Iranian Journal of Chemical Engineering (IJChE)

Abstract Lithium-ion batteries are widely used in various electronic devices and typically discarded after their service life, causing significant environmental damage and resource wastage. Therefore, recycling the valuable components of the batteries, such as graphite, is essential. Graphite, employed as the anode material, is one of the key components targeted for recovery. In graphite recycling operations from spent batteries, critical hydrometallurgical processes include primary and secondary leaching stages using sulfuric acid. In this research, both leaching processes were systematically optimized. The optimal conditions identified for primary leaching were a temperature of 77 °C, a sulfuric acid concentration of 1.75 M, a leaching duration of 4 hours, and a liquid-to-solid graphite powder ratio of 5. Under these conditions, the graphite purity after the primary leaching process was 99.56 wt%. Subsequently, in the secondary leaching stage, a final high purity of 99.98% was achieved for the graphite product. To evaluate the electrochemical performance of the recycled graphite, galvanostatic charge-discharge tests were conducted, which demonstrated a specific capacity of 350 mAh/g. This capacity is comparable to that of commercial graphite, confirming the effectiveness of the developed recycling process.

Abstract Given the high share of energy consumption in the building sector and the need to enhance thermal performance in cold climates, this study investigates the effect of the paraffin-based phase change material RT22HC on improving the thermal efficiency of a double-skin building facade. This material has a melting temperature in the range of 20–23°C (peak 22°C) and a latent heat storage capacity of about 190 kJ/kg, which enables storing and releasing heat at an approximately constant temperature. The aim of the study is to analyze the impact of removing thermal insulation and replacing it with an air cavity containing PCM on heating and cooling loads during cold periods in the city of Tabriz. Energy modeling was performed using DB software, and the heat transfer analysis was conducted with the Finite Difference algorithm. Three scenarios were examined: a base facade; a double-skin facade with PCM and thermal insulation; and a double-skin facade with PCM and an air cavity. The results showed that in the third case, the melting and solidification mechanism of RT22HC reduced heat flux and increased temperature stability; such that the annual sensible heat load decreased from 27276.61 kWh to 9985.8 kWh (equivalent to 63%). Moreover, indoor temperature fluctuations and mean radiant temperature differences decreased, improving thermal comfort conditions. Overall, the low thermal conductivity (0.2 W/m·K) and high heat capacity of PCM led to proposing this material as an effective substitute for conventional thermal insulations in DSF facades in cold climates.

Abstract The pyrolysis of polyethylene terephthalate (PET) was investigated across a broad range of final temperatures, from 478°C to 640°C, yielding various products. Infrared radiation was employed as the heat source in this study. To minimize experimental deviations, each test under fixed conditions was repeated twice, and the results were compared for consistency. The primary objective was to evaluate the quantitative and qualitative differences in the products generated through this novel heating method, aiming to enhance the understanding of the pyrolysis process and the influence of the heating rate on the final outputs. Pyrolysis was conducted in a vertical tubular reactor housed within an infrared furnace. The average heating rates varied significantly, ranging from approximately 20.61°C/min in the slowest test to 161.12°C/min in the fastest one. The solid residue (char) resulted from PET pyrolysis was analyzed. The yields of 87.5% and 91% were recorded for the slowest and fastest heating rates respectively. These char samples were assessed using Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) to compare their quantity and quality. The findings revealed that the heating rate during the infrared pyrolysis of PET has a direct correlation with the quantity of valuable products, but an inverse relationship with their quality. 

Abstract In this novel study, various heat exchangers are compared to identify the most efficient one for heat transfer. This investigation involves shell and tube, double pipe, and plate heat exchangers, of which each is filled with different nanofluids. Following several hours of operation, output temperatures are recorded. The effects of nanofluids, containing aluminium oxide, magnesium oxide, and silicon oxide, at concentrations of 0.2%, 0.4%, and 0.6% are simulated. These simulated results are then compared with laboratory findings. Among the tested nanofluids, the most significant enhancement in the heat transfer coefficient is demonstrated by magnesium oxide, achieving a 40% improvement. Additionally, graphs illustrating the increase in the heat transfer coefficient and Nusselt number for Reynolds numbers of 900, 600, 300, and 1800 are obtained and compared. Finally, tables summarizing the tests performed on different heat exchangers using various nanofluids are presented. Using laboratory-obtained temperatures, several parameters are calculated, including the logarithmic mean temperature difference, heat loss from hot water, heat gain by cold water, overall heat transfer coefficient, and total heat transfer. Based on these analyses, the shell and tube heat exchanger was purposed as the most efficient heat exchanger with the overall heat transfer coefficient of 5.06 W/m²K.

Abstract Ultrasonic distillation has been implemented as a green technology for desalination of saltwater due to its low energy consumption. It has also been proposed as an alternative to conventional distillation for separating water-ethanol mixtures, offering easy operating conditions and significant reduction in energy consumption (up to 80%). The Response Surface Methodology (RSM) was employed to optimize key parameters that influence ethanol enrichment, which includes initial ethanol concentration, solution height, and the quantity of ultrasonic modules. A central composite design (CCD) was utilized to reduce the number of experimental trials while formulating a predictive mathematical model. The findings suggest that elevated initial ethanol concentrations and an augmented number of modules significantly improved the ethanol concentration in the collected mist. Under optimal conditions—65% ethanol concentration, 2.5 cm solution height, and three modules—the purity of ethanol attained was akin to that achieved through conventional distillation techniques, accompanied by markedly diminished energy consumption. This research illustrates the potential of ultrasonic distillation for ethanol separation, offering operational efficiency and reduced energy demands.

Abstract This paper presents a machine learning-based approach for accurately predicting pyrolysis product yields. Methods such as Linear Regression (LR), K-Nearest Neighbors (KNN), Decision Tree (DT), Support Vector Regression (SVR), Random Forest (RF), and Neural Networks (NN) leverage operating conditions and/or ultimate/proximate analysis data, eliminating the need for reaction kinetics. This innovative approach offers a broader range and higher accuracy of feedstock compared to traditional kinetics-based methods. The KNN model demonstrated superior performance, achieving a correlation coefficient greater than 0.998 and an RMSE of 0.64. These findings provide valuable insights for engineers and practitioners, facilitating the efficient design and operation of pyrolysis units.The selectivity exhibited a notable increase from 2.46 to 5.27. This improvement in selectivity can primarily be attributed to the significantly higher increase in the solubility coefficient of CO₂ compared to that of CH₄.

Abstract Humidification-dehumidification (HD) desalination has been identified as a sustainable, reliable, and energy-efficient technology for producing freshwater on a small scale. VP-HD systems operated at one-stage, multi-stage, and multi-feeding vacuum humidification-over atmospheric pressure dehumidification arrangements can be the recent modifications of an HD system. The present study offers a theoretical investigation and experimental verification of two VP-HD systems, encompassing both sub-atmospheric pressure humidification and over-atmospheric dehumidification. Two designs are evaluated, one comprising a three-stage humidification setup and the other featuring a three-feeding one-stage humidification apparatus. The results show which design has better performance than previous conventional and variable pressure HD systems. The parametric analysis reveals that an upsurge in freshwater generation is observed with an increase in air temperature, feed salinity, and a decrease in humidifier pressure. Additionally, an optimal water-to-air ratio is identified. The study further highlights that multi-stage humidification yields better results concerning freshwater productivity and specific power consumption. Three-stage humidification is found to be the most efficient in terms of freshwater production and specific power consumption, achieving the highest values of 1.93 L h^-1 m^-2 and 0.21 kWh L^-1, respectively. The agreement between theoretical and experimental outcomes is deemed satisfactory.

Abstract A hydrothermal method was used to synthesize different photoanodes for their application in dye-sensitized solar cells (DSSC). These photoanodes included WO₃, TiO₂, Graphene-TiO₂, WO₃-TiO₂, and a nanostructure of Graphene-WO₃-TiO₂. The morphology of the nanoparticles was analyzed using the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), ultraviolet-visible spectroscopy (UV-vis), and Fourier-transform infrared spectroscopy (FTIR). The results demonstrated that the graphene-WO₃-TiO₂ nanostructure had a large surface area, having provided more active sites for the efficient conversion of solar energy.  Notably, the DSSC incorporating the graphene-WO₃-TiO₂ nanoparticle electrode outperformed cells based solely on TiO₂ and WO₃, achieving a higher short-circuit current density of 7.5 mA.cm^-2, an open-circuit voltage of 0.68 V, a fill factor of 0.46, and a power conversion efficiency of 2.4%. In contrast, the pure TiO₂ and WO₃ cells only achieved efficiencies of 0.88% and 0.69% Respectively.  The excellent electron mobility of the ternary nanostructure facilitated the charge trapping and injection into the conductive substrate, reducing recombination. Additionally, the scattering effect of the WO₃ nanorods and graphene enhanced the light harvesting in the photoanode, leading to an increase in the overall efficiency of the solar cell. These findings highlight the potential of the synthesized graphene-WO₃-TiO₂ nanostructure as a promising photoanode material to be applied in DSSC.

Abstract Current research has simulated polymer oxide/metal oxide nanofibers (nanocomposites) through the COMSOL Multiphysics software. The oil was placed inside a cylindrical tank covered with a thin layer of phase change material nanocomposites. A combination of polyethylene glycol (PEG) as a the phase change material (PCM) and polyamide 6 (PA6) as a support matrix for nanofibers were used. The effect of some parameters such as the type of metal oxide nanoparticles (Al₂O₃, Fe₂O₃, TiO₂, and CuO), the ratio of metal oxide to polymer (2% and 8% by weight), and time (600 and 4800 s) on some thermophysical properties such as changes in temperature, density and thermal conductivity were investigated. The simulation results showed that the most suitable system for thermal management is related to the presence of nanoparticles and PCM with the highest weight percentage. It was also found that the use of the nanofibers of phase change materials is very effective in improving thermal management and temperature control. As a result, they can be used as suitable materials for storing and transferring energy. The addition of 8% nanoparticles led to a 22.5% increase in thermal conductivity. Also, by providing the same initial and boundary conditions for all cases, the amount of melting in the presence of nanoparticles with a high percentage (8%) was higher than the with a low percentage (2%). As a result, the addition of nanoparticles to increase the melting rate can be very useful for various heat management purposes such as energy storage.

Abstract In this experimental investigation, the heat transfer and pressure drop of helical tubes with various helical diameters have been studied considering air injections. The tube was rested in vertical form and was put under the constant heat flux. The flow had a downward form and the air was injected into the water stream outside the helical tube. According to the findings, air injection has a notable impact on the heat transfer coefficient of each helical tube. The results showed that employing air bubbles could increase the Nusselt Number by up to  14 %. To make an acceptable comparison among all states, the Cost Benefit Ratio (C.B.R.) factor was evaluated. The results showed that the pipes with bigger diameters had the best C.B.R. factor values. It means that the air injection in the tubes with larger diameters was more beneficial than in the tubes with smaller helix diameters. The best value was attained for the helix diameter of 18 cm and the VF of 0.33 with a C.B.R. factor of 0.84. Also, the worst value was 1.18 for a helix diameter of 10 cm.

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 A continuous process was designed and optimized at a conceptual stage for the biodiesel production from waste vegetable oils. Unlike previous studies, the process was optimized taking into account the technical and economic considerations, simultaneously, to find the optimum operating conditions fort he commercial scale productions. The effect of major variables on the yield of the process was studied by modeling esterification and transesterification reactors. The mole fraction of free fatty acids (FFAs) in the feedstock, production rate, conversion and molar ratio of the reactants in both reactors were chosen as major variables. By considering the economic potential as the objective function of the process optimization, the optimum mole fraction of FFA was obtained as about 0.50 (24 wt %). Also, the optimum values of the conversion and molar ratio of the reactants in the esterification and transesterification reactors were found as        82-89 % (depending on the different production rates), 11:1 and 96 %, 8:1 respectively. It was found that the economic potential increases linearly as the production rate increases. Therefore, the production rate should be set at its maximum possible practical value. The break-even point at the optimum values of these variables, as mentioned above, occurs at the production rate of 157 ton/yr.

Abstract Different methods of urban sewage sludge energy recovery such as burning, gasification, pyrolysis and digestion based on the net energy production efficiency, advantages and disadvantages and complexity of these processes have been investigated in this article. The best method for energy production from sludge was selected among different methods according to energy and the amount of the greenhouse gas production. The capacity of the constructed power plant was calculated and investigated economically for each scenario. Quantitative and qualitative information on sludge was required to carry out this research so Ekbatan wastewater treatment sludge was analyzed. The results showed that the sludge of this treatment plant has 5.7% solids, containing 65.7% volatiles and the dry heat value is about 15100 kJ/kg. It was found that the best scenario for sludge energy production in this treatment plant is a digestion process with pure net energy production of 73.2 × 107 kJ/d. The energy recovery in an anaerobic digester can prevent the emission of 16,680 tons of CO2 annually and release about 1,460 tons of CO2 per year. The chemical analysis shows that the selected sludge has a potential production of 25m3 of CH4 for each m3 of sludge. The annual amount of biogas that can be recovered from municipal treatment plant is 836543 m3. On the other hand, the biogas can be used to generate electricity. The power of the plant is about 216.8 kW that with the construction of this power plant, an annual saving of 1.5 million dollars will occur.

Abstract The effects of greenhouse gases (GHG) on the growth of global warming, and increase of GHG and air pollutant emissions for energy production have forced the need of energy recovery which is normally wasted in industrial plant. The present research work focused on the GHG and air pollutant emissions reduction employing pressure waste energy recovery. Pressure break-down via Joule-Thomson valve is a neat potential for waste energy recovery in gas refineries, which may also be provide by using a turbo-expander instead of commercial valves. Based on this ground, an exergy analysis is carried out for Joule-Thomson valve. The results showed that the exergy loss is higher than 6.5 MW and it is possible to recover about 1.9 MW of exergy loss. On the other hand, it was found that about 16900MWh of electrical energy can be produced by recovering the energy of waste pressure, which may leads to less consumption of the load and gas in refinery power unit. Consequently, equal the gas consumption reduction, 12056 ton CO2e of GHG and 54.6 ton of air pollutant emissions is reduced annually. Economical evaluation of utilizing a turbo-expander instead of a valve proved that this altering scenario is deducible and practical. Economical indexes, namely, IRR and NPV are found to be equal to 25.51% and 929571 US$, respectively. Moreover, sensitivity analysis conducted on each specific state certified the obtained results.

Abstract Abstract Energy crisis is a major challenge in the current world. Latent heat thermal energy storage (LHTES) systems are known as equipment with promising performance by which thermal energy can be recovered. In the present study a comprehensive theoretical and experimental investigation is performed on a LHTES system containing PEG1000 as phase change material (PCM). Discussed topics can be categorized in three parts. At first, a one dimensional mathematical model is introduced for a heat exchanger containing flat slabs of PCM. To consider the latent heat of phase change, effective heat capacity is used in the model. Secondly, through eight experiments designed by using factorial method, effects of inlet air velocity and temperature on the outlet stream is investigated. The results proved that having a determined temperature difference between inlet air and the PCM in both hot and cold cycles can enhance the efficiency. Finally, the feasible applications of a LHTES system for controlling the temperature swing in a greenhouse is studied numerically and the results are compared with experimental values. As a result, by using this passive coolant system diurnal internal temperature can be reduced for 10 °C.

Abstract In the present study, the main focus was on plasma pyrolysis and gasification of organic waste, specifically polyethylene and cotton waste and exploring the energy recovery possibilities from the gases obtained after the plasma pyrolysis and gasification. In pyrolysis the gases formed are Syn gas (H2 + CO), CH 4, higher hydrocarbons along with soot particles. The waste is disintegrated using thermal plasma (which is generated using graphite plasma torch) in oxygen starved environment (pyrolysis) and also in partial oxidation condition (gasification). Experiments have been carried out by varying pyrolysis chamber temperature from 500 0C to 700 0C and polyethylene and cotton are fed into the pyrolysis chamber. It has been observed that plasma pyrolysis of polyethylene in the temperature range of 500 to 700 0C yields H 2 as main component around 30-40% volume basis along with CO, CO2, CH 4, C2H 6, C2H 4, C2H 2 and soot particles whereas pyrolysis of cotton, on the other hand provides less H 2 around 15-20 %. However, it has also been observed that in plasma gasification H2, CO, CH 4 content in the exhaust gases reduces to some extent (2-5%). The theoretical and experimental energy recovery comparisons have also been carried out.

Abstract Electricity generation in a duel chamber microbial fuel cell (MFC) consisting of graphite anode electrode, platinum cathode electrode and Nafion 117 membrane was investigated. Anaerobic sludge was used as the source of microorganisms in the anode chamber. Acetic acid as the sole carbon source along with other nutrients was added to
the anode chamber in a batch or repeated-batch modes. System curves and polarization curves were obtained in different operational conditions and the internal resistance of the system was calculated. Electricity generation by MFC in both batch and repeated-batch modes was modeled using a biofilm based hypothesis and the results were compared with experimental data.

Abstract Heterogeneous photocatalytic degradation of Polynuclear Aromatic Hydrocarbons (PAHs) contaminated soil in the Pars Economic and Energy Zone was carried out under laboratory conditions to evaluate the potential use of this technology for in situ remediation. Analysis of soil samples show that contaminated soil is primarily related to the concentration of phenanthrene. Hence phenanthrene is used for photocatalytic degradation under laboratory conditions. Soil samples were spiked with two phenanthrene concentrations (50 and 100 mg kg-1), loaded with catalyst TiO2 and exposed to uv light with 125 W power. Different catalyst loads (1, 2, 3 and 4 % w/w) were tested in phenanthrene contaminated soil (50 mg kg-1) for up to 16h exposure. Both the catalyst and phenanthrene concentration show no influence on the kinetics of the phenanthrene degradation. The results indicated that the optimum removal condition was at 2% w/w catalyst and 100% w/w water with 85% degradation efficiency. The degradation efficiency of other PAHs was also assessed with the optimum condition. This paper shows that photocatalytic is a particularly important methodology, in which a major process is being made in the oxidative methods for the degradation of organics such as PAHs in contaminated soil