International Journal of Chemical Kinetics最新文献

In this work, the optimum process conditions and kinetics of the green synthesis of isobutyl cinnamate using deep eutectic solvents (DESs) as catalysts were investigated. Isobutyl cinnamate is a spice with low toxicity and is widely used in the food industry. However, there is a lack of reports on its green synthesis. Three DESs were prepared by adjusting the mixing ratio of choline chloride (ChCl) and p-toluenesulfonic acid (PTSA). Response surface methodology with Box-Behnken design (RSM-BBD) was used to optimize the process parameters of the esterification of cinnamic acid with isobutanol. The effects of catalyst loading, stirring speed, cinnamic acid/isobutanol molar ratio, and temperature on the conversion of cinnamic acid over time were evaluated. Using ChCl-PTSA as a catalyst, the kinetics data and chemical equilibrium constants of the esterification were determined at a temperature range of 353.15–383.15 K. The pseudo-homogeneous (PH) model based on activity was then adopted to describe the kinetics of the reaction, and the relative deviations between the experimental values and the calculated ones by PH model are less than 5.5%. Thermodynamic data (Δ_rH⁰, Δ_rS⁰, Δ_rG⁰) for the esterification reaction was calculated as well. In addition, the results of six consecutive cycles of the catalyst showed that ChCl-PTSA has good stability and recyclability.

This study undertakes a detailed theoretical investigation into the iso-pentanol radical isomerization and decomposition kinetics and the mechanism development of the iso-pentanol oxidation. The CCSD(T)/CBS//M08-HX/6-311+G(2df,2p) method was adopted to calculate the reaction potential energy surface. The reaction rate coefficients were calculated by variational transition state theory (VTST) with multistructural torsional (MS-T) partition function and small curvature tunneling (SCT) correction. Moreover, the pressure-dependent rate coefficients were determined using the system-specific quantum Rice-Ramsperger-Kassel theory (SS-QRRK). The variational and tunneling effects were discussed, and the dominant reaction channels were identified. It reveals that the isomerization reactions play a significant role at low temperatures, while the decomposition reactions dominate the high-temperature regime. Notably, the quantitative rate expressions for iso-pentanol radical decomposition reactions were also obtained. Furthermore, a new kinetic model incorporating the calculated rate coefficients was constructed, exhibiting satisfactory prediction performance on ignition delay times and improved predictive accuracy of species mole fractions. This work provides accurate rate data of isomerization and decomposition kinetics and contributes to a more comprehensive understanding of the iso-pentanol oxidation mechanism.

Catalytic aqueous-phase reforming (APR) of wet biomass such as microalgae and activated sludge is a potential technique for the production of H₂-rich gaseous products. In the present work, model compounds such as ethylene glycol, xylose and alanine were selected as representatives of the polyols, carbohydrates and proteins in wet biomass. APR trials were performed in a stirred batch reactor using commercial Pt/Al₂O₃ and Ru/Al₂O₃ catalysts. The reforming reactions were investigated at different conditions: temperature (T), 498 to 518 K, feed concentration, 1 to 5 wt. %, catalyst loading (ω), 2 to 6 kg/m³, and reaction time (t), 1 to 6 h. The commercial Pt/Al₂O₃ catalyst exhibited higher reforming activity. The influence of reaction parameters on turnover frequency (TOF_H₂), hydrogen yield (Y-H₂) and carbon-to-gas conversion (C to G conversion) was studied. The values of TOF_H₂ for Pt/Al₂O₃ were measured at T = 518 K, ω = 2 kg/m³ and t = 3 h using 1 wt% feed and these values were 19.2, 4 and 6 1/min for ethylene glycol, xylose and alanine. The values of TOF_H₂ over Ru/Al₂O₃ under identical conditions were: ethylene glycol–12.4, xylose–1.4 and alanine–5.4 1/min. The activation energies for H₂ production from ethylene glycol, xylose and alanine over Pt/Al₂O₃ and Ru/Al₂O₃ catalysts were determined. APR of the mixture of model compounds was also studied over laboratory-made Pt/Al₂O₃ and Ru/Al₂O₃ catalysts at the optimum reaction conditions. Thus, this work has provided crucial insights into the production of H₂ from model compounds of wet biomass using Al₂O₃-supported catalysts.

Advanced biofuels have the potential to supplant significant fractions of conventional liquid fossil fuels. However, the range of potential compounds could be wide depending on selected feedstocks and production processes. Not enough is known about the engine relevant behavior of many of these fuels, particularly when used within complex blends. Simulation tools may help to explore the combustion behavior of such blends but rely on robust chemical mechanisms providing accurate predictions of performance targets over large regions of thermochemical space. Tools such as automatic mechanism generation (AMG) may facilitate the generation of suitable mechanisms. Such tools have been commonly applied for the generation of mechanisms describing the oxidation of non-oxygenated, non-aromatic hydrocarbons, but the emergence of biofuels adds new challenges due to the presence of functional groups containing oxygen. This study investigates the capabilities of the AMG tool Reaction Mechanism Generator for such a task, using diethyl ether (DEE) as a case study. A methodology for the generation of advanced biofuel mechanisms is proposed and the resultant mechanism is evaluated against literature sourced experimental measurements for ignition delay times, jet-stirred reactor species concentrations, and flame speeds, over conditions covering φ = 0.5–2.0, P = 1–100 bar, and T = 298–1850 K. The results suggest that AMG tools are capable of rapidly producing accurate models for advanced biofuel components, although considerable upfront input was required. High-quality fuel specific reaction rates and thermochemistry for oxygenated species were required, as well as a seed mechanism, a thermochemistry library, and an expansion of the reaction family database to include training data for oxygenated compounds. The final DEE mechanism contains 146 species and 4392 reactions and in general, provides more accurate or comparable predictions when compared to literature sourced mechanisms across the investigated target data. The generation of combustion mechanisms for other potential advanced biofuel components could easily capitalize on these database updates reducing the need for future user interventions.

The reaction of the 1-naphthyl radical C₁₀H₇• (A2•) with molecular (³O₂) and atomic oxygen, as part of the oxidation reactions of naphthalene, is examined using ab-initio and DFT quantum chemistry calculations. The study focuses on pathways that produce the intermediate final products CO, phenyl and C₂H₂, which may constitute a repetitive reaction sequence for the successive diminution of six-membered rings also in larger polycyclic aromatic hydrocarbons. The primary attack of ³O₂ on the 1-naphthyl radical leads to a peroxy radical C₁₀H₇OO• (A2OO•), which undergoes further propagation and/or chain branching reactions. The thermochemistry of intermediates and transition state structures is investigated as well as the identification of all plausible reaction pathways for the A2• + O₂ / A2• + O systems. Structures and enthalpies of formation for the involved species are reported along with transition state barriers and reaction pathways. Standard enthalpies of formation are calculated using ab initio (CBS-QB3) and DFT calculations (B3LYP, M06, APFD). The reaction of A2• with ³O₂ opens six main consecutive reaction channels with new ones not currently considered in oxidation mechanisms. The reaction paths comprise important exothermic chain branching reactions and the formation of unsaturated oxygenated hydrocarbon intermediates. The primary attack of ³O₂ at the A2• radical has a well depth of some 50 kcal mol⁻¹ while the six consecutive channels exhibit energy barriers below the energy of the A2• radical. The kinetic parameters of each path are determined using chemical activation analysis based on the canonical transition state theory calculations. The investigated reactions could serve as part of a comprehensive mechanism for the oxidation of naphthalene. The principal result from this study is that the consecutive reactions of the A2• radical, viz. the channels conducting to a phenyl radical C₆H₅•, CO₂, CO (which oxidized to CO₂) and C₂H₂ are by orders of magnitude faster than the activation of naphthalene by oxygen (A2 + O₂ → A2• + HO₂).

Cyclopentane (C₅H₁₀) and tetrahydrofuran (C₄H₈O) are both five-membered ring compounds. The present study compares the auto-ignition of cyclopentane and tetrahydrofuran in a high-pressure shock-tube (20 atm). Twelve different mixtures were investigated at two different fuel initial mole fractions (1% and 2%): at X_fuel = 1%, three equivalence ratios, kept constant between cyclopentane and tetrahydrofuran, were studied (0.5, 1, and 2), whereas three X_fuel/X_O2 were investigated when X_fuel = 2%. A detailed kinetic mechanism was developed to reproduce cyclopentane and tetrahydrofuran auto-ignition. The agreement between our experimental results and the modeling is very good. This mechanism was used to explain the similarities and differences observed between cyclopentane and tetrahydrofuran auto-ignition.

Present study involves the investigation of the esterification kinetics between butyric acid and n-butanol. This reaction was conducted in a batch reactor, utilizing homogeneous methanesulfonic acid (MSA) catalyst. Response surface methodology (RSM) was conducted prior to the kinetic study using “Design Expert; version-11.0” for finding the causal factors influencing the conversion of butyric acid. Most important factors identified with their limits against conversions (during optimization of the process using RSM) were taken up to critically analyze the effect of them on butyric acid conversion. Concentration and activity-based model of the process were proposed assuming second order reversible reaction scheme using homogeneous MSA catalyst. During the study of non-ideal behavior of the system, UNIFAC model was adapted for assessing the activity coefficients of species present in equilibrated liquid phase. Experimental data were used to evaluate kinetic and thermodynamic parameters such as rate constants, activation energy, enthalpy, and entropy of the system. The endothermic nature of esterification was confirmed by positive value of enthalpy obtained. The effect of various levels of causal variables like temperature (60–90°C), catalyst concentration (0.5–1.5 wt.%), and molar ratio of n-butanol to butyric acid (1–3) on conversion kinetics of butyric acid was investigated during transient and equilibrium phase of the reaction. It has been observed that molar ratio of butanol to butyric acid has the highest influence on the conversion. The rate equation derived offered a kinetic and thermodynamic framework to the generated data. It also exhibits a notable degree of conformity of predicted data to the experimental ones and effectively characterizes the system across different reaction temperatures, reactant molar ratio, and catalyst concentration.

The fate of Coumaphos in the environment was evaluated through meticulous emulation and analysis of the intricate pedospheric matrices. The fate-determinative investigations entailed a meticulous examination of Coumaphos's behavior, encompassing adsorption and desorption characteristics and its decomposition rate via hydrolysis, photolysis, and intrinsic biological degradation in soil. The interactions between Coumaphos molecules and soils were found to be robust, with physiosorption being the predominant mode of interaction. Thermodynamic analysis, based on the negative values of Gibbs free energy (−23,569 to −15,798 kJ/mol), indicated exothermic and spontaneous adsorption processes. The highest adsorption capacity (K_d(ads) = 34.97 μg/mL) was observed in soils with a notable organic matter content (1.99%), exhibiting a C-type isotherm that was confirmed through linear and Freundlich models. Analytical techniques such as ultraviolet-visible spectrophotometry and gas chromatography-mass spectrometry were employed to determine the fate of Coumaphos in soil matrices. The minimum half-lives of Coumaphos in hydrolysis, biodegradation, and photolysis experiments were 203, 52, and 69 days, respectively. These findings highlight the strong affinity of Coumaphos for the selected agricultural soils, indicating limited potential for transformation. Moreover, findings highlight the potential for further optimization of these degradative routes to devise practical strategies for environmental remediation utilizing natural processes.

The kinetics of the reaction of H-atom with carbonyl sulfide (OCS) has been investigated at nearly 2 Torr total pressure of helium over a wide temperature range, T = 255–960 K, using a low-pressure discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction H + OCS → SH + CO (1) was determined under pseudo-first order conditions, monitoring the kinetics of H-atom consumption in excess of OCS, k₁ = 6.6 × 10⁻¹³ × (T/298)³ × exp(−1150/T) cm³ molecule⁻¹ s⁻¹ (with estimated total uncertainty on k₁ of 15% at all temperatures). Current measurements of k₁ at intermediate temperatures (520–960 K) appear to reconcile previous high and low temperature data and allow the above expression for k₁ to be recommended for use in the extended temperature range between 255 and 1830 K with a conservative uncertainty of 20%.

In this study, the kinetics and mechanism of UV/O₃ synergistic oxidative digestion of dissolved organic phosphorus (DOP) were investigated, focusing on the ozone direct oxidation and hydroxyl radical oxidation parts of glufosinate and triphenyl phosphate (TPhP). The p-chlorobenzoic acid (p-CBA) was selected as the probe compound, and two kinds of reaction kinetic models were proposed by competitive kinetic method with R_ct according to the different scale of rate constants of hydroxyl radical oxidation. Under the condition of weakly alkaline (pH = 9.0) and weakly acidic environment (pH = 5.0), the second-order rate constants of glufosinate and TPhP was determined indirectly to be ko_{3/glufosinate} = (2.903 ± 0.247)M⁻¹s⁻¹ and ko_3/TPhP = (3.307 ± 0.204) M⁻¹s⁻¹ by ozone direct oxidation, and k_{·OH/glufosinate} = (1.257 ± 1.031) × 10⁹ M⁻¹s⁻¹ and k_·OH/TPhP = (7.120 × 10⁸ ± 0.963) M⁻¹s⁻¹ by hydroxyl radical oxidation, respectively. The comparison of the contribution levels of the two parts to the digestion process showed that the contribution levels in the digestion of glufosinate and TPhP processes both the contribution of ·OH were higher than those of ozone, 86.3% and 72.6%, respectively.