Effect of external factors on the increase in the extraction rate in a vibration treatment on the dynamic interfacial layer

Vibration treatment of a dynamic interfacial layer in the extraction system constituted by an aqueous solution of a salt of a rare-earth element and a solution of di-(2-ethylhexyl)phosphoric acid in heptane (toluene) results in an increase in the process rate. This increase is characterized by an acceleration coefficient defined as the ratio between the lanthanide concentrations in the organic phase after equal intervals of time in systems with and without vibrations. It is shown that the acceleration coefficient depends on the concentration of the extractive agent, initial concentration of an element being extracted, solution pH, and phase contact duration. The observed behavior is explained in terms of the process model suggested by the authors. According to this model, the effect depends on the relative contributions made by a number of interfacial phenomena accompanying the extraction of a lanthanide with solutions of di-(2-ethylhexyl)phosphoric acid in diluents and, in particular, by the spontaneous surface convection and structuring in the interfacial layer.     

Hydrodechlorination of chlorobenzene in the presence of Ni/Al2O3 prepared by laser electrodispersion and from a colloidal dispersion

The low-percentage Ni/Al₂O₃ catalysts with active metal contents of 0.0002–0.1 wt % were prepared using the laser electrodispersion (LED) method and by means of supporting from a colloidal dispersion (CD). Their composition and physicochemical properties were determined by atomic absorption spectrometry, transmission electron microscopy (TEM), and XPS. With the use of TEM, it was found that average size of nickel particles in the LED catalysts was smaller than that in the CD catalysts. According to XPS data, the supporting of a metal onto a substrate by the LED method makes it possible to obtain samples containing Ni metal with a low active metal content (0.03 wt %). They exhibited a high initial activity in the hydrodechlorination reaction of chlorobenzene in a vapor phase, which was performed in a flow system at temperatures of 100–350°C. The CD catalysts were active in this reaction only at temperatures of 300–350°C. Reductive treatment led to the deactivation of LED catalysts and increased the activity and stability of samples prepared by supporting from a CD. The possible reasons for the observed changes are considered.     

Gas-Phase Hydrodechlorination of Chlorobenzene over Alumina-Supported Nickel Catalysts: Effect of Support Structure and Modification with Heteropoly Acid HSiW

Kinetics and Catalysis - The physicochemical and catalytic properties of 6%Ni/Al2O3 catalysts in the gas-phase hydrodechlorination of chlorobenzene (CB) are studied. The catalysts are synthesized...     

The hydrodechlorination of chlorobenzene in the vapor phase in the presence of metal-carbon nanocomposites based on nickel,palladium, and iron

Metal-carbon nanocomposites based on nickel, palladium, and iron and bimetallic palladium-nickel-carbon nanocomposites were for the first time used as catalysts of hydrodechlorination of chlorobenzene in the vapor phase in the atmosphere of hydrogen. Nickel and Pd-Ni nanoparticles completely coated by a carbon layer not only were stable to oxidation and agglomeration but also exhibited considerable activity in hydrodechlorination of chlorobenzene at temperatures much lower than those at which dechlorination on carbon carriers occurred. The dependence of catalytic properties (activity, selectivity, and stability) on temperature and nanocomposite composition was studied. Depending on the nature of the metal, the composition of bimetallic particles and temperature the selectivity could be changed, and the reaction could be directed toward the formation of benzene or cyclohexane. Carbon coating was stable under reaction conditions at least up to 350°C and did not hinder hydrodechlorination. Substrate adsorption likely occurred on the outside carbon surface of composite particles. The activity and structure of Ni@C composite remained almost unchanged after triple cycling over the temperature range from 50 to 350°C in a flow system.     

ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> binary oxides as promising supports for palladium catalysts of hydrodechlorination

Deposited palladium catalysts of the hydrodechlorination of 1,3,5-trichlorobenzene were studied. Pure zirconium and aluminum oxides and ZrO₂-Al₂O₃ mixtures with 1, 5, and 10 mol % Al₂O₃ prepared by coprecipitation were used as supports. Palladium was deposited by the precipitation of its hydroxide on supports. Catalysts on binary supports (ZrO₂ + 1% Al₂O₃ and ZrO₂ + 5% Al₂O₃) exhibited higher activity and stability in hydrodechlorination compared with catalysts on pure supports. The suggestion was made that the high activity and stability of these systems in hydrodechlorination was related to the formation of binary oxide in the interaction of ZrO₂ with palladium oxide at the stage of annealing of the catalyst precursor. Binary oxide, which was a center of the activation of the C-Cl bond, was simultaneously a source of active hydrogen. The presence of various palladium states in catalysts was substantiated by the temperature programmed reduction method.     

Spontaneous Surface Convection and Extraction (Stripping) Rate in Systems with Tributyl Phosphate and Di(2-ethylhexyl) Hydrogen Phosphate

Russian Journal of Applied Chemistry - Extraction of rare earth elements with solutions of di(2-ethylhexyl) hydrogen phosphate or tributyl phosphate in heptane, toluene, or tetrachloromethane is...     

Catalytic properties of Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of Ce _x Zr_1–x O₂ double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N₂ that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for Ce _x Zr_1–x O₂ (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.     

Self-assembling structures in the extraction of some rare earth elements in systems with D2EHPA

Effect of different factors on the formation of self-assembling structures in a dynamic interfacial layer in LnA₃-H₂O-D2EHPA-solvent extraction systems was studied. Increase in temperature was shown to inhibit the formation of the self-assembling structures. An exposure of dynamic interfacial layer to mechanical vibrations using a microvibrator was found to prevent structurization and provide higher aggregative stability of disperse system. The structure deteriorates when exposed to vibration and decomposes to aggregates at rather high power. On the extraction of rare earth elements (REE) of yttrium subgroup, the system partially recovers its properties after termination of exposure to vibration, i.e., it is coagulation and thixotropic and becomes condensation in time.