn this work, we report the preparation of thermally and mechanically resistant high-surface (24-cm2) nanocomposite MFI-alumina and FAUalumina membranes by pore-plugging synthesis inside the macropores of α-alumina multilayered tubular supports. The MFI membranes were prepared from a clear solution precursor mixture being able to easily penetrate into the pores of the support. The MFI membranes were evaluated in the separation of n-/i-butane mixtures. The synthesis reliability was improved by mild stirring. The most selective MFI membranes were obtained for supports with mean pore sizes of 0.2 and 0.8 μm. The MFI effective thickness could be reduced to less than 10 μm by impregnating the support with water prior to synthesis and by diluting the synthesis mixture. The best MFI membrane offered an excellent tradeoff between selectivity and permeance at 448 K, with separation factors for equimolar n-butane/i-butane mixtures up to 18 and n-butane mixture permeances as high as 0.7 μmol$\cdot$s-1$\cdot$m-2$\cdot$Pa-1.Furthermore, a novel nanocomposite FAU membrane architecture has been obtained by an original synthesis route including in situ seeding using a cold gel-like precursor mixture, followed by growth of the FAU material by hydrothermal synthesis in two steps using a clear solution of low viscosity. This new membrane showed interesting performance in the separation of an equimolar CO2/N2 mixture at 323 K, with CO2/N2 separation factors and mixture CO2 permeances up to 12 and 0.4 μmol$\cdot$s-1$\cdot$m-2$\cdot$Pa-1,respectively

DAMAGE EVALUATION ON STONE MATERIALS OF THE RICHINI COURTYARD (MILAN, ITALY)

It has been recognized that air pollutants interact with carbonate surfaces and cause major damage to architectural heritage. The focus of the present study is to evaluate the damage on the stone materials that have been used for the realization of Richini courtyard. The courtyard was designed in the seventeenth century by Francesco Maria Richini in the complex of Ca 'Granda Hospital, currently home to the University of Milan. Since 1990 has been the subject of an important conservative intervention. At a distance of twenty years after the restoration, "Richini Project" aims to make an assessment of the effectiveness and durability of the solutions used. This study lies in the framework of this project. At this purpose the quantification of soluble salts within the stone samples, collected on the four sides of the courtyard, has been performed by ion chromatography. A widespread sulfatation phenomenon has been put in evidence with differences in intensity among the sides because of different exposition to the atmospheric agents. Atmospheric particulate matter (PM) present on the stone surfaces has been examined. In fact PM is involved in the formation of the black crusts that sometimes cover the surfaces. A new methodology has been set up for the quantification of organic carbon (OC) and elemental carbon (EC), which are mainly responsible of the blackening of those areas. PM major inorganic constituents (cations and anions) have been also quantified and observations by SEM-EDX have allowed the identification of metals that may act as catalysts in the reactions of degradation

Characterization and optimization of CPW electro-optic modulators for microwave and MM-wave applications

The paper presents a discussion on the experimental characterization and microwave modelling of coplanar electro-optic modulators on lithium niobate substrates. To introduce the issue, a discussion is presented on the design criteria for travelling-wave modulators. In particular, we show that attenuation is a main concern if modulation bandwidths in excess of 20 GHz are sought, while velocity matching can be achieved with comparative ease, as a survey of the available structures shows. Finally, the experimental characterization and modelling of some conventional modulator structures is presented, with the aim to assess their operating limits in terms of modulation bandwidth