Iranian Journal of Chemical Engineering (IJChE)

Abstract Abstract
In this work, the role of appropriate mixing for mercaptan removal from Kerosene using caustic soda has been investigated in the pilot scale. Static mixer at different condition has been used as a passive mixing tool to achieve proper mixing and consequently high performance of mercaptan removal. Two lengths of static mixer including 20 and 40 cm as well as two pitches 1 and 3 mm were considered in a straight line. NaOH was injected to the Kerosene line to remove ( convert it to disulfide) the mercaptan. The effect of mixer length, mixer element pitch at different flow rates of Kerosene, including 2, 18 and 30 mL/s was investigated on the mercaptan removal. The experimental results showed that the concentration of mercaptan in the pilot line outlet will decrease as the flow rates of Kerosene decreases. Also, at a fixed flow rate of Kerosene, increasing the length of the static mixer and decreasing its element pitch caused the mercaptan to decrease due to proper mixing. Computational Fluid Dynamics (CFD) modeling technique was employed to describe the experimental results, fluid flow pattern, and mixing performance. Qualitative predicted results of CFD modeling show a good agreement with the experimental data.

Abstract In this research samples of PVOH were synthesized at various reaction conditions (temperature, time, and amount of catalyst). First at 25˚C and 45˚C and constant catalyst weight samples of PVOH were prepared with different degree of hydrolysis at various times. For investigation of the effects of temperature, at times 20 and 40 min and constant weight of catalyst PVOH was prepared at various temperatures. Increasing the time and temperature of the hydrolysis reaction caused increasing degree of hydrolysis and reducing the molecular weight of the samples. Considering the variation of reaction condition, the effects of each parameter on molecular weight, degree of hydrolysis and conversion were investigated individually and also collective. Also, by an artificial neural network method, using experimental results (temperature, time and catalyst amount as input and conversion, degree of hydrolysis and molecular weight as output) a network by Levenberg-Marquardt (LM) back propagation with tan-sigmoid transfer function was established. Finally, the established model presented a good prediction capability and enabled us to predict the output in terms of arbitrary in puts. PVOH is an important polymer and prediction its properties during production significantly improves the quality of the products. Neural network technique is used to model the chemical processes to predict the behavior of the process. In this research we investigated the effects of various processing parameters on the properties of PVOH.

Abstract The performance of the solid acid fuel cell by CsH2PO4 electrolyte was analyzed using the present model of the electrochemical reaction and transport phenomena, which are fully coupled with the governing equations. Development of such a model requires creating the three-dimensional geometry and its mesh grid, discretization of momentum, mass and electric charge balance equation and solving the equations based on the information of electrical and electrochemical models in different areas of the cell consisting of porous electrodes, gas channels, and the solid parts like the current collector. The model equations were solved employing a finite elements technique solver of cell potential. Different parameters including current density (i), cell potential (V), cell power and concentration distribution of hydrogen, oxygen and water vapor have been investigated in this study. Also, the effect of different voltages on the concentration distribution of all the mentioned species through the cell length are taken into account. Comparing the polarization curve values with the experimental results shows a good agreement between the computed and experimental values (Maximum error is less than 4%). The results showed that there is a noticeable difference between H2, O2 and H2O concentration through the cell length subjected to various voltages. This difference was more apparent at lower voltages due to higher current density and higher consumption of species. The polarization curve is well consistent with the model and experimental data which verify the present simulation results.

Abstract Varnish and sludge formation are considered as one of the most common problems in lubrication and hydraulic systems. In order to simulate the condition of sludge formation, base stock lubricant (Group 1 API) has been selected and exposed to heat in a laboratory setup. Sludge formation process accelerated in the laboratory scale and solid liquid equilibrium data were extracted. Then solid-liquid equilibrium has been modeled using SAFT equation of state through sludge formation. The results for prediction of sludge formation showed that the absolute average deviations between experimental and theoretical results were less than 1.4%. The calculated results for solubility coefficient of the oxidation byproducts from SN100 (solvent neutral Group I) base stock in fresh (un-oxidized) oil were in good agreement with the experimental data, and average deviation between calculated and experimental data was less than 6.5%. The amount obtained for binary interaction parameter K_ij was – 0.0447. It is shown that SAFT equation of state has the capability of solid liquid equilibrium.

Abstract Longitudinal heat conduction is an important parameter in the cryogenic field, especially in cryogenic heat exchangers. In the present work, the parasitic effect of tube wall longitudinal heat conduction on temperature measurement has been studied in cryogenic laminar hydrogen flow. The effects of various parameters such as wall cold end temperature, wall thermal conductivity, gas volumetric flow, and tube wall thickness have been investigated by finite element method. The model was also validated versus the data obtained from experiments. The simulations showed that the temperature decrease in gas flow occurs in the end section of tube length. This section is independent of tube cold end temperature and causes for large temperature measurement error in laminar flows. Results showed that a few millimeters change in temperature sensor position results in measurement errors up to 80 %. The higher tube wall thermal conductivity and tube wall thickness result in higher parasitic effects of longitudinal heat conduction.

Abstract This paper addresses an experimental investigation in the hydrodynamic behavior of a modified slotted sieve tray. Slotted sieve tray (Push valve sieve tray) is a sieve tray that the push valves have been utilized on the tray deck to eliminate liquid gradients and non-uniformity of liquid distribution on the tray. The air-water system was used in an industrial scale experimental rig with an internal diameter of 1.2 m. The dry pressure drop, total pressure drop, weeping and entrainment of the modified slotted sieve tray were measured and compared with the conventional sieve tray. Weeping and pressure drop data for the tray was correlated. Results show the better hydrodynamic behavior of the modified push valve sieve tray than a conventional sieve tray. This modification can be an effective and inexpensive way to debottleneck sieve tray columns, because it has good characteristic of sieve tray and eliminate the disadvantage of sieve tray by increasing the operating window of the tray.

Abstract Guanidine hydrochloride has been widely used in the initial recovery steps of active protein from the inclusion bodies in aqueous two-phase system (ATPS). The knowledge of the guanidine hydrochloride effects on the liquid-liquid equilibrium (LLE) phase diagram behavior is still inadequate and no comprehensive theory exists for the prediction of the experimental trends. Therefore the effect the guanidine hydrochloride on the phase behavior of PEG4000+ potassium phosphate+ water system at different guanidine hydrochloride concentrations and pH was investigated in this study. To fill the theoretical gaps, the typical of support vector machines was applied to the k-nearest neighbor method in order to develop a regression model to predict the LLE equilibrium of guanidine hydrochloride in the above mentioned system. Its advantage is its simplicity and good performance, with the disadvantage of an increase the execution time. The results of our method are quite promising: they were clearly better than those obtained by well-established methods such as Support Vector Machines, k-Nearest Neighbour and Random Forest. It is shown that the obtained results are more adequate than those provided by other common machine learning algorithms.

Abstract Simulation of a process and analysis of its resulting data in both dynamic and steady-state conditions are fundamental steps in understanding the process in order to design and efficient control of system as well as implementing operational cost reduction scheme. In the present paper, steady and unsteady state simulation of Amir Kabir1, 3 butadiene purification units has been done by using Aspen and Aspen Dynamic software together with the Peng- Robinson equation of state to investigate the system responses to the disturbances.
In the unsteady state simulation mode; the flow rates, pressure, temperature and level (FPTL) were controlled by Proportional-Integral-Derivative (PID) controllers in the unit. Finally, transient responses to changes such as feed temperature, feed flow rates, steam flow rates and the duties of the re-boiler of columns in unit were gained. For reaching to purified 1,3 butadiene, sensitivity of the process to the fluctuations of feed temperature and on the duties of the re-boilers of the columns is noticeable .

Abstract In this paper, three-dimensional incompressible laminar fluid flow in a rectangular microchannel heat sink (MCHS) using Al2O3/water nanofluid as a cooling fluid is numerically studied. CFD prediction of fluid flow and forced convection heat transfer properties of nanofluid using single-phase and two-phase model (Eulerian-Eulerian approach) are compared. Hydraulic and thermal performance of microchannels are investigated according to the results of the friction factor, pumping power, average heat transfer coefficient, thermal resistance, average temperature of the walls and entropy generation. In addition, due to the CFD results, two correlations for predication of Nusselt number and friction factor are presented. Comparing the predicted Nusselt number using single-phase and two-phase models with experimental data shows that the two-phase model is more accurate than single-phase model. The results show that increasing the volume fraction of nanoparticles leads to increases the heat transfer coefficient and reduces the heat sink wall temperature, but it leads to the undesirable effect of increase in pumping power and total entropy generation.

Abstract The main focus of this study is improvement of the steam-methane reforming (SMR) process by in-situ CO2 removal to produce high hydrogen content synthesis gas. Sorption-enhanced (SE) concept is applied to improve process performance. In the proposed structure, the solid phase CO2 adsorbents and pre-reformed gas stream are introduced to a gas-flowing solids-fixed bed reactor (GFSFBR). One dimensional mathematical model is developed to evaluate the effect of adsorbents on the efficiency of SMR at steady-state condition. To prove the accuracy of the considered model, simulation results are compared against available industrial plant data. Modeling results represent that application of SE method in SMR enhances syngas production and reduces CO2 content. The reported data indicate that by overcoming thermodynamic limitations and controlling coke formation, CH4 conversion and H2 yield improve about 23% and 29%, respectively. For more investigation, sensitivity analyses of some related parameters of the pre-reformed gas are performed to predict optimum conditions. Finally, the proposed GFSFBR for the SMR process leads to higher hydrogen production and H2/CO ratio. As the last part, non-dominated sorting genetic algorithm-II is applied to perform multi-objective optimization of the SE-SMR.

Abstract In modern refineries, hydrogen is widely used for the production of clean fuels. In this paper, a new method is presented in order to use hydrogen more effectively in refineries. This new method is based on combination of linear programming with imperialist competitive algorithm (ICA) in order to optimize the hydrogen distribution network. In this new approach, optimization is performed in two levels. In one level the hydrogen network layout is proposed by ICA and in the other level the total annual cost and utility are optimized by the linear programming. Thus, the minimum cost and the optimal configuration of the hydrogen distribution network are obtained. Finally, to illustrate the application of this method two cases are studied.

Abstract In the Bayer process, the reaction of silica in bauxite with caustic soda causes the loss of great amount of NaOH. In this research, the bound-soda losses in Bayer process solid residue (red mud) are predicted using intelligent techniques. This method, based on the application of regression and artificial neural networks (AAN), has been used to predict red mud bound-soda losses in Iran Alumina Company. Multilayer perceptron (MLP), radial basis function (RBF) networks and multiple linear regressions (MLR) were applied. The results of three methodologies were compared for their predictive capabilities in terms of the correlation coefficient (R), mean square error (MSE) and the absolute average deviation (AAD) based on the experimental data set. The optimum MLP network was obtained with structure of two hidden layer including 13 and 15 neurons in each layer respectively. The results showed that the RBF model with 0.117, 5.909 and 0.82 in MSE, AAD and R, respectively, is extremely accurate in prediction as compared with MLP and MLR.

Abstract Utilization of membrane humidifiers is one of the methods commonly used to humidify reactant gases in polymer electrolyte membrane fuel cells (PEMFC). In this study, polymeric porous membranes with different compositions were prepared to be used in a membrane humidifier module and were employed in a humidification test. Three different neural network models were developed to investigate several parameters, such as casting solution composition, membrane thickness, operating pressure, and flow rate of input dry air which have an impact on relative humidity of the exhausted air after humidification process. The three mentioned models included Feed- Forward Back- Propagation (FBP), Radial Basis Function (RBF), and Feed- Forward Genetic Algorithm (FFGA). The developed models were verified by experimental data. The results showed that the feed- forward neural network models, especially FFGA, were suitable for prediction of the effect of membrane composition and operating conditions on the performance of this type of membrane humidifiers

Abstract Current drug-eluting stent (DES) technology is not optimized with regard to the pharmacokinetics of drug release, more research on the drug-eluting stent design and flux of drug release to the arterial wall is necessary. Considering a three-dimensional (3D) cylindrical mathematical model, a novel free drug mass transfer release has been formulated and applied for better estimation of the drug concentration in the tissue. The transport equations involved both convection and diffusion equations. Besides, a reversible reaction in the arterial wall was considered. The present model was solved by an appropriate numerical simulation method and the predicted results were compared with in vivo data. To find out the rate-limiting step, the time scale analysis was also applied. The obtained results showed that the binding process is more limited by convection and diffusion, where convection is the rate-controlling step. It is also demonstrated that the presented approach has advantages over the prior free drug mass transfer models, including better data prediction and satisfying mass transfer consistency.

Abstract ne"> The osmotic dehydration of three agricultural products including carrot, zucchini and turnip has been studied in this research. The effect of several factors including temperature, sample to osmotic solution weight ratio and the concentration of the osmotic solutes on the osmotic dehydration of these agricultural products were investigated experimentally. The experimental studies consist of two different concentrations (10%, and 20 W/W% for carrots, 30%, and 50 W/W% for zucchini and 40%, and 50 W/W% for turnips), two different vegetable/solution weight to weight ratios (1:10 and 1:15 for all materials) and two different temperatures (30°C and 50°C for carrots and zucchini and 40°C and 50°C for turnips). Three dietary coatings including pectin, carboxymethyl cellulose and corn starch have been selected to control the solids uptake during the osmotic process. The Azuara model proved to be the most accurate correlation to describe the kinetics of the osmotic dehydration of these three agricultural products. The root mean square error of the Azuara model for solid gain in different conditions was between 0.014 and 0.065 for carrots, 0.011 and 0.030 for zucchini and 0.008 and 0.014 for turnips. The root mean square error of the Azuara model for water loss in different conditions was between 0.008 and 0.016 for carrots, 0.003 and 0.008 for zucchini and 0.009 and 0.017 for turnips.

Abstract "> In the present study, transesterification of soybean oil to Fatty Acid Methyl Ester (FAME) was carried out in the microreactor. The system performance was investigated in the presence of hexane as a cosolvent. Furthermore, the effect of number of micromixer’s inlets on the mixing was one of the objectives in this work. For the goals mentioned above, three different experiments were done with and without cosolvent in two and three inlet micromixers under optimum conditions. Both flow pattern observations and Gas Chromatgoraphy (GC) characterization of FAME samples demonstrated that cosolvent technique and micromixer application could significantly influence the FAME yield in biodiesel production.

Abstract In this study a new and robust procedure is presented to solve synthesis of isothermal reactor networks (RNs) which considers more than one objective function. This method uses non-dominated sorting genetic algorithm II (NSGAII) to produce structural modification coupled with quasi linear programming (LP) method for handling continuous variables. The quasi LP consists of an LP by adding a search loop to find the best reactor conversions as well as split and recycle ratios which are much easier to solve. To prevent complexity and ensure optimum solution, only ideal continuous stirred tank reactors (CSTRs), plug flow reactors (PFRs) and PFR with recycle stream are considered in producing reactor networks. Also, to avoid differential equations which appear in design equations of PFR reactors, CSTRs in series are replaced for each PFR. Results show that the proposed method finds better solutions than those reported in the literature.

Abstract "> Despite numerous studies of shell and helically coiled tube heat exchangers, a few investigations on the heat transfer and flow characteristic consider the geometrical effects like coil pitch. Moreover, this scarcity is highlighted for the shell side of this type of heat exchangers. This study reports experimental and Computational Fluid Dynamics (CFD) investigations on heat transfer and flow characteristics of a shell and helically coiled tube heat exchanger. The experiments were carried out using a helically coiled tube, which was placed in a cylindrical shell. Hot and cold water were used as the process fluids on the tube and shell side, respectively. The CFD modeling technique was employed to describe the experimental results, fluid flow pattern, and temperature profiles as well as dead zones in the heat exchanger. Quantitative predicted results of CFD modeling show a good agreement with the experimental data for temperature. The effect of the coil pitch on heat transfer rate was numerically studied and it was found that the heat transfer coefficient intensifies with an increase in coil pitch. The average turbulent kinetic energy (k) for the old coil tube and twice coil pitch heat exchanger was computed as 2.9×10-3 and 3.3×10-3 m 2 /s2, respectively. This indicates an increase of about 14% in flow turbulent kinetic energy. Nusselt numbers were compared with those estimated using published correlation and a mean relative error (MRE) of 14.5% was found between the experimental and predicted data. However, a good agreement was obtained in lower shell Reynolds numbers (lower than Re=200).

Abstract > In this paper, extraction of starch and protein from potato during leaching in a batch extractor, using distilled water as the solvent, was investigated. The experiments were carried out by soaking bulk of infinite slab shape potato samples in distilled water in a temperature and agitation controlled batch extractor at the three temperatures of 30, 45 and 55ºC. A mathematical model was developed for prediction of mass transfer during the leaching process, by defining a partition factor (K) as the ratio of the concentration on the surface of the body to that in the bulk of solution. Diffusion coefficients of the solutes and moisture were obtained by fitting the experimental data of solute loss and moisture gain to the first six terms of the series solution of the mathematical model by using a non-linear regression analysis. The diffusivity values for starch, protein and moisture were evaluated between 0.273u10-10 and 1.577u10-10 m2/s, with adjustment parameter R2 values in the range of 0.941 to 0.986 and mean relative error (MRE) values between 0.092 and 0.356, respectively. Results showed that the proposed model could be used for explaining the diffusion of solutes and moisture into the potatoes, during the leaching process, with acceptable degree of goodness.

Abstract The computational fluid dynamics (CFD) simulations of gas turbine combustor were performed for CH4/air flow with swirl flames. The flow dynamics and velocity fields were numerically studied and the results compared with the experimental data obtained by laser measurements. Two-dimensional (2D) and three-dimensional (3D) simulations were performed with consideration of a two-step oxy-combustion reaction kinetics model. The Eddy Dissipation Concept (EDC) combustion model was used in the numerical analysis. The numerical results obtained by EDC model were in good agreement with the experimental data. However, an error analysis showed that the simulated mean velocity components obtained by 3-D geometry were more consistent with the experimental data than those obtained by 2-D geometry.

Abstract e"> The adsorption behavior of three amphiphilic ionic liquids (ILs), 1-alkyl-3- methylimidazolium chloride {[Cnmim][Cl], n=68}at the interface of n-butyl acetate + water system was studied with IL concentration range of 1.00×104-1.00×101 mol·dm3 and temperature range of 293.2-318.2 K. The ILs behave as strong surfactants in this chemical system and significantly reduce the interfacial tension with the order of their alkyl chain length and is consistent with their hydrophobicity nature. An almost linear decrease of interfacial tension with temperature was also relevant. The experimental data were satisfactorily reproduced with Szyszkowski equation, implying an ideal ILs adsorption. In this regard, the Langmuir maximum interface excess and equilibrium adsorption constant were obtained at different temperatures for each IL. Accordingly, effectiveness of adsorption and adsorption tendency increase with the alkyl chain length. At the saturated interface, increasing temperature leads to declining Langmuir maximum interface excess due to disrupting surrounding water molecules around ILs hydrophobic portions. However, adsorption tendency of ILs increases slightly with temperature.

Abstract The effective parameters on Ohmic heating in static system containing biosolid-water were studied. The effects of distribution of particles, salinity and electric field strength on electrical conductivity, profiles of temperature, heat generation have been investigated. The experimental data verification with simulation results using computational fluid dynamics (CFD) method were carried out. Governing equations (heat transfer and electrical equations) were discretized with finite element method. The experimental data and CFD results showed that in Ohmic heating process, the current diffusion in all the products is faster than traditional methods and the diffusion rates are equal for both biosolid-liquid phases.

Abstract > The hydrodynamic characteristics of dense conical fluidized bed were investigated experimentally and numerically. Experimental studies have been carried out in a bed containing TiO2 particles belonging to A/C boundary of Geldart's classification with a wide particle size distribution. Pressure measurements and an optical fiber technique allowed determining the effect ofhigh bed particles loading on the minimum fluidization velocity, local solid volume fraction and solid velocity. Two-fluid model approach with three different drag models and boundary conditions (BCs) consisting ofno-slip, partialslip and free-slip BC is presented for the numerical predictions. In this paper, we show the Gidaspow drag function with k-Â turbulent model by applying the partial-slip BC can improve the numerical results at high particle loading.

Abstract The distillation process remains as the most common method ofseparation in chemical process industries. The energy used from this process accounts for an estimated 3% of the world energy consumption. The Dividing-Wall Column (DWC) for separation of multi-component mixtures has recently become a major concern ofindustries. The design ofDWC is based on Thermally Coupled Distillation System (TCDS) eliminating some of the operational equipment. This paper presents the results of simulation of a DWC by using 3-simple sequence column model based on shortcut method by a commercial chemical Engineering software for purification of1,3 butadiene unit. From the results, it is shown, by using a DWC instead of two conventional sequential column, the heat duties ofboth the condenser and the reboiler are reduced about 28.5% and also desirable purity ofthe key-components for the case ofstudy have been achieved.

Abstract In this paper, drag coefficient of infinite quadralobe catalytic particle with non-circular cross sections has been investigated by Computational Fluid Dynamics (CFD) methods and for this purpose FEMLAB Multiphysics V2.3 based on finite element methods have been used. A new simple correlation for drag coefficient of infinite quadralobe particle
has been established over the range of Reynolds numbers from 0.01 up to 1000. A comparative study has been made between the numerical results of this study and the available data in the literature. The predicted drag coefficient of infinite cylinder shows good agreement with experimental data within a converging quantitative error of less than 7% up to Reynolds number of 1000. The drag coefficient results for cross flow on infinite quadralobe particle shows higher value in comparison with cylindrical particle. In addition, influence of different number of particles (single, two, three and four particles) and orientation angle of particles on drag coefficient have been investigated.