Thermochemical Applications Research Articles

Ca-based materials derived from calcined cigarette butts for CO2 capture and thermochemical energy storage

Cigarette butts (CBs) are one of the most common types of litter in the world. Due to the toxic substances they contain, the waste generated poses a harmful risk to the environment, and therefore there is an urgent need for alternative solutions to landfill storage. Thus, this work presents a possible revalorization of this waste material, which implies interesting environmental benefits. CBs were used as sacrificial templates for the preparation of CaO-based materials by impregnation with calcium and magnesium nitrates followed by flaming combustion. These materials presented enhanced porosity for their use in the Calcium Looping process applied either to thermochemical energy storage or CO2 capture applications. The influence of the concentration of Ca and Mg in the impregnating solutions on the multicycle reactivity of the samples was studied. An improved multicycle performance was obtained in terms of conversion for both applications.

Influence of Sr-Site Deficiency, Ca/Ba/La Doping on the Exsolution of Ni from SrTiO3

Cermet catalysts formed via exsolution of metal nanoparticles from perovskites promise to perform better in electro- and thermochemical applications than those synthesized by conventional wet-chemical approaches. However, a shortage of robust material design principles still stands in the way of widespread commercial adoption of exsolution. Working with Ni-doped SrTiO3 solid solutions, we investigated how the introduction of Sr deficiency as well as Ca, Ba, and La doping on the Sr site changed the size and surface density of exsolved Ni nanoparticles. We carried out exsolution on 11 different compositions under fixed conditions. We elucidated the effect of A-site defect size/valence on nanoparticle density and size as well as the effect of composition on nanoparticle immersion and ceramic microstructure. Based on our experimental results, we developed a model that quantitatively predicted a composition’s exsolution properties using density functional theory calculations. The model and calculations provide insights into the exsolution mechanism and can be used to find new compositions with high exsolution nanoparticle density.

Experimental evaluation of an indirectly-irradiated packed-bed solar thermochemical reactor for calcination–carbonation chemical looping

The two-step calcium oxide based calcination–carbonation cycle is studied for carbon dioxide capture and solar thermochemical energy storage applications. An indirectly-irradiated packed-bed solar thermochemical reactor is experimentally evaluated using simulated high-flux solar irradiation provided by a multi-source solar simulator. Experimental runs include a single calcination reaction step as well as single and multiple (up to four) consecutive calcination–carbonation cycles. The samples are characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The reactor temperature peaked at 1,035°C. The average solar-to-chemical conversion efficiency, defined as the ratio of heat consumed by the reaction to radiant heat supplied to the reactor, was found to be between approximately 1.3% and 8.6% for the five performed experimental runs. The necessary advancements to the presented reactor design identified during the experimental campaign include improvements in thermomechanical characteristics of ceramic and metallic parts of the reactor to prevent fast mechanical and chemical degradation, application of more robust high-temperature reaction chamber seals, and optimisation of reactor geometry and gas flow patterns towards spatially more uniform thermal conditions and chemical reaction rates.

A Review of Oxygen Carrier Materials and Related Thermochemical Redox Processes for Concentrating Solar Thermal Applications.

Redox materials have been investigated for various thermochemical processing applications including solar fuel production (hydrogen, syngas), ammonia synthesis, thermochemical energy storage, and air separation/oxygen pumping, while involving concentrated solar energy as the high-temperature process heat source for solid-gas reactions. Accordingly, these materials can be processed in two-step redox cycles for thermochemical fuel production from H2O and CO2 splitting. In such cycles, the metal oxide is first thermally reduced when heated under concentrated solar energy. Then, the reduced material is re-oxidized with either H2O or CO2 to produce H2 or CO. The mixture forms syngas that can be used for the synthesis of various hydrocarbon fuels. An alternative process involves redox systems of metal oxides/nitrides for ammonia synthesis from N2 and H2O based on chemical looping cycles. A metal nitride reacts with steam to form ammonia and the corresponding metal oxide. The latter is then recycled in a nitridation reaction with N2 and a reducer. In another process, redox systems can be processed in reversible endothermal/exothermal reactions for solar thermochemical energy storage at high temperature. The reduction corresponds to the heat charge while the reverse oxidation with air leads to the heat discharge for supplying process heat to a downstream process. Similar reversible redox reactions can finally be used for oxygen separation from air, which results in separate flows of O2 and N2 that can be both valorized, or thermochemical oxygen pumping to absorb residual oxygen. This review deals with the different redox materials involving stoichiometric or non-stoichiometric materials applied to solar fuel production (H2, syngas, ammonia), thermochemical energy storage, and thermochemical air separation or gas purification. The most relevant chemical looping reactions and the best performing materials acting as the oxygen carriers are identified and described, as well as the chemical reactors suitable for solar energy absorption, conversion, and storage.

First experimental characterization of CaCl2 coated heat exchanger for thermochemical heat transformer applications in industrial waste heat recovery

This study aims at evaluating the performance of a heat exchanger coated with CaCl2 (PVA polyvinyl alcohol used as binder) for Thermochemical Heat Transformers (THT) applications in industrial waste heat recovery.For this purpose, an experimental test bench has been built allowing to test operating temperatures up to 160 °C. A model heat exchanger plate is used to test two configurations: a thick layer of CaCl2 to model a packed bed reactor (used as reference) and a CaCl2-PVA deposit to model a coated reactor.For the packed bed configuration, results comparable to that of the literature are obtained with a specific power of 180 W/kg obtained for a temperature lift of 60 K. A high sensitivity to temperature lift is identified with a decrease of the specific power down to 38 W/kg for a lift of 77 K. The coated heat exchanger configuration achieves significantly higher performance with a specific power up to 341 W/kg for a temperature lift of 63 K. However, the analysis of the repeatability tests highlights a rapid change in temperature profiles highlighting a change in properties of the CaCl2/PVA compound material. Next steps will consist in enhanced material formulation and change in deposit protocol and to move to work at small reactor scale to assess system performance.

Challenges and Opportunities in Engineering the Electronic Structure of Single-Atom Catalysts.

Controlling the electronic structure of transition-metal single-atom heterogeneous catalysts (SACs) is crucial to unlocking their full potential. The ability to do this with increasing precision offers a rational strategy to optimize processes associated with the adsorption and activation of reactive intermediates, charge transfer dynamics, and light absorption. While several methods have been proposed to alter the electronic characteristics of SACs, such as the oxidation state, band structure, orbital occupancy, and associated spin, the lack of a systematic approach to their application makes it difficult to control their effects. In this Perspective, we examine how the electronic configuration of SACs can be engineered for thermochemical, electrochemical, and photochemical applications, exploring the relationship with their activity, selectivity, and stability. We discuss synthetic and analytical challenges in controlling and discriminating the electronic structure of SACs and possible directions toward closing the gap between computational and experimental efforts. By bringing this topic to the center, we hope to stimulate research to understand, control, and exploit electronic effects in SACs and ultimately spur technological developments.

Pyrolysis of tea and coffee wastes: effect of physicochemical properties on kinetic and thermodynamic characteristics

Physicochemical properties, kinetic pyrolysis and thermodynamic study of spent green tea, pure spent coffee grounds, spent coffee grounds blended with 50% torrefied barley and coffee husk were experimentally investigated using thermogravimetric analysis under an inert atmosphere to evaluate their thermochemical application. Five isoconversional methods were applied to determine effective activation energy (Ea) of the pyrolysis processes. All methods showed good agreement by determining fluctuating Ea values (150–500 kJ mol−1). Complex Ea profiles with conversion were divided into four stages corresponding to thermal degradation of main biomass constituents (extractives, hemicellulose, cellulose and lignin), indicating that extractives decomposition was the least demanding reaction while lignin decomposition was the most demanding. The kinetic process was verified by reconstruction according to the Friedman parameters. The thermodynamic parameters were evaluated to determine the energy demand and efficiency throughout the process. The values obtained for physicochemical properties such as volatile matter (> 68%) and higher heating value (> 17 MJ kg−1), average Ea (223–319 kJ mol−1) and significant energy efficiency implied that these types of biomass waste have significant reactivity and consequently the highest potential for the production of bioenergy and a range of high-value chemicals and materials.

MgCl2-MXene based nanohybrid composite for efficient thermochemical heat storage application

Thermochemical heat storage is a practical approach for overcoming the challenge in solar energy applications. Herein, we synthesize a novel MgCl2/MXene (Ti3C2Tx) composite sorbent by impregnation method for low-temperature thermochemical heat storage application. Various techniques, including Thermogravimetric coupled with Differential Scanning Calorimetric (TG-DSC), X-Ray, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were applied to characterize the mechanical and thermal properties of MgCl2/MXene composites. The result showed that Ti3C2Tx possess a larger specific surface area and the hydrophilic groups allow maximum MgCl2 adsorption without structural distortion. The TG-DSC studies showed that the fourth DSC peak of MgCl2 (181.33 °C) is shifted in composites MX/Mg 15 % (159.63 °C) and MX/Mg 10 %, (141.67 °C) toward lower dehydration temperature. The cyclicability study demonstrated that in the 10 consecutive rehydration cycles, MgCl2 shows 45 % decrease in the enthalpy, while Mg/MX 10 % and Mg/MX 15 % composites record 4 % and 10 % decrease, respectively. Water uptake kinetics highlighted that at 85 % RH, the highest water sorption was recorded for Mg/MX 15 % where it absorbs 2.21 g/g mass. The energy storage density result reveals that the maximum loading rate of MgCl2·6H2O reaches 97.6 wt% for Mg/MX 15 % showed the highest enthalpy 2227 J/g at 85 % RH. Therefore, all the results indicate that MXene-based salt composites play an important role in thermochemical heat storage application, leading to a potential candidate for long-term heat storage.

A and B site Co-doping of CaMnO3: a route to enhanced heat storage properties

By co-doping CaMnO3 with La and Fe (LaxCa1−xMn1−yFeyO3), it is possible to tailor the material thermodynamics, reduction extent, together with operating temperature range for thermochemical heat storage application.

Design of metal hydride reactor for medium temperature thermochemical energy storage applications

Design of metal hydride reactor for medium temperature thermochemical energy storage applications

Nanoengineering of MgSO4 nanohybrid on MXene substrate for efficient thermochemical heat storage material

2D MXene nanohybrid is a next-generationenergy-storage material. Here, we demonstrate a novel thermochemical heat storage material using magnesium sulfate heptahydrate/titanium carbide and MXene (MgSO4/Ti3C2Tx) with improved hydration/dehydration enthalpy, superior thermal conductivity, good cyclic ability, maximum water sorption performance, and larger thermal energy conversion. The TG-DSC fitted with a Wetsys flow humidity generator shows outstanding thermal performance and larger hydration for MgSO4/Ti3C2Tx (1963 J/g) and dehydration (1861 J/g) enthalpies with 5 % fluctuation as compared to pure MgSO4 (38 %). The cyclicability results showed that MgSO4/MXene has good stability of TCMs across several charging/discharging cycles (up to 20 cycles), confirming that the MXene matrix avoids hydrated salt agglomeration and displays an average of 12 % fluctuation. This illustrates that prepared composites potentially improve storage performance. The MgSO4/Ti3C2Tx nanohybrid exhibit a better radiation absorption and 45 % longer backup than the pristine MgSO4 salt. TEM study revealedthat maximum salt contents can be located in the interlayer gaps, predicted sheets thickness of the MgSO4/MXene layer to be 16 Åand the Ti3C2Tx layers to be 7.3 Å. Nanohybrid has stronger water sorption than MgSO4 due to MXene nanosheets larger interlayer gaps. The results conclude that the resultant MgSO4/MXene has excellent long-term thermal energy storage, photo-to-thermal conversion and larger water sorption performance. The study validates the effectiveness of nanohybrid material as a promising candidate for thermochemical heat storage applications and set to pave the way to explore other hybrid systems to improve the efficiency of thermochemical energy storage systems.

Investigation on the structure evolution and thermochemical conversion characteristics of lignite after different pretreatment

Despite the importance of hydrothermal treatment dewatering (HTD) as a means of utilizing lignite efficiently and cleanly, there have been relatively few studies on its downstream combustion and gasification characteristics. Particularly, what kind of thermochemical process is more favourable, which has not been investigated. At the same time, conventional flue gas treatment (FTD) is a relatively mature lignite pretreatment technology and is selected for comparative analysis. The present study examined the thermochemical characteristics and physicochemical structure of upgraded lignite by HTD and FTD processes. A combined process with great practical application foreground is proposed. Results showed that both HTD and FTD processes can profit dehydration and deoxidation of lignite. HTD process has a better effect in terms of dehydration because of the high amount of O-containing functional group removal. In terms of aromaticity and coal-rank, upgraded lignite treated with HTD is inferior to that treated with FTD. The comprehensive combustion characteristics indexes of upgraded lignite are increased by HTD and decreased by FTD, indicating that the HTD process promotes the combustion reactivity of upgraded lignite. HTD and FTD processes both decrease the gasification reactivity of upgraded lignite. Compared with the HTD, the FTD process is more likely to reduce the gasification rate. Compared with effective coal rank and the concentration of oxygen functional groups, the revived microstructure of upgraded lignite has a greater impact on combustion and gasification reactivity. The HTD process was more prone to the breakdown of chemical groups rather than crosslinking. These findings are consistent with the results of kinetic analysis. In general, compared with FTD, upgraded lignite by HTD process is in favor of downstream thermochemical application. The comparison of different thermochemical characteristics, including combustion, gasification, pyrolysis, are analyzed. The effective application with combined process of HTD and pyrolysis and waste water coke slurry have industrial application prosperity.

Chemical Looping Reforming with Perovskite-Based Catalysts for Thermochemical Energy Storage

The performance of a perovskite-based oxygen carrier for the partial oxidation of methane in thermochemical energy storage applications has been investigated. A synthetic perovskite with formula La0.6Sr0.4FeO3 has been scrutinized for Chemical Looping Reforming (CLR) of CH4 under fixed-bed and fluidized-bed conditions. Temperature-programmed reduction and oxidation steps were carried out under fixed-bed conditions, together with isothermal reduction/oxidation cycles, to evaluate long-term perovskite performance. Under fluidized-bed conditions, isothermal reduction/oxidation cycles were carried out as well. Results obtained under fixed-bed and fluidized-bed conditions were compared in terms of oxygen carrier reactivity and stability. The oxygen carrier showed good reactivity and stability in the range 800–1000 °C. An overall yield of 0.6 Nm3 of syngas per kg of perovskite can be reached per cycle. The decomposition of CH4 catalyzed by the reduced oxide can also occur during the reduction step. However, deposited carbon is easily re-gasified through the Boudouard reaction, without affecting the reactivity of the material. Fluidized-bed tests showed higher conversion rates compared to fixed-bed conditions and allowed better control of CH4 decomposition, with a H2:CO ratio of around 2 and CO selectivity of around 0.8. However, particle attrition was observed and might be responsible for a loss of the inventory of up to 9%w.

Preparation and characterization of metal organic framework based composite materials for thermochemical energy storage applications

Using the chromium-based metal organic framework (MIL-101(Cr)) as a host matrix two composite materials were synthesized with Na2S2O3 (10 and 30% w/w) towards thermochemical energy storage (TCES) applications. The prepared composites were characterized using multiple techniques viz. Powder X-ray Diffractometer (PXRD), Dynamic Vapour Sorption (DVS) analyser and Thermogravimetric-Differential Scanning Calorimeter (TG-DSC), etc. The prepared composites were found to exhibit octahedral structures with salt in the pores. The MIL-101(Cr) with 30% Na2S2O3 (w/w) was estimated to yield a high energy storage density (1099.5 J/g) due to its high water vapour adsorption capacity. These composites were subjected to ten continuous adsorption and desorption processes using the DVS analyser to determine their stability for intended applications. The synthesized composites offered good water vapour adsorption capacity, energy storage density, and excellent stability with very little mass variations across the tested cycles. Based on the experimental results, the authors recommend the composite sorbents for TCES applications.

Oxidative torrefaction and torrefaction-based biorefining of biomass: a critical review

Torrefaction is a vital pretreatment technology for thermochemical biorefinery applications like pyrolysis, gasification, and liquefaction. Oxidative torrefaction, an economical version of torrefaction, has recently gained much attention in the renewable energy field. Recent literature on inert and oxidative torrefaction was critically reviewed in this work to provide necessary guidance for future research and commercial implementations. The critical performance parameters of torrefaction for thermochemical biorefinery applications, such as solid yield, energy yield, carbon enhancement, higher heating value (HHV) enhancement, and energy-mass co-benefit index (EMCI), were also analyzed. Agricultural waste, woody biomass, and microalgae were considered. The analysis reveals that woody biomass could equally benefit from oxidative or inert torrefaction. In contrast, inert torrefaction was found more suitable for agricultural wastes and microalgae. Using flue gas as the oxidative torrefaction medium and waste biomass as the feedstock could achieve a circular economy, improving the sustainability of oxidative torrefaction for thermochemical biorefineries. The significant challenges in oxidative torrefaction include high ash content in torrefied agricultural waste, the oxidative thermal runaway of fibrous biomass during torrefaction, temperature control, and scale-up in reactors. Some proposed solutions to address these challenges are combined washing and torrefaction pretreatment, balancing oxygen content, temperature, and residence time, depending on the biomass type, and recirculating torrefaction gases.

Optical design optimization for improved lamp-reflector units in high-flux solar simulators.

High flux solar simulators are artificial solar facilities developed to imitate the on-sun operations of concentrating solar power technologies but under a well-controlled lab-scale environment. We report the optical enhancement of different high flux solar simulators for solar thermal and thermochemical applications. The solar simulator enhancement is numerically conducted by optimizing the geometry of ellipsoidal reflectors at focal lengths of 1600, 1800, and 2000 mm. The Monte Carlo ray-tracing technique is employed to evaluate the optical performance of different reflector designs. The typical seven-lamp solar simulator arrangement in hexagonal configuration is modeled to analyze the optical performance at different focal lengths. In addition, different xenon arc lamps are modeled with rated powers of 3000, 4000, 4500, and 5000 W for assessing the radiative flux characteristics of the proposed solar simulators. After the optimization, theoretical results show that peak fluxes and radiative powers of 7.2-14.3MW/m2 and 5.06-10.4 kW, respectively, can be achieved with the proposed designs of solar simulators for the different rated powers. Compared with a commercial reflector, theoretical peak flux and power can be improved up to 36% and 17.9%, respectively, with the proper combination of lamp-reflector units. We provide design alternatives to select a more suitable light source at low-rated powers (≤5000W) and different focal lengths of the reflector, which simplifies the complexity of the design and improves the performance of solar simulators.

Thermochemical energy applications of green transition metal doped MIL–100(Fe)

Recently metal organic frameworks (MOFs), already known as adsorbent materials, have gained increasing research interest in thermal energy storage and conversion. MOF-water working pairs have been envisaged to provide the next revolutionary advancement in the existing sorption-based thermal energy storage and conversion systems. Herein, a promising MOF for high water sorption, MIL–100(Fe), and its transition metal-doped (Ni2+ and Co2+) derivatives are produced following a green synthesis procedure. The synthesized materials were tested in water sorption measurements using a thermogravimetric technique. The experimentally obtained adsorption data were correlated with the Sun-Chakraborty adsorption isotherm model. As an example of thermal energy conversion, an adsorption chiller is considered, and hence cooling cycles were drawn using the sorption data. The cooling cycles revealed that the nickel-doped MIL–100(Fe) demonstrates the highest value of the specific cooling effect (450.79 kJ kg−1) among the studied MOFs. Inverse gas chromatography technique was employed to investigate the surface free energy of the parent and doped MIL–100(Fe) MOFs. It was found that nickel-doped MIL–100(Fe) had the highest total surface free energy of 105.41 mJ m−2. Surfaces’ Lewis acid-base activities and the work of cohesion and adhesion (towards water molecules) were investigated. The surfaces’ properties were correlated with the water adsorption isotherms, which can provide crucial information for developing optimal adsorbents targeting water as the adsorbate for an efficient and effective thermal energy storage and conversion system.

Novel Synthesis and Structural Investigations of ZnSO4/MgCl2 Composite Hydrated Salt for Enhanced Thermochemical Heat Storage Applications

Novel Synthesis and Structural Investigations of ZnSO4/MgCl2 Composite Hydrated Salt for Enhanced Thermochemical Heat Storage Applications

Fast Redox Kinetics in SrCo1−xSbxO3−δ Perovskites for Thermochemical Energy Storage

The use of perovskite materials for thermochemical energy storage and oxygen separation has been gaining momentum in recent years due to their ability to topotactically exchange large volumes of oxygen, and their chemical and structural flexibility. B-site substituted SrCoO3-δ derivatives have previously been investigated as promising materials for intermediate temperature solid oxide fuel cell cathodes due to the stabilization of a 3 C perovskite structure with high electronic and ionic conductivity that allows large oxygen storage capabilities. Here, antimony-substituted strontium cobalt oxides are investigated and identified as new candidate materials for thermochemical oxygen separation applications. In this work we shed light on the exceptional redox kinetics and cyclability of antimony-substituted variants undergoing oxygen exchange at intermediate temperatures (500 to 800 °C). Through the use of density functional theory and isothermal gas atmosphere switching, we demonstrate how the inductive effect of the more electronegative antimony dopants in the Co position, facilitates the kinetics of metal oxide oxidation, whilst hindering reduction reactions. SrCo0.95Sb0.05O3−δ was identified to isothermally evolve 3.76 cm3 g−1 of oxygen at 500 °C and calculated to produce up to 10.44 cm3 g−1 under temperature-swing reaction configurations aligning with previously reported materials.

Exploration of Highly Porous Biochar Derived from Dead Leaves to Immobilize LiOH·H2O Nanoparticles for Efficient Thermochemical Heat Storage Applications

The inadequate utilization of low‐grade energy from industrial waste heat and solar energy calls for an efficient thermochemical heat storage material. The fabrication of a low‐cost but highly efficient composite comprising highly porous biochar and LiOH·H2O nanoparticles for heat storage applications is reported. The biochar is prepared by the KOH‐assisted pyrolysis of dead banyan leaves, and its microstructure and surface properties can be finely tuned by varying the KOH‐to‐biomass ratio. Such biochar can be mediated to possess a large specific surface area and total pore volume reaching as high as 1255.03 m2 g−1 and 3.65 cm3 g−1, respectively, superior to most previously reported biochar/biocarbon derived from different kinds of waste biomass. Besides, adequate functional groups and a hierarchical porous structure consisting of micropores and mesopores are demonstrated in the prepared biochar. The subsequent hydrothermal reaction with a short duration yields a biochar‐LiOH·H2O composite, where LiOH·H2O can be homogeneously immobilized with a nanoscale size within the porous biochar matrix. Thus, an enormous biochar/LiOH·H2O nanoparticles interface can be obtained, resulting in fast hydration reactions with water molecules. Consequently, a significant heat storage density of as high as 3089.6 kJ kg−1 is achieved within only 10 min, outstripping some recently reported thermochemical heat storage systems.