Computational study on OH radical reaction with CHF<sub>2</sub>CHFCHF<sub>2</sub>(HFC‐245ea) between 200 and 400 K

Ali, Mohamad Akbar; Rajakumar, B.

doi:10.1002/kin.20569

Cited by 9 publications

(5 citation statements)

References 45 publications

(76 reference statements)

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“…Applying basis statistical thermodynamic principles, the equilibrium constant of the rapid pre-equilibrium between the reactants and the prereactive complex is given as Under high-pressure conditions, an equilibrium distribution of reactants is maintained in a unimolecular process, and the classical TST formula can be applied to calculate k 2 where k B is Boltzmann’s constant, h is Planck’s constant, R is the ideal gas constant, T is temperature in Kelvin, Q TS is the molecular partition function of the transition state, Q preRC is the molecular partition function of the prereactive complex, and κ( T ) is the asymmetric Eckart tunneling factor. − Transition state theory corrected for tunneling effects has been successfully used to calculate the rate coefficients for hydrogen abstraction reactions. − …”

Section: Methodsmentioning

confidence: 99%

Bimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

2015

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The bimolecular thermal reactions of carboxylic acids were studied using quantum mechanical molecular modeling. Previous work1 investigated the unimolecular decomposition of a variety of organic acids, including saturated, α,β-unsaturated, and β,γ-unsaturated acids, and showed that the type and position of the unsaturation resulted in unique branching ratios between dehydration and decarboxylation, [H2O]/[CO2]. In this work, the effect of bimolecular chemistry (water-acid and acid-acid) is considered with a representative of each acid class. In both cases, the strained 4-centered, unimolecular transition state, typical of most organic acids, is opened up to 6- or 8-centered bimolecular geometries. These larger structures lead to a reduction in the barrier heights (20-45%) of the thermal decomposition pathways for organic acids and an increase in the decomposition kinetics. In some cases, they even cause a shift in the branching ratio of the corresponding product slates.

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Section: Methodsmentioning

confidence: 99%

Bimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

2015

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“…TST corrected for tunneling effects has been successfully used previously to calculate the rate coefficients for hydrogen abstraction reactions. − Partition functions were corrected for 1-D hindered rotation, where appropriate, using the method outlined by Pfaendtner et al by means of code developed internally (written in the Python programming environment). All of the kinetics presented in this work were determined at the M06-2X/6-311++G(2df,p) level of theory.…”

Section: Methodsmentioning

confidence: 99%

Comparison of Unimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

2013

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Quantum mechanical molecular modeling is used [M06-2X/6-311++G(2df,p)] to compare activation energies and rate constants for unimolecular decomposition pathways of saturated and unsaturated carboxylic acids that are important in the production of biofuels and that are models for plant and algae-derived intermediates. Dehydration and decarboxylation reactions are considered. The barrier heights to decarboxylation and dehydration are similar in magnitude for saturated acids (∼71 kcal mol(-1)), with an approximate 1:1 [H2O]/[CO2] branching ratio over the temperature range studied (500-2000 K). α,β-Unsaturation lowers the barrier to decarboxylation between 2.2 and 12.2 kcal mol(-1) while increasing the barriers to dehydration by ∼3 kcal mol(-1). The branching ratio, as a result, is an order of magnitude smaller, [H2O]/[CO2] = 0.07. For some α,β-unsaturated acids, six-center transition states are available for dehydration, with barrier heights of ∼35.0 kcal mol(-1). The branching ratio for these acids can be as high as 370:1. β,γ-Unsaturation results in a small lowering in the barrier height to decarboxylation (∼70.0 kcal mol(-1)). β,γ-Unsaturation also leads to a lowering in the dehydration pathway from 1.7 to 5.1 kcal mol(-1). These results are discussed with respect to predicted kinetic values for acids of importance in biofuels production.

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“…Kinetic rate constants and parameters where obtained according to where k B is Boltzmann’s constant, h is Planck’s constant, R is the ideal gas constant, T is temperature in Kelvin, Q TS is the molecular partition function of the transition state, Q R is the molecular partition function of the reactant, E TS and E R are the energies of the transition state and reactant, respectively, and κ( T ) is the asymmetric Eckart tunneling factor. − Transition state theory corrected for tunneling effects has been successfully used to calculate the rate coefficients for hydrogen abstraction reactions. − …”

Section: Methodsmentioning

confidence: 99%

Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation

et al. 2016

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We demonstrate a synthetic route toward the production of propene directly from poly(β-hydroxybutyrate) (PHB), the most common of a wide range of high-molecular-mass microbial polyhydroxyalkanoates. Propene, a major commercial hydrocarbon, was obtained from the depolymerization of PHB and subsequent decarboxylation of the crotonic acid monomer in good yields (up to 75 mol %). The energetics of PHB depolymerization and the gas-phase decarboxylation of crotonic acid were also studied using density functional theory (DFT). The average activation energy for the cleavage of the R'C(O)O-R linkage is calculated to be 163.9 ± 7.0 kJ mol(-1). Intramolecular, autoacceleration effects regarding the depolymerization of PHB, as suggested in some literature accounts, arising from the formation of crotonyl and carboxyl functional groups in the products could not be confirmed by the results of DFT and microkinetic modeling. DFT results, however, suggest that intermolecular catalysis involving terminal carboxyl groups may accelerate PHB depolymerization. Activation energies for this process were estimated to be about 20 kJ mol(-1) lower than that for the noncatalyzed ester cleavage, 144.3 ± 6.4 kJ mol(-1). DFT calculations predict the decarboxylation of crotonic acid to follow second-order kinetics with an activation energy of 147.5 ± 6.3 kJ mol(-1), consistent with that measured experimentally, 146.9 kJ mol(-1). Microkinetic modeling of the PHB to propene overall reaction predicts decarboxylation of crotonic acid to be the rate-limiting step, consistent with experimental observations. The results also indicate that improvements made to enhance the isomerization of crotonic acid to vinylacetic acid will improve the direct conversion of PHB to propene.

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Computational study on OH radical reaction with CHF₂CHFCHF₂(HFC‐245ea) between 200 and 400 K

Cited by 9 publications

References 45 publications

Bimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

Bimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

Comparison of Unimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation

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Computational study on OH radical reaction with CHF2CHFCHF2(HFC‐245ea) between 200 and 400 K

Cited by 9 publications

References 45 publications

Bimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

Bimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

Comparison of Unimolecular Decomposition Pathways for Carboxylic Acids of Relevance to Biofuels

Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation

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Computational study on OH radical reaction with CHF₂CHFCHF₂(HFC‐245ea) between 200 and 400 K