Iranian Journal of Chemistry and Chemical Engineering
Volume:28 Issue: 4, Jul-Aug 2009

Microporous hydroxy-sodalite zeolite membranes with different morphologies were synthesized via secondary growth technique with vacuum seeding on tubular α-Al2O3 supports at two different synthesis conditions (i.e. two different routes). Microstructures of the synthesized membranes were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) and single gas permeation using H2 and N2. Also, the effect of seeding time on microstructure and performance of the synthesized hydroxy-sodalite top-layers was investigated at four different levels (60, 120, 180 and 240 s). Permeation test was carried out in order to attain a more exact comparison of both applied routes and seeding times. Microstructure of the synthesized hydroxy-sodalite zeolite membrane layers and the effects of the investigated factors on the elimination of inter-crystalline pores were evaluated by the permeation of single gases (H2 and N2) under different pressure differences at ambient temperature. The permeation results confirmed the high quality of the hydroxy-sodalite zeolite membranes manufactured via the first route at seeding time of 60s for the hydrogen purification under extremely low temperatures (< 200 K) and/or extremely high pressures (> 100 bars).

Nanoparticles of zinc sulfide as undoped and doped with copper were used as photocatalyst in the photodegradation of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) as nitramine explosives under UV and Vis irradiations. Photoreactivity of doped zinc sulfide was varied with dopant, mole fraction of dopant to zinc ion, pH of solution, dosage of photocatalyst and concentration of explosive. The characterization of nanoparticles was studied using XRD patterns, UV-Vis spectra and TEM image. The maximum degradation efficiency was obtained in the presence of Zn0.95Cu0.05S as nanophoto-catalyst. The effect of dosage of photocatalyst was studied in the range of 50-200 mg/L. It was seen that 150.0 mg/L of photocatacyst is an optimum value for the dosage of photocatalyst. The most degradation efficiency was obtained in neutral pH of 7.0 with study of photodegradation in pH amplitude of 2-12. In the best conditions, the degradation efficiency of HMX and RDX was obtained 92-94 %. A gradual decrease in the degradation efficiency was observed at the first two cycles.

Some of the most destructive accidents of 1980s and 90s which occurred in process industries were domino accidents. Although domino accidents are among the most destructive industrial accidents, there are not much pioneering works done on quantification of them. The analytical formulation of the domino accidents is usually complex and need a deep knowledge of probability rules. Even if the case is formulated, errors in calculation such as round-off error, is very probable as the values used all have small quantities and the number of possible scenarios are too high. In this paper, a new methodology based on Monte Carlo Simulation (MCS) technique is proposed for frequency estimation of domino accidents. The applicability and flexibility of this method is evaluated while applying it to estimate domino frequencies in a case study very similar to a real industrial plant. The simulation technique has shown advantages in comparison to analytical probability methods. The major advantage is non-dependency of the accuracy of results to complexity of the system. In addition by using simulation techniques, failure probability can be calculated as a function of time.

Removal of cesium from synthetic aqueous solution through adsorption on vermiculite, under batch equilibrium experimental condition at six initial values of pH (3, 4, 6, 9, 11 and 12) and five temperatures (25, 50, 75, 85 and 95 °C) has been investigated. It is necessary to propose a suitable model for a better understanding of the mechanism of cesium adsorption on vermiculite. For this propose the suitability of the Langmiur, Freundlich and Redlich-Peterson (R-P) adsorption models for equilibrium data were investigated. The parameters in the adopted adsorption isotherm models were determined by Eviews software. The study of equilibrium isotherm shows that the best model for analysis of experimental data is Redlich-Peterson model with correlation coefficient higher than 0.99(both for temperature and pH). The results showed that increasing of pH and temperature increased the adsorption ability of vermiculite. Optimum conditions for adsorption were determined as T=75 °C, pH=9, vermiculite dose=1.5 g and contact time of 24 hr. Finally the thermodynamic constants of adsorption phenomena, H° and S° were found to be 2.672 kJ/mol and 0.563 kJ/mol K in the range of 25-95 °C respectively. The negative value of the Gibbs free energy G demonstrates the spontaneous nature of cesium adsorption onto vermiculite

Development of pore network models for real porous media requires a detailed understanding of physical processes occurring on the microscopic scale and a complete description of porous media morphology. In this study، the microstructure of porous media has been represented by three dimensional networks of interconnected pores and throats which are designed by an object oriented approach. Afterwards، the connectivity of the system has been optimized by an optimization algorithm. To validate the methodology، a network of a carbonate sample is constructed. In this model، the geometrical characteristics of the pores and throats، such as their shapes، effective radii and lengths، are selected from the image analysis of SEM picture and statistical distribution methods based on the mercury injection test results. Then the constructed network is further tuned according to laboratory measured porosity، absolute permeability and capillary pressure. Having built a flexible and detailed model، its prediction of relative permeability and saturation variation along a core plug are compared with experimental data for both drainage and imbibition phenomena. This comparison shows good matches for almost all experimentally measured data.

In this work, the solubility of nicotine extracted from tobacco leaves, found in the north of Iran, in supercritical carbon dioxide has been measured. Also the effects of pressure, temperature, extraction dynamic time, and the organic co-Solvent on the amount of nicotine extracted from tobacco leaves have been investigated. It should be stressed that in order to reduce significantly the number of experiments, the experiments have been specified based on the Taguchi experimental design. The results obtained from the experiments showed that at the specified pressure, temperature, volume of modifier and dynamic time, the maximum amount of nicotine can be extracted. The experimental data collected in this research has been correlated using the Redlich-Kwong (R.K) equation of state. The results showed that the conventional cubic R.K equation of state can accurately correlate the experimental solubility data with good accuracy.

Diesel engine emission standards are being more stringent as it gains more publicity in industry and transportation. Hence، designers have to suggest new controlling strategies which result in small amounts of emissions and a reasonable fuel economy. To achieve such a target، multi-objective optimization methodology is a good approach inasmuch as several types of objective are minimized or maximized simultaneously. In this paper، this technique is implemented on a closed cycle two-zone combustion model of a DI (direct injection) diesel engine. The main outputs of this model are the quantity of NOx، soot (which are the two main emissions in diesel engines) and engine performance. The optimization goal is to minimize NOx and soot while maximizing engine performance. Fuel injection parameters are selected as design variables. A neural network model of the engine is developed as an alternative for the complicated and time-consuming combustion model in a wide range of engine operation. Finally design variables are optimized using an evolutionary genetic algorithm، called NSGA-II.

Cement powder size classification efficiency significantly affects quality of final product and extent of energy consumption in clinker grinding circuits. Static and dynamic or high efficiency air separators are being used widely in closed circuit with multi-compartment tube ball mills, High Pressure Grinding Rolls (HPGR) and more recently Vertical Roller Mills (VRM) units in cement plants to classify comminuted clinker particles at finish grinding stage. Therefore, simulation of air separators is of critical importance in order to provide tools that can assist cement plants engineers in their routine clinker grinding circuit optimization efforts. In this paper, Air Separator Simulator (ASSIM), a newly developed simulator implemented in VB™ which provides a user-friendly process analysis and optimization environment will be introduced. First, a review of mathematical modeling of cyclone separators is presented. Then, the details of ASSIM and the results of its testing using industrial data from J. K. White Cement Works plant will be discussed. The simulator is mainly based on the Whiten function to model air separators and predicts fine and coarse output streams particle size distributions and flow rates. ASSIM performance was verified and validated by comparing its outputs with measured data collected around an operating air separator. Preliminary software tests indicate the accuracy and precision of the developed code in predicting various properties of output streams as sum of least squares between predicted results and actual data is less than 0.01.

An improved chemical regeneration of the granular activated carbon (GAC) exhausted by the color (pigments and pollutants) from citric acid fermentation solution (CAF) was investigated. In the experiments، improved means were adopted to advance the traditional chemical regenerating method and the adsorption capacity of the first time renewed GAC is 103 % of original GAC. Using oxidant and surfactant in addition to just using NaOH solution can recover 10 % more adsorption capacity of renewed GAC. The adding dosage of oxidant is good at 3 % of exhausted GAC weight; that of surfactant is good at 0. 1 %. Hot water as cheap reagent was found to be much helpful to the regeneration efficiency. Comparing with steam regeneration high regeneration yield (>95 %) of this method was an attractive economic factor. The result of this investigation can offer an advanced chemical regeneration method to regenerate exhausted GAC from citric acid refine industry.

A dissolved methane sensor based on silicone tube was designed, constructed and optimized. The silicone tube diameter, silicone tube length and helium flow rate (as the carrier gas(were considered as process parameters to be optimized. A continuous stream of helium (50 mL/min) was directed through the tubing, sweeping out the dissolved methane which diffused through the walls of the tubing from the fermentation broth. The probe was made of silicone rubber tubing, 10 cm in length with inner and outer diameters of 0.25 cm and 0.35 cm, respectively (Detakta Company; NO. 02502). A semi-conductor methane gas sensor (Figaro TGS 2611) - which is highly sensitive and selective to methane gas - was used to measure the dissolved methane continuously. Henry’s law along with a special circuit experimental method was applied for calibration. The output concentration was displayed in mg/l (or ppm) of dissolved gas. The accuracy and response time of this system are ± 2 % and 2 minutes, respectively. Moreover, a control system was installed for recycling methane gas during fermentation.

The excessive biological sludge production is one of the disadvantages of aerobic process such as SBR. So the problem of excess sludge production along with its treatment، and disposal in aerobic processes in municipal and industrial waste water can be seen in many parts of the world even in our country. to solve the problem of excess sludge production، reducing in by oxidizing some of the sludge by Ozone is a suitable idea، thus reducing the biomass coefficient as well as the sewage sludge disposal. In this study، Two SBR reactors with of 20 liter being controlled by on-line system are used. After providing the steady state in the reactors، along the 8 month research sampling and testing parameters such as COD، MLSS، MLVSS، DO، SOUR، SVI، residual ozone and Yield coefficient were done. The results showed that during the solid retention time of 10 days the kinetic coefficient of Y and Kd was 0. 58 (mg Biomass / mg COD) and 0. 058 (1/day) respectively. At the next stage of research، different concentrations of ozone in one liter of the returned sludge to reactor were used to reduced the excess biological sludge production. The results showed that the 20 mg ozone per gram of MLSS in one liter of the returned sludge to reactor is able to reduce Yield coefficient from 0. 58 to 0. 28 (mg Biomass/mg COD)، In other words، the biological excess sludge by 52 %. but the soluble COD increased slightly in the effluent and the removal percentage decreased from 92 in blank reactor to 64 in test reactor. While the amount of SVI and SOUR in this consumed ozone concentration reduced 9 mgO2/h. gVSS and 20 ml/g respectively. No sludge was seen in the 25 mg ozone concentration per gram of MLSS in one liter of the returned sludge to reactor.

Phytoremediation is an emerging environmental-friendly technology that can be a promising solution to remediate oil-polluted soils. The impact of high amount of hydrocarbons on growth characteristics of burningbush and common flax was evaluated in this survey. The influence of organic fertilizers was also assessed on growth of plant species in oil-contaminated soil. Soil samples in which plants showed the best growth were analyzed for residual total petroleum hydrocarbons (TPHs) by GC-FID. Burningbush was employed for the first time in the history of phytoremediation of oil-polluted soils in this research. The two studied plant species demonstrated promising remediation efficiency in highly contaminated soil; however, petroleum hydrocarbon contamination depressed growth of surveyed plants significantly. Utilization of peat fertilizer improved plants’ growth parameters in highly oil-contaminated soil. Flax and burning bush reduced TPHs levels in contaminated soil by 87.63 and 65.29 percent, respectively, in comparison to initial concentration.