Nashrieh Shimi va Mohandesi Shimi Iran
Year:2006 | Volume:25 | Issue:2|Papers Count:14

Soluble alkaline silicates have been prepared by a novel economical method from Bazman silica (quartz) mine. The raw material (quartz) has been characterized by XRD, XRF and sectioning techniques. XRF analysis shows that Bazman mine has a pure reserves of quartz (98.9% SiO2). After milling and sieving, the quartz powder and the chosen base were reacted in presence of some additives in electric furnace. In this method, additives have an important role in decreasing the reaction temperature from T>1000 °C to 300<T<400 °C. The products have been characterized by XRD and XRF. The method is modified to achieve very high yields (>90%) at low temperatures and minimum use of additives.

By using exact hard sphere limit and the new GEhs (excess Gibbs free energy of hard spheres), an equation is derived for calculating the Gibbs free energy of mixing (DGmix). This equation is applicable to liquid-liquid equilibrium calculations of polymer/solvent mixtures. Then the liquid-liquid equilibrium equations are achieved by analytical methods. These equations are reliable for determining the phase diagrams and also UCST and LCST points of various solutions. Results obtained are relatively in good agreement with the experimental data.

In this work, partitioning of α-amylase and Bovine Serum Albumin (BSA) in aqueous two-phase systems was investigated. The two-phase aqueous systems contained polyethylene glycol (PEG) and phosphate salts. Results, show bi-nodal curves for the phases at equilibrium. The effects of molecular weight and concentration of PEG, phosphate salts, pH and presence of sodium chloride on partition coefficients of the α-amylase and BSA were investigated. The results show that by increasing the molecular weight of PEG from 2000 to 15000, the partitioning tendency of α-amylase to the top phase (or light phase, rich in PEG) nearly doubles. Also, on increasing the weight ratio of phosphate to PEG, and in the presence of sodium chloride, the partition coefficient of both α-amylase and BSA show an increase. When the weight ratio of phosphate to PEG was increased from 0.48 to 3.73 for the system containing PEG 15000 and NaH2PO4, the partition coefficient of α-amylase was increased from 0.76 to 1.44. Whereas, for the system containing NaH2PO4 and PEG 2000, on addition of 0.25 molar sodium chloride, the α-amylase partition coefficient increases 6 times. The effect of pH on the partition coefficient of α-amylase depends on the type of system. The results show that in the case of BSA the partition coefficient is higher for higher molecular weights of PEG and also for higher phosphate to PEG ratio. By decreasing the PEG molecular weight from 15000 to 2000, the partition coefficient increases 3 times, depending on the weight percent of phosphate salts. However, for systems containing BSA, addition of NaCl to the systems can cause either an increase or decrease in the partition coefficient of BSA.

Pollution is a global issue with real impacts on both the environment and human health. There are interminable debates on the absolute magnitude of these impacts and the best way to regulate them, but the simplest way to minimize pollution is not to produce it. One of the pollutants at petrochemical industry is wastes from the urea plant. Waste minimization by means of process modification and process design potentially offers a very powerful procedure to reduce pollution. In this paper, the waste treatment section of Shiraz petrochemical plant was evaluated and a modified procedure was delivered. According to this method, the concentration of pollutants reduces to less than 10 ppm. Waste treatment section has been simulated with HYSYS software and the results confirm accuracy of the procedure.

Systems of lipidic reverse micelles exist in cellular membrane. So, investigation and modeling of such systems permits one to study the invitro intracellular interactions. In this study, the solubilization of DNA in biocompatible lipidic reverse micelles was investigated. It was observed that DNA was solubilized in this system under special in vitro conditions. Circular dichroic (CD) showed the spectra of DNA with the characteristic look of supercoiled DNA with “Z” conformation. The observation of dynamic light scattering (DLS) showed a giant reverse micelle, DNA-containing reverse micelles, with a peak around 700 nm radius, with a corresponding peak around 2 nm for empty reverse micelles.

The method of pervaporation to produce high quality Rosa damascena essences from the rose extract was studied. A simple equation was developed to predict the flux of non polar, high boiling point aromatic components of the extract and was validated against experimental data published in the literature. Based on the published data of water pervaporation from PDMS membranes, the nonlinear correlation of the aroma flux with the downstream pressure was illustrated. The aroma fluxes were weak in the downstream pressure of 2000 Pa down to 500 Pa; however, by decreasing the pressure lower than 500 Pa and in particular by approaching the normal vapor pressure of the aroma, flux was increased strongly. Using the component flux, the composition of the pervaporated essence was evaluated at two pressures of 5 and 200 Pa.

Formaldehyde is a highly valuable and important chemical which is usually obtained by catalytic oxidation of methanol in fixed bed reactors. In the present work, this process is investigated in a fluidized bed reactor. For this purpose, a stainless-steel fluidized bed reactor with 22 mm diameter and 50 cm length with ability of temperature and material flow rate controls was constructed and various operational parameters effecting the reactor performance was studied. Results are compared with 3 three-phase models and the model’s precision in predicting the reactors behavior determined. The results indicate that under suitable conditions, the methanol conversion to formaldehyde increases up to 89% and by increasing the gas velocity in the fluidized bed, it is reduced, apparently due to the reduction in the residence time (reduced contact between the methanol with the formaldehyde). The analysis of the models indicate that the highest deviation belongs to the Shiau-Lin model with 23% error and the best fit is found for the model by El-Halwagi, Rafai with 10% error. Therefore, in this reaction, due to the smallness of the reactor diameter compared to it’s length, the recycle flows is found to be of less importance.

In the present work, first a brief review is done on different dynamic optimization methods. Dynamic optimization of Ethylene Dichloride (EDC) thermal cracking reactor for Vinyl Chloride Monomer (VCM) production is analyzed. This reactor is a plug flow type reactor. The objective of this project is to determine the optimum external wall temperature profile along the reactor to maximize the VCM product at the end of reactor. Differential algebraic equations derived from modeling of reactor are used as constraints in the optimization process. The problem is converted to an optimal control problem format with using the Pontryagin theory to solve it. A steepest descent algorithm is used in iterational computation. The main advantage of this method lies in the fact that a good initial guess for the decision variables is achieved that is not critical to convergence. The algorithm is then executed by coding with Pascal programming language in Delphi (ver.7) software environment. After execution, the optimum profiles of the state and control variables are analyzed as result of the program.

Terpene compounds are the main ingredients of the citrus fruit skin flavors. The most important of these terpenes is Limonene, which is a heat sensitive compound. Extraction methods based on extraction with solvents, hydro-distillation, supper critical fluid (CO2) extraction (SFE-CO2) and cold press were commonly used to extract essential oils. In this paper, the supercritical fluid extraction of bitter orange essential oil was studied using fresh bitter orange peel as raw material and CO2 as solvent. The influence of different operation conditions was analyzed in the pressure range from 100 to 300 atm and temperatures from 35 to 55 °C for a static time of 20 minutes. In these experiments, the duration of dynamic time varied from 15 to 35 minutes and also the concentration of co-solvent (methanol) was increased from 0 to 10% (v/v). Limonene was the principal component extracted, the optimum conditions for limonene extraction were P=300 atm, T=45 °C, dynamic time=15 min and concentration of co-solvent=10% (v/v). In these conditions limonene represents more than 94% of the essential oil.

Heavy metal cations exist in the industrial waste streams from factories and mines. Most of them are very toxic and harmful to human kind and its environment. In this research, removal of some cations from a simulated waste stream was investigated. Most of researches were investigated the removal of cations without presence of other cations. This paper intends to investigate the effect of the ionic interference on the heavy cations removal with synthetic zeolites A and P, which were synthesized from Iranian natural clinoptilolite. In this concern, effects of various parameters such as reaction time, temperature, and pH, concentration of the ingoing heavy metal cations (i.e. pb2+, Zn2+, Cd 2+ and Ni2+) as well as the effect of ionic interference were investigated. The results obtained from batch and column operations were shown that it is possible to reduce the concentration of these cations to an acceptable level based on the environmental standards, by using these zeolites.  

Escherichia coli ATCC11105 was immobilized in calcium alginate beads to catalyze production of 6-aminopenicillanic acid (6-APA) from penicillin G (potassium salt). Cell concentration in beads was found to be an important factor influencing the maximum velocity and specific activity of beads, and the optimum value of alginate to cell suspension ratio was 1.33. The effect of other important factors such as substrate penicillin G concentration, buffer pH, and the temperature on immobilized cell performance were also studied, and the optimal conditions were found to be 2% substrate, pH 7.5, and 45 °C, respectively. Under the optimal reaction conditions, the immobilized cells retained 90% of the initial activity after 25 repeated batches of 6 hours each.