Scientia Iranica
Volume:19 Issue: 3, 2012

The presence of carbon dioxide and water molecules as impurities in crude natural gas decreases the quality of natural gas. Recently, the catalytic treatment of this toxic and acidic gas has become a promising technique by converting CO2 to methane gas in the presence of H2S gas; thus, enhancing methane production and creating an environmentally friendly approach to the purification of natural gas. A series of catalysts based on nickel oxide were prepared using the wetness impregnation technique and aging, followed by calcination at 400 °C. Pd/Ru/Ni(2:8:90)/ Al2O3 catalyst was revealed as the most potential catalyst, and achieved 43.60% of CO2 conversion, with 6.82% of methane formation at 200 °C. This catalyst had the highest percentage of 52.95% CO2 conversion and yielded 39.73% methane at a maximum temperature of 400 °C. In the presence of H2S in the gas stream, the conversion dropped to 35.03%, with 3.64% yield of methane at a reaction temperature of 400 °C. However, this catalyst achieved 100% H2S desulfurization at 140 °C and remained constant until the reaction temperature of 300 °C. Moreover, the XRD diffractogram showed that the catalyst is highly amorphous in structure, with a BET surface area in the range of 220–270 m2 g- 1. FESEM analysis indicated a rough surface morphology and non-homogeneous spherical shape, with the smallest particles size in the range 40–115 nm.

Gas-phase acidities of nucleosides, combined with the knowledge of deprotonation sites, could improve our understanding of chemical reactions to biological systems. In this paper, we mainly focus our attention on the influence of cation coordination on acidities of multiple sites in cytosine nucleosides. The acidities of multiple sites in M+-L (where L represents cytosine nucleosides and M+ is an alkali metal ion, including Li+, Na+ and K+) complexes have been investigated theoretically, employing B3LY P/6−311++G(d,p) basis sets. The geometrical characters, gas-phase acidities, sugar puckering and electronic properties of non-deprotonated and/or deprotonated complexes have been investigated. The shifted values are a consequence of a combination of metal ion coordination to OH and NH groups and efficient stabilization of the deprotonated species. For instance, after complexation with Li+, Na+, and K+, the of O2′H of the cytidine molecule shifts from 346.2 to 251.6, 258.0, and 275.7 kcal mol−1, respectively. Moreover, for a given coordination site, the metal ion changes the gap between the most and least acidic groups, with respect to that in neutral nucleosides. Such dependence of acidities on the coordination region of the metal ion suggests that acidities of active groups could be controlled by modulating the metal ion coordination site and the type of metal ion.

A humidity sensor based on KCl-doped nanoporous Ti0.9Sn0.1O2 has been developed by the sol–gel method and Pluronic P123 as the organic template on alumina substrates, and their humidity sensing properties have also been also investigated at different sintering temperatures. It is found that 50 mol% KCl doped nanoporous Ti0.9Sn0.1O2 thin film, sintered at 500 °C for 4 h, shows the best humidity sensing properties, and its impendence decreases more than four orders of magnitude from 109 Ω to 105 Ω with good linearity in the Relative Humidity (RH) range of 11%–95% at 25 °C. The response and recovery time of this sensor are about 11 and 14 s, respectively. High sensitivity, narrow hysteresis loop, rapid response and recovery, prominent stability and good repeatability are obtained. A possible mechanism is suggested to explain the humidity sensitive properties.

Dithiocarbamic acids and thiols are employed in the Bargellini reaction to generate useful intermediates for the synthesis of organic molecules. This is the first time that dithiocarbamic acids are used as nucleophile in this reaction.

A general regularity was found based on an effective pair potential of Lennard-Jones LJ (12, 6), for both dense, nonmetallic and nonionic fluids and solids according to which (Z−1)v2 linearly varies with respect to ρ2 for each isotherm, and this equation of state (EoS I) is known as LIR. However, despite the fact that Ne is a simple spherical species, unexpectedly, its solid and liquid phases both show a significant deviation from EoS I. In this work, we have investigated the accuracy of the EoS I for other systems, including quantum light molecules, such as D2, H2 and He, in both fluid and solid states at different temperatures. Like Ne, we have noticed that these systems do not well obey the EoS I. Then, using a simple van der Waals equation, it is shown that significant deviations in dense systems of light molecules are because of the unbalance between repulsive and attractive interactions, due to the importance of the quantum effect. Also, we notice that at higher temperatures and for heavier species, LIR is valid due to a decrease in the quantum effect. We have shown that the hard-sphere fluid remarkably deviates from LIR. Two other EoSs have also been examined.

The para-aminobenzoic acid (PABA) product is an amphoteric component that has three forms in an aqueous solution. PABA can titrate with strong acid or a strong base. The conjugated acid of PABA can ionize in two sections, and two peaks can be detected to overlap. In this situation, the correct resolution and quantitation of the analytes is not possible, An UV spectrophotometric acid-base titrations method is proposed for the quantitative determination of PABA products in pharmaceutical samples. The acid-base equilibrium model is included in the Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) method. This method makes data evaluation possible, even when spectra of contributing substances are highly overlapping or reaction intermediates have to be detected. Furthermore, quantification of analytes is possible in the presence of unknown interferents if pure analyte standards are available. The results obtained indicate a recovery of >91% and relative error of <9% in the proposed approach for the PABA product.

Nano- TiCl4.SiO2 is an efficient, readily available and reusable catalyst for the synthesis of 1, 2, 4, 5-tetrasubstituted imidazoles using benzil, aromatic aldehyde and an amine in the presence of ammonium acetate. The one-pot procedure is very simple with good to excellent yields.

Because of their relative simplicity of design and straightforward thermal approach, visbreaking processes will not be ignored or absent from the refinery of the future. However, new and improved approaches are important for the production of petroleum products. These will include advances in current methods, minimization of process energy losses, and improved conversion efficiency. In addition, the use of additives to encourage the preliminary deposition of coke-forming constituents is also an option. Depending upon the additive, disposal of the process sediment can be achieved by a choice of methods.

A green and environmentally benign protocol for squaric acid catalyst electrophilic substitution reactions of indole derivatives, with various aldehydes in water, in good to excellent yields, is developed. The advantages of low sensitivity towards moisture and oxygen, high tolerance of different functional groups, green reaction media and efficient recyclability make this organocatalyst suitable for both laboratory and industrial scale synthesis of bis(indolyl)methanes under very mild conditions.

In this study, the flow of a fiber filled viscoelastic matrix through planar contractions is investigated. It was found that by adding fiber to the matrix vortex, the intensity increases. Fiber orientation along “x” and “y” axes was studied too. It was found that fiber orientation could be used for determining the flow regime through the contraction geometry. The rigidity condition of fibers, which needs the trace of the orientation tensor to be unity everywhere in the domain, is correct except near walls and the reentrant corner, which is slightly less than one. In these regions, the stress magnitude is higher, which results in more numerical errors, and which further leads to some error in predicting the orientation tensor. The first normal stress difference distribution along different axes was also studied in this article. It was found that increasing the volume concentration of fibers results in first normal stress difference intensification.

In this study, the exergy analysis of a 11 KW triangular channel geometry PEM fuel, due to some parameters such as; input oxygen temperature (TO2), input hydrogen temperature (TH2), cell temperature (Tcell), input pressure (P), oxygen flow rate () and hydrogen flow rate (), is investigated experimentally. A series of experiments are carried out to investigate the influence of the above parameters on the polarization curve and irreversibility under normal conditions. A PEM fuel cell with a 25 cm2 active area and a Nafion 117 membrane with 4 mg Pt cm−2 for the anode and cathode is employed as a membrane electrode assembly. The results show that an increase in the inlet temperature of oxygen and hydrogen, cell temperature and inlet pressure can enhance cell performance, exergy efficiency and reduce the irreversibilities of the cell.

In poorly developed fractured rocks, the contribution of individual fracture on rock conductivity should be considered. However, due to the lack of data, a deterministic approach cannot be used. The conventional way to model discrete fractures is to use a Poisson process, with prescribed distribution, for fracture size and orientation. Recently, a stochastic approach, based on the idea that the elastic energy due to fractures follows a Boltzmann distribution, has been used to generate realizations of correlated fractures in two dimensions. The elastic energy function has been derived by applying the appropriate physical laws in an elastic medium. The resulting energy function has been used in the simulated annealing algorithm to generate the realizations of two dimensional fracture networks. The main contribution of this work is to extend this technique to 3D, and to better incorporate geological field observations. In 3D, the method has adjusted the orientation of fractures to three orthogonal sets. Moreover, we investigate the effects of boundary condition, fracture size distribution, and the anisotropy of the medium. We have observed that far field stress can control the orientation of fractures. As a result, this fracture modeling technique can be used to stochastically generate sub-seismic fractures.

The electrochemical behavior of certain pyrazolin-5-ones was investigated at the dropping mercury electrode by employing DC polarography. The variables that influence the electrode process were extensively studied. All compounds under investigation gave two well defined polarographic waves. The mechanism for the electrode process was proposed in acid, as well as in basic media. The results obtained in polarography were compared with those obtained in cyclic voltammetry.

The solubility of acetaminophen in SuperCritical-Carbon Dioxide (SC- CO2) with and without menthol as a cosolvent was measured at various temperatures (313, 328 and 343) K, and within pressures ranging from (10 to 25) MPa. It should be stated that the cosolvent, menthol, has chiral isomers with different melting points. Therefore, the effects of both menthol (I) with a lower melting point and menthol (II) with a higher melting point, as cosolvents on the solubility of acetaminophen in SC- CO2, were studied. The experimental data collected in this work were obtained using a static flow apparatus. The experiments were replicated at least three times and the data reported are the average of the replicas. Finally, the data reduction for the solubility of acetaminophen in SC- CO2 in the presence and in the absence of menthol (I) and menthol (II), were correlated, using the semi-empirical equations proposed by Chrastil and Mendez-Santiago & Teja. The results obtained from these equations were in good agreement with the experimental data.