Reaction Coefficient Research Articles

Simulator Aids Design, Analysis of Acidizing Jobs With Fluoroboric Acid

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 205893, “Novel Simulator for Design and Analysis of Matrix Acidizing Jobs With Fluoroboric Acid in Sandstone Reservoirs,” by Mohammed Qamruzzaman, SPE, Mandeep Khan, and Dhirendra C. Roy, SPE, ONGC, et al. The paper has not been peer reviewed. _ Matrix acidizing with fluoroboric acid (HBF4) has gained special attention because of its deeper penetration of in-situ generated hydrofluoric (HF) acid and stabilization of formation fines by binding them to the pore surface. While numerous mathematical models exist in the literature for design and evaluation of conventional mud acid treatments, few attempts have been made in developing a laboratory-validated model that can do so for fluoroboric acid treatments. The complete paper presents a novel mathematical model that has been developed that takes into account the chemical kinetics and equilibrium aspects of important reactions and fluid flow inside the reservoir rock. Mathematical Modeling Because the complete paper contains numerous equations, it is essential for understanding the authors’ description of their mathematical model. The authors identify three benefits of their approach from a modeling point of view. First, it reduces the total number of chemical reactions taking place, which greatly simplifies computational complexity while maintaining reasonable accuracy. Second, the inclusion of separate chemical reactions for silica gel precipitation may require fixing the average value of stoichiometric coefficients for reactions between HF/hexafluorosilicic acid (H2SiF6) and slow- and fast-reacting minerals. This becomes challenging to do beforehand, especially when different types of clays are present with relatively equal proportions in the reservoir. Third, all resulting nondimensional numbers can be estimated easily by measuring effluent acid concentration during coreflooding. The following assumptions have been incorporated into the model: - The reservoir and core are assumed to be homogeneous and isotropic. - Flow is assumed to be one-dimensional. - All fast-reacting minerals are grouped together as a single fast-reacting mineral. - All slow-reacting minerals are grouped together as single slow-reacting mineral. - The reaction of HF with fast- and slow-reacting minerals is assumed to be first-order with respect to HF. - Changes in porosity are small and diffusion/gravity/thermal effects are neglected. Laboratory Studies Laboratory studies were performed on sandstone core samples from a prominent payzone in northeastern India to generate data for model validation. Core plugs of 1.5-in. diameter were taken from the same block to prevent mineralogical heterogeneities. Samples were characterized with X-ray diffraction (XRD) analysis and porosity measurements. This payzone was selected because it consists of a diverse range of minerals. Thus, a model that can be validated with the coreflooding from this sample could, in principle, apply to any other sandstone reservoir.

Second-order time discretization for reaction coefficient estimation of bilinear parabolic optimization problem with Neumann boundary conditions

Second-order time discretization for reaction coefficient estimation of bilinear parabolic optimization problem with Neumann boundary conditions

Revisiting the initial reaction rates for TMS combustion and a new evidence for metastable silica nanoparticles in the gas-phase synthesis

Nanomaterials from gas-phase synthesis are tapping into new fields of application in research and industry due to their unique size-dependent properties. To produce tailored nanoparticles, the synthesis starting from the precursor decomposition to the particle formation must be fully understood. Tetramethylsilane is used as a precursor for the synthesis of silica nanomaterials in flames. The precursor starts to decompose by H-abstraction. Reaction rates for H-abstraction of tetramethylsilane (TMS) by +O/+H/+OH radicals are determined by means of quantum chemical calculations. The rate expressions are obtained in the temperature range from 300 to 1400 K: kH = 6,025,735 (T/K)2.1731exp(-(+2613.840 K)/T) cm3mol−1s−1 for the total bimolecular reaction coefficient of TMS with hydrogen atoms, kOH = 10,179,818 (T/K)1.7790 exp(-(+152.739 K)/T) cm3mol−1s−1 for TMS with OH radicals, and kO = 93,100 (T/K)2.4797 exp(-(+889.166 K)/T) cm3mol−1s−1 for TMS with O(3P) radicals, respectively. The reaction rates are implemented into the TMS reaction mechanism of Janbazi et al. [1], and a better agreement of the TMS reactivity in the flame is achieved. Experiments are conducted to obtain the mass deposition rates with a Quartz-Crystal-Microbalance (QCM) in a wide range of different equivalence ratios. The equivalence ratio is varied between ϕ = 0.6–1.2, and precursor amounts of 400, 600 and 800 ppm are used. These QCM-experiments are complementary to the MBMS-studies from Karakaya et al. [1–3] but use the same flame conditions to extend the data set. The results reveal that metastable particles exist in the reaction zone of the flame. Depending on flame conditions, their concentration decreases towards the end of the reaction zone, but particles subsequently grow again in the recombination zone of the flame. The mechanisms, which describe the reactivity of the metastable nanoparticles, are tentatively proposed. The understanding of the mechanisms can open up the way for tailored nanoparticles with different structures and stoichiometries.

The weakening effect of the inhibition of CO2 on the explosion of HCNG with the increase of hydrogen: Experimental and chemical kinetic research

To explore the inhibitory effect of CO2 on HCNG (Hydrogen enriched compressed natural gas) explosion and its chemical kinetic mechanism, the explosion pressure and flame of CO2/HCNG/Air (hydrogen ratio: 0–0.6, CO2 addition: 3 vol%, 6 vol%, and 9 vol%) were tested in a 20 L spherical explosion tank at normal temperature and normal pressure. The experiment results shown that: as the addition of CO2 increases, the inhibition effect on HCNG explosion flame and pressure becomes more obvious. The larger the H2 ratio, the more difficult it is to inhibit HCNG explosion flame and pressure. To explore the chemical kinetics reasons for the above laws, the chemical kinetic parameters (such as free radical formation rate and temperature sensitivity coefficient) of the explosion reaction under the above conditions were calculated by CHEMKIN-PRO. The results indicate that CO2 mainly acts as a stable third body in the reaction system, thereby slowing down the growth of explosion chain reactions. In addition, as the main product of the CH4 oxidation reaction, CO2 has a certain weakening effect on the CH4 oxidation reaction. As the proportion of H2 increases, the elementary reactions such as 3# and 84# that generate ·H radicals are promoted, increasing the concentration of ·H radicals in the reaction system. Therefore, the dominant role of 38# on the temperature rise of the reaction system is enhanced, and the contribution of the CH4 oxidation reaction to the temperature rise of the reaction system is weakened. This is the chemical kinetic reason that CO2 has a weak inhibitory effect on the energy release of the HCNG explosion reaction when the proportion of H2 is large. The research results can provide a theoretical basis for the development of HCNG explosion prevention and control technology.

Study on Load–Slip Curve of a PBL Shear Key at a Steel–Concrete Composite Joint

The steel–concrete composite truss adopts a new type of steel-concrete composite joint with high rigidity and load-carrying capacity. In order to more conveniently and clearly grasp the working mechanism of Perfobond Leiste (PBL) shear keys in the core area of new composite structures such as steel–concrete composite trusses, the lack of strong theoretical support for the theoretical formula of load–slip relationships in the entire loading process of single PBL shear keys is solved. By proposing a straight–curved–straight three-stage simplified load–slip curve with respect to the PBL shear key, the stress process of the PBL shear key is divided into three stages—the elastic stage, plastic stage, and strengthening stage—based on the compressive yield and failure critical point of tenon concrete in the shear key. With reference to the calculation method of the bearing capacity of the order pile under horizontal loads and by calculating the shear stiffness of the shear key, a theoretical formula suitable for separating the load–slip relationship of a single PBL shear key in the entire loading process of the ear plate composite joint is proposed. The results show that, in the elastic section, the slope of the curve is related to the concrete reaction coefficient and the material parameters of the penetrating steel bar; moreover, in the strengthened section, the coefficient is related to the shear modulus of the penetrating steel bar, and a more uniform length distribution of the penetrating steel bar between the two joint plates will improve the initial stiffness of the PBL shear key to a certain extent. The results of the proposed method are in good agreement with the finite element results and experimental values. This research study’s results can provide a convenient design method for the design of the internal PBL shear keys of new composite structure joints, promoting the promotion and application of new composite structures and advancing the development of the engineering field.

Comprehensive Theoretical Study on Four Typical Intramolecular Hydrogen Shift Reactions of Peroxy Radicals: Multireference Character, Recommended Model Chemistry, and Kinetics.

Intramolecular hydrogen shift reactions in peroxy radicals (RO2• → •QOOH) play key roles in the low-temperature combustion and in the atmospheric chemistry. In the present study, we found that a mild-to-moderate multireference character of a potential energy surface (PES) is widely present in four typical hydrogen shift reactions of peroxy radicals (RO2•, R = ethyl, vinyl, formyl methyl, and acetyl) by a systematic assessment based on the T1 diagnostic, %TAE diagnostic, M diagnostic, and contribution of the dominant configuration of the reference CASSCF wavefunction (C02). To assess the effects of these inherent multireference characters on electronic structure calculations, we compared the PESs of the four reactions calculated by the multireference method CASPT2 in the complete basis set (CBS) limit, single-reference method CCSD(T)-F12, and single-reference-based composite method WMS. The results showed that ignoring the multireference character will introduce a mean unsigned deviation (MUD) of 0.46-1.72 kcal/mol from CASPT2/CBS results by using the CCSD(T)-F12 method or a MUD of 0.49-1.37 kcal/mol by WMS for three RO2• reactions (R = vinyl, formyl methyl, and acetyl) with a stronger multireference character. Further tests by single-reference Kohn-Sham (KS) density functional theory methods showed even larger deviations. Therefore, we specifically developed a new hybrid meta-generalized gradient approximation (GGA) functional M06-HS for the four typical H-shift reactions of peroxy radicals based on the WMS results for the ethyl peroxy radical reaction and on the CASPT2/CBS results for the others. The M06-HS method has an averaged MUD of 0.34 kcal/mol over five tested basis sets against the benchmark PESs, performing best in the tested 38 KS functionals. Last, in a temperature range of 200-3000 K, with the new functional, we calculated the high-pressure-limit rate coefficients of these H-shift reactions by the multi-structural variational transition-state theory with the small-curvature tunneling approximation (MS-CVT/SCT) and the thermochemical properties of all of the involved key radicals by the multi-structural torsional (MS-T) anharmonicity approximation method.

Flow Characteristics of Electrochemical Catalytic Reduction of CO2 in Microchannel

Human beings need abundant material support and energy supply in their exploration of the universe. The sustainable supply of materials is an important condition for long-term space exploration. In situ resource utilization technology (ISRU) is an important way to realize the sustainable development of space exploration, which uses the abundant raw materials in outer space to transform energy and materials. In this paper, a microfluidic reaction device based on in situ resource utilization is designed, which converts H2O and CO2 into O2 and organic matter through photoelectrocatalysis. The flow and mixing process of gas-liquid two-phase flow was studied, and both the characteristics of mass transfer and the chemical reaction of fluids in the microchannel were studied. The dynamic process of the fluid-in-microchannel chemical reaction was expounded, and a prediction model of the volumetric mass transfer coefficient was proposed. The results show that the mass transfer coefficient of the chemical reaction is affected by the gas-liquid flow characteristics, and the mass transfer affects the rate of the chemical reaction. The material conversion of in situ resources by using the microchannel device can improve efficiency and accurately control the reaction products.

Isotope Exchange Reaction of OH− Anion with HD at Temperatures from 15 K up to 300 K: Ion Trap Study

This paper presents the results of an experimental study of the reaction of OH− anions with HD molecules leading to the formation of OD− anions. The study’s main goal was to obtain the temperature dependence of the reaction rate coefficient and determine the reaction’s enthalpy. This study was carried out at astrophysically relevant temperatures from 15 to 300 K. The reaction was studied using a temperature-variable cryogenic linear 22-pole radio-frequency ion trap. The rotational temperature of the OH− anions in the ion trap was characterized by near-threshold photodetachment spectroscopy. At 15 K, the measured reaction rate coefficient is 5 × 10−10 cm3 s−1. With increasing temperature, the reaction rate coefficient decreases monotonically to 5 × 10−11 cm3 s−1 at 300 K. Comparing with the previously determined rate coefficient of the reverse reaction of OD− anions with H2, we obtained the temperature dependence of the equilibrium constant. The enthalpy and entropy of the title reaction were determined in the studied temperature range as ΔH = (−23.9 ± 0.7 ± 2.6sys) meV and ΔS = (−8.5 ± 1.2 ± 1.4sys) J mol−1 K−1, respectively.

Salts and double tartratogermanates/stannates of 3d-metals as modifiers of unsaturated oligoesters

The paper presents the results of the systematic research into effects of 3d-metals acetates, acetylacetonates and double tartrategermanates/stannates on the modification of polyglycol maleine phthalate. The copolymerization parameters of the prepared modified oligoesters with methyl methacrylate monomer and threeethyleneglycoldimethacrylate oligomer were determined. Modifiers were added to the reaction mixture before the start of polycondensation of maleic and phthalic anhydrides with ethylene glycol at the temperature of 1750C. The kinetics of copolymerization at the initial stages was determined by the dilatometry at the temperatures of 500C to 600C. It was established that the modification of polyglycol maleinate phthalate with the studied compounds allows significantly increasing the rate and reducing the temperature coefficient of the copolymerization reaction. There advantages of the investigated double multi-metal mixed ligand coordination compounds as modifiers were proved as compared to the standard industrial systems, acetylacetonates and metal acetates. The presented modifiers are able to improve significantly the characteristics of the semi-finished products in the industrial manufacturing of copolymers without the significant change of the technological process.

Analysis of an LDG-FEM for a two-dimensional singularly perturbed convection-reaction-diffusion problem with interior and boundary layers

This article is concerned with a two-dimensional singularly perturbed convection-reaction-diffusion interface problem. In the considered problem, the convection and reaction coefficients and the source term have discontinuities along interface lines, which are parallel to the x- and y-axes. The coefficient of the highest-order term is a small positive parameter denoted by ε. Due to discontinuities in the coefficients and the source term, interior and boundary layers appear in the solution when ε approaches zero. A Local Discontinuous Galerkin method is constructed on an appropriate Shishkin mesh. The test functions in the Local Discontinuous Galerkin method are piecewise polynomials that lie in the space Qr of piecewise polynomials of degree at most r in each variable, where r is a positive integer. We established that the error in the computed solution converges at the rate of O((N−1ln⁡N)r+12) in an energy-norm. Numerical results are given to support the theoretical results.

Impact of M Dwarfs Ultraviolet Radiation on Prebiotic Chemistry: The Case of Adenine.

To date, several exoplanets have been found to orbit within the habitable zone of main sequence M stars (M dwarfs). These stars exhibit different levels of chromospheric activity that produces ultraviolet (UV) radiation. UV may be harmful to life, but it can also trigger reactions of prebiotic importance on the surface of a potentially habitable planet (PHP). We created a code to obtain the adenine yield for a known adenine synthesis route from diaminomaleonitrile (DAMN). We used computational methods to calculate the reaction coefficient rates (photolysis rate J and rate constant K) for the intermediate molecules DAMN, diaminofumaronitrile (DAFN), and 4-aminoimidazole-5-carbonitrile (AICN) of the adenine synthesis route. We used stellar UV sources and a mercury lamp to compare the theoretical results with experiments performed with lamps. The surface UV flux of planets in the habitable zone of two active M dwarfs (Proxima Centauri and AD Leonis) and the prebiotic Earth was calculated using the photochemical model ATMOS, considering a CO2-N2-H2O atmosphere. We obtained UV absorption coefficients for DAMN and DAFN and thermodynamic parameters that are useful for prebiotic chemistry studies. According to our results, experiments using UV lamps may underestimate the photolysis production of molecules of prebiotic importance. Our results indicate that photolysis reactions are fast with a yield of 50% of AICN in 10 s for the young Sun and ∼1 h for Proxima Centauri b. Planets around active M dwarfs may provide the most favorable environment for UV-mediated production of compounds relevant to the origins of life. The kinetic reaction AICN + HCN  adenine is the bottleneck of the pathway with reaction rates <10-22 L/(mol·s).

A systematic analysis of chemical mechanisms for ethylene oxidation and PAH formation

Accurate prediction of soot formation and evolution remains a formidable challenge due to the complex interaction between gas-phase composition and solid-phase particles. Recent studies have shown that the choice of gas-phase mechanisms is of primary importance in affecting predictability. In this work, a systematic analysis of ethylene (C2H4) combustion mechanisms denoted as KAUST, Stanford, Aachen, Polimi, ABF, DLR/UT, Naples, Caltech, and SJTU, which have been widely used in the soot community, is performed to investigate their differences in fundamental chemistry, polycyclic aromatic hydrocarbon (PAH) chemistry, and soot prediction. It is found that the nine mechanisms exhibit large differences even in predicting canonical combustion properties (e.g., ignition delay time, laminar flame speed, and extinction strain rate), indicating significant variations in the fundamental chemistry. This is due to the fact that although most mechanisms share very similar dominant fuel-oxidation reactions, there are notable differences in the rate coefficients of sensitive reactions used in these mechanisms. Owing to the uncertainties in the fundamental chemistry, the predictions of C2H2 from the nine mechanisms show significant differences, which contributes to the differences in soot precursor prediction, in conjunction with the difference in benzene (A1) formation pathways demonstrated by the element flux analysis of the C atom. Furthermore, it is found that PAHs containing two rings play a dominant role in soot formation for most mechanisms. Moreover, it is observed that while Caltech and SJTU significantly under estimate soot formation, they reasonably reproduce its sensitivity to strain rate. These results indicate that despite substantial advances in the development of C2H4 oxidation and PAH formation chemistry, the various existing mechanisms lead to significant differences in predicting soot concentrations which can be traced back to considerable differences in both fundamental chemistry and PAH chemistry. This suggests that the fundamental chemistry should be calibrated or improved before further development of PAH chemistry and soot models.

Static Design for Laterally Loaded Rigid Monopiles in Cohesive Soil

Rigid monopiles with small slenderness ratios (i.e., ratio of monopile embedded length to outer diameter) are widely used as foundations to resist lateral load and moment transferred from superstructures, e.g., large diameter steel pipes used by offshore wind turbines and piers in electric utility industry or sound barriers. A design model for laterally loaded rigid monopiles in cohesive soil is presented in this paper. The proposed design model assumes a constant depth of rotation point as well as a trilinear distribution model of soil lateral reaction along the embedded length of the monopile, and introduces a mobilization coefficient of soil reaction to quantify the magnitude of soil reaction mobilized under a certain load applied at the monopile head. The relationship between the mobilization coefficient and monopile head rotation is established by back-analyzing test results measured from series of laterally loaded pile tests, and then a general design procedure for a laterally loaded rigid monopile in cohesive soil is recommended. The feasibility and reliability of the proposed design model is validated against three cases of numerical simulations on laterally loaded piles in cohesive soils. It shows that this study’s proposed design model produces a relatively satisfactory prediction of the nonlinear load-deformation response, and can be used for laterally loaded monopile design in the sites with undrained shear strength being uniform or increasing linearly with depth.

Theoretical kinetics investigations of the reaction HO + SO ↔ H + SO2 on an accurate full‐dimensional potential energy surface

AbstractThe reaction HO + SO → H + SO2 (Rt) and its reverse (R‐t) play an important role in environment and the combustion of sulfur‐containing fuels. However, their kinetics is of high uncertainty as its reaction profile is complicated with multiple deep complexes and channels. In this work, the kinetics and mechanisms of Rt and R‐t are studied comprehensively based on a newly developed full‐dimensional accurate potential energy surface (PES) with the aid of machine learning. This highly accurate PES is interfaced with the software Gaussian. Then reliable information, including the energy, structures, and vibrational frequencies of the stationary points, as well as the minimum energy path and variational analysis can be efficiently determined. The variational transition state theory (VTST) and Rice−Ramsperger−Kassel−Marcus (RRKM) theory are employed to obtain the rate coefficients of each elementary reaction. The temperature‐ and pressure‐dependent rate coefficients of Rt are derived by the RRKM‐based master equation with hindered rotor and free rotor model considered. In addition, the effect of isotope substitution for the hydrogen is investigated on the reaction kinetics. Meanwhile, the quasi‐classical trajectory (QCT) calculation is performed on the PES‐2020 to obtain the temperature‐dependent reaction kinetics.

The Effect of Foundation Shape on Subgrade Reaction Coefficient

This paper numerically examines the effect of foundation shape on the subgrade reaction coefficient. The distribution of the subgrade reaction coefficient on the foundation area and the values of this coefficient in different regions are studied. A method is also introduced to determine the subgrade reaction coefficient of unusually shaped foundations sometimes encountered in practice. It has been shown that it is possible to divide the foundation area into several regions, and the subgrade reaction coefficient of each part is a multiplier of the central point reaction coefficient. The reaction coefficient of a trapezoidal foundation is equal to the reaction coefficient of a rectangular foundation with a similar area, and the length of the rectangle is the same as the height of the trapezoid. Also, the settlements of two foundations are equal. An L-shaped foundation’s reaction coefficient is a product of multiplying the reaction coefficient of a rectangular foundation to a ratio of the rectangular area by an L-shaped area if the settlements of the two foundations are equal. Besides, the reaction coefficient of a ring-shaped foundation is a product of multiplying the reaction coefficient of a circular foundation with the same outside diameter by the ratio of the circular area to the ring area if the settlements of both foundations are the same.

Data-driven ensemble learning approach for optimal design of cantilever soldier pile retaining walls

Cantilever soldier pile retaining walls are used to ensure the stability of excavations. This paper deploys ensemble machine learning algorithms towards achieving optimum design of these structures. A large dataset was developed consisting of 40,569 combinations of pile geometry, external loading, soil properties, and concrete unit cost, with two different values of soil reaction coefficient. Optimum pile diameter that minimizes the total cost of the retaining wall was computed considering the structural load-carrying capacity as the optimization constraint. The dataset was split into training and testing sets at 70% to 30% ratio. The predictive accuracy of the ensemble machine learning models was appraised on the testing dataset using various statistical metrics. Model performance was also evaluated for its ability in predicting the optimum pile diameter. The developed models demonstrated excellent predictive accuracy. Furthermore, the effect of different input variables on the model predictions was explained using the SHapely Additive exPlanations (SHAP) approach. Through the SHAP algorithm, the pile length was identified as the design variable having the most significant effect on the optimum pile diameter. The study demonstrates ensemble learning techniques as a viable alternative to the traditional techniques in the optimum design of cantilever soldier pile retaining walls.

Supersymmetry and convection–diffusion–reaction equations

In this work, we are concerned with generating solutions of a class of Convection–Diffusion–Reaction (CDR) equation from the solutions of another CDR equation through the Darboux transformations. The method is elucidated by cases with certain types of the reaction coefficients. We have also discussed briefly supersymmetric pairs of CDR equations connected through similarity solutions.

Behavior of a new laterally top-loaded post-grouted micropile in highly porous lateritic soil

The use of micropiles has been increasing in recent years, mostly for horizontally loaded cases. Given the little information about this foundation type under lateral top-loading, especially in high-porosity and collapsible soils, a total of four transversal loading tests were carried out in a new post-grouted micropile configuration with length of 17 m and diameter of 0.3 m, two in natural soil moisture conditions and two in flooded conditions. Load-displacement curves and the horizontal reaction coefficient of the new micropile were obtained. Results were compared with other pile types laterally tested under the same conditions and in the same geological and geotechnical contexts. Generally, results were better than the other pile types, mainly under saturated condition. The new micropile proved to be a better and more efficient alternative for local lateritic soil treatment when compared with the soil-cement treatment.

Kinetics of the Simplest Criegee Intermediate CH2OO Reaction with tert-Butylamine

The kinetics of the simplest Criegee intermediate (CH2OO) reaction with tert-butylamine ((CH3)3CNH2) was studied under pseudo-first-order conditions with the OH laser-induced fluorescence (LIF) method at the temperature range of 283-318 K and the pressure range of 5-75 Torr. Our pressure-dependent measurement showed that at 5 Torr─the lowest pressure measured in the current experiment─this reaction was under the high-pressure limit condition. At 298 K, the reaction rate coefficient was measured to be (4.95 ± 0.64) × 10-12 cm3 molecule-1 s-1. The title reaction was observed to be negative temperature-dependent; the activation energy of (-2.82 ± 0.37) kcal mol-1 and the pre-exponential factor of (4.21 ± 0.55) × 10-14 cm3 molecule-1 s-1 were derived from the Arrhenius equation. The rate coefficient of the title reaction is slightly larger than (4.3 ± 0.5) × 10-12 cm3 molecule-1 s-1 of the CH2OO reaction with methylamine; the electron inductive effect and the steric hindrance effect might play a role in contributing to such difference.

Unimolecular Reactions of 2,4-Dimethyloxetanyl Radicals.

Alkyl-substituted oxetanes are cyclic ethers formed via unimolecular reactions of QOOH radicals produced via a six-membered transition state in the preceding isomerization step of organic peroxy radicals, ROO. Owing to radical isomer-specific formation pathways, cyclic ethers are unambiguous proxies for inferring QOOH reaction rates. Therefore, accounting for subsequent oxidation of cyclic ethers is important in order to accurately determine rates for QOOH → products. Cyclic ethers can react via unimolecular reaction (ring-opening) or via bimolecular reaction with O2 to form cyclic ether-peroxy adducts. The computations herein provide reaction mechanisms and theoretical rate coefficients for the former type in order to determine competing pathways for the cyclic ether radicals. Rate coefficients of unimolecular reactions of 2,4-dimethyloxetanyl radicals were computed using master equation modeling from 0.01 to 100 atm and from 300 to 1000 K. Coupled-cluster methods were utilized for stationary-point energy calculations, and uncertainties in the computed rate coefficients were accounted for using variation in barrier heights and in well depths. The potential energy surfaces reveal accessible channels to several species via crossover reactions, such as 2-methyltetrahydrofuran-5-yl and pentanonyl isomers. For the range of temperature over which 2,4-dimethyloxetane forms during n-pentane oxidation, the following are the major channels: 2,4-dimethyloxetan-1-yl → acetaldehyde + allyl, 2,4-dimethyloxetan-2-yl → propene + acetyl, and 2,4-dimethyloxetan-3-yl → 3-butenal + methyl, or, 1-penten-3-yl-4-ol. Well-skipping reactions were significant in a number of channels and also exhibited a markedly different pressure dependence. The calculations show that rate coefficients for ring-opening are approximately an order of magnitude lower for the tertiary 2,4-dimethyloxetanyl radicals than for the primary and secondary 2,4-dimethyloxetanyl radicals. Unlike for reactions of the corresponding ROO radicals, however, unimolecular rate coefficients are independent of the stereochemistry. Moreover, rate coefficients of cyclic ether radical ring-opening are of the same order of magnitude as O2 addition, underscoring the point that a competing network of reactions is necessary to include for accurate chemical kinetics modeling of species profiles for cyclic ethers.