جستجوی مقالات مرتبط با کلیدواژه « reaction kinetics » در نشریات گروه « شیمی »

Titanium dioxide nanotubes TNTs were synthesized by anodization in a fluoride-based electrolyte, TNTs are commonly working as photocatalytic under ultraviolet UV irradiation via its wide bandgap, and it was expanded under visible light irradiation by doping with other metals or metals oxides, herein TNTs were doped by copper oxides Cu2O and CuO to produce copper oxides /titanium oxide nanotubes CuOx /TNT. The prepared catalysts (TNTs and CuOx/TNT) were characterized by XRD, FTIR, SEM and, EDX, while catalysts activity was investigated for oxidization of Dibenzothiophene DBT under ultraviolet UV and visible light VL irradiations, the feedstock is model fuel (heptane contains DBT as a sulfur component)  was oxidized by hydrogen peroxide H2O2. Results showed that TNT has a moderate catalysis effect under UV irradiation and a low catalysis effect under VL irradiation. CuOx/TNT catalyst exhibited good sensitivity for VL radiation. The study investigated the effect of initial DBT concentration, oxidant dosage, reaction temperature, contact time, and type of irradiation on oxidation desulfurization ODS reaction by using TNT and CuOx/TNT catalysts, the results showed that DBT removal efficiency was increasing with temperature (56.2, 80.4 and 91.2 at 40,50, and 60 °C respectively at 100 minutes) and oxidant amount  ( 66.4, 80.4, and 86.1 by adding 5,10,15 ml of oxidant respectively at 100 minutes) while it decreases with the increasing initial BDT concentration (94.8, 80.4, and 86.1 when using 100,150, and 200 ppm as initial DBT concentration at 100 minutes). The kinetics calculations exhibited that  ODS reaction under VL irradiation follows pseudo-first-order reaction at CuOx/TNT catalyst with reaction rate constants of  0.00076, 0.0108, and 0.0141 min-1 at 40,50, and 60°C respectively, the activation energy for the reaction is 26.8 kJ/mol, negative ΔS (-0.218 kJ/mol.K) and positive ΔH and ΔG for DBT oxidation under UV irradiation.

The kinetics of the hydrolysis of Alizarin dye (ALZ) in the basic medium is investigated for the purpose of wastewater treatment. ALZ represents a group of aromatic dyes, that are heavy, toxic, and non-biodegradable. The kinetics of the reaction was followed by UV-Vis spectrophotometry and ab-initio computational methods. The effects of initial concentration, ionic strength, and temperature were studied. The kinetic salt effect (ionic strength) demonstrated that OH– is part of the rate-determining step of the reaction. Unlike common reactions, anti-Arrhenius behavior was observed within the temperature range of 25-50°C. Therefore, the apparent activation energy was determined to be -23.91 kcal/mol. Using theoretical quantum calculations, the reaction under study was investigated using the density functionals B3LYP and B97D3, and final energies were obtained using the 2nd order Møller−Plesset (MP2) theory. A complex reaction mechanism is suggested that involves the formation of an intermediate that combines the ALZ anion and water molecule attached by H-bonding. The mechanism accounted for the anti-Arrhenius behavior and the negative Ea. The standard reaction enthalpy (ΔH298) obtained using the B97D3 Grimme’s functional was within the range of the experimental Ea value.

Cobalt and Molybdenum oxides supported on graphene catalyst CoMo/G were prepared then its activity for hydro-desulfurization reaction HDS was examined in this research. The catalyst was characterized by X-ray diffraction XRD, Fourier transform infrared spectroscopy FTIR, and energy dispersive spectroscopy EDS while surface morphology was tested by scanning electronic microscopy SEM and atomic force microscopy AFM. The texture properties (specific surface area and pore volume) are measured by the Brunauer, Emmett and Teller BET method. The catalyst activity investigation was conducted by heavy naphtha HDS reaction in a fixed bed reactor, this study investigated the effect of temperature (250-325) ºC, Liquid Hourly Space Velocity LHSV (3-6) hr.-1 and hydrogen partial pressure (1-1.3) MPa while gas/oil ratio was kept a constant 50 ml/ml, these variables’ impact was designed and analyzed by Taguchi design of experiment DOE with using MINITAB software. The results showed that sulfur removing percentage SR% increases with both increasing of temperature and hydrogen partial pressure whereas LHSV has the opposite effect on SR%. HDS reaction kinetics parameters were estimated by experiment results employing Levenberg-Marquardt and SPSS software version 20; the results showed the HDS reaction which followed 1.863 order, reaction rate constant and activation energy, is 32.309 kJ/mol.

The leaching kinetics of smithsonite ore in acetic acid solutions, an environmental friend, and natural reagent was investigated. The influence of parameters such as reaction temperature, particle size, solid-liquid ratio and acid concentration was studied in order to reveal the leaching kinetics of smithsonite ore. In this study, experimental and statistical methods were carried out in order to analyze the kinetics data to investigate a kinetics model which describes the dissolution. The results indicate that the unreacted shrinking core model for fluid-solid heterogeneous reactions was favorable for the leaching process. The apparent activation energy of the leaching process was found as 74 kJ/ mol. It was determined that the leaching rate of smithsonite was controlled by the chemical reaction below.

The aim of this study is to explore the capability of subcritical methanol to reduce the acidity of naphthenic acids and to determine reaction kinetics for large-scale reactor design.The experiments were carried out in a 25 mL autoclave reactor (China) at temperatures of 70-120oC, Methanol Partial Pressures (MPPs) of 0.1-1.5 MPa, and reaction times of 0-60 min. The total acid number content of the samples was analyzed using ASTM D 974 techniques. Experimental results reveal that total acid number reduction of naphthenic acids increased with increasing reaction temperature, MPP, and reaction time. Approximately 74.20% total acid number was reduced at a temperature of 120oC, a MPP of 1 MPa, and a reaction time of 60 min. Experimental data revealed that total acid number removal reaction kinetics followed second-order kinetics with an activation energy of 11.27 kcal/mol. Therefore, subcritical methanol is able to reduce the total acid number of naphthenic acids without the addition of any catalyst.