Iranian Journal of Chemical Engineering (IJChE)

Abstract This study evaluates the effectiveness of the aluminum sulfate coagulation in treating the wastewater from thermal power plants to efficiently remove pollutants. Key operational parameters—the pH of the wastewater (5 to 9), dosage of coagulant (10 to 40 mg/L), and mixing time (10 to 30 minutes)—were systematically investigated for their impact on the removal of chemical oxygen demand (COD) and total dissolved solids (TDS). The coagulation mechanism involves the hydrolysis of aluminum sulfate, generating charged species that neutralize particle charges, followed by adsorption, bridging, and floc formation, which together promote the aggregation and sedimentation of pollutants. Utilizing the response surface methodology (RSM) with the Design Expert software, the process was optimized, revealing that a pH near 7.4, dosage of approximately 40 mg/L of the coagulant, and mixing time of around 22 minutes maximize the treatment efficiency. Under these conditions, the removal of COD and TDS reached 71.1% and 97.3% respectively, demonstrating the potential of this approach for the sustainable and cost-effective wastewater treatment in thermal power plant operations.

Abstract The optimization of membrane bioreactor (MBR) equipped with a submerged flat-sheet polyethersulfone (PES) membrane for the wastewater treatment from dairy processing facilities was investigated. The effects of key parameters such as the hydraulic retention time (HRT, from 8 to 16 hr), mixed liquor suspended solids (MLSS, 3000 to 9000
mg/L), and rate of aeration (Qair: 1 and 2 L/min) on COD removal efficiency were systematically investigated. Through the response surface method (RSM), the maximum the COD removal efficiency of 92.67% was obtained under the optimal conditions of HRT: 13.83 hr, MLSS: 7239.84 mg/L, and Qair: 1.75 L/min. The statistical analysis identified MLSS as the most influential factor in the COD removal efficiency, accounting for 30% of the variation, followed by HRT with
16%, and the rate of aeration showing the least impact of 8%. A notable reduction in the UV absorbance of wastewater between 200 and 500 nm, after treatment using MBR under optimal conditions, signified successful targeting of toxic or colored pollutants. Finally, a mechanism for the wastewater treatment in MBRs, which included the biological degradation, adsorption on the surface of biomass and membrane, and separation through membrane filtration, was proposed.

Abstract The preparation of ethylcellulose (EC) nanofibers (NFs) by the electrospinning method was optimized by Taguchi design. A Taguchi design was performed for electrospinning parameters such as EC concentration, voltage, ethanol/water ratio in the solvent, and feed rate in four levels (array L16).  EC solutions with a certain concentration were prepared in ethanol-water solvents with a certain ratio. The solutions were then stirred at a constant temperature for four hours and left overnight. Electrospinning parameters such as temperature 30 ˚C, distance between syringe needle and collector 10 cm, aluminum foil 20 micrometers as collector, collector speed 400 rpm, and electrospinning time 2.5 hours are constant in all electrospinning experiments, but voltage and feed rate were changed according to the experimental design. The resulting EC fibers were imaged by scanning electron microscopy (SEM). The SEM images of EC fibers were processed by Image J software, and the average diameter of EC fibers in each experiment was calculated. The results of the diameter of the electrospun EC fibers showed that all the fibers had a diameter of less than 100 nm. Also, the results of the diameter of EC fibers were analyzed based on the analysis of variance, and it was found that the ethanol/water ratio in the solvent (34.9%), the feed rate (23.5%), the voltage (22.1%), and the EC concentration (17.5%), respectively, had the greatest contribution to the diameter of EC fibers. Under optimal conditions, EC fibers with a diameter of 41 nm were prepared.
 

Abstract In the present study, a new method has been suggested to solve the problems of the very low solubilityof sulfide ores in acidic solution and also the production of toxic impurities for the first time. In this work, the polyoxometalate (POM) oxidizer was applied for the dissolution of sulfide ores, extraction of metals, and removal of toxic and harmful wastes. In this procedure, POMs were used as strong oxidizers of sulfur compounds to dissolve sulfide ores. Also, acid was applied as a solvent and catalyst to increase the reaction rate. The Taguchi experimental design along with the ProMax simulation software was applied for studying the leaching of sulfide ores by POM oxidizers as a novel plan in experimental to industrial scales. The optimum data achieved by the Taguchi method was used as the input data to the simulation and sensitivity analysis of the process was executed by the ProMax software. The effects of curicital operating parameters such as the concentration of acid (C_A) in the 60-90 g/l range, the  reaction temperature (T_R) with the values of 60-90 ºC, the rotation rate (R) with the amounts of 50- 300 rpm, the retention time (τ) in the 0.5-2.0 h range, the concentration of polyoxometalate oxidizer with the values of 0.1- 0.5 g/l, the acid types of H₂SO₄, HNO₃, HCl, H₃PO₄, the grain sizes of sulfide ores (Sparticle) in the 0.5-3.0 mm range and polyoxometalate with the types of [Mo₆O₁₉]^2-, [Mo₈O₂₆]^4-, [V₁₀O₂₈]^6- and [H₂W₁₂O₄₀]^10- on the extraction efficiency of metals and removal of toxic heavy metals from sulfide ores by polyoxometalates were investigated. The optimum conditions to extract maximize metals from the sulfide ores were obtained as the C_A; 80 g/l, T_R; 90 ºC, R; 300 rpm, τ; 1.0 h, m POMs; 0.5g/l, acid type of H₂SO₄, S_grain;1.0 mm and POMs type of [H₂W₁₂O₄₀]^10-. Under optimized conditions, the extraction efficiency of zinc, copper, and lead and the removal of toxic heavy metals from sulfide ores were determined as above 85%, 81%, 83%, and 99.9% receptivity.

Abstract Amine gas sweetening is a process in which acidic gases including hydrogen sulfide (H₂S) and carbon dioxide (CO₂) are removed by a solution of water and amines. Many parameters influence the sweetening process. Knowledge about the important parameters and their degree of importance is of great interest to achieve the optimum condition. Nine effective parameters including the CO₂ and H₂S contents of the feed, the temperature and pressure of the feed, the tray number and pressure of the absorber, the lean amine temperature, and the concentrations of Methyl Diethanol Amine (MDEA), and Piperazine (PZ) have been chosen as effective variables, while CO₂/H₂S recovery and total process energy have been considered as response variables.  After the verification of the present study with real plant data, the experimental layout was designed by the Plackett-Burman approach, and the model validation has been confirmed by ANOVA. The results of the present study showed that the most effective parameters in the CO₂ recovery are the absorber tray number and PZ concentration, while in the H₂S recovery, the absorber tray number is the most important variable. Regarding the total energy of the proces, feed temperature, PZ concentration, absorber tray number, lean amine temperature, and feed pressure are obtained as important variables. The optimum condition has been obtained in the feed and absorber pressures of 5758.9, and  1458.9 kPa respectively, with the feed and lean amine temperature of 0.11 and 50  respectively, the concentrations of 17.57 and 3.8 wt.% of MDEA and  PZ respectively, the absorber tray number of 20 and the mass flow rates of 792 and 103.6 kg/h of CO₂ and H₂S respectively. Under the mentioned conditions, the CO₂ and H₂S recovery were achieved at 99.99 % while the total energy of the process was 3.56 Mw.

Abstract The Ethanol-water separation involves a well-known azeotrope that confines the achievement of the ethanol purity to the values higher than 95 wt% using straightforward distillation. Many attempts have been made to identify how it can be possible to produce ultra-pure ethanol (99.95 wt%) for various valuable applications. In practice, minimizing the total cost of the process is of high importance beside having the finished product with utmost purity. As a consequence, finding the best process conditions imposed to apply the simulation and statistical optimization methods in combination. Numerical optimization provides the best trade-offs to achieve the goals. In this research, the separation of the ethanol/water mixture (87 wt%) was simulated using azeotropic distillation in Aspen plus^© environment. Indeed, cyclohexane was chosen as an effective azeotrope-former. The UNIQUAC equation was used to describe the phase behavior. The two-column arrangement, in which the first column was used to dehydrate ethanol and the second to recover the entrainer, was applied in this simulation. The effect of important process variables, including the number of the trays in columns and the feed-tray position in each tower on the total capital cost were investigated. Finally, the process variables were optimized via the Response Surface Methodology to minimize the total cost of the process. The results uncovered that the total capital cost would be minimized if the number of the trays in the azeotropic (C1) and recovery (C2) columns were set to 34 and 40, whereas, the feed-tray numbers were adjusted to 19 and 9 respectively.

Abstract Optimization of the homogeneous rhodium-catalyzed methanol carbonylation reactor to reduce CO2 emissions is studied in this line of research. In this paper, the steady-state homogeneous rhodium-catalyzed methanol carbonylation reactor is simulated using Aspen HysysV.9 software, by comparing the simulation results with industrial information, a mean relative error (excluding methanol) of 4.8% was obtained, which indicates the high accuracy of the simulation. The central composite design (CCD) and genetic algorithm (GA) with the aid of a simplified process simulation were used to estimate the effect of individual variables (liquid level, the temperature of the catalyst-rich recycle stream, the mole ratio of CO to methanol (MeOH) in the feed, and flow rate of dilute acid stream) and their mutual interactions to reduce CO2 emissions. It is obtained that the liquid level percentage of 46%, the catalyst-rich recycle stream temperature of 120 °C, CO: MeOH molar ratio equal to 1.13:1, and the dilute acid flow rate of 513.14 kmol/hr lead to CO2 reduction by 34%.

Abstract The optimization of the ammonia synthesis plant to increase the production of ammonia is studied in this line of research. In this paper, the steady-state ammonia synthesis is simulated using the Aspen HysysV.11 software. By comparing the simulation results with the industrial information, a mean relative error of 7.71 % was obtained, which indicated the high accuracy of the simulation. Then, four effective variables were selected from among 11 independent variables by the Plackett-Burman method. The effects of the Hydrogen flow in the feed stream, Recycle stream pressure, Feed stream temperature, and input temperature of the third reactor were investigated, and the response surface design method of the central composite design was performed to plant optimize. It is obtained that the Hydrogen flow in the feed stream is equal to 6255 , the feed stream pressure is equal to 205 bar, the temperature of the excess stream inlet in the first reactor is equal to 663 K, and the temperature of the stream inlet of the second reactor is 677.5 K which increased the ammonia production by 7.5 %.

Abstract A batch process was developed for the production of biodiesel from high free fatty acid feedstocks. The mixed-integer nonlinear programming (MINLP) problem, caused due to applying the hierarchical procedure together with Malone’s algorithm for the conceptual design, was solved. Meanwhile, the optimum states of major process parameters such as the utilization of the process equipment, paralleling, splitting, and the merging of unit operations, the process cycle time (CT), and the combination of batch and continuous units were determined. Based on the present optimization study, the optimum value of the process cycle time and the optimum number of the esterification reactors in series were obtained as 3.257 h/batch and 3 stages respectively. The batch process was found to be suitable for a capacity of less than 260 tons/yr, while the continuous process was suitable for a capacity of greater production rates. The results showed that the production rate had a direct effect on the economic potential of the process and that it should be set at its maximum possible practical value. Also, the break-even point for the optimum state occurred at the production rate of 130 tons/yr.

Abstract The removal of Acrylonitrile (AN) from waste gas streams using biological methods, due to their better performance, has recently gained more attraction. The purpose of this research is modeling the AN removal by a bio-filter. The validation of the model is done by using the experimental data of a bench-scale bio-filter bed column including yard waste compost and shredded hard plastics and thickened municipal activated sludge. In this work the kinetics of the biodegradation of Acrylonitrile is first investigated. Then equations of the biofilm and air are obtained at a steady state and constant temperature. The unknown parameters of the model are determined by the least square optimization method along with solving the model equations using MATLAB. For inlet concentrations less than 1 g/m³ the model results show reasonable similarities to the experimental data. The effect of various parameters on the bio-filter performance is evaluated. The Peclet number, biofilm thickness and biomass concentration are the most important parameters. The proposed model can be useful for design purposes.

Abstract Vegetable oils are proved as valuable feedstocks in the biofuel production. Some common issues of cracking of vegetable oils–as an effective method for the biofuel production- are related to the glycerol decomposition during the cracking process. Transesterification, which can remove glycerol from vegetable oil molecules, is performed before the thermal cracking to adjust the problems. This study has been aimed at surveying the efficiency of transesterification and the thermal cracking integration to produce bio-gasoline and bio-oil from castor oil. In transesterification, methanol as alcohol and KOH as catalyst were used, and the catalyst concentration, reaction temperature, and alcohol to oil ratio were effective variables. Statistical studies demonstrated the interactions among parameters and the yield of the methyl ester production as 96.7 % under the optimized conditions. Results showed that in the thermal cracking two parameters, of the feed flowrate and temperature, influenced the product yield significantly without any interaction. Under the optimum conditions, to maximize the bio-gasoline production, 28 % of bio-gasoline and     88.6 % of bio-oil were produced. The lack of acrolein, as a toxic component, the negligible amount of the generated water in the product, the high octane number, the significant amount of the heat of combustion of bio-gasoline, and being in criteria of standard gasoline as per ASTM D4814 for the distillation curve and RVP of bio-gasoline, were the great advantages of the cracking of the transesterified caster oil. Therefore, the bio-gasoline produced via the thermochemical conversion of castor oil could be used as a fuel for spark-ignition engines or as an octane enhancer with gasoline, i.e., by adding 10 % of bio-gasoline to the refinery gasoline, the octane number increased from 95 to 105.

Abstract The main objective of this research is to analyze optimization and the thermal performance of circular porous fins with four different profiles, rectangular, convex, triangular and concave under fully wet conditions. In this research, a linear model was used for the relationship between humidity and temperature. Also, modeling is assumed one-dimensional and the temperature changes only in the direction of the radius of the fin. Moreover, the thermal conductivity and heat transfer coefficient are a function of porosity and temperature, respectively. The governing equations are solved using the Galerkin method and the finite difference method and the use of the Gauss-Seidel algorithm. In this study, the effect of different parameters including relative humidity, Darcy number and Rayleigh number and porosity on temperature distribution, fin efficiency, and fin effectiveness was investigated. The results showed that the efficiency, effectiveness, and heat transfer rate to the base for the rectangular profile is higher than other profiles.
In this research, the Nelder-Mead algorithm is used for optimization. The results showed that to maintain optimal conditions, the ratio of thickness to fin length should be increased by increasing relative humidity or decreasing the Darcy number, Rayleigh number and porosity.

Abstract A three-layer artificial neural network (ANN) model was developed to predict the remained DO (deoxygenation) in water after DO removal with an enzymatic granular biocatalyst (GB), based on the experimental data obtained in a laboratory stirring batch study. The effects of operational parameters such as initial pH, initial glucose concentration and temperature on DO removal were investigated. On the basis of batch reactor test results, the optimum value of operating temperature, glucose concentration and pH were found to be 30oC, 80 mM and 7, respectively. After back-propagation training, the ANN model was able to predict the remained DO with a tangent sigmoid function (tansig) at hidden layer with 7 neurons and a linear transfer function (purelin) at the output layer. The linear regression between the network outputs and the corresponding targets were proven to be satisfactory with a correlation coefficient of 0.995 for three model variables used in this study.

Abstract Catalytic naphtha reforming is one of the most important processes in which, low quality naphtha is converted into high octane motor gasoline. In this study, a mathematical model was developed and was used for investigation the effect of temperature, pressure, hydrogen to hydrocarbon ratio on the octane number, the yield of product and the undesirable phenomena of coke deposition in a semiregenerative catalytic reforming unit. The result of the model was compared to the plant data to verify the model accuracy. Then, the model was used to find the optimal condition for the maximum value of octane number and yield of product and the minimum value of coke deposition. The optimum condition of the process is estimated using genetic algorithm optimization method as an efficient optimization method. In the optimal condition, the octane number and the yield of the product are improved 0.3% and 1.23% respectively, and the coke deposition is reduced 2.1 %.

Abstract This paper reports the results of experimentally removing ammonia from synthetically prepared ammonia solution using a micro scale mixing loop air stripper. Effects of various operational parameters (such as: pH, air flow rate, wastewater flow rate and initial ammonia concentration) were evaluated. By increasing the pH from 10 to 12.25 the amount of KLa increased from 0.26 to 0.73 hr-1. A considerable enhancement, about 150%, can be found for KLa by changing the air flow rate from 280 to 700 mL/min under fixed condition. The wastewater flow rate can also the value of KLa from 0.22 to 0.59 hr-1. The values of KLa increased only about 20% by changing the initial concentration of ammonia in the range between 50 and 500 mg/L. The results showed that improving in air stripping using microchannel was successfully carried out with enhancing overall volumetric mass transfer coefficient (KLa) and providing higher mass transfer capabilities compared with other types of strippers, even for lower amounts of used air. The enhancement of mass transfer is happened by efficient mixing induced by the employed microchannel. It has been demonstrated that wastewater flow rate and air flow rate have significant effects on KLa. The optimal stripping conditions and mathematical modeling for ammonia removal and the relation between the parameters were determined using Response Surface Methodology (RSM) with Central Composite Design (CCD) method. The results demonstrate the advantages the proposed system over convention stripper types.

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 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 this study, response surface methodology (RSM) based on central composite design (CCD) was applied for investigation of the effects of ultrasonic waves, temperature and solvent concentration on viscosity reduction of residue fuel oil (RFO). Ultrasonic irradiation was employed at low frequency of 24 kHz and power of 280 W. The results showed that the combination of ultrasonic waves and solvent injection caused to further reduce of viscosity. To obtain optimum conditions and significant parameters, the results were analyzed by CCD method. In this method, maximum viscosity reduction (133 cSt) was attained in ultrasonic irradiation for 5 min, temperature of 50 °C and acetonitrile volumetric concentration of 5 % by means of experimental and three dimensional response surface plots. The kinematic viscosity decreased from 494 cSt to 133 cSt at the optimum conditions. In addition, a multiple variables model was developed by RSM which the second-order effect of ultrasonic irradiation time was significant on viscosity reduction of FRO. Finally, a comparison between the RSM with artificial neural network (ANN) was applied. The results demonstrated that both models, , were powerful to predict of kinematic viscosity of RFO. The results demonstrated that both models, RSM and ANN, with R2 more than 0.99 were powerful to predict kinematic viscosity of RFO.

Abstract The major active component in licorice is glycyrrhizic acid which is very useful in the pharmaceutical industry. In the present work, the extraction of glycyrrhizic acid in licorice is carried out in a stirred reactor as well as under indirect sonication in an ultrasonic bath. Batch extraction is carried out in a glass reactor of 150 mL capacity equipped with a six bladed glass turbine for agitation. Ultrasound assisted extraction has been carried out in a dual frequency ultrasound cleaning bath. The glycyrrhizic acid is analyzed using HPLC. Various process parameters such as solvent concentration, power, frequency of ultrasound, extraction temperature and solvent to solute ratio, which affect the extraction yield are optimized for both techniques. In ultrasound assisted extraction with final optimized conditions, i.e. 50% ethanol as solvent, 230 W power, 40:1 solvent to solute ratio, 30∫C temperature and 40 kHz frequency, 95.69% extraction is obtained in 20 minutes, whereas in extraction using stirred reactor only 68% extraction is observed in 60 minutes. Kinetic of the extraction process is studied and volumetric mass transfer coefficients as well as theoretical yield for different process parameters are estimated.

Abstract The ultra-high molecular weight polyethylene (UHMWPE) was prepared using titanium tetrachloride (TiCl4) supported by MgCl2 (ethoxide type), accompanied by triisobutylaluminium (TIBA) as co-catalyst. These all constituted the Ziegler–Natta
catalytic system. MgCl2 is one of the best supports for Ziegler-Natta catalyst in order to increase its yield.In the present study, the process variables were investigated through response surface methodology (RSM) to optimize the productivity of the catalyst and also the molecular weight of the polymer. Taking this into consideration a three-level Box-Behnken design for three factors with temperature (X1), monomer pressure (X 2), and [Al]/[Ti] molar ratio (X 3) as the independent variables were selected. Different molar ratio of [Al]/[Ti] is achieved by changing the amount of the co-catalyst.The dependent variables were productivity and molecular weights of the prepared polymers. Specifically, using these three parameters at three levels including 50, 60, and 70°C for temperature; 4, 6, and 8 bar for pressure; and 150, 250, and 350 for [Al]/[Ti] molar ratio. The RSM yielded optimum reaction conditions equal to: temperature of 55°C, pressure of 8 bar, and [Al]/[Ti] molar ratio of 230. Under these optimum conditions, the productivity and molecular weight were 2628 g PE/mmolTi.h and 5.09×10 6 g/mol, respectively.

Abstract Water flooding, the oldest and most common EOR method, increases the displacement efficiency in a reservoir and also maintains the reservoir pressure for a long period of time. In Iran, water injection is widely used as a method to enhance recovery from oil reservoirs. Defining the optimized injection rates and injection patterns, dependent on the geological structure of the reservoir, is essential in operational and economical decisions for reservoir management. In this paper, the Capacitance-Resistive Model is used to find interwell connectivity, and optimized injection rates in a synthetic field. In this approach, the reservoir receives injector rate variations as an input signal, while the producer responses determine the injector/producer pair connectivity quantitatively. This model is used to predict oil production for a specific reservoir, if the production/injection rate and bottomhole pressure data are available. The results show that the Capacitance-
Resistive model has the capability to be used for the production history matching and to optimize the injection rate in different wells of a reservoir during the immiscible flooding to maximize the oil production. Moreover, they show that any change in oil and water prices can significantly influence the optimized water injection rates.

Abstract This paper reports a study to find optimum conditions for oil extraction from vetiver root. For this purpose, the influence of temperature and pressure on the extraction yield is investigated. In addition, the effects of supercritical fluid flow rate and particle diameter on optimum temperature and pressure have been studied. The results show that optimum pressure is a strong function of particle diameter and solvent flow rate. However, the results reveal that the optimum temperature is independent from particle diameter and solvent flow rate.

Abstract At present, gas engineers use the simple Campbell’s equation to determine the proper length of parallel gas pipelines. The Campbell’s equation was proposed for horizontal pipelines with the assumption that the gas compressibility factor and temperature throughout the pipeline are constant. Therefore, the Campbell’s equation has a notable error for an inclined pipeline. In this paper, the Campbell’s equation was extended in a way that it can be used for inclined pipelines. In order to make a comparison between the extended and original equations, a pipeline with different slopes was used. The results show that in the case of using a pipeline with more than 2 degrees in slope, the resultant error is increased to 11 percent by using the original Campbell’s equation. For validation of the extended Campbell’s equation, the results of this equation are compared to the results of HYSYS software (version 3.1) in which the temperature and gas compressibility factor are not considered constant. The results indicate that the average error of the extended equation is less than 2 percent.

Abstract In low-temperature processes, heat rejected from separation columns is removed by refrigeration systems to heat sinks (reboilers & pre-heaters), process streams, other refrigeration streams, or external utilities. The need for efficient utilization and recovery of energy in sub-ambient gas separation processes is still challenging. Performance and reliability of Simulated Annealing (SA) for simultaneous design and optimization of such systems has been investigated previously. In this work, the effect of different refrigerants satisfying a set of process cooling duties at different temperatures is addressed. Cost reduction can be realized by encompassing both effective screening of heat-integrated separation columns and selecting the best refrigerants. A 29.7% cost savings has been shown through a case study. Afterwards, a comprehensive thermodynamic analysis has been carried out on achieved solutions to verify the accuracy of existing shortcut models and robustness of optimized structure. It has been shown that exergy analysis using two different approaches (i.e. stream wise and unit operation wise) are the same, which indicate the accuracy of the used models. Moreover, we have indicated that both utility costs and exergy losses can be considered as an objective function when optimizing the designs.

Abstract An industrial ethane thermal cracking reactor was modeled assuming a molecular mechanism for the reaction kinetics coupled with material, energy, and momentum balances of the reactant-product flow along the reactor. To carry out the multi-objective optimization for two objectives such as conversion and ethylene selectivity, the elitist non-dominated sorting genetic algorithm was used. The Pareto optimum set was obtained successfully and finally the effect of the decision variable was discussed.