Radical Reaction Model Research Articles

Free radical reaction model for n -pentane pyrolysis

Abstract A mathematical mechanism of the n -pentane pyrolysis process based on free radical reaction model was presented. The kinetic parameters of n -pentane pyrolysis are obtained by quantum chemistry and the reaction network is established. The solution of the stiff ordinary differential equations in the n -pentane pyrolysis model is completed by semi implicit Eular algorithm. Then the pyrolysis mechanism based on free radical reaction model is built, and the computational efficiency increases 10 times by algorithm optimization. The validity of this model and its solution method is confirmed by the experimental results of n -pentane pyrolysis.

Assessment of a Cost-Effective Approach to the Calculation of Kinetic and Thermodynamic Properties of Methyl Methacrylate Homopolymerization: A Comprehensive Theoretical Study.

In this work, we carried out a comprehensive density functional theory (DFT) study on the basis of a trimer-to-tetramer radical reaction model to assess a cost-effective approach to perform the calculation of kinetic and thermodynamic properties of methyl methacrylate (MMA) free-radical homopolymerization. By comparing results from several different functionals (PBE, M06-2X, wB97XD, KMLYP, and MPW1B95), in conjunction with a series of basis sets (6-31G(d,p), 6-31+G(d,p), 6-31G(2df,p), 6-311G(d,p), 6-311+G(d,p), 6-311+G(2df,p), 6-311+G(2df,2p)), we show that calculations using M06-2X/6-311+G(2df,p)//B3LYP/6-31G(2df,p) provide an activation energy of 5.25 kcal mol(-1) for the homopropagation step, which is within 1 kcal mol(-1) of the experimental value. However, this method predicts a heat of polymerization of 17.37 kcal mol(-1) that is larger than the experimental value by 3.5 kcal mol(-1). MPW1B95/6-311+G(2df,p) on the B3LYP/6-31G(2df,p) geometries produces a heat of polymerization value within 1 kcal mol(-1) of experimental data, yet overestimates the activation energy by 3 kcal mol(-1). In addition, we evaluated the performance of ONIOM MO:MO calculations on the geometry optimization of species comprising our MMA polymerization model and found that ONIOM(B3LYP/6-31G(2df,p):B3LYP/6-31G(d)) is capable of producing geometries in very good agreement with the full B3LYP/6-31G(2df,p) calculations. Subsequent calculations of energies using M06-2X/6-311+G(2df,p) based on the ONIOM geometries provided an activation energy value comparable to that based on the full B3LYP/6-31G(2df,p) geometries.

Reactivity of Gas-Phase Radicals with Organic Surfaces

In chemical reactions at the gas–surface interface, the heterogeneity in structure of reaction sites plays a critical role in determining surface reactivity. This Perspective describes reaction mechanisms in such systems and details the use of in situ scanning probe microscopy to investigate reactions of gas-phase radicals with self-assembled alkanethiolate monolayers on gold surfaces. For both atomic hydrogen and atomic chlorine reagents, the presence of defects in the alkanethiolate surface order has a substantial influence on what reactions can occur and the speed at which they do so. Data acquired from a series of images were modeled using kinetic Monte Carlo simulations, and a surface radical reaction model was developed to explain the observed evolution of surface structure as the reactions proceed.

Simplifi cation of A Radical Reaction Model Based on Dynamic Sensitivity Analysis: Evaluation of SoftCADS Performance

Simplifi cation of A Radical Reaction Model Based on Dynamic Sensitivity Analysis: Evaluation of SoftCADS Performance

Development of Ozone Self-Decomposition Model for Engineering Design

Recently, due to the advancement of O3/H2O2 treatment processes, it has been necessary to further develop the ozone self-decomposition radical model, which includes a variety of radical reactions, because the hydroxyl radical concentration as well as the ozone concentration must be taken into consideration. In this study, an ozone self-decomposition model that is meaningful for environmental engineering design under the practically encountered pH condition in the time scale of water treatment is proposed. First, an overall description model of ozone self-decomposition is developed based on the experimental results. The evaluation clarifies that the ozone self-decomposition can be formulated by a second-order reaction and the rate constant is enhanced 5 times and 2.2 times with increase of one pH unit and 5°C increase of temperature, respectively. Then a radical reaction model was developed. All of the reaction rate constants included in the model are obtained from the literature review except for the reaction rate constant of ozone with hydroxyl radical, which is obtained as 9.0 × 105 M−1s−1 based on experimental data. Good agreements of calculated results by the model with experimental results under the pH range from 2.7 to 7.8 over 10 minutes are obtained. This radical model of ozone self-decomposition will be applicable in analyzing other reactions, such as the effect of bicarbonate/carbonate ion on ozone self-decomposition, reaction with organic matter, the fate of micropollutants and by-products with ozone as well as hydroxyl radical.

New Approach for Optimization of Ozone-Hydrogen Peroxide Water Treatment

A new radical reaction model for the ozone-hydrogen peroxide treatment, which was much simpler than current models such as SBH and TFG, has been developed by computer simulation in order to investigate a new reactor for this treatment process. It was revealed that the simulation results by using this new developed model were in good agreement with the experimental results in terms of the variation in the concentration of ozone in both gas and liquid phase, hydrogen peroxide and TOC, indicating the appropriateness of this new model. Thus, it was considered that this new model was very convenient for analysis of radical reactions because of its simplicity.

Analysis of the density effect on partial oxidation of methane in supercritical water

Partial oxidation of methane was conducted in supercritical water at O 2/CH 4 ratios of 0.03 at 673 K with a flow-type reactor. The main products were CO, methanol, formaldehyde and a small amount of CO 2 and H 2. With increasing water density, methane conversion increased due to the formation of formaldehyde. A free radical reaction model was applied to this reaction and it was confirmed that the dependence of selectivities for CO and CO 2 on pressure could be well described. The experimental results and model prediction shows that an increase of water density shifted product distribution to partial oxidation products and formaldehyde was found to play an important role in the product selectivity and the partial oxidation chemistry.

オゾン／ＵＶプロセスのためのＣＦＤシミュレータの開発

A new Computational Fluid Dynamics (CFD) simulator for the ozone/UV process has been developed. The radical reaction model used in this simulator was validated by comparing both calculation and experimental results obtained from a completely stirred tank reactor system. Using this simulator, the distributions of relevant substances such as dissolved ozone, hydroxyl radical and organic compounds in the reactor can be investigated. The simulation results of the conventional ozone/UV reactor, i.e., the tube-type reactor where a UV lamp is inserted in parallel to water flow, showed that this conventional reactor is inefficient because hydroxyl radical concentration is high only at the inlet where ozonecontaining water flows in. Furthermore, the results obtained from the simulations with various UV intensity distributions of the lamp showed that the intensified irradiation around the inlet caused 20% improvement in the organic removal efficiency. Thus, the developed simulator is expected to contribute towards the optimization of the ozone/UV reactor for decomposing refractory pollutants.

Development of a simulator for ozone/UV reactor based on CFD analysis

A new CFD (Computational Fluid Dynamics) simulator for an O3/UV reactor where ozone dissolved water flows under the irradiation of UV, has been developed by combining a fluid dynamics model with a complex radical reaction model. The radical reaction model used in this simulator was found to be reasonable, because the results obtained from the simulation of a completely stirred tank reactor (CSTR) system were in good agreement with the experimental results, e.g., the concentrations of total organic carbon (TOC), hydrogen peroxide and dissolved ozone obtained from a lab-scale CSTR. Furthermore, by using this CFD simulator, the distributions of substances such as hydroxyl radical (OH*) and hydrogen peroxide in the O3/UV reactor have been investigated. These distributions showed that this CFD simulator was considered to be reasonable. In addition, the simulation results suggested that conventional reactors were not optimized.

Mechanistic modeling of the wall reactions in the pyrolysis of pentachloroethane

AbstractThe thermal dehydrochlorination C2HCl5 → C2Cl4 + HCl has been studied in a static system between 565 and 645 K at pressures ranging from 5 to 21 torr. The course of the reaction was followed by measuring the pressure rise in the conditioned quartz reaction vessel and by analyzing the products by gas chromatography. The observed experimental results and data from the literature for flow systems can be explained quantitatively in terms of a radical reaction model involving heterogeneous chain initiation and termination steps. The rate constants have been deduced for reactions of Cl, Cl2, and C2HCl5 over reactor walls covered with a pyrolytic carbon film and for reactions of adsorbed Cl atoms. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 322–330, 2002

Mechanism of the pyrolysis of 1,2‐dichloroethane in the absence and presence of added chlorine

AbstractA detailed radical reaction model, both homogeneous and heterogeneous, is shown to describe quantitatively published initial rates of the pyrolysis of 1,2‐dichloroethane in the gas phase. These data were obtained in conditioned static reactors with different surface‐to‐volume ratios, in the absence (at 703 K) and presence (at 572 K) of chlorine. The pressures of 1,2‐dichloroethane and chlorine vary from 20 to 500 torr and from 0 to 16 torr, respectively. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 316–321, 2002

KINETICS OF BETA-CAROTENE DEGRADATION AT TEMPERATURES TYPICAL OF AIR DRYING OF FOODS

Degradation of β-carotene was studied in a model system at temperatures between 60 and 80°C in order to formulate a kinetic model useful in the optimization of air drying processes. Two previously reported kinetic analyses were used: a first order model and a simplified free radical reaction model. In both cases the models fit the experimental data but neither is entirely satisfactory since the kinetic parameters reflected an initial concentration dependence. This dependence disappeared at high carotene initial concentrations and also when the thickness of the lipid layer was increased either by using a support with a lower specific surface area or by adding a saturated fatty acid. These results indicate that at high concentrations oxygen diffusion becomes a limiting factor. When using food systems, a first order model seemed a better choice for the simulation of the carotene degradation. Results could not be directly related to those of the model system, probably because the model was too simple, and did not contain the pro- and anti-oxidant components naturally occurring in foods.