Chemical Looping Process Research Articles

Exergy, techno-economic and environment analysis of food waste plasma gasification and syngas chemical looping processes

To mitigate the problem of food waste, this study investigated two food waste treatment processes: plasma gasification hydrogen production and plasma gasification coupled with chemical looping, for converting food waste into high-quality hydrogen energy. Based on Aspen Plus software simulation results, the exergy, economic, and environmental benefits of the hydrogen production system were analyzed. Food waste hydrogen production using plasma gasification technology exhibits a high production capacity and economic input. Its hydrogen production capacity is 6.47 t/t H2 with a corresponding product cost of 2449.82 USD/t H2. The high economic input is mainly owing to the high power consumption of the plasma torches. Plasma gasification coupled with chemical looping can employ high-temperature gas to generate power, which can partially alleviate electricity consumption. In addition, in terms of thermodynamic benefits, the exergy efficiencies of plasma gasification hydrogen production and plasma gasification coupled with chemical looping are 31.44% and 54.31%, respectively. Plasma gasification coupled with chemical looping is more environmentally friendly based on the acidification and global warming potentials. The proposed novel process promotes food waste resource treatment and energy reuse.

CO2 conversion to CO by LaCo1−xFexO3 (x = 0, 0.25, 0.5, 0.75, 1) perovskite phases at low temperature

This paper reports conversion of CO2 to CO via reverse water-gas shift chemical looping process on LaCo1−xFeO3 perovskites at low temperature as a potential solution for CO2 mitigation. Reactions of LaCo1−xFexO3 phases with x = 0, 0.25, 0.5, 0.75, 1 under hydrogen atmospheres, and subsequently, carbon dioxide, were investigated by in-situ high-temperature X-ray powder diffraction and thermogravimetry. The perovskites show linear thermal expansion up to around 250 ºC under hydrogen atmosphere, followed by a phase change due to formation of oxygen vacancies, and finally, the materials decompose into La2O3 and metallic Co/Fe. Incorporating Fe improves the stability of the reduced phase. Partial reduction and decomposition temperatures under hydrogen were determined. After reduction of the perovskite samples, reactions with CO2 were analyzed. CO2 conversion increases with Fe loading, with LaCo0.50Fe0.50O3 being the material with optimal balance between RWGS-CL activity and long-term stability during five cycles. It reaches a maximum CO yield of 0.25 mol(molperovskite·cycle)−1 and a maximum rate of 3.9 mmol(molperovskite·min)−1 at 550 °C.

Ilmenite: A promising oxygen carrier for the scale-up of chemical looping

To tackle the scale-up of Chemical Looping Processes, the production of efficient and affordable oxygen carriers appears of paramount importance. Ilmenite is an ore-derived oxygen carrier which can be considered surely abundant and cheap. The preparation and the characterization of its reactivity are presented in the following paper. The paper describes briefly the performance of ilmenite relating it to other oxygen carriers, its thermodynamic properties, the kinetics and its use with fuels (solid, liquid and gaseous, including biofuels). Key features for an oxygen carrier are represented by costs and environmental sustainability, oxygen transport capacity and reactivity, as well as specific issues related to its use in fluidized bed reactors, namely agglomeration and attrition behavior. In addition, information about mutual interaction with fuel, considering also the influence of impurities, coke deposition or its effect on the gasification rate of solid fuels, is reported.

Enhanced decomposition of biomass tar using low concentration copper doped hematite in direct chemical looping process

Biomass tar is an unavoidable side product in the biomass direct chemical looping process. It is necessary to eliminate tar as it may cause operational problems, such as fouling and blocking in the downstream equipment. Innovative in-situ tar removal through oxidation and catalysis of oxygen carrier is attractive because it can decrease the decomposition temperature and simplify the process components. This work studied the decomposition enhancement of biomass tar (toluene as tar compound) using low concentration copper-doped hematite. Both experiments and simulations were conducted to investigate the effect of copper concentration on toluene conversion. The main finding was that low concentration (1–3 mol%) of copper-doped hematite could significantly enhance the tar conversion, which was elevated by up to 200% and 142% at 600 and 700 °C, respectively; whereas the copper concentration played an insignificant role, thus 1% copper-doped one was recommended for practical application. Furthermore, this result was partially supported by comparing oxygen vacancy formation energy in density functional theory calculations.

Effect of CuO addition on the performance of V2O5-based oxygen carriers for chemical-looping oxidation of H2S for efficient sulfur recovery from natural gas

Integrating Chemical-Looping process with Selective Oxidation of H2S (CLSO) at low temperature is a novel method to achieve efficient desulphurization and sulfur recovery from nature gas. In CLSO process, a reducible catalytic oxygen carrier (COC) is need to cyclically transport oxygen from air to H2S in gaseous fuels. For energy saving, it must have adequate catalytic sites that can selectively convert H2S to elemental sulfur at temperature as low as possible, meanwhile COCs do not combust nature gas, and for continuously operation the reduced COCs can be fully regenerated with air. COC development is key issue for the successful deploying CLSO process. Based on CLSO concept given by previous work (Kane, 2019), this study developed various V2O5-based COCs with and without CuO addition using TiO2- and Al2O3- supports of stableporousstructures, trying to improve the overall performance of COCs. By cyclic CLSO experiments, the desirable features of the new COCs were examined, and the effects of CuO addition on oxygen transport, catalytic behaviors, and chemical stabilities were specially assessed. This study also revealed the selective oxidation reaction mechanisms of H2S with these V2O5-based COCs, and identified the roles of CuO in catalytic redox reaction. It is demonstrated that the reactivities of V2O5 phase was greatly promoted as supported on porous supports; CuO phase enhanced significantly oxygen transport capacities of COCs as it was reduced to metallic copper in selective oxidation of H2S. Elemental sulfur deposition, H2S adsorption, and metallic sulfide formation put impacts to selectivity, and further study to improve COC selectivity is needed.

Synthesis of Methanol From a Chemical Looping Syngas for the Decarbonization of the Power Sector

Abstract One promising pathway for carbon capture and utilization is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes. Methanol is an interesting fuel for gas turbines engines, due to its potential reduction of NOX and particulate emissions along with the absence of SO2 emissions. In this work, methanol production from the syngas generated by a three-reactors chemical looping process is investigated by mass and energy balances. The cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by the injection of a reducing agent; an oxidizer reactor, where FeO reacts with CO2 and H2O to produce a syngas; an air reactor, where Fe3O4 is regenerated to Fe2O3 by ambient air. The produced syngas is then sent to a methanol synthesis plant. Several syngas compositions deriving from different CO2/(H2O+ CO2) molar fractions (1–3) at the oxidizer inlet are taken into account. The resulting methanol flow rates are almost equal in all investigated configurations (about 0.35 t/h). From an energy standpoint, the required electric power is greater for higher hydrogen mole fractions in the syngas. However, the case with 75% H2 content is characterized by the greatest methanol yield (12.6%), carbon efficiency (23%) and a high feed/recirculation ratio (0.80), thus representing the most indicated configuration among the investigated ones. Finally, by burning methanol in a gas turbine, the total CO2 emissions are halved with respect to the case without the system (if the CO2 associated with biogenic carbon in the reducer reactor is considered as net-zero).

Pelletized SiO2-supported La0.5Ba0.5FeO3 for conversion of CO2 to CO by a reverse water-gas shift chemical looping process

Perovskite oxides, such as La0.5Ba0.5FeO3 (LBF), are promising materials for converting CO2 to CO through low-temperature reverse water–gas shift chemical looping (RWGS-CL). To transition toward industrialization, this study focused on forming perovskite-oxide/silica composite pellets (25 wt% LBF) with sufficiently high crushing strength, with materials prepared by extrusion and tableting methods. X-ray fluorescence (XRF) and diffraction (XRD) confirmed that the resulting material is 26.6 wt% LBF on SiO2 with a combined structure of LBF and SiO2 components. Temperature-programmed reduction (TPR) and oxidation (TPO) experiments revealed that CO2 is converted to CO at 550 °C by LBF/SiO2 pellets, higher than LBF by 50 °C. CO2 chemisorption was determined to be 62.2 μmol/gLBF. DRIFTS-MS experiments confirmed that adsorbed CO2 is dissociated to CO. High material stability is proven by long-term RWGL-CL experiments combined with XRD and XPS. The CO2 to CO yields were 2.21, 2.41, and 2.35 mmol/gLBF of 10 mm tableting pellets, 6 mm tableting pellets, and extrusion pellets, respectively. Deactivated pellets are able to be regenerated by air thermal treatment following intentional reduction. All pellets showed stable redox properties in 50 cycles of semi-batch reactor experiments, indicating that LBF/SiO2 pellets are candidate materials for further scale-up evaluation.

Clean Syngas and Hydrogen Co-Production by Gasification and Chemical Looping Hydrogen Process Using MgO-Doped Fe2O3 as Redox Material

Gasification converts biomass into syngas; however, severe cleaning processes are necessary due to the presence of tars, particulates and contaminants. The aim of this work is to propose a cleaning method system based on tar physical adsorption coupled with the production of pure H2 via a chemical looping process. Three fixed-bed reactors with a double-layer bed (NiO/Al2O3 and Fe-based particles) working in three different steps were used. First, NiO/Al2O3 is used to adsorb tar from syngas (300 °C); then, the adsorbed tar undergoes partial oxidization by NiO/Al2O3 to produce CO and H2 used for iron oxide reduction. In the third step, the reduced iron is oxidized with steam to produce pure H2 and to restore iron oxides. A double-layer fixed-bed reactor was fed alternatively by guaiacol and as tar model compounds, air and water were used. High-thermal-stability particles 60 wt% Fe2O3/40 wt% MgO synthetized by the coprecipitation method were used as Fe-based particles in six cycle tests. The adsorption efficiency of the NiO/Al2O3 bed is 98% and the gas phase formed is able to partially reduce iron, favoring the reduction kinetics. The efficiency of the process related to the H2 production after the first cycle is 35% and the amount of CO is less than 10 ppm.

A novel Ni–MoCxOy interfacial catalyst for syngas production via the chemical looping dry reforming of methane

<h2>Summary</h2> Modulating the oxygen-metal interface that enables efficient and selective C–H activation remains challenging. Herein, we present a novel MoC_xO_y oxygen carrier for syngas production via the chemical looping CH₄–CO₂ reforming (CL-DRM) reaction. Molybdenum carbide additive induces the re-dispersion of Ni particles from Al₂O₃ surface to α-MoC driven by the strong interaction between Ni and α-MoC. A dynamic structure transformation between MoC_x and MoC_xO_y occurs and new Ni–MoC_xO_y interfaces form during the redox cycling, which is discovered to be crucial for the low-temperature CH₄ activation using surface construction experiments and <i>in-situ</i> spectroscopic methods. As a result, Ni–(α-MoC)/Al₂O₃ exhibits near 100% selectivity to syngas with a H₂/CO ratio of 2:1 at 500°C, which is a significantly lower temperature than that of conventional systems. This study first employs molybdenum carbide as an oxygen storage material (OSM) in CL-DRM reaction, paving the way of utilizing transition metal carbides as OSMs in chemical looping processes.

Defect Chemistry and Chemical Looping Performance of La1-xMxMnO3 (M = Sr, Ca, (x = 0-0.5)) Perovskites.

La1−xMxMnO3 (M = Sr, Ca, (x = 0–0.5)) materials of the perovskite structure are synthesized by a co-precipitation method. They are subsequently investigated for their performance in a chemical looping process (fuel CH4) using thermogravimetric analysis with simultaneous reaction. The goal of this work is to determine the relation between the defect chemistry of the materials and their behavior in chemical looping processes. A defect model is proposed that provides an explanation of the dependency of the Oxygen Transfer Capacity and of the CO2/CO selectivity on composition. It appeared that the fuel may react with various types of oxygen available within the materials, generated by different mechanisms. The relative amounts of each oxygen type determine the CO2/CO selectivity and depend on the material composition as well as on the partial pressure of oxygen used for regenerating the materials.

Density Functional Theory Study on the Reduction of NO by CO Over Fe3O4 (111) Surface

ABSTRACT 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.

Review of chemical looping process for carbonaceous feedstock Conversion: Rational design of oxygen carriers

• Metal oxides as oxygen carriers and corresponding performances in the chemical looping partial oxidation process for hydrogen/syngas production are summarized. • The regulation strategies for further improving reactivity and cycling stability are discussed. • The ion diffusion and surface reactions are anatomized via theory calculations and characterizations. The chemical looping partial oxidation (CLPO) process as a technology of chemical looping process (CLP) is recognized as a potential strategy for the efficient and clean conversion of fuels into syngas/H 2 . Herein, in view of the importance of low-cost high-performance metal oxides as oxygen carriers (OCs) for this conversion, we systematically review the classification and CLPO applications of such OCs and discuss the improvement of OC reactivity and stability via the creation of metal–metal or metal–support synergism, the generation of oxygen vacancies, and the enhancement of deactivation resistance. Further, we present the results of theoretical and experimental characterizations probing ion diffusion and surface reactions to provide insights into the related reaction mechanisms and touch on the challenges and opportunities of developing metal oxides with excellent reactivity and long-term cycling stability in CLP. Thus, this review facilitates the design and performance regulation of OCs for future energy conversion systems.

Oxygen separation via chemical looping of the perovskite oxide Sr0.8Ca0.2FeO3 in packed bed reactors for the production of nitrogen from air

A redox chemical looping process is investigated as an add-on deoxygenation unit for the production of high-purity nitrogen from air using pressure swing adsorption systems. A material screening study indicated the non-stoichiometric perovskite oxide Sr0.8Ca0.2FeO3−δ as a promising candidate redox material with fast kinetics and a 75% greater gravimetric oxygen capacity compared to state-of-the-art SrFeO3 at the desired process conditions. Granules of Sr0.8Ca0.2FeO3 were manufactured and characterised according to their thermodynamic and kinetic redox properties. A lab scale packed-bed reactor was experimentally tested as proof-of-concept and used to validate a convection–diffusion model of mass transfer within the reactor. The model was further applied for scaling up to a production of 1000 Nm3h−1 of high-purity nitrogen. The results indicate good performance of the packed-bed configuration and a favourable energy demand compared with existing nitrogen production technologies. The proposed technology could greatly extend the useable oxygen impurity range of pressure swing adsorption systems for nitrogen production.

Iron-Poor Ferrites for Low-Temperature CO2 Conversion via Reverse Water–Gas Shift Thermochemical Looping

CO2 utilization via the reverse water–gas-shift (RWGS) reaction for the production of CO and then long-chain hydrocarbons is a potentially scalable method to mitigate rising global CO2 emissions, if appreciable CO yields can be achieved at low reaction temperatures. Here, we report that Fe0.35Ni0.65Ox achieves, to the best of our knowledge, a record high experimentally measured CO yield of 80 mL CO/gMOx/cycle at low reaction temperatures (500 °C for both oxidation and reduction steps) in a chemical looping (CL) process. This reported yield is substantially higher than previously reported RWGS-CL metal oxides at 500 °C. We identified the composition of the metal oxide Fe0.35Ni0.65Ox using the Calculation of Phase Diagrams (CALPHAD) methodology to screen and filter through many combinations of metal oxides. We then experimentally tested this Fe0.35Ni0.65Ox metal oxide for chemical looping RWGS and utilized X-ray characterization techniques and CALPHAD to find that a spinel to metallic phase transition gives Fe0.35Ni0.65Ox its noteworthy CO yield and oxygen capacity. We emphasize the importance of thermodynamics calculations and CALPHAD screening to quickly search through the vast design space of metal oxides to greatly reduce the amount of necessary experimentation.

Application of the magnetic material in incineration bottom ash as oxygen carrier for biomass chemical looping gasification

Concerns about the cost of oxygen carrier (OC) manufacturing and the promotion of resource recovery have led to increasing research interest in the application of solid waste as an alternative to OC for chemical looping process (CLP). Magnetic materials in municipal solid waste incineration bottom ash (denoted as IMF) with ferrous metals as the main component were investigated as potential OCs for biomass chemical looping gasification (BCLG). An iron-based synthetic OC (called syn-75) was prepared for comparative studies. Thermogravimetric analysis (TGA) of IMF coupled chemical looping combustion (CLC) of CO in a fluidized bed confirmed its excellent reactivity and stability. Of all the IMFs tested (IMF-2 to IMF-6 classified by particle size), IMF-4 exhibited the highest CO combustion efficiency (up to 92 %) due to its highest iron content. However, reduction rates do not always follow the order of iron content. For instance, IMF-4 (Fe2O3%=73.3 %) illustrated better performance than syn-75 (Fe2O3 % = 78.0 %) in syngas production from biomass chemical looping gasification (BCLG), suggesting that other active phases in IMF-4 may be involved to exert a synergistic effect, which can promote deeper reduction of iron oxides, echoed from X-ray diffractometry (XRD) results. In addition, IMFs demonstrate limited surface coking throughout the BCLG process. These findings mainly endorse IMF as a promising natural OC for BCLG.

Low-Temperature Light-off MnOx -Na2 WO4 -Based Catalysts: A Step Forward to OCM Process Industrialization.

Oxidative coupling of methane (OCM) catalyzed by MnOx -Na2 WO4 -based catalysts has great industrial potential to convert CH4 directly to C2-3 products, but the high light-off temperature is a big challenge to OCM commercialization. The reaction mechanism studies disclosed that O2 /CH4 -activation relevant "Mn2+ ↔Mn3+ " redox cycle is tightly linked with the catalyst light-off. One concept is thus put forward that the OCM light-off temperature could be lowered once a "Mn2+ ↔Mn3+ " redox cycle was established to be triggered at low temperature over MnOx -Na2 WO4 -based catalysts. The relevant studies in recent years are reviewed, showing that the establishment of low-temperature light-off "Mn2+ ↔Mn3+ " redox cycle over the MnOx -Na2 WO4 -based catalysts indeed works effectively toward a low-temperature light-off OCM process. Moreover, three perspectives for the OCM industrialization are discussed based on this concept, including monolithic catalyst, fluidized-bed method and chemical-looping process.

Chemical looping technology – a manifestation of a novel fluidization and fluid-particle system for CO2 capture and clean energy conversions

Chemical looping is broadly defined to represent processes that use chemical intermediates to decompose a reaction into two or more sub-reaction steps. Metal oxides are the typical chemical intermediates used for the chemical looping reactions although other metal derivatives are also used. Based on its intended applications, chemical looping encompasses calcium looping for CO 2 capture and redox looping for clean energy conversion applications. The redox looping has a longstanding history and has been demonstrated at multiple scales under various operating conditions since its conceptual inception about 120 years ago. Even with such extensive and prolonged efforts, redox looping is yet to be realized sustainably at a commercial level, while the calcium looping has been demonstrated for commercial applications. With growing concerns of climate change due to emissions of industrial greenhouse gases, efforts in developing redox looping processes as a promising fossil energy conversion technology with CO 2 emission control have been invigorated since the beginning of the 21st century. Metal oxide reaction engineering and particle science and technology have been the two enabling technical thrust areas, pivotal to advance the chemical looping concept to industrial practice. This article highlights some salient features of the chemical looping processes including a description of their historical development and illustration of the material screening and synthesis of oxygen carrier particles along with the representative process operational behavior. Recognizing that the configuration of chemical looping systems in their key operational scheme is established on the framework of circulating fluidized bed (CFB) systems, this article emphasizes the relevant characteristics of fluidization and fluid-particle systems with which the chemical looping technology is conducted. Both the fundamental and applied aspects of chemical looping processes and their associated CFB operation are discussed. • Chemical looping has garnered significant attention due to its inherent advantages. • The development of processes has been over 120 years. • Material screening and synthesis of oxygen carrier is the core. • System is related to many characteristics of fluidization and fluid-particle topic. • Fundamental and applied aspects of chemical looping processes are discussed.

Precursor engineering of hydrotalcite-derived redox sorbents for reversible and stable thermochemical oxygen storage

Chemical looping processes based on multiple-step reduction and oxidation of metal oxides hold great promise for a variety of energy applications, such as CO2 capture and conversion, gas separation, energy storage, and redox catalytic processes. Copper-based mixed oxides are one of the most promising candidate materials with a high oxygen storage capacity. However, the structural deterioration and sintering at high temperatures is one key scientific challenge. Herein, we report a precursor engineering approach to prepare durable copper-based redox sorbents for use in thermochemical looping processes for combustion and gas purification. Calcination of the CuMgAl hydrotalcite precursors formed mixed metal oxides consisting of CuO nanoparticles dispersed in the Mg-Al oxide support which inhibited the formation of copper aluminates during redox cycling. The copper-based redox sorbents demonstrated enhanced reaction rates, stable O2 storage capacity over 500 redox cycles at 900 °C, and efficient gas purification over a broad temperature range. We expect that our materials design strategy has broad implications on synthesis and engineering of mixed metal oxides for a range of thermochemical processes and redox catalytic applications.

Hydrogen and ammonia production from low-grade agricultural waste adopting chemical looping process

Chemical looping hydrogen production (CLH2) is a new technology used to produce hydrogen (H2) from fuels while separating CO2 simultaneously. This research aims to build an integrated conversion system of rice husks, a high energy potential biomass, to H2 with high energy efficiency. The developed system mainly consists of superheated steam drying, steam gasification, chemical looping, and Haber-Bosch processes. Three different systems are developed and compared. The first and second systems employ direct chemical looping (DCL) using H2O and CO2 as gas enhancers for the reducer, respectively, while the third system adopts syngas chemical looping (SCL). Exergy recovery and process integration technologies are adopted to enhance energy and exergy efficiencies. A mixture of Fe2O3 and Al2O3 is used as oxygen and heat carriers in the CLH2 module. Process modeling, optimization, and evaluation of both energy and exergy efficiencies are conducted using Aspen Plus. Some crucial operating parameters, including reactor temperature, pressure, the oxygen carrier flow rate, and gas enhancer flow rate, are selected to evaluate the performance of the system, especially in terms of efficiency. The highest achievable H2, NH3, and net power efficiencies are 51.8%, 38.09%, 0.65%, respectively, when DCL is adopted with CO2 as a gas enhancer during the reduction.

Synthetic-Gas Production through Chemical Looping Process with Concentrating Solar Dish: Temperature-Distribution Evaluation

The energy crisis and the adaptation of the global energy structure promote the development of renewable energies, in particular solar energy, also for syngas production. In this work, attention was focused on solar devices, necessary to provide high-temperature heat for the reduction reaction of metal oxides involved in the chemical looping driven by solar energy. Thermochemical processes for synthetic-gas production and CO2 sequestration were investigated using a concentrating solar thermal system. This paper proposes a useful forecasting model of the receiver temperature to make a realistic estimate of the system’s producibility for the different periods of the year. The model proposed was validated in the winter season, and the predicted temperature varied below 5% considering the real experimental data (442–472 °C). The validated model was used to evaluate the temperature receiver in spring and in summer, when the thermal level is reliable for thermochemical processes. From the spring season until the completion of the summer season, optimum conditions inside the receiver were reached (above 1000 °C). These preliminary findings could be used for the development of large-scale production systems.