International Journal of Chemical Kinetics最新文献

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.

The interaction of cetyltrimethylammonium bromide (CTAB) with orange II has been studied spectrophotometrically. CTA-Orange II complex was isolated from an aqueous solution with chloroform. The results indicate that the CTAB interacts in 1:1 stoichiometry with orange II. CTAB capped FeNPs were used as an adsorbent to the removal of CTA-Orange II complex. Energy dispersive x-ray spectroscope (EDX), Fourier transform infrared spectroscope (FTIR), surface scanning microscope (SEM), and transmission electron microscope (TEM) were used to determine the morphology of FeNPs. The effect of contact time, pH, and concentration of orange II were examined on the removal of dye and surfactant. The removal of orange II followed pseudo-second-order kinetic and Langmuir isotherm model. The maximum adsorption capacity (Q_max) of CTAB-FeNPs for orange II was 1288.9 mg/g at 30°C. CTA-Orange II complex was adsorbed onto the adsorbent through several types of interaction (e.g., electrostatic attractions, van der Waals interactions, hydrogen bonding and n-π stacking interactions). The sorption of orange G was also studied at different CTAB concentrations. The results implied that the maximum sorption amount was almost half of the orange II adsorption. The findings reveal the feasibility of CTAB capped FeNPs to be used as an excellent and low-cost adsorbent for the removal of various water pollutants, more specifically anionic dyes.

The kinetics of heterogeneous catalytic reactions is a topic of theoretical and practical importance that combines theoretical and experimental efforts to achieve a deeper insight into the process. Theoretical aspects are concerned with determination of the process mechanism, whereas in practical applications kinetic experiments are applied to assist reactor design and scaling up of various processes. These approaches overlap; basis of the assumed mechanism that consists of many elementary steps, it is possible to find a kinetic equation for which precision is verified by comparison with experimental data. The method most often applied requires finding a single step that has the strongest influence on the process rate. This “classical approach” fails if the rate of two or more steps has comparable values, the precision of the determined kinetic rate becomes only average or even low. Such accuracy was observed, among others, for the gas-phase hydrogenation of propene. The reaction is easy to carry out and proceeds under mild conditions; the byproducts are not observed. It suggests that there cannot be a single dominating effect step on the process rate. In this work, the application of the polynomial kinetic idea to the gas-phase hydrogenation of the propene process realized in practice is tested. An attempt of obtaining a handy and precise relationship, without insignificant parameters was made. To realize this, the theoretical form of the polynomial kinetic was derived, and then, using statistical analysis of estimated polynomial parameters, the kinetic relationship was simplified. The final version of the kinetic polynomial and some selected kinetic equations taken from the literature were compared with respect to precision. The differences were significant: the precision of anticipation of the kinetic rate by the polynomial kinetic was 5% higher than for the power law and 12% higher than for the LHHW kinetic.

The work presented here establishes the experimental findings of the reaction between secondary/tertiary propargylic alcohol (PA) and 1,3,5-trimethoxybenzene (TMB) in the presence of acetonitrile solvent (MeCN) based on theoretical calculations. When secondary PA reacts, the reaction goes via S_N2 pathway, where the reaction barrier is about 14.32 kcal/mol. On the other hand, tertiary PA reacts with TMB via S_N2′ and S_N1′ pathway, and the corresponding reaction barriers are 17.59 and 17.86 kcal/mol. Other possible pathways, namely, S_N1, S_N1′, etc. for secondary PA, and S_N2, S_N1 pathways for tertiary PA are also investigated and the associated barrier heights are found higher. Rates of those reactions are also calculated considering the rate-determining steps only. Reaction of secondary PA with TMB is found to be much faster than the reaction of tertiary PA and the results are in accordance with the experimental findings.

The reactions of pyrazine, pyridazine, and pyrimidine with hydroxyl radicals are theoretically studied. The barrier heights obtained with different electronic structure methods indicate that the reactions can competitively proceed via either abstraction of a hydrogen atom by an OH radical or OH addition to carbon sites. However, the rate constants computed within the temperature range 200 to 1500 K suggest that tunneling play a role resulting in large branching ratios in favor of hydrogen abstraction channels at lower temperatures.

The quest for cleaner environments is a global concern. Hence, the investigation of degradation of the indigo carmine dye (IC) with peroxydisulphate ion in an aqueous sulphuric acid system with a view to understanding its kinetic degradation and mechanism. The degradation depicts first-order kinetics in [S₂O₈²⁻] and [IC], and the degradation mole ratio of IC: S₂O₈²⁻ is 1:1. The degradation rate is dependent on the change in ionic strength and medium permittivity of the system. Also, added ions (NH₄⁺ and NO₃⁻) influence the degradation rate of the dye which further supported the outcome of the change in ionic strength. Free radical participation is ruled out. The experimental rate law is given as (Kk₃[H⁺])[IC][S₂O₈²⁻]. Owing to the absence of detectable intermediates in the degradation process, an outer-sphere mechanism is proposed. The study is significant in textile industries and medical settings for making environments less toxic with a well-understood degradation rate pathway.

Methylcyclohexane (MCH) is the simplest alkylated cyclohexane, and has been widely employed in surrogate models to represent the cycloalkanes in real fuels. Thus, extensive experimental and kinetic modeling studies have been performed to understanding the combustion chemistry of MCH. However, through a detailed literature analysis, there still lack a systematic theoretical study on the abstraction reactions of MCH, which are the main initial oxidation pathway of MCH. Herein, this work reports a systematic ab initio chemical kinetic study on the abstraction reactions of MCH with different radicals/species. Specifically, reaction rate constants of 30 abstraction reactions of MCH with H/O/OH/O₂/HO₂/CH₃ at different sites are computed using transition state theory (TST) by using quantum chemistry calculation results at DLPNO-CCSD(T)/CBS//M06-2X/cc-pVTZ level. The computed results are incorporated into a detailed mechanism to simulate newly measured ignition delay times (IDTs) of MCH in this work at equivalence ratios of 0.5, 1.0, and 2.0, pressures of 2 and 5 bar, temperatures ranging from 1140 to 1640 K. The updated detailed mechanism demonstrates improvement in the prediction of IDTs, especially at fuel-rich conditions. The fuel concentration and dilution effect on the IDTs are discussed, and a general Arrhenius expression is adopted to fit the IDTs from both this work and literature work. This work should be valuable for further optimization of detailed kinetic mechanisms and also for gaining insight into the combustion chemistry of MCH.