Sharif Digital Repository

Different aliphatic and aromatic aldehydes such as isobutyraldehyde, ethanal, n-propanal, n-butanal, n-hexanal, n-octanal, and substituted benzaldehydes were cyclotrimerized into their corresponding 2,4,6-trialkyl-1,3, 5-trioxanes in the presence of commercial bulk zinc oxide at room temperature under neat conditions within a short span of time with high yield and excellent selectivity. Liquid products were formed as a separate phase and were decanted easily, whereas solid products were isolated by simple extraction. Effect of different additives, mol % of catalyst, kind of substrate, and reaction temperature were examined on the progress of cyclotrimerization reaction  

The oxidative desulfurization of a real refinery feedstock (i.e., non-hydrotreated kerosene with total sulfur mass content of 0.16%) with a mixture of hydrogen peroxide and acetic acid was studied. The influences of various operating parameters including reaction temperature (T), acid to sulfur molar ratio (nacid/nS), and oxidant to sulfur molar ratio (nO/nS) on the sulfur removal of kerosene were investigated. The results revealed that an increase in the reaction temperature (T) and nacid/nS enhances the sulfur removal. Moreover, there is an optimum nO/nS related to the reaction temperature and the best sulfur removal could be obtained at nO/nS8 and 23 for the reaction temperatures of 25... 

We have studied the phase formation of a CoSi2 layer by solid-state reaction of ternary Co/WxTa(1-x)/Si(1 0 0) systems. The effect of cosputtered WxTa(1-x) nanometric interlayers, with different values of x (0, 0.25, 0.5, 0.75 and 1), on the degree of texturing of a CoSi2 layer and disilicide formation of the refractory metals has been investigated. The annealed samples, in a temperature range of 400-1000 °C, were analysed by x-ray diffraction, sheet resistance measurement, scanning electron microscopy, and energy-dispersive x-ray techniques. Using W0.25Ta0.75 and W interlayers, the best (1 0 0) texture of the CoSi2 layer with a thermal stability in the range of 900-1000 °C was produced. In... 

In this report, the efficacy of different factors such as temperature of reaction, time of reaction and depth of bed are investigated in a process of recovery of zinc oxide from zinc ore concentration residues in a fluidized bed furnace. Under optimum conditions, there was more than 93.5% zinc oxide in products  

Biodiesel as an alternative fuel for fossil diesel has many benefits such as reducing regulated air pollutants emissions, reducing greenhouse gases emissions, being renewable, biodegradable and non-toxic. In this study, used frying oil was applied as a low cost feedstock for biodiesel production by alkali-catalyzed transesterification. The design of experiments was performed using a double 5-level-4-factor central composite design coupled with response surface methodology in order to study the effect of factors on the yield of biodiesel and optimizing the reaction conditions. The factors studied were: reaction temperature, molar ratio of methanol to oil, catalyst concentration, reaction time... 

Ultrahigh-molecular-weight polyethylene (UHMWPE)/graphene nanocomposites with molecular weights as high as 3 × 106 g/mol were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. Effects of [Al]/[Ti] molar ratio, temperature, monomer pressure, and polymerization time on productivity of the catalyst have been investigated. Increasing [Al]/[Ti] molar ratio from 128 to 320, increased productivity from 1667 g PE/mmol Ti.h to maximum value which was 2420 g PE/mmol Ti.h. Further [Al]/[Ti] ratio decreased the productivity. Reaction temperature effect investigation reveals that the optimal activity was obtained at 60°C. the polymerization productivity increases... 

Propane dehydrogenation was carried over a commercial Pt-Sn/γ-Al 2O3 catalyst at atmospheric pressure and reaction temperatures of 580, 600, and 620°C and WHSV of 11 h-1 in an experimental tubular quartz reactor. Propane conversions were measured for catalyst time on stream of up to nine days. The amounts of coke deposited on the catalyst were measured after one, three, six, and nine days on stream using a thermogravimetric differential thermal analyzer (TG-DTA) for each reaction temperature. The coke formation kinetics was successfully described by a coke formation model based on a monolayer-multilayer mechanism. In addition, catalyst deactivation was presented by a time-dependant... 

In this study, some stabilized magnetite based ferrofluids were synthesized using Dextran as a stabilizing agent. In order to achieve optimum experimental conditions for synthesizing ferrofluids as MRI contrast agents, the Taguchi method was used. This approach was employed to design and minimize the number of required experiments. By using the Taguchi orthogonal (L16) array, four parameters including solution temperature and alkalinity, reaction temperature and stirring rate were selected at four predetermined levels for 16 experiments. Synthesizing processes established based on this set of experimental conditions were carried out and the obtained ferrofluids were characterized using PCS,... 

Thermal cracking of a vacuum distillation residue of the Abadan refinery in Iran was performed under delayed coking conditions to investigate the effect of operating conditions on the yield and sulfur content of products. At reaction temperatures of 440-500 °C and pressures of 1, 3, and 5 bar, the products included gases, liquids, and coke. The yields of liquid products were higher at 1 bar compared to those for higher pressures. Increasing the reaction temperature at a given reaction pressure led to an increase in the yield of liquid products. Increasing the reaction pressure at a given reaction temperature led to higher yields of coke and gases as well as a decrease in the sulfur content... 

Oxidative dehydrogenation of propane (ODHP) in a fixed-bed reactor over synthesized vanadia nanocatalysts was investigated physicochemically. Several vanadium pentoxide (V2O5) nanostructures including rod-, belt-, tube-, needle- and flower-like forms were successfully synthesized via reflux and hydrothermal processes utilizing different templates such as monoamines, diamines, aromatic and alcoholic amines. The morphologies of the obtained products were found to be sensitive to the types of templates used. Nanorods obtained were 1.4 μm in length and about 97 nm in width while the VO2(B) nanotubes were of about 76 nm average diameter and up to 1.2 μm long. The diameters of the V2O5 nanotubes... 

Some cis-dioxomolybdenum (VI) complexes with tridentate Schiff base ligands derived from salicylaldehyde and aminophenols, aminoalcohol or o-aminobenzenethiol were examined as catalysts for epoxidation of different aliphatic and aromatic olefins, with tert-butyl hydroperoxide as oxidant. All complexes exhibited high activity and selectivity for epoxidation of aliphatic substrates during a short time period (95% conversion of cyclooctene after 30 min). The epoxide yield increased with the nucleophilic character of olefin. The catalysts activation strongly depends on the reaction temperature and nature of the solvent. Epoxidation of olefins by these catalysts is inhibited by ligands or... 

Conjugated Linoleic Acid (CLA), Glycerol (G) and sunflower oil blends with varying concentration were subjected to enzymatic esterification using a 1, 3-specific immobilized lipase. CLA was used as acyl due to its purported health benefits. The transesterified lipids were evaluated for free fatty acids (FFA) and composition of fatty acids by gas chromatography. Lipozyme RM IM is preferred for enzymatic esterification because of more CLA incorporation and less free fatty acids at the end of reaction than Lipozyme TL IM. Response surface methodology (RSM) was used to determine the effects of three variables Glycerol concentration, reaction temperature, and amount of enzyme on the lipase... 

Abstract: A metal-free method for activation of hydrogen peroxide (H2O2) is introduced using piperidinium trifluoroacetate (PPHTFA) ionic liquid as catalyst. The catalyst has been used for selective oxidation of thioanisole to its corresponding sulfoxide at room temperature. It was found that the selectivities were reduced by increasing the reaction temperature. In this work, no organic solvents or metallic salts were used for activation of H2O2. Mechanistic studies suggested that the reaction proceeds via in situ formation of trifluoro hydroperoxy species as an active catalytic intermediate. Formation of the catalytic intermediate was screened by NMR, IR and Mass Spectroscopy analysis.... 

In this paper, the combination of dry reforming and partial oxidation of methane on nickel catalysts supported on mesoporous MgAl2O4 was investigated. The support was prepared by a facile sol-gel route using propylene oxide as a gelation agent. The characterizations of the catalysts were performed by BET, XRD, TPR, TPO, TPH, UV–vis, CO-dispersion, SEM and TEM techniques. In addition, the effects of nickel content, reaction and reduction temperatures, feed ratio and the GHSV value on the physicochemical and catalytic properties were studied. The results revealed that the nickel content had an optimum value of 7.5 wt% and the catalyst with this content of nickel exhibited the highest activity.... 

As a refractory ceramic, the thermal instability of aluminium titanate (AT or Al2TiO5) has been in the crosshairs of research works in recent years. The studies have indicated that different parameters such as atmosphere, grain size, additives, oxygen pressure, and synthesis method can bilaterally affect the thermal decomposition of AT ceramic and resultant physicomechanical properties. In the present study, the AT nanostructure was synthesized by a citrate sol-gel method and influence of nanostructuring nature on its thermal instability and reaction pathway was explored in some details. It was shown that the reduction of grain size down to 30 nm can destabilize AT, so that the reaction... 

Modeling and simulation of fixed bed three-phase catalytic reactors are considered for wet air catalytic oxidation of phenol to perform a comparative numerical analysis between tricklebed and packed-bubble column reactors. The modeling involves material balances both for the catalyst particle as well as for different fluid phases. Catalyst deactivation is also considered in a transient reactor model to investigate the effects of various parameters including reactor temperature on catalyst deactivation. The simulation results indicated that packed-bubble columns were slightly superior in performance than trickle beds. It was also found that reaction temperature was the most effective... 

The effect of oxygenate modifiers on the performance of PtSnγAl 2O3 catalyst in dehydrogenation of propane was studied. Dehydrogenation reaction was carried out in a fixed-bed quartz reactor in the temperature range of 575620 °C. Two types of oxygenate modifiers, namely water and methanol, were added to the feed. The optimum amounts of water for reaction temperatures of 575, 600 and 620 °C were 84, 120 and 140 ppm, respectively. The optimum amounts of methanol for the same reaction temperatures were 9.9, 25 and 50 ppm, respectively. Any further addition of water or methanol beyond these optimum levels resulted in a loss in activity. The addition of water or methanol led to the formation of... 

In this study the kinetic modeling of visbreaking reactions for a number of vacuum residue feeds was investigated using available experimental data from the literature. A continuous lumping model was developed for kinetic analysis of visbreaking reactions. The normalized boiling point was used to describe each feed as a continuous mixture and the concentration distribution of the mixture would change under reaction conditions. A continuous model with five adjustable parameters was used to describe visbreaking reactions, and these parameters were optimized for each feed for reaction temperatures in the range of 400-430 C using available experimental data. The model was able to accurately... 

CuInS2 nanoparticles as the visible (wurtzite, 1.67 eV) or near infrared (chalcopyrite, 1.50 eV) light absorbing material in thin film solar cells, were synthesized using facile, one step heating up method by dissolving of CuCl, InCl3 and SC(NH2)2 as precursors in oleylamine (OLA) alone or in combination with oleic acid (OA) and 1-octadecene (ODE) as solvent. The phase, size, morphology, and size distribution were controlled by the coordination ability between solvent molecules and metal precursors, reaction temperature and time. The presence of higher amounts of thiourea or OA to OLA led to the formation of chalcopyrite phase in comparison to wurtzite structure. Also, higher reaction... 

Site reactivity of some enol-imines derived from N-aryl formamides with pentachloropyridine under basic conditions in dry CH3CN was investigated. The aromatic nucleophilic substitution of pentachloropyridine with enol-imines occurs at the 4-position of pyridine ring by both oxygen and nitrogen site of enol-imines. Nucleophilic attack by the oxygen of enol-imine gave corresponding oximino compounds as a mixture of E- and Z-isomers. In contrast, nucleophilic attack by the nitrogen of enol-imine gave the unexpected N,N-di-substituted aryl compounds. The structures of all the compounds were confirmed by IR, 1H NMR, 13C NMR and 19F NMR spectroscopy as well as elemental analysis and...