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The present study investigated the performance of iron ore mixed with carbide slag (CS) as oxygen carrier in a batch-fluidized bed reactor using Datong bituminous coal as fuel. The effects of mixing mass ratio and reaction temperature on the CLC process of coal were investigated. The results showed that iron ore mixed with carbide slag accelerated the CLC process of coal compared with iron ore alone. Reaction temperature had a crucial effect on carbon conversion of coal, but higher than 900°C resulted in a decreased reactivity of CS-mixed oxygen carrier. Multiple redox cycle tests were also conducted to study the stability of CS-mixed oxygen carrier. It was found that though a continuing decreasing reactivity was observed for CS-mixed oxygen carrier, it still has higher CO2 yield and lower CO yield than those of undecorated one. SEM analysis revealed that sintering occurred on the surface of CS-mixed oxygen carrier, resulting in the deterioration of reactivity. The reason for the promoted performance of CS-mixed iron ore seems to be the catalytic effect of carbide slag on the water-gas shift reaction, converting CO to H2, for H2 is more reactive toward iron ore. [ABSTRACT FROM AUTHOR]

Upscaling of the laboratory oxygen carriers while keeping comparable performance as laboratory powders remains a challenge in the field of chemical looping combustion (CLC). In this work, two perovskite compositions of CaMn0.375Ti0.5Fe0.125O3 (termed CMTF8341) and CaMn0.5Ti0.375Fe0.125O3 (CMTF8431) have been fabricated by means of spray granulation. The fabricated granules were evaluated by redox cycles under CLC conditions and showed comparable performance with laboratory-prepared powders, i.e. high oxygen transfer capacity and fast redox kinetics. Under chemical looping oxygen uncoupling (CLOU) conditions, it has been found that steam leads to a slower kinetics and lower oxygen transfer capacity for these two compositions. When it comes to sulphur effect on the oxygen carriers, redox cycles with deep reduction showed no influence with H2S since the CaSO4 formed in air decompose but it affected the materials under mild CLOU due to calcium sulphate formed under such condition. Nonetheless, redox performance can be recovered by deep reduction with an enhanced oxygen capacity. These two oxygen carriers showed no degradation as compared to other tested minerals in the field of CLC. Microstructure analyses from SEM showed high degree of structure integrity after redox cycles at temperatures up to 1050 °C for the CMTF8341. Good mechanical strength was evidenced from cold attrition test, and the lifetime of the two granules was also predicted based on a standard reference. [ABSTRACT FROM AUTHOR]

Iron or its oxides (FexOy) commonly exist in the ash of fossil fuel and biomass, and are used as oxygen carriers in chemical looping process, and Fe3O4 is a main occurrence. The NO reduction mechanisms by CO over Fe3O4 (111) surface was investigated via density functional theory (DFT) calculations. An optimized unit cell of Fe3O4 was constructed. The interaction between molecules and cell surface was described by the calculated adsorption properties and electronic structures. Results showed that the most stable adsorption of NO/CO belongs to chemisorption and NO has higher adsorption energy than CO. NO can be absorbed onto Fe3O4 surface to form (NO)2 dimer structure, which easily decomposes via a small energy barrier. (NO)2 dimer mechanism is a possible pathway for the reduction of NO by CO over Fe3O4, following three steps: 2NO → (NO)2*, (NO)2* → N2O + O*, O* + CO* → CO2. After the decomposition, the intermediate species N2O molecule and the remaining O atom adsorbed strongly on the Fe3O4 surface can be removed by CO. CO also promotes the gaseous decomposition of N2O. DFT results also showed O2 will prevent NO reduction reaction. The calculated reaction rate constants further verify the existence of (NO)2 dimer mechanism and the rate-limiting step is the removal of the surface O atom. [ABSTRACT FROM AUTHOR]

Indirect combustion with the chemical looping combustion (CLC) of solid oxygen carriers is one of the most promising technologies for capturing carbon dioxide (CO2) in energy production from fossil fuels since the separation of the generated CO2 is inherent to the process itself. Therefore, the cost associated with capturing this gas will be significantly reduced. This technology transfers oxygen from air to fuel through a metal oxide that acts as an oxygen carrier, avoiding direct contact between air and fuel. This oxygen carrier circulates in a fluidized bed reactor called a reduction reactor and an oxidation reactor. (1) This research work has focused on evaluating the behavior of oxygen carriers based on the original and improved manganese mineral (copper-impregnated mineral) named for this study, OXMN009 and OXMN009P, respectively. (2) Equilibrium experiments were carried out on a thermogravimetric balance (TGA) to evaluate the kinetic behavior of these oxygen transporters OXMN009 and OXMN009P, using the gases methane (CH4), carbon monoxide (CO), and hydrogen (H2). (3) The enhanced solid oxygen carrier OXMN009P exhibited good performance for the CLC process with gaseous fuels in terms of reactivity and combustion efficiency, having high reactivity and oxygen transfer properties due to copper impregnation. (4) The results show that OXMN009P has comparable reactivity to other manganese-based materials reported in the literature. It may be an effective option for carbon dioxide capture, as it uses metal oxides as the oxygen transporters (TO). (5) These oxygen transporters, OXMN009 and OXMN009P, are used in a cyclic process that prevents the formation of nitrogen oxides by keeping the air and fuel separate. (6) Thermogravimetric balance (TGA) experiments were conducted to evaluate the kinetic behavior of these copper-modified oxygen transporters. (7) It was found that OXMN009P improved the reactivity and oxygen transfer properties due to copper impregnation. The kinetic parameters obtained in the TGA indicate that the reaction is non-thermal and requires less energy to initiate. (8) The results show that OXMN009P has reactivity comparable to other manganese-based materials reported in the literature and can be an effective option for carbon dioxide capture. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) has been validated as one of the most promising technologies for fossil fuel combustion, which can produce high-purity CO2 streams ready for capture and sequestration in power production. The selection of an appropriate oxygen carrier is one of the most important issues for the CLC process, and the reduction kinetics investigation of the oxygen carrier with fuel gas can provide the basis for CLC reactor design and simulation optimization. In this study, copper ore was chosen as an oxygen carrier, and the oxygen release property of copper ore under a nitrogen environment at various temperatures (1073–1193 K) was first investigated in a thermogravimetric analyzer (TGA). Subsequently, the reduction kinetics of copper ore with CO and H2 were evaluated by the TGA at temperatures ranging from 773 K to 1073 K, using a continuous stream of 5, 10, 15, 20, 25, and 30 vol. % of CO or H2 balanced by CO2 or N2. It was found that the reaction rates of these reactions accelerated with the increase in temperature and fuel gas concentration in inlet gas. Both the oxygen release process of copper ore and the reduction process of copper ore with reducing gases can be described by the unreacted shrinking core model (USCM). The reaction mechanism function for the oxygen-releasing and reduction process of copper ore oxygen carrier was varied. The activation energy of the oxygen-releasing process, reduction process with CO, and reduction process with H2 were calculated as 99.35, 5.08, and 4.28 kJ/mol, respectively. The pre-exponential factor ranged from 1.96 × 10−1 to 1.84 × 103. The reaction order depended on the fuel gas, which was 1 and 0.86, respectively, for reaction with CO and H2. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) offers a novel approach to simultaneous power generation and carbon capture. However, the commercial viability of CLC depends on durable and cost‐effective oxygen carriers (OCs). This study assesses the impact of water vapor (WV) on the attrition of red mud OC, crucial for industrial CLC deployment. Findings indicate a significant reduction in the average attrition rate, from 0.06%/h to 0.03%/h, attributed to the limitation of Fe2O3 reduction, resulting in reduced volumetric and temperature changes in the presence of WV. A developed volume‐based model reveals attrition contributions in the order of chemical > mechanical >> thermal stresses, influencing OC particle surface morphology. Remarkably, the formation of the iron‐oxide layer remains unaffected by WV, reducing agents (CO or H2), or superficial velocities, suggesting scalable iron recovery from attrition with enhanced flexibility in future applications. [ABSTRACT FROM AUTHOR]

Efficient activation and the conversion of methane to value‐added products have long attracted interest. Chemical looping reforming has become a competitive technology to transform methane into syngas that can act as raw material for various chemicals. In this paper, the methane chemical looping reforming reactivity of the Ce−Co composite oxygen carriers fabricated with different preparation methods, including solution combustion, ball‐milling, hydrothermal, and co‐precipitation method, are investigated on a fixed‐bed. Various bulk/surface characterizations (TEM, XRD, BET, XPS, Raman, etc.) were applied to reveal the effect of preparation methods on the properties of these oxygen carriers. The results indicate that the oxygen carrier prepared by the solution combustion method exhibits excellent methane conversion, high syngas yield, and desirable H2/CO ratio, as well as stable regenerability because of its relatively small crystal size, large specific surface area, high oxygen vacancy concentration and Ce3+/Ce4+ ratio. This work may be helpful in the preparation of highly active and stable oxygen carriers for chemical looping reforming reaction of methane. [ABSTRACT FROM AUTHOR]

The chemical looping reforming and combustion of methane have attracted increasing interest as processes for clean energy and syngas production, with potential to reduce carbon dioxide emissions. Previous literature on the development of oxygen carriers evidenced the effects that oxygen availability exerts on the selectivity of the oxidation reaction. In the present paper, we evaluate the performance of chromite sand (Chro), cerium dioxide (CeO2), and mixed cerium–copper oxide (Ce–Cu) as oxygen carriers for either reforming or combustion according to their oxygen availability. The oxides are tested in 2 to 5 min reduction intervals in a CH4/N2 mixture (5, 10 and 20% vol.) followed by regeneration in O2/N2 (3, 5, or 21% vol.), with redox cycles conducted either at 850 °C or 950 °C. The obtained rank of selectivity towards complete CH4 combustion is Ce–Cu > CeO2 > Chro. Another relevant finding is the role of the degree of carrier conversion in promoting partial or total oxidation. In particular, the selectivity towards CO2 markedly decreases at increasing carrier conversion, disclosing new strategies for process design and optimization by controlling the carrier conversion degree. [ABSTRACT FROM AUTHOR]

The pure H2 production procedure for polymer fuel cell applications by the chemical loop reforming of methanol in the presence of 0.3CoFe2O4-0.4ZrO2 as an oxygen carrier in a micro-channel reactor was studied and the results of this study showed that the production of pure H2 is possible only if the coke deposition is controlled. By optimizing the reduction time to 7 minutes, the coke deposition controlled and pure H2 flow was produced with an average yield of 2.6%, which was an interesting result and so far, this degree of purity of H2 has not been reported by the chemical loop reforming of methanol. To increase the yield of pure H2 in this study, a two-layer catalyst concept is proposed in the form of an additional layer coating with high resistance to coke and suitable reactivity with methanol from NiO/MgAl2O4 to 10% on 0.3CoFe2O4-0.4ZrO2 layer. Optimizing the reduction time using the concept of double-layer oxygen carrier showed that the use of 20% nickel concentration with a reduction time of 11 minutes increased the yield of H2 with 100% purity, which increased by 42% in the double-layer arrangement compared to the singlelayer state, and it is a promising result for the concept of double-layer oxygen carrier in this process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Mixed Cu/Mg ferrites were characterized for the first time as oxygen carriers. • Positive impact of Mg doping on mechanical durability was proven. • Highest reaction rate toward fuel was achieved for Cu 0.75 Mg 0.25 Fe 2 O 4 (1.19 wt.%/min). • Mg-rich OCs exhibited increased reactivity toward fuel in 610–730 °C. Waste wood biomass is considered a renewable energy source. Combining biomass combustion with emerging clean combustion technologies such as chemical looping combustion (CLC) can yield effective and affordable carbon capture and, consequently, lead to negative net emissions of greenhouse gases. Oxygen carrier (OC) is a crucial material in CLC technology that must exhibit certain properties, such as high durability, good chemical stability during numerous red-ox cycles and, important for the combustion of solid fuels, the capability of spontaneously releasing oxygen in a process referred to as chemical looping with oxygen uncoupling (CLOU). In this work, a series of nine Cu x Mg 1-x Fe 2 O 4 spinel-based materials were synthetized and evaluated for the first time as potential OCs for a waste biomass combustion. Their properties, such as oxygen transport capacity and reactivity with biomass (wood chips) as a fuel, were evaluated in a function of temperature (900–1000 °C). Tested oxygen carriers were characterized with an excellent oxygen transport capacity in CLOU process (up to 2.78 wt%) and good reaction rates with the fuel (up to 1.19 wt. %/min), and regeneration rates (up to 3.8 wt. %/min). High conversion of the waste biomass was also achieved (98.9 %). Moreover, new findings revealed a strong positive effect of magnesium addition on mechanical strength (crushing strength > 4 N for samples with Mg content above 0.5). [ABSTRACT FROM AUTHOR]

The redox kinetics of the oxygen carriers are crucial in Chemical‐Looping Combustion (CLC) systems. The random pore model (RPM) was widely used to investigate the macroscale redox kinetics of oxygen carriers in previous studies, in which the reaction rate constants were obtained just by fitting the experimental data. This study presents a first principle based rate equation (1pRE) applied to the RPM to calculate the reaction rate constants directly using density functional theory (DFT). The 1pRE is integrated with the RPM that accounts for the effect of pore size distribution derived from the surface area evolution of reaction interface and product layer diffusion, thus bridging the gap between the microscale elementary surface reactions and macroscale overall conversion. The developed 1pRE predicts the reduction kinetics of Fe2O3 oxygen carriers accurately, thereby facilitating the optimization of design processes for oxygen carrier materials and the scale up of CLC reactors. [ABSTRACT FROM AUTHOR]

This article describes a general study of manganesebased 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. [ABSTRACT FROM AUTHOR]

Developing the bifunctional oxygen carrier with excellent oxygen mobility and catalytic activity is the key to chemical looping combustion coupled CO 2 hydrogenation to light olefins. In this study, a series of K/La y Co x Fe 1-x O 3 (x = 0, 0.2, 0.4, 0.6, y = 0.2, 0.4, 0.8) with oxygen vacancy-active metal dual active centers were constructed by the Co doping-La defect synergistic strategy to evaluate the oxygen release and catalytic performance. The results indicated that K/La 0.4 Co 0.4 Fe 0.6 O 3 had high oxygen mobility, and its reduced state can be directly used for CO 2 hydrogenation to light olefins (C 2 =-C 4 =). The selectivity of C 2 =-C 4 = was close to 30%, and the conversion rate of CO 2 was 36%. Combined with various characterizations, the synergy of Co doping and La defects increased the oxygen vacancy and promoted the exsolved CoFe alloy under the reduction induction of chemical looping combustion. In situ DRIFTS reveals the dynamic equilibrium of the Formate-Methoxy mechanism and RWGS-FTS pathway. Oxygen vacancies are found to enhance the conversion of CO 2 via the formate pathway, while metal active phases alter the product distribution by changing the evolution of intermediates. The Co 7 Fe 3 and oxygen vacancy on K/La 0.4 Co 0.4 Fe 0.6 O 3 promotes the formation of CH x ∗ and C–C coupling through various intermediates, improving the selectivity of light olefins. • K/La 0.4 Co 0.4 Fe 0.6 O 3 exhibits "oxygen-catalysis" bifunctional properties. • Co-doping and La-defects increase oxygen vacancies and promote metal exsolution. • The oxygen vacancies and the exsolved metal provide dual active centers. • The reaction underwent a dual path through multiple intermediates. [ABSTRACT FROM AUTHOR]

Copper slag contains a large variety of resources that can be used, and is a kind of 'artificial ore'. This study proposed that the abundant metal oxides in copper slag can be used as oxygen carriers with high added value that can be applied to chemical looping combustion technology. The structure of oxides in copper slag can be transformed by copper concentrate to improve its oxygen-carrying and oxygen-releasing properties. Based on this, Cu–Fe composite oxygen carriers were prepared from copper slag in this paper. It is found that heating rate has a certain effect on the phase formation of oxygen carriers during preparation. Under experimental conditions, a heating rate of 2 °C min−1 is more suitable for preparing oxygen carriers. In addition, it is found that the composite oxygen carrier generated by the mixed calcination of copper slag and copper concentrate has a synergistic effect with CuFe2O4 phase. Oxygen decoupling and oxygen transport capacity and reaction activity were all improved. [ABSTRACT FROM AUTHOR]

A clear understanding of the structural transformation of copper-oxide-based oxygen carriers accompanying their reduction by fuels helps to design more efficient oxygen carriers for chemical looping combustion. Herein, density functional theory calculations have been performed on the bulk CuO, CuO(111) surface, and (CuO)32 cluster models with the same number of CuO molecular units to investigate structural transformation accompanying the reduction. The results showed that the averaged reaction energies of desorbing an oxygen molecule from the bulk and surface models are roughly the same [246.2 kJ/(mol O2) and 245.9 kJ/(mol O2), respectively]. The slab model does not significantly lower the overall reaction energy compared to the bulk model. In contrast, the averaged reaction energy using the cluster model is significantly lower [127.5 kJ/(mol O2)] than that of bulk and slab models. The key structural difference is the obvious Cu–Cu bond formation in the cluster model, which would result in nucleation of a metallic Cu phase. The results also showed that different states can be reached by desorbing different number oxygen atoms in a single step, corresponding to different reaction rates, when the system reaches the same level of reduction. These results demonstrate the complexity of reactions involving solid state materials and are consistent with the structural diversity observed experimentally. This study illustrates the importance of particle sizes and reaction conditions in the formation of suboxides during CuO reduction. [ABSTRACT FROM AUTHOR]

Double-perovskite Ca2AlMnO5+δ exhibits promising oxygen uptake and release capacity at intermediate temperatures (400–700 °C), which makes it an interesting candidate for in situ oxygen production in an integrated gasification combined cycle (IGCC) process. Experiments were conducted at 10 bars by alternating gas feeds of air and various sweep gases to a packed bed filled with 300 g of granular oxygen carrier materials. These realistic operating conditions demonstrated that 15–20% oxygen can be introduced to the sweep gas, which is sufficient for autothermal gasification of solid fuels in IGCC. Argon performed slightly better than CO2 as a sweep gas, presumably because of some CO2 absorption or the higher O2 partial pressure of CO2 that inhibited O2 release. Further O2 concentration increases can be expected from increasing the temperature under reduction by feeding a fuel gas to combust with the released O2, but experiments with H2 did not produce the desired effect because the combustion reaction was too slow at the optimal reactor temperature (~ 600 °C). In general, the reduction stage was more prone to kinetic limitations, as illustrated by a significant decrease in O2 concentration when the sweep flowrate was increased. A longer oxidation stage to fully charge the oxygen carrier also increased O2 concentrations in the sweep, but this requires a process integration such as IGCC where the large quantity of warm depleted air can be effectively utilized. Furthermore, the enthalpy of oxidation of Ca2AlMnO5+δ was obtained from density functional theory modeling, equilibrium conditions in thermogravimetric analysis, packed bed experiments and directly from differential scanning calorimetry. The enthalpy of oxidation obtained by these techniques range from − 166 to − 196 kJ mol−1 O2. [ABSTRACT FROM AUTHOR]

Chemical looping applications offer a variety of options to decarbonise different industrial sectors, such as iron and steel and hydrogen production. Chemical looping with water splitting (CLWS) is a chemical looping technology, which produces H2 while simultaneously capturing CO2. The selection of oxygen carriers (OCs) available to be used in CLWS is finite, due to the thermodynamic limitations of the oxidation with steam for different materials at the relevant process temperatures. Iron‐based materials are one of the most widely studied options for chemical looping combustion (CLC), touted for their relative abundance and low cost; likewise, for CLWS, iron is the most promising option. However, when the reduction of iron oxide (Fe2O3) is extended to wüstite (FeO) and iron (Fe), agglomeration and sintering problems are the main challenge for fluidisation. This work presents iron and tungsten mixed oxides as the OCs for a family of chemical looping applications. The OCs were produced via co‐precipitation; performance assessment was conducted in a thermogravimetric analyser and a lab‐scale fluidised bed reactor over continuous redox cycles. The use of tungsten combined with iron results in a solid solution of tungsten within the Fe2O3 matrix that produced a more mechanically stable material during operation, which performed well during multiple redox cycles with no apparent decrease in the oxygen transport capacity and showed no apparent agglomeration. Furthermore, materials containing tungsten showed a resistance to carbon deposition, whereas the reference Fe2O3 showed peaks of CO and CO2 during the oxidation period, thus indicating carbon deposition. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper five bimetallic Fe2O3‐MnO2 oxygen carriers supported on TiO2 were evaluated for direct hard coal combustion via chemical looping path. The oxygen carriers were obtained via mechanical mixing and high‐temperature calcination. The samples contained varying amounts of Fe2O3 (20–50 wt.%) and MnO2 (65–30 wt.%) but an identical amount of inert material (15 wt.%). Both the impact of the oxygen carrier's composition and the process temperature on their reactivity with the selected hard coal were evaluated. The amount of manganese in the oxygen carriers correlated positively with their reactivity toward the fuel. It was concluded that after eight reaction cycles the oxygen carriers remained resilient for side reactions with the ash residue. Thus, the physicochemical stability of the presented oxygen carriers was proved. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Chemical looping with oxygen uncoupling, a variant of chemical looping combustion, requires chemically and physically stable oxygen carriers over long‐term redox cycling. Copper‐based oxygen carriers are characterised by high oxygen release rates but experience sintering at high temperatures. The use of layered double hydroxides (LDHs), prepared via co‐precipitation, as oxygen carrier precursors has been shown to effectively limit deactivation of copper‐based mixed metal oxides (MMOs) over extended redox cycling. The LDH‐derived MMOs have highly dispersed metal oxide within a stable support; the high dispersion of metals is due to the LDH precursor structure. In this work, a fluidised bed reactor (FBR) was used to study the intrinsic kinetics of oxygen release from CuO/MgAl2O4 oxygen carriers synthesised via the LDH‐MMO design strategy. The long‐term performance of MMOs with higher loadings of CuO, calcined from LDHs with higher Cu contents, was also investigated using an FBR. The intrinsic kinetics were determined using a kinetic model incorporating an effectiveness factor. By minimising the effects of intra‐ and inter‐particle mass transfer, the activation energy and the pre‐exponential factor of the lower loading MMOs were determined to be 51 ± 3 kJ mol−1 and 0.0567 s−1, respectively. All MMOs showed excellent stability over 100 redox cycles in a thermogravimetric analyser. However, the pH during co‐precipitation of the LDHs affected the stability of the MMOs in an FBR. The MMOs calcined from LDHs synthesised at pH 9.5 disintegrated during operation, whilst those produced from LDHs synthesised at pH 11 maintained high conversion and physical integrity over 100 redox cycles. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Biomass conversion with carbon capture and storage (Bio‐Energy CCS; BECCS) is one of the options considered for mitigating climate change. In this paper, the carbon capture technology chemical‐looping combustion (CLC) is examined in which the CO2 is produced in a stream separate from the combustion air. A central research topic for CLC is oxygen carriers; solid metal oxides that provide oxygen for the conversion process. Biomass and waste‐derived fuels contain reactive ash compounds, such as potassium, and interactions between the oxygen carrier and the ash species are critical for the lifetime and performance of the oxygen carrier. This work develops and demonstrates an improved method for studying the interactions between ash species and oxygen carriers. The method uses a lab‐scale reactor operating under fluidized conditions, simulating CLC batch‐wise by switching between feed gas. The novelty of the setup is the integrated system for feeding solid particles of ash model compounds, enabling the simulation of ash species accumulating in the bed. Ilmenite is a benchmark oxygen carrier for solid fuel conversion and was used in this study to evaluate the method using K2CO3 as a model ash compound. Experiments were done at 850 and 950°C. Methane conversion in CLC cycles and fluidization was evaluated with gas analysis and pressure drop measurements. Scanning electron microscopy and energy dispersive X‐ray spectroscopy (SEM‐EDS) and X‐ray diffraction (XRD) analysis of bed particles were done after the experiments to establish changes in the morphology and composition of the ilmenite. The method for feeding the ash model compound was concluded to be satisfactory. At 950°C, K accumulated in the particles forming K‐titanates and agglomeration was enhanced with K2CO3 addition. The agglomeration mechanism was solid‐state sintering between the Fe‐oxides forming on the particle surfaces. The bed defluidized at 950°C, but no such effect was seen at 850°C. The method is suitable for studying the Fe‐Ti‐K system with ilmenite and potassium without the influence of other ash species. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Low-Carbon Chemistry & Chemical Engineering is the property of Low-Carbon Chemistry & Chemical Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The structural properties of selected (Ba1−xSrx)PbO3 ceramics were examined at 14–1148 K using X-ray powder diffraction (XRD). These materials are attractive due to their variety of applications, such as, for example, high-temperature thermoelectric energy conversion. Attention was paid to this paper as a continuation of the previous examinations of higher Sr2+ concentrations. The type of perovskite distortion and temperatures of the structural phase transitions (SPTs) were determined from the splitting of certain pseudocubic lines. At this point, for example (Ba0.3Sr0.7)PbO3 showed three temperature-induced SPTs. When the amount of Sr increased in the samples, no phase transition was observed, which is contrary to the data previously demonstrated in the literature. The quality of the ceramics was examined by scanning electron microscopy-energy dispersion X-ray spectroscopy (SEM-EDS), demonstrating their homogeneity and uniform elements dispersion. As a result of profound crystal investigations, confirmed by thermogravimetric analysis and quadrupole mass spectroscopy (TGA-QMS), a phase diagram was prepared for the (Ba1−xSrx)PbO3 system based on our former and recent study. Also, the investigation of a new application for the (Ba1−xSrx)PbO3 family is presented in this paper for the first time. The TGA analysis was conducted on Illinois#6 hard coal to evaluate the capability of perovskites to be used in the chemical looping combustion (CLC) process in a range of temperatures 1073–1173 K. Due to its thermal stability and reactivity, Ba0.9Sr0.1PbO3 is the material with the greatest potential to be applied as an oxygen carrier. The combination of strontium and barium offers encouraging results compared to the pure barium and strontium lead oxide perovskites. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) reduces the CO 2 capturing cost, elevates combustion efficiency, and prevents NOx formation. This study applied Fe 2 O 3 /SiO 2 and Fe 2 O 3 /Al 2 O 3 oxygen carriers to react with H 2 , CO and CH 4 under different operating setup and examined the interference of H 2 S. Examination was also conducted on the reaction kinetics, cycle test, and characterization of oxygen carriers. Reduction of oxygen carrier from Fe 2 O 3 to between FeO and Fe occurred during the reaction. The higher syngas concentration led to higher diffusion capacity and promoted utilization of oxygen carriers. Carbon deposition was enhanced by excess concentration of CO and CH 4. Involvement of H 2 S led to declining of performance due to the presence of carbonyl sulfide (COS) and FeS. With Fe 2 O 3 /SiO 2 , application of multiple redox cycles reduced the utilization value to 43 % due to formation of Fe 2 SiO 4. Analysis of exhausted gas after reaction was applied in study of proposed reaction mechanism. Study of reaction kinetics using Type I deactivation test indicated a well fitted result with experimental data with R2 in the range of 0.9605–0.9976. Thus, compared to other studies with discussion only on CO, H 2 , or CH 4 in CLC, this study offered a comprehensive research on interruption of H 2 S, characterization, and reaction kinetics. [Display omitted] • 40 wt% Fe 2 O 3 /SiO 2 performed better in single syngas than 40 wt% Fe 2 O 3 /Al 2 O 3. • Utilization value of 73.8 % was achieved by 40 wt% Fe 2 O 3 /Al 2 O 3 in 10 % CO+ 15 % H 2. • Great regeneration capacity in redox cycle was presented by 40 wt% Fe 2 O 3 /Al 2 O 3. • Poor performance due to COS formation was ignited by H 2 S in the system. • CH 4 led to severe masking results from carbon deposition and declined the performance. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are porous crystalline materials with exceptional properties. The tremendous synthetic tunability of MOFs has emerged to be beneficial for many applications. This review study discusses the roles of MOFs in hydrogen fuel cell technology, including the synthesis of oxygen reduction catalysts, hydrogen storage materials, and ion carriers for polymer electrolyte membranes (PEMs). Various chemical modification approaches have been identified, namely: (1) confinement of guest species into the pores of MOFs, (2) modification of the organic ligands with functional groups, and (3) carbonization of MOFs. The tunable properties of MOFs have offered an improvement toward their desired application. The primary properties are surface area, which correlates with the availability of active sites that lead to an improvement in electrochemical performance. Finally, the outline concerning commercializing fuel cell technologies with MOFs is tabulated along with a future perspective in addressing some of the current limitations in the studies. [ABSTRACT FROM AUTHOR]

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A series of transition-metal doped Cu–Fe spinel oxygen carriers (M-CuFe 2 O 4 , M = Mn, Cr, Co and Ni) were synthesized and examined for their sulfur resistance by 500 ppm H 2 S in N 2 atmosphere. The results showed that H 2 S vulcanized the M-CuFe 2 O 4 surfaces and led to the generation of metal sulfide. The gaseous sulfur product was mainly SO 2. The interaction between sulfur and CuFe 2 O 4 was weakened when doping transition-metal into Fe site of CuFe 2 O 4 , especially Cr as dopant. The increase of temperature had an obvious impact on the reaction between H 2 S and the adsorbed oxygen species. Cr dopant reduced the enrichment of sulfur element on the surface, and it showed the weakest affinity towards sulfur because of the lowest orbital hybridization between S and Cr atom below the Fermi level. Moreover, the energies barriers of H 2 S dissociation over Cr–CuFe 2 O 4 surface were obviously higher than those over CuFe 2 O 4. • The effect of dopants on sulfur resistance of Cu–Fe spinel was explored. • The dopants hinder the conversion of gaseous sulfur into solid sulfur. • Temperature obviously affects the reaction between H 2 S and adsorbed oxygen species. • Cr is the most effective dopant in improving sulfur resistance of Cu–Fe spinel. [ABSTRACT FROM AUTHOR]

Bioenergy with Carbon Capture and Storage (BECCS) technologies are fundamental to reach negative CO2 emissions by removing it from the atmosphere and storing it underground. A promising solution to implement BECCS is pressurized Chemical Looping Combustion (CLC), which involves coupling a pressurized CLC reactor system to a turboexpander. The typical configuration chosen is to have an air reactor and a fuel reactor based on coupled circulating fluidized beds. The fluidization regime in both reactors is preferred to be fast fluidization to enhance gas particle contact and solids circulation among reactors. To design the two reactors, Aspen Plus software was used, given that the new version has a module for fluidized bed modeling. At first, the oxygen carrier was designed ex novo, but given that it is a composite compound mainly made by nickel oxide freeze-granulated on alumina (Ni40Al-FG), the molecular structure has been inserted in Aspen Plus. Then, based on the power of the gas turbine, the power output per kg of evolving fluid (in this case, depleted air) is calculated using Aspen Plus. Once the nitrogen content in the depleted air is known, the total air at the inlet of the air reactor is calculated. The fuel reactor is modeled by inserting the reduction reactions for nickel-based oxygen carriers. The paper presents a useful methodology for developing pressurized Chemical Looping Combustors to be coupled to gas turbines for power generation. The provided data will be cross-validated with 0D-models and experimental results. [ABSTRACT FROM AUTHOR]

Reduction behavior of commercial natural hematite with respect to degrees of particle packing was studied using a thermogravimetric analysis (TGA) approach. Understanding of temporal mass variations of oxygen carriers such as hematite during reduction is critical to enabling successful industrial applications including ironmaking and chemical looping combustion processes. Gravimetric evolutions of carrier particles as a whole are influenced by how individual particles are physically configured in relation to a reaction gas, especially when the particles are stacked on top of each other, leaving bottom particles less reacted or in some cases unreacted in a static environment. This work reports effects of particle stacking on reduction behaviors of commercial natural hematite isothermally at 800 °C in 10 CO–90% N2 gas environment. Current results indicated, mass evolution kinetics were slowed with more initial mass as stacking layers tended to decrease the available surface area to mass ratio with depth and impeded gas diffusion to particles at deeper locations. Post-SEM analysis revealed an interesting phenomenon where the commercial natural hematite particles subjected to the present experimental approach resulted in a reversed reduction sequence; more reduced phase (metallic iron) was produced inside surrounded by less reduced phase (wüstite). The present work suggested the design of reactors may benefit by considering how the particles are arranged in the reactors. [ABSTRACT FROM AUTHOR]

Selenium is one of the most volatile toxic elements in coal, and its emissions must be strictly controlled. Chemical looping combustion (CLC) is a clean and efficient technology for coal. Herein, the iron‐based oxygen carrier (OC) was used as an adsorbent to study the migration and emissions of selenium during the CLC of coal. Due to the oxidation and adsorption of selenium by iron‐based OC, most of the selenium was retained in OC or distributed in the CO2 stream. The proportion of gaseous selenium released into the atmosphere was less than 10%—significantly lower than that from the traditional combustion process of coal, which had a value of 91.79%. The presence of OC increased the distribution phase of selenium, promoted the conversion of gaseous selenium to solid selenium, and reduced selenium emissions in flue gas. During CLC of coal, the fuel reactor (FR) temperature and the number of OC re‐oxidation cycles played an important role in the emissions and retention of selenium. The increasing FR temperature increased the gaseous selenium in the CO2 stream, reduced the particulate selenium absorbed by OC, and reduced the selenium emissions in the atmosphere. After 10 continuous CLC cycles, the selenium concentration in OC increased from 0.889 to 8.20 mg kg−1. The continuous cycling of CLC could realize the enrichment of selenium from coal to OC. Furthermore, the migration and transformation mechanism of selenium during CLC was deduced by experiments and thermodynamic simulation. This research provides a suitable reference for reducing selenium emissions and developing CLC technology. [ABSTRACT FROM AUTHOR]

Chemical looping is a novel fuel conversion and material separation technology. It can be applied to obtain sulphur through selective oxidation of H2S. Further, chemical looping combustion (CLC) of sulphur can generate SO2 with a high concentration without NOx formation. The high SO2 concentration is adjustable and facilitates large‐scale H2SO4 production. In this study, we examined the thermodynamics of the CLC of sulphur for H2SO4 production, which has not been reported previously. We analyzed the effects of reactor temperature and sulphur to Fe2O3 oxygen carrier (OC) ratios on sulphur allotrope transformations and on the distributions of reaction products. Moreover, the reactors were operated auto‐thermally. Based on this design, we examined the effects of fuel reactor (FR) and air reactor temperatures on the minimum recirculation of the OC, as well as the gas and solid products and heat released from the air reactor. Our results showed that the CLC of sulphur with Fe2O3 OC could occur through an auto‐thermal process. The FR in a sulphur CLC system should be operated over a temperature range of 800–950°C, with an Fe2O3 OC recirculation between 45 and 143 kg/kgS(s). Furthermore, when the FR was operated in the auto‐thermal mode, we achieved 100% SO2 conversion. The findings of this study may be applied to reactor design for large‐scale H2SO4 production through CLC of sulphur. [ABSTRACT FROM AUTHOR]

Over 40% of global energy-related CO2 emissions are due to the combustion of fossil fuels for electric energy generation. Albeit CO2 capture and storage have been identified as promissory actions to mitigate its emissions, the problem separating N2 and CO2 remains. A very effective solution for the former problem is to obtain the combustion CO2 as a pure molecule, which is possible using the Chemical Looping Combustion (CLC) technology, which uses a solid oxygen carrier to transport the oxygen from an oxidating media (regeneration reactor) to a reducing media (combustion reactor). One of the key issues to apply CLC is to find or develop some material, suitable from the kinetic and thermodynamic points of view, for the reduction-oxidation cycles taking place inside combustion and regenerator reactors. The evaluation of "oxygen carrier" candidates for CLC is based on reactivity (rates and conversions), resistance to carbon accumulation, and "regenerability", which means the ability of the material for cyclic reduction and oxidation. Another challenging issue to use CLC processes is the loss of oxygen carrier; this problem involves the use of supported metals on materials, such as zirconia, Al2O3, etc. Preparation of this kind of supported carriers requires time, money, and equipment. Meanwhile, the natural mineral ore named ilmenite, which consists of a mixture of iron and titanium oxides, and do not need to be supported, has been seen as promising to increase CLC efficiency as oxygen carrier. In this work, the performance of ilmenite is compared with some other oxygen carriers used in CLC. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) is a novel technology for the combustion of fuels with inherent CO2 capture. CLC is based on the transference of oxygen from air to fuel by means of an oxygen carrier which is based on a metal oxide. CuO/Al2O3 (14 wt.% CuO) and Fe2O3/Al2O3 (20 wt.% Fe2O3) particles have been used in several CLC units with different results when methane combustion was evaluated. In order to shed light on the main processes affecting methane conversion in CLC, a mathematical model for a dual circulating fluidized bed (DCFB) system was developed to simulate the behavior of CuO/Al2O3 and Fe2O3/Al2O3 in a CLC unit. The model consists of the coupling of individual fuel and air reactor models to simulate steady state of the CLC unit. Individual models consider both the fluid dynamics of the fluidized beds at the high velocity regime and the corresponding kinetics of oxygen carrier reactions, that is, reduction in the fuel reactor and oxidation in the air reactor. The model was validated using results obtained in a 120 kWth CLC unit with CuO/Al2O3 and Fe2O3/Al2O3 particles. The validated model was used to simulate the performance of these materials in the 10 MWth CLC unit. Desing parameters of the fuel and air reactors as well as the suitable particle size of the oxygen carriers were determined in order to achieve the complete combustion of natural gas in the CLC unit as a function of the oxygen carrier properties. © 2022 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Clean Coal Technology is the property of Clean Coal Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Clean Coal Technology is the property of Clean Coal Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Chlorine substitution has been considered as one of the key steps of polychlorinated dibenzodioxin/furan (PCDD/Fs) generation. The introduction of oxygen carriers (OCs), especially in chemical looping combustion (CLC), provides the platform of directed regulation for the chlorine substitution process. Methods: Density functional theory (DFT) calculations with code VASP 5.4 were employed to investigate the free energy of PCDD/Fs adsorption on different surfaces. 12378-PCDD, which is the product of a one-step chlorine substitution for toxic 2378-PCDD, has been selected as the calculation case, and the regulation mechanisms on the inter-isomeric conversion of 12378-PCDD were identified by calculating the energy barrier and action angle. Results: It was found that the chlorine substitution of 12378-PCDD, particularly in 4# position, 9# position, and 6# position, emerged a tendency to increase the difficulty in turn, which conforms to the principle of distal preference. Besides, the influence from CaO adsorption on the crystalline surface of the iron-based oxygen carrier (OC) has been analyzed and it was verified that CaO adsorption can significantly increase the energy barrier for the chlorine substitution of 12378-PCDD. Meanwhile, the action angle was proposed to evaluate the parameters of adsorption process, and the adsorption of CaO can not only change the action angle between the 12378-PCDD molecule and the lattice surface, but also can modulate the energy barrier order of chlorine substitution among PCDD isomers. In addition, the loading component modulation was carried out to further confirm the feasibility of modulating the chloride substitution pathway, which proved the influence degree of loading component. And accordingly, the stretching analysis of the inactive component provides a theoretical basis for the subsequent study of the directional regulation of the PCDDs isomer generation pathway. Finally, the chlorine substitution rules and directed regulation mechanisms of PCDD/Fs isomers were obtained, which provides a modification direction for the structural components of OCs. [ABSTRACT FROM AUTHOR]

Chemical Looping Combustion is a promising midterm solution to mitigate CO2 emission, by carrying out indirect fuel combustion and allowing inherent separation of CO2. During the CLC process, an oxygen carrying material is subjected to successive oxidation‐reduction reactions at high temperature which induce significant material degradation. CuO/Al2O3 based materials have been widely considered as promising oxygen carriers (OC). However, the oxygen carrier ageing mechanisms (active phase migration and interactions with the support, phase transitions) are not well understood. Herein, an in‐depth overview of the material evolution is achieved by employing a multi‐scale characterization approach. At the μm‐scale, copper migration within the alumina support has been observed using Scanning Transmission X‐ray Microscopy (STXM) and Scanning Electron Microscopy (SEM). The spatial distribution of the Cu−Al species provides information on copper mobility and the different phases interactions. A comprehensive mechanism is proposed concerning the redox behaviour of the CuO/Al2O3 system, relating the diffusion of the Cu‐species, the active phase‐support interactions, and the role of copper in the Al2O3 support phase transition to the temperature and the number of redox cycles. Understanding the ageing process of CuO/Al2O3 materials paves a way to design more stable oxygen‐carriers. [ABSTRACT FROM AUTHOR]

Chemical Looping Combustion (CLC) is a technology that efficiently combines power generation and CO2 capture. In CLC, the fuel is oxidized by a metal oxide called an oxygen carrier (OC). CLC uses two reactors: a fuel reactor and an air reactor. The fuel reactor oxidizes the fuel and reduces the OC. The air reactor oxidizes the OC using air and then the OC is cycled back to the fuel reactor. It is typical for both the fuel and the air reactors to be fluidized beds (FBs). In this research, an Aspen Plus model was developed to simulate a CLC system. Aspen Plus has recently included a built-in FB unit operation module. To our knowledge, no literature has been reported using this FB module for simulating fluidized bed combustion or gasification. This FB unit process was investigated in Aspen Plus and a kinetic based model was used and compared the simulation results to experimental data and the commonly used Gibbs equilibrium model. The FB unit and the kinetic model well fit the experimental data for syngas and methane combustion within 2% of the molar composition of syngas combustion and within 4% for the methane combustion. An advantage of this model over other kinetic models in literature is that the core shrinking model kinetic rate equations have been converted into a power law form. This allows Aspen Plus to use a calculator instead of an external Fortran compiler. This greatly simplifies the modeling process. The reaction rate equations are given for all reactions. A sensitivity analysis of the reaction kinetics was conducted. All data, code, and simulation files are given. [ABSTRACT FROM AUTHOR]

Chemical looping with O2 uncoupling aims at using an oxygen carrier (OC) with O2 uncoupling behaviour to promote fuel conversion. Natural ilmenite ores have been considered highly promising OCs for chemical looping technology; however, they do not possess any O2 uncoupling behaviour. Mn‐modified ilmenite ores as OCs are capable of O2 uncoupling, while most of them are synthesized via complicated procedures by using costly chemicals. In this study, a strategy of calcination treatment on ilmenite ores mixed with manganese ores has been established to introduce Mn into the ilmenite OCs, endowing them with O2 uncoupling behaviour in a simple and low‐cost manner. The O2 uncoupling behaviour from Mn‐modified ilmenite ores is mainly due to the newly formed (Fe1−xMnx)2O3/(Fe1−xMnx)3O4 crystal phases generated during the calcination treatment, which also alleviate the thermodynamic limit of the Mn2O3‐Mn3O4 redox pair. As a result, the Mn‐modified ilmenite ore OCs can release O2 at high temperatures when decreasing the oxygen partial pressure. But more importantly, the reduced OCs can be restored in the air isothermally. This established simple calcination treatment method can be used as a low‐cost strategy for producing ilmenite‐based OCs with O2 uncoupling behaviour. The O2 uncoupling behaviour is expected to be beneficial to chemical looping combustion of fuels, promote fuel conversion, minimize OC loading, and reduce energy consumption. [ABSTRACT FROM AUTHOR]

Over the past two decades, chemical looping combustion (CLC) has been extensively investigated as a promising means to produce electric power while generating a concentrated carbon dioxide stream for sequestration. We note that the chemical looping strategy can be extended well outside of combustion-based carbon capture. In fact, application of the chemical looping strategy in areas beyond combustion can result in somewhat unexpected energy and carbon dioxide savings without producing a concentrated CO2 stream at all. Furthermore, it allows the looping-based technologies to tap into applications such as chemical production – a $4 trillion per year industrial sector with high energy and carbon intensities. The key resides in the design of effective oxygen carriers, also known as redox catalysts in the context of selective chemical conversion through chemical looping catalysis (CLCa). This contribution focuses on the design and applications of mixed oxides as multi-function reaction media in CLCa. Since typical mixed oxide oxygen carriers tend to be nonselective for hydrocarbon conversion, the first part of this article presents generalized design principles for surface modification of mixed oxides to improve their selectivity and catalytic activity. Applications of these redox catalysts in chemical looping – oxidative dehydrogenation (CL-ODH) of a variety of light alkanes and alkyl-benzenes are presented. This is followed with a discussion of computation assisted mixed oxide design based upon thermodynamic criteria. Finally, a few new directions for the chemical looping technologies are introduced. [ABSTRACT FROM AUTHOR]

Continuously rising concentrations of CO 2 in the atmosphere has led to significant negative impacts on the environment which propelled research efforts to replace fossil fuel-based energy with clean energy sources. However, the reliance on fossil fuel as the main energy source is projected to stay for many years to come, and therefore developing cleaner pathways to utilize fossil fuels for energy generation is paramount. Chemical looping combustion (CLC) has emerged in recent years as a promising technology for CO 2 capture in power plants and other CO 2 intensive industries. A key cornerstone for CLC is the development of efficient oxygen carriers with high oxygen capacity, fast kinetics, cyclic stability, mechanical strength, and low cost. The research progress in this field is rapidly growing to tackle the major materials and operational challenges to advance the knowledge toward a commercial scale CLC application. This work provides an overview of the significant advancements achieved over the past seven years in the development of synthetic metal oxide-based oxygen carriers. A summary of key performance indicators used to evaluate oxygen carriers is presented in this study to enable for a systematic assessment of the oxygen carriers' properties and performance. This work is focused on summarizing and critically reviewing the literature on the development of oxygen carriers such as Ni, Cu, Fe, Mn, Co-based metal oxides and combined/mixed oxygen carriers in the past seven years. Studies of naturally occurring materials and waste materials used as oxygen carriers are excluded from this review which is mainly focused on synthetically prepared materials. Significant efforts were dedicated to investigating the role of the supports, synthesis methods, promotors, and other factors affecting the CLC performance of synthetic oxygen carriers using solid, liquid, and gaseous fuels. This review also outlines the main challenges, research needs and opportunities for future progress to highlight potential pathways to develop synthetic oxygen carriers in an environmentally friendly, and cost-effective manner. [Display omitted] • Extensive research has been performed on CLC recently 2016–2022. • CLC Performance indicators and equipment are briefly presented. • Oxygen carriers are keystone for the development and commercialization of CLC. • Use of single synthetic oxygen carriers in CLC over the last 5 years is reviewed. • Effects of different factors on CLC performance are comprehensively discussed. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and simulation of an industrial-scale chemical looping combustion (CLC) power plant, including all process units (reactors, flue gas treatment units, heat integration, steam cycle, and CO2 compression train). A model of a 525 MWth CLC power plant was built using a rigorous representation of the solid fuel and oxygen carrier. Petcoke was considered the main fuel of interest in this study, and it is compared with other solid fuels. The flue gas compositions obtained with the model show that cleanup units are mandatory to comply with CO2 quality requirements. High levels of flue gas treatment, including 97.1% deNOx and 99.4% deSOx, are needed to achieve typical specifications for captured CO2. This is mainly due to the high level of contaminants in the fuel, but also to the absence of nitrogen in the CLC flue gas, thus resulting in higher concentrations for all substances. The high level of flue gas treatment is thus one of the important challenges for solid fuel combustion in CLC. The overall CO2 capture efficiency of the plant is estimated to be as high as 94%. Regarding the energy balance, a process net efficiency of 38% is obtained. Comparing the results with other available technologies shows that CLC exhibits one of the highest net plant efficiencies and carbon capture rates. CLC is thus a promising technology to produce clean energy from solid fuels. Finally, based on a sensitivity analysis, it is shown that process efficiency is mainly affected by the design and performance of the CLC furnace, the steam injection rate in the fuel reactor, the char separation efficiency, and the excess oxygen in the air reactor. [ABSTRACT FROM AUTHOR]

The development of oxygen carriers with good reactivity and anti-sulfur ability is imperative in the chemical-looping combustion (CLC). In this work, the reaction characteristics of Al-doped Cu–Fe spinel (Al–CuFe 2 O 4) were investigated based on experiments and density functional theory calculations. The results showed that the reduction stage of Al–CuFe 2 O 4 reaches the maximal reaction rate at 452 °C. The corresponding weight loss is about 9.71%, higher than that of CuFe 2 O 4 (8.78%). It demonstrates that Al–CuFe 2 O 4 shows better reaction activity than CuFe 2 O 4 at lower temperature. Doping Al can increase the reactivity of Cu–Fe spinel-type oxygen carrier towards CO adsorption and reduce the O vacancy formation energies. Moreover, the adsorption behaviors indicate that H 2 S can hardly adsorb on the Al–CuFe 2 O 4 surface in molecular form, and the adsorption energies of HS∗ and S∗ decrease while the energy barriers of H 2 S dissociation increase. Doping Al weakens the interaction between sulfur species and Cu–Fe spinel-type oxygen carrier, thus Al–CuFe 2 O 4 also exhibits good anti-sulfur ability. [Display omitted] • Experimental and theoretical studies on Al–CuFe 2 O 4 reaction mechanism were offered. • Conversion of Al–CuFe 2 O 4 to Cu·Al–Fe 3 O 4 leads to the largest CO consumption peak. • Al–CuFe 2 O 4 shows better reactivity towards CO than CuFe 2 O 4 at lower temperature. • Al dopant can weaken the interaction between CuFe 2 O 4 and sulfur species. [ABSTRACT FROM AUTHOR]

Copyright of Clean Coal Technology is the property of Clean Coal Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biomethane power generation, particularly chemical looping combustion technology, has garnered significant attention recently due to its ability to capture CO 2 in situ. In this study, dual bed layers oxygen carriers (DBL) for chemical looping combustion of methane were designed. The LaFe 0.93 Ni 0.07 O 3 oxygen carrier with excellent CH 4 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 LaFe 0.93 Ni 0.07 O 3 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 LaFe 0.93 Ni 0.07 O 3 by red mud, while the double bed system showed high stability in the long-term redox cycle. The limitedly increased crystallite size of LaFeO 3 , 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. • A tandem reactions strategy for improving the efficiency of chemical looping combustion of methane in fixed bed reactor was provided. • The obvious increased crystal size and coarsening particles can be alleviated by the double bed layer design. • The double bed layer design provides supports for direct utilization of red mud. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3DOM LF 0.85 N 0.15 /Pd@S-1 owns high reactivity, excellent OSC and structural stability. • Pd@S-1 reduces the reaction temperature of chemical looping in a large degree. • Hierarchical pore promotes the adsorption and diffusion ability of gas molecules. Chemical looping reforming of CH 4 coupled with CO 2 reduction technology offers a compelling way for effective CO 2 emission with the production of syngas and CO. However, the reaction temperature in chemical looping is relatively higher (>800 °C). To solve this problem, it is critical to explore efficient oxygen carriers. In this work, 3DOM LF 0.85 N 0.15 /Pd@S-1 oxygen carrier with hierarchical pore structure obtained high reactivity. 3DOM LF 0.85 N 0.15 /Pd@S-1 contained three major components, playing different roles. The 3DOM LF 0.85 N 0.15 with ordered macroporous structure possessed excellent oxygen storage capacity and diffusion property. Pd clusters as active sites promoted CH 4 activation and strengthen Lewis acid sites. Silicalite-1 zeolite, with larger surface area and well-defined microporous structure, exhibited superior adsorption properties and used as an ideal support to encapsulate Pd clusters. The well-dispersed Pd clusters further strengthened the reducibility at low temperature. Among all samples, 3DOM LF 0.85 N 0.15 /Pd@S-1 exhibited highest reactivity and stability during the successive chemical looping. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modified ferric sludge with high aluminate cement and copper oxide as an oxygen carrier. • Improved stability and reactivity of OC observed with addition of CuO. • FSCuO10 achieved stable performance of > 92 % across 50 cycles. • FSCuO10 showed minimal agglomeration and attrition of < 4 % after 50 cycles. • FSCuO10 achieved stable performance throughout 300 cycles. This study focuses on enhancing the performance of water treatment sludge as an oxygen carrier (OC) for chemical looping combustion (CLC) of municipal solid waste (MSW) syngas. High aluminate cement was introduced to augment the OC's mechanical strength, concurrently preventing inter-particulate agglomeration, resulting in a commendable and low agglomeration rate of 3.44% after 50 cycles. The inclusion of CuO proves to be instrumental in boosting the OC's reactivity, mitigating the loss of active components due to the addition of cement support. Notably, FSCuO10 (Ferric sludge with 10% CuO addition) demonstrates over 92% CO efficiency throughout 50 cycles, affirming the success of the dual modification of FS. The investigation also delves into comprehending the reduction process, agglomeration pathways, and the impact of varied CuO percentages has on OC performance. Extensive characterizations were conducted to elucidate OC transformations and their consequential effects on reactivity, physical characteristics, and overall performance. A noteworthy observation includes the outward migration of iron and copper during CLC, contributing to the stabilization of reactivity. In summary, the modifications implemented on FS, yield an improved OC for CLC purposes, maintaining its novelty and cost-effectiveness. The novelty stems from the interactions between CuO and FS, leading to improved reactivity and stability, as well as the extended CLC, which demonstrates the longevity of the OCs. This research contributes to the circularity of waste-derived products by effectively repurposing water treatment sludge and improving sustainable waste management practices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Formation of KFeO 2 is confirmed via XRD and thermodynamic calculation. • The reactivity of the ilmenite is enhanced with WSA addition. • The reactivity of ilmenite peaks at 10 % WAS addition. • Ilmenite with 10 %WSA addition exhibits highly developed pore structure. • Ilmenite with 10 %WSA addition exhibits the highest oxygen release capability. Chemical looping combustion (CLC) offers a promising approach for biomass utilization. The utilization of biomass as the primary fuel in CLC (bio-CLC) is a way to generate negative CO 2 emissions and thus interesting for climate change mitigation. However, the presence of ash in biomass raises concerns about the performance variation of the oxygen carrier during CLC. This study investigated the impact of adding wheat straw ash (WSA) to the ilmenite oxygen carrier throughout the CLC process. The effects of WSA addition ratio (0–15 %) and cycle number on the performance of oxygen carrier were evaluated. The results showed a progressive enhancement followed by a subsequent reduction in the performance of ilmenite with the increase of WSA addition ratio, and the peak reactivity of ilmenite was attained with 10 % WSA addition. Addition of 15 % WSA resulted in severe particle sintering, causing a slight diminishment in ilmenite reactivity. Furthermore, the mechanisms of the performance variation of ilmenite with WSA addition were explored. The superior redox reactivity and oxygen release capability of the ilmenite with 10 % WSA addition were evidenced by X-ray photoelectron spectroscopy and hydrogen temperature-programmed reduction analysis, respectively. Notably, X-ray diffraction and thermodynamic calculation confirmed the formation of KFeO 2 , which significantly enhanced the reactivity of ilmenite. The specific surface area of the ilmenite was greatly enlarged with 10 % WSA addition, and a porous structure was evidenced by scanning electron microscope. The findings suggest the interaction between the WAS and ilmenite enhances the reactivity of the ilmenite with an optimal WAS addition ratio of 10 %, providing a guidance for the long-term operation of CLC. [ABSTRACT FROM AUTHOR]

• Perovskite C a M n O 3 - δ was synthesized from natural ores through a simple process. • CaMnO 3 phase absorbs more Fe, Al, and Si present in the Mn ore compared to CaMn 2 O 4. • CLOU and reactivity of C a M n O 3 - δ were tested in both batch and CLC reactor system. • Low attrition was found after 29 h operation with CH 4 in the CLC reactor system. The potential for low cost of CO 2 capture using chemical-looping combustion (CLC) should not be compromised by costs associated with the oxygen carrier. This justifies studies of oxygen carrier materials with reasonable production costs. In this study, a perovskite calcium manganite (C a M n O 3 - δ), was synthesized from manganese ore and limestone through a straightforward process involving mixing with polyvinyl-alcohol, sintering, crushing and sieving. The calcium manganite produced exhibited two primary crystalline phases: CaMnO 3 (perovskite) and CaMn 2 O 4 (marokite). Experiments were conducted using both a batch fluidized-bed reactor and a 300 W CLC reactor system in continuous operation to assess the oxygen uncoupling and reactivity of the calcium manganite. The results show that the oxygen uncoupling ability increases with temperature. Full syngas conversion was achieved at relatively low temperatures and low fuel-reactor bed mass over fuel power ratio in the 300 W unit. Elevated temperatures and ratio of fuel-reactor bed mass over fuel power enhance methane conversion significantly. The attrition of the calcium manganite was low, around 0.1 wt%/h for the last 15 h operation with methane. Batch reactor tests of fresh and used materials showed that there was no reduction in reactivity after 29 h of fuel operation. [ABSTRACT FROM AUTHOR]

• Iron-based oxygen carriers with different structures are prepared using compression molding. • Fe 2 O 3 /CuO@MgO oxygen carriers show superior cyclic stability due to precluding the diffusion of Fe3+ ions. • The ion diffusion mechanism during cyclic redox process for iron-based oxygen carriers is proposed. Iron-based oxygen carriers as one of the most commonly used oxygen carriers in chemical looping combustion, shows poor cycling stability. In this work, spinel-structured, Fe 2 O 3 @MgO core–shell structure, and Fe 2 O 3 /CuO@MgO core–shell structure oxygen carriers were prepared using compression molding. The effects of deep reduction and oxidative regeneration processes on the cyclic stability of oxygen carriers with different structures were investigated using thermal gravimetric analyzer. The mechanisms for the changes in the cyclic stability were explored through a series of characterization analyses. The results showed that the reduction process of spinel oxygen carriers generated Fe-Mg solid solution, which was unfavorable to deep reduction, and phase separation occurred during 5 cycles. Due to the migration of Fe3+ ions to the surface, surface was seriously sintered, deteriorating the cyclic stability of spinel oxygen carriers. For Fe 2 O 3 @MgO oxygen carrier, the deep reduction can be realized, but the interdiffusion phenomenon of Fe2+ and Mg2+ occurred after 5 reductions, and the generation of (MgO) x (FeO) 1−x solid solution impeded the deep reduction. The addition of CuO in the core of oxygen carriers to form Fe 2 O 3 /CuO@MgO could inhibit the interdiffusion of Fe2+ and Mg2+, and maintained the oxygen carrying capacity up to more than 95 % in 10 cycles. Meanwhile, CuO synergized with Fe 2 O 3 to enhance the reduction and oxidation reactivity of the oxygen carrier. On this basis, the ion diffusion mechanism during the deep reduction and oxidation of iron-based oxygen carriers with different structures was proposed. This study provides guidance for the modification of iron-based oxygen carriers with superior cycling stability. [ABSTRACT FROM AUTHOR]