Chemical Looping Research Articles

DFT insights into oxygen vacancy formation and chemical looping dry reforming of methane on metal-substituted CeO2 (111) surface

DFT insights into oxygen vacancy formation and chemical looping dry reforming of methane on metal-substituted CeO2 (111) surface

The process optimization and exergy efficiency analysis for biogas to renewable hydrogen by chemical looping technology

The study on biogas-Chemical Looping Hydrogen Production (biogas-CLHP) highlights its potential to produce high-purity hydrogen with recycling waste bioenergy. It delves into the gas-solid reaction characteristics and optimizes crucial process parameters for the fixed-bed CLHP system. Movement rate equations for the reaction fronts of Fe2O3-Fe3O4 (Rf1), Fe3O4-FeO (Rf2), and FeO-Fe (Rf3) are formulated, aiding in clarifying CO breakthrough curves. The identified convergence temperatures (Tm) under CO and H2 atmospheres are 916 °C and 907 °C, respectively. Rf1 and Rf2 converged above Tm, which leads to the disappearance of the Fe3O4 region in oxygen carrier (OC) beds. A theoretical model for calculating the reduction solid conversion (Xaver) is established, accurately characterizing Xaver under varying reaction times, H2/CO ratios, and temperatures. By using the Particle Swarm Optimization (PSO) algorithm and thermodynamic analysis, the study determines the optimal length-radius ratio (L/r), reduction temperature (T), and H2/CO ratio (α) for the OC bed as 12.5, 916 °C, and 0.72, respectively, at which a maximum conversion ratio of 43.55 % is achieved. Based on optimal parameters, the results of Aspen simulation reveal energy and exergy efficiencies of 74.9 % and 70.8 %. Generally, this research comprehensively outlines the process dynamics, optimizes key parameters, and evaluates exergy efficiency of the biogas-CLHP system.

Enhanced performance of red mud oxygen carrier for chemical looping combustion via tandem reactions

Biomethane power generation, particularly chemical looping combustion technology, has garnered significant attention recently due to its ability to capture CO2 in situ. In this study, dual bed layers oxygen carriers (DBL) for chemical looping combustion of methane were designed. The LaFe0.93Ni0.07O3 oxygen carrier with excellent CH4 partial oxidation was applied in upper bed layer and low-cost red mud was located into lower bed layer. This tandem reaction showed much higher methane conversion (87.1 %) than that over the single oxygen carrier of red mud (33.9 %) and the mechanically mixed oxygen carrier of LaFe0.93Ni0.07O3 and red mud (77.7 %). In addition, the mechanically mixed sample showed a quick deactivation, with the methane conversion dropping 54.2 % after 40 redox cycles due to the encapsulation of the active LaFe0.93Ni0.07O3 by red mud, while the double bed system showed high stability in the long-term redox cycle. The limitedly increased crystallite size of LaFeO3, as well as completely replenished lattice oxygen, were responsible for superior activity and stability of DBL. This study provides a new strategy to improve the efficiency of chemical looping combustion of methane in fixed bed reactor by tandem reactions over different oxygen carriers with complementary functions in terms of activity and cost.

Chemical Looping Ammonia Decomposition Mediated by Alkali Metal and Amide Pairs for H2 Production and Thermal Energy Storage

AbstractAmmonia decomposition to H2 (ADH) is one of the key reactions in the ammonia‐based energy system. Recent research has been focused on developing more active and affordable catalysts, however, few can operate below 500 °C and typically require the expensive metal ruthenium. Herein, a fundamentally different thermal ADH via a chemical looping process (CLADH) mediated by alkali metal and its amide pairs, which can work under lower temperatures than the catalytic process, is reported. This CLADH consists of two steps: 1) Ammoniation step ̶ NH3 reacts with Na or K to generate NaNH2 or KNH2, respectively, accompanied by releasing one‐third of H2 in NH3 at room temperature; 2) Decomposition step ̶ NaNH2 or KNH2 decomposes to N2 and H2 with the regeneration of Na or K which can be performed above 275 °C. Additionally, due to the significant enthalpy change in the two‐step reactions of this CLADH, −78.0 kJ mol−1 for the first step and 123.9 kJ mol−1 for the second, using the Na and NaNH2 pair—suggest potential for thermal energy storage. This work not only reports an alternative route to produce H2 from NH3, but also unravels the potential of chemical looping process for thermal energy storage.

Reaction Characteristics and Kinetics for the Interaction between Biomass and Silico-Ferrite of Calcium and Aluminum (SFCA)-Type Oxygen Carrier in Chemical Looping Gasification

Reaction Characteristics and Kinetics for the Interaction between Biomass and Silico-Ferrite of Calcium and Aluminum (SFCA)-Type Oxygen Carrier in Chemical Looping Gasification

Experimental and process simulation on solid fuel chemical looping cascade utilization conversion technology aiming hydrogen generation

In this work, a novel chemical looping process towards hydrogen generation based on the cascade utilization of components in solid fuels (like biomass and coal) with different reactivity (pyrolysis gas and char) was proposed, aiming for energy conversion from carbon-intensive fuels to carbon-free renewable hydrogen via the material migration of iron oxides. Biomass, represented by sawdust, is an important part among various renewable energy sources and a typical solid fuel with great potential. Therefore, in the most concerned reduction stage, experiments were conducted mainly using sawdust to investigate the effects of various parameters (temperature, oxygen/fuel ratio, residence time) on the carbon conversion involved in char in the primary reduction stage, gas/solid spatiotemporal distribution in the deep reduction stage and subsequent H2 generation performance, and kinetic parameters were fitted for different reduction stages. Process simulation was further conducted based on the actual experimental results. The proposed process demonstrated satisfactory applicability to solid fuels with different characteristics, and biomass was more suitable for hydrogen production. Compared with chemical looping combustion process, a significant improvement of sawdust-fueled energy conversion efficiency from 33.26 % to 51.76 % and a decrease of OCs theoretical circulation rate (27.77 %) were achieved under the chemical looping process aiming hydrogen generation.

Unraveling the Mechanism of Catalyzed Melt-Phase Polyester Depolymerization via Studies of Kinetics and Model Reactions.

Developing a mechanistic understanding of catalyzed melt-phase depolymerization processes is of utmost importance to the rapidly expanding field of circular polymers with a closed chemical loop. Herein, we present a methodology to probe the mechanism of metal-catalyzed melt-phase depolymerization of polyesters utilizing an approach centered on studies of kinetics by thermogravimetric analysis and model reactions. Kinetic parameters associated with the prototypical Lewis-acid-catalyzed depolymerization of representative polyesters, including poly(δ-valerolactone) (PVL), poly(lactic acid), and poly(γ-butyrolactone), are elucidated. Focusing on PVL for further investigation of the depolymerization mechanism, effects of its molar mass, topology, and end-group chemistry are examined in detail. Overall, a catalyzed ring-closing depolymerization process to monomer from the polyester hydroxyl-chain ends is proposed as the key mechanistic step, although the process has a relatively large zip length (≈ 320) and follows nonimmortal depolymerization kinetics.

Numerical simulation of gasifier optimization for combined hydrogen production and carbon reduction in a chemical looping gasification (CLG) system

Chemical looping gasification (CLG) for combined hydrogen production and carbon capture represents a significant pathway for the clean, low-carbon utilization of traditional fossil fuels. Currently, a significant knowledge gap remains concerning the interplay between reactor configuration optimization and the complex gas–solid interactions in the CLG systems. This study integrates reactive computational fluid dynamics-discrete element method (CFD-DEM) simulations with a coarse-grained model (CGM) to analyze 3D coal-based CLG systems. The spatiotemporal distributions of gas–solid flow dynamics and thermochemical characteristics are revealed. It is found that increasing the gasifier height enhances fuel conversion and hydrogen production but compromises CO2 absorption. Smaller reactor diameters induce excessively rapid gas–solid flows, leading to incomplete fuel conversion and reduced hydrogen yield, while larger diameters cause uneven flows, significantly deteriorating hydrogen production and carbon absorption efficiency. Based on the simulation findings, the optimal height-to-diameter ratio for the gasifier in a CLG system is approximately 28.8, optimizing H2 production while maintaining efficient CO2 absorption. Moreover, the superficial gas velocity has a multifaceted influence on the hydrogen production and carbon reduction performance in the CLG process, necessitating a comprehensive consideration of its effects on fuel reaction time, gas–solid interactions, and other factors.

Study on K-modified Ca-based dual-functional materials for carbon capture and in-situ methane dry reforming

Integrated carbon capture and in-situ methane dry reforming (ICCU-DRM) is a promising technology for chemical looping transformation, this process involves the sequential switching of feedstocks within a single reactor, allowing CO2 capture to occur before methane dry reforming without direct CO2-CH4 contact. However, a significant challenge in the ICCU-DRM process is the disparity between the optimal temperatures required for carbon capture and dry reforming, with the latter necessitating considerably higher temperatures. This could lead to substantial CO2 losses when the reaction temperature is elevated to the optimal level for dry reforming. To address this issue and improve CO2 conversion efficiency, this study explores K doping in synthesizing a dual-functional material, NiCa1.6K0.4@Al2O3, through extrusion-spheronization. The synthesized material exhibits a stable pore structure and a large internal surface area, crucial for enhancing CO2 capture. The optimum temperature for DRM is around 800 °C. Notably, the formation of 1K2Ca(CO3)2 during the calcination of NiCa1.6K0.4@Al2O3, with a thermal decomposition temperature of approximately 800°C, plays a crucial role in minimizing CO2 release during the heating process, thereby significantly improving the CO2 conversion. To evaluate the impact of K doping on the material, the samples were subjected to carbon capture at 650 °C and dry reforming of methane at 750 °C. The results showed that the CO2 conversion rate of NiCa1.6K0.4@Al2O3 reached 52.8%, compared to only 18.9% for NiCa2@Al2O3 under the same conditions. Moreover, this study also investigates the impact of carbon capture temperature, dry reforming temperature, and catalytic metal loading on the performance of the ICCU-DRM process.

Enhancing the performance of spinel La-doped CoFe2O4 oxygen carriers for chemical looping hydrogen generation

Chemical-looping hydrogen generation (CLHG) is a clean and efficient method for sustainable hydrogen production. The industrial advancement of the CLHG technology hinges on the development of highly active and selective oxygen carriers (OCs). In this study, the performances of three spinel OCs (ZnFe2O4, CoFe2O4, and NiFe2O4) were investigated in a fixed-bed reactor. CoFe2O4 demonstrated the best reactivity and highest hydrogen yield. In addition, doping CoFe2O4 with varying amounts of La further improved its performance. The highest hydrogen yield (393mL/g) was observed for CoFe2O4 doped with 10 % by mass of La. The characterization results indicated that La not only facilitated the formation of oxygen vacancies but also accelerated lattice oxygen transfer. Furthermore, an optimized La doping level was found to boost the crystallinity of the oxygen carrier, leading to improved cycling performance. The insights gained from probing the performance of La-doped CoFe2O4 OCs are expected to contribute to the development of novel OCs for scaled-up CLHG technology.

4-E comparative analysis of two novel chemical looping hydrogen generation-based systems with near-zero carbon emissions

To achieve the near-zero carbon emissions from chemical looping hydrogen generation (CLHG) power plant, two novel systems were proposed in this study: one integrates CLHG with ammonia decomposition for hydrogen production (ADHP) and CO2 hydrogenation to methanol (CHM), while the other integrates CLHG with CHM and CO2 compression storage (CCS). The performance of these two integrated systems was evaluated through analyses of economy, energy, exergy, and ecology (4E). The findings reveal that the CLHG-CHM-CCS system is more economically competitive and environmentally favorable than the CLHG-ADHP-CHM system. Its maximum net present value increases by 2.373×108 $, and annual CO2 emissions decreases by 361.401 t. Meanwhile, the system's profitable allowable maximum purchasing price of natural gas increases by 0.036 $/Nm3, while its minimum selling price of methanol decreases by 47.583 $/t. However, the CLHG-ADHP-CHM system exhibits improvements in both energy efficiency and exergy efficiency, with improvements of 1.88% and 2.34%, respectively, compared to the CLHG-CHM-CCS system. Moreover, reactors within the CLHG subsystem account for 42.60% of its total exergy loss, offering a potential 3.275 MW improvement.

Study on interaction mechanism of steam coupling biomass sludge gasification to syngas with pickling sludge as oxygen carrier

A process of producing hydrogen-rich syngas by chemical looping steam gasification is proposed, using pickling sludge (PS) as the oxygen carrier and paper-making sludge(PMS) along with municipal sludge(MS) as the fuel. The reaction characteristics of producing hydrogen-rich syngas through the gasification of PMS and MS were studied. The effects of temperature, steam flow rate and the blended ratio of PS on carbon conversion rate and gasification reaction efficiency were discussed, and the migration mechanisms of the main elements were explained. The results show that FeF3 in PS exhibits stronger activity than conventional Fe2O3 in catalyzing the gasification of PMS and MS at high temperature. With the blended mass ratio of 1:1 of PS, the carbon conversion rate of PMS and MS was increased by 11.8% and 42.5%, and the gasification efficiency was increased by 11.1% and 25.85%. The Fe3+ in PS catalyzed the cleavage of C-H bonds in biomass sludge, and Fe3+ was reduced to form the intermediate product FeCr2O4 with tar cracking function. After the gasification reaction, the Fe in PS was completely converted to Fe3O4 under the action of MS, while the CaO in PMS promoted the valence cycle of Fe to some extent, resulting in partial Fe being fully cycled to Fe3+ to form γFe2O3. In addition, the CaO can fix the F element in PS to form CaF2, thus reducing the environmental hazard.

Chemical looping gasification of biomass char in fluidized bed and CO2-enriched atmosphere

Chemical looping gasification of biomass char in fluidized bed and CO2-enriched atmosphere

Near-zero emission trigeneration system coupling molten salt methane pyrolysis with solid oxide fuel cell based on carbon capture and utilization: Thermodynamic and exergoenvironmental evaluation

Natural gas-based energy systems have garnered widespread attention for their potential to facilitate the transition from traditional to renewable energy sources. Among these, methane pyrolysis technology stands out as a promising pathway. Consequently, a novel methanol-electricity-carbon trigeneration system featuring methane pyrolysis coupled with chemical looping combustion, methanol synthesis, and solid oxide fuel cell unit was designed. To validate this innovative concept, thermodynamic model of the process was developed. Compared to conventional single-generation system, the proposed system demonstrated superior thermodynamic performance, with energy efficiency of 69.51 %, representing improvement of 28.78 %. Sensitivity analysis indicated that optimal carbon utilization-to-storage ratio of 0.68 effectively balanced environmental benefits with energy conversion efficiency. Additionally, the CO2 capture rate and emission of the proposed system reached impressive 99.24 % and 2.15 kg/MWh, respectively, confirming its carbon mitigation potential. Based on this, exergoenvironmental analysis demonstrated that rb,k of the novel system was 21.14 %, indicating room for further environmental impact reduction. Moreover, due to the high rb,k of 16.61 % for the preheater-2 identified as a key component for optimization. Finally, the economic analysis verified the system’s feasibility, showing the annual net income of 6774.06 k$. This novel concept highlights the potential of natural gas-based systems in optimizing carbon utilization and energy efficiency, contributing to a more environmentally sustainable energy infrastructure.

Conversion of CO2(g) to CO(g) via reverse water–gas shift cycle on mixed cerium/praseodymium oxides at 500 °C

Reactions of cerium/praseodymium oxides under hydrogen atmospheres, and subsequently, carbon dioxide, involved in chemical looping reverse water–gas shift cycles (RWGS) at 500 °C were investigated by in-situ high-temperature X-ray powder diffraction, FTIR and thermogravimetry. The RWGS cycle is a critical chemical process for converting carbon dioxide into useful products, such as carbon monoxide, which can be used to synthesize fuels and chemicals. The mixed oxides exploit the redox properties of Ce and Pr, which can switch between oxidation states, making them suitable for oxygen incorporation and release during the RWGS process allowing them to react with H2(g), and subsequently with CO2(g), promoting their interaction and conversion into H2O(g) and CO(g). Pure cerium and praseodymium oxides showed poor CO2(g) conversion efficiency. However, we found that nanometric Ce/Pr mixed oxides exhibit enhanced oxyreduction performance suitable for this application, particularly with a composition of 75 mol% Ce and 25 mol% Pr, significantly improved performance, achieving an average CO(g) yield of 0.6 mmol/(goxide.cycle) and a maximum rate of 0.26 mmol/(goxide.min). Pr enhances oxygen mobility in CeO2, which improves the dissociation of C═O bonds in CO2(g). This is because the remaining oxygen atoms are delivered more quickly to the support sink, thereby cleaning up the vacant sites generated during the reduction step. These findings suggest that Ce/Pr mixed oxides are highly effective for CO2(g) conversion to CO(g) via RWGS cycle, offering a potentially viable option for industrial application.

Unmatched Redox Activity of the Palladium-Doped Indium Oxide Oxygen Carrier for Low-Temperature CO2 Splitting.

The chemical conversion of CO2 into value-added products is the key technology to realize a carbon-neutral society. One representative example of such conversion is the reverse water-gas shift reaction, which produces CO from CO2. However, the activity is insufficient at ambient pressure and lower temperatures (<600 °C), making it a highly energy-intensive and impractical process. Herein, we report indium oxide nanofibers modified with palladium catalysts that exhibit significantly potent redox activities toward the reduction of CO2 splitting via chemical looping. In particular, we uncover that the doped palladium cations are selectively reduced and precipitated onto the host oxide surface as metallic nanoparticles. These catalytic gems formed operando make In2O3 lattice oxygen more redox-active in H2 and CO2 environments. As a result, the composite nanofiber catalysts demonstrate the reverse water-gas shift reaction via chemical looping at record-low temperatures (≤350 °C), while also imparting high activities (CO2 conversion: 45%). Altogether, our findings expand the viability of CO2 splitting at lower temperatures and provide design principles for indium oxide-based catalysts for CO2 conversion.

Kinetic analysis of solid fuel combustion in chemical looping for clean energy conversion

Chemical looping combustion (CLC) offers an advanced, eco-friendly method for converting solid fuels into energy with inherent CO2 capture, presenting a cost-efficient solution. The kinetics of solid fuel CLC, crucial for reactor design, are not well-understood, limiting its application and optimisation. Conducting a comprehensive kinetic analysis of solid fuel CLC is crucial, as it examines the combustion of both volatiles and fixed carbon, thereby addressing existing knowledge gaps and advancing clean conversion of solid fuels. In this study, a comprehensive kinetic analysis method for the first time has been applied to investigate the kinetics of CLC of low-volatile semi-anthracite coal with CuO at temperatures of 700–950 °C under varied oxygen excess ratios (0.5, 1.0, and 2.0). The results show that the combustion of coal in CLC can be divided into three distinct stages. The combustion of coal with CuO initiates with the combustion of volatiles interacting with solid CuO at 450–580 °C, where the combustion efficiency varies between 3–6 wt%. This is followed by a complex simultaneous mechanism involving gas-phase volatiles and solid-phase CuO, as well as gas-phase oxygen and solid-phase fixed carbon under non-isothermal conditions. The combustion efficiency is ranged 19–71 wt% at the temperature ranges from 580 °C to the isothermal temperatures of 750–950 °C. The activation energy for the combustion of volatiles was determined as Ea = 119 kJ/mol, whereas the initial combustion of fixed carbon in the non-isothermal stage ranged between Ea = 39–53 kJ/mol. The rate of combustion is initially limited by the oxygen diffusion rate from CuO, but with additional oxygen carriers and increased temperature, the reaction becomes constrained by first-order kinetics. Upon reaching the isothermal stage, the final combustion phase between fixed carbon and gas phase oxygen occurs, and the combustion efficiency increases to 77–96 wt% at 750–950 °C. The activation energy for fixed carbon combustion under the isotherm stage was approximately Ea = 234 kJ/mol, with a reaction rate constant (k0) of 7.84 × 109 min−1. This pioneering study not only clarifies the multi-stage kinetics of solid fuel CLC, bridging significant gaps in current knowledge but also sets the foundation for the enhanced design and efficiency of CLC systems for cleaner energy production.

Economic and Environmental Analyses of an Integrated Power and Hydrogen Production Systems Based on Solar Thermal Energy

This study introduces a novel hybrid solar–biomass cogeneration power plant that efficiently produces heat, electricity, carbon dioxide, and hydrogen using concentrated solar power and syngas from cotton stalk biomass. Detailed exergy-based thermodynamic, economic, and environmental analyses demonstrate that the optimized system achieves an exergy efficiency of 48.67% and an exergoeconomic factor of 80.65% and produces 51.5 MW of electricity, 23.3 MW of heat, and 8334.4 kg/h of hydrogen from 87,156.4 kg/h of biomass. The study explores four scenarios for green hydrogen production pathways, including chemical looping reforming and supercritical water gasification, highlighting significant improvements in levelized costs and the environmental impact compared with other solar-based hybrid systems. Systems 2 and 3 exhibit superior performance, with levelized costs of electricity (LCOE) of 49.2 USD/MWh and 55.4 USD/MWh and levelized costs of hydrogen (LCOH) of between 10.7 and 19.5 USD/MWh. The exergoenvironmental impact factor ranges from 66.2% to 73.9%, with an environmental impact rate of 5.4–7.1 Pts/MWh. Despite high irreversibility challenges, the integration of solar energy significantly enhances the system’s exergoeconomic and exergoenvironmental performance, making it a promising alternative as fossil fuel reserves decline. To improve competitiveness, addressing process efficiency and cost reduction in solar concentrators and receivers is crucial.

Thermodynamic analysis on the coupling effects of operating parameters in sorption-enhanced chemical looping gasification with rice husk as feedstock

Sorption-enhanced chemical looping gasification (SECLG) has a favorable ability to produce H2-rich syngas without any extra separation process. To comprehensively investigate the performances, the temperature in the fuel reactor (FR) side TFR, molar ratio of steam or CaO to carbon (λsteam/C, λCaO/C), circulation ratio of oxygen carrier to carbon (λOC/C) are changed to test their effects on the products. Then the coupling effects on SECLG are deeply analyzed by changing two and three of the operating parameters. Results demonstrate that under fundamental conditions, the sorption enhancement becomes unavailable when the temperature is higher than 775 °C but decreasing λsteam/C and increasing λOC/C can elevate this critical temperature. Increasing the λOC/C or λsteam/C can enhance the H2 concentration first, then weaken H2 concentration. The maximum value of H2 concentration is 62.47% when λOC/C = 0.4 and λsteam/C = 1.9. When the FR temperature is lower than 775 °C, there is an optimal λOC/C for maximizing the H2 concentration at a specific temperature. When the temperature is 650 °C, λOC/C = 0.5 and λsteam/C = 1.9, the maximum value of H2 concentration can reach 95.73% in SECLG.

Removal performance of Nitrogen, sulfur and chlorine pollutants during chemical looping combustion of textile dyeing sludge using red mud as an oxygen carrier

Textile dyeing sludge (TDS) is a solid waste produced by the textile industry, which contains a large number of N, S and Cl components. Direct heat treatment of TDS will cause a large number of N, S, Cl pollutants to be released. This study verified the possibility of chemical looping combustion (CLC) of TDS using alkaline WS900 red mud (RM) oxygen carrier, which is rich in Na/Ca, to remove N, S and Cl pollutants at the same time. Raising the reaction temperature in the range of 750–900 °C, prolonging the residence time and increasing the oxygen excess coefficient can promote the oxidation performance of WS900 to NOx precursor, while CO2 atmosphere inhibits the oxidation ability. After 10 cycles of CLC, the Cl fixation rate of WS900 is still close to 100% and its S fixation rate is more than 97%. It can maintain more than 90% of carbon conversion and 86% of CO2 selectivity. Compared with the pyrolysis condition, the removal rate of N pollutants is about 67%. Alkaline RM is also neutralized after absorbing acid gases during CLC, which is convenient for its further treatment and utilization.