Sharif Digital Repository

In the present study, the thermodynamics and mechanisms of vanadium extraction by a mixture of bis-2-ethylhexyl phosphoric acid (D2EHPA) and tri-n butyl phosphate (TBP) from sulfate medium were investigated. It was found that the maximum extraction percent of vanadium occurs at pH 1.8 under ambient conditions; this phenomenon was ascribed to the predominant presence of cationic species of vanadium (VO2+) at this pH. Based on the Fourier Transform Infrared (FT-IR) spectrums, the POH bond of D2EHPA was found responsible for the extraction of VO2+ species through a cationic exchange mechanism. Employing the slope analysis method showed that the stoichiometric reaction... 

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction, removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production. For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used. Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogenation method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor... 

A mathematical model is presented to simulate the multiple heterogeneous reactions with complex set of physicochemical and thermal phenomena in a moving bed of porous pellets. This model is based on both heat and mass transfer phenomena of gaseous species in a porous medium including chemical reactions at interfaces whose areas vary during the conversion. This model accounts for both the exothermic and endothermic reactions which can be equimolar or nonequimolar. Furthermore it considers simultaneously the reactions in the nonisothermal transient condition. A powerful technique based upon finite volume fully implicit approach has been implemented to solve the complicated governing equations... 

Catalytic paraffin dehydrogenation for manufacturing olefins is considered to be one of the most significant production routes in the petrochemical industries. A reactor kinetic model for the dehydrogenation of propane to propylene in a radial-flow reactor over Pt-Sn/Al2O3 as the catalyst was investigated here. The model showed that the catalyst activity was highly time dependent. In addition, the component concentrations and the temperature varied along the reactor radius owing to the occurring endothermic reaction. Moreover, a similar trend was noticed for the propane conversion as for the propylene selectivity, with both of them decreasing over the time period studied. Furthermore, a... 

Magnesium nanopowder (MgNP) of 17 nm average size was produced by planetary ball milling of Mg (φ=229 μm) with 10 wt% NaCl (φ=406 μm) for 50 h. NaCl was omissible by dissolution in saturated KOH. Partial oxidation of MgNP occurred, however, in presence of KOH. MgNP-NaCl mixture was, therefore, used for transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD), differential scanning calorimetry (DSC) and Sieverts equilibrium investigation. DSC analysis of ammonium perchlorate showed one endothermic and three exothermic reactions. MgNP did not noticeably affect on the initial endothermic reaction. But it decreased transformation temperatures of the... 

Depending on the type of dopant metal, many kinds of zircon based pigments are produced and blue vanadium pigment is the most important one of them. In this study, blue zircon ceramic pigments were synthesized from intermediate product, resulting from decomposition of zircon sand with NaOH. In this regard, various amounts of sulfuric acid, water, NH4VO3 as colorant, NaF as mineralizer and extra quartz were added to the prepared Na 2ZrSiO5. Role of quartz was to omit the repercussions of presence of free zirconia in the composition. The main objective of this work is to assess various reactions at different temperatures during blue pigment synthesis. Phase analysis was done by X ray... 

Post-deposition annealing effects on nanomechanical properties of granular TiO2 films on soda-lime glass substrates were studied. In particular, the effects of Na diffusion on the films' mechanical properties were examined. TiO2 photocatalyst films, 330 nm thick, were prepared by dip-coating using a TiO2 sol, and were annealed between 100 °C and 500 °C. Film's morphology, physical and nanomechanical properties were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, differential thermo-gravimetric analysis, and nanoindentation. Contrary to expectations, the maximum film hardness was achieved for 300°C annealing, with a value of 0.69 ± 0.05 GPa....