Alessandro Galia

Electrochemical oxidation of organics in water: Role of operative parameters in the absence and in the presence of NaCl

The electrochemical oxidation of organics in water was investigated theoretically and experimentally to determine the role of several operative parameters on the performances of the process in the presence and in the absence of sodium chloride. Theoretical considerations were used to design the experimental investigation and were confirmed by the results of the electrochemical oxidation of oxalic acid (OA) at boron doped diamond (BDD) or IrO(2)-Ta(2)O(5) (DSA-O(2)) anodes in a continuous batch recirculation reaction system equipped with a parallel plate undivided electrochemical cell. Polarization curves and chronoamperometric measurements indicated that, in the presence of chlorides, the anodic oxidation of OA is partially replaced by an indirect oxidation process. This result was confirmed by electrolyses experiments that show that, in the presence of suitable amount of chlorides, oxidation of OA takes place mainly by a homogeneous process. Interestingly, a very different influence of the nature of the anodic material, the flow rate and the current density on the performances of the process arises in the absence and in the presence of chlorides so that optimization of the two processes requires very different operative conditions. In the absence of chlorides, high current efficiency (CE) is obtained at BDD when most part of the process is under charge transfer controlled kinetics, i.e. when low current densities and high flow rates are imposed. On the other hand, in the presence of NaCl, higher CE are generally obtained at DSA anode when high current densities and low flow rates are imposed, i.e. when a high concentration of chemical oxidants is obtained as a result of the chloride oxidation. The effect of other operative parameters such as the OA concentration and the pH were further investigated.

Electrochemical reduction and carboxylation of halobenzophenones

Abstract The electrochemical reduction of a series of halogenated benzophenones XC6H4COC6H4Y (1) was studied in aprotic solvents, in the absence and presence of CO2, by cyclic voltammetry (CV) and controlled-potential electrolysis. The mechanism of electroreduction in dimethylformamide (DMF) has been investigated in some detail. Most of the compounds undergo reductive carbonhalogen bond cleavage in the time window of CV. The radical anions derived from difluorobenzophenones (X=Y=4-F; X=2-F, Y=4-F) as well as from the 3-chloro derivative are quite stable with a cleavage rate constant (kc) of the order of 10−2 s−1 or less. With 4-chloro-, 2-chloro-, 4,4′-dichloro- and 2,4′-dichorobenzophenones, kc of 1 − has values in the range 4–254 s−1 in DMF. In the presence of CO2 all radical anions react quite rapidly with CO2, carboxylation of 1 − being much faster than dehalogenation. Controlled-potential electrolyses were carried out in DMF, MeCN and N-methyl-2-pyrrolidinone (NMP) in an undivided cell using a compact graphite cathode and an aluminium sacrificial anode. The principal product under these conditions was always the α-hydroxyacid XC6H4C(OH)(CO2H)C6H4Y. In NMP under 1 atm of CO2, acid yields around 90% were obtained except in the case of 2-chloro- and 2,4′-dichlorobenzophenone, where acid yields of 58 and 68% were obtained, respectively.

A new simple static method for the determination of solubilities of condensed compounds in supercritical fluids

Abstract A simple static method based on gravimetric measurements has been adopted to measure the solubility of benzenecarboxylic acid, 2-hydroxy-benzenecarboxylic acid, 4-hydroxy-benzenecarboxylic acid and 1,8-dihydroxyanthraquinone along several isotherms in the temperature range 318–357 K and the pressure interval 7–23 MPa. Solubility data have been correlated with the Zieger–Eckert approach, using the Fedor atomic and group contribution method to estimate the solubility parameter and the molar volume of the solutes. A good agreement was obtained between data reported in the literature and those determined using the proposed method which allows one to measure solubility mole fraction as low as 10 −5 . Provided that a suitable analytical technique is adopted the method can be extended also to multicomponent systems.

Integrated production of fresh water, sea salt and magnesium from sea water

Abstract Seawater desalination is becoming an important source of fresh water in several countries all around the world. One of the main drawbacks of desalination processes, however, is related to the disposal of large quantities of concentrated brine, which is an always-present by-product of the process. An integrated production of fresh water and salts may be achieved using the discharge brine from a desalination plant as a feed for conventional salt ponds, with the advantages of using brine more concentrated than sea water and, in the case of thermal desalination plants, warmer than sea water. By doing so, the process is faster as a consequence of the enhancement of evaporation rate on the surface of ponds. The above concept has been proposed already several years ago, but only rare examples exist of real applications. A pilot test has been performed in the last 4 years in Trapani (Italy), where a 36,000-m3/d multiple effects desalination with thermal vapour compression plant is operating very close to...

Catalytic systems based on transition metals for the carbonylation of methanol to dimethylcarbonate

Abstract The results of an investigation on catalytic systems arising from the electrochemical activation of salts and complexes of several transition metals for the carbonylation of methanol to dimethylcarbonate (DMC) are reported. Metals were tested as inorganic salts or complexes with ligands such as 2,2′-bipyridine (bipy), 1,6-bis (2-oxyphenyl)-2,5-diaza-1,5-hexadiene (salen), 2,4-pentanedionate (acac), triphenylphosphine (TPP) in methanol at room temperature saturated with carbon monoxide at atmospheric pressure. Best faradic yields vs DMC were observed as follows: CuCl(bipy): 84.8%; PdCl 2 (bipy): 64.0%; CoCl 2 : 26.0%; RhCl 3 : 25.0%; AgBF 4 (bipy): 10.2%; AuCl 3 : 9.4%; Cr(acac) 3 : 6.7%; PtCl 2 (bipy): 2.1%; NiCl 2 : 1.8%. The influence of the ligand on faradic yields has been also investigated.

Electrochemical activation of transition metal complexes for the carbonylation of methanol to dimethylcarbonate

Abstract The preliminary results on the electrochemical activation of catalytic systems based on copper and cobalt complexes for the carbonylation of methanol to dimethylcarbonate at room temperature and atmospheric pressure are reported. Faradic yields up to 70%, with very high selectivity towards dimethylcarbonate, were observed with CuCl(2,2′-bipyridine). Positive results were also obtained, although with poorer catalytic activity, with other complexes such as CuCl(tetramethylethylenediamine), [Co(1,6-bis(2-oxyphenyl)-2, 5-diaza-1,5-hexadiene)]0.5 H2O and Co(2,4-pentanedionate)2.

A one-pot method to enhance dissolution rate of low solubility drug molecules using dispersion polymerization in supercritical carbon dioxide

The surfactant assisted polymerization of 1-vinyl-2-pyrrolidone in supercritical carbon dioxide in the presence of Piroxicam, selected as a model of a low aqueous solubility drug, was studied in order to prepare in a single step a polymeric composite to enhance the rate of dissolution of the pharmaceutical compound. Reactive entrapping was carried out at 65 degrees C in the P range 21-38MPa. Under proper operative conditions we obtained the composite under the form of sub-micron spherical particles with relatively narrow particle size distribution. Drug loadings higher than 12% (w/w) were obtained and XRD and Raman spectroscopy suggest that the anti-inflammatory agent is dispersed in the matrix with a non-crystalline structure. The dissolution rate of the drug from the composites was significantly faster both than that of the pure compound and of its physical mixture with the polymer. Collected results suggest that the proposed one-pot process can be used to prepare polymer based composites to increase bioavailability of low solubility drugs without utilization of toxic solvents and under mild temperature conditions.

Midinfrared FT-IR as a Tool for Monitoring Herbaceous Biomass Composition and Its Conversion to Furfural

A semiquantitative analysis by means of midinfrared FT-IR spectroscopy was tuned for the simultaneous determination of cellulose, hemicellulose, and lignin in industrial crops such as giant reed (Arundo donax L.) and switchgrass (Panicum virgatum L.). Ternary mixtures of pure cellulose, hemicellulose, and lignin were prepared and a direct correlation area/concentration was achieved for cellulose and lignin, whereas indirect correlations were found for hemicellulose quantification. Good correspondences between the values derived from our model and those reported in the literature or obtained according to the official Van Soest method were ascertained. Average contents of 40–45% of cellulose, 20–25% of hemicellulose, and 20–25% of lignin were obtained for different samples of giant reed species. In the case of switchgrass, a content of 36% of cellulose, 28% of hemicellulose, and 26% of lignin was achieved. This analysis was also carried out on giant reed and switchgrass residues after a mild hydrolysis step carried out with dilute hydrochloric acid for the production of furfural with good yield. Reasonable compositional data were obtained, thus allowing an indirect monitoring which helps the optimization of the hydrothermal pretreatment for furfural production from hemicellulose fractions.

Electrochemical Oxidation of Carboxylic Acids in Water at Boron-Doped Diamond (BDD) Anodes in the Range of Potential of Oxygen Evolution: Detection Measurements and Studies on the Reaction Mechanism

The electrochemical oxidation in water solutions of selected carboxylic acids (namely oxalic, formic, acetic, maleic, and succinic) at boron-doped diamond (BDD) anodes was investigated by polarization and chronoamperometric measurements. In the presence of low concentrations of carboxylic acids, current densities changed approximately linearly with the acid concentrations. Furthermore, when the current densities were plotted as a function of the chemical oxygen demand, a similar response was observed for all the investigated acids with the exception of oxalic acid. For high carboxylic acid concentrations, the linear variation is often loosen and different behaviors are observed depending on the nature of the acid and on the value of the applied working potential. Smaller increases of current densities were observed in water solutions of NaCl as a result of the chlorides oxidation to active chlorine. The effect of pH, boron doping level, BDD pretreatment, and of the nature of the supporting electrolyte on the amperometric response of carboxylic acids was also studied in detail. Some theoretical considerations were briefly presented in order to rationalize the observed behaviors.

Supercritical-fluid extraction of chlorofluoroalkanes from rigid polyurethane foams

Abstract Preliminary results about a process for recovering expanding agents chlorofluoroalkanes (CFCs) both trapped in the cavities and dissolved in the polymer from rigid polyurethane foams are reported. The performances of liquid and supercritical carbon dioxide, and of CO 2 -propane supercritical mixtures were compared. Better results in terms of extraction time and amount of extracted CFCs were obtained with finely ground materials and supercritical propane-carbon dioxide fluids.