International Journal of Chemical Kinetics最新文献

Rate coefficients, k₁, for the gas-phase OH radical reaction with the heterocyclic ether C₄H₄O (1,4-epoxybuta-1,3-diene, furan) were measured over the temperature range 273–353 K at 760 Torr (syn. air). Experiments were performed using: (i) the photochemical smog chamber THALAMOS (thermally regulated atmospheric simulation chamber, IMT NE, Douai-France) equipped with Fourier Transform Infrared (FTIR) and Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) detection methods and (ii) a photochemical reactor coupled with FTIR spectroscopy (PCR, University of Crete, Greece). k₁(273–353 K) was measured using a relative rate (RR) method, in which the loss of furan was measured relative to the loss of reference compounds with well-established OH reaction rate coefficients. k₁(273–353 K) was found to be well represented by the Arrhenius expression (1.30 ± 0.12) × 10⁻¹¹ exp[(336 ± 20)/T] cm³ molecule⁻¹ s⁻¹, with k₁(296 K) measured to be (4.07 ± 0.32) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The k₁(296 K) and pre-exponential quoted error limits are 2σ and include estimated systematic errors in the reference rate coefficients. The observed negative temperature dependence is consistent with a reaction mechanism involving the OH radical association to a furan double bond. Quantum mechanical molecular calculations show that OH addition to the α-carbon (ΔH_r(296 K) = −121.5 kJ mol⁻¹) is thermochemically favored over the β-carbon (ΔH_r(296 K) = −52.9 kJ mol⁻¹) addition. The OH-furan adduct was found to be stable over the temperature range of the present measurements. Maleic anhydride (C₄H₂O₃) was identified as a minor reaction product, 3% lower-limit yield, demonstrating a non-ring-opening active reaction channel. The present results are critically compared with results from previous studies of the OH + furan reaction rate coefficient. The infrared spectrum of furan was measured as part of this study and its estimated climate metrics are reported.

Hexamethyldisiloxane (HMDSO) is one of the main impurities in the syngas produced from sewage and landfill plants. In order to utilize this syngas or control the characteristics of the generated silica particles, it is crucial to understand the chemical kinetics of HMDSO combustion. This study investigated the process of HMDSO combustion using synchrotron radiation mass spectrometry (SRMS), gas chromatography (GC), and ReaxFF molecular dynamics simulations. First, the force field used for ReaxFF simulation was validated by comparing the energies of different bond lengths, bond angles, and dihedral angles with the ones from DFT calculations. Good agreements were found. Then, ReaxFF simulations of HMDSO combustion with this force field were conducted under various conditions, which include different equivalence ratios (0.67, 1.0, and 1.5) and temperatures ranging from 2000 to 3500 K. The oxidation characteristics of HMDSO were analyzed, including the evolution of gas products and particle formation. Finally, based on the results from experiments and ReaxFF simulations, the reaction pathways, reaction lists, and reaction kinetics data during HMDSO combustion were obtained. A detailed reaction mechanism was proposed and validated by applying it in modeling the H₂/HMDSO/O₂ combustion systems. The temperature and part of the gas products such as CO and CO₂ as well as SiO could be well predicted.

The esterification reaction of n-butanol and acetic acid has been performed in batch reactor in the presence of different homogeneous acid catalyst, namely sulfuric acid, nitric acid, and para toluene sulfonic acid (p-TSA). The objective of present research work is to investigate kinetic behavior of esterification reaction over the temperature range of 60°C–80°C. The effect of reaction parameter such as catalyst loading varied from 1% to 5% v/v and acid to alcohol molar ratio of 1:1, 1:3, and 1:5 has been observed. A pseudo homogeneous kinetic model has been applied. Kinetic parameters such as equilibrium constant, reaction rate constant, enthalpy, activation energy, and entropy were calculated by the experimental data for different acid catalyst system. It was observed that sulfuric acid gives higher conversion 73% than p-TSA 68.5% and nitric acid 66.25% at temperature of 80°C, 1:1 molar ratio and 3% catalyst concentration. The activation energy was estimated 36448.49, 23324.31 and 19060.156 J/mol K for three different catalyst sulfuric acid, nitric acid and p-TSA respectively. The enthalpy and entropy of the esterification reaction of acetic acid with n-butanol over three different catalysts has been calculated (Enthalpy: 25.788 KJ/mol, 12.256 KJ/mol, 28.320 KJ/mol, Entropy: 88.1 J/mol K, 45.298 J/mol K, 91.44 J/mol K) and found enthalpy is having positive value that shows reaction is endothermic.

Detailed chemical kinetic mechanisms for the synthesis of complex organic molecules in the interstellar medium are at an early stage of developement. That such synthesis must take place is well-known from chemical analysis of sampled asteroids. As molecular complexity increases the number of possible structural isomers also increases with the consequence that the nascent species may adopt a different spatial arrangement, to the lowest energy one. As part of a program of investigations of the hydrogen atom transfer reaction or tautomerization of imidic acid–amide species H-O=C-N- $�\rightleftharpoons$ O=C-N-H we have studied the kinetics for a number of nucleobases, namely cytosine, thymine and uracil where a cyclic form of tautomerism (lactim–lactam) is encountered. Together with a fourth, 5-aza-uracil (1,3,5-triazine-2,4(1H,3H)-dione), we report on the rates of reaction at low temperatures 50–200 K for both the direct unimolecular process and the similar transformation mediated by an additional water molecule. We show that these tautomerization reactions can be categorized into three classes, and highlight the importance of quantum mechanical tunneling on the rate constants at these low temperatures. We further present some thermochemistry data, such as formation enthalpies, entropies, isobaric heat capacities and enthalpy functions.

This study reports the effect of substituents in the ortho position of polyaniline on the adsorption capacity to remove the anionic dye methyl orange (MO) from an aqueous solution. The aim of this study is the synthesis of polyaniline (PANI) and its derivatives, poly-o-methylaniline (poly-o-toluidine, POT) and poly-o-methoxyaniline (poly-o-anisidine, POA) for the adsorption removal of MO dye. All polymers were obtained by oxidative polymerization of the corresponding monomers and characterized by scanning electron microscopy (SEM) and infrared spectroscopy (IR). The average particle size of the polymer was about 200 nm. The effect of various parameters such as pH, temperature, adsorption time and initial concentration was analyzed. It was found that the adsorption capacity for dye removal increases from 50.68 to 222.56 mg g⁻¹ for PANI, from 16.89 to 66.57 mg g⁻¹ for POT, and from 97.26 to 532.54 mg g⁻¹ for POA with an increase in the initial dye concentration from 5 up to 50 mg L⁻¹. For all polymers, the equilibrium state of MO adsorption was reached in 50 min. The results showed that MO adsorption on PANI, POT, and POA is well described by a pseudo second order kinetic model. Isothermal studies have shown that adsorption is in good agreement with the Langmuir isotherm model, as evidenced by higher values of correlation coefficients. Based on the data of thermodynamic studies, it was concluded that MO adsorption on PANI, POT, and POA is spontaneous and endothermic.

Kinetic triplets—apparent activation energy (E_a), pre-exponential factor (A), and the reaction model—were estimated for the thermal degradation of three primary virgin and waste plastics, as well as mixed plastics waste. Model-free iso-conversional FWO, KAS, Starink, Kissinger and Vyzovkin and Friedman methods were employed for the kinetic analysis. The apparent activation energy was determined by the integral methods as 206.5-209.1 kJ mol⁻¹ and 195.6-198.8 kJ mol⁻¹ for the virgin and waste high-density polyethylene (HDPE), 211.6-214.1 kJ mol⁻¹ and 183.1-186.6 kJ mol⁻¹ for the virgin and waste polypropylene (PP), 144.0-163.1 kJ mol⁻¹ and 159.7-167.1 kJ mol⁻¹ for the virgin and waste polystyrene (PS), and 173.6-178.9 kJ mol⁻¹ for the mixed plastics waste respectively. E_a was found to follow the trend HDPE > PP > PS with higher values for HDPE and PP virgin samples than that for their waste and marginally smaller for the virgin PS than its waste. Degradation of all plastic samples followed Avrami-Erofeev equation with n varying between 1.0 and 1.8. The effect of conversion on E_a suggested the degradation of both virgin and waste HDPE to consist of multiple parallel reactions while that of others to be more complex. FTIR analysis of the evolved gases was used to explain the possible reaction mechanism. A small difference between the enthalpy change and the apparent activation energy (6-7 kJ mol⁻¹) for all plastic samples indicated favourable pyrolysis reactions. The estimated kinetic parameters and thermodynamic properties showed the stability of different plastics as HDPE > PP > PS.

Half-life values of organic peroxides at elevated temperature conditions are important in characterizing the reactivity and are often available in literature or through vendors. However, there is often lack of details/accuracy on methods used to obtain these values, as well as differences in methods across vendors and publications, thus resulting in discrepant reactivity profile. To address this, a method involving calorimetric experiment and thermo-kinetic modeling was developed. The current approach was applied on five peroxides samples to obtain kinetic parameters and estimate their half-life in the temperature range of interest. The measurements were performed by DSC under non-isothermal conditions on the dilute peroxide solutions (∼0.12 M in mineral oil) and the data were kinetically treated according to three model-based and one model-free kinetic equations. A very good agreement was found between the half-life calculated by all kinetic methods, but significant differences were noticed with the kinetic parameters reported in literature. Additionally, the obtained half-life results, based on non-isothermal measurements developed kinetic models, were validated through isothermal calorimetric testing. Given the accuracy and robustness of our results, the current method can be applied to estimate half-life of organic peroxides at elevated temperature conditions.

The present paper aims to investigate the efficiency of thermal activation persulfate in eliminating the organic dye “Basic Fuchsin” (BF). In addition, the study attempts to elucidate the effect of different operating parameters, such as persulfate dosage (0.44–4.4 mM), the initial solution pH of (3–10), and temperature (25–50°C), on the process. The effects of various anions and water matrices on BF discoloration were investigated. Thus, the findings revealed that 94.15% of BF can be eliminated using persulfate at a concentration of 4.4 mM and a temperature equal to 50°C. It occurs under the following operating conditions: oxidation time of 60 min, initial pH equal to 6, the pollutant concentration of 10 ppm, and stirring speed equal to 300 rpm. Furthermore, the kinetic study indicated that the degradation of the BF dye using PS followed a first-order pattern with rate constants varying within a range of 15.3 × 10⁻³–43.2 × 10⁻³ min⁻¹. Based on the Arrhenius equation, the activation energy of the studied process was determined to be 29 kJ mol⁻¹, suggesting that a moderate activation energy is required for BF discoloration. The results of the thermodynamic study confirm that the oxidation process is non-spontaneous and endothermic. Coexisting inorganic anions delayed BF discoloration to varying degrees, and the inhibitory action followed the following order: carbonate > chloride > sulfate > nitrate. Organic pollutants oxidation by the thermal activation of the persulfate is a simple and effective method for the depollution of waste textile water.

A new heterogeneous K₂CO₃ supported by a layered double hydroxide (LDH), Mg–Al hydrotalcite, was prepared and used as a catalyst for the biodiesel preparation by a tri-component coupling transesterification of methanol, vegetable oil, and methyl acetate. K₂CO₃/Mg-Al exhibits high catalytic activities, and biodiesel yield can reach 99.48% within 20 min under 60°C, with 6 wt.% of K₂CO₃/Mg-Al, 1:1:12 molar ratio of rapeseed oil, methyl acetate, and methanol. Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, nitrogen physical adsorption, thermogravimetry analysis, and CO₂-chemical adsorption were used to assess the physical properties of the prepared K₂CO₃/Mg-Al. Using the tri-component coupling transesterification, 12.2% cost reduce can be get by reducing the cost from 8458 to 7424 ¥/t compared with di-component transesterification containing oil and methanol as resource.

In this study, the gas phase reaction of chlorine atoms with three first-generation oxidation products of monoterpene: (myrtenal C₁₀H₁₄O, nopinone C₉H₁₄O, and ketolimonene C₉H₁₄O) were investigated using a relative technique method. These compounds result from the atmospheric oxidation of monoterpene compounds such as α/β – pinene and limonene. Experiments were performed at temperature range 298–353 K and atmospheric pressure in synthetic air bath gas. Cl atoms were generated by UV photolysis of dichloride (Cl₂). The reaction was followed using a proton-transfer reaction mass spectrometer (PTR-MS) and/or Fourier-transform infrared spectroscopy (FTIR) to monitor the concentrations of the investigated species simultaneous with several reference compounds as a function of time. The rate constants were obtained and the Arrhenius expressions (cm³ molecule⁻¹ s⁻¹) obtained were established over the temperature range of 298–353 K:

k_{nopinone + Cl} =  (5.0  ±  1.2) ×  10⁻¹⁰ exp ( − (406  ±  78) /T)

k_{ketolimonene + Cl} =  (8.88 ±  1.3) × 10⁻¹⁰ exp( − (246 ± 46)/T)

k_{myrtenal + Cl} =  (13.5 ±  6.4) × 10⁻¹⁰ exp( − (535 ±  153)/T)

Based on rate constants, the atmospheric lifetimes (τ) of targeted compounds with respect to reaction with chlorine atoms were estimated and expected to be less than 1 day. There results led to conclude that the reaction with chlorine atoms can be an effective tropospheric loss pathway mainly in regions presenting relatively high chlorine concentrations.