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AbstractA suitable adsorbent for the treatment of nitrite in wastewater was investigated using a macroporous styrene divinylbenzene strong base polymer for 10−3 M to 6 x 10−3M NaNO2 at room temperature using a batch protocol. The supernatant concentrations were determined rapidly and inexpensively by an electrochemical method. To investigate the sorption mechanism and the rate-determining step, four kinetic models were investigated. The pseudo-second order kinetic model best fit the nitrite adsorption onto the polymer. The highest correlation coefficient (0.9999) and chi square (7.59 x 10−4) values were obtained for 0.046 to 0.276 g L−1 NO2- which is characteristic of chemosorption. The results demonstrate that the investigated polymer is suitable at room temperature for removing nitrites for water to the legally allowed values for 10−3 M to 1.5 x 10−3 M NaNO2 but dilution is required for higher concentrations. [ABSTRACT FROM AUTHOR]

The compensation effect in heterogeneous catalytic reactions is related to an appropriate change in the activation energy. A compensation effect is expected if a linear relationship between activation energy and pre‐exponential factor, or activation enthalpy and entropy, takes place for a reaction in the presence of different catalysts. This study aims to identify the occurrence of the compensation effect in CO oxidation reaction to CO2 catalyzed by CuO/Al2O3, Ni/TiO2, Ni/Al2O3, and Pd/Al2O3. [ABSTRACT FROM AUTHOR]

Considering that 13CO2 is an appropriate precursor material in 13C labelling of various organic, inorganic and biological molecules, in this study the CO oxidation reaction is investigated for covert 13CO to 13CO2. CO oxidation was performed in a plug flow reactor over three Ni/Al2O3 catalysts (Ni loadings of 5 wt.%, 7 wt.%, and 10 wt.%) prepared by the wet impregnation method. Ni/Al2O3 catalysts present excellent catalytic activity in CO oxidation: catalytic performance improves with rising reaction temperature and with increasing metal loading. Among the investigated Ni catalysts, 7 wt.% Ni/Al2O3 is considered the most promising candidate for CO oxidation due to the wide temperature range for catalytic performance, as well as the best distribution of the smallest Ni nanoparticles, and the best metal dispersion corresponding to a very good metal surface area. Also, 7 wt.% Ni/Al2O3 was stable over 30 h time-on-stream with a mean CO conversion value of 90% at 250 °C. The good catalytic activity of this catalyst was validated in 13CO total conversion to 13CO2. [ABSTRACT FROM AUTHOR]

In the present study, adsorption isotherms and thermodynamics were performed using aqueous solutions of chromium (VI) and an anion exchange resin which was have not yet been characterized for this ion. The adsorption results were fitted to Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin-Pyzhev sorption models. The highest correlation factor (R2) was observed for the Freundlich isotherm which indicates sorption upon a heterogeneous surface. The thermodynamic parameters such as the Gibb's free energy (ΔG°), the standard enthalpy (ΔH°), and the standard entropy (ΔS°) were determined, indicating that the chromium (VI) adsorption process was spontaneous and endothermic. This study contributes to a clearer understanding of the Cr (VI) adsorption onto the studied anion resin. Our target is to found materials suitable with the world's growing interest in the treatment of wastewater. [ABSTRACT FROM AUTHOR]

In the present study, batch experiments were performed to remove chromium (VI) from aqueous solutions using an anion exchange resin. In order to investigate the kinetic mechanism which controls the chromium (VI) adsorption, four kinetic models were used: pseudo-first order, pseudo-second order, the Elovich equation and the intraparticle diffusion model. In reaction with 1,5 diphenylcarbazide, chromium (VI) forms a complex, which was analyzed at 540 nm using a spectrophotometer after 7 min. The Cr (VI) adsorption process was well described by the pseudo-second order kinetic model for 0.1 to 0.3 g/L Cr (VI). [ABSTRACT FROM AUTHOR]

A new experimental study on simultaneous separation of 15N and 14N by 15N/14N exchange in Nitrox system under pressure is presented. The influence of the 10M HNO3 flow rate and of the pressure on the isotopic separation was measured on a packed column equipped with product and waste refluxer. The experimental data show that the separation of 15N and 14N is improved by column operation at pressure. By using the additional column section in the top of waste refluxer all nitrogen oxides were converted into nitric acid and NOx losses, in the top of isotopic separation plant, were not more observed. The pressure in the 0.6- 1.6 atm range of the sulfur dioxide, feeding the product refluxer, can be utilized providing similar results for 15N, 14N separation for 3.14 10M HNO3 mL/cm²·min flow rate in the packed separation column. [ABSTRACT FROM AUTHOR]

The Fe(III) adsorption onto Dowex-Marathon resin was well described by pseudo-second order kinetics with a high correlation factor for all the experimental concentrations. The results were analyzed by Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. The activation energy E (7.96 ± 0.2 kJ/mol) indicates a physisorption process as in the case of U(VI) adsorption onto the same resin. The thermodynamic parameters: ∆ G° = (−7.91) ÷ (−13.68) kJ/mol, ∆ H° = 35.60 ± 0.89 kJ/mol and ∆S° = 143.31 ± 3.58 J/mol K, were determined, the Fe(III) adsorption being spontaneous and endothermic. [ABSTRACT FROM AUTHOR]

The reduction of HSO to SO occurs with a relatively good efficiency only at high temperatures, in the presence of catalysts. Some experimental results, regarding conversion of sulfuric acid (96 wt.%) to sulfur dioxide and oxygen, are reported. The reduction has been performed at 800 - 900°C and atmospheric pressure, in a tubular quartz reactor. The following commercial catalysts were tested: Pd/AlO (5 wt.% and 0.5 wt.% Pd), Pt/AlO (0.1 wt.% Pt) and α-FeO. The fresh and spent catalysts were characterized by X-Ray diffraction and BET method. The highest catalytic activity was determined for 5 wt.% Pd/AlO, a conversion of 80% being obtained for 5 hours time on stream, at 9 mL h flow rate of 96 wt.% HSO. A conversion of 64% was determined for 0.5 wt.% Pd/AlO and 0.1 wt.% Pt/AlO. For α-FeO, a less expensive catalyst, a conversion of 61% for about 60 hours was obtained. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

An experimental study on 14N and 15N simultaneous separation using the chemical exchange in NO, NO2-HNO3 system under pressure is presented. The influence of the pressure and of the interstage 10 M HNO3 flow rate on the separation of 14N and 15N was measured on a packed column with product and waste refluxers. At steady state and 1.8 atm (absolute), the isotopic concentration at the bottom of the separation column was 0.563 at% 15N, and in the top of the column was 0.159 at% 15N. The height equivalent to a theoretical plate and interstage 10 M HNO3 flow rate values, obtained in these experimental conditions, allows the separation of 14N highly depleted of 15N and of 15N at 99 at% 15N concentration. [ABSTRACT FROM AUTHOR]