Search Results (174)

The mixed oxides of Ni/ZrO₂, Ni-Ca/ZrO₂, Ni-Ba/ZrO₂, and Ni-Ba-Ca/ZrO₂ were prepared using the co-precipitation method at a pH of precisely 8.3. The catalytic mixed oxides of Ni/ZrO₂, Ni-Ca/ZrO₂, Ni-Ba/ZrO₂, and Ni-Ba-Ca/ZrO₂ were characterized using x-ray diffraction XRD, Brunauer Emmett Teller (BET), scanning electron microscopy (SEM), and metal dispersion for the screening of phase purity, surface area, and morphology. The mixed oxides are subjected to CO₂-TPD to quantify the basicity of every composition. The mixed oxide catalysts of Ni/ZrO₂, Ni-Ca/ZrO₂, Ni-Ba/ZrO₂, and Ni-Ba-Ca/ZrO₂ were screened for oxythermal reforming of CH₄ with CO₂ in a fixed bed tubular reactor at 800 °C. Among all catalysts, the Ba- and Ca- loaded Ni-Ba-Ca/ZrO₂ showed high conversion by the decomposition of methane and CO₂ disproportionation throughout the time on stream of 29 h. The high activity with stability led to less coke formation over Ni-Ba-Ca/ZrO₂ over the surface. The stable syngas production with an active catalyst bed contributed to the improved bimetallic synergy. The high surface basicity of Ni-Ba-Ca/ZrO₂ may keep actively gasifying the formed soot and allow for further stable reforming reactions. Full article

Catalytic CO₂ methanation represents a promising process route for converting carbon dioxide into methane, a valuable energy carrier. This study investigates the performance of Ni-based catalysts on mixed silica and MgO support materials for CO₂ methanation. Silica was derived from rice husk (SiO₂(RH)), representing a sustainable, cost-effective source for catalyst support, and MgO was used as a reference and to enhance the catalytic activity of the Ni-based catalysts through admixture with SiO₂(RH). The results were compared to CO₂ methanation over Ni-based catalysts on reduced iron ore from natural siderite (siderite_reduced), providing another abundant source for catalyst support. The experiments were conducted in a tubular reactor with a feed gas composition of H₂:CO₂:N₂ = 56:14:30, feed gas flow rates ranging from 4.01 to 14.66 m³·kg⁻¹·h⁻¹ (STP), and reaction temperatures of 548–648 K. The highest CO₂ conversion with the Ni/SiO₂(RH) catalyst was 39.01% at a methane selectivity of 92.64%. The use of mixed silica and MgO supports (SiO₂(RH)/MgO) for nickel revealed a beneficial effect, enhancing CO₂ conversion and methane formation. In this case, methane selectivities consistently exceeded 91.57%. Superior methane selectivity and CO₂ conversion were obtained with Ni/MgO catalysts and Ni/SiO₂(RH)/MgO catalysts with high MgO fractions, highlighting the fundamental effect of MgO in the catalyst support for CO₂ methanation. Full article

This study examines the use of a1 mm-diameter tubular microreactor submerged in a temperature-controlled water bath to activate potassium persulfate (KPS) via thermal, Fe²⁺-catalyzed, and combined thermo-catalytic processes for degrading the persistent textile dye Safranin O (SO). The efficiency of these methods was evaluated under varying conditions, including KPS, dye, and Fe^2⁺ flow rates, solution pH, reactor length, and water matrix quality (deionized water, tap water, seawater, and secondary effluent from a wastewater treatment plant (SEWWTP)) across bath temperatures of 30–80 °C. Total organic carbon (TOC) analysis validated the results. Maximum dye conversion (up to 89%) occurred at 70 °C, with no improvement beyond this temperature, mainly due to radical-radical recombination. Longer reactors (2–6 m) enhanced conversion, though this effect diminished at higher temperatures due to efficient thermal activation. Increasing dye flow rates reduced removal efficiency, particularly above 50 °C, highlighting kinetic and mass transfer limitations. Persulfate flow rate increases improved conversion, but a plateau emerged at 80 °C. At lower temperatures (30–40 °C), Fe²⁺ addition significantly boosted SO conversion in deionized water. Between 40 and 50 °C, conversion rose from 30.27% (0 mM Fe²⁺) to 85.91% (0.2 mM Fe²⁺) at 50 °C. At higher temperatures (60–80 °C), conversion peaked at 70 °C for lower Fe²⁺ concentrations (100% for 0.01–0.05 mM Fe²⁺), but higher Fe²⁺ levels (0.1–0.2 mM) caused a decline above 60 °C, dropping to 68.44% for 0.2 mM Fe²⁺ at 80 °C. Deionized, tap, and mineral water showed similar performance, while river water, secondary effluent, and seawater inhibited SO conversion at lower temperatures (30–60 °C). At 70–80 °C, all matrices achieved efficiencies comparable to deionized water for both thermal and thermo-catalytic activation. The thermo-catalytic system achieved >50% TOC reduction, indicating significant organic matter mineralization. The results were comprehensively analyzed in relation to thermal and kinetic factors influencing the performance of continuous-flow reactors. Full article

The periodate/hydrogen peroxide (PI/H₂O₂) system is a recently developed advanced oxidation process (AOP) characterized by its rapid reaction kinetics, making it highly suitable for continuous-flow applications compared to conventional batch systems. Despite its potential, no prior studies have investigated its performance under flowing conditions. This work presents the first application of the PI/H₂O₂ process in a tubular microreactor, a promising technology for enhancing mass transfer and process efficiency. The degradation of textile dyes (specifically Basic Yellow 28 (BY28)) was systematically evaluated under various operating conditions, including reactant concentrations, flow rates, reactor length, and temperature. The results demonstrated that higher H₂O₂ flow rates, increased PI dosages, and moderate dye concentrations (25 µM) significantly improved degradation efficiency, achieving complete mineralization at 2 mM PI and H₂O₂ flow rates of 80–120 µL/s. Conversely, elevated temperatures negatively impacted the process performance. The influence of organic and inorganic constituents was also examined, revealing that surfactants (SDS, Triton X-100, Tween 20, and Tween 80) and organic compounds (sucrose and glucose) acted as strong hydroxyl radical scavengers, substantially inhibiting dye oxidation—particularly at higher concentrations, where nearly complete suppression was observed. Furthermore, the impact of water quality was assessed using different real matrices, including tap water, seawater, river water, and secondary effluents from a municipal wastewater treatment plant (SEWWTP). While tap water exhibited minimal inhibition, river water and SEWWTP significantly reduced process efficiency due to their high organic content competing with reactive oxygen species (ROS). Despite its high salt content, seawater remained a viable medium for dye degradation, suggesting that further optimization could enhance process performance in saline environments. Overall, this study highlights the feasibility of the PI/H₂O₂ process in continuous-flow microreactors and underscores the importance of considering competing organic and inorganic constituents in real wastewater applications. The findings provide valuable insights for optimizing AOPs in industrial and municipal wastewater treatment systems. Full article

A steady-state tubular reactor for total oxidation reaction under typical industrial conditions in the removal of volatile organic components (VOC) is described using a one-dimensional heterogeneous reactor model with intraparticle diffusion, using a fully developed Langmuir–Hinshelwood reaction rate expression. The effectiveness factor, accounting for these intraparticle diffusion limitations, is calculated with a generalized Thiele modulus. The actual inclusion of this factor shows that higher operational reactor temperatures can be possible, since this diffusion limitation restricts the heat production inside the catalyst particle. Special attention is given to the outlet concentration of propane, taken as the model VOC, and runaway criteria, reported in the literature, are evaluated. Furthermore, the well-known Barkelew criterion (to evaluate runaway for exothermic reactions) is implemented for practical and safe reactor design. This work identifies that the critical couples populating the Barkelew diagram are positioned lower (up to a 50% difference, compared to Barkelew’s original report), so that operation of the reactor under higher hydrocarbon molar inlet fractions is possible while maintaining safe performance. Full article

This article deals with the removal of manganese from water via ultrafiltration and the oxidation of manganese with chlorine dioxide or potassium permanganate before ultrafiltration. The dose of oxidizing agents, time of contact with water, and manganese concentration in raw and treated water were monitored. A fully automated ultrafiltration device with membrane module UA-640 (Microdyn-Nadir) was used. A tubular reactor with a static mixer was used to reach a sufficient contact time for water with an oxidizing agent, enabling the oxidation of manganese in water. The concentration of Mn in the water source ranged from 0.150 to 0.250 mg/L Mn. The results of the experiments showed that in the case of chlorine dioxide, the efficiency of removing Mn from water of 74.31% was achieved at a flow rate of 60 L/h, a dose of 0.4 mg/L ClO₂ and a retention time of 30.5 min; the concentration of Mn in the treated water was 0.037 mg/L, while in the case of KMnO₄ the efficiency was up to 100% at a flow rate of 650 L/h, a dose of 0.3 mg/L Mn (determined after adding KMnO₄) and a retention time of 2.8 min; the concentration of Mn in the treated water was below the detection limit of 0.005 mg/L of the measuring device. Pilot plant experiments confirmed the efficiency of ultrafiltration, demonstrating the possibility of decreasing the manganese concentration below the limit for drinking water using the considered method. Full article

Tetrafluoroethylene (TFE), as a key basic chemical raw material, has an irreplaceable position in strategic emerging industries involving high-end materials, electronics, chemicals, and pharmaceuticals. Currently, TFE is industrially produced via the vapor cracking of difluoromonochloromethane (R22). However, there is a gap between China and the developed countries in the high-end tetrafluoroethylene monomer, the purity of tetrafluoroethylene monomer is difficult to reach the high purity requirement of 99.999%, and the content of the key impurities that determine the nature of the functional materials is high, which leads to a series of problems of instability in the performance of the high-end and special products and high media loss. To enhance the purity of TFE monomers produced by the pyrolysis reactor of R22 and water vapor, the fluid dynamics simulations of the reactor model were conducted using Ansys Fluent. The reactor model was initially constructed using Space Claim, followed by mesh generation with Fluent Meshing and other relevant configurations. Both cold-state and thermal-state simulations were performed. The cold-state simulation analyzed the effects of temperature, flow velocity, and turbulence models on the turbulent gas flow and mixing processes within the reactor model. The thermal-state simulation examined the impacts of reaction process variations on internal temperature, turbulence, component distribution, and outlet component concentrations during the actual reaction process. Finally, the inlet flow rate and structure of the reactor were optimized. The results indicated that the optimal inlet flow rates for R22 and water vapor were 0.2–0.3 kg/s and 0.4–0.5 kg/s, respectively. In practical production, the internal fluid mixing achieved an optimal value after modifying the inlet structure to a T shape. This study provides new insights into the pyrolysis reaction and lays the foundation for further improving the purity of TFE monomers. Full article

The generation of pyrolysis liquids and gases with poor quality is a limiting factor for the development of the recycling process of fiber-reinforced plastic waste. In this article, the life cycle assessment (LCA) of an advanced two-step pyrolysis process to recycle glass fiber-reinforced polyamide waste is presented. First, the solid waste is pyrolyzed by heating up at 3 °C/min to 500 °C in a tank reactor. The generated volatiles are subsequently thermally cracked at 900 °C in a tubular packed bed reactor. The process is able to reclaim the glass fibers similarly to the conventional one reactor pyrolysis, while producing liquids and gases with better properties. The large quantity of oxygenated pyrolysis oils generated in the conventional pyrolysis are cracked into gaseous hydrocarbons, CO, CO₂ and a minor aqueous liquid. The pyrolysis gases become the main product of the process, presenting an interesting composition of hydrogen (39.9 vol.%), methane (22.5 vol.%), carbon monoxide (19.5 vol.%) and ethylene (10.8 vol.%). The LCA shows that advanced pyrolysis demonstrates better environmental performance than conventional pyrolysis, avoiding fossil resource scarcity and reducing global warming by half and human carcinogenic toxicity by one third. Full article

This paper provides an optimization analysis of the hydrothermal liquefaction (HTL) process of sewage sludge to biocrude oil in a continuous plug-flow reactor. The increase in flow rate led to enhanced swirling flow, which significantly improved convective heat transfer. The composition and yield of biocrude oil produced in the process (HTL) can vary significantly depending on the type of feedstock used. Using process simulation principles and a kinetic model, this study thoroughly evaluated the mass and energy balance of the HTL reaction, considering heat and mass momentum exchange in a multiphase system. Therefore, it is useful to use a transient flow model to determine the influence of process parameters on optimization. A parametric study with multiphase profiles along the reactor axis allowed tracing of interphase flow trajectories for optimal conditions in order to maximize the process efficiency of biocrude oil production. Through optimization of process parameters, there was a significant improvement in the conversion of sewage sludge to biocrude oil in the continuous HTL process. The optimal conditions were where the reaction mass maintained in the liquid phase enabled the stabilization of process parameters, preventing evaporation and heat loss by increasing the energy process efficiency. Full article

In this study, the integration of microwave-assisted technology into fixed-bed configuration processes is explored aiming to characterize and address its challenges with a customized multimodal microwave cavity. This research focuses on evaluating the uncertainty in contactless temperature measurement methods as spectral thermographic cameras and infrared pyrometers, microwave heating performance, and the thermal homogeneity within fixed beds containing microwave–susceptor materials, including the temperature-dependent dielectric characterization of such materials, having different geometry and size (from 120 to 5000 microns). The thermal inhomogeneities along different bed configurations were quantified, assessing the most appropriate fixed-bed arrangement and size limitation at the employed irradiation frequency (2.45 GHz) to tackle microwave-assisted gas–solid chemical conversions. An increased temperature heterogeneity along the axial profile was found for finer susceptor particles, while the higher microwave susceptibility of coarser grades led to increased temperature gradients, ΔT > 300 °C. Moreover, results evidenced that the temperature measurement on the fixed-bed quartz reactor surface by a punctual infrared pyrometer entails a major error regarding the real temperature on the microwave susceptor surface within the tubular quartz reactor (up to 230% deviation). The experimental findings pave the way to assess the characteristics that microwave susceptors and fixed beds must perform to minimize thermal inhomogeneities and optimize the microwave-assisted coupling with solid–gas-phase reactor design and process upscaling using such multimode cavities. Full article

The tubular flocculation reactor is a new and efficient device for treating algae-containing wastewater. The introduction of bubbles during the reaction process can effectively shorten the time required for floc separation. However, the impact of bubbles on floc formation and removal in the tubular flocculation reactor is not well understood. To further clarify the effect of bubbles on the reactor’s operation, this study employed a uniform experimental design, varying the flow rate, chemical dosage, bubble reaction distance, and bubble injection rate in the reactor to examine the influence of bubbles under different operating conditions. The results indicated that as the bubble reaction distance increased from 0 m to 7.6 m, the removal efficiency increased from 60% to 70%, the floc size increased from 160 μm to 165 μm, and the fractal dimension decreased from 2.1 to 1.9. When the bubble volume increased from 5% to 30%, the removal efficiency increased from 50% to 80%. Under constant bubble conditions, the rising speed of the flocs increased from 0.4 mm·s⁻¹ to 1.2 mm·s⁻¹, while the removal efficiency increased from 30% to 90%. A logarithmic correlation was observed between the rising speed and removal efficiency. A linear relationship was found between the floc rising speed and the floc size, with floc size increasing from 200 μm to 800 μm and the rising speed increasing from 0.4 mm·s⁻¹ to 2.3 mm·s⁻¹. An exponential relationship was found between the fractal dimension and the rising speed, with the rising speed decreasing from 2.3 mm·s⁻¹ to 0.4 mm·s⁻¹, while the fractal dimension increased from 1.93 to 2.02. Full article

The chemical looping reforming of methane using an SrFeO₃ oxygen carrier to produce synthesis gas from solar energy was experimentally investigated and validated. High-temperature solar heat was used to provide the reaction enthalpy, and therefore the methane feedstock was entirely dedicated to producing syngas. The two-step isothermal process encompassed partial perovskite reduction with methane (partial oxidation of CH₄) and exothermic oxidation of SrFeO_3-δ with CO₂ or H₂O splitting under the same operating temperature. The oxygen carrier material was shaped in the form of a reticulated porous foam structure for enhancing heat and mass transfer, and it was cycled in a solar-heated tubular reactor under different operating parameters (temperature: 950–1050 °C, methane mole fraction: 5–30%, and type of oxidant gas: H₂O vs. CO₂). This study aimed to assess the fuel production capacity of the two-step process and to demonstrate the potential of using strontium ferrite perovskite during solar cycling for the first time. The maximum H₂ and CO production rates during CH₄-induced reduction were 70 and 25 mL/min at 1000 °C and 15% CH₄ mole fraction. The increase in both the cycle temperature and the methane mole fraction promoted the reduction step, thereby enhancing syngas yields up to 569 mL/g during reduction at 1000 °C under 30% CH₄ (778 mL/g including both cycle steps), and thus outperforming the performance of the benchmark ceria material. In contrast, the oxidation step was not significantly affected by the experimental conditions and the material’s redox performance was weakly dependent on the nature of the oxidizing gas. The syngas yield remained above 200 mL/g during the oxidation step either with H₂O or CO₂. Twelve successive redox cycles with stable patterns in the syngas production yields validated material stability. Combining concentrated solar energy and chemical looping reforming was shown to be a promising and sustainable pathway toward carbon-neutral solar fuels. Full article

Effective vessel design is crucial for the viability and practicality of microalgae cultivation, aiming for high biomass production. This study tested two different 5-litre vessel designs for cultivating Chlorella vulgaris, aiming to produce a high biomass and evaluate lipid production. The study varied pH medium (6.5–10.5), light intensity (200–1000 lux), and CO₂ concentrations (5–15%) to assess each reactor’s performance. The aerated vessel (tubular shape) produced 21.05% lipid concentration, while the fabricated vessel (oval shape) produced 20.14% at optimum conditions. The aerated vessel performed best at pH 10.5, 5% CO₂, and 1000 lux light intensity, whereas the fabricated vessel’s optimum conditions were pH 10.5, 15% CO₂, and a white LED system. The highest biomass was 0.432 g/L in aerated tubular vessels and 0.281 g/L in fabricated oval-shaped vessels. Both systems performed well and are suitable for further study with other microalgae types. Full article

Decarbonization of hard-to-abate industrial sectors, namely the extractive industries, has become an imperative, and thus, processes such as carbon capture and utilization (CCU) have been explored thoroughly and seem to be a promising solution. Carbon dioxide (CO₂) catalytic hydrogenation employing green hydrogen (H₂) to produce synthetic methanol (MeOH) aims to utilize industrial-captured carbon. A thermodynamic and kinetic analysis of a pilot scale methanol synthesis reactor was conducted by modeling the process using Aspen Plus V12 software. The methanol synthesis model consists mainly of a multi-tubular packed-bed reactor with a thermal oil heat recovery system, a product separator, and an internal recycle loop for optimal efficiency. The reactor has a 5 kg h⁻¹ methanol production capacity, and its heat recovery system achieves an overall heat reduction of 64.1% and can retrieve 1.293 kWh per kg of methanol produced. The overall carbon conversion achieved is 80.6%. Valuable information concerning the design and profile of the reactor is provided in this study. Full article

This research on biodiesel production aims to improve energy processes to advance towards a sustainable economy. This study focuses on improving the biodiesel conversion efficiency in a helical tubular reactor coupled with a static mixer. A 2³ factorial design was used to evaluate how variables such as the molar ratio of alcohol–oil (4:1–8:1), residence time (4–8 min), and catalyst concentration (0.5–1 wt%) affect the transesterification process. Soybean oil and methanol were used, with NaOH as a catalyst at 60 °C. The results show that the residence time and catalyst concentration are key factors in increasing biodiesel production by up to 10%. An experimental yield of 84.97% was obtained with a molar ratio of 6:1 alcohol–oil, 0.9 wt% NaOH, and a reaction time of 6 min. The experimental design predicted a yield of 91% with a molar ratio of 4:1 alcohol–oil, 1 wt% NaOH, and a reaction time of 8 min, with a deviation of 1.88% from the experimental values. The fit of the experimental model was R² = 0.9632. These findings are valuable for improving the transesterification process and the development of biodiesel in continuous flow reactors. Full article