ChemEngineering

22 pages, 7747 KB

Open AccessArticle

Crack the Shell by Unlocking the Polyphenol Power of Hazelnut Waste with Ultrasound

by Jana Šic Žlabur, Margareta Đumbir, Anamarija Peter, Jona Šurić, Sandra Voća, Martina Skendrović Babojelić, Filip Varga and Mia Dujmović

ChemEngineering 2026, 10(2), 27; https://doi.org/10.3390/chemengineering10020027 - 6 Feb 2026

Abstract

Hazelnut (Corylus avellana L.) shells, typically discarded as agro-industrial by-products, represent a potentially valuable source of bioactive polyphenolic compounds with significant antioxidant properties. This study aimed to evaluate and compare the polyphenol composition and antioxidant capacity of the kernels and shells of [...] Read more.

Hazelnut (Corylus avellana L.) shells, typically discarded as agro-industrial by-products, represent a potentially valuable source of bioactive polyphenolic compounds with significant antioxidant properties. This study aimed to evaluate and compare the polyphenol composition and antioxidant capacity of the kernels and shells of two hazelnut varieties, ‘Rimski’ and ‘Istarski duguljasti’. High-intensity ultrasound-assisted extraction (UAE) was applied to enhance the recovery of bioactive compounds under optimized conditions (80% ethanol, high amplitude, and 25 min treatment). The extracts were analyzed for total polyphenols, total flavonoids, total non-flavonoids, and individual phenolic compounds. Hazelnut shells exhibited significantly higher levels of total polyphenols, flavonoids, and antioxidant capacity compared to kernels. The dominant individual polyphenolic compounds identified in the shell were kaempferol, gallic acid, naringin, rutin trihydrate, quercetin-3-glucoside, chlorogenic acid, quercetin, ferulic acid, rosmarinic acid, and vanillic acid. Application of UAE notably improved extraction efficiency and overall yield compared to conventional extraction methods. The findings underscore hazelnut shells as a nutritionally and functionally valuable by-product and confirm UAE as a green, efficient extraction technique. These results provide a strong basis for developing high-value-added products for the cosmetic, pharmaceutical, and food industries, thereby supporting circular bioeconomy and sustainable chemistry principles. Full article

(This article belongs to the Special Issue Advances in Sustainable and Green Chemistry)

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17 pages, 2085 KB

Open AccessArticle

Performance Evaluation of Nano Ag/Co Modified Hydroxyapatite Catalyst Synthesized via Dielectric Barrier Discharge for Highly Efficient Toluene Oxidation

by Shu-Yao Zhang, Xue-Min Wang, En-Peng Deng, Ya-Ni Zhang, Hui Zhu, Qiang Chen, Si-Wen Pan and Yu-Xin Miao

ChemEngineering 2026, 10(2), 26; https://doi.org/10.3390/chemengineering10020026 - 5 Feb 2026

Abstract

In this study, a series of Ag/Co-HA catalysts were synthesized using a plasma-assisted method. Plasma is a partially ionized gas composed of electrons, ions, neutral molecules, free radicals, photons, and excited-state substances, which can serve as a highly reactive medium for catalyst modification. [...] Read more.

In this study, a series of Ag/Co-HA catalysts were synthesized using a plasma-assisted method. Plasma is a partially ionized gas composed of electrons, ions, neutral molecules, free radicals, photons, and excited-state substances, which can serve as a highly reactive medium for catalyst modification. Its unique discharge characteristics can effectively regulate the dispersion of active sites, electronic structure, and metal–support interactions. The study compared the performance of catalysts prepared by the traditional high-temperature calcination method with those treated by rapid plasma in the toluene oxidation removal reaction. The results showed that the catalyst treated by dielectric barrier discharge (DBD) plasma exhibited excellent low-temperature catalytic activity, achieving 100% toluene conversion and approximately 75% CO₂ selectivity at 275 °C, while the catalyst prepared by traditional calcination only achieved 73% toluene conversion and approximately 50% CO₂ selectivity at 285 °C. This study provides a simple preparation method for the Ag/5Co-HA-P catalyst. Due to the plasma treatment’s ability to precisely control the catalyst structure, along with advantages such as low energy consumption, short processing time, and environmental friendliness, it holds significant application prospects in the field of VOCs treatment. Full article

(This article belongs to the Special Issue Advanced Functional Materials and Interfaces for Electrochemical Energy Storage and Environmental Catalysis)

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24 pages, 1974 KB

Open AccessReview

Catalytic Oxidation of Alkanes and Cycloalkanes: Overview

by Aygun Zabit Aliyeva, Ulviyya Aliman Karimova, Sahib Gadji Yunusov, Michael Vigdorowitsch and Sevinj Abdulhamid Mammadkhanova

ChemEngineering 2026, 10(2), 25; https://doi.org/10.3390/chemengineering10020025 - 3 Feb 2026

Abstract

Selective functionalisation of inert C(sp³)–H bonds in alkanes and cycloalkanes remains one of the main challenges in the field of environmentally sustainable chemistry. This review provides a critical assessment of current catalytic strategies, in particular addressing the persistent problem of overoxidation [...] Read more.

Selective functionalisation of inert C(sp³)–H bonds in alkanes and cycloalkanes remains one of the main challenges in the field of environmentally sustainable chemistry. This review provides a critical assessment of current catalytic strategies, in particular addressing the persistent problem of overoxidation and low selectivity. Going beyond traditional compartmentalised summaries, this work identifies a significant trend towards the integration of non-traditional activation methods, including ultrasonic cavitation, photocatalysis, and nanosecond pulse discharges, in both homogeneous and heterogeneous systems. Key contributions include a comparative analysis of radical control strategies, in particular highlighting how intermediate hydroperoxides can be used to shift reaction pathways towards selectivity of over 97% for alcohols and ketones. In addition, we discuss the emerging role of carbon nanomaterials (e.g., fullerenes and brominated nanotubes) as active electron-rich carriers and catalysts that lower the energy barriers for C–H activation under mild, ‘green’ conditions. The review concludes that the future of scalable hydrocarbon oxidation lies in ‘hybrid’ approaches such as stabilising active metal centres in protective matrices (zeolites, polymers) while using physical stimuli (ultrasound) to overcome diffusion limitations. This unique perspective highlights the transition from purely chemical catalyst design to integrated process intensification, offering a roadmap for energy-efficient and environmentally friendly industrial technologies. Full article

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19 pages, 8765 KB

Open AccessArticle

Kinetics of Decomposition in Alkaline Media NaOH and Ca(OH)₂ of Thallium Jarosite

by Hernán Islas, J. Eliecer Méndez, Francisco Patiño, Sayra Ordoñez, Iván A. Reyes, Paola B. Bocardo, Martín Reyes, Miriam Estrada and Mizraim U. Flores

ChemEngineering 2026, 10(2), 24; https://doi.org/10.3390/chemengineering10020024 - 3 Feb 2026

Abstract

Thallium is one of the most toxic elements on the planet, and one alternative method for its precipitation is through jarosite-type compounds. Therefore, in this work, the kinetics of thallium jarosite were evaluated in an alkaline medium (NaOH and Ca(OH)₂). Experiments [...] Read more.

Thallium is one of the most toxic elements on the planet, and one alternative method for its precipitation is through jarosite-type compounds. Therefore, in this work, the kinetics of thallium jarosite were evaluated in an alkaline medium (NaOH and Ca(OH)₂). Experiments were conducted to assess the effect of medium concentration from 0.03 M to 5.5 × 10⁻⁴ M and the effect of temperature from 20 °C to 60 °C. The sigmoidal curves showed an induction period, during which there was no release of sulfur or thallium ions into the solution, nor the formation of solid byproducts, according to the X ray diffraction (XRD) results. Similarly, a progressive conversion period was observed, evidenced by the release of sulfur and thallium ions into the solution and the formation of amorphous solids. Finally, a stability zone is reached, indicating that the decomposition reaction has ended, as there are no changes in the concentration of sulfur and thallium ions in the solution. The reaction was monitored by determining S using Inductively Coupled Plasma (ICP). The experimental results for the progressive conversion period show a better fit to the chemically controlled shrinking core kinetic model. The reaction order for the kinetics in NaOH medium is 1.09 for the induction period and 0.89 for the progressive conversion period, while for Ca(OH)₂ medium it is 0.78 for the induction period and 0.47 for the progressive conversion period. The activation energies for the progressive conversion period in the two proposed media are 91.87 kJ mol⁻¹ in NaOH and 71.14 kJ mol⁻¹ in Ca(OH)₂, indicating that the controlling mechanism in both systems is the chemical reaction. For the induction period, the activation energies are 101.52 kJ mol⁻¹ and 79.45 kJ mol⁻¹, respectively, indicating that the chemical reaction also controls the initiation of the reactions. The high activation energy in both reaction media suggests that high concentrations of OH⁻ and high temperatures are required to initiate the decomposition reaction. Thallium jarosite precipitates a large amount of thallium and requires high energy to decompose, so it could be a viable alternative in thallium retention. Full article

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24 pages, 2451 KB

Open AccessArticle

Calculation, Measurement and Validation for Estimating the Biomass of the Biofilm on Microcarriers

by Tamás Kloknicer, Gergő Bálint Sárfi, Dániel Benjámin Sándor and Anita Szabó

ChemEngineering 2026, 10(2), 23; https://doi.org/10.3390/chemengineering10020023 - 2 Feb 2026

Abstract

Traditional carriers play a major role in wastewater treatment worldwide due to their reliability, ease of production, well-established analytical methods, and strong treatment performance. Recent studies indicate that polyvinyl-alcohol-based microcarriers may surpass conventional media, as their smaller size, higher porosity, and increased specific [...] Read more.

Traditional carriers play a major role in wastewater treatment worldwide due to their reliability, ease of production, well-established analytical methods, and strong treatment performance. Recent studies indicate that polyvinyl-alcohol-based microcarriers may surpass conventional media, as their smaller size, higher porosity, and increased specific surface area enable them to retain substantially more biomass within reactors. However, their practical application remains limited because fewer analytical methods and studies exist for these materials, largely due to their small dimensions and heat sensitivity, and their behaviour under industrial conditions—including their kinetics—has yet to be fully characterised and validated. This study aims to address these gaps by reviewing existing biomass measurement standards and highlighting their limitations when applied to microcarriers and by proposing alternative experimental approaches better suited for evaluating biomass on such sensitive yet high-capacity carriers. We present a set of experimental methods (still subject to further refinement) that demonstrate reliable performance with these materials, and to validate our approach, we quantified biomass in both in vitro systems and containerised-scale technologies, reaching up to 14 kg/m³ during winter and 8.7 kg/m³ in spring. Laboratory-scale experiments showed that both heterotrophic and autotrophic cultures can achieve high biomass levels of up to 21 kg/m³ and 16 kg/m³, respectively. Heterotrophs exhibited lower growth inhibition under shear stress, while autotrophs displayed a distinct shear-force niche around 0.09 µN within the reactor. Full article

(This article belongs to the Special Issue Advances in Chemical Engineering and Wastewater Treatment)

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19 pages, 4096 KB

Open AccessArticle

Kinetics of Propene Oxidation to Acrolein over Bismuth Molybdates

by Tomislav Penović, Vesna Tomašić, Aleksandra Sander, Stanislav Kurajica and Zoran Gomzi

ChemEngineering 2026, 10(2), 22; https://doi.org/10.3390/chemengineering10020022 - 2 Feb 2026

Abstract

The conversion of alkanes/alkenes into useful intermediates is highly important in the chemical industry. In this study, the physicochemical properties and catalytically active forms of bismuth molybdates (BiMo) were investigated using the selective oxidation of propene to acrolein as a model reaction. The [...] Read more.

The conversion of alkanes/alkenes into useful intermediates is highly important in the chemical industry. In this study, the physicochemical properties and catalytically active forms of bismuth molybdates (BiMo) were investigated using the selective oxidation of propene to acrolein as a model reaction. The catalysts were prepared by two methods, coprecipitation and spray-drying, with emphasis on spray-drying. The catalysts were characterized using X-ray diffraction, N₂ adsorption/desorption isotherms, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The catalytic properties of the BiMo samples were studied in a conventional fixed-bed reactor operated under different reaction conditions. The one-dimensional (1D) pseudohomogeneous model was applied to describe the obtained experimental results. The experimental kinetic data were correlated with two complex kinetic models based on multiple reactions (parallel and serial reaction systems). The proposed models were verified by comparing computer simulation data with experimental laboratory results. This study aimed to extend the understanding of the relationship between catalyst composition/structure and catalyst activity/selectivity for different BiMo structures, and to propose kinetic models using two approaches based on parallel and series reactions, in line with efforts to improve the valorization of light olefins. Full article

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24 pages, 3277 KB

Open AccessArticle

Yttrium Sulfate Recovery Using Ethanol as Antisolvent in a Fluidized Bed Reactor

by Jacolien Sussens, Jemitias Chivavava and Alison E. Lewis

ChemEngineering 2026, 10(2), 21; https://doi.org/10.3390/chemengineering10020021 - 2 Feb 2026

Abstract

Antisolvent crystallization is a promising method for recovering rare earth elements (REEs). While it offers high theoretical yields of Y₂(SO₄)₃·nH₂O from aqueous leach solutions, the recovery is constrained by kinetic limitations. This study examined the [...] Read more.

Antisolvent crystallization is a promising method for recovering rare earth elements (REEs). While it offers high theoretical yields of Y₂(SO₄)₃·nH₂O from aqueous leach solutions, the recovery is constrained by kinetic limitations. This study examined the crystallization of Y₂(SO₄)₃·nH₂O in a fluidized bed reactor (FBR) using ethanol, focusing on the effects of the organic-to-aqueous (O/A) ratio and flow rates on yield and crystal properties. O/A ratios of 0.9 and 1.1 were investigated with an initial Y³⁺ concentration of 0.87 g/L and a crystallization time of 3 h. The system exhibits multiple rate-limiting steps. At low O/A ratios (0.9), extended induction times indicate either nucleation rate-limitations despite high supersaturation or the possible formation of an initial metastable phase, requiring extended crystallization time for near-equilibrium yields. At high O/A (1.1), elevated supersaturation accelerates nucleation and achieves ~82% yield in 3 h; however, crystal growth exhibited a remaining rate limitation. Lower supersaturation and slower mixing at O/A = 0.9 favored growth, producing crystals with D50 > 34 µm. This work explores how operational parameters influence crystallization behavior while achieving practical yields and acceptable crystal characteristics within a reasonable timeframe. The FBR provided controlled operation, enabling consistent product formation and process flexibility. Full article

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19 pages, 2797 KB

Open AccessArticle

Enhancing Operational Reliability in Industrial PTA Oxidation Reactors Using a Robust Cascade Control Scheme

by Andri Kapuji Kaharian, Theo Adiwinata, Riezqa Andika and Abdul Wahid

ChemEngineering 2026, 10(2), 20; https://doi.org/10.3390/chemengineering10020020 - 2 Feb 2026

Abstract

Maintaining stable pressure in the oxidation–compressor section of purified terephthalic acid (PTA) plants is essential for ensuring efficient and reliable operation. Conventional single-loop proportional integral derivative (PID) controllers frequently perform inadequately because of the large pressure drop between the compressor discharge and reactor [...] Read more.

Maintaining stable pressure in the oxidation–compressor section of purified terephthalic acid (PTA) plants is essential for ensuring efficient and reliable operation. Conventional single-loop proportional integral derivative (PID) controllers frequently perform inadequately because of the large pressure drop between the compressor discharge and reactor inlet, which should ideally remain at approximately 1.2 kg/cm² above the reactor pressure setpoint but can reach up to 2.8 kg/cm² due to downstream vapor-phase disturbances. Through this study, we aimed to address this issue by developing a robust cascade pressure control strategy to improve pressure stability and reduce energy losses. Dynamic process models were constructed using system identification techniques to represent real plant behavior, and the best-performing models—identified based on minimum root mean square error (RMSE)—were determined using the Wade method for pressure indicating controller PIC-101, the Lilja method for PIC-102, and the Smith method for pressure differential indicating controller PDIC-101. The proposed cascade configuration was tuned using the Lopez ISE method and evaluated under representative disturbance scenarios. The results showed that the cascade controller significantly improved pressure control, enhanced disturbance rejection, and lowered the risk of reactor shutdowns compared with the conventional proportional-integral PI-based approach. Overall, this study demonstrated that model-driven cascade control can enhance robustness, operational reliability, and energy efficiency in large-scale PTA oxidation processes. Full article

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15 pages, 1948 KB

Open AccessArticle

Advanced Oxidation of PET-Derived Monomers Using Excimer Radiation and Hydrogen Peroxide: Kinetic and Operational Insights

by María Gómez, María Claudia Montiel, Elisa Gómez, Asunción María Hidalgo, Fuensanta Máximo and María Dolores Murcia

ChemEngineering 2026, 10(2), 19; https://doi.org/10.3390/chemengineering10020019 - 29 Jan 2026

Abstract

Growing environmental concern over plastic pollution has increased the need to address the persistence of PET-derived monomers, such as bis(2-hydroxyethyl) terephthalate (BHET) and terephthalic acid (TPA). This work examines the use of excimer radiation lamps combined with hydrogen peroxide (H₂O₂ [...] Read more.

Growing environmental concern over plastic pollution has increased the need to address the persistence of PET-derived monomers, such as bis(2-hydroxyethyl) terephthalate (BHET) and terephthalic acid (TPA). This work examines the use of excimer radiation lamps combined with hydrogen peroxide (H₂O₂) to enhance advanced oxidation processes (AOPs) for their degradation. This approach stands out for its high selectivity, absence of mercury, and lower production of toxic byproducts. Experimental tests assessed how different operational factors affect pollutant degradation, such as the initial pollutant concentration (50–200 mg/L), the reaction volume (125–500 mL), and the H₂O₂:monomer mass ratio (0:1–6:1 for BHET and 0:1–4:1 for TPA). For BHET, the best results occurred with a 5:1 mass ratio, while TPA degraded optimally with a 3:1 ratio, with a 250 mL reaction volume and a 100 mg/L initial concentration for both compounds. Under these conditions, total degradation of the initial monomers was achieved in around 30 and 80 min for BHET and TPA, respectively, and at the end of the reaction, COD decreased by 46% and 32% relative to their initial values. In both cases, hydrogen peroxide was crucial since UV radiation alone led to much lower degradation efficiency. These results emphasize the need to optimize operational conditions for greater efficiency and establish a starting point for future use of excimer technology in the treatment of wastewater contaminated with PET and its derivatives. Additionally, the degradation data closely matched a pseudo-first-order kinetic model (R² ≈ 1), confirming its reliability for predictive analysis, which is of high importance for the simulation and optimization of the process. Full article

(This article belongs to the Special Issue Advances in Chemical Engineering and Wastewater Treatment)

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13 pages, 661 KB

Open AccessArticle

A Preliminary Investigation into the Influence of Low-Intensity Natural Mid-Infrared and Far-Infrared/Near-Microwave Emissions on the Aroma and Flavor of a Young Dry Red Wine

by Sanghoon Lee, Changgook Lee, Hyunhee Jeong, Sejun Kim, Eok Kyun Lee and Alan J. Buglass

ChemEngineering 2026, 10(2), 18; https://doi.org/10.3390/chemengineering10020018 - 29 Jan 2026

Abstract

Brief treatment of a bottled young dry red wine with low-intensity natural emissions in the mid-infrared and far-infrared/near-microwave regions of the electromagnetic spectrum resulted in moderate changes in the concentrations of certain odorants in the wine headspace (vapor), as shown by headspace–solid-phase microextraction–gas [...] Read more.

Brief treatment of a bottled young dry red wine with low-intensity natural emissions in the mid-infrared and far-infrared/near-microwave regions of the electromagnetic spectrum resulted in moderate changes in the concentrations of certain odorants in the wine headspace (vapor), as shown by headspace–solid-phase microextraction–gas chromatography/mass spectrometry (HS-SPME-GC/MS). The headspace levels of certain long-chain ethyl carboxylate esters and methyl salicylate were somewhat enhanced, whereas those of certain aromatic monohydric alcohols, a succinate ester, and oak lactone were somewhat depleted. A tentative explanation of these results is offered whereby waveform treatment results in general re-organization of non-covalent associations of both odorant (volatile) and non-volatile components in wine, leading to the preferential extra release of certain odorants into the headspace (vapor phase) and preferential increased trapping of certain other odorants in wine (liquid phase). Full article

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23 pages, 6146 KB

Open AccessArticle

Intensification of Mixing Processes in Stirred Tanks Using Specific-Power-Matching Double-Stage Configurations of Radially and Axially Pumping Impellers

by Lena Kögel, Achim Gieseking, Carina Zierberg, Mathias Ulbricht and Heyko Jürgen Schultz

ChemEngineering 2026, 10(2), 17; https://doi.org/10.3390/chemengineering10020017 - 26 Jan 2026

Abstract

Mixing processes in stirred tanks are widely applied across various industries, but still offer significant potential for optimization. A promising strategy is the use of double-stage impeller setups instead of conventional single impellers. While multi-impeller configurations are common in tall vessels, their benefits [...] Read more.

Mixing processes in stirred tanks are widely applied across various industries, but still offer significant potential for optimization. A promising strategy is the use of double-stage impeller setups instead of conventional single impellers. While multi-impeller configurations are common in tall vessels, their benefits for standard tanks with a height-to-diameter ratio of 1 are largely unexplored. This study systematically investigates the flow fields of single, identical, and mixed double-stage configurations of a Rushton turbine, a pitched-blade turbine, and a retreat curve impeller. To ensure balanced power input in mixed configurations, a refined method for harmonizing specific power via impeller diameter adjustment is proposed. Stereo particle image velocimetry is applied to visualize flow fields, supported by refractive-index matching to enable measurements in a dished-bottom tank. The results reveal substantial flow deficiencies in single-impeller setups. In contrast, double-impeller setups generate novel and significantly improved velocity fields that offer clear advantages and demonstrate strong potential to enhance process efficiency across various mixing applications. These findings provide new experimental insights into the characteristics of dual impellers and form a valuable basis for the design and scale-up of stirred tanks, contributing to more efficient, reliable, and sustainable mixing processes. Full article

(This article belongs to the Special Issue Process Intensification for Chemical Engineering and Processing)

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16 pages, 1740 KB

Open AccessArticle

Optimization of Conditions for Ethyl Acetate Extraction of Mono-, Di-, Triglycerides and Free Fatty Acids from Soapstock Using Response Surface Methodology

by Svetlana Zhizhkun, Lauma Laipniece and Igors Astrausks

ChemEngineering 2026, 10(1), 16; https://doi.org/10.3390/chemengineering10010016 - 14 Jan 2026

Abstract

Soapstock (SS), a by-product of vegetable oil refining, is a promising source of a mixture of mono-, di-, triglycerides, and free fatty acids (MDTG-FFA), a valuable feedstock for biodiesel production. In this study, the selective extraction of MDTG-FFA from SS using green solvents [...] Read more.

Soapstock (SS), a by-product of vegetable oil refining, is a promising source of a mixture of mono-, di-, triglycerides, and free fatty acids (MDTG-FFA), a valuable feedstock for biodiesel production. In this study, the selective extraction of MDTG-FFA from SS using green solvents (ethyl acetate, ethyl formate, methyl acetate, isopropyl acetate, and isobutanol) was investigated. Ethyl acetate showed the highest efficiency, allowing the elimination of the phosphatide (PL) precipitation step with acetone. The process optimization was carried out by response surface methodology with central composite design. Statistical analysis confirmed the significance of the obtained models: F-values were 4.55 (p = 0.013) for MDTG-FFA and 9.62 (p = 0.00074) for PL. Regression analysis revealed a good fit of the experimental data with quadratic models for MDTG-FFA and PL, with coefficients of determination (R²) of 0.804 and 0.897, respectively. The optimum extraction parameters were a solvent-to-dry-matter-of-SS ratio 5:1, time 10.2 min, and initial extraction temperature 21.7 °C. Under these conditions, maximum MDTG-FFA yields of 12.6% and 13.4% were achieved for the two batches of SS, respectively, with minimum PL yields of 0.02% and 0.1%. The obtained MDTG-FFA extracts rich in free fatty acids represent a promising feedstock for biodiesel production. The proposed method provides a rational, resource-efficient, and environmentally preferable extraction of valuable components from SS. Full article

(This article belongs to the Topic Green and Sustainable Chemical Processes)

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25 pages, 5522 KB

Open AccessArticle

Green Synthesis of ZnO Nanoparticles: Effect of Synthesis Conditions on Their Size and Photocatalytic Activity

by Veronika Yu. Kolotygina, Arkadiy Yu. Zhilyakov, Maria A. Bukharinova, Ekaterina I. Khamzina and Natalia Yu. Stozhko

ChemEngineering 2026, 10(1), 15; https://doi.org/10.3390/chemengineering10010015 - 14 Jan 2026

Abstract

Green technologies are actively being used to produce nanosized zinc oxide, which is in demand for water purification processes to remove pollutants. Despite the success of the green synthesis of ZnO nanoparticles, no scientific approach exists for selecting plant extracts to produce nanoparticles [...] Read more.

Green technologies are actively being used to produce nanosized zinc oxide, which is in demand for water purification processes to remove pollutants. Despite the success of the green synthesis of ZnO nanoparticles, no scientific approach exists for selecting plant extracts to produce nanoparticles with the desired properties. This study shows that the antioxidant activity of the plant extracts used is a key parameter influencing the properties of the resulting ZnO nanoparticles. This conclusion is based on the results of nanoparticle synthesis with the use of various plant extracts. The antioxidant activity of the extracts increases in the following order: plum–gooseberry–black currant–strawberry–sea buckthorn. The synthesized ZnO nanoparticles were characterized by UV–visible spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The catalytic properties of ZnO nanoparticles were tested under the degradation of a synthetic methylene blue dye after exposure to UV light. We found that with an increase in the AOA of plant extracts, the size of the nanoparticles decreases, while their photocatalytic activity increases. The smallest (d = 13 nm), most uniform in size (polydispersity index 0.1), and most catalytically active ZnO nanoparticles with a small band gap (2.85 eV) were obtained using the sea buckthorn extract with the highest AOA, pH 10 of the reaction mixture and 0.1 M Zn(CH₃COO)₂∙2H₂O as a precursor salt. ZnO nanoparticles synthesized in the sea buckthorn extract demonstrated the highest dye photodegradation efficiency (96.4%) compared with other nanoparticles. The established patterns demonstrate the “antioxidant activity–size–catalytic activity” triad can be considered as a practical guide for obtaining ZnO nanoparticles of a given size and with given properties for environmental remediation applications. Full article

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15 pages, 2845 KB

Open AccessArticle

One-Step CO₂-Assisted Pyrolysis of Spent Coffee Grounds: A Simpler Route to Highly Porous Biochar Compared with Two-Step Pyrolysis–CO₂ Activation

by Ancuţa Balla, Cristina Marcu, Maria Mihet, Irina Kacsó, Septimiu Tripon, Alexandru Turza and József-Zsolt Szücs-Balázs

ChemEngineering 2026, 10(1), 14; https://doi.org/10.3390/chemengineering10010014 - 14 Jan 2026

Abstract

Spent coffee grounds (SCG) are an abundant, carbon-rich residue that can be valorized through thermochemical conversion into biochar. Conventional CO₂ activation is typically performed in a two-step process, which is time- and energy-consuming. This study aims to evaluate whether a one-step CO [...] Read more.

Spent coffee grounds (SCG) are an abundant, carbon-rich residue that can be valorized through thermochemical conversion into biochar. Conventional CO₂ activation is typically performed in a two-step process, which is time- and energy-consuming. This study aims to evaluate whether a one-step CO₂-assisted pyrolysis can produce biochar with comparable or enhanced structural and textural properties while simplifying the process. We compare a two-step pyrolysis process followed by CO₂ activation with a one-step CO₂-assisted route for producing biochar from SCG. CO₂ treatment markedly increases surface area (from 9.8 m²∙g⁻¹ to 550.6–671.0 m²∙g⁻¹) and pore volume. FTIR and Boehm titration indicate depletion of oxygenated surface groups, while N₂ adsorption–desorption analyses and SEM reveal a more uniform micro/mesoporous texture for the one-step sample. Although fixed carbon decreases due to gasification, the one-step route delivers superior textural properties in a single thermal stage, reducing energy demand. These results highlight one-step CO₂-assisted pyrolysis as an efficient, scalable option for producing high-porosity biochar from coffee waste. Full article

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15 pages, 1465 KB

Open AccessArticle

Experimental Study of Hydrodynamics During Fluid Flow from a Nozzle in a Differential-Contact Centrifugal Extractor

by Sergey Ivanovich Ponikarov and Artem Sergeevich Ponikarov

ChemEngineering 2026, 10(1), 13; https://doi.org/10.3390/chemengineering10010013 - 12 Jan 2026

Abstract

Modern processes to produce rare-earth elements, strategic metals, and nuclear fuel reprocessing require highly efficient liquid–liquid extraction in systems characterized by high viscosity, elevated interfacial tension, and small density differences. Traditional gravity-driven extractors exhibit low performance under these conditions, whereas centrifugal extractors enable [...] Read more.

Modern processes to produce rare-earth elements, strategic metals, and nuclear fuel reprocessing require highly efficient liquid–liquid extraction in systems characterized by high viscosity, elevated interfacial tension, and small density differences. Traditional gravity-driven extractors exhibit low performance under these conditions, whereas centrifugal extractors enable rapid mass transfer and nearly complete phase separation. Differential-contact annular centrifugal contactors offer the highest flexibility and efficiency, but their optimization is limited by the lack of experimental data on the hydrodynamics of liquid flow through perforated nozzles in a rotating field. This limitation hinders the development of accurate computational fluid dynamics (CFD) models (e.g., ANSYS Fluent), reliable equipment scale-up, and the design of optimized contactor configurations. The present study addresses this gap by experimentally determining the flow velocity of liquids through nozzles of various geometries across a wide range of centrifugal accelerations. From these data, a universal power-law correlation was derived, linking the flow rate to rotor speed, nozzle geometry, and the physicochemical properties of the phases. The proposed correlation provides a robust experimental basis for numerical model validation, computational design, and optimization of next-generation differential-contact centrifugal extractors. Full article

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17 pages, 612 KB

Open AccessArticle

Drying Methods Applied to Ionic Gelation of Mangaba (Hancornia speciosa) Pulp Microcapsules

by Jordan Heiki Santos Uemura, João Renato de Jesus Junqueira, Ângela Christina Conte Theodoro, Jefferson Luiz Gomes Corrêa, Thaisa Carvalho Volpe Balbinoti and Juliana Rodrigues do Carmo

ChemEngineering 2026, 10(1), 12; https://doi.org/10.3390/chemengineering10010012 - 12 Jan 2026

Abstract

Brazil is one of the richest countries in biodiversity, with biomes that host countless native species of ecological and economic relevance. Among its native fruits, mangaba (Hancornia speciosa) stands out for its nutritional relevance. However, its industrial use remains limited by [...] Read more.

Brazil is one of the richest countries in biodiversity, with biomes that host countless native species of ecological and economic relevance. Among its native fruits, mangaba (Hancornia speciosa) stands out for its nutritional relevance. However, its industrial use remains limited by seasonality, perishability, and harvesting difficulties. This study evaluated the effects of different drying techniques—convective (CD), microwave (MWD), and infrared (IRD)—on the physical and chemical properties of mangaba pulp microcapsules obtained by ionic gelation, including drying kinetics. Drying time varied markedly among treatments, ranging from 25 (MWD) to 185 (IRD) min. In general, the Page modified model provided the best fit for drying kinetics. Physical analyses revealed that IRD produced microcapsules with higher wettability (43.33 s), lower hygroscopicity (203.01 g/100 g), and higher bulk (0.382 g/cm³) and particle density (1.339 g/cm³). CD resulted in greater dispersibility (248.45%) and porosity (0.732), whereas MWD showed the lowest water absorption index (1.78). Regarding bioactive compounds, IRD retained the highest ascorbic acid content, CD preserved more antioxidant activity, and MWD presented the highest total phenolic content. Overall, despite the different processes, mangaba microcapsules retained relevant levels of bioactive compounds, confirming the potential of ionic gelation combined with drying as an effective preservation strategy. Full article

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17 pages, 4456 KB

Open AccessArticle

Sustainable Adsorption of Rhodamine B and Heavy Metals Using Sewage Sludge-Derived Biochar

by Yerkanat N. Kanafin, Assylzhan Mukhametrakhimova, Rauza Turpanova and Stavros G. Poulopoulos

ChemEngineering 2026, 10(1), 11; https://doi.org/10.3390/chemengineering10010011 - 9 Jan 2026

Abstract

The sustainable management of sewage sludge remains a key environmental challenge for rapidly urbanizing regions such as Kazakhstan. This study explores the potential of sewage sludge-derived biochar as an efficient, low-cost adsorbent for removing Rhodamine B (RhB) dye and toxic metals from water. [...] Read more.

The sustainable management of sewage sludge remains a key environmental challenge for rapidly urbanizing regions such as Kazakhstan. This study explores the potential of sewage sludge-derived biochar as an efficient, low-cost adsorbent for removing Rhodamine B (RhB) dye and toxic metals from water. Sewage sludge was pyrolyzed at 700 °C (BC) and subsequently activated with hydrochloric acid (BCH) and sodium hydroxide (BCN) to improve its surface functionality and porosity. The morphology, surface area, porosity, and functional groups of the obtained biochars were characterized using SEM-EDS, BET, FTIR, and XRD analyses. Batch adsorption experiments demonstrated that the pseudo-second-order kinetic model (R² = 0.99) best described the data, indicating chemisorption-controlled uptake. Experimental RhB adsorption capacity was 14.53 mg/g for BCH at RhB concentration of 75 mg/L after 120 min. Moreover, BCH exhibited enhanced metal adsorption capacities of 22.85 mg/g (Cu²⁺), 17.55 mg/g (Zn²⁺), 15.08 mg/g (Cd²⁺), 7.97 mg/g (Cr³⁺), and 3.68 mg/g (As³⁺). These results confirm that acid activation significantly improves adsorption efficiency compared with pristine biochar due to increased surface area and the introduction of oxygen-containing functional groups. Overall, sewage sludge-derived biochar shows strong potential as a sustainable adsorbent for dye and heavy metal removal. Full article

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16 pages, 2943 KB

Open AccessArticle

Carbon Filters Modified with Synthesized TiO₂, Fe₃O₄ and CaO via Mechanical Milling for Methylene Blue Adsorption

by Fatima Pamela Lara-Castillo, Jorge Carlos Ríos-Hurtado, Sergio Enrique Flores-Villaseñor, Alejandro Pérez-Alvarado, Rumualdo Servin-Castañeda, Gloria I. Dávila-Pulido and Adrián A. González-Ibarra

ChemEngineering 2026, 10(1), 10; https://doi.org/10.3390/chemengineering10010010 - 8 Jan 2026

Abstract

Although carbon filters (CF) can exhibit limited adsorption/selectivity for certain emerging pollutants and operating conditions, incorporating carbon–metal-oxide composites provides a platform to study how surface chemistry, charge distribution and oxide dispersion influence adsorption behavior. This study investigates the incorporation of metal oxides (Fe [...] Read more.

Although carbon filters (CF) can exhibit limited adsorption/selectivity for certain emerging pollutants and operating conditions, incorporating carbon–metal-oxide composites provides a platform to study how surface chemistry, charge distribution and oxide dispersion influence adsorption behavior. This study investigates the incorporation of metal oxides (Fe₃O₄, TiO₂ and CaO) into a commercial carbon filter via mechanical milling, focusing on fundamental changes in surface properties and methylene blue (MB) adsorption mechanisms. The synthesized oxides were characterized by X-ray diffraction and scanning electron microscopy, confirming crystalline structures with crystalline sizes between 11 and 23 nm. Composite filters with varying oxide contents (10–30 wt%) were evaluated for point of zero charge (PZC), surface charge distribution and methylene blue (MB) adsorption. The kinetic experiments were adjusted to pseudo-second order (PSO). Although the maximum adsorption capacity (2.75 mg·g⁻¹ for CaO-modified filters) is lower than commercially activated carbons, this work clarifies how oxide type and dispersion control adsorption performance and interaction mechanisms. Langmuir and Freundlich models revealed monolayer adsorption with favorable dye-surface interactions. These models provide key insights into the role of oxide type and pH in the dye removal process. Full article

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21 pages, 2489 KB

Open AccessArticle

Assessment of the Yield and Bioactive Compounds of Jambu (Acmella oleracea) Flowers and Leaves Extracted with CO₂, 1,1,1,2-Tetrafluoroethane (R-134a), and Propane

by Marcos Antônio Avibar Ruzza, Raquel Laina Barbosa dos Santos, Nikolas Ramos Bernardes, Carlos Toshiyuki Hiranobe, Dener da Silva Souza, Michael Jones da Silva, Erivaldo Antônio da Silva, Renivaldo José dos Santos and Leandro Ferreira-Pinto

ChemEngineering 2026, 10(1), 9; https://doi.org/10.3390/chemengineering10010009 - 7 Jan 2026

Abstract

This study compares the extraction of oils and bioactive compounds from Acmella oleracea using supercritical CO₂, pressurized R-134a, and propane under systematically designed experimental conditions. Extraction yields ranged from 1.16–3.35% for CO₂, 1.90–2.35% for R-134a, and 1.30–5.42% for propane. [...] Read more.

This study compares the extraction of oils and bioactive compounds from Acmella oleracea using supercritical CO₂, pressurized R-134a, and propane under systematically designed experimental conditions. Extraction yields ranged from 1.16–3.35% for CO₂, 1.90–2.35% for R-134a, and 1.30–5.42% for propane. Propane achieved the highest yields and the fastest plateau (~35 min), producing extracts dominated by unsaturated fatty acids (linoleic acid ≈ 85%). Supercritical CO₂ generated the most diverse chemical profile, combining alkamides (spilanthol), triterpenoids (β-amyrone), and lipids, with a plateau at approximately 50 min, whereas R-134a selectively enriched β-amyrin acetate (~70%) with intermediate kinetics (~45 min). These yield values are typical for non-oilseed species, in which the low natural abundance of the target metabolites renders solvent selectivity more relevant than the total extract mass. Statistical modeling (R² > 0.96) confirmed that pressure was the main driver of CO₂ and propane extraction, whereas temperature dominated R-134a performance. The distinct selectivity patterns revealed by Gas chromatography–mass spectrometry (GC-MS) indicate that each solvent generates compositionally different extracts aligned with specific industrial applications in cosmetics, pharmaceuticals, and nutraceuticals. The unified comparison of these three fluids under a consistent experimental design provides practical insights for rational solvent selection: propane favors unsaturated lipids, CO₂ preserves multifunctional compositions, and R-134a targets triterpenoid esters, supporting the economic feasibility of producing enriched, solvent-free plant extracts. Full article

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