Intrinsic Kinetics Research Articles

On the intrinsic reaction kinetics of polypropylene pyrolysis

On the intrinsic reaction kinetics of polypropylene pyrolysis

Catalyst-enhanced autothermal chemical looping reforming: Intrinsic SMR kinetics and numerical simulation

In this work, we propose a catalyst-enhanced autothermal chemical looping reforming (CE-aCLR) to address the environmental concerns associated with toxic Ni-based oxygen carrier (OC) and the low fuel conversion related to the low reactivity of Fe-based OC. In this process, a non-toxic noble-metal-based steam methane reforming (SMR) catalyst is employed for methane conversion, while a Fe-based OC is employed for oxygen transfer between two reactors. Firstly, a commercial Rh-based SMR catalyst is studied in a micro-fixed bed reactor and its intrinsic reaction kinetics are determined. Then, a 1-D CE-aCLR model is developed based on a verified multi-scale aCLR model to facilitate analyzing commercial-scale feasibility. This model accounts for the essentials of the reactor hydrodynamics, mass and heat transfer, detailed reaction kinetics, and the influence of the solids residence time distribution in the fuel reactor. The main dimensions of a commercial CE-aCLR unit are determined and this unit is simulated using the developed model. The results demonstrate the feasibility of the novel, environmentally friendly process that enables high methane conversion using Fe-based OC within realistically sized reactors and an acceptable solid circulation rate. Moreover, sensitivity study shows that the CE-aCLR allows using OCs with low activity (potentially low cost) while maintaining high CH4 conversion.

Challenges in Unravelling the Intrinsic Kinetics of Gas Reactions at Rotating Disk Electrodes by Koutecky–Levich Equation

Challenges in Unravelling the Intrinsic Kinetics of Gas Reactions at Rotating Disk Electrodes by Koutecky–Levich Equation

Kinetic modelling of biomass fast devolatilization using Py-MS: Model-free and model-based approaches

Feasibility using quantitative data obtained from a micropyrolyzer coupled to an evolved gas analysis technique, mass spectrometry, for kinetics determination has been long demonstrated. This paper describes for the first time how to obtain intrinsic kinetics for fast devolatilization of biomass and its lignocellulosic fractions (e.i., holocellulose and lignins). The main challenge with online detection is assessing the time lag related to transport phenomena between the reactor and the detector. To do this, an experimental method was developed to derive the real-time biomass devolatilization profile; this provided 'corrected' datasets. Preliminary kinetic parameters were obtained from the differential isoconversional Friedman method combined with real-time sample temperature history. Not considering the effect of thermal lag and the delay in detecting pyrolysis products by the MS leads to a certain level of inaccuracies. Isoconversional activation energy (Eα) dependencies obtained in the absence of heat and mass transfer limitations for biomass and its components highly varied with conversion, confirming the multi-step nature of the fast pyrolysis process. After demonstrating the modeling limitations of a constant activation energy model (CAEM), both isoconversional functions were parametrized to propose a variable activation energy model (VAEM) and used as initial inputs for the distributed activation energy model.

Intrinsic kinetics of low temperature methane steam reforming on Ru/La-Al₂O₃ catalyst

This study focuses on investigating the intrinsic kinetics of methane steam reforming over a lanthanum promoted Ru/La-Al₂O₃ catalyst at low temperatures ranging from 475 to 550 °C and 140 kPa. To facilitate the research, high-throughput experimentation was employed using 16 integral fixed bed reactors. The steam reforming reaction was influenced by co-reactants and products. In this work, we proposed a reaction mechanism and developed a kinetic model to understand the underlying process. The findings indicate that methane dissociative adsorption is the rate-determining step, and CO is identified as the most abundant surface intermediate. The developed kinetic model not only provides the best fit to the experimental data but also statistically significant and thermodynamically consistent.

Matching relation between intrinsic kinetics and liquid-liquid mass transfer of medium-rate reaction: Take 1,1,2-trichloroethane dehydrochlorination as an example

The apparent rate of heterogeneous medium-rate reaction is jointly controlled by liquid-liquid mass transfer performance and intrinsic kinetics. Realizing the matching of them can significantly enhance the efficiency of the reaction. Here, the dehydrochlorination reaction of 1,1,2-trichloroethane with NaOH solution is used as an example to investigate the matching relation between intrinsic kinetics and mass transfer efficiency of medium-rate reactions. Firstly, an apparent reaction model considering mass transfer performance, intrinsic kinetics and physical properties of the system was established. The accuracy of the model was experimentally verified in a standard stirred tank. Based on the model, the mass transfer coefficient matching the intrinsic reaction kinetics at 51 ℃ should beyond 100 s−1, which requires to be achieved in mass transfer intensification reactors instead of conventional stirred tank. Therefore, a rotor-stator homogenizer and a rotating packed bed were used. The experimental results in these two reactors well demonstrated the model prediction.

Kinetics of acetic acid and isoamyl alcohol liquid esterification over Amberlyst-70

This work is a kinetic study on liquid phase esterification between acetic acid and isoamyl alcohol using Amberlyst-70 as catalyst. There are not scientific papers with fitted kinetic models for this esterification system using this catalyst. Experiments were carried out in a laboratory batch reactor at controlled temperature conditions. Molar feed ratio (between 2 and 0.5), temperature (between 353.15 K and 383.15 K) and catalyst load (between 0.5 wt% and 2.0 wt%) were the manipulated experimental conditions. Measured composition profiles were used to fit the parameters for three versions of the pseudohomogeneous model (PHM) that differ in their activity model. At the end, a PHM model based on molar fractions is recommended to explain composition changes due to the esterification reaction. Calculated values for activation energy and chemical equilibrium constant are E = 43 kJ/mol and KE = 5.22, respectively. In accordance with the Weisz-Prater criterion, intraparticle mass transport effects were appreciable in experimental kinetic tests due mainly to the particle size used (0.363 mm). In order to take into account diffusional effects, the effectiveness factor was calculated using the Maxwell-Stephan equations. Therefore, adjusted models are the intrinsic kinetics and they can be used to simulate and design reactors and reactive distillation operations.

Thermal analysis and performance improvement of heat transfer in sample cell of Sieverts apparatus

In a Sieverts apparatus, the poor heat transfer performance of a sample cell leads to inaccuracy in kinetics test of hydrogen storage materials. Consequently, the analysis of heat transfer of the reaction process in the sample cell is essential. However, it is difficult for traditional detection methods to track the physical and chemical dynamic changes in the sample cell. In this paper, the finite element method was used to simulate the reaction process in the sample cell. A two-dimensional numerical model was designed to characterize the hydrogen absorption process in order to investigate the link between the heat transfer performance of the sample cell and the reaction kinetics. It was found that the reaction kinetics would be close to the intrinsic kinetics of the materials as its amount decreased. However, the decreased amount of hydrogen storage materials had a restricted effect on the increase of the reaction rate. The relevant amount of hydrogen storage material was recommended based on the comprehensive analysis of this study. In addition, the improvement of the thermal conductivity of the MH reaction bed and sample cell material improved the heat transfer performance to a certain extent. Finally, the relationship among the amount of hydrogen storage material, thermal conductivity and absorption time was established through the simulation analysis, which provided some schemes for optimizing the reaction kinetics testing accuracy of Sieverts apparatus.

Intrinsic kinetics of catalytic hydrogenation of 2-nitro-4-acetylamino anisole to 2-amino-4-acetylamino anisole over Raney nickel catalyst

The catalytic hydrogenation of 2-nitro-4-acetylamino anisole (NMA) is a less-polluting and efficient method to produce 2-amino-4-acetamino anisole (AMA). However, the kinetics of catalytic hydrogenation of NMA to AMA remains obscure. In this work, the kinetic models including power-law model and Langmuir-Hinshelwood-Hougen-Watson (LHHW) model of NMA hydrogenation to AMA catalyzed by Raney nickel catalyst were investigated. All experiments were carried out under the elimination of mass transfer resistance within the temperature range of 70–100 °C and the hydrogen pressure of 0.8–1.5 MPa. The reaction was found to follow 0.52-order kinetics with respect to the NMA concentration and 1.10-order kinetics in terms of hydrogen pressure. Based on the LHHW model, the dual-site dissociation adsorption of hydrogen was analyzed to be the rate determining step. The research of intrinsic kinetics of NMA to AMA provides the guidance for the reactor design and inspires the catalyst modification.

Overall Water Splitting on The NiS/NiS2 Heterostructures Featuring Self‐Equilibrium Orbital Occupancy

AbstractEfficient electrochemical overall water splitting requires bi‐functional catalysts that work for both hydrogen and oxygen evolution reactions (HER/OER). A heterostructure is thus proposed to maintain its optimal interactions with H/O‐containing intermediates. A so‐called “orbital occupancy self‐equilibrium” strategy is employed theoretically and experimentally to design such bi‐functional catalysts, namely the incorporation of the V species into a NiS/NiS2 heterostructure. Owing to the variable valences of both Ni and V species, the electrons are controllably reoriented over the interfacial V─S─Ni bond. The as‐generated dynamic and self‐equilibrium of the electron environment modify an optimal adsorption harmony toward various H/O‐containing intermediates on this heterointerface, enhancing intrinsic activity and reaction kinetics for the HER, the OER, and overall water splitting. This V‐NiS/NiS2 catalyst exhibits an overpotential of only 94 and 220 mV at a current density of 10 mV cm–2 for the HER and the OER, respectively. This proposed strategy is expected to be workable for other catalysts with variable metal valences and provide insights for an agile interfacial electron allocation on heterostructure catalysts.

Two‐step flow synthesis of Olaparib in microreactor: Route design, process development and kinetics research

Olaparib is a top-selling pharmaceutical approved for the treatment of ovarian cancer. Herein, a two-step cascaded flow process was developed to synthesize Olaparib in microreactor. Since two different acyl groups are in the piperazine ring of Olaparib, a highly selective monoacylation route of piperazine is crucial for the efficient synthesis of Olaparib. For the first step (i.e., the monoacylation of piperazine), N,N'-carbonyldiimidazole was screened as coupling reagent due to its excellent selectivity, safety and greenness, a high monoacylation yield of 83 % was obtained in the microreactor. To understand the selective monoacylation reaction more deeply, the intrinsic kinetics was investigated based on mechanism cognition and experimental data. The established kinetic model was in good agreement with the experimental results in validation experiments. To further realize continuous manufacturing, the following step (i.e., amidation) was cascaded with the monoacylation in a microreactor system, Olaparib was continuously synthesized in the two-step cascaded microreactor with an overall yield of 78 % within 25 min. Relative to existing processes, the reaction steps were reduced, the economy and efficiency were remarkably improved, indicating efficient process intensification.

Solvent Mediated Interactions on Alkene Epoxidations in Ti-MFI: Effects of Solvent Identity and Silanol Density

Selective alkene oxidation rates within zeolite pores reflect differences in contributions from thermodynamic nonidealities introduced by noncovalent interactions at solid–liquid interfaces and spatial constraints enforced by the zeolite topology. Epoxidation turnover rates for 1-hexene in Ti-MFI zeolite differ by 1000-fold across 10 combinations of solvents, including alcohols and acetonitrile, over Ti-MFI with distinct silanol defect densities. Solvent mediated noncovalent interactions persist across an extended binding environment that influences the stability of epoxidation transition states. Apparent activation enthalpies (ΔHApp⧧) and entropies (ΔSApp⧧) span 80 kJ mol–1 and 200 J mol–1 K–1, respectively, with the most positive values for both appearing in methanol. Hydrophilic (i.e., (SiOH)x defect rich) Ti-MFI-OH catalysts in methanol give the greatest turnover rates because entropic gains associated with the disruption of hydrogen-bonded networks of intrapore methanol and water dominate activation free energies. In situ infrared spectra show that the adsorption of 1,2-epoxyhexane to Ti sites disturbs the equilibrium solvent structure within pores in ways that reflect the density of the hydrogen bond donor and acceptors near active sites. This interpretation agrees with measured enthalpies for adsorption of 1,2-epoxyhexane to Ti active sites within solvent filled pores that correlate with ΔHApp⧧ across solvent and catalyst combinations. The displacement of solvent molecules and the associated rupture and formation of hydrogen bonds among solvents, pore walls, and nearby reactive molecules during catalysis and adsorption events incur substantial excess contributions that govern the reaction rates and barriers. These realizations explain the particular success of alkene epoxidations in mixtures of H2O2 and methanol over hydrophilic forms of Ti-MFI in industrial processes (e.g., the hydrogen peroxide–propylene oxide process). These findings demonstrate the gains achieved by appropriately pairing organic solvents with microporous catalysts to manipulate the intrinsic kinetics of reactions and the thermodynamics of adsorption at solid–liquid interfaces.

CO2-TBAB semi-clathrate hydrate dissociation behaviour in individual capsules: A new two-stage numerical model and parametric study

Gas hydrates have a wide implementation in the capture, storage, transport and utilisation of a range of gases, in which the dissociation kinetics is of great importance to gas transport and recovery efficiency. Encapsulation has been proven an effective technique to enhance gas–liquid mass transfer and thus improve gas hydrate formation kinetics. However, the dissociation behaviour of gas hydrate in individual capsules remains unknown. In this work, the dissociation kinetics of encapsulated CO2-TBAB semi-clathrate hydrates in different shapes are experimentally investigated under various operating conditions, and, for the first time, a two-stage numerical model is developed which integrates mass transfer, heat transfer and the intrinsic gas hydrate reaction kinetics to simulate the gas hydrate dissociation process. The effects of temperature, pressure, capsule volume and capsule geometry on gas hydrate dissociation kinetics are investigated. The results reveal that the proposed model is capable of capturing two distinct experimentally-observed dissociation stages, a rapid and subsequently slow stage according to the measured dissociation rate. Surface-to-volume ratio of the capsule and the dissociation driving force are the two main factors influencing the dissociation kinetics. The ring-shaped capsule exhibits the most efficient dissociation process due to its high surface-to-volume ratio and long transition time to the slow dissociation stage. This work enhances the understanding of gas hydrate dissociation behaviour in individual capsules and guides the manipulation of dissociation for efficient hydrate-based gas transport and recovery.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Modelling and experimental validation of reaction chamber simulating indoor air decontamination by photocatalytic paint

A photocatalytic paint for the air decontamination was tested under different operating conditions in a reaction chamber that simulates an indoor room. An experimental design was applied to cover a wide range of indoor air conditions (irradiation level, air flow rate, relative humidity and inlet pollutant concentration). It was proposed to develop a first principles model capable of predicting the outlet contaminant concentration from the continuous reaction chamber or the evolution of the reactant concentration operating the chamber in batch mode. The main inputs for the model were: i) optical properties of the paint, ii) characteristics and dimensions of the radiation source, iii) dimensions and operating conditions of the reaction chamber, and iv) intrinsic photocatalytic kinetics previously determined. The developed models showed a very good agreement with experimental measurements. The proposed methodology could be extended considering all indoor environmental conditions to simulate air decontamination in real applications of photocatalytic paints.

Novel Co-doped nickel hydroxyfluorides with rapid electron transfer for high-performance supercapacitors

Transition metal electrode materials are promising for applications in high-energy and power-density rechargeable energy devices. However, their poor intrinsic conductivities and limited redox kinetics hinder the rapid energy supply at high current densities. Herein, a series of Co-doped nickel hydroxyfluorides (Co-Ni(OH)F) was constructed as new electrode materials to maximize the charge storage ability at different current densities. The introduction of Co did not only induce abundant defects for regulating the electronic structure but also fine-tuned the surface morphology and shortened the ion/electron diffusion distance. The coexistence of multiple oxidation states of Ni and Co species provided abundant redox processes and effectively enhanced the electrochemical activities. The relationship between Co2+ doping and the increase in conductivity of the system was further confirmed by the calculated density of states (DOS). The optimized Co-Ni(OH)F (Co=20%) electrode material exhibited an ultrahigh specific capacity of 3380.2 F g−1 at a current density of 1 A g−1. Even at an enhanced current density of 20 A g−1, the optimized electrode showed a superior capacity retention rate of 78.4%. After 5000 cycles at a high current density of 30 A g−1, the electrode retained 76.3% of its original capacity. Furthermore, the Co-Ni(OH)F (Co=20%)//Bi2O3 asymmetric device delivered an ultrahigh density of 139.8 Wh kg−1 at a power density of 800 W kg−1, suggesting superior energy density than previously reported systems. Overall, new insights into the rational design of novel high-capacity and high-rate electrode materials were provided, promising for the construction of advanced energy devices.

Oxidized Kinetic Normal Distribution Models for Sophisticated Electrochemical Windows

The electrochemical window (EW) of electrolytes is considered the essential bottleneck of the voltage range for lithium batteries, which is theoretically overestimated previously. In this work, we present an innovative strategy to quantify the EW without experiential parameters accurately. This strategy encompasses energy states and statistical distribution from both thermodynamic and oxidized kinetic aspects. Verified by linear sweep voltammetry, which specializes in intrinsic redox kinetics of reactants and excludes the influences of products, the most restrictive factor among the effects of condensation, thermal motion, solvent, electric field, and catalysis determines the practical EW. For polyethylene oxide (PEO) and ethylene carbonate (EC)-dimethyl carbonate (DMC) with glassy carbon, the solvent effect is the restriction, while for EC-DMC with LixCoO2, the catalysis effect of the LixCoO2 surface is the restriction. This work provides an effective criterion for accurate prediction, guiding the electrolyte system design to satisfy the expected EW.

Ionothermally Synthesized Nanoporous Ti0.95W0.05Nb2O7: a Novel Anode Material for High‐Performance Lithium‐Ion Batteries

AbstractAlthough TiNb2O7 is regarded as a fast‐rechargeable lithium‐ion battery (LIB) anode material, the intrinsic poor electrochemical kinetics of TiNb2O7 still dramatically impedes its development. Herein, an ionothermal synthesis‐assisted doping strategy is proposed for the preparation of a new W6+‐doped TiNb2O7 material (Ti0.95W0.05Nb2O7) with nanoporous structure (denoted as NPTWNO). The improved Li+ diffusion coefficient of NPTWNO suggests that the ionic‐liquid‐templated nanoporous architecture improves the Li+ diffusion kinetics. The density functional theory computational study reveals that the doped W6+ successfully boosts the electronic conductivity due to the narrowed conduction‐valance bandgap resulted from charge redistribution, which is reflected by the electrochemical impedance spectroscopy data. With the simultaneously enhanced Li+ diffusivity and electronic conductivity, NPTWNO achieves fast‐rechargeability in LIBs. Therefore, this work indicates the potential of ionothermal synthesis‐assisted doping strategy on energy storage materials and offers NPTWNO material with promising electrochemical performance.

Realizing Excellent Structural and Thermoelectric Performance in Mg3Sb2-Based Alloys by Manipulating Mg Intrinsic Migration Kinetics with Interstitial Ni Doping

N-type Mg3Sb2 is attracting increasing focus for its outstanding room-temperature (RT) thermoelectric (TE) performance; however, achieving reliable n-type conduction remains challenging due to negatively charged Mg vacancies. Doping with compensation charges is generally used but does not fundamentally resolve the high intrinsic activity and easy formation of Mg vacancies. Herein, a robust structural and thermoelectric performance is obtained by manipulating Mg intrinsic migration activity by precisely incorporating Ni at the interstitial site. Density functional theory (DFT) indicates that a strong performance originates from a significant thermodynamic preference for Ni occupying the interstitial site across the complete Mg-poor to -rich window, which dramatically promotes the Mg migration barrier and kinetically immobilizes Mg. As a result, the detrimental vacancy-associated ionized scattering is eliminated with a leading room-temperature ZT up to 0.85. This work reveals that interstitial occupation in Mg3Sb2-based materials is a novel approach promoting both structural and thermoelectric performance.

Intrinsic Role of Volatile Solid Additive in High-Efficiency PM6:Y6 Series Nonfullerene Solar Cells.

Organic nonfullerene solar cells (ONSCs) have made unprecedented progress, however, morphology optimization of ONSCs has been proven to be particularly challenging relative to classical fullerene-based devices. In this work, we report a novel volatile solid additive (VSA), 2-hydroxy-4-methoxybenzophenone (2-HM), for achieving high-efficiency ONSCs. 2-HM functions as a universal morphology-directing agent for several well-known PM6:Y6 series nonfullerene blends, viz. PM6:Y6, PM6:BTP-eC9, PM6:L8-BO, leading to a best efficiency of 18.85% at the forefront of reported binary ONSCs. VSAs have recently emerged, while the intrinsic kinetics is still unclear. Herein, we employ a set of in-situ and ex-situ characterizations to first illustrate the molecule-aggregate-domain transition dynamic process assisted by the VSA. More specifically, we unlock the role of 2-HM in individual donor PM6 and acceptor Y6 systems, and further reveal the function of 2-HM in altering the PM6:Y6 bulk heterojunction blends for enhanced photovoltaic performance. We believe the achievement brings not only a deep insight into emerging volatile solid additive, but also a new hope to further improve the molecular ordering, film microstructure and relevant performance of ONSCs. This article is protected by copyright. All rights reserved.