International Journal of Chemical Kinetics最新文献

The periodic sinc function interpolation offers a compelling solution to address the issue of noise in the analysis of thermogravimetric analysis (TGA) data, thereby enhancing the outcomes of differential techniques such as the Friedman isoconversional method. In this study, we introduce a novel approach that leverages the periodic sinc function interpolation to directly obtain smooth reaction rates from TGA data, eliminating the reliance on numerical differentiation methods. The efficacy of this method has been confirmed through its application to noisy experimental data derived from the thermal decomposition of various polymers, showcasing its robustness. Readers are provided with the corresponding code for Gnu Octave, serving as a free alternative to MATLAB. Additionally, the activation energies calculated from the experimental data using both the Friedman method and periodic sinc function interpolation closely align with those determined by the integral Vyazovkin method, emphasizing the validity and reliability of this new approach.

Creation of complex chemical mechanisms for hydrocarbon pyrolysis and combustion is challenging due to the large number of species and reactions involved. Reactive molecular dynamics (RMD) enables the simulation of thousands of reactions and the discovery of previously unknown components of the reaction network. However, due to the inherent imprecision of reactive force fields, it is necessary to verify RMD-obtained reaction paths using more accurate methods such as Density Functional Theory (DFT). We demonstrate a method for identification and confirmation of reaction pathways from RMD that supplement an established mechanism, using the example of benzene formation from n-heptane and iso-octane pyrolysis. We establish a validation workflow to extract reaction geometries from RMD and optimize transition states using the Nudged-Elastic-Band method on semi-empirical and quantum mechanical levels of theory. Our findings demonstrate that the widely recognized ReaxFF parameterization, CHO2016, can identify known pathways from a established soot formation mechanism while also indicating new ones. We also show that CHO2016 underestimates hydrogen migration barriers by up to $��40��{�\mathrm{kcal}��\mathrm{mol}�}^{�-�1�}�$ as compared to DFT and can lower activation barriers significantly for spin-forbidden reactions. This highlights the necessity for validation or potentially even reparametrization of CHO2016.

Oxalyl chloride, $�{\text{(ClCO)}}_2$, is widely used as a photolytic source of Cl atoms in reaction kinetics studies. $�{\text{(ClCO)}}_2$ photolysis is typically assumed to produce Cl atoms with an overall yield of 2 via three-body dissociation, $��{\text{(ClCO)}}_2�+�h�\nu �\to �\text{Cl}�+�\text{CO}�+�{\text{ClCO}}^{\ast }�$, followed by fast subsequent ClCO unimolecular decomposition of either the energetically excited $�{\mathrm{ClCO}}^{\ast }$ fragment, $��{\text{ClCO}}^{\ast }�\to �\text{Cl}�+�\text{CO}�$, or the thermalized ClCO radical, $��\text{ClCO}�+�M�\to �\text{Cl}�+�\text{CO}�+�M�$. However, a study

The experimental data over CuO/ZnO/ZrO₂ catalyst for a wide range of operating conditions were used to develop the kinetics of the reaction CO₂ hydrogenation to methanol. Three kinetic models such as the power law model, the Graaf kinetic model, and the Park kinetic model were tested against the experimental data. Both the mechanistic models have been developed based on the Langmuir-Hinshelwood-Hougen-Watson approach and are specific only to the methanol synthesis from CO/CO₂ hydrogenation. In an attempt to reduce the number of parameters in the two models, the abridged forms of these models were also tried. Overall, 25 kinetic rate equations were tested and the best-fit kinetic rate expression with optimized parameters was worked out. Both the integral and differential methods of kinetic analysis were employed and their efficacy in finding the best-fit expression was compared. The MATLAB built-in function fminsearch was employed to perform the regression of the data. The Graaf model in its parent form, but with the new optimized values of the parameters, was found to be the best-fit rate model. The Graaf kinetics, with re-estimated parameters, could be helpful in designing and simulating a methanol synthesis reactor operating on CO₂ and H₂ feed and utilizing a CuO/ZnO/ZrO₂ catalyst.

Reduction of large combustion mechanisms is usually conducted based on the detection and elimination of redundant species and reactions. Reaction elimination methods are mostly based on sensitivity analysis, which can provide insight into the kinetic system, while species elimination methods are more efficient. In this work, the species-targeted local sensitivity analysis (STLSA) method is proposed to evaluate the importance of species and eliminate non-crucial species and their related reactions to simplify kinetic models. This paper comprehensively evaluates the effectiveness of STLSA across various combustion scenarios, including high and low-temperature ignition and laminar flame speed, using diverse mechanisms like USC Mech II, JetSurf 1.0, POLIMI_TOT_1412, NUIGMech1.1 and so on. Comparisons with graph-based methods, such as DRG and DRGEP, highlight STLSA's superior efficiency and accuracy. Moreover, STLSA is compared to species-targeted global sensitivity analysis (STGSA), demonstrating significant computation cost savings and comparable model reduction capabilities. The study concludes that STLSA is a robust and versatile tool for mechanism reduction, offering substantial improvements in computational efficiency while maintaining high accuracy in predicting key combustion properties.

As part of a series of studies of hydrogen-atom transfer or tautomerization reactions of imidic acid–amide species, $���H�─�O�═�C�─�N�─��\rightleftharpoons ��O�═�C�─�N�─�H��$, we report the rate constants for a set of 24 five-membered cyclic compounds at low, 50–300 K, and high, 500–1500 K, temperatures. These rate constants are for both the high temperature direct reaction and for that mediated by an additional water molecule which facilitates the hydrogen transfer reaction at low temperatures. In the latter case we show that the rate of reaction from a pre-reaction complex can be rapid at temperatures down to 50 K on a 1 ms timescale and is dominated by quantum mechanical effects as evaluated by small-curvature and quantised-reaction-states tunnelling. In addition, we present thermochemical data such as enthalpies of formation, entropies, isobaric heat capacities and enthalpy functions for these largely unknown species which span a range of compounds from pyrolidinone to oxo-tetrazoles.

The kinetics of total organic carbon (TOC) destruction during supercritical water gasification (SCWG) of glucose were studied at 400–500°C and 25 MPa in a 600 mL batch reactor. Both TOC and water concentrations are critical for the conversion of TOC in supercritical water, especially at longer residence times. Initially, it was assumed that the TOC destruction reaction followed first-order kinetics ignoring the water concentration. However, experimental results showed that the feed-to-water ratio had a significant effect on TOC decomposition. Considering the water concentration in the reaction, the reaction orders of TOC (2.35) and water (1.45) were calculated using nonlinear regression analysis (the Runge-Kutta method). The estimated pre-exponential factor (k’) and activation energy (E) were calculated to be 8.1 ± 2/min and 90.37 ± 9.38 kJ/mol respectively.

Drug-surfactant interaction increases the solubility of poorly water-soluble drugs and design better pharmaceutical formulations. The degree of interaction of nepafenac (NP), a nonsteroidal anti-inflammatory prodrug was studied with ionic surfactant molecules such as cationic surfactant cetrytrimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) in an aqueous medium at room temperature. NP made mixed micelles with CTAB and SDS. To investigate the influence of interactions, conductivity measurements, UV–visible spectroscopy, and fluorescence measurements were recorded. The quantification of NP–surfactant interactions was investigated using various mathematical models. The CMC values determined from conductivity measurements of pure surfactants were 0.96 mM for CTAB and 8.14 mM for SDS near to their literature values. At different mole fractions of NP in UV measurements, binding constants from lnKb were found 0.025 and 0.123 and number of NP molecules per micelles (n) 67, 46 for CTAB and SDS, respectively. The mixed micelles of NP–CTAB and NP–SDS revealed that CTAB has a strong interaction with NP than SDS. The Benesi–Hildebrand relationship, Stern–Volmer and Kawamura replica for the partition coefficient were used to confirm the findings. We are confident that the host–guest interaction mechanism can contribute to a better understanding of molecular recognition in the phospholipid membrane model.

Laminar flame speeds of methanol/air mixtures at 338–398 K are measured by the heat flux method, extending the range of equivalence ratio up to 2.1. And a new optimized methanol mechanism with 94 reactions is proposed by using the particle swarm algorithm, adjusting 20 Arrhenius pre-exponential factors in their uncertainty domains. The optimized model is compared with eight methanol combustion mechanisms and experimental data published in recent years, covering a wide range of initial temperatures (298–1537 K), pressures (0.04–50 atm) and equivalence ratios (0.5–2.1). The results show that the optimized mechanism not only improves the accuracy of ignition delay time with rapid compression machine at low temperature but also moderately improve the description of laminar flame speed in lean and stoichiometric conditions. Meanwhile, the optimized model significantly enhances the prediction accuracy of CH₃ and CH₂O radical, and perfectly captures the evolution trend of HCO radical in laminar flat flame. Overall, the optimized mechanism provides the best overall description of the currently available measurements, leading to more accurate and comprehensive prediction of ignition delay time, laminar flame speed and species concentration.

A novel boron-containing novolac (triphenyl borate-formaldehyde resin, TPBF) was synthesized. The structure, thermoplasticity, molecular weight, and molecular weight distribution of TPBF have been characterized with FT-IR, melt viscosity, ¹³C NMR and GPC. The thermal stability of TPBF was investigated by TGA, indicating the thermal stability of TPBF was much better than that of normal novolac (phenol-formaldehyde resin, PF). TPBFs with different molar ratios of formaldehyde to benzene ring in triphenyl borate (TPB) were also synthesized and compared for molecular size, polydispersity and thermal stability. Further, the thermal degradation kinetics of TPBFs and PF were studied by TGA using Madhusdanan-Krishnan-Ninan method and the activation energies were calculated at different degradation stages. It was found that the thermal degradations of TPBFs and PF are a multistage reaction and the degradation reactions in every stage follow the first order reaction mechanism. Finally, the activation energies of thermal degradations of novolac increase with the introduction of boron, the progress of degradation reaction as well as the increase of molar ratios.