Decomposition Rate Coefficient Research Articles

Thermal decomposition of alkenes: role of allylic C-C bond cleavage

Thermal decomposition of alkenes is critical in many chemical processes. In the alkene moiety, allylic CC bonds are significantly weaker than alkylic and vinylic CC bonds. To address literature discrepancies in the rate of allylic CC bond cleavage, the current work investigates the thermal decomposition of two prototype molecules, namely 1-hexene (k1) and 4-methyl-1-pentene (k2). The formation of product allyl radicals is tracked using a highly sensitive UV laser diagnostic to determine the rate coefficients of k1 and k2 over 1178–1359 K in a shock tube. Both reactions exhibit a positive Arrhenius temperature dependence, with the decomposition of 4-methyl-1-pentene occurring 1.5–3 times faster than that of 1-hexene. Values of k1 adopted in literature models vary by an order of magnitude.By integrating our previous measurements of 1-butene and 1-pentene decomposition (Zhou et al., 2024), this work establishes a comprehensive set of rate rules that encompasses the decomposition of allylic-primary (P), allylic-secondary (S21 and S22), and allylic-tertiary (T) CC bonds. At 1200 K, the decomposition of a tertiary allylic CC bond (kT) occurs 42 times faster than that of the primary CC bond (kP). Notably, our established rate rules caution against commonly adopted analogies between the rate coefficients of the thermal decomposition of 1-butene and 1-pentene, as kS21 proceeds 3–7 times faster than kP.The implementation of these rate rules in various kinetic models of alkenes and biofuels greatly enhances the accuracy of their predictions. This work thus contributes to a deeper understanding of the mechanisms underlying soot formation during from the combustion of unsaturated fuels.

High-Temperature Pyrolysis Study of 2-Methyl-2-butanol behind Reflected Shock Wave: Shock Tube and Computational Study.

Pyrolysis of a branched alcohol, 2-methyl-2-butanol (2M2BOH), was carried out behind the reflected shock wave in the temperature range of 1011-1303 K and under pressures varying from 9.3 to 14.6 atm. Qualitative and quantitative analysis of the postshock mixture was performed using gas chromatography-mass spectrometry and gas chromatography with a flame ionization detector, respectively. The rate coefficients for the C-C and C-O bond cleavage reaction pathways were calculated using the variational transition-state theory. The Rice-Ramsperger-Kessel-Marcus/Master equation was employed to calculate the rate coefficients for the H2O-elimination reactions, unimolecular dissociation, and isomerization reaction pathways. The overall decomposition rate coefficient for the 2-methyl 2-butanol (2M2BOH) was estimated to be , where activation energy is given in kcal mol-1. The reaction path analysis was performed, which gives information regarding the contribution of individual intermediate species toward the decomposition of 2M2BOH. A set of reactions was proposed and used to simulate the combustion chemistry of 2M2BOH, which consists of 48 reactions and 39 species. The experimentally measured and simulated mole fractions for the reactant and products showed reasonably good agreement. This work additionally investigates the effect of branching on the decomposition kinetics of long-chain alcohols.

Allylic-alkylic C-C bond decomposition in 1-butene and 1-pentene

1-Butene and 1-pentene are critical intermediates in the oxidation and pyrolysis of larger alkanes and alcohols. Their thermal decomposition plays important role in fuel consumption under combustion conditions, yet seldom investigated. In this work, we studied the title reactions behind reflected shock waves over temperatures of 1178 – 1416 K and pressures near 1.2 bar. We monitored absorbance time-history of the product allyl radicals by employing a sensitive UV diagnostic scheme at a wavelength of 220 nm. We extracted the target rate coefficients by simulating the measured absorbance profiles with detailed kinetic models. Our determined rate coefficients of 1-butene (k1) and 1-pentene (k2) thermal decomposition may be expressed as (unit s−1):k1(1C4H8→CH3+aC3H5)=1.52×1016e(−37937T)k2(1C5H10→C2H5+aC3H5)=3.84×1014e(−31434T)We believe the current work provides the first direct measurements of these reactions. Our 1-butene thermal decomposition rate coefficients exhibit a positive Arrhenius temperature dependence. Around 1350 K and 1 bar, 1-butene decomposition proceeds ∼ 4.5 times faster than n-butane, and ∼ 66 times faster than 1,3-butadiene. Our work extends the literature measurements of 1-butene decomposition to temperatures higher than 1310 K. Literature measurements above 1000 K underestimate our rate coefficients by ∼ 20 %. Additionally, our 1-butene rate coefficients provide an analogy to bio-derived molecules containing similar allylic-alkylic C-C bonds, such as methyl-3-hexenoate. For 1-pentene thermal decomposition, we observed the product allyl radicals starting from 1178 K compared to 1213 K in 1-butene measurements. Thus 1-pentene decomposition proceeds 2 – 6 times faster than 1-butene, and shows a gentler Arrhenius temperature dependence. The current literature models exhibit a range of rate values that vary by an order of magnitude, resulting in noticeable discrepancies. Our study addresses this issue by providing much-needed clarity and precision. Furthermore, we implemented our rate coefficients in literature kinetic models and evaluated their influence on ignition delay time (IDT) and speciation measurements. The results indicate that our rate coefficients generally improved the model performance.

Experimental and modeling study of the N, N-dimethylformamide pyrolysis at atmospheric pressure

As a polar solvent, N, N-Dimethylformamide (DMF) is a potential source of volatile organic compounds during industrial processing. The potential energy surface and pressure-dependent rate coefficients of DMF primary and secondary thermal decomposition were theoretically investigated by automatic ab initio calculations. A singlet aminohydroxycarbene route generating CO is found to be the most energetically favored channel among the unimolecular initiation reactions with a tight transition state. A kinetic model was proposed for DMF pyrolysis prediction and validated against the speciation data newly obtained from synchrotron vacuum ultraviolet photoionization mass spectrometry in a flow reactor within 773 K–1048 K and literature data in a jet stirred reactor within 450 K–900 K at atmospheric pressure. Satisfactory agreements were obtained for the major intermediates and products, but the model failed to capture the formation of some oxygenated compounds, possibly due to the missing reaction pathway for bimolecular addition. During pyrolysis, DMF is mainly consumed by the hydrogen abstraction reaction as the relatively high CN bond energy hinders the barrierless homolytic cleavage. Unlike aldehydes where the carbonyl site is favored, H-abstraction from DMF methyl sites is prevalent, although the acylamino group readily undergoes decarbonylation and β-scission forming oxygenated and nitrogenous parts. Consequently, CO and HCN are the major pyrolysis products. Besides, by incorporating essential high temperature kinetics, extended validation was conducted against the available intermediate temperature autoignition delay times (1000–1350 K, 2 bar) and laminar burning velocity data, and the reason for the discrepancy between the model prediction and experiments was inferred according to the sensitivity analyses.

Shock Tube/Laser Absorption Measurements of the High-Temperature Spectra and Decomposition of Propyl Ethers.

This work presents measurements of temperature-dependent absorption spectra and thermal decomposition rates of propyl ethers, specifically di-n-propyl ether (DnPE) and diisopropyl ether (DiPE), which are two renewable fuel candidates. We employed a broadband rapid-tuning MIRcat-QT laser, operating in the scan/fixed-wavelength mode in combination with a shock tube. Spectral measurements were performed over the wavelength range of 8.4-11 μm (909.1-1190.5 cm-1), covering the strongest infrared absorption bands of the studied ethers, at temperatures of 559-853 K and pressure near 1 bar. These high-temperature spectra help in selecting the optimum wavelength for sensitive and selective measurements of the target ethers. Based on the criteria of high sensitivity, minimum interference, and insensitivity to temperature and pressure variations, we selected a wavelength of 1121.82 cm-1 for high-temperature diagnostics of DnPE and DiPE. Absorption cross sections at the selected wavelength of 1121.82 cm-1 were measured over 550-1500 K, and pressures ranging from 0.3-1.4 bar. This diagnostic was then applied to study the high-temperature pyrolysis of these ethers by measuring their time histories behind the reflected shock waves. Our experimentally measured overall decomposition rate coefficients for DnPE and DiPE are given as (unit of s-1) kDnPE = 1.25 × 1027 × T-3.483 × exp(-37620 K/T) and kDiPE = 5.26 × 1023 × T-2.857 × exp(-32360 K/T).

Gamma-valerolactone (GVL) as a biofuel: Investigation of GVL thermal decomposition and GVL + OH reaction

Recent works have highlighted the potential of lignocellulosic-derived γ-valerolactone (GVL) as a promising biofuel or a fuel additive. Its detailed chemistry is, however, not yet well-understood. In this work, we present the first high-temperature measurements of GVL + OH reaction behind reflected shock waves over 990–1294 K and pressures ∼ 1.2 bar. Around 990 K, our rate coefficients are ∼3 times faster than the average room-temperature determination. Our measured OH + GVL rate coefficients may be given as (unit: cm3molecule−1s−1):k1=4.87×10−10e(−4440T)We also conducted the first direct measurements of GVL thermal decomposition over 1214–1427 K and pressures ∼ 1.4 bar. GVL decomposition rate coefficients exhibit a similar slope to its acyclic counterpart, ethyl propionate, but GVL decomposes ∼80–120 times slower than ethyl propionate. Our determined GVL thermal decomposition rate coefficients may be expressed as (unit of s−1):k2=2.13×1012e(−28548T)Our experimental work represents the first quantitative measurements of the reactions of the lactone family. Both reactions of the lactone family studied here proceeded slower than the normal-chain counterparts which affirms that ring constraints must be considered in rate coefficient analogies between normal-chain and cyclic molecules.

High-temperature mid-IR absorption and reaction kinetics of 2-methyl-1,3-dioxolane: An experimental and theoretical study

This work reports the mid-IR spectroscopy and reaction kinetics of 2-methyl-1,3-dioxolane (2M13DO). We carried out spectroscopic measurements to deduce temperature-dependent absorption cross-sections of 2M13DO over a broad wavelength range of 8.4–10.5 μm (950–1190 cm−1). For these measurements, we employed a rapidly tuning MIRcat-QT™ laser that can be operated either at a fixed wavelength or scanned mode over wide wavelength regions. By operating the laser at a fixed wavelength, we monitored the decay of 2M13DO behind reflected shock waves over T5 = 1050–1400 K and P5 = 0.7 and 2.6 bar. Our measured concentration time-histories of 2M13DO allowed us to directly extract the overall rate coefficients for the unimolecular decomposition of 2M13DO using the first-order rate law. We did not observe any pressure dependence in the measured rate coefficients, indicating that the reaction is close to the high-pressure limit. By employing the W1U composite method, we explored the important pyrolysis reaction pathways of 2M13DO in the reactive potential energy surface. Three important reaction channels, namely, 2M13DO → CH2CHOCH2CH2OH (IM1), 2M13DO → 2CH3CHO (P3), 2M13DO → CH3 + 1,3-dioxolan-2-yl (P4) were identified. Below 700 K, IM1 forming channel is dominant, whereas CH3CHO formation is dominant under our experimental conditions. Above 1500 K, the radical forming channel (CH3+P4) takes over other channels. At higher temperatures, the contribution of the radical forming channel continually increases, accounting for ∼ 99% at 2000 K. We used the stochastic RRKM-ME model to predict the pressure and temperature dependence of the rate coefficients, k(T, P), and time-resolved species profiles. Our theory showed excellent agreement with the measured rate coefficients. These are the first direct determination of the rate coefficients of the unimolecular decomposition of 2M13DO.

Моделирование процесса распада гидрата метана путем закачки горячей воды

To extract natural gas from hydrates by injection of hot water, the decomposition of natural gas hydrates in a porous medium under the influence of a heat flow was experimentally and numerically simulated. It is assumed that the radial diffusion model describes the decomposition of natural gas hydrates in a porous medium due to the injection of hot water, and the decomposition of hydrates is a first-order reaction. By combining the decomposition reaction rate equation with the heat transfer rate equation and the heat balance equation, the relationship between the accumulatedamount of methane (n -n ) and the decomposition time t was obtained. By comparing the results of the experiment0 Hand numerical simulation, it was found that under the experimental conditions, the hydrate decomposition ratecoefficient is consistent with the results of the obtained analytical dependences.

High-temperature mid-IR absorption spectra and reaction kinetics of 1,3-dioxolane

Cyclic saturated ethers are proposed as alternative fuels for future sustainability. In particular, dioxolanes have been identified as promising biofuel candidates. However, pyrolysis and oxidation of dioxolanes are not well understood. In this work, we measured the temperature-dependent absorption cross-section of 1,3-dioxolane (13DO) in the mid-IR region over 8.4 – 10.5 μm (950 –1190 cm−1). We applied the spectroscopic knowledge to investigate the temperature and pressure dependence of the rate coefficients of the unimolecular decomposition of 13DO over the temperature range of 1000–1400 K and pressures near 0.7 and 2.4 bar. We employed a rapidly tuning MIRcat-QT™ laser in conjugation with a shock tube to carry out high-temperature spectroscopic and pyrolysis measurements. Measured IR spectra of 13DO exhibited a strong temperature dependence. For the kinetic study, we employed the vibrational feature of 13DO near 1120.5 cm−1 to monitor the decay of 13DO quantitatively. The measured rate coefficients did not show any discernible pressure dependence. This indicates that the rate coefficients of the unimolecular decomposition of 13DO are close to the high-pressure limit under the present experimental conditions. In addition, we rationalized the temperature and pressure dependence of the reaction by employing electronic structure/RRKM-ME calculations. Our theoretical model accurately captured the experimental trends of the rate coefficients of the unimolecular decomposition of 13DO.

Investigation of the kinetics of conjugated diolefins using UV absorption spectroscopy

Conjugated diolefins are not only crucial intermediates in larger hydrocarbon pyrolysis and oxidation, but also key species in the formation and growth of polycyclic aromatic hydrocarbons (PAHs). In this work, we employed a sensitive UV laser diagnostic to measure absorption cross-sections and decomposition rates of three conjugated diolefins, namely 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene. The single-pass UV absorption diagnostic achieved a ppm-level detection limit between the wavelengths of 212.5 and 220.5 nm. The use of dilute conditions (119 – 500 ppm fuel in argon) enabled nearly isothermal measurements despite reaction enthalpy. Temperature-dependent absorption cross-sections were measured from room temperature to 1850 K and pressures ranging 0.75 – 1.50 bar in a shock tube. Decomposition of the molecules was observed at temperatures above ∼ 1350 K, and all three molecules exhibited similar activation energy. Around 1800 K, 2,3-dimethyl-1,3-butadiene decomposed twice as fast as isoprene and 4 times faster than 1,3-butadiene. Our measured overall decomposition rate coefficients are given as (unit of s − 1, ± 20% uncertainty):k1(1,3−butadiene)=9.65×109e(−24,338KT)(1411−1823K)k2(isoprene)=1.86×1010e(−24,341KT)(1464−1829K)k3(2,3−dimethyl−1,3−butadiene)=8.64×1010e(−25,845KT)(1401−1822K)1,3-Butadiene decomposition rate coefficients agree well with previous measurement at similar pressures. To our knowledge, this work reports first measurements of the decomposition rate coefficients of isoprene and 2,3-dimethyl-1,3-butadiene. As an additional application of the current UV diagnostic, we measured 1,3-butadiene decay time-histories during fuel-lean oxidation and compared our data with the predictions of AramcoMech 3.0. We updated the model with our measured 1,3-butadiene decomposition rate coefficients, which significantly improved the model prediction of fuel oxidation.

Mosses are Important for Soil Carbon Sequestration in Forested Peatlands

Nutrient-rich peat soils have previously been demonstrated to lose carbon despite higher photosynthesis and litter production compared to nutrient-poor soils, where instead carbon accumulates. To understand this phenomenon, we used a process-oriented model (CoupModel) calibrated on data from two closely located drained peat soil sites in boreal forests in Finland, Kalevansuo and Lettosuo, with different soil C/N ratios. Uncertainty-based calibrations were made using eddy-covariance data (hourly values of net ecosystem exchange) and tree growth data. The model design used two forest scenarios on drained peat soil, one nutrient-poor with dense moss cover and another with lower soil C/N ratio with sparse moss cover. Three vegetation layers were assumed: conifer trees, other vascular plants, and a bottom layer with mosses. Adding a moss layer was a new approach, because moss has a modified physiology compared to vascular plants. The soil was described by three separate soil organic carbon (SOC) pools consisting of vascular plants and moss litter origin and decomposed organic matter. Over 10 years, the model demonstrated a similar photosynthesis rate for the two scenarios, 903 and 1,034 g C m−2 yr−1, for the poor and rich site respectively, despite the different vegetation distribution. For the nutrient-rich scenario more of the photosynthesis produce accumulated as plant biomass due to more trees, while the poor site had abundant moss biomass which did not increase living aboveground biomass to the same degree. Instead, the poor site showed higher litter inputs, which compared with litter from vascular plants had low turnover rates. The model calibration showed that decomposition rate coefficients for the three SOC pools were similar for the two scenarios, but the high quantity of moss litter input with low decomposability for the nutrient poor scenario explained the major difference in the soil carbon balance. Vascular plant litter declined with time, while SOC pools originating from mosses accumulated with time. Large differences between the scenarios were obtained during dry spells where soil heterotrophic respiration doubled for the nutrient-rich scenario, where vascular plants dominated, owing to a larger water depletion by roots. Where moss vegetation dominated, the heterotrophic respiration increased by only 50% during this dry period. We suggest moss vegetation is key for carbon accumulation in the poor soil, adding large litter quantities with a resistant quality and less water depletion than vascular plants during dry conditions.

Substrate degradation, biodiesel production, and microbial community of two electro-fermentation systems on treating oleaginous microalgae Nannochloropsis sp

Electro-fermentation system (EFS) emerges its effectiveness on treating microalgae for biodiesel production, but much is unknown about biodegradation behaviors, biodiesel characteristics, and microbial community. Compared with conventional fermentation system (CFS), microbial electrolysis cell-based EFS (MEC-EFS) and microbial fuel cell-based EFS (MFC-EFS) were investigated for the performance while treating microalgae Nannochloropsis sp. Results indicated that MEC-EFS presented much higher first-order decomposition rate coefficients of carbohydrates and proteins (1.212/d and 0.951/d) than those of CFS (0.615/d and 0.794/d) and MFC-EFS (0.518/d and 0.415/d). Compared with MFC-EFS, MEC-EFS showed better electrochemical performance (2.17 A/m3vs. 0.95 A/m3). Moreover, MEC-EFS reached the highest extracted lipid to biomass ratio (43.3%), followed by MFC-EFS (32.3%) and CFS (27.7%). By strengthened microbial biohydrogenation, MEC-EFS and MFC-EFS had higher saturated fatty acids ratio (78.8% and 70.6%) than that of CFS (56.1%). For MEC-EFS, enriched Ruminococcus and Geobacter in anodic biofilm might contribute to favorable biohydrogenation and electrochemical performance.

Time-Resolved Measurements and Master Equation Modelling of the Unimolecular Decomposition of CH3OCH2

Abstract The rate coefficient for the unimolecular decomposition of CH3OCH2, k 1, has been measured in time-resolved experiments by monitoring the HCHO product. CH3OCH2 was rapidly and cleanly generated by 248 nm excimer photolysis of oxalyl chloride, (ClCO)2, in an excess of CH3OCH3, and an excimer pumped dye laser tuned to 353.16 nm was used to probe HCHO via laser induced fluorescence. k 1(T,p) was measured over the ranges: 573–673 K and 0.1–4.3 × 1018 molecule cm−3 with a helium bath gas. In addition, some experiments were carried out with nitrogen as the bath gas. Ab initio calculations on CH3OCH2 decomposition were carried out and a transition-state for decomposition to CH3 and H2CO was identified. This information was used in a master equation rate calculation, using the MESMER code, where the zero-point-energy corrected barrier to reaction, ΔE 0,1, and the energy transfer parameters, ⟨ΔEdown⟩ × T n, were the adjusted parameters to best fit the experimental data, with helium as the buffer gas. The data were combined with earlier measurements by Loucks and Laidler (Can J. Chem. 1967, 45, 2767), with dimethyl ether as the third body, reinterpreted using current literature for the rate coefficient for recombination of CH3OCH2. This analysis returned ΔE 0,1 = (112.3 ± 0.6) kJ mol−1, and leads to k 1 ∞ ( T ) = 2.9 × 10 12 $k_{1}^{\infty}(T)=2.9\times{10^{12}}$ (T/300)2.5 exp(−106.8 kJ mol−1/RT). Using this model, limited experiments with nitrogen as the bath gas allowed N2 energy transfer parameters to be identified and then further MESMER simulations were carried out, where N2 was the buffer gas, to generate k 1(T,p) over a wide range of conditions: 300–1000 K and N2 = 1012–1025 molecule cm−3. The resulting k 1(T,p) has been parameterized using a Troe-expression, so that they can be readily be incorporated into combustion models. In addition, k 1(T,p) has been parametrized using PLOG for the buffer gases, He, CH3OCH3 and N2.

Organic Carbon Decomposition in Soil Amended With Organic Compost From Slaughterhouse Residues

Decomposition kinetic of applied compost in soil depends on the decomposition rate coefficient (k), environmental conditions and the interactions with soil. However, studies with the aim of determining k values for different materials rarely consider interactions with soil. The objective of the current study was to estimate k value of an organic compost, considering the interactions with the soil. Samples of soil mixed with compost were incubated in hermetic recipients for 126 days and evolved C-CO2 was quantified. Nonlinear models proposed in the present study were fitted to evolved C-CO2 data. Better fitting was found in a model that divided the soil organic matter in four pools (labile and recalcitrant native soil organic matter; protected and unprotected added organic matter), values of k on both native organic matter pools were multiplied by a constant denominated priming (pr) only in the cases where the compost was added to the soil and the amount of C in the protected pool is limited to the soil protection capacity. Organic compost produced using carcasses, sheepfold residues and slaughterhouse residues presented k value equal to 0.01179 day-1 at 31 oC without water stress. Compost application increased in 9.8% the decomposition of the native soil organic matter.

Decomposition of carbon dioxide by recombining hydrogen plasma with ultralow electron temperature

We examined the rate coefficient for the decomposition of CO2 in low-pressure recombining hydrogen plasmas with electron temperatures between 0.15 and 0.45 eV, where the electron-impact dissociation was negligible. By using this ultralow-temperature plasma, we clearly observed decomposition processes via vibrational excited states. The rate coefficient of the overall reaction, CO2 + e → products, was 1.5 × 10−17 m3/s in the ultralow-temperature plasma, which was 10 times larger than the decomposition rate coefficient of 2 × 10−18 m3/s in an ionizing plasma with an electron temperature of 4 eV.

Rapid Aqueous-Phase Hydrolysis of Ester Hydroperoxides Arising from Criegee Intermediates and Organic Acids.

Stabilized Criegee intermediates react with organic acids in the gas phase and at the air-water interface to form a class of ester hydroperoxides, α-acyloxyalkyl hydroperoxides (αAAHPs). A number of recent studies have proposed the importance of αAAHPs to the formation and growth of secondary organic aerosol (SOA). The chemistry of αAAHPs has not been investigated due to a lack of commercially available chemical standards. In this work, the behavior of αAAHPs in condensed phases is investigated for the first time. Experiments were performed with two synthesized αAAHP species. αAAHPs decomposed rapidly in the aqueous phase, with the rate highly dependent on the solvent, temperature, solution pH, and other compounds present in the solution. The measured 1st-order decomposition rate coefficient varied between 10-3 and 10-5 s-1 under the conditions examined in this work. Elucidation of the reaction mechanism is complicated by byproducts arising from the synthetic procedure, but observations are consistent with a base-catalyzed hydrolysis of αAAHPs. The rapid hydrolysis of αAAHPs observed in this work implies their short lifetimes in ambient cloud and fog waters. Decomposition of αAAHPs likely gives rise to smaller peroxides, such as H2O2. The loss of αAAHPs is also relevant to filter extraction, which is commonly practiced in laboratory experiments, potentially explaining contradictory results reported in the existing literature regarding the importance of αAAHPs in SOA.

Numerical Simulation and Sensitivity Analysis for Nitrogen Dynamics Under Sewage Water Irrigation with Organic Carbon

This study is focused on investigating the impacts of organic carbon on the denitrification process of nitrogen transformation and transport. A numerical model, Nitrogen-2D, is modified by considering the impact of organic carbon in the denitrification equation. The modified model is used to simulate the soil nitrogen (including nitrate and ammonium) dynamics under the primary and secondary sewage water irrigation with different organic carbon concentrations. The simulated results of accumulated drainage water amount, soil nitrogen concentration, and nitrogen concentration in the drainage water show that the simulations and measurements are consistent. The comparison of results from the original and improved models shows the necessity to consider the impact of organic carbon. The nitrogen mass balance is calculated to analyze the nitrogen transformation processes quantitatively under different input organic carbon sources. Furthermore, the effect of different input organic carbon sources on the soil nitrogen dynamics is investigated by using the modified Nitrogen-2D model with the calibrated parameters. The input organic carbon source helps to speed up the mineralization and denitrification, which contributes to the slight increase of ammonium concentration and the decrease of nitrate concentration in the shallow soil. Since a large number of soil water and nitrogen transformation and transport parameters are needed when setting up the model, a local sensitivity method is conducted to evaluate the input parameters by the sewage water irrigation case. The results show that the drainage water amount is very sensitive to the exponent n and the coefficient α of the soil water retention function and that the ammonium concentration is very sensitive to the first-order nitrification rate constant, the decomposition rate coefficient in humus pool, and the soil ammonium adsorption coefficient. The nitrate concentration is sensitive to more parameters, especially to the exponent n and the coefficient α in the soil water retention function and to the denitrification rate constant.

Experimental and RRKM Investigations on the Degradation of Ethyl Formate

AbstractA Single pulse shock tube was used to investigate the thermal decomposition of ethyl formate over the temperature range of 909–1258 K and pressure range of 9–17 atm. RRKM (Rice‐Ramsperger‐Kassel‐Marcus) theory was used to estimate the temperature (500–2500 K) and pressure dependent (0.01–100 atm) rate coefficients. The products identified were methane, ethylene, and propane. The initial elementary step for the decomposition of ethyl formate is the unimolecular elimination of ethylene via the reaction CH3CH2OC(O)H → CH2=CH2 + HCOOH. The formed formic acid is further decomposed within the studied temperature range. A detailed reaction mechanism proposed with 21 species and 22 elementary reactions was used to simulate reactant and product distribution over the investigated temperature range. The temperature dependent rate coefficient for the total decomposition of ethyl formate was found to be (909–1258 K)=2.68 × 1011 (s−1) exp (‐42.9 ± 2.2 kcal mol−1/RT). The bond dissociation energies were calculated for the various types of bonds. The calculated total rate coefficient for the thermal decomposition of ethyl formate is (500–2500 K)=3.61 × 1013 (s−1) exp (‐53.4 kcal mol−1/RT) at high pressure limit.

Shock tube study and RRKM calculations on thermal decomposition of 2-chloroethyl methyl ether

The thermal decomposition of 2-chloroethyl methyl ether (2-CEME) was studied in the temperatures between 1175 and 1467 K. The decomposition of 2-CEME happens predominantly via molecular elimination reactions than via CC and CO bond fission channels. The major decomposition products are methane, ethylene and methanol. The minor are acetaldehyde and ethane. The Arrhenius expression for the overall decomposition of 2-CEME was obtained to be ktotalexp(1175−1467K)=(4.12±0.42)×1011exp(−(52.2kcalmol−1±2.6)/RT)s−1. To simulate the distribution of reactant and products over the experimentally studied temperatures between 1175 and 1467 K, a reaction scheme was constructed with 45 species and 71 elementary reactions. The pressure and temperature dependent rate coefficients were calculated for various unimolecular dissociation pathways in 2-CEME using RRKM theory. The high pressure limit temperature dependent rate coefficient for the total decomposition of 2-CEME was obtained to be ktotalCCSDT//M06−2X(500–2000 K) = (2.55 ± 0.21) × 1014 exp (−(67.6 kcal mol−1 ± 3.0)/RT) s−1.

The Borderline between Simultaneous Reverse and Normal Initiation and Initiators for Continuous Activator Regeneration ATRP

Multiple methods for initiation and selecting catalyst concentration exist in atom transfer radical polymerization (ATRP). Among them, simultaneous reverse and normal initiation (SR&NI) ATRP and initiators for continuous activator regeneration (ICAR) ATRP are phenomenologically very similar. In both methods, thermal radical initiators are employed to reduce the catalyst in the higher oxidation state and generate CuI activator in situ. SR&NI and ICAR ATRP generally differ in the amount of catalyst used and in the rate of catalyst reduction. Commonly, SR&NI ATRP requires high catalyst loadings and a quick initial reduction of CuII, while ICAR ATRP relies on slow and continuous reduction of smaller catalyst loadings. However, these criteria might not be sufficient to universally distinguish among both techniques. This article investigates both methods through kinetic simulations and establishes a borderline kinetic criterion. If the polymerization rate depends on the rate of decomposition of the radical initiator, the system follows ICAR ATRP kinetics, and if it depends on the ATRP equilibrium constant, it follows SR&NI ATRP. The transition from one to the other mechanism occurred continuously with an inflection point at a ratio of rate coefficients of radical initiator decomposition to propagation of about kdc/kp ≈ 10–7 M under typical conditions. For faster initiator decomposition and slower propagation ATRP follows SR&NI ATRP, and for slower decomposition and faster propagation it obeys ICAR ATRP kinetics. The analysis to verify which mechanism is in operation is helpful for designing reaction conditions in order to obtain well-defined products.