شیمی و مهندسی شیمی ایران
سال:1395 | دوره:35 | شماره:3 |تعداد مقالات:17

Silver metal was recovered primarily from spent X-ray photographic solution using a horizontal tube furnace. The X-Ray Diffraction (XRD) spectroscopy analysis approved almost 95 percent purity of the recovered silver metal. In the next step, the synthesis of silver nanoparticles from the recovered silver metal proceeded by using chemical reduction method. The proposed method uses ethanol as reducing agent and VinylTriMethoxySilane (VTMS) as stabilizer. Nitrogen gas may be used to provide dry and inert atmosphere. Upon optimized condition spherical nano-sized silver particles with approximately 68 nm diameter are formed. XRD and EDX spectroscopy studies confirmed the formation of silver nanoparticles. The morphology of the silver nanoparticles was studied by using scanning electron microscope.

The aim of this study was to produce Carboxy Methyl Cellulose (CMC) and Poly Vinyl Alcohol (PVA) films and to enhance their properties by reinforcing them with nanoclay particles. Thus, nanocomposite films were prepared with blending of CMC and PVA, as a matrix and several filler loadings of nanoclay particles. The various formulations of nanocomposite films obtained with casting method and their different characterizations were studied. The mechanical and water absorption properties of these films are discussed in this article. Results showed that with increasing filler loading, Tensile Stress (TS), elongation at break (E), and Modulus Of Elasticity (MOE) of the CMC/PVA/nanoclay composites raised, decreased, and enhanced, respectively. In addition, water absorption of films decreased as more filler was incorporated in the composite. X-Ray Diffraction (XRD) patterns showed that films containing 3% clay have proper mixing and exhibited the best dispersion in the CMC/PVA matrix.

Over the past many years, synthesized silica (SiO2) has attracted wide attention because of its unique characteristics, such as low density, low thermal conductivity, high surface area, high thermal shock resistance and high specific strength. In this study, Flower-like a-quartz nano-structures have been synthesized through the hydrothermal method. The synthetic a-quartz powder was obtained using the feedstock of locally kaolin after 15 h. reaction at 180oC. The characterization of the product was investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform InfraRed (FT-IR) spectrometer. The FT-IR spectrum of the nano-crystalline powders confirms the presence of silica. SEM studies have revealed flower-like structures consisting of nano-sheets. In the synthetic quartz, most of the population is of nano-sized and lies between 1 mm to 15 mm. This developed method has many advantages such as synthesis at low temperature and desired pH to yield superior product of desired specification.

Based-on the quasi-planar tetra-dentate Schiff-base ligand, a pair of manganese (III) Schiff-base enantiomers formulated as {[Mn (R, R-3-MeOSalcy) (H2O) (CH3OH)] ClO4} 2 (1) and {[Mn (S, S-3-MeOSalcy) (H2O) (CH3OH)] ClO4} 2 (2) (3-MeOSalcy=N, N′- (1, 2- cyclohexanediylethylene) bis (3-methoxysalicylideneiminato) dianion) have been synthesized and characterized by element analysis. Single X-ray structure analysis showed that the coordination sphere of the Mn (III) ion is an elongated octahedron with the four equatorial positions occupied by N2O2 unit from the Schiff-base ligand and two O atoms of the coordinated solvent molecules completing the additional two axial sites. The mononuclear manganese (III) Schiff-base compounds are self-complementary into a supramolecular dimer structure through the coordinated solvent ligand from one complex and the free O4 compartment from the neighboring complex. Investigation of the magnetic susceptibility of the manganese complexes reveals the overall weak antiferromagnetic interactions between the adjacent mental centers.

A C102H30 graphene sheet has been rolled up to construct Single-Walled Carbon NanoTube Fragments (SWCNTFs) as parts of armchair carbon nanotubes by computational quantum chemistry methods. Non-covalent cation-p interactions of the Na+cation on the central rings of SWCNTFs have investigated. The binding energies of the Na+-SWCNTF complexes versus true strain parameter (R) change in three brands. Structural parameters, electron charge density values, and also effects of aromaticity on the binding energies were gauged. Results show that partially localization of the π electron clouds of SWCNTFs enhances strength of the cation-p interactions in some cases. Thus, changing the π electron clouds of SWCNTs may help to improve surface modification of these materials through the cation-p interactions, which has important applications such as storage of electric energy by transportation of cations through the walls of SWCNTs and enhancement of the hydrogen adsorption compared to pure SWCNTs.

Cadmium can be found in wastewater in high concentrations and can cause dangerous effect on aqueous environment and human health. At present, many methods have been used to heavy metals removal. Among this clean up techniques, adsorption techniques by using low-cost adsorbent are more considerable. In this study, batch adsorption experiments were conducted for removal of cadmium ions from aqueous solutions by using saxaul tree ash as a low-cost adsorbent. The batch experiments were conducted in various conditions as follows: pH (3 to 11), adsorbent dose (0.5 to 6 g/L) g, contact time (15 to 210 min), and initial cadmium concentration (5-50 mg/L). Based on the results, pH=5 with an adsorbent dose of 4 g/L with a 75 min contact time were found to be the optimum for adsorption of cadmium on saxaul tree ash. Also, the results showed that adsorption efficiency is decreased with increase in initial concentrations of cadmium. The isotherm experiments showed that Freundlich model satisfactorily represents the proportional fitting. Therefore, base on the results of this study, saxaul tree ash can be used for efficient removal of cadmium ions from aqueous solution.

Wastes generated from the processing of some fruits still contain large amounts of chemical components such as polyphenols, which are deemed as very effective antioxidants. This study involves the characterization of wastes generation by pink guava processing and selection of the best solvent that will allow us to extract the excess polyphenols via ultra-filtration membrane technology. The wastes were gathered from a juice processing factory in Sitiawan, Perak, Malaysia. The results are conclusive of the fact that the wastes contain quite a large percentage of polyphenols. The highest total polyphenol content was observed in mixture of methanol-water (60% concentration) and pure water as solvents, respectively for 1g of waste per using 25mL of each solvent. This phenomenon is also directly proportional to extraction time and duly concluded that pure water is the effective solvent for retrieving polyphenols from pink guava processing wastes.

In this study, whole lemons were dried using a laboratory convective hot air dryer and the effects of drying temperature on dehydration behaviour and mass transfer characteristics of the lemons were investigated. The drying experiments were conducted using air temperatures of 50, 60 and 75 °C and air velocity of 1 m/s. It was observed that the drying temperature affected the drying time and the drying rate significantly. Drying rate represented no constant period and the entire dehydration process took place in the falling rate period. The usefulness of five mathematical models to simulate the drying kinetics was evaluated and Midilli and logarithmic models were found as the best models describing the drying curves. The effective moisture diffusivity values were obtained to be 1.15×10-10, 2.29×10-10, and 7.63×10-10 m2/s for the applied temperatures, respectively. The activation energy was also determined to be 71.32 kJ/mol. The convective mass transfer coefficient values were calculated by the analytical model and obtained to be 4.078×10-7, 1.023×10-7 and 4.346×10-8 m/s for drying temperatures of 75, 60 and 50 °C, respectively.

In this work, two types of solvents ethanol or water were used in preparation of the LaFeO3 catalysts by citrate sol gel method. The obtained samples were subjected to various calcination temperatures in order to study the catalytic activity and stability for methanol electro-oxidation by XRD, cyclic voltammetry and chronoamperometry. The crystallinity of the LaFeO3 phase in both cases is improved with increasing calcination temperature. The samples prepared using ethanol exhibit higher catalytic properties than those prepared in water for different calcination temperatures. Moreover, the catalyst prepared in ethanol and calcined at 1050 °C, exhibits a high catalytic activity in methanol electro-oxidation and is ~ two times greater than that obtained at 750 °C.

Preformed Particle Gels (PPGs) treatment is one of the most promising solutions to improve conformance control in mature water flooded oil reservoirs. It is very important to be able to evaluate and predict performance of PPGs in porous media. In this paper, we will first introduce new class of enhanced PPGs designed for harsh reservoir conditions (high salinity and temperature) and then present experimental laboratory results looking at viscosity performance of PPGs during injection and flow in porous media. A central composite experimental design coupled with a simple method using a set of 150-cm tubes, were used to comprehensively evaluate the functionality of PPGs rheological behavior under different flow conditions in fractures. The effects of five variables including salinity of water used to prepare the swollen PPGs, tube internal radius, injection velocity, size of PPGs and temperature on the PPGs viscosity were examined. The results showed that PPGs viscosity primarily depends on the injection velocity, tube internal radius, temperature, PPG size, salinity and their two-level interactions. It is also worth to mention that the effect of temperature on PPGs viscosity has not been investigated in previous studies. Finally, a simple mathematical model was introduced to predict the PPGs viscosity at reservoir conditions.

In this research, hydrodynamics of the Bubble Train Flows (BTF) in circular capillaries has been investigated by Direct Numerical Simulation (DNS).The Volume of Fluid Based (VOF) interface tracking method and stream wise direction periodic boundary conditions has been applied. The results show that there exists an appropriate agreement between DNS and experimental correlation results. The recirculation time as an important parameter, which affects the mass transfer of gas-liquid slug flow through the capillaries channel, has been calculated. The effects of different parameters such as capillary length, capillary diameter, unit cell length, and surface tension on recirculation time have been investigated. Afterwards, the DNS based correlation has been proposed for BTF recirculation time in a circular capillary.

The intermittent drying characteristics of an Iranian popular paddy rice variety were experimentally investigated to determine the drying kinetics and obtain the effective moisture diffusivity. A lab-scale fluidized bed dryer was designed and constructed to enable obtaining the required results while controlling critical drying parameters. The effects of drying temperature and tempering period on drying kinetics and moisture diffusivity were studied. The results showed a significant effect on drying performance and effective moisture diffusivity by adding tempering stage. Drying rate improved sharply by implementing the tempering stage, increase of drying air temperature as well as the tempering duration. Several thin layer drying models were fitted separately to experimental data of each drying stages namely pre-tempering and post-tempering and suitability of these models were examined using the statistical analysis. The Midilli and Tow-Term model were found to be the most appropriate one for the first and second drying stages, respectively.

The effects of chemical reaction, thermal stratification, Soret and Dufour numbers on magneto-hydrodynamic free convective heat and mass transfer of a viscous, incompressible, and electrically conducting fluid on a vertical stretching surface embedded in a saturated porous medium are presented. A similarity transform is used to reduce the governing partial differential equations into a system of nonlinear ordinary differential equations, which is solved analytically by means of homotopy analysis method. The results are compared with numerical predictions obtained by fourth order Runge-Kutta method. Close agreement is observed between the two sets of results. The method is led to an expression, which is acceptable for all values of effective parameters and controls the convergence of the solution.

The present Computational Fluid Dynamics (CFD) work deals with the modeling of complete coal direct chemical looping sub-pilot unit which use coal as fuel and ferric oxide supported on alumina as an oxygen carrier. The 2D CFD model of the complete arrangement incorporating both fuel and air reactors and their inter-connecting parts was solved using FLUENT. The CFD model was run with two different sets of reactions - the first set with eleven and second set with eighteen reactions. Computed results for second set of reactions were found to be in good agreement with the published pilot plant data. The CFD model with second set of reactions predicted fuel conversion for Sub-Bituminous Coal (SBC) and Metallurgical Coke (MC) were 95.39% and 87.07% respectively while, the published results were 97-99% and 70-99% respectively. Further, the purity of CO2 in fuel reactor exhaust were 92.34% and 90.19%, while, the published were 99.8% and 99.6% for SBC & MC respectively.