Chemical Looping Process Research Articles

Versatile Low Cost Oxygen Carrier for Chemical Looping Processes Requiring Different Degree of Iron Oxide Reduction

Versatile Low Cost Oxygen Carrier for Chemical Looping Processes Requiring Different Degree of Iron Oxide Reduction

CeO2 enhanced performance of NiFe2O4-CaO for carbon capture and in-situ hydrogenation conversion to CO

NiFe2O4 exhibits excellent redox properties and is widely applied in CaO-NiFe2O4 chemical looping processes. However, rapid sintering of Ni-Fe alloy under reaction conditions limited its industrial applications. The CeO2-NiFe-CaO were synthesized through a physical mixing method with NiFe2O4 as a precursor, and its CO2 capture capacity and in-situ hydrogenation performance were conducted on ICCC-RWGS reaction under different conditions. 20CeO2-NiFe-CaO exhibited a CO yielding of 9.35 mmol/g at 650 °C. During the carbon capture stage, CO2 was adsorbed by CaO, leading to the formation of CaCO3. In the hydrogenation conversion stage, hydroxyl groups were generated on the surface, combining with CaCO3 to produce formate species, further generating H2O and CO. 15CNF-CaO exhibited superior cyclic ICCC-RWGS reaction performance compared to 15NF-CaO, with a CO yield of 1.88 mmol/g after 40 cycles. CeO2 inhibited the sintering of catalytic components, preserving a higher specific surface area and smaller particle size. Furthermore, CeO2 in 15CNF-CaO inhibited carbon deposition and enhanced in-situ hydrogenation performance, exhibiting better CaO regeneration capability and better cyclic stability. These results could provide insight for designing the DFMs for the ICCC-RWGS process.

Reaction kinetics of Ni-Fe oxygen carriers with high performance for chemical looping hydrogen production

The chemical looping hydrogen production (CLHP) process utilizing iron-based oxygen carriers holds promise for practical hydrogen generation applications. However, challenges persist in developing iron-based carriers that are easy to prepare and demonstrate effective reactivity. Our research focuses on evaluating the CLHP reaction performance using bimetallic Ni-Fe oxygen carrier particles, synthesized by a scalable mechanical mixing method. This study unravels the role of Ni in bimetallic Ni-Fe oxygen carriers and investigates the influence of varying nickel-doping ratios on enhancing the reduction reactivity of iron-based oxygen carriers. Compared to the undoped sample, the 20 wt% nickel-doped Fe2O3/Al2O3 (20NiFe) particles enabled a reduction in the reaction temperature by at least 50 K. With the dopant, the methane conversion rate at 923 K is 500% higher than that of carriers without the dopant. Heterogeneous kinetic analysis demonstrates that the global reduction reaction data for the Ni-Fe oxygen carriers fit with the nucleation-nuclei growth model. Through redox reactivity tests and reduction kinetic analysis, 20NiFe shows the lowest apparent activation energy at 53.93 kJ/mol. Furthermore, the kinetic study and quasi in-situ XRD analysis aid in proposing the evolution process of methane reduction reaction for nickel-doped iron-based oxygen carriers, clarifying the role of doping in improving chemical looping reactivity from a kinetic perspective. This work provides valuable guidance for the design and optimization of oxygen carriers, thus accelerating the readiness for industrial deployment of hydrogen production via chemical looping process.

A cradle-to-gate life cycle assessment for clean hydrogen gas production pathway using the CeO2/Ce2O3-based redox thermochemical cycle

The present study is conducted to develop a two-steps redox thermochemical cycle based on combined ceria reduction and methane reforming through the CeO2/Ce2O3 redox pair. This cycle incorporates simultaneous water splitting for hydrogen production. To enhance the accuracy and reliability of the inventory data, the system is simulated using the Aspen Plus software package. Also, the goal of this work is to evaluate the carbon footprint of thermochemical based hydrogen production under different scenarios and to compare it with traditional technologies like steam methane reforming (SMR). The analysis takes into account both the plant manufacturing line (reactors), fuel processing (H2 production), redox particles oxygen carrier manufacturing (OC), H2 compression (power consumption) and H2 storage (pipeline manufacturing). The openLCA software with the European database environmental footprint is employed to compute the total carbon emissions of this thermochemical cycle during its overall life cycle. The study concludes that the base case scenario of this system has an overall GWP of 1751.14 g CO2 eq./kg H2 respectively. In the overall GWP, the share of plant construction and OC production was found to be around 1.67%, and 15.78% respectively. The conventional steam methane reforming is loaded with an overall GWP of 4472.83 g CO2 eq./kg H2. In terms of renewable energy input, the base case scenario of this hydrogen production system results in 1465.73 g CO2 eq./kg H2 with thermal energy produced from renewable sources. Comparative life cycle assessment (LCA) demonstrates that base case of CeO2/Ce2O3 has an 85.41% lower GWP emphasizing its environmental advantages over the SMR and Fe3O4/FeO redox pair carries an 84.06% lower GWP as compared to the conventional SMR with 1483.55 g CO2 eq./kg H2. The present study concludes that the combined ceria reduction and methane reforming chemical looping process with simultaneous water splitting may be a more promising option to produce hydrogen using renewable energy.

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.

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.

Mechanism study on quantification of sulfurization effect on methane decomposition with CuO oxygen carrier

The sulfur-containing impurity in natural gas, coal, and organic solid wastes generally exerts significant impacts on the dynamic evolution of sulfur oxides emission in atmosphere, and results in the degraded reaction performance of chemical looping process. Methane is the main component of natural gas and a typical pyrolysis and gasification product of solid waste, so it is of great significance to quantify the toxicological effects on the conversion of methane. this work realizes the accurate prediction of methane heterogeneous conversion in a multiscale kinetic model, and innovatively establishes a framework for quantifying the toxicological effect on the oxygen carrier particles. The kinetic parameters of methane oxidation over fresh and sulfurized oxygen carriers are calculated using density functional theory, and the sensitivity analysis of rate constant is conducted to forecast the priority of different reactions. Results indicate that the effect of residual sulfur in oxygen carrier is complex and not monotonically inhibited, and the sulfurization significantly limits the methane oxidation reactivity by reducing the reaction rate of the rate-limited dissociation step under the high-temperature condition. The multi-scale kinetic simulations reveal that the maximum instantaneous rate of sulfurized oxygen carrier is decreased by 7.45 %, which is deemed as the attenuation factor of 0.9255 derived from the toxicological effects of sulfurization.

BCLH2Pro: A novel computational tools approach for hydrogen production prediction via machine learning in biomass chemical looping processes

This study optimizes biomass chemical looping processes (BCLpro), a technique for converting biomass to energy, through machine learning (ML) for sustainable energy production. The study proposes an integrated Fe2O3-based ฺBCLpro combining steam gasification for H2 production. Aspen Plus is used as the primary tool to generate extensive datasets covering 24 biomass types with 18 feature inputs in a supervised model. A methodology involving K-Nearest Neighbors (KNN), Extreme Gradient Boosting (XGB), Light Gradient Boosting Machine (LGBM), Support Vector Machine (SVM), Random Forest (RF), and CatBoost (CB) algorithms was employed to predict H2 yields in the BCLpro, utilizing 10-fold cross-validation for robust model evaluation. Findings highlight the CB algorithm's superior performance, achieving up to 98% predictive accuracy, with carbon content, reducer temperature, and Fe2O3/Al2O3 mass ratio identified as crucial features. The algorithm has been developed into a user-friendly tool, BCLH2Pro, accessible via a web server. This tool is designed to assist in reducing costs, optimizing biomass selection, and planning operational conditions to maximize H2 yield in BCLpro systems. Access to the tool can be obtained through the following link: http://bclh2pro.pythonanywhere.com/.

Fuel reactor simulation for coal chemical looping process: Effects of ash on flow behavior

Chemical looping gasification (CLG) is an environmentally friendly strategy for using coal that has significant promise for application in reality. Nevertheless, the process of generating and accumulating ash from coal presents obstacles to the advancement of this technology. To fully comprehend the effects of ash from coal on the internal flow properties of a fuel reactor (FR). The Computational Particle Fluid Dynamics (CPFD) approach was applied to predict the CLG with coal at the FR, uncovering distinctive flow properties of gas-solid reactions. This study investigated the effects of ash particles content, polydispersity and sphericity on the flow behavior within the bed. The simulation accurately predicted the motion of the bubbles within the FR, and the gas phase composition distribution at the outlet is closer to the experimental data. Introducing coal ash creates a reduction in the concentration of ilmenite, resulting in a drop in the rates of the related reactions. The narrow particles diameter distribution among coal ash facilitates the particles arrangement in the bed and improves the overall reaction. The addition of moderately irregular-shaped coal ash particles has a certain positive effect on improving the gas-solid contact.

APPLICATION OF MANGANESE-BASED OXIDES AS OXYGEN CARRIERS IN CHEMICAL LOOPING PROCESSES: A BIBLIOMETRIC ANALYSIS

This article describes a general study of manganese-based oxygen carriers (OCs) in chemical looping (CL) processes between 2006 and 2023 through a careful bibliometric analysis. This was achieved through the selection of scientific articles and checking bibliometric parameters, highlighting the main challenges and the current state of this area of research. Using keywords, 426 documents were found on the Web of Science database and 65 of them were selected using the ProKnow-C method. Analysis of the main articles indicates that these materials have decreased friction rates and a low tendency to agglomerate in reactors with continuous fluidized beds. Furthermore, this study informs the possible optimization of the physicochemical properties of oxygen carriers, with emphasis on the oxygen transport capacity, reactivity, and friction rate. In addition, this research highlighted the great potential of synthetic manganese-based OCs for applications in CL processes.

Removal of Nitrogen Pollutants in the Chemical Looping Process: A Review

Removal of Nitrogen Pollutants in the Chemical Looping Process: A Review

Solar-Driven membrane reactors with wide temperature range for chemical looping dry reforming of Methane: Concept validation and one-dimensional analysis

Solar thermochemical fuel conversion technology offers a significant potential to mitigate the challenges of intermittency and variability inherent in solar energy utilization. Traditional two-step methane chemical looping processes for fuel production are often hampered by complex apparatus requirements, operational intermittency, and persistent temperature variations, contributing to energy loss. In contrast, the chemical looping dry reforming of methane (CL-DRM) membrane reactor technology, as developed in this study, facilitates continuous fuel synthesis under isothermal conditions. Through the construction and analysis of a one-dimensional + one-dimensional model for a single channel of this innovative reactor, the impact of structural and operational parameters on the reactor performance is elucidated. This model enables a swift prediction of the membrane reactor’s operational efficacy. The results indicate that the reactor sustains a high energy conversion efficiency across a broad temperature spectrum, thereby enhancing its adaptability to the dynamic conditions of solar energy input. Notably, temperature and feed ratio (RCH4/CO2) are pivotal determinants of the conversion rate and the concentration of products. At a temperature of 1000 °C, with an optimal RCH4/CO2 ratio of 1, the efficiency is projected to attain 78 %, considering heat dissipation and thermal recovery mechanisms. These results underscore the promise of the solar-driven CL-DRM membrane reactor as a viable and efficient method for solar fuel production. This study provides a new perspective on the design of continuous solar fuel conversion reactors.

Effect of the Conversion Degree on the Apparent Kinetics of Iron-Based Oxygen Carriers.

The role of the oxygen carrier is important in energy conversion processes with fluidized beds, particularly chemical looping technology. It is necessary to establish the relevant kinetics of oxygen carriers that can be applicable for various chemical looping processes. In this study, we analyzed the apparent kinetics of three iron-based oxygen carriers, namely, ilmenite, iron sand, and LD slag, during the conversion of CO, H2, and CH4 in a fluidized bed batch reactor. The effect of both the oxidation degree, presented as the mass conversion degree, and temperature was considered. The results show that the changing grain size (CGS) model is generally applicable in predicting the apparent kinetics of reactions between the investigated iron oxygen carriers and gaseous fuels even at lower oxidation degrees (3-5 wt % reduction). The activation energies of the investigated materials in the conversions of CO, H2, and CH4 obtained from the fittings of the CGS model are about 51-92, 55-251, and 72-211 kJ/mol, respectively. Both the mass conversion degree and temperature influence the reactivity of oxygen carriers in a directly proportional way, especially at temperatures higher than 925 °C. The results of this study are useful for reaction engineering purposes, such as designing a reactor, in chemical looping units, or in any other processes that use oxygen carriers as a bed material.

Understand relations between mechanical/thermal/chemical stresses and attrition of oxygen carrier in chemical looping process

During the chemical looping process, oxygen carriers are subjected to extremely challenging conditions, such as high temperatures, fluidization, and redox reactions, which significantly increase their susceptibility to attrition. Overall, particle attrition is caused by mechanical, thermal, and chemical stresses, but their exact contribution and mechanism are unclear. In this work, five distinct experimental conditions and cold jet attrition tests were established to discern the contributions of different stresses to attrition and their impact on performance. Particle size versus strength was obtained for up to 1320 particles, and hotspot plots were used to reveal the relationship between the two. It was found that thermal stress was the dominant factor only during the pre-attrition phase, contributing 45 % to attrition. And then swiftly superseded by mechanical stress. Chemical stress emerged as the primary cause of attrition during the middle and late stages of the experiments, contributing up to 90 % of attrition. OC‘s strength typically ranged between 6 and 8 N without chemical stress and, conversely, dropped to below 1 N. Furthermore, chemical stress was found to induce an increase in particle volume and oxygen transport capacity, primarily achieved by reducing apparent density. The volume of particles can be enlarged by a factor of 1.56, and the oxygen release rate was increased from 4 % to 5.6 % under chemical stress. And a correlation was observed between apparent density and both attrition rate and strength.

Co-feeding biomass and municipal solid waste for enhanced hydrogen and synthetic natural gas yields employing chemical looping process

Synthetic natural gas (SNG) is a promising alternative to conventional fossil natural gas. This study proposes a chemical looping hydrogen production (CLHP)-based route for SNG synthesis and elucidates the insights and necessities of appropriately co-feeding different types of feedstocks to maximize the yields of hydrogen and subsequent SNG. A study employing microalgae (MA) and refuse-derived fuel (RDF) as biomass and municipal solid waste representatives demonstrates that blending MA with RDF in a proportion of 40 %:60 % (0.4MA-0.6RDF) eradicates oxygen carrier splitting. This boosts fuel-to-hydrogen efficiency from 74.1 % to 77.8 %, as well as subsequent thermal and exergy efficiencies of SNG production from 59.07 % and 55.8 % to 61.3 % and 57.92 %, respectively, compared to the use of MA alone. Nonetheless, blending fuels does not yield substantial economic advantages, as evidenced by the levelized cost of SNG production using pure MA and the 0.4MA-0.6RDF blend remaining at approximately 0.63 USD/Nm3.

Halite-structured (MgCoNiMnFe)Ox high entropy oxide (HEO) for chemical looping dry reforming of methane

The configurational disorder of high entropy oxides (HEOs) promotes the reversible exsolution–redissolution of constituent metal species. This unique feature could be exploited to facilitate cyclic lattice oxygen storage and exchange. Herein, we report an in situ generated, halite-structured (MgCoNiMnFe)Ox HEO, which simultaneously functions as a redox catalyst and an oxygen carrier for dry reforming of methane in a chemical looping process (CL–DRM). Accordingly, the (MgCoNiMnFe)Ox/ZrO2 HEO catalyst exhibits outstanding DRM activity, syngas selectivity and cyclic stability compared to medium-entropy oxides and bimetallic oxides over 100 CL–DRM cycles at 800 °C. XRD analysis verified the entropy-mediated preservation of the alloy/HEO/ZrO2 catalytic structure over CL–DRM cycles. XAFS studies revealed the reversible and cyclic evolution–dissolution of Ni, Fe, Co over redox cycles. The exsolved NiFeCo nanoalloy exhibited high efficiency in activating CH4. This study has demonstrated the potential applications of HEO-based catalysts in efficient chemical looping processes.

Plasma Chemical Looping: Unlocking High-Efficiency CO2 Conversion to Clean CO at Mild Temperatures.

We propose a plasma chemical looping CO2 splitting (PCLCS) approach that enables highly efficient CO2 conversion into O2-free CO at mild temperatures. PCLCS achieves an impressive 84% CO2 conversion and a 1.3 mmol g-1 CO yield, with no O2 detected. Crucially, this strategy significantly lowers the temperature required for conventional chemical looping processes from 650 to 1000 °C to only 320 °C, demonstrating a robust synergy between plasma and the Ce0.7Zr0.3O2 oxygen carrier (OC). Systematic experiments and density functional theory (DFT) calculations unveil the pivotal role of plasma in activating and partially decomposing CO2, yielding a mixture of CO, O2/O, and electronically/vibrationally excited CO2*. Notably, these excited CO2* species then efficiently decompose over the oxygen vacancies of the OCs, with a substantially reduced activation barrier (0.86 eV) compared to ground-state CO2 (1.63 eV), contributing to the synergy. This work offers a promising and energy-efficient pathway for producing O2-free CO from inert CO2 through the tailored interplay of plasma and OCs.

Mercury Adsorption and Oxidation Performance of an Iron-Based Oxygen Carrier during Coal Chemical Looping Process.

During chemical looping combustion (CLC) and chemical looping gasification (CLG) of coal, the release, migration, and speciation of mercury in coal are significantly influenced by oxygen-carrier materials; however, the underlying mechanism remains inadequately addressed. In this work, the effect of a typical iron-based oxygen carrier on the release behavior of mercury from a bituminous coal and a lignite was investigated based on the Ontario-Hydro method. It is found that the effect of the iron-based oxygen carrier is attributed to three aspects: the enhanced release rate of mercury from coal, the adsorption of the released mercury, and the oxidization of gaseous Hg0 into Hg2+. With the increasing temperature, the adsorbance of mercury by the iron-based oxygen carrier decreases, while the oxidation of mercury enhances. Even at 900 °C, the adsorbance of mercury by the oxygen carrier remained at 0.1687 g/g, with a relative content of Hg2+ at 22.55%. Additionally, it was observed that iron-based oxygen carriers can physically absorb both Hg0 and Hg2+, while chemisorption refers to complex-compound formation between the iron-based oxygen carrier and mercury.

Techno-economic analysis of chemical looping processes with biomass resources for energy production and CO2 utilization. Comparison of CLC and CLOU technologies

Bioenergy coupled with carbon capture utilization and storage (BECCUS) is an attractive greenhouse gas mitigation technology that can produce negative CO2 emissions by combining bioenergy resources with the utilization or geological storage of the captured CO2.The main objective of this work was to evaluate the technical and economic feasibility of two BECCUS technologies based on chemical looping concept with two biomass waste as fuels, i.e., swine manure and pine sawdust, for the production of thermal energy and a pure CO2 stream that is subsequently used as raw material in agricultural greenhouses. Direct use of solid biomass resources was considered for the Chemical Looping with Oxygen Uncoupling option, whereas biogas production was the starting point for Chemical Looping Combustion.The profitability of the chemical looping scenarios was assessed through the Levelized Cost of CO2. This parameter was estimated at 218.31 €/t CO2 for the Chemical Looping Combustion scenario, a value much higher than those for the Chemical Looping with Oxygen Uncoupling scenarios (73.04–87.32 €/t CO2) due to the limited conversion degree of the carbon present in the fuel waste to biogas and the need for an additional experimental plant to the Chemical Looping Combustion unit, i.e., the biogas production plant. Comparing the Chemical Looping with Oxygen Uncoupling scenarios, the economic analysis revealed that the profitability of the biomass-fueled chemical looping facility was markedly sensitive to the selling price of the biomass resource. Furthermore, the values of the Levelized Cost of CO2 parameter for the Chemical Looping with Oxygen Uncoupling scenarios were lower than those estimated in other research studies that implemented BECCUS technologies and utilized the captured CO2 for identical purposes. In the particular case of swine manure, this result becomes even more noteworthy since it demonstrates that the energy use of this biomass resource through Chemical Looping with Oxygen Uncoupling technology is an economically profitable and environmentally sustainable solution to the difficult challenge of managing this livestock waste. Therefore, it can be concluded that Chemical Looping with Oxygen Uncoupling processes fed with biomass are a very attractive BECCUS technology for heat generation where, in addition, the pure CO2 stream obtained at the outlet of the fuel reactor can be considered a marketable, high value-added product.

Attrition and morphological analysis of CaCO3 corresponding to oxy-fuel circulating fluidized bed conditions

The specific surface area of CaCO3 has always been an essential parameter for various oxy-fuel combustion processes and chemical looping processes. However, the circulating of bed material through the furnace, cyclone and loop-seal in an oxy-fuel circulating fluidized bed (CFB) reactor may trigger the particle size changes as a result of rapid collisions among particles and friction with the inner refractory wall. Rather than considering only the effect of initial particle size, it is significantly important to emphasize on the change in limestone particle size due to in-reactor attrition. In addition, the changes are further enhanced with calcination reaction that occurred under high-temperature conditions. Herein an investigative account of limestone in a lab-scale CFB process was presented by using two types of fluidizing media (Air, CO2) to determine its attrition and morphological changes under simulated operating conditions for riser and loop-seal. A significant difference in attrition index was observed as calcination of limestone occurred at high temperature under air atmosphere which was not observed under CO2 condition. With similar cross-sectional area observed for both the tested (CO2 condition) and re-carbonated limestone, it was concluded that re-carbonation of calcined lime at high CO2 concentration in the loop-seal resulted in a comparable abrasion resistance that further improved desulfurization performance by reducing the amount of ultra-fine particles generated from limestone.