Kinetics of Solid-Gas Reactions and Their Application to Carbonate Looping Systems

In this work, a first study on kinetics and thermodynamics of thermal decomposition for synthesis of doped LiMn2O4 nanoparticles is presented. The effect of Mg doping concentration on thermal decomposition of synthesis precursors, prepared by ultrasound-assisted Pechini-type sol–gel process, and its significance on nucleation and growth of Mg-doped LiMn2O4 nanoparticles was studied through a method based on separation of multistage processes in single-stage reactions by deconvolution and transition state theory. Four zones of thermal decomposition were identified: Dehydration, polymeric matrix decomposition, carbonate decomposition and spinel formation, and spinel decomposition. Kinetic and thermodynamic analysis focused on the second zone. First-order Avrami-Erofeev equation was selected as reaction model representing the polymer matrix thermal decomposition. Kinetic and thermodynamic parameters revealed that Mg doping causes an increase in thermal inertia on conversion rate, and CO2 desorption was the limiting step for formation of thermodynamically stable spinel phases. Based on thermogravimetry experiments and the effect of Mg on thermal decomposition, an optimal two-stage heat treatment was determined for preparation of LiMgxMn2-xO4 (x = 0.00, 0.02, 0.05, 0.10) nanocrystalline powders as promising cathode materials for lithium-ion batteries. Crystalline structure, morphology, and stoichiometry of synthesized powders were characterized by XRD, FE-SEM, and AAS, respectively.

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“…Kinetic analysis of resulting individual curves, as independent reaction stages, was carried out using the linear form of Equation (5) [ 74 ]:

…”

Section: Resultsmentioning

confidence: 99%

Kinetic and Thermodynamic Studies on Synthesis of Mg-Doped LiMn2O4 Nanoparticles

2020

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“…The direct application of well-known kinetics models [ 30 ] for describing the reaction progress and rate expression faces certain difficulties related to successive reactions, altering of the physical and chemical reactivity of the remaining sample, inter-reaction between gaseous reaction products and the working sample, etc. Hence, it was suggested that the best way to evaluate the temperature impact on the chromite reactions with Cl 2 was to calculate the reaction rate in increments of 5% mass losses in the interval ranging from 5.0% to 85.0% ML.…”

Section: Resultsmentioning

confidence: 99%

Reactivity of Low-Grade Chromite Concentrates towards Chlorinating Atmospheres

et al. 2020

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The most economically important iron-chromium bearing minerals is chromite. In natural deposits, iron(II) is frequently substituted by magnesium(II) while chromium(III) is replaced by aluminum(III) and/or iron(III) forming a complex chromium bearing material. The majority of mined chromite is intended for the production of ferrochrome which requires a chromite concentrate with high chromium-to-iron ratio. Found mostly in the spinel chromite structure, iron cannot be removed by physical mineral processing methods. In this frame, the present work deals with the reaction of chlorine and chlorine+oxygen with selected samples of chromite concentrates for assessing the reactivity of their components towards chlorinating atmosphere, allowing the preferential removal of iron, hence meeting the chromite metallurgical grade requirements. Isothermal thermogravimetric analysis was used as a reliable approach for the kinetic reactivity investigation. Results indicated a wide difference in the thermal behavior of chromite constituents in a chlorinating atmosphere when considering their respective values of apparent activation energy oscillating from about 60 to 300 kJ/mol as a function of the sample reacted fraction. During the chromite treatment by chlorine in presence of oxygen, chromium was recovered as liquid chromyl chloride by condensation of the reaction gas phase.

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“…This latter model also considers the formation of intermediate phases as concentric layers, where appropriate. [ 32 ]…”

Section: Resultsmentioning

confidence: 99%

Solid‐State Reoxidation Kinetics of A/B‐Site Substituted LaMnO₃ During Solar Thermochemical CO₂ Conversion

Nair

Abanades

2020

Energy Tech

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Perovskite oxides exhibit noteworthy performance as efficient oxygen carriers for two‐step thermochemical conversion of CO2 using concentrated solar energy. Herein, the effect of composition on the solid‐state reoxidation kinetics of La0.5Sr0.5MnO3 and LaCo0.5Mn0.5O3 oxygen carriers is investigated. Thermochemical CO2 splitting reactions are conducted at several selected temperatures and a series of kinetic models are explored. Results indicate that the most suitable model describing the reoxidation mechanism depends on the oxygen carrier. A two‐step reaction mechanism is observed for La0.5Sr0.5MnO3 (first‐order model and 2D shrinking core model) depending on the extent of conversion whereas a diffusion controlled (3D‐Ginstling) mechanism is identified for LaCo0.5Mn0.5O3. The values of apparent activation energies (Ea) are remarkably low (≈5 kJ mol−1) and even negative, indicating an “anti‐Arrhenius” behavior. Pre‐exponential factors (A) are found to be low and influenced by the model used. Enthalpies of activation (ΔH‡ = −6 to −18 kJ mol−1) depend on the extent of conversion and composition, whereas entropies of activation (ΔS‡ = −0.33 kJ K−1 mol−1) remain constant. The observed discrepancies in the reoxidation mechanism can probably be attributed to thermal stability aspects, variations in lattice functionalities during the reaction, undesired side reactions, or a combination of these effects.

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Kinetics of Solid-Gas Reactions and Their Application to Carbonate Looping Systems

Cited by 85 publications

References 113 publications

Kinetic and Thermodynamic Studies on Synthesis of Mg-Doped LiMn2O4 Nanoparticles

Kinetic and Thermodynamic Studies on Synthesis of Mg-Doped LiMn2O4 Nanoparticles

Reactivity of Low-Grade Chromite Concentrates towards Chlorinating Atmospheres

Solid‐State Reoxidation Kinetics of A/B‐Site Substituted LaMnO₃ During Solar Thermochemical CO₂ Conversion

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Kinetics of Solid-Gas Reactions and Their Application to Carbonate Looping Systems

Cited by 85 publications

References 113 publications

Kinetic and Thermodynamic Studies on Synthesis of Mg-Doped LiMn2O4 Nanoparticles

Kinetic and Thermodynamic Studies on Synthesis of Mg-Doped LiMn2O4 Nanoparticles

Reactivity of Low-Grade Chromite Concentrates towards Chlorinating Atmospheres

Solid‐State Reoxidation Kinetics of A/B‐Site Substituted LaMnO3 During Solar Thermochemical CO2 Conversion

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Solid‐State Reoxidation Kinetics of A/B‐Site Substituted LaMnO₃ During Solar Thermochemical CO₂ Conversion