مجله پژوهش نفت
پیاپی 59 (بهار و تابستان 1388)

In the present study, the variation of rates of initiation, propagation, and termination reactions as well as the variation of reactants (including monomer and initiator) were investigated by using stochastic methods. The concentration of free radicals was also depicted as a function of monomer conversion. The results show that the concentration of monomer decreases linearly with conversion while the concentration of free radicals is an exponential function of reaction time. In fact, quasi-steady state assumption is not valid for batch systems in the absence of gel effect and the concentration of free radicals changes during the reaction. Considering the fact that the concentration of initiator exponentially falls during the reaction, the concentration of free radical also drops as the polymerization proceeds. Finally, the rate of initiator decomposition declines exponentially while propagation rate drops linearly.

An industrial furnace could be considered as a three dimensional enclosure. The zonal analysis of radiative heat transfer modeling is used for finding the three dimensional temperature distributions. Exchange areas are determined by simplified numerical integration in three dimension for surface-surface, surface-gas, and gas-gas zones for absorbing and emitting media. The effects of some important parameters in the furnaces are described. It is shown that the zonal method is a useful numerical method for considering multi-dimensional thermal performance of gas-filled enclosures.

In this paper, mass transfer modeling of non-spherical drops, when the drops are a segment of an ellipse, was carried out. Predicted results obtained by the new and Handlos-Baron models and experimental data were compared. The dimensions of the non-spherical drops were optimized by using the experimental data. In this work, the Olney’s model using Klee & Treybal drop terminal velocity correlations were utilized to model the hydrodynamics of the column. Mass transfer of the column was also modeled using forward mixing, and the required drop sizes were obtained from experimental data. 95% confidence limits in predicting the plug flow number of transfer units using Handlos-Baron and new model were calculated and the values of this parameter are 32.78% and 11.11% respectively.

Carbon steel has been widely used in oil and petro-chemical industries, and thus, its corrosion is one of the serious problems encountered in these industries. Application of corrosion inhibitors can be considered as an effective way to reduce the degradation of equipment in these industries. Benzimidazole derivatives are heterocyclic organic compounds, which can be used successfully as corrosion inhibitors for carbon steel in acidic media. In this study, the inhibitive properties and adsorption ability of two derivatives of benzimidazole, namely 2-mercaptobenzimidazole and 2- methylbenzimidazole, as well as their effect on corrosion resistance of carbon steel in 1M HCl solution was investigated. The potentiodynamic polarization readings were carried out in HCl solution containing inhibitor concentrations of 0, 50, 100, 150, 200 and 250 ppm. The results showed that the 2-mercaptobenzimidazole was more efficient than 2-methylbenzimidazole. The 2-mercaptobenzimidazole decreased the corrosion rate of carbon steel 88% at 250 ppm, while this value was 54% for 2- methylbenzimidazole at the same concentration. The adsorption of both inhibitors obeys the Langmuir isotherm. The standard free energy of adsorption calculated for both derivatives indicated on physical adsorption. By considering the Tafel slops and equilibrium potentials, the inhibition mechanism of both inhibitors was estimated to be of mixed type

A series of ethylene-propylene-2-ethylidenebicyclo [2.2.1] hept.5-ene terpolymers (EPDM) have been prepared using a VOCl3/Al2Et3Cl3 catalyst under various Al/V ratios and diene concentrations via solution polymerization and characterized by FTIR, Mooney viscosity (ML1+4,125oC), and thermal gravimetery analyzing. The polymerization yield was seen to increase with augmentation of the Al/V ratio and diene concentration and pass through a maximum of about 200 gr polymer/g V. On the other hand, Mooney viscosity decreases with an increase in the two latter parameters. Increasing solvent to monomer ratio increased polymerization yield while it decreased Mooney viscosity. Accordingly, an optimum amount of solvent to monomer ratio (4:1 in mass) was found. One advantage of these polymer systems is that all the measured Tg property remained constant around 232-240 K in the range of incorporated ethylene and diene concentration. It has been observed that when Al/V ratio decreases and diene concentration increases, there is an increment in ethylene incorporation (40-60%), and the results have been compared with the characteristics of two commercial EPDMs (Herlen 563, Vistalon 7500).

Heat transfer is a very important phenomenon for modeling heat equipment and scale up of slurry bubble reactors. For studying local heat transfer coefficient in slurry reactors, a column of 30 cm diameter and of about 3 m height which meets industrial reactor region was designed and constructed. In the experiments, 50-μm SiO2 powder having the same size of the catalyst of Fischer-Tropsch process was used as the solid phase and paraffin and air were used as the liquid and gas phases respectively. A specially designed heat transfer probe was used for measuring local heat transfer which consists of an electrical heat source element and two thermocouples for probing surface and fluid temperature measuring. By using this probe, local heat transfer coefficient was measured and the influence of superficial gas velocity and solid concentration were investigated. In all experiments, slurry phase height to the column diameter ratio was 4. The results showed that increasing the gas velocity from 2 to 25 cm/s leads to an increase in heat transfer coefficient by about 65%; also an increase in the solid concentration increases heat transfer rate.

In this research, the conversion of maleic anhydride to tetrahydrofuran was investigated in a slurry reactor system over bifunctional catalysts composed of Cu/ZnO/ZrO2 and various zeolites. Bifunctional catalysts were prepared by coprecipitating sedimentation method and characterized by surface area and XRD analyses. The experimental results showed that the bifunctional catalyst composed of Cu/ZnO/ZrO2 and H-Y zeolite is the optimum catalyst for the production of tetrahydrofuran from maleic anhydride. Also, it is concluded that the best ratio of hydrogenation catalyst to dehydration catalyst is 3:1. Under this situation, maleic anhydride conversion and tetrahydrofuran selectivity are 100% and 65% respectively. In all experiments, stabilities of catalysts were well. Ultimately, it is deduced that Cu-ZnO-ZrO2/H-Y bifunctional catalyst has a good performance in the production of tetrahydrofuran from maleic anhydride

Graft copolymers of acrylonitrile (AN) styrene (SM) onto polybutadiene (PB) were prepared via seeded emulsion polymerization method using a redox initiator system, cumene hydroperoxide-tetrasodium pyrophosphate-ferrous sulfate-dextrose. The effects of initiator, chain transfer agent, reaction temperature, monomer dropping frequency, polymer to grafting monomer ratio on the grafting efficiency and degree of grafting were investigated. It was found that grafting efficiency and degree of grafting depended upon the concentration and initiator dropping frequency; it increased as the concentration and dropping time were increased. The grafting efficiency and degree of grafting increased by increasing monomer dropping frequency. The amount of free SAN was found to decrease concurrently by increasing monomer dropping time. The optimum temperature and monomer addition time for grafting reaction were 70°C and 120 minutes respectively.