Iranian Journal of Chemical Engineering (IJChE)

Abstract Desmopressin acetate is a potent synthetic peptide hormone. A more acceptable route of Desmopressin acetate is a potent synthetic peptide hormone. That is administered via parenteral, intranasal, and oral routes. A more acceptable route of administration with potentially good bioavailability could be offered by transdermal delivery. The present work reports on the development of water-in-oil (w/o) microemulsions for the transdermal administration of desmopressin acetate. A water-in-oil nano/submicron emulsions for transdermal administration of desmopressin developed. Its skin penetration profiles determined using Franz-diffusion cell. Pseudo-ternary phase diagrams for emulsion regions constructed. Effects of hydrophilic-lipophilic balance (HLB), ratio of surfactants and co-surfactant mixture to oil phase (Smix/oil), and ratio of surfactants to co-surfactant (S/Cs) on skin flux evaluated.
Skin flux was increased when S/Cs and Smix/oil were decreased, and HLB was increased. Optimized formulation was obtained as: HLB=8, S/Cs=3 and Smix/oil=5.4, with average particle size of 69nm. The optimized nano/submicron emulsions increased desmopressin skin flux 4.45 fold relative to drug solution.

Abstract Abstract
Gas to liquid (GTL) process involves heterogeneous catalytic chemical reactions that convert synthesis gas to hydrocarbons and water vapor. A three phase reactor, called Low temperature Fischer-Tropsch (LTFT) is commonly applied for GTL process. In this reactor the gaseous phase includes the synthesis gas, light hydrocarbons and water vapor, the liquid phase is a mixture of the heavy hydrocarbons, and the solid phase is composed of the catalyst and the waxy products. The presence of the liquid phase in LTFT reactor causes mass transfer restriction, affecting the reaction conversion. In this work a numerical simulation of the LTFT fixed bed reactor in trickle flow regime has been accomplished to understand the impact of the liquid phase on the reactor performance. For this purpose, we have developed an axisymmetric two-dimensional multiphase heterogeneous model, where contain carbon monoxide and hydrogen, are transferred into the liquid phase. The reactor consisted of a shell and a tube that was filled with the spherical cobalt catalyst. The reaction conditions were as follows: the wall temperature was 473 K, pressure was 20 bars and a gas hour space velocity (GHSV) was 111 Nml.g_cat^(-1).h^(-1). The numerical simulation results proved the negative impact of the liquid phase on the reaction conversion. The model predictions were evaluated against the reported experimental data and also compared with the result of a numerical pseudo-homogeneous model. It was found that applying the heterogeneous model instead of the pseudo-homogeneous model clearly decreases the deviation of the numerical results.

Abstract Pharmaceutical pollutants are one of the most important issues of modern life and their negative effects on the environment and human health are undeniable. In the present work, the effectiveness of the photocatalytic process was studied by two semiconductors (ZnO and V2O5) in order to remove the Diclofenac Sodium completely under solar irradiation. The study examined the impact of parameters such as the high-level range concentration of pharmaceutical, catalyst dosage, pH changes and time on the photodegradation of Diclofenac Sodium in aqueous solution. All the experiments were carried out under solar and UV irradiation to compare between the two circumstances. The optimum conditions obtained for photodegradation of Diclofenac Sodium were: reaction time 180 min, zinc oxide and vanadium pentoxide = 1 g L-1, Diclofenac Sodium concentration = 300 mg L-1 and pH = 4. In addition, chemical oxygen demand removal was investigated for all the conditions and total degradation was observed by V2O5 under optimum conditions. The study of reaction kinetics was carried out at optimum conditions and approximately a pseudo-first order kinetic model was in agreement with experimental results in each case.

Abstract In this study, nanoporous silica aerogel and silica aerogel-activated carbon composites have been synthesized using a water glass precursor by cost effective ambient pressure drying method. Equilibrium and kinetics of benzene and ethyl benzene adsorption on silica aerogel and its composites have been measured in a batch mode at tree weights of adsorbent. For the first time, the experimental data have been fitted with intra-particle diffusion model for determining of diffusion coefficients. The saturation adsorption capacity of benzene and ethyl benzene vapours was 2033 mg.g-1 and 458 mg.g-1 respectively. The components uptake curves have been described by mathematical models of pseudo first order and pseudo second order models. It has been found that the pseudo first order model fits the experimental data better than the pseudo second order model. Also, the pseudo-second order model could be used for modeling of benzene adsorption over silica aerogel and silica aerogel-2% wt. activated carbon composite at the beginning of adsorption process. The diffusion coefficients of benzene and ethyl benzene within the silica aerogel were in the range of 〖2.16×10〗^(-14) - 〖6.66×10〗^(-13) m2.s-1 and 〖3.65×10〗^(-13) - 〖1.95×10〗^(-12) m2.s-1, respectively.

Abstract Nowadays, forward osmosis (FO) with many advantages in water treatment, are so attractive for researchers and investigators that the studies are going to optimize and increase its efficiency. However one of the most controversial operating malfunctions of FO process is fouling that limits the FO global application. In the following research, vertically aligned carbon nanotube (VACNT) on alumina membrane is introduced with high water permeability and less biofouling potential in forward osmosis for seawater osmotically dilution systems. VACNT membranes were prepared via pyrolysis of polymer into the pores of alumina. The effect of the temperature of pyrolysis process on CNT’s structure are assessed which indicated crystallinity of the CNTs increase in higher pyrolysis temperature of 800 °C. A small scale setup is designed for FO analysis and measurements of biofouling, flux and the effect of osmotic pressure were measured. Furthermore, all analysis were compared with commercial TFC membrane and results demonstrated that VACNT membrane has 40% less biofouling potential and 2 times better flux results.

Abstract The mechanism of air pollutant generation during combustion of gaseous fuels is simulated with ASPEN Plus process simulator release 9.1 -3 (1994). Based on the concept of minimization of total Gibbs free energy of the system, adiabatic flame temperatures for several stoichiometric fuel/air mixtures are calculated. Analysis of combustion products including air pollutants with concentrations as low as 1 ppb is carried out and compared with previous works. Sensitivity analysis to study the effect of changing reaction temperature and fuel/air ratio on pollutant concentrations are also carried out and the results are discussed. Detailed tables and various graphical resul ts are presented, demonstrating the powerful capabilities of ASPEN Plus in combustion modeling and air pollution studies.

Abstract This paper presents the results of an investigation into the treatment of Tehran Refinery effluents in UASB reactors. Four pilot-scale UASB reactors were built with similar dimensions, each with a volume of 45.78 1, and operated in parallel at 37 °C. The sludge seed was prepared from the waste activated sludge of the wastewater treatment unit of the refinery. The organic loading rates were gradually increased from 0.05-0.1 kg COD/m3.d to about 2, 1.5, 0.5 and 1.5 kg COD/m3.d for reactors 1 to 4, respectively, at an influent COD of about 220 mg/l. This is in accordance with hydraulic retention times of 2.5, 4.5 and 8.5 hours for reactors 1 to 3 and 4.5 hours for reactor 4. Methanol was initially added to the reactors in order to increase the microbial activity of the sludge, except for the last one, in order to compare the effect of methanol on start-up. The addition of methanol was stopped after 37 days and the reactors were operated for another 30 days. At this stage, the influent COD was varied between 50-300 mg/l. The results show that the COD removal efficiencies of the reactors are around 30-50%. However, when the influent COD increases above 200 mg/l, the COD removal efficiencies increase up to 70%. It is found that methanol has no significant effect in shortening the start-up period in this case. Scanning Electron Microscopy (SEM) examination and image analysis of the granules of sludge were also performed in order to investigate the structure of granules and the size distribution. Analysis of the biogas shows more than 90% methane content. The results obtained in this research are promising for the anaerobic treatment of refinery wastewaters in UASB reactors.

Abstract  A case study is presented in which two modifications of activated sludge treatment of complex chemical wastewater are experimentally compared: a combination of common activated sludge with powdered activated carbon treatment (PACT), and bioaugmentation of activated sludge treatment (BAST). Industrial wastewater of Pars Oil Refinery that was passed through an oil recovery stage was used to investigate the effect of furfural on two treatment processes in the range between 100-2000 ppm. Furfural was added manually. For comparison, furfural, COD, MLSS (Mixed Liquor Suspended Solids) concentrations and SVI (Sludge Volume Index) were measured daily. The results show a little higher COD removal efficiency in PACT system and the same furfural removal in both methods. But, it should be mentioned that at low HRT (Hydraulic Retention Time), BAST system showed better results in both furfural and COD removal than PACT system. SVI measurement shows that settability of effluent sludge in BAST system was always better than in PACT system. Because of rapid growth of microbial biomass in BAST system, the MLSS concentration in this modification was higher than in PACT system and in this way, BAST system has a lower requirement to return sludge than PACT system. Finally, it could be concluded that BAST system may be an attractive alternative to existing PACT system and if the former is used, it will result in both high performance and optimum conditions with economical operation.

Abstract ge-newline"> One method for conversion of methane to more valuable products is by non-catalytic gas-phase oxidative coupling of methane (OCM), through which methane is converted into ethylene. The product of this process is ethylene, accompanied by acetylene, ethane, a small quantity of three carbon compounds as coupling products, and carbon oxides due to complete oxidation of hydrocarbons. The kinetic model proposed for the OCM process consists of 75 elementary reactions and 23 chemical species. In previous studies, the reactor-kinetic modeling of this process, was implemented in a laboratory micro-reactor at constant temperature and pressure. Considering that this process proceeds with severe variation in the enthalpy, in the present study, in addition to isothermal, the operation of the system has also been modeled for the adiabatic state. The modeling has been carried out in a tubular reactor system. Comparison of the qualitative and quantitative results of the model with experimental data at constant temperature shows that the proposed kinetic model predicts the experimental results properly. Furthermore, in the present study, the effect of various parameters on the operation of the system has also been examined. These studies have been performed in the following ranges of pressure, temperature and CH4/O2 ratio respectively: 1≤ P ≤ 10 (bar), 950≤ T≤ 1100 (K), 4 ≤ CH4/O2 ≤ 10. It has been shown that, by increasing the temperature, the reaction rate increases. Raising the total pressure of the system causes an increase in methane conversion and selectivities of desired products as well as the reaction rate. On the other hand, increasing the residence time in the reactor will result in conversion of desired products to undesirable ones. Finally, it is shown that by decreasing the ratio of methane to inlet oxygen, conversion of methane increases, selectivities of the desired products decrease and the heat released during the reaction rises.

Abstract Deposition of colloidal particles onto surfaces is usually assumed to follow the Derjaguin-Landau-Verwey-Overbeek (D.L.V.O.) theory for colloidal stability. In the work presented here the D.L.V.O theory is extended to include the case where the surface is electronically conducting. The effect of application of an electric field to the surfaces on the rate of deposition of 5.4 µm colloidal particles is simulated.

Abstract

Abstract Analytical gas-permeation models for predicting the separation process across  membranes (exit compositions and area requirement) constitutes an important and necessary step in understanding the overall performance of  membrane modules. But, the exact (numerical) solution methods suffer from the complexity of the solution. Therefore, solutions of nonlinear ordinary differential equations that govern the performance of the membrane modules for gas separations by approximate and asymptotic methods are useful in the design and comparison of processes. In this work, the asymptotic methods were applied for predicting the performance of nanometric tubular ceramic membranes in the separation of binary gas mixtures with cocurrent and countercurrent flow patterns. Also, the exact (numerical) solutions of the governing equations using the fourth order Rung-Kutta technique were proposed. The comparison of the results showed a good agreement between the exact solution and asymptotic analysis methods over the whole range of selectivities (). Because, the asymptotic curves into the former () and latter () boundaries had a suitable overlap with each other to cover the whole range of selectivities. The accuracy of this method was verified by a comparison of the predicted results with different literature experimental data and mathematical models. This result suggests the use of the asymptotic analysis method to provide excellent shortcut, preliminary design information.
 
 
 

Abstract > The motion and shape of a flattened drop and bubble through another continuous liquid phase (conveying phase) are investigated experimentally, using a narrow gap HeleShaw cell. Seven different liquid-liquid systems were tested. In all cases the continuous phase was the more viscous wetting phase. A number of observations on the shape and motion of the elongated flattened drops are noted and discussed. In the capillaritydominated (Ca<1.69×10-6) region, the irregular shape of the discontinuous phase drops changed with time and position, and the drop velocity was much lower than that of the conveying phase. Three different shapes of stabilized elongated drops were observed at higher Capillary numbers. The conditions that lead to the appearance of stabilized elongated drops are discussed. The velocities of these stabilized elongated flattened drops were 2 to 4.7 times higher than that of the conveying liquid. A correlation to predict the elongated flattened drop shape as a function of the dimensionless parameters governing the system is developed based on the experimental results.

Abstract The ternary system of Portland cement-microsilica-limestone has been studied by investigating its set and strength behaviours. A number of different cementitious systems comprised of 0, 10, 15, 20, 25, and 30% limestone powder and 0, 4, 6, 8, 10, 12, 14, and 16% microsilica were designed and prepared. The cementitious systems were then characterized by determining their relative workability and measuring their initial and final setting times and also their 7- and 28-day compressive strengths using paste specimens prepared at a constant W/C-ratio of 0.38. Total 77-day shrinkage of the systems was also measured. The obtained results reveal that both 7- and 28-day compressive strengths increase with increasing microsilica up to 12% and decrease with increasing the percentage of limestone powder. A comparison of the results confirms the possibility of replacing Portland cement by a proportioned mixture of microsilica and limestone powder for enhancing the strength behaviour or producing composite cements containing relatively high proportions of limestone powder with no loss in 7- and 28-day compressive strengths compared to plain cement.

Abstract The influence of different factors on the asphaltene stability in three iranian crude oils was evaluated. Compositional studies and structural characterization of resins and asphaltenes were carried out in order to study a possible relationship between these properties and asphaltene deposition behavior. Low hydrogen to carbon ratios and high aromaticities were the main characteristics of the asphaltenes from more unstable crude oils. According to these results, the stability behavior of asphaltenes was influenced strongly by their structural characteristics. Colloidal stability indexes such as the (aromatic+resins)/(asphaltene+saturates) ratio and (aromatics+resins)/ asphaltene ratio do not play a key role in the asphaltene stability for the studied crude oils.

Abstract Prediction of the dynamic crossflow ultrafiltration rate of a protein solution such as milk poses a complex non-linear problem as the filtration rate has a strong dependence on both the solution physicochemical conditions and the operating conditions. As a result, the development of general physics-based models has proved extremely challenging. In this study an alternative dynamic neuro-fuzzy model for milk ultrafiltration that describes the variation in dynamic permeate flux decline with temperature, transmembrane pressure (TMP), fat percentage, pH and molecular weight cut off (MWCO) has been developed with the experimental data of the pilot spiral wound membrane test rig. By increasing the temperature, TMP, and pH the permeate flux is increased, and by increasing fat concentration the permeate flux is decreased. The MWCO variation indicates a paradoxical permeate flux. Additionally, a hybrid physical model for dynamic prediction of total resistance in the milk ultrafiltration by combination of two neuro-fuzzy (ANFIS) models and a physical model (BLA model) is developed. By increasing the TMP and fat concentration, the total resistance is increased. But by increasing the pH and temperature, the total resistance is decreased. Also, MWCO variation indicates a paradoxical total resistance value.

Abstract The present work is concerned with the development of a new algorithm for determination of the equilibrium composition of gaseous detonations. The elements balance equations, and the second law of thermodynamics (i.e., the minimization of the Gibbs free energy of products), are used to determine the equilibrium composition of the detonation products. To minimize the Gibbs free energy with traditional deterministic methods one needs to solve a set of highly nonlinear equations. The numerical methods in the existing equilibrium codes suffer from several drawbacks such as the divergence possibility in some equivalent ratios, and the possibility of converging to a local relative minimum in the minimization process. To overcome these drawbacks, a genetic algorithm is presented in the present study. Converging to the global minimum of Gibbs function in all equivalent ratios, and having a reasonable CPU time are the notable aspects of the proposed algorithm.
 
 

Abstract Implicit pressure-explicit saturation method (IMPES) is widely used in oil reservoir simulation to study the multiphase flow in porous media. This method has no complexity compared to the fully implicit method, although both of them are based on the finite difference technique. Water coning is one the most important phenomenon that affects the oil production from oil reservoirs having a water drive source. Since the water coning affects final oil recovery, identification of this phenomenon is very important. In order to study this phenomenon, one should determine the critical production rate, the breakthrough time and watercut percentage. The scale of the problem hinders the numerical simulations, IMPES included, for a long running time. A corrected IMPES method is used here to overcome the long running time problem by choosing larger the time step for the coning problem. A water-oil phase flow system in the cylindrical coordinate that is commonly used to simulate water coning phenomenon is solved by the corrected IMPES method. The validity of the model is checked against Aziz and Settari’s model, which is based on a complicated fully implicit method.  The effects of the production rate and the thickness of the oil zone on the breakthrough time have been investigated. The results were found to be in good agreement with the results of previous studies.

Abstract Synthesis of Dimethyl ether from methanol was investigated over H-ZSM-5 and promoted H-ZSM-5 catalysts employing Mg, Na, Zr, Al and Zn components. All samples were characterized by AAS, BET, XRD and TPD analyses. Results of TPD
analysis indicated that the number of weak strength acid sites increased on the surface of Na, Zn and Mg modified H-ZSM-5, while the number of medium strength acid sites increased on the surface of Zr and Al modified H-ZSM-5. Zr- modified H-ZSM-5 zeolite exhibited higher activity (94%) and selectivity (99%) than other materials while all modified catalysts exhibited good stability. Ultimately, it was concluded that production of dimethyl ether from methanol occurred
on acidic sites with medium and/or weak strengths. In this direction, an optimum catalyst for dehydration of methanol to DME with high conversion, selectivity and stability was developed.

Abstract The aim of the present work was to evaluate the effect of soy protein isolate (SPI)-gum arabic (GA) composite on the stability of beverage emulsion prepared as the orange oil-in-water (O/W) emulsion. Response surface methology (RSM) was used to study the influence of the two independent variables, each at three levels (homogenization speed
as x1 (1500, 15700, and 30000 rpm) and GA:SPI ratio as x2 (1, 0.6, and 0.2) on the two dependent variables namely, size of the emulsion droplet (EPS) as y 1 and emulsifying activity (EA) as y 2 . The results were discussed on the two empirical models obtained. Analysis of variance (ANOVA) showed a high coefficient of determination (R2 ) value of 0.937 and 0.979 for EPS and EA, respectively, ensuring a satisfactory adjustment of the second-order regression model with the experimental data. The negative sign for the regression coefficient of x1, indicated that size of the emulsion droplet increased with the decreased level of factor x1 from 30000 to 1500 rpm, while EA increased with increased levels of factor x1 . Thus, GA: SPI ratio with the lowest amount of GA along with the homogenization speed at high level, gave the smallest size of emulsion droplet (1μm). This size corresponded to the high emulsifying activity and stability. Sodium chloride and freeze-thaw cycling are two environmental factors affecting emulsion stability. Results of freeze-thaw cycling test showed a large decrease in the EA of the sample prepared with a low level of SPI:GA ratio and no dependence of the EA on the NaCl concentrations in the range of the tested levels was observed (50-150 mM). Long-term storage stability test (storing the emulsion samples at 4, 16, and 30ºC each for 8 days) showed the size of the emulsion droplet increased with the storage time. Results of use of SPI as a readily available plant source of protein for preparation of the encapsulant for orange oil-emulsion were encouraging, especially when one considers the dependence of the beverage industry on the unreliable source of supply of GA. RSM was successfully applied for the modeling of the emulsion preparation.

Abstract

Abstract In the present study a mathematical model is developed in order to examine the effects of heat and mass transfers on removal efficiency of particulate matters in venturi type scrubbers. The governing equations including the variations of the particulate concentration, gas temperature, droplet temperature, diameter, and velocity are obtained based on the conservation laws and are solved numerically. In order to validate the model, necessary data was measured and collected in a commercial cement plant that uses these types of scrubbers in air pollution control applications. A good agreement between plant data and the model predictions is noticed in general. The results obtained from the model reveal that the existance of temperature difference between the gas and the liquid droplets decreases the overall removal efficiency of particulate matters. This is due to sudden reduction ofrelative velocity between the gas and droplets which is resulted from the existence ofheat and mass transfers between the two fluids, especially in the throat section. In addition, the effects ofvarious operating parameters on the extent ofreduction in the removal efficiency are examined. This study confirms that in most industrial applications ofventuri scrubbers it is necessary to use a direct or an indirect cooling tower in order to decrease the gas temperature before entering the venturi.

Abstract One limitation in the use of hydrophilic polymers as implantable devices is their inherently poor mechanical strength. Using interpenetrating polymer networks (IPNs) consisting of both hydrophilic and hydrophobic networks is an effective method to strengthen these polymers. In this work, a series of poly(dimethyl siloxane) /poly(acrylic acid) sequential IPNs was synthesized and the polymerization kinetics of acrylic acid in the presence of ethylene glycol dimethacrylate as the crosslinker was investigated using ampoule polymerization experiments and DSC analysis. The results from conversion measurements revealed the occurrence of gel effect during acrylic acid polymerization. The properties of the produced IPNs including swelling, morpho-logical, and mechanical properties were also investigated.

Abstract Catalytic combustion of lean premixed mixtures of biogas/air and biogas/hydrogen/air on Pt in a packed bed reactor has been investigated using detailed surface chemistry. Non-equilibrium, adiabatic and one dimensional flow assumptions have been adopted for simulation of the reactor. The interaction between two phases of porous medium is incorporated into the model via heat and mass transfer factors. Radiation heat transfer has been taken into account using effective thermal conductivity. All thermo-physical properties of the gas phase are considered to be temperature and concentration dependent. Two energy equations for two phases of the porous medium along with species transport equations are solved in the model. A mechanism of multi-step surface reactions, suitable for oxidation of lean mixture of methane/air, has been adopted from literature and employed for simulations. This mechanism includes 36 single step reactions with 11 surface and 6 gas phase species. Simulations have been conducted for oxidation of different biogas/air mixtures for the inlet temperature range of 700K to 900K at atmospheric pressure. The effect of the addition of hydrogen to the biogas/air mixtures has also been investigated. It is shown that hydrogen improves oxidation of methane.

Abstract A static to dynamic approach to modeling Asphaltenes has been developed and validated. A new algorithm for static asphaltene modeling uses a multi-solid thermodynamics approach where the equality of fugacity for each component and phase is applied at equilibrium conditions. This is required for minimizing the Gibbs free energy. The fractal distribution function used for the splitting and characterization of heavy components provides accurate results. The precipitation and re-dissolution of asphaltenes are investigated for a relatively heavy crude oil from an Iranian field. A
series of experiments are designed and carried out quantitatively to obtain the permeability reduction in a slim tube. Using a dynamic reservoir simulator, a 3-dimensional asphaltene model is developed to simulate the precipitation, flocculation, deposition and its impact on permeability in a slim tube. With this approach, the asphaltene is defined as a set of component(s) that can precipitate depending on their molar percentage weight in the solution. The simulated permeability reduction due to asphaltene deposition shows good agreement with our experimental data.