Controlled multiphase oxidations for continuous manufacturing of fine chemicals

The feasibility of an integrated continuous biphasic oxidation process was studied, incorporating (i) electrochemical generation of an oxidant, (ii) membrane emulsification and an Oscillatory Flow Reactor (OFR) to facilitate mass-transfer in a biphasic reaction system and (iii) product extraction to enable regeneration of the oxidant. The biphasic, organic solvent-free dihydroxylation of styrene by ammonium peroxodisulfate solutions (including electrochemically generated peroxodisulfate) was investigated as a model reaction, both in batch and in an OFR. Heating of peroxodisulfate in a strongly acidic solution was demonstrated to be essential to generate the active oxidant (Caro’s acid). Membrane emulsification allowed mass-transfer limitations to be overcome, reducing the time scale of styrene oxidation from several hours in a conventional stirred tank reactor to less than 50 min in a dispersion cell. The influence of droplet size on overall reaction rate in emulsions was studied in detail using fast image capturing technology. Generation of unstable emulsions was also demonstrated during the oxidation in OFR and product yields >70% were obtained. However, the high-frequency/high-displacement oscillations necessary for generation of fine droplets violated the plug flow regime. Membrane emulsification was successfully integrated with the OFR to perform biphasic oxidations. It was possible to operate the OFR/cross-flow membrane assembly in plug flow regime at some oscillatory conditions with comparable overall oxidation rates. No mass-transfer limitations were observed for droplets <60 lm. Finally, the continuous post-reaction separation was demonstrated in a single OFR extraction unit to enable continuous regeneration of the oxidant

Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis.

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 [Formula: see text] at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at -10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process

Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 mol gPd-1 h-1 at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at −10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process

Effects of Irradiation on Porous Silicon

Besides the well-known effect of photoluminescence, the impinging of photons and other kinds of particles such as electrons, ions, and muons on porous silicon produces important effects. Some of these effects can modify the structure and properties of the material, distorting the interpretation of data based on the use of irradiation. Some of the irradiation effects are useful in different applications such as photodynamic therapy or display applications. This work is a review of the effects of irradiation on porous silicon.Fil: Koropecki, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Arce, Roberto Delio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin