ChemEngineering

Heavy metal pollution is a worldwide and stringent concern following many decades of industrialization and intensive mining without (in some cases) consideration for environmental protection. This review aims to identify the existing and emerging techniques for heavy metals (HM) removal/recycling from water and wastewater, with an emphasis on cobalt. Unlike many other heavy metals, cobalt has not been considered a detrimental element for the environment and human beings until recently. Thus, several methods and applicable techniques were evaluated to identify the best treatment approaches applicable to cobalt-polluted water and wastewater. The most feasible depollution methods adapted to the source, environment, and economic conditions were investigated and concluded. The operations and processes presented in this paper are conventional and innovative as well, including precipitation, membrane separation, with emphasis on ultrafiltration (UF) and nanofiltration (NF), but also reverse osmosis/forward osmosis (RO/FO), sorption/chemisorption processes, flotation/mechanical separation operations combined with coagulation/flocculation, photocatalysis, and electrochemical processes. For each one, depending on the frequency of use, physicochemical mechanisms and optimal operational conditions were identified to carry out successful cobalt removal and recovery from aqueous environments. Full article

Due to the complex relationship between various parameters affecting gas holdup in bubble column reactors, a unique correlation for gas holdup does not exist. The available correlations proposed in the literature for gas holdup prediction in aqueous alcohol solutions in bubble columns fail to predict gas holdup over a wide range of conditions. Therefore, based on around 1000 data points from the previous studies, an empirical correlation and a trained model were derived using the dimensionless numbers Reynolds, Froude, Eötvös to Morton ratio, and alcohol carbon number. The predictions were compared to experiments with different water–alcohol mediums at various concentrations to validate the correlation and trained model, and a good agreement was observed. However, the ML model was predicting more accurately, and it was indicated that the Reynolds number had the most significant impact on gas holdup, followed by the Eötvös to Morton ratio. Full article

Hydrogen has the potential to decarbonize the energy and industrial sectors in the future, mainly if it is generated by water electrolysis. The proton-exchange membrane water electrolysis (PEMWE) system is regarded as a propitious technology to produce green hydrogen from water using power supplied by renewable energy sources. It offers many benefits, such as high performance, high proton conductibility, quick response, compact size, and low working temperature. Many conceptual and functional parameters influence the effectiveness of PEM, including temperature, pressure of anode and cathode regions, water content and wideness of the layer, and cathode and anode exchange current density. In addition, the anodic half-reaction (known as the oxygen evolution reaction (OER)) and cathodic half-reaction (known as the hydrogen evolution reaction (HER)) perform an important function in the development of PEMWE. The current study aims to present these parameters and discuss their impacts on the performance of PEM. Also, the PEM efficiency is presented. The different methods used to enhance the scattering of OER electrocatalysts and minimize catalyst loading to minimize the price of PEMWE are also highlighted. Moreover, the alternative noble metals that could be used as electrocatalysts in HER and OER to minimize the cost of PEM are reviewed and presented. Full article

This study presents an integrated approach that combines the Levenberg–Marquardt (LM) and Luus–Jaakola (LJ) algorithms to enhance parameter estimation for various applications. The LM algorithm, known for its precision in solving non-linear least squares problems, is effectively paired with the LJ algorithm, a robust stochastic optimization method, to improve accuracy and computational efficiency. This hybrid LM-LJ methodology is demonstrated through several case studies, including the optimization of MESH equations in distillation processes, modeling controlled diffusion in biopolymer films, and analyzing heat and mass transfer during the drying of cylindrical quince slices. By overcoming the convergence issues typical of gradient-based methods and performing global searches without initial parameter bounds, this approach effectively handles complex models and closely aligns simulation results with experimental data. These capabilities highlight the versatility of this approach in engineering and environmental modeling, significantly enhancing parameter estimation in systems governed by differential equations. Full article

Using amine-based solutions is a mature method for CO₂ capture. This study simulates this process at Technology Centre Mongstad (TCM) using a rate-based model in Aspen Plus. The main purpose is to develop a rigorous model for TCM and find the operation limits, maximum utilization capacity, and maximum achievable CO₂ removal efficiency at the plant. The model accuracy is verified by using different scenarios from the test campaign reports at TCM with three main configurations: Combined Heat and Power flue gas, Refinery Residue Fluid Catalytic Cracker flue gas, and cold rich-solvent bypass. The deviation between the experimental data and simulation results is compared. The model shows better accuracy with more detailed input data and accurate practical parameters. The verified model is used with all the TCM configurations to simulate the plant. Aspen Exchanger Design and Rating is also used to design real heat exchangers. To avoid flooding, the maximum gas flow to the absorber column is 52,000 Sm³/h. There is a maximum reboiler duty of 8.4 and 3.4 MW for the Residue Fluid Catalytic Cracker and the Combined Heat and Power flue gas strippers, respectively. The optimum operating condition to achieve a CO₂ removal efficiency of 90% after amine lean loading adjustment, using maximum gas flow, both strippers, and 15% rich-solvent bypass, gives a total specific reboiler duty of 3.0 MJ/kgCO₂. By using a maximum amine flow rate of 230 ton/h, a CO₂ removal efficiency of 98% can be achieved. The optimum modification gives a bypass fraction of 19% and a specific reboiler duty of 3.63 MJ/kgCO₂. Full article

The advanced quality control of the raw mix remains a priority for the cement industry, particularly in recent years, where large quantities of alternative fuels and raw materials are used in clinker production, aiming to reduce the CO₂ footprint. This study presents an adaptive control system with a variable sampling period for regulating raw mix quality in the raw mill (RM) output in a process with four independent inputs and four outputs: the lime saturation factor (LSF), silica modulus (SM), alumina modulus (AM), and SO₃. The three pillars of the system are (1) mill dynamics calculation using exclusively industrial data, (2) the design of the controllers to meet robustness criteria, and (3) performance enhancement through simulators. Our technique periodically adjusts the gains of the controllers based on the mill’s dynamic parameters, which are computed from raw mix laboratory analyses. The presented results correspond to more than 14,000 h of mill operation. The standard deviation of the LSF at the mill outlet ranged from 1.5 to 3, which is equivalent to 1 to 2 standard deviations of LSF reproducibility. The standard deviation of the other moduli was close to the corresponding reproducibility of each. The presented adaptive gain-scheduling controller for LSF can be applicable to a broad range of raw meal grinding systems. Full article

The agriculture and agri-food sectors produce substantial amounts of plant-based waste. This waste presents an identifiable research opportunity to develop methods for effectively eliminating and managing it in order to promote zero-waste and circular economies. Plant-based waste and by-products are acknowledged as valuable sources of bioactive compounds, including cellulose fibers. Direct application of these fibers in non-food sectors such as textiles can reduce the environmental impact of secondary raw materials. This review aims to provide an overview of novel concepts and modern technologies for efficiently utilizing plant-based waste and by-products from the agricultural and agro-industrial sectors to extract fibers for a variety of final applications, including the fashion industry. Two major routes are identified to produce cellulose fibers: the extraction and purification of natural cellulose fibers and the extraction and purification of cellulose pulp that is further processed into manmade cellulosic fibers. Scalability of experimental results at the laboratory or pilot level is a major barrier, so it is critical to develop closed-loop processes, apply standardization protocols, and conduct life cycle assessments and techno-economic analyses to facilitate large-scale implementation. Full article

Although the most promising applications of ionogels require their contact with aqueous media, few data are available on the stability of ionogels upon exposure to water. In this paper, a simple, easy-to-setup and precise method is presented, which was developed based on the continuous conductivity measurements of an aqueous phase, to study the washout of imidazolium ionic liquids (IL) from various silica-based ionogels immersed in water. The accuracy of the method was verified using HPLC, its reproducibility was confirmed, and its systematic errors were estimated. The experimental data show the rapid and almost complete (>90% in 5 h) washout of the hydrophilic IL (1-butyl-3-methylimidazolium dicyanamide) from the TMOS-derived silica ionogel. To lower the rate and degree of washout, several approaches were analysed, including decreasing IL content in ionogels, using ionogels in a monolithic form instead of a powder, constructing ionogels by gelation of silica in an ionic liquid, ageing ionogels after sol–gel synthesis and constructing ionogels from both hydrophobic IL and hydrophobic silica. All these approaches inhibited IL washout; the lowest level of washout achieved was ~14% in 24 h. Insights into the ionogels’ structure and composition, using complementary methods (XRD, TGA, FTIR, SEM, NMR and nitrogen adsorption), revealed the washout mechanism, which was shown to be governed by three main processes: the diffusion of (1) IL and (2) water, and (3) IL dissolution in water. Washout was shown to follow pseudo-second-order kinetics, with the kinetic constants being in the range of 0.007–0.154 mol⁻¹·s⁻¹. Full article

Agro-industries produce over 2 billion tons of agricultural waste annually, including by-products like bagasse, molasses, seeds, stems, leaves, straw, and shells. The use of agro-industrial waste is a way to reduce the impact of industrial processes on the environment. The pea pod is a biomass with a high concentration of cellulose, hemicellulose and some lignin; therefore, it can be used to produce platform chemicals by means of a hydrothermal process. There is limited research on the hydrolysis of pea biomass, but it has been shown to obtain high yields. This study analyzed the effectiveness and selectivity of the hydrothermal process using pea pod biomass with a particle size of 0.5 mm at 180 °C for one hour. A 500 mL reactor was used, with a biomass-to-acid solution ratio of 1:20. The concentration of the acid solution was 0.02 M. The concentrations of sugar, formic acid, levulinic acid, HMF, and furfural produced were measured. Among the catalysts studied, adipic acid catalysis showed the highest yield of 65.16%, with 37.09% of sugar, 16.37% of formic acid, and 11.71% of levulinic acid. On the other hand, the catalysts with chloroacetic acid, butyric acid, anthranilic acid, and phthalic acid were less effective but demonstrated selectivity for sugar production, proving that the liquid phase obtained using the catalyst with those acids can be used as carbon sources for a fermentation process. In general, when comparing the process with or without the use of a catalyst, it is observed that with a catalyst in the reaction, the amount of HMF and furfural produced is reduced and the selectivity with respect to sugar production is increased. Full article

The country of South Africa is facing an energy crisis due to heavy reliance on fossil fuels, resulting in continuous load shedding. The use of renewable energy technologies can help resolve the current electricity crisis in the country. Moreover, waste-to-energy conversion has the potential to greatly contribute to economic development and improve public health. One such technology is biomass, which exploits waste-to-energy conversion. Additionally, solar energy can be utilized to maintain appropriate digester temperatures for optimal biogas yield. The study aims to assemble a portable balloon biogas digester in an enclosed greenhouse cavity and feed it with cow dung. Daily monitoring of pH and temperature (ambient, greenhouse, and slurry) was conducted, while biogas yield was monitored using a serial residential diaphragm flow meter. Furthermore, the composition of methane was monitored using the SAZQ biogas analyzer. The study investigated the impact of temperature on biogas production. The results revealed that the gas production rate of biogas fermentation increased within a certain temperature range. Therefore, maximum biogas production was achieved at a pH of 6.84 to 7.03, and the composition of methane exceeded 50%. Consequently, the study concluded by indicating that the digester housed within a greenhouse envelope, as demonstrated in this novel study, maintains the temperature within the optimal mesophilic range necessary for anaerobic digestion. Full article

Zn-modified ZSM-5 zeolites with different zinc contents were successfully prepared by the impregnation method and compared with unmodified ZSM-5. Their potential for LPG (liquefied petroleum gas) aromatization and the conversion of pyrolysis gases obtained from recycled polypropylene was subsequently evaluated. In this process, various characterization tests were performed on the prepared catalysts, including SEM-EDS (scanning electron microscopy with energy-dispersive spectroscopy), TPD-NH₃ (temperature-programmed desorption of ammonia), and FTIR (Fourier-transform infrared spectroscopy). Under optimized conditions, the best results were obtained with 2% Zn/ZSM-5, which generated a higher production of BTX (benzene, toluene, and xylene) isomers, which are major components of gasoline. Likewise, in catalytic pyrolysis of recycled polypropylene, this catalyst generated a higher production of aromatic compounds. Therefore, this catalyst showed excellent performance in generating valuable hydrocarbons of great industrial interest, particularly aromatics. Full article

Ethyl hydrocinnamate is an ester with a sweet, fruity, honey-like scent commonly used as a flavor and fragrance agent. Due to its chemical structure, it can be easily obtained through enzymatic reactions without the need for harsh substances and processes. This study investigated the immobilization of the commercial lipase Sustine^® 131 onto spent coffee grounds (SCG) as a low-cost support for the enzymatic synthesis of ethyl hydrocinnamate. Spent coffee grounds underwent pretreatment with water, hexane, and ethanol to serve as a lipase adsorption platform and extract valuable bioactive compounds such as polyphenols. The immobilized lipase displayed both hydrolytic and synthetic activities during 12 weeks of storage at room temperature. The optimal reaction conditions for the synthesis of ethyl hydrocinnamate were determined using a Box–Behnken plan. It was shown that the enzyme concentration and the temperature were crucial for achieving high yields of ethyl hydrocinnamate with a conversion rate above 92%. Specifically, at least 18% enzyme concentration and a temperature of 45 °C were necessary. This eco-friendly approach utilized abundant food waste residue as an inexpensive and renewable immobilization support, enabling efficient biocatalytic production of the high-value flavor ester ethyl hydrocinnamate. Full article

This study proposes a new dense membrane for selectively separating CO₂ and O₂ at high temperatures and simultaneously producing syngas. The membrane consists of a cermet-type material infiltrated with a ternary carbonate phase. Initially, the co-doped ceria of composition Ce_0.9Zr_0.05Y_0.05O_2−δ (CZY) was synthesized by using the conventional solid-state reaction method. Then, the ceramic was mixed with commercial silver powders using a ball milling process and subsequently uniaxially pressed and sintered to form the disk-shaped cermet. The dense membrane was finally formed via the infiltration of molten salts into the porous cermet supports. At high temperatures (700–850 °C), the membranes exhibit CO₂/N₂ and O₂/N₂ permselectivity and a high permeation flux under different CO₂ concentrations in the feed and sweeping gas flow rates. The observed permeation properties make its use viable for CO₂ valorization via the oxy-CO₂ reforming of methane, wherein both CO₂ and O₂ permeated gases were effectively utilized to produce hydrogen-rich syngas (H₂ + CO) through a catalytic membrane reactor arrangement at different temperatures ranging from 700 to 850 °C. The effect of the ceramic filler in the cermet is discussed, and continuous permeation testing, up to 115 h, demonstrated the membrane’s superior chemical and thermal stability by confirming the absence of any chemical interaction between the material and the carbonates as well as the absence of significant sintering concerns with the pure silver. Full article

This study explores the adsorption efficiency of biochar derived from palm trees and Ficus nitida for the removal of various contaminants, including Cu(II), Pb(II), iodine, and chlorpyrifos from aqueous solutions. Biochar was prepared using a two-step pyrolysis process for date palm biochar and single-step pyrolysis for Ficus nitida biochar. Characterization techniques such as SEM, EDX, and FTIR revealed a significant surface area and a variety of functional groups in both types of biochar, essential for effective adsorption. The date palm biochar exhibited superior adsorption capacities for Cu(II) and Pb(II) ions, achieving efficiencies up to 99.9% and 100%, respectively, due to its high content of oxygen-containing functional groups that facilitated strong complexation and ion exchange mechanisms. Conversely, Ficus nitida biochar demonstrated a higher adsorption capacity for iodine, reaching 68% adsorption compared to 39.7% for date palm biochar, owing to its greater surface area and microporosity. In the case of chlorpyrifos, Ficus nitida biochar again outperformed date palm biochar, achieving a maximum adsorption efficiency of 87% after 24 h of incubation, compared to 50.8% for date palm biochar. The study also examines the effect of incubation time on adsorption efficiency, showing that the adsorption of chlorpyrifos by date palm biochar increased significantly with time, reaching a maximum of 62.9% after 48 h, with no further improvement beyond 12 h. These results highlight the importance of biochar characteristics, such as surface area, pore structure, and functional groups, in determining adsorption efficiency. The findings suggest that optimizing pyrolysis conditions and surface modifications could further enhance the performance of biochar as a cost-effective and sustainable solution for water purification and environmental remediation. Full article

Aging is a natural process that is also influenced by some factors like the food someone eats, lifestyle decisions, and impacts on general health. Despite the recognized role of nutrition in modulating the molecular and cellular mechanisms underlying aging, there is a lack of comprehensive exploration into potential interventions that can effectively mitigate these effects. In this study, we investigated the potential anti-aging properties of vitamin D by examining its interactions with key molecular targets involved in aging-related pathways. By using molecular docking and dynamics techniques, we evaluate the interactions and stability of vitamins D2 and D3 with key proteins involved in aging pathways, such as SIRT1, mTOR, AMPK, Klotho, AhR, and MAPK. Our results reveal promising binding affinities between vitamin D and SIRT1 forms, with energy values of −48.33 kJ/mol and −45.94 kJ/mol for vitamins D2 and D3, respectively, in aqueous environments. Moreover, molecular dynamics simulations revealed that the vitamin D3–SIRT1 complex exhibited greater stability compared with the vitamin D2–SIRT1 complex. The study calculated the solvation free energy to compare the solubility of vitamins D2 and D3 in water and various organic solvents. Despite their strong interactions with water, both vitamins exhibited low solubility, primarily due to the high energy cost associated with cavity formation in the aqueous environment. Compared with other solvents, water demonstrated particularly low solubility for both vitamins. This suggested that vitamins D2 and D3 preferred binding to aging receptors over dissolving in bulk aqueous environments, supporting their strong therapeutic interactions with these receptors. These findings shed light on the molecular mechanisms underlying vitamin D’s potential anti-aging effects and lay the groundwork for developing nutraceuticals targeting aging and associated diseases. Understanding these mechanisms holds promise for future interventions aimed at promoting healthy aging and enhancing overall well-being. Full article

In the present study, a green and readily effective route is presented, using for the first time, methanesulfonic acid (MSA) as a catalyst to produce alkyl levulinates (ALs) via the addition of alcohols to α-angelica lactone (α-AL). A smooth procedure was developed that resulted in the production of high-purity ALs, with complete conversions and high yields (99.1–99.8%), within 20 to 60 min of reaction in the presence of 0.5 mol% MSA. The reactions were carried out solvent-free, at room temperature, and in atmospheric air. Reaction conditions were optimized, and equimolar amounts of alcohol reagent were used. This work presents the main advantages of the use of a catalyst (MSA) that is low cost, easily biodegradable, and does not release toxic gases into the environment, but has an acidic strength comparable to that of other mineral acids. Therefore, this study proves the remarkable efficiency of MSA as a catalyst in the synthesis of ALs through an economically and environmentally favorable route. Full article

The goal of strict fuel quality regulations is to decrease the levels of sulfur, nitrogen, and aromatic chemicals in gasoline, thereby enhancing environmental safety. Due to the high costs of hydrodenitrification and hydrodesulfurization, many studies are looking for alternative fuel-purifying processes. The straightforward extraction approach using deep eutectic solvents (DESs) has proven to result in the removal of impurities and the enhancement of gasoline quality. Seven DESs were employed in a batch extraction process to purify the model fuel. The TbabFa-0 solvent was chosen for extraction in millireactors with different lengths, volume flows, and solvent ratios. In the millireactor, a slug regime and a laminar flow pattern were established for every process condition. For the chosen process conditions, the diffusion coefficient, volumetric mass transfer coefficient, and distribution ratio were determined. Better separation of all three key components was achieved during extraction in a millireactor using TbabFa-0. The efficiency of extraction with regenerated solvent was lowered by a maximum of 8%, showing the possibility of performing extraction in a millireactor with solvent recirculation. Full article

Non-alcoholic beer is becoming more and more popular every year. Due to the high demand for such drinks, numerous breweries decided to produce non-alcoholic beer. There are various methods to create a beer with a reduced alcohol content. Among them are biological methods influencing the biochemistry of the brewing process and physical methods focused on removing ethanol from ready beer. Thus far, the most popular methods are vacuum rectification and reverse osmosis. This work evaluated another method called pervaporation for non-alcoholic beer production. During the study, low-alcohol beer (0.58 vol.%) was achieved from standard beer (3.62 vol.%) using pervaporation. The colour of the product remained unchanged at level 7 EBC. The concentration of ferulic acid decreased from 11.5 to 9.1 mg/dm³, and maltol was concentrated, reaching a concentration of 38 mg/dm³ in the final retentate during a 5 h process. Full article

The effect of sintering temperature on the structural, magnetic, and dielectric properties of NiCr₂O₄ ceramics was investigated. A powder X-ray analysis indicates that the prepared nanocrystallites effectively inhibit the cooperative Jahn–Teller distortion, thereby stabilizing the high-temperature cubic phase structure with space group Fd-3m. Multiple transitions are confirmed by temperature-dependent magnetization M(T) data. Moreover, the magnetization value decreases and the Curie temperature increases with a decrease in the crystallite size. The low-temperature-dependent real permittivity (ε′-T) for a NiCr₂O₄ crystallite size of 78 nm exhibits a broad maximum at 40 K that is independent of frequency. This establishes a correlation between electric ordering and the underlying magnetic structure. The temperature dependency of the dielectric constant at fixed frequencies for both NiCr₂O₄ crystallite sizes rises with temperature for a certain range of frequencies. A significant improvement is evident: the dielectric constant (ε’) at room temperature reaches approximately 5738 for the sample with 28 nm crystallites, while the 78 nm crystallite sample shows a noticeable drop to ε’~174. The frequency-dependent conductivity curves for both types of NiCr₂O₄ nanocrystallites have different conductivity values. The lower-crystallite-size sample demonstrates higher conductivity values than the 78 nm crystallite size one. This observation is attributed to the decrease in crystallite size, which increases the number of grain boundaries and, consequently, scatters a higher number of charge carriers. Full article