27 research outputs found
Comprehensive Review on Two-Step Thermochemical Water Splitting for Hydrogen Production in a Redox Cycle
No full textThe interest in and need for carbon-free fuels that do not rely on fossil fuels are constantly growing from both environmental and energetic perspectives. Green hydrogen production is at the core of the transition away from conventional fuels. Along with popularly investigated pathways for hydrogen production, thermochemical water splitting using redox materials is an interesting option for utilizing thermal energy, as this approach makes use of temperature looping over the material to produce hydrogen from water. Herein, two-step thermochemical water splitting processes are discussed and the key aspects are analyzed using the most relevant information present in the literature. Redox materials and their compositions, which have been proven to be efficient for this reaction, are reported. Attention is focused on non-volatile redox oxides, as the quenching step required for volatile redox materials is unnecessary. Reactors that could be used to conduct the reduction and oxidation reaction are discussed. The most promising materials are compared to each other using a multi-criteria analysis, providing a direction for future research. As evident, ferrite supported on yttrium-stabilized zirconia, ceria doped with zirconia or samarium and ferrite doped with nickel as the core and an yttrium (III) oxide shell are promising choices. Isothermal cycling and lowering of the reduction temperature are outlined as future directions towards increasing hydrogen yields and improving the cyclability.ChemE/Catalysis Engineerin
Computational Investigation of Microreactor Configurations for Hydrogen Production from Formic Acid Decomposition Using a Pd/C Catalyst
No full textThe need to replace fossil fuels with sustainable alternatives has been a critical issue in recent years. Hydrogen fuel is a promising alternative to fossil fuels because of its wide availability and high energy density. For the very first time, novel microreactor configurations for the formic acid decomposition have been studied using computational modeling methodologies. The decomposition of formic acid using a commercial 5 wt % Pd/C catalyst, under mild conditions, has been assessed in packed bed, coated wall, and membrane microreactors. Computational fluid dynamics (CFD) was utilized to develop the comprehensive heterogeneous microreactor models. The CFD modeling study begins with the development of a packed bed microreactor to validate the experimental work, subsequently followed by the theoretical development of novel microreactor configurations to perform further studies. Previous work using CFD modeling had predicted that the deactivation of the Pd/C catalyst was due to the production of the poisoning species CO during the reaction. The novel membrane microreactor facilitates the continuous removal of CO during the reaction, therefore prolonging the lifetime of the catalyst and enhancing the formic acid conversion by approximately 40% when compared to the other microreactor configurations. For all microreactors studied, the formic acid conversion increases as the temperature increases, and the liquid flow rate decreases. Further studies revealed that all microreactor configurations had negligible internal and external pore diffusion resistances. The detailed models developed in this work have provided an interesting insight into the intensification of the formic acid decomposition reaction over a Pd/C catalyst
APICAL VAPOUR LOCK EFFECT -PHENOMENON RELATED TO ENDODONTIC IRRIGATION - A REVIEW.
No full textInternational Journal of Advanced Research (IJAR
Single-Shade Universal Composites in Restorative Dentistry: A Review of Omnichroma
No full textThe emergence of single-shade universal resin composites marks a paradigm shift in restorative dentistry, simplifying the complex and error-prone process of colour matching. OMNICHROMA (Tokuyama Dental) is the foremost product in this category, employing a sophisticated "Smart Chromatic Technology" based on structural colouration rather than traditional pigment inclusion. This comprehensive review synthesizes recent in vitro and clinical evidence, focusing on OMNICHROMA\u27s unique mechanism, optical performance, clinical efficacy, and physical properties, including surface roughness and repair bond strength. Literature confirms OMNICHROMA’s superior blending effect, leading to excellent visual colour matching across the VITA classical range, often comparable to dedicated multi-shade composites. While instrumental colour measurements sometimes exceed perceptibility thresholds for specific optimal shades, the material\u27s strong chameleon effect ensures high visual acceptability and patient satisfaction, confirming its clinical reliability in both anterior and posterior restorations. Furthermore, OMNICHROMA demonstrates comparable resistance to aging effects and successful repairability when appropriate surface conditioning is utilized, solidifying its position as a reliable, time-saving aesthetic solution
CO<sub>2</sub> Capture and Reduction: Placing the process in an industrial framework
No full textCapturing and utilizing the emissions of CO2 has become a method to reduce the occurring emissions from industrial flue gases. One of the methodologies to capture and use the CO2 is through the CO2 capture and reduction (CCR) process. This process uses a bi-functional catalyst to capture CO2 from diluted gas streams and subsequently reduce it to CO in the presence of H2. The obtained product (syngas) can be further used as feedstock in for example the Fischer-Tropsch process. To implement a novel technology in industry, thetechnology itself should be economical feasible.To determine the feasibility of the process a technoeconomical analysis is executed. The analysis uses process parameters obtained by evaluating the catalytic activity of the bifunctional catalysts. Two catalyticsystems have been evaluated: Cu-K/𝛾-Al2O3 and FeCrCuK/PMG20. Effect on the synthesis conditions of Cu-K/𝛾-Al2O3 were also investigated. Cu-K/𝛾-Al2O3without additional drying steps during the synthesis shows a higher CO2 capacity and a faster CO production rate compared to the other catalysts. Furthermore, toestimate the H2 requirement in an industrialized process the consumption of H2 during the process has been quantified.To ensure a continuous process operation, a two reactor process has been proposed in the techno-economical analysis. The sizing and subsequent cost of the process equipment has been determined by utilizing the obtained process parameters. Besides the capital costs, the operating costs were also estimated to determine the profitability of the process. After the monetary benefit of selling the syngas was determined, it could be stated that the process is profitable under certain conditions. The process is profitable if the used H2 source has a buying price below 2.4 to ensure a profitable process.Applied Science
Hydrogen emissions from an electrolysis unit
No full textHydrogen is expected to play a vital role as an energy carrier in the future decarbonized system. Currently, a large portion of the hydrogen produced comes from the steam reforming of methane present in natural gas, which produces significant amounts of carbon dioxide emissions. However, with the growing need to reduce greenhouse gas emissions, a shift from fossil fuels to renewable energy sources is required. As a result, there is a growing emphasis on green hydrogen, i.e., hydrogen generated using renewable power. Green hydrogen has been growing at an exponential rate since 2020 and is expected to account for the majority of hydrogen production by 2050. However, a few studies have recently suggested that hydrogen may indirectly contribute to global warming. It is believed that hydrogen delays the decomposition of methane, a strong greenhouse gas, and thus extends its lifetime in the atmosphere. If green hydrogen is to be the primary fuel in the energy transition, hydrogen emissions from an electrolysis unit should be investigated.This project focuses on identifying the sources of hydrogen emissions from an electrolysis unit. The goal is to comprehend the depth of this potential issue and investigate possible solutions. This project is carried out in collaboration with Worley, a market leader in the design, construction, and delivery of green H2 facilities. The leakage estimates for the green hydrogen alkaline electrolysis plant are based on Worley’s in-house data. Venting during startup and shutdowns when power is unavailable, as well as hydrogen crossover in the electrolyzer, have been identified as two major contributors to hydrogen emissions. Solutions such as flaring systems to combust the vented hydrogen and battery energy systems to reduce frequent shutdowns and startups are investigated. To reduce emissions from hydrogen crossover, a reactor is modeled to explore the catalytic recombination of hydrogen and oxygen. These solutions are subjected to a techno-economic analysis to determine their viability.Flare systems and battery energy systems are both deemed feasible. In the longrun, however, installing a battery energy system would be preferable to combusting the hydrogen product. In comparison to other battery technologies such as Li-ion and lead-acid batteries, vanadium redox flow battery systems have been found to provide the maximum incentives and highest optimal capacities at the lowest overall costs. To avoid emissions from hydrogen crossover in a low-pressure alkaline electrolysis unit, the most cost-effective design involves a single-stage compression followed by a scrubber, heater, and reactor. However, this design is still costly because the annualized costs are four times greater than the costs offset by emissions reductions per year. Governments can encourage the adoption of such solutions by providing financial incentives to businesses.Electrical Engineering | Sustainable Energy Technolog
Hydrogenation of carbon dioxide (CO₂) to fuels in microreactors: a review of set-ups and value-added chemicals production
No full textClimate change, the greenhouse effect and fossil fuel extraction have gained a growing interest in research and industrial circles to provide alternative chemicals and fuel synthesis technologies. Carbon dioxide (CO2) hydrogenation to value-added chemicals using hydrogen (H2) from renewable power (solar, wind) offers a unique solution. From this aspect this review describes the various products, namely methane (C1), methanol, ethanol, dimethyl ether (DME) and hydrocarbons (HCs) originating via CO2 hydrogenation reaction. In addition, conventional reactor units for the CO2 hydrogenation process are explained, as well as different types of microreactors with key pathways to determine catalyst activity and selectivity of the value-added chemicals. Finally, limitations between conventional units and microreactors and future directions for CO2 hydrogenation are detailed and discussed. The benefits of such set-ups in providing platforms that could be utilized in the future for major scale-up and industrial operation are also emphasized
Apexification of Immature Necrotic Tooth with MTA using Platelet Rich Fibrin as an Internal Matrix
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