شیمی و مهندسی شیمی ایران
سال:1394 | دوره:34 | شماره:1 |تعداد مقالات:20

Grinding (solvent-free) method was used as a superior technique to prepare mesoporous photocatalysts of ZnO, ZnS, ZnO / ZnS, CdO, CdS and CdO / CdS-SBA-15. In this technique, the nitrate, acetate and chloride salts of zinc and/or cadmium were grinded with as-synthesized SBA-15 as a mesoporous material. The controllable sulfurationis was used to prepare ZnS, ZnO/ZnS, CdS and CdO/CdS-SBA-15 at temperature of 80oC. The advantages of grinding technique were: i) the elimination of solvent and thus decrease of expense and ii) the complete incorporation of metal salts in the nanochannel of mesoporous material in a short time. X-ray powder diffraction, N2 adsorption-desorption and FT-IR spectroscopy were used to characterize the prepared materials. The highly dispersed semiconductors in SBA-15 demonstrate an active photodegradation of Congo red in aqueous solution. The nanocomposites of ZnO/ZnS and CdO/CdS in channels of SBA-15 showed the highest photocatalytic activity. The photocatalytic activity of ZnO-, ZnS- and ZnO/ZnS-SBA-15 were also dependent on the salt precursor of zinc. The prepared composite photocatalysts of zinc/SBA-15, by using ZnCl2 as salt precursor, indicated the higher activity.

In this study fullerene functionalized using oleum (H2SO4·SO3), followed by the hydrolysis of the intermediate cyclosulfated fullerene as well as an oxidizing agent was employed to functionalize the fullerenes. Ruthenium was then added by the impregnation method or deposited on the functionalized fullerene. Subsequent to this step, Response Surface Methodology (RSM) was used to study the cumulative effect of various parameters including, pressure, temperature, time and loading. In order to maximize the hydrogenation of nitrobenzene (NB) to aniline (AN) these latter parameters were optimized. Furthermore, catalytic activity was evaluated over a temperature range of 25–150oC, hydrogen pressure of 1-30 atm, ruthenium content of 1-15% (w/w) and reaction time of 30-180 min in a bench scale reactor. The optimized model predicted that the hydrogenation should be at a maximum level (approximately 100%) with the following conditions; Ru loading of 15%, reaction temperature of 150oC, reaction time of 180 min and hydrogen pressure of 22.33 atm.

A statistical mechanical based equation of state has been employed to calculate the liquid density of lead, mercury, bismuth and lead-bismuth and lead-lithium eutectic alloys. The equation is basically that of Song, Mason and Ihm [Ihm G, Song Y, Mason EA. J. Chem. Phys.1991; 94: 3839] which is modified by Ghatee and Boushehri. Three temperature dependent parameters are required to use this equation of state. The second virial coefficient B2, an effective van der Waals co- volume, b and a correction factor a. B2 is predicted from a corresponding states correlation with two scaling parameters, melting point temperature, Tm and liquid density at melting point, pm. Liquid densities are predicted from melting point up to several hundred degrees above the melting point. The results are fairly consistent with experiment. In order to evaluate the correlation equation, Tao and Mason equation of state is applied to the above cited liquid metals and liquid density results are compared to the present equation. Obviously, the first equation acts better.

In this study, removal of methylene blue by electro-coagulation method using aluminum and iron electrodes was investigated. The influence of the operating parameters such as contact time, current density, anode type, inter-electrodes distance, initial and final pH and energy consumption rate was determined. Dye removal was increased with increases in solution pH, current density and contact time and then decreased for increase in initial dye concentration and electrodes distance. The results show that the electrochemical method has significant efficiency in removal of methylene blue, higher efficiency was observed for iron (Fe) electrode; namely 100% and 95.78% of dye was removed by iron and aluminum electrode; respectively, after 24 min contact time. For a given current density, the removal efficiency and energy consumption rate showed that iron electrode was superior to aluminum in removal of methylene blue. In the case of iron as anode type, the required energy for complete dye decolorization was 3.8 kWh/m3; for 98% dye removal, the required energy was observed to be 4.3 kWh/m3 in the case of aluminum as anode type. In general, complete methylene blue can be removed at operating parameters condition of iron as anode, distance between electrodes of 1cm, solution pH of 9 and current density of 50 A/m2 for 24 min electro-coagulation time.

The paper introduced effects of modified pyrolysis tar on flue gas desulfurization. This experiment selected the pyrolysis tar as the raw material, researched the effects on desulfurization performance under different modification solution, concentration, solid liquid ratio of pyrolysis tar and modified solution, calcination temperature and calcination time by 16 group orthogonal experiments. The results showed that: (1) The significance of five factors impact on the modified pyrolysis tar desulfurization performance in order was: types of the modified solution>modification solution concentration>calcination time>solid-liquid ratio>calcination temperature. (2) The modified effects of nitric acid and phosphoric acid were better. (3) The higher nitrate concentration, the better modified effect of pyrolysis tar. (4) The rate of desulfurization increased mainly associated with acidic groups on the surface of the pyrolysis tar, desulfurization performance get better along with the acidic groups increasing.

In this study, the blast furnace slag was used as absorbing bed and then, its ionic adsorption was studied. For this reason, various experimental parameters such as pH, contact time and the primary ion concentration were investigated. The remaining concentrations of ions such as; Mn2+ and Fe2+ in water were measured by atomic adsorption spectroscopy. The chemical and phase composition of slag, before and after ion removal, was investigated. SEM, FTIR, XRD, and EDAX, was used to have a clear understanding of the mechanism of ions removal by slag. The results showed that the removal mechanism of metal ions is carried by adsorption and ion exchange processes. The ionic radius is one of the determining parameters on the process at higher concentration of ions. This study demonstrates that steel slag can be considered as a viable and cost-effective alternative to commercial activated carbon or ion-exchange resins.

The removal of uranium and any other heavy metals from wastewater might be achieved via several chemical or physical treatment techniques. Biosorption process has been considered as a potential alternative way to remove contaminants from industrial effluents. Moreover the surface of biosorbent was characterized by SEM. The biosorption characteristics of uranium (VI) on pretreated A. niger were evaluated as a function of pH (3.0-7.0), biomass concentration (0.05-0.4 g dry biomass/100 mL), initial uranium concentration (10-500 mg/L) and contact time (30-1440 min). The results revealed that the optimum pH was 5.0 for the adsorption of U (VI) by pretreated A. niger. The maximum adsorption capacity of U (VI) by pretreated A. niger in concentration less than 100mg/L uranium was increased significantly in comparison with live and dead biomass of A. niger. The metal removal was rapid with 86.4% metal sorption (43.2 mgU/g dry biomass) taking place in 30 min and the equilibrium was achieved in 240 min. The maximum uranium removal was 98.43% (16.41 mgU/g dry biomass) in concentrations 0.3g dry biomass/100mL. Adsorption process could be well defined by Langmuir isotherm with R2 values 0.985. The kinetic data fitted through the pseudo-second-order kinetic model with the R2 value of 0.998.

In the present work, the integral equations method is used to calculate transport properties of polar fluids. For this goal, we use the Stockmayer potential and examine theoretically the thermal conductivity of several refrigerant mixtures such as R125+R134a, R125+R32, R125+R152a, R134a+R32, R152a+R32, R134a+R143a, and R125+R143a. We solve numerically the Ornstein-Zernike (OZ) equation using the Hypernetted Chain (HNC) approximation for binary fluid mixtures and obtain the pair correlation functions. Finally, the temperature dependence of thermal conductivity is studied using Vesovic-Wakeham method and compared with available results.

In the present attempt, flow behavior and thermal convection of one type of nanofluids in a disc geometry was investigated using Computational Fluid Dynamics (CFD). Influence of gravity induced sedimentation also has been studied. The commercial software, Fluent 6.2, has been employed to solve the governing equations. A user defined function was added to apply a uniform external magnetic field. Obtained results showed that the critical value for Rayleigh number is near 1708, so simulations are in good agreement with the theoretical value for critical Rayleigh number. In addition, it was found that gravity causes separation of phases and sedimentation of nanoparticles, besides, increase in natural convection due to presence of gravity, leads to heat transfer enhancement. In addition, results indicate that, thermal forces are able to disrupt agglomerates when ratio of thermal energy to dipole-dipole contact energy becomes more than unity.

A one-dimensional, transient and thermal degradation model for predicting responses of composite materials when are exposed to the fire is presented. The presented model simulates ablation of composites with different layers of materials and considers material properties as functions of temperature. The reactions are modeled by using Arrhenius-type parameters and density-temperature diagrams which are obtained by specific experimental techniques such as thermogravimetric analysis. This transient thermal model has been implemented in form of a computer code by means of new numerical methods in order to predict the temperature distribution in the liner, the amount of char and erosion, and the liner thickness variations with time. By using implemented computer code, ablation phenomena in a glass-filled phenolic composite has been simulated with the same parameters of a similar experiment. The results are in a good agreement with the experimental data and the model can successfully be used in the design of thermal protection shields as an aid of material and thickness selection.

This paper deals with optimal operation of a three-product Dividing-Wall Column (DWC). The main idea is to design a control structure, through a systematic procedure for plantwide control, with an objective to achieve desired product purities with the minimum use of energy. Exact local method is used to find the best controlled variables as single measurement or combination of measurements based on the idea of self-optimizing control. It concluded that it is possible to have better self-optimizing properties by controlling linear combinations of measurements than by controlling conventional individual measurements. Dynamic validation showed that the proposed control structure with the aid of low-complexity simple PI controller stabilized the plant, rejected the effect of disturbances and made DWC to produce product with desired specifications.