Role of some thiadiazole derivatives as inhibitors for the corrosion of C-steel in 1 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

Inhibition of C-steel corrosion by some thiadiazole derivatives (I–VI) in 1 M H₂SO₄ was investigated by weight loss, potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques. The presence of these compounds in the solution decreases the double layer capacitance, increases the charge transfer resistance and increase of linear polarization. Polarization studies were carried out at room temperature, and showed that all the compounds studied are mixed type inhibitors with a slight predominance of cathodic character. The effect of temperature on corrosion inhibition has been studied and the thermodynamic activation and adsorption parameters were calculated and discussed. Electrochemical impedance was used to investigate the mechanism of corrosion inhibition. The adsorption of the compounds on C-steel was found to obey Langmuir’s adsorption isotherm. The synergistic effect brought about by combination of the inhibitors and KSCN, KI and KBr was examined and explained. The mechanism of inhibition process was discussed in the light of the chemical structure and quantum-chemical calculations of the investigated inhibitors.     

Joint effect of halides and ethanol extract of <Emphasis Type="Italic">Lasianthera africana</Emphasis> on inhibition of corrosion of mild steel in H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

Inhibitive and adsorption properties of ethanol extract of Lasianthera africana for inhibition of corrosion of mild steel in H₂SO₄ were studied using gravimetric, thermometric, gasometric, and infrared (IR) methods. The extract was found to be a good inhibitor of corrosion of mild steel in H₂SO₄. Inhibitive properties of the extract were attributed to enhancement in adsorption of the inhibitor on mild-steel surface by saponin, alkaloid, tannin, flavanoid, cardiac glycoside, and anthraquinone (present in the extract). Also, adsorption of the inhibitor was found to be exothermic, spontaneous, and consistent with assumptions of Langmuir and Temkin adsorption isotherms. Synergistic study revealed that, of the investigated halides, only KCl may enhance adsorption of the inhibitor, whereas KBr and KI antagonized its adsorption. Based on the decrease in efficiency of the inhibitor with temperature, with values of activation energy and free energy of adsorption below the threshold values of −40 and 80 kJ mol⁻¹, respectively, a physical adsorption mechanism has been proposed for adsorption of ethanol extract of Lasianthera africana on the surface of mild steel.     

Dissolution of colemanite in (NH<Subscript>4</Subscript>)2SO<Subscript>4</Subscript> solutions

Turkey is the country having the richest boron ores in the world, and colemanite, tincal and ulexite are the ores being mined mostly in Turkey. These ores are used in the production of various boron compounds of which the production methods are generally patented. Colemanite ore also is reacted with sulfuric acid to product boric acid. Produced by this method, boric acid contains various impurities which reduce the market value and are difficult to remove. This study investigated the reaction between colemanite and ammonium sulfate as an alternative method to produce boric acid. Particle size, ammonium sulfate concentration, solid to liquid ratio and reaction temperature were chosen as parameters. In results, the conversion rate was increased by decreasing particle size and solid to liquid ratio, by increasing ammonium sulfate concentration and temperature. A semi-empirical model with 40.46 kJmol⁻¹ activation energy representing this process was found as follows: 1−(1−X)^1/3=2.12×10²·C^1.38·R^−0.75·(S/L)^−0.44·e^−4866/T·t^0.61.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Effect of H<Subscript>2</Subscript>O<Subscript>2</Subscript> modification of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>@carbon for m-xylene oxidation to isophthalic acid

The production of isophthalic acid (IPA) from the oxidation of m-xylene (MX) by air is catalyzed by H₃PW₁₂O₄₀ (HPW) loaded on carbon and cobalt. We used H₂O₂ solution to oxidize the carbon to improve the catalytic activity of HPW@C catalyst. Experiments reveal that the best carbon sample is obtained by calcining the carbon at 700 °C for 4 h after being impregnated in the 3.75% H₂O₂ solution at 40 °C for 7 h. The surface characterization displays that the H₂O₂ modification leads to an increase in the acidic groups and a reduction in the basic groups on the carbon surface. The catalytic capability of the HPW@C catalyst depends on its surface chemical characteristics and physical property. The acidic groups play a more important part than the physical property. The MX conversion after 180 min reaction acquired by the HPW@C catalysts prepared from the activated carbon modified in the best condition is 3.81% over that obtained by the HPW@C catalysts prepared from the original carbon. The IPA produced by the former is 46.2% over that produced by the latter.     

Effect of the nature of the support of a cobalt catalyst on the synthesis of hydrocarbons from CO,H<Subscript>2</Subscript>, and C<Subscript>2</Subscript>H<Subscript>4</Subscript>

The effect of the nature of the support of a Co catalyst on the synthesis of hydrocarbons from CO, H₂, and C₂H₄ was studied in this work. It was found that the introduction of ethylene into synthesis gas resulted in an increase in the yield of liquid hydrocarbons. In this case, the conversion of C₂H₄ was complete and the degree of its involvement into the synthesis of C₅₊ hydrocarbons depended on the concentration of this component in the starting mixture and the nature of the support. Specific features of the adsorption of CO and C₂H₄ on the used Co catalysts were determined using a temperature-programmed desorption method.     

Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Characteristics of phosphate adsorption on ferric hydroxide synthesized from a Fe<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript> aqueous solution discharged from a hydrometallurgical process

Ferric hydroxide adsorbent was prepared by a chemical treatment process with H₂O₂, NaOH, and aeration from a Fe₂(SO₄)₃ aqueous solution as a side product discharged from the hydrometallurgical process used to extract neodymium. The ferric hydroxide was used as an adsorbent to prevent eutrophication in water. At the time of synthesis, the most important process variable is the pH condition, which, in this experiment, was changed from pH 3 to 13. The cost of synthesizing ferric hydroxide was sharply reduced by using ferric sulfate, which is considered a side product of the aforementioned hydrometallurgical process, as a starting material, and an adsorbent with high adsorption ability was prepared by controlling the pH level. Microstructural characterization of the synthesized ferric hydroxide revealed particles with a specific surface area of 194.2 m²/g and an average pore diameter of 2.66 nm at pH 6 and 298 K. A column-type packed-bed adsorption experiment was conducted under the following conditions: a flow rate of 0.567 BV/min (3.2 mL/min), 298 K, and atmospheric pressure. The results of the adsorption performance test indicated that the adsorption efficiency of phosphate at concentrations of 10 ppm was 100% at a flow rate of 0.567 BV/min within a contact time of 2 min, and the maximum adsorption capacity for phosphate ions was 65 mg/g.     

Effect of CO<Subscript>2</Subscript> concentration on the performance of different thermodynamic models for prediction of CH<Subscript>4</Subscript>+CO<Subscript>2</Subscript>+H<Subscript>2</Subscript>O hydrate equilibrium conditions

Accurate prediction of phase equilibria regarding CH₄ replacement in hydrate phase with high pressure CO₂ is an important issue in modern reservoir engineering. In this work we investigate the possibility of establishing a thermodynamic framework for predicting the hydrate equilibrium conditions for evaluation of CO₂ injection scenarios. Different combinations of equations of state and mixing rules are applied and the most accurate thermodynamic models at different CO₂ concentration ranges are proposed.     

Hydrolysis of titanium(IV) in the TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript>-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system during the preparation of a titanium silicate pigment

The hydrolysis of titanium(IV) sulfate during boiling in the presence of silica gel particles is considered. The scenario of solid-phase formation involves the sedimentation of hydrated titanium(IV) onto reactive silica gel particles; and individual phases of silicon(IV) and titanium(IV) hydroxides are formed. The quantitative ratio between the phases of the hydrated composition dictates the properties of its thermolysis products. Composition-property diagrams are plotted to determine the optimum parameters at which the titanium silicate product has high pigment properties.     

CeO<Subscript>2</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZSM-5 sorbents for high-temperature H<Subscript>2</Subscript>S removal

Performance of CeO₂-La₂O₃/ZSM-5 sorbents for sulfur removal was examined at temperature ranging from 500 oC to 700 oC. The sulfur capacity of 5Ce5La/ZSM-5 was much bigger than that of CeO₂/ZSM-5. H₂ had a negative impact on the sulfidation; however, CO had little influence on sulfur removal. The characterization results showed that CeO₂ and La₂O₃ were well dispersed on ZSM-5 because of the intimate admixing of La₂O₃ and CeO₂, the major sulfidation products were Ce₂O₂S and La₂O₂S, the XRD and SEM results revealed that ZSM-5 structure could remain intact during preparation and sulfidation process, the H₂-TPR showed that the reducibility of CeO₂ can be remarkably enhanced by addition of La.     

Determination of hydrogenation ability and exchange current of H<Subscript>2</Subscript>O/H<Subscript>2</Subscript> system on hydrogen-absorbing metal alloys

A detailed analysis of potential versus time measurements at galvanostatic charge/discharge conditions (external current change from −1 to +1 mA cm⁻²) for two La–Ni alloys in Ar-saturated 0.1 M KOH solution is presented. It is shown that passivation of the electrodes does not affect the potential jump as a result of current switching over. The value of potential jump allows to calculate the exchange current density for H₂O/H₂ system on the tested material. Anodic potential of the hydrogenated electrode (at i _a = const) linearly increases with logarithm of time which allows to evaluate precisely time necessary for oxidation of hydrogen absorbed during cathodic charging. The method described enables to determine effectiveness of hydrogen absorption by materials applied for negative electrodes of NiMH batteries.     

Structure of an atmospheric-pressure H<Subscript>2</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame doped with iron pentacarbonyl

This paper presents the measurement and simulation data on the thermal and chemical structure of an atmospheric-pressure premixed H₂/O₂/N₂ flame doped with iron pentacarbonyl Fe(CO)₅. Soft ionization molecular beam mass spectrometry was used to measure concentration profiles of the combustion products of iron pentacarbonyl: Fe, FeO₂, FeOH, and Fe(OH)₂. A comparison of experimental and simulated concentration profiles showed that they are in satisfactory agreement for FeO₂ and Fe(OH)₂ and differ significantly for Fe and FeOH. Thus, the previously proposed kinetic model for the oxidation of iron pentacarbonyl was tested and it was shown that the mechanism needs further elaboration.     

Interaction of O<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and H<Subscript>2</Subscript>O<Subscript>2</Subscript> with an activated carbon

The results of the modification of AG-OV-1 activated carbon under various conditions (by atmospheric oxygen at elevated temperatures and by hydrogen peroxide or ozone) are given. The effect of the used modifier on changes in the porosity, surface state, and adsorption capacity of activated carbon is evaluated.     

Evaluating the ability of separation and adsorption of SO<Subscript>2</Subscript> by nano-CuO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> in high concentrations and moderate temperatures

Nano CuO-Fe₂O₃/TiO₂ adsorbents were made with different compositions of metal oxides using precipitation- desorption method. The adsorbents were applied for adsorption of SO₂ at high concentrations ranging from 10,000 to 30,000 ppm and temperatures between 523 and 627 K. Adsorption experiments were applied for adsorbents in a laboratory fixed bed adsorption column. The adsorption capacity was measured by calculating the area under the adsorption curve using the integral method. The results showed that temperature is the most affecting factor on the adsorption capacity. The highest adsorption capacity was obtained by using 17, 8 and 75 wt% of CuO, Fe₂O₃ and nano TiO₂, respectively. Characteristics of the best sorbent were determined by using Fe-SEM, XRD and nitrogen adsorption-desorption analyses.     

Visible light-irradiated degradation of alachlor on Fe-TiO<Subscript>2</Subscript> with assistance of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

0.1 Fe/Ti mole ratio of Fe-TiO₂ catalysts were synthesized via solvothermal method and calcined at various temperatures: 300, 400, and 500 °C. The calcined catalysts were characterized by XRD, N₂-adsorption-desorption, UV-DRS, XRF, and Zeta potential and tested for photocatalytic degradation of alachlor under visible light. The calcined catalysts consisted only of anatase phase. The BET specific surface area decreased with the calcination temperatures. The doping Fe ion induced a red shift of absorption capacity from UV to the visible region. The Fe-TiO₂ calcined at 400 °C showed the highest photocatalytic activity on degradation of alachlor with assistance of 30 mM H₂O₂ at pH 3 under visible light irradiation. The degradation fitted well with Langmuir-Hinshelwood model that gave adsorption coefficient and the reaction rate constant of 0.683 L mg⁻¹ and 0.136 mg/L·min, respectively.     

The role of TiO<Subscript>2</Subscript> layers deposited on YSZ on the electrochemical promotion of C<Subscript>2</Subscript>H<Subscript>4</Subscript> oxidation on Pt

The electrochemical promotion of Pt/YSZ and Pt/TiO₂/YSZ catalyst-electrodes has been investigated for the model reaction of C₂H₄ oxidation in an atmospheric pressure single chamber reactor, under oxygen excess between 280 and 375 °C. It has been found that the presence of a dispersed TiO₂ thin layer between the catalyst electrode and the solid electrolyte (YSZ), results in a significant increase of the magnitude of the electrochemical promotion of catalysis (EPOC) effect. The rate enhancement ratio upon current application and the faradaic efficiency values, were found to be a factor of 2.5 and 4 respectively, higher than those in absence of TiO₂. This significantly enhanced EPOC effect via the addition of TiO₂ suggests that the presence of the porous TiO₂ layer enhances the transport of promoting O²⁻ species onto the Pt catalyst surface. This enhancement may be partly due to morphological factors, such as increased Pt dispersion and three-phase-boundary length in presence of the TiO₂ porous layer, but appears to be mainly caused by the mixed ionic-electronic conductivity of the TiO₂ layer which results to enhanced O²⁻ transport to the Pt surface via a self-driven electrochemical promotion O²⁻ transport mechanism.     

Enhancement of NO absorption in ammonium-based solution using heterogeneous Fenton reaction at low H<Subscript>2</Subscript>O<Subscript>2</Subscript> consumption

A novel NO removal system is designed, where NO is initially oxidized by ?OH radicals from the decomposition of hydrogen peroxide (H₂O₂) over hematite and then absorbed by ammonium-based solution. According to the high performance liquid chromatography (HPLC) profile and the isopropanol injection experiments, the ?OH radicals are proved to play a critical role in NO removal. The NO removal efficiency primarily depends on H₂O₂ concentration, gas hourly space velocity (GHSV), H₂O₂ feeding rate and reaction temperature, while the flue gas temperature slightly affects the NO removal efficiency. The low H₂O₂ consumption makes this system a promising technique in NO removal process using wet-method. The evolution of catalyst in reaction is analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The nitrite ion and nitrate ion in aqueous solution are detected by the continuous phase flow analyzer. Finally, the macrokinetic parameters of the NO oxidation are obtained by using the initial rate method.