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•Five benchmark values are calculated for 24 reactors: Apparent reaction rate constant (k), Space time yield (STP), Photocatalytic space time yield (PSTY), Specific removal rate (SRR) ...and Electrical energy consumption (EEC)•Although micro-reactors seems to have highest efficiency. But when throughput is considered, the better performance is observed for LED based packed bed reactor due to numerous interconnected micro-channel pockets.•For an ideal photocatalytic reactor design two important parameters are to be balanced: Technical viability and Economical feasibility. Technical viability includes high Throughput and Performance (mass transfer), whereas Economic viability includes Energy efficiency (photon transfer) and Cost.•Apart from optimizing the process parameters(UV light intensity, Dissolved oxygen, flow rate, type of pollutant, pollutant concentration, catalyst load, irradiation time, ozonation, hydrogen peroxide, air flow rate, temperature, pH), the wavelength of light source, pollutant absorption wavelength and band gap energy of photocatalyst should be correlated and carefully chosen for an effective photocatalytic process.
Photocatalytic reactor design for environmental applications is a major challenging task in heterogeneous photocatalysis because all the three components involved in the process are in different phases: pollutant - fluid, catalyst – solid and light photons - massless particles. Heterogeneity of photocatalysis makes the reactor design highly inter-disciplinary involving the knowledge of chemical, mechanical and environmental engineering concepts. So far literatures have focused on optimizing process parameters for specific pollutants, but the holistic approach in designing a photocatalytic reactor has been unclear. This article reviews about all types of photocatalytic reactors and compares them with calculated five benchmarks: Apparent reaction rate constant (k), Space time yield (STY), Photocatalytic space time yield (PSTY), Specific removal rate (SRR), Electrical energy consumption (EEC). It is interpreted that in designing a photocatalytic reactor, four important aspects are to be considered: Throughput, Performance, Energy efficiency, Cost. This review article calculates the above said 5 benchmarks for 24 reactor designs and highlights the important parameters to build an effective photocatalytic reactor.
Nitrate enrichment, which is mainly caused by the over-utilization of fertilisers and industrial sewage discharge, is a major global engineering challenge because of its negative influence on the ...environment and human health. To solve this serious problem, many technologies, such as the activated sludge method, reverse osmosis, ion exchange, adsorption, and electrodialysis, have been developed to reduce the nitrate levels in water bodies. However, the applications of these traditional techniques are limited by several drawbacks, such as a long sludge retention time, slow kinetics, and undesirable by-products. From an environmental perspective, the most promising nitrate reduction technology is enabled to convert nitrate into benign N
, and features low cost, high efficiency, and environmental friendliness. Recently, electrocatalytic nitrate reduction has been proven by satisfactory research achievements to be one of the most promising methods among these technologies. This review provides a comprehensive account of nitrate reduction using electrocatalysis methods. The fundamentals of electrocatalytic nitrate reduction, including the reaction mechanisms, reactor design principles, product detection methods, and performance evaluation methods, have been systematically summarised. A detailed introduction to electrocatalytic nitrate reduction on transition metals, especially noble metals and alloys, Cu-based electrocatalysts, and Fe-based electrocatalysts is provided, as they are essential for the accurate reporting of experimental results. The current challenges and potential opportunities in this field, including the innovation of material design systems, value-added product yields, and challenges for products beyond N
and large-scale sewage treatment, are highlighted.
Photoinduced chemical transformations have received in recent years a tremendous amount of attention, providing a plethora of opportunities to synthetic organic chemists. However, performing a ...photochemical transformation can be quite a challenge because of various issues related to the delivery of photons. These challenges have barred the widespread adoption of photochemical steps in the chemical industry. However, in the past decade, several technological innovations have led to more reproducible, selective, and scalable photoinduced reactions. Herein, we provide a comprehensive overview of these exciting technological advances, including flow chemistry, high-throughput experimentation, reactor design and scale-up, and the combination of photo- and electro-chemistry.
MgO/MgCO3 reaction system is considered as a promising candidate of thermochemical heat storage. Most relevant studies focus on the improving the material chemical reaction performance. The reaction ...process inside the reactor has been less studied. In this study, a comprehensive multi-physics model is developed to analyze the decarbonization process of the MgO/MgCO3 reaction system. Impacts of various factors on the reaction process, including the injected energy flux density, reactor height and configuration of the thermal conductive plate (represented by thermal conductive area ratio) were analyzed. The heat transfer process is identified as the primary hindrance. By increasing the thermal conductive area ratio from 0.085 to 1.16, overall reaction time is decreased by 77 % and temperature difference from the top to bottom is decreased by 86 K. Additionally, a prediction model is developed using machine learning method and the prediction error is less than 5 %. Based on the predictive model, a design guideline was further developed so that various critical factors in reactor design could be explored and optimal choices could be obtained without consuming excessive computational resources. The identified influence laws of key factors and the proposed machine learning-based reactor design guideline may provide valuable insights for future thermochemical reactor designs.
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•Multi-physical field modelling of MgO/MgCO3 decarbonization is established.•The heat transfer process is founded as the primary hindrance.•Adding thermal conductive plate optimized the temperature distribution obviously.•Machine learning prediction model is trained based on multi-physics simulation data.•The reactor design could be completed by the trained machine learning model easily.
•Primary strategies for removing tar were assessed.•Tar formation represents the major challenge of biomass gasification.•Tar concentration depends on biomass nature, process conditions and reactor ...design.•Primary methods may not be efficient enough to completely remove tar.•Reactor design plays a critical role on tar conversion and gasification efficiency.
In the current energy scenario, the production of heat, power and biofuels from biomass has become of major interest. Amongst diverse thermochemical routes, gasification has stood out as a key technology for the large-scale application of biomass. However, the development of biomass gasification is subjected to the efficient conversion of the biochar and the mitigation of troublesome by-products, such as tar. Syngas with high tar content can cause pipeline fouling, downstream corrosion, catalyst deactivation, as well as adverse impact on health and environment, which obstruct the commercialization of biomass gasification technologies. Since the reduction of tar formation is a key challenge in biomass gasification, a comprehensive overview is provided on the following aspects, which particularly include the definition and complementary classifications of tar, as well as possible tar formation and transformation mechanisms. Moreover, the adverse effects of tar on downstream applications, human health or environment, and tar analyzing techniques (online and off-line) are discussed. Finally, the primary tar removal strategies are summarized. In this respect, the effect of key operation parameters (temperature, ER and S/B), catalysts utilization (natural and supported metal catalysts) and the improvement of reactor design on tar formation and elimination was thoroughly analyzed.
The electrochemical synthesis of chemicals and fuel feedstocks has been demonstrated to be a sustainable and “green” alternative to traditional chemical engineering, where oxygen evolution reaction ...(OER) plays a vital role in coupling with various cathodic reactions. While tremendous attention, involving both research and review topics, has been focused on pushing the limit of OER catalysts’ activity, the long-term stability of OER catalysts, which may play an even more important role in large-scale electrolysis industrialization, has been much less emphasized. Until this point, few systematic strategies for developing OER catalysts with industrially relevant durability have been reported. In this review, critical mechanisms that could influence OER stability are summarized, including surface reconstruction, lattice oxygen evolution, and the dissolution-redeposition process of catalysts. Moreover, to bridge the gap between lab-scale OER tests and large-scale electrocatalysis applications, stability considerations in electrolyzer design for long-term operation are also discussed in detail. This review provides catalyst and reactor design principles for overcoming OER stability challenges and will focus more attention from the field on the great importance of OER stability as well as future large-scale electrocatalysis applications.
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Recently, clean energy conversion through electrocatalysis is evolving rapidly as a promising alternative to fossil-fuel energy systems. However, electrolyzers have always suffered from long-term stability challenges, especially for the anodic oxygen evolution reaction catalysts. So far, other than high-cost noble-metal catalysts such as IrO2, no catalysts with industrially relevant stability for oxygen evolution process in acidic and neutral conditions have been demonstrated. Thus, mechanisms that lead to catalytic instability require further investigation and deep understanding to guide future catalyst design.
In order to explore both the origins of and solutions to the stability challenges, this review provides a comprehensive overview and analysis on mechanistic studies of OER catalytic stability. Surface reconstruction of catalysts under oxidation potential during oxygen evolution is one of the causes of catalyst degradation. In addition, lattice oxygen can sometimes participate in the reaction pathway and induce structural instability of catalysts. In addition, redeposition of dissolved ions onto the catalyst surface is a process that gains less attention but can greatly influence the catalytic stability. Besides the catalyst consideration, critical elements of electrolyzers are also discussed in this review to provide insights in electrolysis operation under more realistic conditions. Based on the studies summarized in this article, we also provide potential strategies to design stable OER catalysts. By appropriately tuning the components, structures, dissolution, and redeposition rates of catalysts, we believe that the development of catalysts with long-term stability for oxygen evolution reaction can be achieved in the near future.
Oxygen evolution reaction (OER) plays a vital role in clean energy conversion through electrochemical synthesis of chemicals and fuel feedstocks. However, OER catalysts have always suffered from long-term stability challenges. This review timely summarizes critical reaction mechanisms that could influence OER stability, discusses stability considerations for reactor designs, and proposes future perspectives and potential strategies for designing stable OER catalysts to overcome these challenges.
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The potential for directly converting CO2 to valuable liquid fuels utilizing green and renewable electricity has sparked significant interest in CO2 electroreduction (CO2RR). In ...recent years, CO2 conversion to formate/formic acid (HCOO−/HCOOH) has witnessed fast growth due to its economic and technological viability combined with the development of highly selective catalysts and practical electrolyzes. In this review, we summarize and discuss recent advances in HCOOH generation from CO2 reduction in terms of (1) the rationale behind choosing HCOOH as a CO2 electroreduction product, (2) mechanistic pathways to form HCOOH, (3) novel electrocatalyst developments for enhanced HCOOH production, and (4) electrolyzer designs that tackle practical challenges in scalability, reaction rate, and product impurities. Finally, a brief outlook on future opportunities in this field is offered to accelerate the industrialization of CO2RR to HCOOH.
Ionic liquids (ILs) offer a wide range of promising applications because of their much enhanced properties. However, further development of such materials depends on the fundamental understanding of ...their hierarchical structures and behaviors, which requires multiscale strategies to provide coupling among various length scales. In this review, we first introduce the structures and properties of these typical ILs. Then, we introduce the multiscale modeling methods that have been applied to the ILs, covering from molecular scale (QM/MM), to mesoscale (CG, DPD), to macroscale (CFD for unit scale and thermodynamics COSMO-RS model and environmental assessment GD method for process scale). In the following section, we discuss in some detail their applications to the four scales of ILs, including molecular scale structures, mesoscale aggregates and dynamics, and unit scale reactor design and process design and optimization of typical IL applications. Finally, we address the concluding remarks of multiscale strategies in the understanding and predictive capabilities of ILs. The present review aims to summarize the recent advances in the fundamental and application understanding of ILs.
Continuous-flow chemistry has recently attracted significant interest from chemists in both academia and industry working in different disciplines and from different backgrounds. Flow methods are now ...being used in reaction discovery/methodology, in scale-up and production, and for rapid screening and optimization. Photochemical processes are currently an important research field in the scientific community and the recent exploitation of flow methods for these methodologies has made clear the advantages of flow chemistry and its importance in modern chemistry and technology worldwide. This review highlights the most important features of continuous-flow technology applied to photochemical processes and provides a general perspective on this rapidly evolving research field.
(Solar) Photochemistry in flow benefits from better, more uniform irradiation than in batch, resulting in shorter, more selective reactions and efficient scale-up.Photochemical multiphasic reactions fully exploit the photon- and mass-transfer enhancement properties offered by flow chemistry.Flow photochemistry is gaining popularity in the pharmaceutical industry due to the many advantages demonstrated in the chemistry itself and the large potential for automation.
This review provides an overview of the recent achievements in catalytic process development for alkyne hydrogenations. It underlines the necessity of simultaneous optimization over different length ...scales from molecular/nanoscale of active phase, up-to macro-scale of catalytic reactor design. One case study, the hydrogenation of 2-methyl-3-butyn-2-ol, is analyzed in detail to illustrate the practical application of this approach. Finally, it presents the personal view of the authors concerning the new trends and paths available in the field.
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