Search Results (52)

Low-concentration methane emissions from mines can be recovered using different reactor designs. Here, different artificial intelligence network techniques were employed to predict thermal performance of a basalt-fiber-bundle thermal flow-reversal reactor and investigate the influence of input parameters. The Back Propagation (BP) model gave the best accuracy (R² = 0.974 for outlet temperature, 0.967 for thermal efficiency), exceeding that of traditional Computational Fluid Dynamics (CFD) simulations. For the present design, when flow velocity exceeded 1.5 m/s, the outlet gas temperature shifted from rising to falling, explained by the heat transfer between the gas and the solid inside the flow channel. Increasing the length of the flow-reversal period in the high-temperature phase reduced the outlet temperature, e.g., an increase from 60 s to 200 s decreased the outlet temperature by 34.1 K. Increasing inlet methane concentration (e.g., from 0.3% to 0.8%) first showed a slight improvement in thermal efficiency but further increase accelerated the oxidation reaction rate inside the reactor, reducing the temperature difference between the solid and gas in the channel, which slowed the heat exchange process and resulted in a downward trend in efficiency. The results indicate that the reactor can handle a wide range of exhaust gas concentrations, being suitable to treat low-methane-concentration exhaust gas. The BP model helped to establish the theoretical basis for setting optimal parameters values for the operation of the proposed reactor. Full article

Using Excel and its Solver feature, a novel method of analyzing the component reactions of an overall reaction is outlined. As an example, autothermal reforming (300–700 °C) of acetic acid (AA), a significant component of pyrolysis oil, was considered. The overall reaction can be viewed as comprising five individual reactions: reforming, oxidation, water–gas shift, reverse Boudouard, and methanation. A laboratory apparatus was set up in which acetic acid, air, and water were continuously fed to a BASF dual-layer catalytic reactor in plug flow at 1 atm. For this setup, it is easy to construct a material balance in Excel in which five factors, f_i, are defined which represent the fraction of reactant going to each of the individual five reactions. Using the Solver feature of Excel, it can readily be determined which of the five factors f_i produce the best match of the calculated exit gas composition with the measured gas concentrations for CO, CO₂, H₂, CH₄, and O₂. Furthermore, a program such as GasEq or Aspen can then be used to calculate the theoretical equilibrium gas composition at a given condition. Using this equilibrium gas composition and Solver, the individual (f_i)_equilb can be calculated. Thus, the ratio f_i/(f_i)_equilb is an indication of how close each component reaction is to equilibrium. In this way, an idea is gained of which of the individual component reactions need to be improved or inhibited or if operating parameters should be adjusted. For the specific case of autothermal reforming of acetic acid, the steam reforming reaction requires at least 600 °C to approach equilibrium. In contrast, the oxidation reaction goes to equilibrium throughout the temperature range, completely consuming oxygen. The water–gas shift reaction appears to approach equilibrium to the extent of 71–90% throughout the temperature range. The reverse Boudouard reaction is favored at lower temperatures; in fact, coking was predicted and found at the low temperature of 300 °C. Full article

This review covers the current state, challenges, and future directions of catalytic combustion technologies for mitigating fugitive methane emissions from the fossil fuel industry. Methane, a potent greenhouse gas, is released from diverse sources, including natural gas production, oil operations, coal mining, and natural gas engines. The paper details the primary emission sources, and addresses the technical difficulties associated with dilute and variable methane streams such as ventilation air methane (VAM) from underground coal mines and low-concentration leaks from oil and gas infrastructure. Catalytic combustion is a useful abatement solution due to its ability to destruct methane in lean and challenging conditions at lower temperatures than conventional combustion, thereby minimizing secondary pollutant formation such as NO_X. The review surveys the key catalyst classes, including precious metals, transition metal oxides, hexa-aluminates, and perovskites, and underscores the crucial role of reactor internals, comparing packed beds, monoliths, and open-cell foams in terms of activity, mass transfer, and pressure drop. The paper discusses advanced reactor designs, including flow-reversal and other recuperative systems, modelling approaches, and the promise of advanced manufacturing for next-generation catalytic devices. The review highlights the research needs for catalyst durability, reactor integration, and real-world deployment to enable reliable methane abatement. Full article

The paper describes the conversion of carbon dioxide into methanol in a chemical reactor under standard operating conditions. Electro-analytical techniques, cyclic voltammetry, and chrono-amperometry characterize the process. The electrochemical redox reaction develops using various catalyzers to evaluate the performance of the carbon dioxide conversion into methanol process under variable chemical conditions. The results of the applied technique showed an incomplete redox reaction with an electronic change of z = 2.84 on average, below the ideal number, z = 6, that may be due to methanol decomposition (reverse reaction) because the system operates with a reaction constant above the equilibrium value. The methanol production may improve by draining the methanol/water solution from the chemical reactor to reduce the methanol concentration in the electrochemical cell, shifting the forward reaction towards the formation of methanol, increasing the electron change number, which approaches the ideal value, and improving the methanol production efficiency. The draining process shows a significant increase in methanol formation, which depends on the draining flow rate and the catalyzer type. A simulation process shows that if we operate in optimum conditions, with no methanol decomposition through a reverse reaction, the redox reaction fulfills the ideal condition of maximum electronic change. The experimental tests validate the simulation results, showing a relevant increase in the electron change number with values up to z = 4.2 for optimum draining flow rate conditions (0.2 L/s). The experimental results show a relative increase factor of 4.7 in methanol production, meaning we can produce more than four times more methanol compared with no draining techniques. The data analysis shows that the draining flow rate has a threshold of 0.2 L/s, beyond which the extent of the reaction reverses, reducing the methanol formation due to a chemical reaction disequilibrium. The paper concludes that using the draining method, the methanol production mass rate increases significantly from an average value of 20.9 kg/h for non-draining use, considering all catalyzer types, to a range between 91.9 kg/h and 104.3 kg/h, depending on the flow rate. Averaging all values for different flow rates and comparing with the non-draining case, we obtain an absolute methanol production mass rate of 77 kg/h, meaning an incremental percentage of 469.1%, more than four times the initial production. Although the proposed methodology looks promising, applying this procedure on an industrial scale may suffer from restrictions since the chemical reactions intervening in the methanol formation do not perform linearly. According to experimental tests, the best option among the six catalyzers used for methanol production is the plain copper, with copper oxides (Cu₂O, CuO) and copper Sulphur (CuS) as feasible alternatives. Full article

This study evaluated the effectiveness of individual clean-in-place (CIP) steps in removing biofilms from reverse osmosis (RO) membranes under dynamic flow conditions using the Centers for Disease Control (CDC) biofilm reactor. Biofilms were developed in the laboratory under continuous flow, using mixed-species bacterial isolates obtained from 10-month-old RO membrane biofilms from a commercial facility. Individual CIP chemicals, representative of those used in commercial protocols, were tested against 24 h-old biofilms. Additionally, a complete six-step sequential CIP process was conducted under dynamic conditions, consisting of treatments with alkali, surfactant, acid, enzyme, a secondary surfactant, and sanitizer. All experiments were performed in quadruplicate, and data were subjected to statistical analysis. Among individual treatments, the acid step was the most effective, significantly outperforming the other CIP cleaning steps by reducing bacterial counts from 5.62 to 4.10 log units, a 96.98% reduction. The full six-step CIP protocol reduced counts to 2.24 log units, indicating the persistence of resistant cells. The presence of viable cells post-treatment highlights the limited efficacy of the tested CIP chemicals in fully eradicating mature biofilms. Additionally, skipping any step in the membrane cleaning can significantly compromise the efficiency and performance during production. These findings suggest that biofilms grown in vitro under dynamic conditions using the CDC reactor exhibit a more robust assessment of the CIP treatments in accomplishing the biofilm control. This study highlights the need for optimized, scientifically validated CIP protocols targeting biofilms to improve cleaning efficacy and food safety. Full article

Endotoxins, lipopolysaccharides released from the outer membrane of Gram-negative bacteria, pose a significant risk in healthcare environments, particularly in Central Sterile Supply Departments (CSSDs), where the delivery of sterile pyrogen-free medical devices is critical for patient safety. Traditional methods for controlling endotoxins in water systems, such as ultraviolet (UV) disinfection, have proven ineffective at reducing endotoxin concentrations to comply with regulatory standards (<0.25 EU/mL). This limitation presents a significant challenge, especially in the context of reverse osmosis (RO) permeate used in CSSDs, where water typically has very low conductivity. Despite the established importance of endotoxin removal, a gap in the literature exists regarding effective chemical-free methods that can meet the stringent endotoxin limits in such low-conductivity environments. This study addresses this gap by evaluating the effectiveness of the eBooster™ electrochemical technology—featuring proprietary electrode materials and a reactor design optimized for potable water—for endotoxin removal from water, specifically under the low-conductivity conditions typical of RO permeate. Laboratory experiments using the B250 reactor achieved >90% endotoxin reduction (from 1.2 EU/mL to <0.1 EU/mL) at flow rates ≤5 L/min and current densities of 0.45–2.7 mA/cm². Additional real-world testing at three hospitals showed that the eBooster™ unit, when installed in the RO tank recirculation loop, consistently reduced endotoxin levels from 0.76 EU/mL (with UV) to <0.05 EU/mL over 24 months of operation, while heterotrophic plate counts dropped from 190 to <1 CFU/100 mL. Statistical analysis confirmed the reproducibility and flow-rate dependence of the removal efficiency. Limitations observed included reduced efficacy at higher flow rates, the need for sufficient residence time, and a temporary performance decline after two years due to a power fault, which was promptly corrected. Compared to earlier approaches, eBooster™ demonstrated superior performance in low-conductivity environments without added chemicals or significant maintenance. These findings highlight the strength and novelty of eBooster™ as a reliable, chemical-free, and maintenance-friendly alternative to traditional UV disinfection systems, offering a promising solution for critical water treatment applications in healthcare environments. Full article

This study focuses on optimizing the Reverse Water Gas Shift (RWGS) reaction system using a membrane reactor to improve CO₂ conversion efficiency. A one-dimensional simulation model was developed using FlexPDE Professional Version 8.01/W64 software to analyze the performance of ZSM-5 membranes integrated with 0.5 wt% Ru-Cu/ZnO/Al₂O₃ catalysts. The results show that the membrane reactor significantly outperforms the conventional Packed Bed Reactor by achieving higher CO₂ conversion (0.61 vs. 0.99 with optimized parameters), especially at lower temperatures, due to its ability to remove H₂O and shift the reaction equilibrium selectively. Key operational parameters, including temperature, pressure, and sweep gas flow rate, were optimized to maximize membrane reactor performance. The ZSM-5 membrane showed strong H₂O selectivity, with an optimum operating temperature of around 400–600 °C. The problem is that many reactants permeate at higher temperatures. Subsequently, a Half-MPBR design was introduced. This design was able to overcome the reactant permeation problem and increase the conversion. The conversion ratios for PBR, MPBR, and Half-MPBR are 0.71, 0.75, and 0.86, respectively. This work highlights the potential of membrane reactors to overcome the thermodynamic limitations of RWGS reactions and provides valuable insights to advance Carbon Capture and Utilization technologies. Full article

Reverse osmosis (RO) concentrate often contains high levels of sulfate and calcium ions due to the use of antiscalants, leading to significant calcium sulfate supersaturation and creating favorable conditions for induced crystallization. This study utilized a combination of static and dynamic experiments to investigate the key factors influencing the removal of calcium sulfate from RO concentrate via induced crystallization. The static experiments examined the effects of seed crystal concentration, stirring speed, reaction temperature, and the molar ratio of SO₄²⁻ to Ca²⁺ on removal efficiency, with response surface methodology (RSM) employed to analyze the interactions among these factors. In the dynamic experiments, gypsum particles were used as seed crystals in a fluidized bed reactor to study the impact of initial seed crystal dosage and influent flow rate on the removal performance. Optimization strategies for stable operation were also explored. The static experiments revealed that seed crystal concentration was the most critical factor affecting removal efficiency. Under optimal conditions, the calcium ion concentration in the treated water could be reduced to 453 mg/L, achieving a removal rate of 63.8%. In the dynamic experiments, the effluent calcium ion concentration was reduced to 724 mg/L, with a removal rate of 52.5%. However, prolonged continuous operation led to a gradual increase in effluent calcium ion levels, which could be mitigated by recycling seed crystals from the settling zone back to the reaction zone. Characterization of the induced seed crystals and simulation calculations demonstrated that Ca²⁺ and SO₄²⁻ reacted to form calcium sulfate crystals, primarily as CaSO₄·2H₂O, which adhered to the seed crystal surfaces. The growth of the seed crystals, indicated by an increase in particle size, correlated with the volume of water treated. This study provides valuable insights and data for the application of calcium sulfate-induced crystallization as a method to reduce sulfate and calcium ion concentrations in RO concentrate, offering a viable approach to water softening and resource recovery. Full article

In response to the growing demand for potable water, this study presents a practical methodology for designing and fabricating a hybrid desalination system that integrates reverse electrodialysis and electrodialysis using 3D-printing technology. The hybrid system combines the energy generation potential of RED with the salt removal capabilities of ED, reducing energy consumption. Customized reactors were designed to enhance flow distribution and ion exchange, with computational fluid dynamics simulations validating the hydrodynamic performance. The reactors were fabricated using 3D printing, allowing rapid, cost-effective production, with functional reactors constructed in under 24 h. The system achieved a 15% reduction in salt concentration within one hour, with a specific energy consumption of 0.1388 Wh/m³ and a water recovery rate of 50%. These results demonstrate the functionality of the RED-ED hybrid system for achieving energy savings and performing water desalination. This methodology provides a scalable and replicable solution for water treatment applications, especially in regions with abundant salinity gradients and limited freshwater resources, while offering a multidisciplinary approach that integrates physicochemical and engineering principles for effective device development. Full article

Hydrogen and carbon monoxide over-equilibria have been found computationally in kinetic dependencies of methane-reforming catalytic reactions (steam and dry reforming) using the conditions of the conservatively perturbed equilibrium (CPE) phenomenon, i.e., at the initial equilibrium concentration of hydrogen or carbon monoxide. The influence of the pressure, temperature, flow rate and composition of the initial mixture on the position of the CPE point (the extremum point) was investigated over a wide domain of parameters. The CPE phenomenon significantly increases the product concentration (H₂ and CO) at the reactor length, which is significantly less than the reactor length required to reach equilibrium. The CPE point is interpreted as the “turning point” in kinetic behaviour. Recommendations on temperature and pressure regimes are different from the traditional ones related to Le Chatelier’s law. The obtained results provide valuable information on optimal reaction conditions for complex reversible chemical transformations, offering potential applications in chemical engineering processes. Full article

Medium-voltage (MV) distribution networks that are spread through larger territory and threatened by extreme weather conditions are sometimes formed by very long underground cable lines. In such circumstances, a significant amount of capacitive reactive power flow can be generated. If, concurrently, there is low power demand in the network, it can result in significant reverse reactive power flows and voltage rise issues. This paper proposes a general approach for analyzing and mitigating voltage rise issues and demonstrates it using an example of a real distribution network that operates under the described conditions. Previous studies that dealt with this problem did not include the allocation of multiple shunt reactors in a larger distribution network, modeling a high number of lines that create reverse reactive power flows, and modeling the main distribution transformers, which are the locations where voltage rise predominantly occurs. In this paper, we demonstrate that precise allocation and placement of multiple shunt reactors in a fully modeled, larger distribution system, including transformer models, can reduce reverse reactive power flows, thereby improving voltage in the distribution system. If hourly control of the power factor from the distributed generation unit is also implemented, the voltage can be further improved. Full article

Ventilation air methane (VAM) from coal mining is a low-grade energy source that can be used in combustion systems to tackle the energy crisis. This work presents a numerical analysis of the thermal and stabilization performance of a VAM-fueled thermal reversal reactor with three fixed beds. The effects of the combustion chamber/regenerator height ratio (β), heat storage materials, and porosity on the oxidation characteristics are evaluated in detail. It is shown that the regenerator temperature tends to vary monotonically with β due to the coupling effect of the gas residence time and heat transfer intensity. The optimal β is determined to be 4/6, above which the system may destabilize. Furthermore, it is found that regardless of the methane volume fraction, the regenerator with mullite inserted has the highest temperature among the heat storage materials investigated. In contrast, the temperature gradually decreases and the system becomes unstable as SiC is adopted, signifying the importance of choosing proper thermal diffusivity. Further analysis reveals that the porosity of the heat storage materials has little effect on the system stability. Decreasing the porosity can effectively reduce the oscillation amplitude of the regenerator temperature, but it also results in greater pressure losses. Full article

The kinetics of methanol synthesis remains debatable for various reasons, such as the lack of scientifically conclusive agreement about reaction mechanisms. The focus of this paper is on the evaluation of the intrinsic kinetics of the methanol synthesis reaction based on CO₂ hydrogenation and the associated reverse water–gas shift as overall reactions. The industrial methanol synthesis catalyst, Cu/ZnO/Al₂O₃/MgO, was used for performing the kinetic studies. An optimal kinetic model was assessed for its ability to predict the experimental data from differential to integral conditions, contrary to the typical fitting of only the integral conditions’ data (common practice, as reported in the literature). The catalyst testing and kinetic evaluations were performed at various temperatures (210–260 °C) and pressures (40–77 bar), and for different stoichiometric numbers (0.9–1.9), H₂/CO₂ ratios (3.0–4.4) and carbon oxide ratios (0.9–1.0), in an isothermal fixed bed reactor, operated in a plug-flow mode. Experiments with CO in the feed were also generated and fitted. Different literature kinetic models with different assumptions on active sites, rate-determining steps, and hence, model formulations were fitted and compared. The original Seidel model appeared to fit the kinetic data very well, but it has twelve parameters. The modified model (MOD) we propose is derived from this Seidel model, but it has fewer (nine) parameters—it excludes CO hydrogenation, but it takes into consideration the morphological changes of active sites and CO adsorption. This MOD model, with three active sites, gave the best fit to all the data sets. Full article

Reactor temperature manipulation to increase product yields of chemical reactions is a known technique used in many industrial processes. In the case of exothermic chemical reactions, the well-known Le Chatelier’s principle predicts that a decrease in temperature will displace the chemical reaction toward the formation of products by increasing the value of the equilibrium constant. The reverse is true for endothermic reactions. Reactor temperature manipulation in an industrial system, however, affects the values of many variables, including physical properties, transport parameters, reaction kinetic parameters, etc. In the case of reactive absorption, some variables change with increasing temperatures due to solute absorption, while others change in such a way that the solute absorption rate decreases. For example, temperature drop increases product formation for exothermic reactions but reduces the value of transport parameters, leading to decreasing interfacial concentrations and absorption rates. Therefore, temperature manipulation strategies must be designed carefully to achieve the process goals. In this work, we theoretically study the use of temperature as a tool to increase CO₂ absorption by solvents in a semi-batch reactor. A computer code has been developed and validated using reported experimental data. Calculated results demonstrate an increase in absorbed CO₂ of more than 28% with respect to the highest temperature used. Despite high agitation and high gas flow rate, the system is mass transfer controlled at short times, becoming kinetically controlled as time increases. An operating strategy to decrease cooling energy costs is also proposed. This study reveals that reactor temperature manipulation can be an effective process to improve CO₂ absorption by solvents in two-phase semi-batch reactors. Full article

The recent energy crisis revealed that there is a strong need to replace hydrocarbon-fueled industrial nitrogen fixation processes by alternative, more sustainable methods. In light of this, plasma-based nitrogen fixation remains one of the most promising options, considering both theoretical and experimental aspects. Lately, plasma interacting with water has received considerable attention in nitrogen fixation applications as it can trigger a unique gas- and liquid-phase chemistry. Within this context, a critical exploration of plasma-assisted nitrogen fixation with or without water presence is of great interest with an emphasis on energy costs, particularly in plasma reactors which have potential for large-scale industrial application. In this work, the presence of water in a multi-pin plasma system on nitrogen oxidation is experimentally investigated by comparing two pulsed negative DC voltage plasmas in metal–metal and metal–liquid electrode configurations. The plasma setups are designed to create similar plasma properties, including plasma power and discharge regime in both configurations. The system energy cost is calculated, considering nitrogen-containing species generated in gas and liquid phases as measured by a gas analyzer, nitrate sensor, and a colorimetry method. The energy cost profile as a function of specific energy input showed a strong dependency on the plasma operational frequency and the gas flow rate, as a result of different plasma operation regimes and initiated reverse processes. More importantly, the presence of the plasma/liquid interface increased the energy cost up to 14 ± 8%. Overall, the results showed that the presence of water in the reaction zone has a negative impact on the nitrogen fixation process. Full article