Search Results (607)

Ethanol upgrading via catalytic C–C coupling, commonly known as the Guerbet reaction, offers a sustainable route to produce 1-butanol, a high-performance biofuel. To address gaps in the mechanistic understanding of the catalytic reaction, we investigated the process involving a fixed-bed reactor, operated at 275–325 °C, 21 bar, and weight hourly space velocities of 0.25–2.5 g_EtOH/(g_cat·h), using helium as a carrier gas, with a 5:1 He/EtOH molar ratio. The catalyst was a MgO–Al₂O₃ mixed oxide (Mg/Al = 2:1), derived from a hydrotalcite precursor. A detailed kinetic model was developed, encompassing 15 species and 27 reversible steps (10 sorption and 17 reaction steps), within a 1+1D sorption–reaction–transport framework. Four C₄-forming pathways were included: aldol condensation to form crotonaldehyde, semi-direct coupling to form butyraldehyde and crotyl alcohol, and direct coupling to form 1-butanol. To avoid overfitting, Arrhenius parameters were grouped by reaction type, resulting in sixty rate parameters and one active site-specific density parameter. The optimized model achieved high accuracy, with an average prediction error of 1.44 times the experimental standard deviation. The mechanistic analysis revealed aldol condensation as the dominant pathway below 335 °C, with semi-direct coupling to crotyl alcohol prevailing above 340 °C. The resulting model provides a robust framework for understanding and predicting complex reaction networks in ethanol upgrading systems. Full article

A novel modified oyster shell (MOS-800) was developed to enhance phosphorus sequestration and recovery from wastewater. Approximately 33.3% of phosphate was eliminated by the MOS-800, which also exhibited excellent pH regulation capabilities. In semicontinuous tests, a synergistic phosphorus separation was achieved through the coupling process of CaCl₂/MOS-800 and a circulating fluidized bed (CFB), resulting in an 86.5% phosphate separation. In continuous flow experiments, phosphorus elimination reached 98.2%. Material characterization revealed that hydroxyapatite (HAP) was the primary component of the crystallized products. Additionally, MOS-800 released 506.5–572.2 mg/g Ca²⁺ and 98.1 mg/g OH⁻. A four-stage heterogeneous crystallization mechanism was proposed for the coupling process. In the first stage, Ca²⁺ quickly reacted with phosphate to form Ca-P ion clusters, etc. In the second stage, these clusters packed randomly to form spherical amorphous calcium phosphate (ACP). In the third stage, the ACP spheres were transformed and rearranged into sheet-like HAP crystallites, Finally, in the fourth stage, the HAP crystallites aggregated on the surface of crystal seeds, also with the addition of crystal seeds and undissolved MOS-800, potentially catalyzing the heterogeneous crystallization. These findings suggest that the CaCl₂/MOS-800/CFB system is a promising technique for phosphate recovery from wastewater. Full article

In recent years, packed-bed systems have emerged as an attractive design for thermal energy storage systems due to their high thermal efficiency and economic feasibility. As integral components of numerous large-scale applications systems, packed-bed thermal energy stores can be successfully paired with renewable energy and waste heat to improve energy efficiency. An analysis of the thermal performances of two packed beds (hot and cold) during six-hour charging and discharging cycles has been conducted in this paper using COMSOL Multiphysics software, utilizing the optimal design parameters that have been determined in previous studies, including porosity (0.2), particle diameters (4 mm) for porous media, air as a heat transfer fluid, magnesia as a storage medium, mass flow rate (13.7 kg/s), and aspect ratio (1). The performance has been evaluated during both the charging and discharging cycles, in terms of the system’s capacity factor, the energy stored, and the thermal power, in order to understand the system’s performance and draw operational recommendations. Based on the results, operating the hot/cold storage in the range of 20–80% of the full charge was found to be a suitable range for the packed-bed system, ensuring that the charging/discharging power remains within 80% of the maximum. Full article

Numerous studies have been conducted employing various techniques to remove pollutants from water bodies. Among these techniques, adsorption a surface phenomenon that utilises adsorbents derived from agricultural residues has shown considerable potential for the removal of contaminants such as heavy metals. However, most of these investigations have been carried out at the laboratory scale, with limited efforts directed towards predicting the performance of these systems at an industrial level. Accordingly, the present study aims to model a packed bed column at industrial scale for the removal of Pb(II) and Ni(II) ions from aqueous solutions, employing biomass derived from oil palm residues as the adsorbent material. To achieve this, Aspen Adsorption was used as a modelling and simulation tool to evaluate the impact of bed height, inlet flow rate, and initial concentration through a parametric assessment. This evaluation incorporated the Freundlich, Langmuir, and Langmuir–Freundlich isotherm models in conjunction with the Linear Driving Force (LDF) kinetic model. The results indicated that the optimal operating parameters included a column height of 5 m, a flow rate of 250 m³/day, and an initial metal concentration of 5000 mg/L. Moreover, all models demonstrated removal efficiencies of up to 94.6% for both Pb(II) and Ni(II). An increase in bed height resulted in longer breakthrough and saturation times but led to a reduction in adsorption efficiency. Conversely, higher flow rates shortened these times yet enhanced efficiency. These findings underscore the potential of computational modelling tools as predictive instruments for evaluating the performance of adsorption systems at an industrial scale. Full article

D-allulose is a rare sugar with promising applications in food and health industries, owing to its low caloric value and multiple health benefits. In this study, we systematically investigated a thermostable D-allulose 3-epimerase (TcDAEase) from Thermogemmatispora carboxidivorans for food-compatible continuous production. The enzyme exhibited remarkable thermostability, with over 70% activity retained at 80 °C, and showed broad pH tolerance across the range of 8.0 to 13.0. Notably, TcDAEase exhibited high catalytic activity toward D-allulose and D-fructose even without the addition of metal ions. Moreover, food-grade Mg²⁺ was identified as enhancing enzyme activity by 14.3%, thus ensuring compliance with Generally Recognized as Safe (GRAS) standards for food applications. To improve industrial applicability, the enzyme was immobilized using a chitosan-diatomaceous earth (DE) matrix via three-step adsorption–crosslinking–embedding strategy. The immobilized TcDAEase achieved 48.7% ± 2.4% activity recovery and retained 90.3% ± 1.5% activity over seven reaction cycles. Furthermore, continuous production of D-allulose was realized in a packed-bed reactor, operating stably at 60 °C, pH 8.0 and 5 mM Mg²⁺ for 150 days, producing 756 kg of D-allulose with a conversion yield exceeding 89.7% of the theoretical maximum. Overall, this study provides a feasible strategy for the continuous and efficient production of high-value-added D-allulose in the food industry. Full article

Textile dyeing wastewater is one of the most challenging industrial effluents to treat due to its high concentrations of persistent organic compounds and nitrogenous substances. Conventional treatment methods often fall short in achieving both sufficient removal efficiency and environmental safety. In this study, we aimed to remove the total nitrogen (T-N) and total organic carbon (TOC) of dyeing wastewater from an industrial complex in D City, Korea, by applying bipolar and packed bipolar electrolysis using aluminum (Al) electrodes and activated carbon (AC). The system was operated for 60 min under varying conditions of applied voltage (5–15 V), electrolyte type and concentration (non-addition, NaCl 5 mM, NaCl 10 mM, Na₂SO₄ 5 mM, Na₂SO₄ 10 mM), and AC packing amount (non-addition or 100 g/L). The highest T-N and TOC removal efficiencies were observed at 15 V, reaching 69.53% and 63.68%, respectively. Electrolyte addition significantly improved initial treatment performance, with NaCl 10 mM showing the best results. However, Al leaching also increased, from 549.83 mg/L (non-addition) to 623.06 mg/L (NaCl 10 mM). When AC was used without electrolysis (control experiment), the T-N and TOC removal efficiencies were limited to 30.24% and 29.86%, respectively. In contrast, AC packing combined with 15 V electrolysis under non-addition achieved 86.04% T-N and 77.98% TOC removal, while also reducing Al leaching by 40.12%. These results suggested that electrochemical treatment with AC packing under non-addition conditions offers the best balance between high treatment efficiency and low environmental impact. These findings demonstrate that the synergistic use of packed activated carbon and electrochemical treatment under additive-free conditions can overcome the limitations of conventional methods. This study contributes to the development of more sustainable and effective technologies for treating high-strength industrial wastewater. Full article

This study explores the production of anhydrous ethanol from discarded fruits, aiming to determine optimal fermentation conditions and evaluate the feasibility of a green separation technology. Fermentation experiments were performed using juices from Psidium guajava (S1), Carica paapaya (S2), and mucilage residues of Coffea arabica (S3). All fermentations were carried out at a pH of 4.5 for 7 days in 1 L bioreactors. A full 2² factorial design was applied to evaluate the effects of two variables: yeast type (commercial Saccharomyces cerevisiae [CY] vs. native yeast [NY]) and temperature (21 °C vs. 30 °C). Higher ethanol concentrations were achieved with CY at 30 °C, yielding 6.79% ethanol for S3. A multi-criteria matrix prioritized coffee residues due to their high ethanol yield, biomass availability, and economic viability. The ethanol was dehydrated using a packed-bed bioadsorption system with crushed corn, which increased purity from 6.7% v/v to 98.9% v/v in two stages, while avoiding azeotropic limitations. Energy analysis revealed low specific consumption (3.68 MJ/kg), outperforming conventional distillation. The results of this study, obtained at operating temperatures of 30 °C and 21 °C, a pH of 4.5, and an operating time of 7 days in a 1L bioreactor, demonstrate ethanol concentrations of 6.79%, confirming the technical feasibility of using agricultural waste as a raw material and validating the efficiency of a bioadsorption-based dehydration system. These findings address the current gap in integrating green ethanol separation with low-cost agricultural residues and highlight a sustainable alternative for decentralized bioethanol production. Full article

The scarcity of phosphorus resources and the excessive accumulation of phosphates in aquatic environments pose significant threats to ecological systems and human health, while traditional treatment methods often fail to achieve effective resource recovery and reuse. This study aims to develop an efficient method for phosphate removal and resource recycling through the modification of reed straw (MRS) by introducing amine groups. Key operational parameters such as packed bed height, flow velocity, and initial solute concentration were systematically investigated to optimize MRS’s adsorption efficiency. Experimental results demonstrated that under optimized conditions, MRS achieved a maximum phosphate adsorption capacity of 8.337 mg/g and maintained over 80% efficiency after nine adsorption–desorption cycles. Utilizing the desorbed solution as a nutrient solution significantly enhanced maize seedling growth, increasing stem height by 23.8%, fresh weight by 51.3%, and phosphorus content by 80.7%. These findings highlight MRS’s potential, not only as an effective phosphate adsorbent, but also as a means of successful phosphorus resource recovery and recycling, indicating promising applications in environmental remediation and resource management. Full article

This study evaluated the odor mitigation potential of rice husk biochar in a simulated dairy bedded pack over 21 days. Biochar was incorporated into a dairy manure–sawdust mixture at 5% and 10% dry weight. Emissions of key odorous compounds—ammonia (NH₃), sulfur compounds, volatile fatty acids, phenol, p-cresol, and indole—were evaluated. Odor units were assessed to determine perceived odor reduction. Biochar significantly reduced NH₃ and dimethyl sulfide (DMS) emissions: NH₃ by 27% and 43%, and DMS by 53% and 75%, at 5% and 10% application, respectively. The NH₃ reduction was attributed to ammoniacal nitrogen adsorption, while the DMS reduction likely resulted from enhanced air permeability suppressing anaerobic bacterial activity. The 5% biochar treatment, achieving 63% and 70% of the NH₃ and DMS reductions attained by the 10% treatment, respectively, offers a more practical and cost-effective option. Other odorous compounds were not significantly affected. A temporary reduction in odor units was observed on day 7. Rice husk biochar contains 14.5% atomic Si, primarily as silica, which supports structural stability but hinders pore development, reducing adsorption efficiency. These findings demonstrate the importance of biochar’s physicochemical properties in odor mitigation. Future research should evaluate long-term field performance, microbial interactions, and silica modification strategies. Full article

This study demonstrated the effectiveness of using autoclaved aerated concrete AAC waste as a low-cost filtering material for removing hydrogen sulfide (H₂S) from gas streams. A long-term experiment (89 days) was conducted in a packed bed reactor to purify synthetic biogas composed of N₂, CO₂, H₂S, and O₂. Optimal H₂S removal efficiencies, reaching up to 100%, were achieved under highly acidic conditions (pH ≈ 1–3) and low oxygen concentrations (<1%). In the presence of oxygen, calcium oxides in the AAC waste react with H₂S to form gypsum (CaSO₄ 2H₂O). The simultaneous removal of both oxygen and H₂S by AAC waste, following an approximate 2:1 molar ratio, may be particularly beneficial for biogas streams containing unwanted traces of oxygen. The transformation and lifespan of AAC waste were monitored through sulfur accumulation in the material and pressure drop measurements, which indicated structural changes in the AAC waste. At the end of its lifespan, the AAC waste exhibited an H₂S removal capacity of 185 g_H2S kg_AAC⁻¹. This innovative and sustainable process not only provides a cost-effective and environmentally sound solution for the simultaneous removal of H₂S and O₂ from biogas, but also promotes waste valorization and aligns with circular economy principles. Full article

Powder bed fusion using a laser beam (PBF-LB) offers a suitable alternative to manufacturing Ti65 with intricate geometries and internal structures in hypersonic aerospace applications. However, issues such as undesirable surface roughness, defect formation, and microstructural inhomogeneity remain critical barriers to its wide application. In this study, a coupled discrete element method–computational fluid dynamics (DEM-CFD) model was utilized to investigate the spreading behavior of Ti65 powder in a multi-layer PBF-LB process. The macro- and microscopic characteristics of the powder beds were systematically analyzed across different layers and regions under various spreading velocities. The results show that the packing density and uniformity of the powder beds in multi-layer PBF-LB of Ti65 powder improves as the number of solidified layers increases. Poor bed quality is observed in the first two layers due to a strong boundary effect, while a stable and denser powder bed emerges from the fourth layer. The presence of a previously solidified region strongly influences its neighboring unsolidified areas, enhancing density in the upstream region and causing looser packing downstream. Additionally, due to the existence of a solidified region, the height of the powder bed progressively decreases along the spreading direction. Full article

The objective of this study was to model an adsorption column bed with biomass residues using computational software to remove Pb (II) at the industrial level and analyse the effects of parametric variation. For this purpose, several simulations of the adsorption column were performed using Aspen Adsorption software, evaluating the effects of varied height, inlet flow rate, and initial concentration on the adsorption process performance. The Langmuir II and Freundlich models are established as isotherm models, and the linear driving force (LDF) model is established as the kinetic model. The findings showed that Freundlich–LDF obtained efficiencies of up to 99.9% and Langmuir II–LDF efficiencies of up to 99.7%. The optimal simulation conditions were a column height of 4 m, an initial Pb (II) concentration of 3000 mg/L, and an inlet flow rate of 250 m³/d. This study presents a novel engineering approach to predict the potential performance of columns packed with organic waste-derived biomasses in multi-scale Pb (II) removal using computer-aided engineering tools. Full article

In this study, a novel adsorbent was developed by synthesizing Zn-Al layered double hydroxide (LDH) incorporated with silver nanoparticles (Ag-NPs), and its effectiveness in bromide removal from aqueous solutions was systematically evaluated. The X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analyses confirmed the integration of Ag-NPs within the LDH, ensuring uniform chemical composition and structural integrity. A series of controlled batch trials, each varying a single parameter (adsorbent dose, contact time, or temperature) confirmed that over 95% of bromide (initially 5320 μg/L) was removed under optimized conditions. LDH/Ag-NPs exhibited superior performance, with kinetics well described by a second-order reaction model. Thermodynamic analysis confirmed the spontaneous and exothermic nature of bromide adsorption, with ΔG° values ranging from −2.03 to −0.73 kJ/mol as the temperature increased from 22 °C to 52 °C. In continuous-flow experiments, packed-bed column tests illustrated that LDH/Ag-NPs maintained more effective bromide removal than LDH alone over extended periods. Conductivity measurements further supported this enhancement, with LDH/Ag-NPs reducing final conductivity to 139 µS/cm, compared to 212 µS/cm for LDH. Furthermore, this study revealed the notable antimicrobial activity of LDH/Ag-NPs, as evidenced by a significant reduction in bacterial growth compared to LDH alone, highlighting its dual functionality for both bromide adsorption and water disinfection. Overall, the incorporation of Ag-NPs into LDH offers a promising strategy for developing multifunctional and sustainable water treatment systems. Full article

Liquid fuels obtained from CO₂ and green hydrogen (i.e., e-fuels) are powerful tools for decarbonizing economy. Improvements provided by Process Intensification in the existing conventional reactors aim to decrease energy consumption, increase yield, and ensure more compact and safe processes. This review describes the advances in the production of methanol, dimethyl ether, and hydrocarbons by Fischer–Tropsch using different Process Intensification tools, mainly membrane reactors, sorption-enhanced reactors, and structured reactors. Due to the environmental interest, this review article focused on discussing methanol and dimethyl ether synthesis from CO₂ + H₂, which also represented the most innovative approach. The use of syngas (CO + H₂) is generally preferred for the Fischer–Tropsch process; hence, studies examining this process were included in the present review. Both mathematical models and experimental results are discussed. Achievements in the improvement of catalytic reactor performance are described. Experimental results in membrane reactors show increased performance in e-fuels production compared to the conventional packed bed reactor. The combination of sorption and reaction also increases the single-pass conversion and yield, although this improvement is limited by the saturation capacity of the sorbent in most cases. Full article

The aim of this study was to determine claw health and lameness prevalence in cows housed in CBPs in southern Germany. Eight farms that housed their dairy cows in CBPs were visited for data collection once in the warm season and once in the cold season between January and December 2023. The first visit was during hoof trimming of the herd to identify claw disorders, score lameness, and assess the bedded pack resting area. Lameness was scored again and the bedded pack resting area assessed at the second visit. To compare claw health at cow and farm levels, a cow claw score (CCS) and a farm claw score (FCS) were calculated using geometric severity scores. The prevalence of lameness at cow level was 9.4% in the cold season and 11.1% in the warm season, which were lower than values reported in studies that investigated cubicle free-stall barns. The low prevalences of lameness and claw disorders were reflected in a CCS of 8 and FCS of 9, which are defined as excellent. Based on our results, CBPs are associated with low lameness prevalence and favourable claw health. Full article