Oxide Oxygen Carriers Research Articles

Enhanced syngas production via plastic rubber chemical looping gasification: Role of iron–nickel oxide oxygen carriers

To meet the growing demand for efficient waste management solutions, a novel method called Plastic Rubber Chemical Loop Gasification (PRCLG) offers an innovative and effective approach to the thermal treatment of rubber and plastic waste, producing high-purity fuel and hydrogen-rich syngas. In this study, iron-nickel oxide was synthesized and used as an oxygen carrier to facilitate the PRCLG process. The impact of these oxygen carriers on syngas production was thoroughly investigated, and the evolution of the oxygen carrier's activity was analyzed through changes in the microenvironment during the gasification process. Experimental results showed that under pyrolysis conditions at 750 °C, the syngas yield was 1142 mL/g. After introducing a controlled atmosphere with 1.5 mL/h of water vapor, the syngas yield increased to 2150 mL/g. Further enhancement of the syngas yield using a catalyst resulted in a yield of 3562 mL/g, with a carbon conversion rate of 94%. The study confirmed that optimal syngas yields were achieved at 750 °C, highlighting the importance of precise temperature control. Over ten cycles spanning 600 min, the iron-nickel oxide oxygen carrier exhibited stable performance, demonstrating its durability and effectiveness. This innovative PRCLG method not only provides a solution for the disposal of rubber and plastic waste but also contributes to the production of valuable energy resources, aligning with sustainable development goals and advancing waste-to-energy technologies.

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

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

CFD modelling of a chemical looping combustion system − Exploring the potential of natural oxygen carriers

Research advancements in Carbon Capture technology has allowed for Chemical Looping Combustion (CLC) to emerge as a promising technique which can be feasibly implemented into existing power plant infrastructures. In this study, a 120 kWth interconnected Dual Circulating Fluidized Bed (DCFB) reactor has been studied, which uses methane fuel and NiO/Al2O3 particles as oxygen carrier. Two-dimensional transient CFD simulations have been conducted for the DCFB – CLC system using an Eulerian – Eulerian model coupled with heterogeneous reactions and the results have been compared to existing literature. Using the same methodology, two natural ore potential oxygen carriers in Pakistan: Hematite (Fe-based) and Hausmannite (Mn-based) have been evaluated for the same pilot scale apparatus. The fuel conversion and combustion efficiencies have been evaluated for the oxygen carrier particles and have been compared with the original system. The results show that Fe ore provides lesser combustion efficiency as compared to NiO, whereas Mn ore exhibits extremely high reactivity. In retrospect, the use of a mixed (Fe-Mn) oxide oxygen carrier can be considered as a viable option.

A nickel-modified perovskite-supported iron oxide oxygen carrier for chemical looping dry reforming of methane for syngas production

The chemical looping dry reforming of methane (CLDRM) process, which converts methane and carbon dioxide into syngas, is an environmentally friendly greenhouse gas utilization strategy. In this work, it is demonstrated that a nickel-modified perovskite-supported iron-based oxygen carrier (Ni-Fe2O3/La0.8Sr0.2FeO3) significantly enhances the reactivity of CLDRM in the temperature range of 770–800 °C while maintaining high CO selectivity and oxygen capacity, as well as good carbon deposition resistance. With the addition of nickel, the methane conversion is 52 % higher than that without nickel at 800 °C. Rational coupling of the oxygen carrier components achieves over 99 % CO selectivity. 160 consecutive isothermal cycles confirm the outstanding stability of Ni-Fe2O3/La0.8Sr0.2FeO3. Based on the experimental results and characterizations, the evolution scheme and synergistic effects between the components of the Ni-Fe2O3/La0.8Sr0.2FeO3 oxygen carrier for CLDRM reaction are proposed. The results provide a pathway for oxygen carrier design to decrease the reforming temperature while maintaining excellent reaction performance in iron-based chemical looping systems.

Interaction of SO2 with a Cu–Mn oxide oxygen carrier during chemical looping with oxygen uncoupling

During chemical looping combustion with oxygen uncoupling (CLOU) fuel-sulfur species impact the reactivity of Cu–Mn oxide oxygen carrier with CH4. SO2 oxidation to SO3 competes with fuel for available O2 and lowers CH4 conversion.

Dopant-Enhanced harmonization of α-Fe2O3 oxygen migration and surface catalytic reactions during chemical looping reforming of methane

The rate-matching between oxygen migration and surface catalytic reaction of oxygen carrier (OC) is a critical determinant for the reaction selectivity of the chemical looping reforming (CLR) of methane. However, the theoretical mechanism behind this rate-matching relationship is still unclear. Herein, we propose to use density functional theory (DFT) combined with microkinetic simulations to establish a model integrating the methane oxidation reactions with oxygen migration kinetics on α-Fe2O3 oxygen carrier. Our calculated results reveal that the transition metals (TMs)-doping such as Co, Ni, and Cu after Fe element in the periodic table can accelerate the oxygen migration rate as it promotes the upshift of the O p-band center. Moreover, a suitable oxygen migration energy barrier of about 1.0 eV is helpful to enhance the harmonization of α-Fe2O3 oxygen migration and surface catalytic reactions. Based on this, Ni-doping in α-Fe2O3 is predicted to be able to enhance the oxygen migration rate to match the rate of first-step methane dissociation, thereby simultaneously improving the reaction rate and the selectivity in the CLR of methane to syngas. These results could help to understand the relationship between oxygen migration and surface catalytic reaction rates and pave the way for the rational design of metal oxide oxygen carriers.

Chemical looping gasification of biomass using rare earth oxides doped ferric oxide oxygen carrier for hydrogen‐rich syngas production

AbstractAn efficient oxygen carrier (OC) is in great demand in the biomass chemical looping gasification (BCLG) process. In the present study, an innovative rare earth oxide doped ferric oxide OC (Fe2O3−REaOb) derived from the Nd‐Fe‐B sintered magnet waste scraps was employed for the BCLG process for hydrogen‐rich syngas production. The critical variables, including the temperature of gasification, the mass ratio of OC/biomass, the mass ratio of steam/biomass, and the cycle performance of the novel OC, were investigated regarding syngas yield and carbon conversion efficiency. Results found that the optimum conditions were achieved at 900°C, with a mass ratio of OC to biomass of 3:1 and a mass ratio of steam to biomass of 0.4, and a syngas yield of 1.19 Nm3/kg with an H2/CO mole ratio of 2.45, and a carbon conversion efficiency of 76.80% was reached. Additionally, a comparison between Fe2O3−REaOb OC, Fe2O3−Al2O3 OC, and Fe2O3−CeO2 OC was also conducted, with Fe2O3−REaOb OC demonstrating a superior performance. The synergistic effects between REaOb and Fe2O3, particularly the generation of perovskite oxide NdFeO3, contributed to the excellent performance of the Fe2O3−REaOb OC during the BCLG process. The outward diffusion of Fe and sintering of the OC reduced the syngas yield and carbon conversion efficiency by about 16.00% and 25.00% over the 20 redox cycles of the BCLG process. In summary, Fe2O3−REaOb can be an efficient and promising OC for hydrogen‐rich syngas production in the BCLG process.

Low-temperature chemical looping oxidation of hydrogen for space heating

Chemical looping combustion (CLC) is an advanced combustion process in which the combustion reaction splits into two parts; in the first reaction metal oxides are used as oxygen suppliers for fuel combustion and then in the second reaction, reduced metal oxides are re-oxidised in an air reactor. Although this technology could be applicable for the safe implication of “low-temperature oxidation of hydrogen”, there is limited understanding of oxygen carrier reduction stages and the oxidation mechanism of hydrogen throughout the process. The novelty of this research lies in its pioneering investigation of low-temperature oxidation of hydrogen through chemical looping technology as a safe and alternative heating system, using three distinct metal oxide oxygen carriers: CuO, Co3O4, and Mn2O3. The oxidation of hydrogen over these oxygen carriers was comprehensively studied in a fixed-bed reactor operating at 200–450 °C. XRD analysis demonstrates that CuO directly reduced to metallic Cu at 200–450 °C, instead of following a sequential reduction step CuO→Cu4O3→Cu2O→Cu throughout the temperature. Co3O4 was reduced to a mixture CoO and Co at 450 °C, which may refer to a sequential reduction step Co3O4→CoO→Co with increasing the temperature. Decreasing the reduction temperature led to an elevation in CoO formation. Mn2O3 can also reduce to a mixture of Mn3O4 and MnO at temperatures between 250 and 400 °C. Compared to temperature, the increase in the residence time did not show any further reduction in Mn2O3. SEM results showed that most of the metal oxide particles were evenly dispersed on the supports. Based on the experimental results, a potential reduction stage of CuO, Co3O4 and Mn2O3 was proposed for low-temperature hydrogen oxidation, which could be a potential application for space heating using safe hydrogen combustion.

Using cerium modified ferric oxide as oxygen carrier for enhancement of fuel efficiency

Using oxygen carrier to relieve uneven mixing of fuel and air under harsh conditions (high temperature and short residence time) is a promising strategy to improve fuel efficiency. In this paper, a range of cerium modified ferric oxide oxygen carriers with excellent redox capability and stability was fabricated to investigate the ethylene rapid oxidation performance and the gas–solid surface reaction of ethylene and iron oxide was studied with density functional theory. The experimental results show that the oxygen carrier with the mole ratio of ferrum: cerium is 9:1 performed the best ethylene oxidation characteristic, because the addition of cerium improved oxygen vacancy capacity to enhance the oxidation for ethylene and its pyrolysis products, which was also confirmed with density functional theory study. Due to the role of both, the ethylene and its pyrolysis products were converted into carbon dioxide and water quickly and effectively (carbon dioxide yield >92%).

CO2 utilization in chemical looping gasification and co-gasification of lignocellulosic biomass components over iron-based oxygen carriers: Thermogravimetric behavior, synergistic effect, and reduction characteristics

Efficient CO2 utilization in the thermochemical conversion of biomass plays an important role in creating a future low-carbon economy. This study attempts to explore the CO2-assisted chemical looping gasification and co-gasification process of lignocellulosic biomass components (hemicellulose, cellulose, and lignin) with iron oxide oxygen carriers using thermogravimetry and differential thermal analysis. Three different iron oxide oxygen carrier-to-biomass (O/B) ratios were taken into account to deeply understand the thermal degradation characteristics of individual components (O/B ratio: 0) and their blending with iron oxide oxygen carriers (O/B ratio: 0.5 and 1). Meanwhile, the reduction characteristics of three major biomass components were also investigated in terms of X-ray diffraction (XRD), synergistic interaction, and reduction degree. Experimental results suggest that the existence of iron oxide oxygen carriers could accelerate the reaction kinetics under the reactive CO2 environment, arising from the competitive relationship between the direct reduction reaction by char in biomass and the Boudouard reaction at high temperatures (600–950 °C). Interestingly, the reoxidation behavior of the reduced iron oxide is observed at high temperatures, especially for lignin. Among all the tested biomass materials, their ability to reduce iron oxide oxygen carriers under the CO2 atmosphere follows the order of biomass mixture (1:1:1 wt%)>lignin>xylan>cellulose. Moreover, the findings indicate that significant synergistic interaction exists during the CO2-assisted chemical looping co-gasification process.

Fluidized bed reforming of methane by chemical looping with cerium oxide oxygen carriers

Methane reforming is an industrial process for hydrogen production having a high CO2 footprint that can be mitigated either by using renewable methane, or by recycling carbon dioxide from capture. Methane reforming assisted by an oxygen carrier was currently investigated, being an attractive option for production of hydrogen and carbon monoxide mixtures. The distinctive aspect of present research was the development of three different granular materials based on CeO2 to be used in fluidized beds, obtained by pelletization and calcination at 900 and 1200 °C of CeO2 or CeO2/Al2O3 powder. Fluidization and abrasion tests were performed at cold and hot conditions, showing the best attrition resistance of materials calcined at the highest temperature, with attrition rate equal to 0.3 %/h. Conversely, thermogravimetric tests at 900 °C revealed the best performance of CeO2 granules sintered at lower temperature with respect to the others in terms of oxygen supply capacity, achieving 0.55 of conversion degree. Reforming and regeneration cycles were performed in fluidized bed at 940 °C with CeO2/Al2O3 granules, providing instantaneous methane conversion up to 37 %, high carrier conversion (0.87) and low carbon deposition (2.9 mg/g) during the reforming step.

Core-shell-like Fe2O3/MgO oxygen carriers matched with fluidized bed reactor for chemical looping reforming

• A novel core–shell-like structure Fe-based microsphere is designed. • The particle size of microsphere is affected by the nucleation rate and growth rate. • The Fe-based microsphere shows high chemical looping reforming stability that attributed to the core–shell-like structure. • The formation mechanism of Fe-based microsphere can be expanded to other metal oxide oxygen carrier. Large Fe 2 O 3 /MgO microspheres with core–shell-like structures were synthesized via hydrothermal precipitation method based on the difference solubility product constants of ferrous carbonate and magnesium carbonate. The particle morphology of the Fe 2 O 3 /MgO microspheres is dominated by polyvinylpyrrolidone (PVP), while the diameter of the Fe 2 O 3 /MgO microspheres is affected by the relative nucleation rate and growth rate. The diameter of the Fe 2 O 3 /MgO microspheres decreases with increasing PVP concentration due to the enhanced steric hindrance which inhibits the growth of crystals by hindering the collisions and aggregation between crystals. The particle diameter also decreases with increasing urea concentration, which is attributed to the enhanced nucleation rate of crystals. The reactivity of the core–shell-like Fe 2 O 3 /MgO microsphere used as oxygen carriers for chemical looping dry reforming was also investigated in a fluidized bed reactor. The core–shell-like Fe 2 O 3 /MgO microspheres show good sintering resistance and remarkable cycle stability due to the effective inhibition of iron ion diffusion and surface enrichment.

Diffusion transport characteristic of carbon monoxide within calcium sulfate slit in chemical looping hydrogen production: Molecular dynamics simulation

Chemical looping hydrogen production is a kind of technology for high-carbon energy cleaning and low-carbon utilization with great development potential, which can realize H2 production and CO2 separation at low cost. CaSO4 oxygen carrier, as the non-metal oxide oxygen carrier, is not only cheap in price and friendly to the environment, but also high in amount of oxygen carried and excellent in the thermodynamic reaction property. For the key problem of its popularization and application – low reaction rate, this paper investigated the diffusion transport characteristics of the fuel gas molecule, which was one of key microprocesses affecting the reaction rate, in the channel of CaSO4 oxygen carrier. Based on the channel of CaSO4 oxygen carrier and the slit model, the influence of the slit width, reaction temperature and coverage rate of doped element Na or Fe of oxygen carrier on the internal diffusion behavior of CaSO4 oxygen carrier was investigated by the molecular dynamics simulation. The results show: CO molecules physical adsorb on CaSO4 slit surface; Increase of the slit width will reduce the binding of CaSO4 surface on single CO molecule, but CO molecular diffusion capacity will increase first and then decrease; The temperature rises will result in the growth of CO molecular diffusion capacity, because CO molecule to be easy to diffuse to the unoccupied reaction site; After Na and Fe is loaded on CaSO4 slit surface, CO molecular diffusion capacity is greatly improved, and the diffusion coefficients of CO molecule are 27 and 28 times of pure CaSO4 slit surface, respectively. The calculation results can provide theoretical basis for the structural design and channel optimization of calcium-based oxygen carrier for chemical looping hydrogen production.

Reactivity Study of Bimetallic Fe-Mn Oxides with Addition of TiO2 for Chemical Looping Combustion Purposes

The objective of the research was to prepare Mn-based materials for use as oxygen carriers and investigate their reactivity in terms of their applicability to energy systems. The family of Fe2O3-MnO2 with the addition of TiO2 was prepared by mechanical mixing method and calcination. Five samples with addition of Fe2O3 (20, 30, 35, and 50 wt.%) to MnO2 (65, 55, 50, 35, and 85 wt.%) with constant amount of inert TiO2 (15 wt.%) were prepared. The performance of TiO2 supported Fe-Mn oxides oxygen carriers with hydrogen/air in an innovative combustion technology known as chemical looping combustion (CLC) was evaluated. Thermogravimetric analysis was used for reactivity studies within a wide temperature range (800–1000 °C). Comprehensive characterization contained multipurpose techniques for newly synthesized materials. Moreover, post-reaction experiments considered morphology analysis by SEM, mechanical strength testing by dynamometry, and crystal phase study by XRD. Based on wide-ranging testing, the F50M35 sample was indicated as the most promising for gaseous fuel combustion via CLC at 850–900 °C temperature.

Investigations on the chemical looping with oxygen uncoupling process using Indian coal and copper oxide oxygen carrier

In this study, the effectiveness of CuO as an oxygen carrier (OC) in chemical looping with oxygen uncoupling (CLOU) process was investigated using three Indian coals with varying origin and nature. The thermogravimetric analysis (TGA) experiments were performed with coal to OC mass-ratio of 1:20, 1:30, and 1:40 at varying temperatures of 800, 850, 900, 950 °C. The mass loss profiles of coal/CuO indicated that the CLOU combustion reaction was the most suitable with a mass ratio of 1:30 and at 850 °C. Multicyclic combustion-reoxidation performance (for 45 h) also showed sufficiently good repeatability with minor agglomeration. Besides, the kinetic triplet, such as apparent activation energy (Ea), pre-exponential factor (A), and kinetic model function, g(x), were estimated for reactions in the pyrolysis and combustion zones applying the Coats and Redfern model on the TGA mass loss data. From mathematical model fitting, it was found that the three-dimensional Jander-diffusion model provides an excellent fit to the experimental data for the selected temperature zones, and the combustion reaction kinetics is likely to be a diffusion dominated process. The estimated apparent activation energies for three coals studied in this work were in the range of 38.3–60.1 kJ/mol and 102.6–129.0 kJ/mol in the temperature zone of 400–600 °C and 600–950 °C, respectively. The findings of the present study suggest first-time that the Indian coal-based CLOU process using CuO OC is promising, and the derived kinetic information will be useful for CLOU reactor design using Indian coal and CuO OC.

In-situ analysis of the Al-Fe-Mn-Cu oxide oxygen carrier for chemical looping applications

A novel Al-Fe-Mn-Cu oxide oxygen carrier, termed Gen3, was developed by NETL and prepared using natural ore and pigment grade materials. Gen3 was subjected to 10 cycles of reduction-oxidation (redox) through confocal laser scanning microscopy (CLSM) and thermogravimetric analysis (TGA), separately. TGA results indicated that Gen3 shows promise as an oxygen carrier, repeatably lending approximately 6% of its mass to oxygen carrying capacity. CLSM characterization led to the identification of different swelling behaviors among particles of ‘smooth’ (spinel-S) vs. ‘rough’ (spinel-R) surface morphologies, labeled based on appearance before redox cycling. Spinel-R particles exhibited homogeneous chemistry and porosity. Spinel-S particles showed much more localized porosity, specific to high-Cu areas. Gen3 particle volume increased 60% for spinel-S particles and 30% for spinel-R particles over the course of 10 redox cycles. All conditions showed some degree of separation of the complex Al-Fe-Mn-Cu spinel. Primary observed phases included Al-rich spinel, Fe-rich spinel, and Cu/CuO. Al-rich spinel and Cu/CuO in exposed Gen3 at times formed a lamellar structure of alternating Al-rich and Cu-rich layers in exposed Gen3 near areas rich in Cu. An additional Si-O-K-type phase was also observed that likely arose from the impurities involved in pigment grade materials and natural ores. Segregation increased with level of exposure. Si-rich regions and Fe-rich spinels showed extremely low porosity; a more evenly mixed Al-Fe-Mn-Cu spinel showed moderate porosity; Cu and Cu-rich spinel by far showed the highest porosity.

CuO/ZrO2 modified by WO3 oxygen carriers for chemical looping with oxygen uncoupling

The use of mixed metal oxides as oxygen carriers for chemical looping with oxygen uncoupling (CLOU) applications has shown great potential compared to single metal oxide-based oxygen carriers. In this work, the effects of adding WO3 to CuO/ZrO2 oxygen carriers on the oxygen capacity and rate indices for CLOU applications are investigated using nitrogen gas environment. Two synthesis methods were used to prepare the CuO-WO3/ZrO2 oxygen carriers, namely the coimpregnation and sequential impregnation, to evaluate the role of the oxygen carriers’ preparation method. The resulting oxygen carriers were thoroughly characterized using XRD, ICP-OES, SEM-EDS and H2-TPR characterization techniques to evaluate the physicochemical properties of the mixed oxide oxygen carriers. The oxygen transport capacity was found to significantly increase for the WO3-modified oxygen carriers compared with the single metal oxide CuO/ZrO2 which was due to the formation of a Cu-W intermediate phases that was found to enhance the redox characteristics of the oxygen carriers. Moreover, the sample synthesized via coimpregnation method displayed higher oxygen release capacity than the sequentially impregnated sample. This was ascribed to the formation a Cu-rich intermediate phase (Cu3WO6) possessing higher Cu/W ratio on the coimpregnated sample compared with a CuWO4-x phase with lower Cu/W ratio and larger crystallite structure formed on the sequentially impregnated oxygen carrier. The mixed metal oxide oxygen carriers also showed a stable redox performance which highlights the potential of WO3 as a modifier to Cu-based oxygen carriers to enhance the oxygen capacity and subsequently decrease the solids inventory. The proposed WO3-based promotors offer significant trait to synthesize Cu-based oxygen carriers with excellent properties for CLOU applications.

Stable Mixed Fe-Mn Oxides Supported on ZrO2 Oxygen Carriers for Practical Utilization in CLC Processes

The objective of the research was to prepare Fe-based materials for use as oxygen carriers (OCs) and investigate their reactivity in terms of their applicability to energy systems. The performance of ZrO2 supported Fe-Mn oxide oxygen carriers with hydrogen/air in an innovative combustion technology known as chemical looping combustion (CLC) was analyzed. The influence of manganese addition (15–30 wt.%) on reactivity and other physical properties of oxygen carriers was discussed. Thermogravimetric analyses (TGA) were conducted to evaluate their performance. Multi-cycle tests were conducted in TGA with oxygen carriers utilizing gaseous fuel. The effect of redox cycle number and temperature on stability and oxygen transport capacity and redox reaction rate were also evaluated. Physical-chemical analysis such as phase composition was investigated by XRD, while morphology by SEM-EDS and surface area analyses were investigated by the BET method. For screening purposes, the reduction and oxidation were carried out from 800 °C to 1000 °C. Three-cycle TGA tests at the selected temperature range indicated that all novel oxygen carriers exhibited stable chemical looping combustion performance, apart from the reference material, i.e., Fe/Zr oxide. A stable reactivity of bimetallic OCs, together with complete H2 combustion without signs of FeMn/Zr oxide agglomeration, were proved. Oxidation reaction was significantly faster than the reduction reaction for all oxygen carriers. Furthermore, the obtained data indicated that the materials have a low cost of production, with superior reactivity towards hydrogen and air, making them perfect matching carriers for industrial applications for power generation.

Exploring the migration and transformation of lattice oxygen during chemical looping with NiFe2O4 oxygen carrier

Chemical looping (CL) technology using an oxygen carrier (OC) offers a versatile platform to convert various fuels (e.g., CH4, coal, and biomass) to value-added products (e.g., heat, syngas, and H2) in a clean and efficient approach. Currently, the migration and transformation mechanisms of lattice oxygen in spinel OCs were not extensively investigated, which are considered the cornerstone of OC. In this work, the release-uptake paths of lattice oxygen and the chemical reaction laws at interface were studied in detail using a composite metal oxide (NiFe2O4) as an OC through (in-situ) XPS technology coupled with fixed bed experiments. Mechanistic studies indicate that the chemical reaction interface is fixed on the surface of OC particles, and the concentration gradient between the surface and the bulk drives the transmission of lattice oxygen to achieve the reduction or oxidation of OC. Additionally, an important hydroxyl ions formation process of OC is confirmed by an in-situ XPS.

Reduction Characteristic of CaSO4-CuO Combined Oxygen Carrier Under CO Atmosphere

CaSO4 oxygen carrier is considered to be a potential oxygen carrier (OC) for Chemical Looping Combustion because of its high oxygen capacity and low price. But its reactivity is lower than the main metal oxide oxygen carriers, and it deactivates due to sulfur loss as well as sintering at high reaction temperatures above 920 ℃. To improve the performance of CaSO4-based oxygen carrier, small amounts of CuO particles were mixed mechanistically with CaSO4 particles to use as combined oxygen carrier in this work. The reduction reactions of CaSO4 oxygen carrier, CuO oxygen carrier and CaSO4-CuO combined oxygen carrier under CO atmosphere were investigated. The effects of reaction factors including reaction temperature, the oxygen-carrying ratio of CuO to CaSO4 and mass of oxygen carrier, on the reductions have been investigated in this study. XRD, SEM-EDS, BET and gas analyses were performed to investigate the variations of solid phase, element compositions in solid residual and sulfur release with reaction time. The results show that the addition of CuO increases the reactivity of the CaSO4-based oxygen carrier while also suppressing the release of the gas sulfur. For the individual reduction of CaSO4 by CO, with the increase of CaSO4 mass (500 - 1200 mg), CO2 yield also increases until 1000 mg stops and SO2 released rises remarkably; An increase in the reaction temperature aggravated the SO2 emission. The carbon dioxide generation efficiency also increases with an increase in temperature, but decreases when the temperature exceeds 950 ℃ due to sintering of the oxygen carrier particles; With respect to the reaction of CuO with CO, CO2 yield does not change significantly with increasing temperature, due to the sintering of the CuO oxygen carrier in a high temperature reaction environment;For the combined oxygen carrier: a.As the reduction reaction temperature increases, the reduction reaction performance of the combined oxygen carrier is enhanced within the reaction temperature range of 750~900℃. b. CaO the use of CuO additives not only improves the CO conversion rate, but also inhibits the release of gas sulfide. As the oxygen carrying fraction of CuO increases, SO2 released is reduced and the SO2 release time is delayed. What� more, the solid products after reduction reaction mainly contain CaS, CaO, CuO, Cu2O and CaSO4, and no copper sulfide is detected. c. When the oxygen-carrying ratio of CuO to CaSO4 is increasing from 15% to 20%, CO2 yield increases greatly.