Scientia Iranica
Volume:18 Issue: 6, 2011

Doped polyaniline (PANI) was obtained by the polymerization of aniline, using chemical oxidative polymerization in the presence of ammonium peroxydisulfate [(NH4)2S2O8]. The doped PANI was dedoped by ammonia solution. The electrospinning method was applied to solutions involving PANI–PVA, PANI–PVA–AgNO3, where PV A=poly(vinyl alcohol) and PANI=polyaniline. Micro to nanofibers were obtained in the cases of PANI–PVA and PANI–PVA–AgNO3. The SEM technique was used to investigate the morphology of the accumulated fibers or particles on the Al surface collector. Thermal analysis performed on PANI–PVA composite fibers indicated an endothermic peak at 280–420 °C, accompanied by 90% weight loss. The presence of Ag in the case of Ag containing composite fibers was confirmed by EDAX.

In the present work, a quantum mechanical calculation was clarified as to how the ylides exist in solution as a mixture of two geometrical isomers (Z- and E-) in a major or minor form. In addition, kinetic studies were undertaken for the reaction between triphenylphosphine, di-tert-butyl acetylenedicarboxylate in the presence of a protic/nucleophilic reagent, such as acetyl acetone. To determine the kinetic parameters of the reaction, it was monitored by UV spectrometry. The values of the second order rate constant (k2) were calculated using standard equations within the program. At the temperature range studied, the dependence of the second order rate constant (Ln k2) on the reciprocal temperature was in a good agreement with the Arrhenius equation. This provided relevant plots for calculating the activation energy of the reaction. Furthermore, useful information was obtained from studies of the effect of solvents, the structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylate) and also the concentration of reactants on the rate of reaction. The proposed mechanism was confirmed according to the obtained results and steady state approximation. The first and third (k3) steps of the reaction were recognized as the determining rates and fast steps, respectively, on the basis of experimental data.

The binding of Mg2+, Ca2+, Zn2+ and Cu+ metal cations to 2′-deoxyguanosine has been analyzed, using the hybrid B3LYP, Density Functional Theory (DFT) method and 6–311++G(d,p) orbital basis sets. Coordination geometries, absolute metal ion affinities, and free energies for the most stable complexes formed by Mg2+, Ca2+, Zn2+ and Cu+ with the nucleoside, 2′-deoxyguanosine, have been determined. Furthermore, the influences of metal cationization on the strength of the N-glycosidic bond, torsion angles and angle of Pseudorotation (P) have been studied. With respect to the results, it has been found that metal binding significantly changes the values of the phase angle of Pseudorotation (P) in the sugar unit of these nucleosides. In all modified forms, the length of the C1′–N9 bond increases. The Mulliken population analysis on atomic charges has been carried out on the optimized geometries. Natural Bond Orbital (NBO) analysis was also performed to calculate the charge transfer and natural population analysis of the complexes. Quantum Theory of Atoms In Molecules (QTAIM) was also applied to determine the nature of interactions.

Supported nitric acid on polyvinylpolypyrrolidone was found to be an efficient, environmentally friendly, mild nitrating agent for the nitration of substituted phenols in dichloromethane at room temperature with moderate yields.

The three-component Strecker reaction of a wide range of aldehydes or ketones and different amines with trimethylsilyl cyanide (TMSCN) was efficiently catalyzed by the nano-ordered mesoporous borosilicate (B-MCM-41) at room temperature to afford the corresponding α-amino nitriles in high to quantitative yields in short reaction time. B-MCM-41 showed higher catalytic activity than Fe(III)-modified MCM-41 (Fe-MCM-41). Furthermore, the use of EtOH increased the rate of reaction remarkably compared to CH2Cl2 or CH3CN. The B-MCM-41 catalyst can be recovered at least 4 times without significant loss of its catalytic activity.

Ionic liquid 3-methyl-1-sulfonic acid imidazolium chloride/ FeCl3, as well as ionic liquid 1, 3-disulfonic acid imidazolium chloride/ FeCl3 catalytic systems, efficiently catalyzes the condensation of benzene-1, 2-diamine with aromatic aldehydes in the presence of atmospheric air as a green oxidant in ethyl acetate at room temperature to afford benzimidazole derivatives in high yields and in short reaction times. The reaction is also efficiently performed when carboxylic acids are used instead of aldehydes.

The objective of this study is the investigation of formaldehyde degradation in a bioreactor with pumice stone as a support. The reactor was tested at different synthetic wastewater concentrations with total COD of 500, 1000 and 1500 mg/L, respectively, at 24 h hydraulic retention time. The effect of feed composition was tested by changing the ratio in order to analyze the impact of formaldehyde concentration. The average formaldehyde and COD removal efficiencies obtained in the reactor were 97.1% and 88%, respectively. The maximum COD and formaldehyde removal efficiencies occurred at the of 4/1 at. The effect of toxic shock on reactor performance was examined; the reactor has good resistance against a sudden increase in formaldehyde concentration. The formaldehyde concentration threshold at which toxic effects severely inhibited the biological process was 1370 ppm. So a fixed film bioreactor packed with pumice stone could be recommended for the treatment of formaldehyde-containing wastewater.

The effect of oxygenate modifiers on the performance of Pt–Sn/γ–Al2O3 catalyst in dehydrogenation of propane was studied. Dehydrogenation reaction was carried out in a fixed-bed quartz reactor in the temperature range of 575–620 °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 at the expense of selectivity loss of propylene. The propylene yields, however, passed a maximum at the optimum amounts of added oxygenates. The addition of water and methanol in the optimum amounts resulted in a substantial reduction of coke formation as well. The improved propane conversions in the presence of optimum amounts of added water or methanol could be explained in terms of enhanced β H-elimination step in propane dehydrogenation mechanism in the presence of hydroxyl groups.

Asphaltene precipitation may occur during pressure depletion or gas injection processes in a reservoir. This phenomenon is an important problem during oil production, because it can result in formation damage and the plugging of wellbore and surface facilities. In this work, the precipitation of asphaltenes in an Iranian crude oil, under different pressures, is measured, using an experimental set up based on high-pressure isothermal expansion and also atmospheric titration. For the particular oil investigated, compositional data, precipitation phase diagrams, and bubble point and onset pressures are reported. Also, in this work, the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT), the Solid model and the Flory-Huggins model are used, to correlate onset pressures and solvent ratios at the onset point of precipitation for different solvents. The results show that the PC-SAFT EOS correlates more accurately with the experimental results over a wide composition interval.

Reservoir characterization, especially during early stages of reservoir life, is very uncertain, due to the scarcity of data. Reservoir connectivity and permeability evaluation is of great importance in reservoir characterization. The conventional approach to addressing this is computationally very expensive and time consuming. Therefore, there is a great incentive to produce much simpler alternative methods. In this paper, we use a statistical approach called the percolation theory, which considers a hypothesis wherein the reservoir can be split into either permeable (i.e. sand/fracture) or impermeable flow units (i.e. shale/matrix), and assumes that the connectivity of permeability contrasts controls the flow. We developed master curves for the reservoir connectivity and its associated uncertainty, as well as the effective permeability and its associate uncertainty curves. To validate the approach, we have used the data set of the North Pars gas field located at the North of the South Pars field in the Persian Gulf. We have shown that the percolation approach gives reliable predictions when compared with results from a conventional reservoir modeling approach. Moreover, the first approach, as obtained from algebraic manipulation, is very fast, whereas the latter is very costly and time consuming.

The drying of saffron stigma was investigated in a laboratory infrared dryer. The effect of temperature on the drying rate of samples at various temperatures (60,70…110 °C) was studied. The drying time decreased with an increase in drying air temperature. The constant-rate period is absent from the drying curve. The drying of saffron occurred in the falling rate period. Four, thin-layer drying models, namely, Lewis, Handerson and Pabis, Page, and Midilli and Kucuk, were fitted to drying data. The performance of these models was investigated by comparing the determination of coefficient (R2) and Root Mean Square Error (RMSE) between the observed and predicted moisture ratios. Among these models, in each of six drying temperatures, the Midilli and Kucuk model gave the best results and showed good agreement with the experimental data obtained from the experiments, including the thin layer drying process. In all drying temperatures, the amounts of R2 were higher than 0.999, and the amounts of RMSE were less than 0.012. According to results, it can be said that the Midilli and Kucuk model adequately described the drying behavior of saffron stigmas at a controlled temperature range 60–110 °C in an infrared dryer.

Rice bran is one of the most important co-products in the rice milling. In this research, antioxidant activity of two Iranian rice bran varieties, Fajr and Tarem, extracted by three different solvents (methanol, ethanol and ethyl acetate) was evaluated. The order of antioxidant activity was evaluated by measurement of total phenolic content, antioxidant activity in linoleic acid system, reducing power and scavenging capacity by DPPH radical. The methanolic extract of Fajr rice bran showed a total phenolic content of 3.31 mg Gallic acid/gr rice bran and a DPPH free radical-scavenging activity of 93.91%, achieved at 50 mg/ml concentration, and a percent inhibition of linoleic acid peroxidation of 68.01% with reducing power. These results indicated that the methanolic components of the rice bran extracts might potentially be natural antioxidants.

Immiscible gas injection is one of the most common enhanced oil recovery methods used under various reservoir conditions. In this work, the immiscible recycle gas injection, as an EOR scenario for improving recovery efficiency in one of the south-west Iranian oil reservoirs, is simulated by a commercial simulator, ECLIPSE. The reservoir fluid is light oil, with an API of 43. The oil bearing formations are carbonate, and so a dual porosity/dual permeability behavior was chosen for better representation of the fracture system. Different sensitivity analyses with respect to several parameters like the number and location of injection/production wells, production/injection rate, completion interval etc., are performed. It has been observed that in conjunction with the number of wells, 1 injection/2 production well pattern was the most efficient case. Also, the well oil production rate of 200 SM3/Day and the well bottom-hole pressure of 75 bar provided higher oil recovery. Completion of injection wells in fracture and production wells in matrix have better oilfield efficiency in comparison to other cases. Finally, we proposed optimum conditions for the immiscible recycle gas injection in this reservoir, which maximizes oil recovery efficiency.