Iranian Journal of Chemistry and Chemical Engineering
Volume:25 Issue: 3, May-Jun 2006

Personal samplers or in general blunt body samplers are widely used in occupational hygiene for collecting air contaminants in the work environments. This work is part of an ongoing research into the performance evaluation of personal samplers, particularly in terms of their aerodynamic properties. Velocity profiles have been measured around and within typical cylindrical sampling devices, placed inside of a wind tunnel. A two-component fibre optic laser Doppler anemometer (LDA) is employed to measure the flow field around as well as within the samplers under the test. A variety of conditions, i.e., suction flux, wind speed and orifice size, have been examined. Extensive tests have been carried out in order to verify the reproducibility and reliability of measurements. The results show that reproducibility of the measurements at upstream of samplers are within 1% of the mean velocity. However, analysis of extensive data revealed the presence of noticeable electrostatic effect within and around the sampling device. Attempts were made to eliminate the presence of the electrostatic effect by, for example, spraying the nonconductive sampler with an anti electrostatic liquid, and wire earthing of a sampler made from cooper, but unfortunately these measures were found to be fruitless in eliminating the electrostatic effects. It should nevertheless, be said that the observed velocity is found to be more stable for small inlet orifice size of 4 mm and high suction flux of 3 l/min and this may be because the charged particles have less time to interact with the field produced by the sampler.

Bamboo structured carbon nanotubes are grown on Co-Mo/MCM-41 catalyst in the temperature range of 873-973 K by thermal chemical vapor deposition of acetylene. It was found that the purified carbon nanotubes have open tips and the metals of the catalyst are not encapsulated. Thus, the bamboo structure seems to grow from the base. Pore size distribution of the product is quite narrow and is in the range of 2- 5 nm similar to the catalyst pore size distribution. The results of this study demonstrate that by manipulating the template, the pore size distribution of the final product may be controlled. This way the prepared carbon nanotubes with controlled porosity are better suited for the application of gas adsorption as well as in catalyst synthesis.

The extraction-separation of lanthanum and europium ions with bis(2-ethylhexyl) phosphoric acid (DEHPA) in cyclohexane was improved by adding 12-crown-4 (12C4) to the aqueous phase as a masking agent. In the presence of this crown ether the extraction curve of lanthanum ions versus pH shifts to the higher pH region, while the curve is not influenced for the europium ions. Consequently the separation of these ions is enhanced. The treatment of the extraction data in the presence of 12C4 allows to determine the stability constant of the lanthanum-crown ether complex in the aqueous phase. The results have been compared with those reported using 18-crown-6 (18C6). This comparison shows that the improvement in the separation of La/Eu in the presence of 12C4 is the same order as in the presence of 18C6. The influence of temperature on the extraction of the studied cations in the absence and the presence of 12C4 by DEHPA in cyclohexane is studied in the range 293-305 K. This study leads to assess the thermodynamic parameters i.e. the free energy (Gº), enthalpy (Hº) and entropy (Sº) changes associated with the extraction process as well as those of the complexation of lanthanum ions by 12C4 in aqueous phase.

In this study, effects of solid concentration, temperature, and initial Fe2+ concentration on bioleaching of sulfide mineral (chalcopyrite) obtained from Sarcheshmeh Copper Mine in the region of Kerman located in the south of Iran were investigated. A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans has been isolated from a typical chalcopyrite copper concentrate of the mentioned mine. Bioleaching experiments were carried out in two batch air-lift bioreactors with recycling stream. One reactor contained 2 liters of medium and 10% (v/v) inoculum while in the other reactor, control bioleaching testes were carried out with sterilized concentrate without inoculum by the addition of 40 ml of 0.5% (v/v) formaline in ethanol. The results indicate that the efficiency of copper extraction is dependent on all of the aforementioned variables. In addition, results show that the effects of solid concentration and temperature had more effect compared to the initial Fe2+ concentration. Maximum copper recovery was achieved 70% at pH=1.5, initial Fe2+ concentration=7g/L and pulp density = 10% (w/v) in bioreactor, after 10 days.

The Michelsen stability and multiphase flash calculation by direct minimization of Gibbs free energy of the system at constant temperature and pressure, was used for systems containing gas hydrates. The solid hydrate phase was treated as a solid solution. The fugacities of all components of the hydrate phase were calculated as a function of compositions by the rearranged model of van der Waals and Platteeuw. Using this rearranged model enables the use of multiphase flash algorithm for systems containing gas hydrates. Based on this calculation for hydrate phases, we can determine amounts of hydrate formed and structure stability based on a minimum Gibbs free energy criterion

Attempts have been made for the first time to produce a friction material with thermal sensitive modulus by the inclusion of combined plastic/rubber properties of thermoplastic elastomers (TPE) as viscoelastic polymeric materials into the formulation for the purpose of increasing the damping behavior. In order to evaluate the viscoelastic parameters such as loss factor (tan δ) and elastic modulus (E’) for the friction material, dynamic mechanical analyzer (DMA) was used. Styrene-butadiene-styrene (SBS), styrene-ethylene-butylene-styrene (SEBS) and nitrile rubber/polyvinyl chloride (NBR/PVC) blend systems were used as TPE materials. However, NBR/PVC and SEBS were found to be more effective in damping behavior. All the friction materials containing TPEs exhibited more damping behavior at a wide range of temperature compared with the reference sample.

In this work, the precipitation and re-dissolution of asphaltenes were studied for an Iranian relatively heavy crude oil. A series of experiments were designed and carried out to quantitatively examine the reversibility of asphaltenes precipitation upon the change in the solvent concentration along with the temperature. n-Heptane was used as the precipitant, and a temperature range of 30 to 70C was applied to perform the temperature reversibility tests. Experiments were conducted in both porous and non-porous media. As a porous medium, a slim tube apparatus was used which is a one- dimensional model reservoir. Generally, the experiments showed that the precipitation is completely reversible for oil under study upon both composition and temperature changes

The Propose of this paper is to introduce a new model for crude oil fouling in preheat trains of crude distillation unit. The experimental results of Australian light crude oil with the tube side surface temperatures between 200 -260oC and fluid velocity ranged 0.25 to 0.4m/s were used. The activation energy of chemical reaction depends on the surface temperature has been calculated. The model includes two parts. In the first part it deals with a term for fouling formation and the second part with a term for fouling removal due to chemical and tube wall shear stress respectively. By using the proposed model for Australian crude oil based on Saleh et.al.data the fouling formation rate has been calculated and the threshold curves to identify fouling and no fouling formation zones have been drawn. Finally, a model was developed for various temperatures and shows better results in relation to available models.

A new isolated strain of Sporobolomyces ruberrimus H110 was cultivated on technical glycerol as carbon source and effect of different temperatures and pH on the growth and pigmentation was studied. The maximum concentration of total carotenoid was 3.84 mg/g including torularhodin (3.70 mg/g) and β-carotene (0.14 mg/g) using 19ºC at pH 6, but the highest amount of the maximum specific growth rate was obtained (µmax = 0.094 h-1) at 27ºC. The growth yield (Yx/s) was equal to 0.52 ± 0.01 g g-1 with a correlation coefficient value of 0.98.

Microbiological analyses of soil chronically exposed to petroleum complex compounds of some oil springs in south of Iran resulted in isolation and purification of a new native thermophilic strain which is capable to desulfurize petroleum sulfur compounds by 4-S mechanism. Dibenzothiophene (DBT) was selected as a complex sulfur compound model and many experiments were done to identify the metabolic pathway. The results of these experiments show that DBT is ultimately converted to 2-hydroxybiphenyl (2-HBP) and sulfite. This is a special metabolic pathway in that there is no effect on the carbon skeleton of organic compounds and would be ideal for desulfurization to upgrade the petroleum products because it keeps the remaining hydrocarbon molecules fully active as energy sources without any loss of their thermal units. At the next step, some physical and chemical properties of main culture were optimized as follows: 6gr/lit glucose, 4gr/lit ammonium chloride, 0.15 mM DBT, pH= 7 and temperature= 45°C. During 6 days, growing cells of this microorganism can convert 87.5% of DBT in 250 ml flask. At last, kinetic analysis has been done and Michaelis-Menten equation qualified. Equation parameters Vmax and KM calculated and data led to 0.548 mM h−1 and 0.458 mM, respectively.

In this study, the degradation potential of five polycyclic aromatic hydrocarbons (PAHs) by aerobic mixed bacterial cultures was investigated. Microorganisms were isolated from hydrocarbon contaminated soils of Shadegan wetland located in southwest of Iran. The degradation experiments were conducted in liquid cultures. PAH or PAHs concentration was 100 mg/L at the beginning of degradation experiments. After ten days incubation, the mixed culture was capable of degrading phenanthrene completely and anthracene 80%, pyrene 60%, fluorene 30%, and fluoranthene 20%, individually. Optimal temperature and pH were as 30 C and 7.0 respectively. Results showed that in samples containing a mixture of the five PAHs, fluoranthene could degrade cometabolically and the rate of degradation increased from 20 to 44%. It was observed also that PAHs degradation could be enhanced by the individual addition of yeast extract or glucose. The isolated mixed culture is valuable in bioremediation of PAH-contaminated environments