Iranian Journal of Chemistry and Chemical Engineering
Year:2008 | Volume:27 | Issue:2|Papers Count:15

Output characteristics of fuel cells are affected by a large number of parameters such as geometry, dimensions, construction materials and conditions of supplying fluids. In present paper a mathematical model followed by a two-dimensional numerical approach has been presented to study the fuel cell parametrically. Effect of oxygen concentration at gas diffusion layer entrance, temperature and pressure of the fluid in channels and thickness of membrane for various current densities were studies. The results show that increasing pressure and input oxygen concentration as well as decreasing membrane thickness improve power density and raise limiting current density.

A new model based on a combination of the polymeric multigrain and multilayer models has been developed to predict the polymerization rate, particle growth, morphology, effective parameters on broadening of the molecular weight distribution, number and weight average of the molecular weight, isotacticity index and bulk density of polymer. Mathematical correlations and the kinetics used in this model are based on the polymeric multigrain and the multilayer models, respectively. In the modeling, multiplicity of active site using different kinetics parameters as well as deactivation of catalyst during the polymerization have been considered,. Moreover, it considers mass transfer effects on polymerization characteristics. The Effects of physico-chemical aspects of catalyst associated with the polymerization in slurry phase are also considered in this model. In addition, the effects of more important model parameters including time step, number of layers and number of active sites on the produced polymer features are reviewed. The model predictions show that propagation rate constant, multiplicity of active site, concentration of any individual active site type, and the initial size of the catalyst particles have considerable effects on the properties of final polymer. The results obtained from simulation with this new combined model confirm at least better qualitative prediction of the polymerization characteristics in comparison with simulation results of the multigrain model (MGM) and the two models mentioned above.

The effects of some synthetic sweeteners on the rheological and physical properties of guar gum in dilute solutions were investigated. Measurements include the determination of intrinsic viscosity and the particle size, surface weighted mean [D3, 2], volume weighted mean [D4, 3] and specific surface area of arabic gum and synthetic sweeteners mixtures. The concentration of these sweeteners were 0, 0.1, 0.2% w/w for aspartame, acesulfame-k and cyclamate, and 0, 0.001, 0.002% w/w for neotame. Gum was evaluated for intrinsic viscosity by various models i.e. Huggins, Kraemer, Tanglertpaibul and Rao equations. The results showed that the values obtained for intrinsic viscosity were different upon various equations used. The plot of relative viscosity versus concentration, obtained from Tanglertpaibul and Rao model described best the phenomenon. Sweeteners had no significant effect on intrinsic viscosity of guar gum solutions.

The value of the permeability in fluid flow through porous media is important for process investigation. In low Reynolds number, the classic Darcy’s law suitable for simulation of fluid flow. In present paper, and experimental study for evaluation of preformed fiber permeability has been done. Also, the deviations from the classical Darcy’s law by experimental and numerical simulation of the Navier-Stokes equations was studied, and the coefficient of inertial term was evaluated. The fluid flow in a geometry which is similar to the experimental system has been modeled as the Stokes flow on multi particles. Kozeny-Carmen relation for characteristic diameter of particles has been used as the characteristic dimension in numerical analysis. Numerical solution has been done based on the boundary elements method and the results are used for the K calculations. With experimental investigations for the fluid flows with higher Reynold’s number, the coefficients for Forchheimer term could be obtained.

In present paper, a numerical analysis for a rectangular cavity filled with a anisotrop porous media has been studied. It is assumed that the horizontal walls are adiabatic and impermeable, while the side walls of the cavity are maintained at constant temperatures and concentrations. The buoyancy force that induced the fluid motion are assumed to be cooperative. In the two extreme cases of heat-driven (N£1) and solute-driven (N³1) natural convection, scale analysis is applied to predict the order of magnitudes involved in the boundary layer regime. Especially, the effects of anisotropic properties on heat and mass transfer have been considered. The variation of Nusselt and Sherwood numbers for values of permeability ratio for a wide range of thermal Rayleigh number, buoyancy ratio, and Lewis number are presented. It is demonstrated that the anisotropic properties of the porous medium considerably modify the heat and mass transfer rates from that expected under isotropic conditions.

The basics of quantum mechanics and statistical thermodynamics were used to predict the potential energy and intermolecular forces of asphaltene molecules. The parameters associated with the chemical structure were also estimated for a specific asphaltene molecule to predict the Mie potential function. Based on the structural results, a new form of the Virial EOS with Peneloux correction was developed to estimate the density, solubility parameter and a correction factor that accounts for the structural effect of asphaltene. In this way, asphaltenes were considered as polymer-like compounds consisting of aggregates of a monodisperse. Finally, three new correlations were developed to predict the key parameters of asphaltenes, namely structural coefficient, density and solubility as functions of temperature and molecular weight. The correlations facilitate the calculation of the numerical methods of these parameters. These parameters were also compared successfully with the results found by the Soave Redlich Kwong equation of state. Meanwhile, at first the stage asphaltene was extracted and the roughness of the asphaltene coating in different rpm was studied by using of image analysis confocal microscopy.

Differential scanning calorimetry (DSC), temperature programmed desorption mass spectrometry (TPD-MS) and small angle neutron scattering (SANS) were used to investigate CO2 uptake by the Wyodak coal. The adsorption of carbon dioxide on Wyodak coal was studied by DSC. The exotherms evident at low temperatures are associated with the uptake of CO2 suggesting that carbon dioxide interacts strongly with the coal surface. The reduction in the value of the exotherms between the first and second runs for the Wyodak coal suggests that some CO2 is irreversibly bound to the structure even after heating to 200°C. DSC results also showed that adsorption of CO2 on the coal surface is an activated process and presumably at the temperature of the exotherms there is enough thermal energy to overcome the activation energy for adsorption. The adsorption process is instantly pursued by much slower diffusion of the gas molecules into the coal matrix (absorption). Structural rearrangement in coal by CO2 is examined by change in the glass transition temperature of coal after CO2 uptake at different pressures. The amount of gas dissolved in the coal increases with increasing CO2 pressure. TPD-MS showed that CO2 desorption from the Wyodak coal follows a first order kinetic model. Increase in the activation energy for desorption with pre-adsorbed CO2 pressure suggests that higher pressures facilitate the transport of CO2 molecules through the barriers therefore the amount of CO2 uptake by the coal is greater at higher pressures and more attempts are required to desorb CO2 molecules sorbed at elevated pressures. These conclusions were further confirmed by examining the Wyodak coal structure in high pressure CO2 by SANS.

To resolve handling problem of nanoparticles, due to their small size, a new methodology of electro-spraying and freeze-drying was developed for colloidal nanoparticles of silica and titania to transform them to the solid macro-scale nanoparticle assemblies. The assemblies were then redispersed in an aqueous system to investigate the effect of formulation of original solutions and the process parameters on reversibility of the system to a stabilized colloidal condition. The electro-spraying was employed to control the size of droplets and consequently the size of nanoparticle assemblies in the freeze-drying. High speed digital video recording of the spray process revealed that within a narrow range of voltage, the size of droplets reduced sharply to a minimum value, where a narrow size distribution was obtained. Non-destructive structural analysis of the freeze-dried nanoparticle assemblies using X-ray micro-tomography represented different structures of the nanoparticle assemblies depending on type of nanoparticles. The stability analysis of redispersed nanoparticles in water (using centrifugal stability analyzer) and their size distribution (obtained by nano-sizer) showed different stability conditions. These Conditions were affected by the physicochemical properties of the nanoparticle assemblies and the process parameters. In terms of titania, it was found that with an appropriate formulation of PEG solution (as binder of assemblies) and optimum size of the nanoparticle assemblies it was possible to produce assemblies having adequate strength and good re-dispersion properties.

In this research the experimental and theoretical studies on different Enhanced Oil Recovery (EOR) techniques, i.e. Water Flooding (WF), Gas Injection (GI) and Water Alternating Gas process (WAG) were performed on specimens taken from an Iranian carbonate offshore reservoir at the reservoir condition. The experimental results for each specified techniques were compared with the corresponding results obtained from a simulation model. In the case of WF and GI, the injection rates were set to be 0.1, 0.2 and 0.5 cc/min while for the WAG experiments, with two WAG ratios 1 and 2 and with 7, 7, and 10 cycles, the injection rates were 0.1, 0.2 and 0.5 cc/min. The results obtained from the experiments revealed that in all cases the amount of recovered oil is increased. Furthermore, the results showed that increase in the recovery of oil is significant in the case of the WAG injection with optimum rate of injection fluids comparing to those of the WF and GI scenarios. It was also pronounced that the recovery of oil with WAG ratio 2 is more than that with ratio 1. It should be mentioned that samples for sea water and pure methane were considered to be as injection fluids. It was also shown that the experimental results can be accurately correlated with a black oil numerical simulator, Eclipse100.

In present paper, the potential of auto-ignition of heavy oil during in-situ combustion (ISC) process was studies. Kinetic studies were carried out using Thermo Gravimetric Analyzer (TGA), Differential Scanning Calorimetry (DSC) and Accelerating Rate Calorimetric (ARC) techniques. Effects of oxygen partial pressure, reservoir pressure and clay on auto ignition condition were investigated on a number of different heavy oil samples fro south west Iran mixed with silica sand or crushed carbonate rock and clay. Based on the experimental results obtained by TGA runs, the kinetic equation was derived for different oil samples in the presence of different sands. Effect of partial pressure of oxygen in the injected air was studied. Results showed that at atmospheric pressure, the peak of low temperature combustion (LTC) by producing CO was initiated at 300°C when air was injected. Also, enriching the injected air by oxygen lowers the LTC by up to 50°C. When the experiments were extended to reservoir pressure (1300 psi), it was found that activation energy in the LTC region was lowered. As a result, initiation of LTC was started at 115°C when air was injected. The DSC experiments, under non-isothermal condition showed that increasing the oxygen partial pressure resulted in more heat being evolve during the high temperature combustion reactions. Also, effect of clay as a catalyst was studied and it was found that the activation energy decreases considerably when clay is present in the system. The decrease in activation energy was from 359 to 149 kj/gmole for one sample.

The waste tyres represent a source of energy and valuable hydrocarbon products. Waste tyres were pyrolysed catalytically in a batch reactor under atmospheric pressure. The effects of basic catalysts (MgO and CaCO3) were studied on the pyrolysis products. The distribution ratio of gas, liquid and char with MgO and CaCO3 were 24.4:39.8:35.8 wt % and 32.5:32.2:35.2 wt % respectively at 350oC for 2hr catalytic pyrolysis. The physical and chemical properties of the pyrolzed products obtained were characterized. Both catalysts produced 25% wt of aliphatic hydrocarbons but with the use of magnesium oxide the aromatic hydrocarbons increased (55%) and polar hydrocarbons (20%) decreased as compared to calcium carbonate catalyst (50% aromatic and 25% polar hydrocarbons). As far as the distillation data and fuel tests are concerned, the oil fractions with both catalysts fulfill the present specifications of diesel fuel commercial products.

The main goal of this study is to investigate the capability of zeolites A and P synthesized from Iranian natural clinoptilolite for uranium uptak. The removal of uranium (VI) from aqueous solution via ion exchange by zeolites in a single component system with various contact times, temperatures and initial concentrations of uranium (VI) was investigated. The experimental results were fitted to the Langmuir and Dubinin-Radushkevich isotherms to obtain the characteristic parameters of each model. Both the Langmuir and Dubinin-Radushkevich isotherms were found to good represent the measured adsorption data. Using the thermodynamic equilibrium constants obtained at two different temperatures, various thermodynamic parameters, such as DGo, DHo, and DSo have been calculated. The thermodynamics of uranium (VI) ion and zeolite system indicates the spontaneous and endothermic nature of the process. It was noted that an increase in temperature resulted in a higher uranium loading per unit weight of the adsorbent.

Aqueous two-phase systems (ATPS) have been emerged as a powerful extraction method for the downstream processing of bio-molecules. The aim of this work was to investigate the possibility of utilizing ATPS for the separation of recombinant Bacillus sphaericus phenylamine dehydrogenase (PheDH). Polyethylene glycol (PEG) and ammonium sulfate systems were selected for our experiment. The effect of different elements such as; type and concentration of PEG, concentration of (NH4)2SO4, pH, phase volume ratio (VR) and tie-line length (TLL) on the extraction behavior and selective separation was also studied. Desirable conditions for differential partitioning was obtained in 8.5 % (w/w) PEG-6000, 17.5 % (w/w) (NH4)2SO4 and VR, 0.25 at pH 8.0. PheDH was mainly concentration into the upper PEG-rich phase in all tested systems. The partition coefficient (K), recovery (R %), yield (Y %), TLL and selectivity were achieved, 58.7, 135 %, 94.42 %, 39.89 % (w/w) and 2174, respectively. From the experimental results, it was revealed that the PEG molecular weight, (NH4)2SO4 concentration, TLL and pH of system had strong impacts on partition features. The extraction efficiency was increased with elevation of pH and TLL values. In present paper, we described the partitioning behavior in PEG/(NH4)2SO4 ATPS in order to evaluate the applicability of ATPS for Partitioning and recovery of PheDH.

Zn/AcOH on silica gel converts a range of structurally different sulfoxides to their corresponding thioethers in excellent yields under microwave irradiation. It has been found that chemoselective deoxygenation of sulfoxides can be achieved in the presence of other reducible functional groups such as acetals, acids, amides, esters, ketones, nitriles.

An experimental study of the phase inversion behavior of liquid–liquid dispersion has been conducted in a spray extraction column for systems of toluene/water, n-hexane/water, CCl4/water, toluene/water+glycerol (25% wt), toluene+CCl4 (25% wt)/water and toluene/acetic acid (5% wt)/water. The effects of physical properties, mass transfer and column geometry on phase inversion have been investigated. The results show that the dispersed phase hold up sufficient for phase inversion increases in o/w dispersion and decreases in w/o dispersion by increasing interfacial tension. Also, it was found that by increasing the viscosity of aqueous phase, dispersed phase hold up decreases at phase inversion point in both o/w and w/o dispersions. The tendency to phase inversion increases in o/w dispersion with an increase in density difference of two phases. It was observed that dispersed phase hold up at phase inversion point decreases in the presence of mass transfer, when the direction of mass transfer is from dispersed phase to continuous phase. The results show that dispersed phase holdup increases with drop size at phase inversion point and column diameter has an important effect on phase inversion because of wall effect.