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Iron (Fe) is a promising candidate for energy carriers due to its high energy density, abundance, and transportability. Energy is released during the combustion of iron powder. Iron oxide particles are the product of combustion, which can be easily collected and reduced back to metallic iron, thus enforcing an iron fuel cycle. Electrochemical reduction of iron oxide in alkaline media is a promising approach for the reduction process as it is CO2-free and requires low temperature/energy. In the context of the iron fuel cycle, we promote electroreduction with dendrite-rich structures rather than compact deposit layers for easy harvesting and conversion of deposits to iron powder. This study presents the design and performance of an electrochemical reactor with a rotating disc system, designed for the continuous production of electrolytic iron powder. The reactor facilitates an integrated and automated process of electroreduction of iron oxide (from electroreduction to cleaning, drying, and dendrite/powder harvesting). Our proof of concept experiments show that iron deposits with dendritic structures can be produced in various conditions (anode configurations and rotating speeds), and are mainly located on the disc edge. The growth of dendrites at the edge of the disc favour harvesting and conversion to iron powder. Current efficiencies of more than 85-90 % are achieved in this study. Insights from the present study open new perspectives for the circularity of the iron fuel cycle. Furthermore, this technique provides a novel contribution to powder production in sustainable iron/steel-making technologies.

Renewable energy intermittency demands efficient storage solutions. Iron powder is proposed as a promising candidate for energy carriers due to its high energy density, abundance, and transportability. Energy is released by the combustion of iron powder, yielding iron oxides that can be easily collected and reduced back to metallic iron – a process termed the iron fuel cycle. Electrochemical reduction of iron oxide in alkaline media offers a carbon-neutral and low-temperature/energy approach for this reduction process [1]. In the previous study, we proved that electroreduction with dendrite-rich structures can facilitate easier harvesting and conversion of electrolytic iron deposits to powder form [1-2]. The present study reports the design and performance of an electrochemical reactor featuring a rotating disc system, tailored for continuous electrolytic iron powder production. The reactor combines the electroreduction process from the iron oxide reduction process to subsequential steps (cleaning, drying, and dendrite/powder harvesting), offering an integrated and automated solution [3]. Proof-of-concept experiments demonstrate the feasibility of producing iron deposits with dendritic structures under various conditions. Dendritic iron growth at the disc's edge enhances harvesting and conversion to iron powder where current efficiencies of 85-90% are achievable [4-5]. Analysis using a scanning electron microscope (SEM) also reveals the deposit microstructures under various conditions. This research advances the understanding of (iron oxide) “powder-to-powder” (iron) electroreduction for the circularity of the iron fuel cycle and introduces innovative powder production techniques for sustainable iron/steel-making technologies.

An electrochemical cell for converting metal salt or metal oxide to metal comprises a) a mixture comprising an electrolyte and metal salt or metal oxide; b) an anode submerged in the mixture; c) a cathode partially submerged in the mixture and moveable along a closed loop path; and d) a harvester disposed at an exposed portion of the cathode outside of the mixture, wherein an electrical charge supplied to the electrochemical cell reduces the metal salt or metal oxide to metal at and disposed onto the cathode, and wherein the harvester removes the metal from the exposed portion of the cathode. Methods and systems for converting metal salt or metal oxide to metal are also disclosed including continuous methods and systems.

Low-temperature electrochemical reduction (electroreduction) is considered to be a suitable method for iron oxide reduction due to its attractive aspects, such as its CO2-free operation and low electric energy consumption and temperature requirements. Aiming at metallic iron of powder form as product, our research promotes dendritic electrodeposition rather than to grow compact deposition layers as in conventional electrowinning methods. Proof-of-concept experiments are performed using a single parallel plate electrode, immersed in a mixture of micro-sized hematite (Fe2O3) powder and strong aqueous alkaline (NaOH, 50%wt, 18 M) electrolyte. The effects of current density, hematite mass fraction, temperature, and particle size on deposit morphology and Faradaic efficiency are also investigated. It is found out that the dendritic structures are more likely to grow in a non-homogeneous environment, e.g. when experiments carried out without stirring or with local heating. Furthermore, the dendrites are located primarily on the side and edge of the cathode, indicating a diffusion-controlled mechanism. A cathodic deposition of metallic iron with a high Faradaic efficiency (> 90%) is successfully accomplished. The present findings provide new insight into the production of electrolytic iron powder (e.g. in the metal fuel application) and the acceleration of sustainable ironmaking technologies.

Fatty acid methyl esters are extensively used compounds in the industry, but they are perhaps most widely known for their application as biodiesel. In this study, we propose the rotor–stator spinning disc reactor (RS-SDR) as an intensified reactor for the production of fatty acid methyl esters. The RS-SDR relies on the generation of high shear forces in the small gap of a disc, rotating at high speeds, and a stationary wall, to improve on mass and heat transfer rates. Here, we have illustrated the benefits of mass transfer intensification for this reaction by performing the homogeneous base-catalyzed reaction in both a single-stage and a scaled-up multistage RS-SDR. A high level of productivity could be obtained in the multistage reactor (7.78 × 103 mol mR–3 min–1 at a conversion of 82%). Furthermore, we also performed a heterogeneous transesterification reaction with calcined sodium silicate as a slurry catalyst. We were able to obtain a productivity of 214 mol mR–3 min–1 in the RS-SDR (72% conversion, with a residence time of 8 min). In comparison, the batch heterogeneous system had 47% conversion during the same time period of operation. The high slurry concentrations of up to 20 wt % (based on oil weight fraction) did not lead to clogging or fouling in the reactor. These results demonstrate the potential of the RS-SDR for the transesterification reaction.

Many chemical reactions contain heterogeneous reagents, products, byproducts, or catalysts, making their transposition from batch to continuous-flow processing challenging. Herein, we report the use of a photochemical rotor–stator spinning disk reactor (pRS-SDR) that can handle and scale solid-containing photochemical reaction conditions in flow. Its ability to handle slurries was showcased for the TiO2-mediated aerobic photodegradation of aqueous methylene blue. The use of a fast rotating disk imposes high shear forces on the multiphase reaction mixture, ensuring its homogenization, increasing the mass transfer, and improving the irradiation profile of the reaction mixture. The pRS-SDR performance was also compared to other lab-scale reactors in terms of water treated per reactor volume and light power input.

Surfactants such as quaternary ammonium salts (QAS) have been in increasing demand, for emerging new applications. Recent attempts at process intensification of their production have disclosed the need for a better understanding of QAS thermal stability. This work aims to determine the degradation kinetics of various QASs and the associated solvent effects. The degradation kinetics of four methyl carbonate QASs were determined in various polar solvents in stainless steel batch autoclaves. urn:x-wiley:05388066:media:kin21537:kin21537-math-0001H NMR spectrometry was employed for offline analysis of the reaction mixtures. The kinetic parameters were then used to compare the thermal stability of the four compounds in the polar solvents. Water showed no degradation, and methanol (MeOH) was the solvent that provided the second-best stability. Water–MeOH mixtures may provide an overall optimum. Moreover, and longer long-chain substituents increased the degradation rate. Thermogravimetric analysis was used to obtain the thermal stability in a solid state, that is, solventless environment. Isoconversional analysis showed that no reliable kinetic parameters could be determined. Nevertheless, the data did allow for a comparison of the thermal stability of 14 different QASs. Furthermore, the relative instability of the compounds in the solid state demonstrated the challenges of solventless QAS production.

In this paper, micromixing is investigated in two Spinning Disk Reactors for liquids with increased viscosity. Glycerol and CMC were used as viscosity modifiers and micromixing characterization was performed by means of the Villermaux–Dushman method. For the first time, the effects of increasing the pH of the bulk solution leading to the disproportionation reaction of iodine are successfully modeled. A kinetic model is proposed to account for the presence of glycerol as a co-solvent. Micromixing efficiency decreases with increasing viscosity, yet the results are in line with the proportionality to the Kolmogorov timescale. The viscosity can be significantly increased using CMC as a viscosity modifier; however, due to the viscoelastic behavior of CMC, the effective viscosity decreases in the high shear environment inside the reactor. This leads to a much higher micromixing efficiency. It is shown that micromixing times can be estimated provided that the rheology of the liquids is known.

Electrowinning is the electrodeposition of metals from their oxides which are either solvent or suspended in an electrolyte solution. It receives increasing attention in the last decade as the promotion of CO2-free metal production. The design of the electrochemical cell is essential for the process performance, e.g., Faradaic efficiency. In this experimental study, we focus on the effect of different cathode materials on the electrodeposition performance of iron. Experiments are conducted in a lab-scale parallel-plates cell with the electrolyte composed of the aqueous sodium hydroxide (NaOH) 50%wt, 18 M (pH = 14.5) and micron-sized iron oxide powder with a mass fraction of around 20%. Different electrode materials are tested as the cathode for iron electrodeposition, including copper, stainless steel, graphite, and nickel mesh plates, whilst a nickel gauze is used as the anode. Characterizations of the deposition are conducted to obtain microstructural analysis and element identification. As a result, different deposit types and morphology are observed from the experiments. Stainless steel shows the highest current efficiency. The electrolyzed iron in all electrodes shows high purity (above 98%). The results from this study provide some guidance in designing key industrial processes of iron electrowinning

Iron is a prospective candidate for energy carriers in the energy transition era with high energy density. In this concept, energy is released by the combustion of iron powder whilst the solid product - iron oxide - can be collected and reduced back to metallic iron, forming a recyclable iron fuel cycle. The electrochemical technique is considered to be a suitable reduction method as it has attractive aspects including low electric energy consumption, low temperature, direct usage of renewable energy, and a short process chain. In this study, the performance of iron electrodeposition is investigated using an electrolysis cell containing a suspension of micron-sized combusted iron powder in aqueous NaOH (50%wt, 18 M) at a temperature of 110C. The parallel plate electrolyzer used in these experiments consists of a stainless-steel plate (cathode) and a nickel gauze (anode). The effects imposed by varying current density, iron oxide composition, and iron oxide particle diameter on Faradaic efficiency and reduced iron yield are evaluated. Additional experiments using a rotating disc electrode (RDE) are also conducted to determine the system's diffusion coefficient under different operating conditions. Generally, cathodic deposition of metallic iron is successfully achieved, and the morphology of the deposited iron depends on the operation conditions including the current density and heterogeneity of the flow system. The obtained results open new perspectives for efficient and cost-effective iron production/regeneration.