Gas-phase reaction of CCl2F2 (CFC-12) with methane

Journal of Hazardous Materials, 2010

The gas-phase reaction of a mixture of waste refrigerant gases, namely R22 (CHClF(2)), R12 (CCl(2)F(2)) and R134a (CH(2)FCF(3)) with CH(4) has been investigated over the temperature range of 873-1133K. The investigation was undertaken as an initial assessment of the viability of this process as a treatment option for waste mixtures of hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFC), chlorofluorocarbons (CFCs) and as a potential route for the synthesis of CH(2)=CF(2) (VDF). During the reaction, CH(2)=CF(2) is observed as the major product formed and a 43% selectivity to CH(2)=CF(2) is obtained at 1073K. A detailed mechanism is developed based on the mechanistic analysis from kinetic modeling, with the initiation reaction involving the formation of Cl radicals from CCl(2)F(2). Good agreement is achieved between the predictions and experimental results. Based on a mechanistic analysis, a summary of the major reaction pathways is proposed, which is consistent with the experimental observations.

Industrial & Engineering Chemistry Research, 2006

The reaction of CHClF 2 with CH 3 Br was studied over the temperature range of 773-1123 K at atmospheric pressure in an alumina tubular reactor. At temperatures <923 K, the major products are C 2 F 4 and CH 2 dCF 2 . The rate of formation of CH 2 dCF 2 increases with temperature and, at 1123 K, CH 2 dCF 2 becomes the dominant product. Other important products detected include CH 4 , CH 2 Br 2 , C 2 H 2 , C 2 H 4 , CH 3 Cl, and C 3 H 2 F 4 (CH 2 d CFCF 3 ). It is concluded that the formation of CH 2 dCF 2 occurs via the reaction of CH 3 with CF 2 . To support this conclusion, the potential energy surface for reaction between the carbene, CF 2 , and the radical (CH 3 ) has been investigated by quantum chemical techniques, using density functional (B3LYP//6-31G(d)) and MP2// 6-31G(d) methods. Stationary points on the surface have been computed at a high level of theory, using G3B3 methods. Recombination between CF 2 and CH 3 initially produces the intermediate, CF 2 CH 3 , which then forms CH 2 dCF 2 and elemental hydrogen. Simulations using the MultiWell suite of programs indicate that, over the temperature range of 700-2000 K, there is essentially no stabilization of CF 2 CH 3 and that the reaction between CF 2 and CH 3 leads only to the production of CH 2 dCF 2 and elemental hydrogen. Over the temperature range of 700-2000 K, the rate constant for CF 2 + CH 3 f CH 2 dCF 2 + H can be well approximated by the expression 2.1 × 10 13 T -0.207 cm 3 mol -1 s -1 .

The Journal of Physical Chemistry A, 2019

The thermal decomposition of trifluoroacetic acid and carbonyl fluoride (CF 2 O) has been extensively studied because of their importance in the oxidation of hydrochlorofluorocarbons in the atmosphere. We hitherto present the study of the thermal reaction between these two molecules. The reaction mechanism was studied using Fourier transform infrared spectroscopy in the temperature range of 513−573 K. The reaction proceeds homogeneously in the gas phase through the formation of a reaction intermediate, here characterized as CF 3 C(O)OC(O)F (detected for the first time in this work), the major final products being CF 3 C(O)F, HF, and CO 2. We demonstrate that the reaction is first-order respect to each reagent, second-order global and the mechanism consists of two steps, the first being the rate-determining one. The E a = 110.1 ± 6.1 kJ mol −1 and A = (1.2 ± 0.2) × 10 −12 cm 3 molec −1 s −1 values were obtained from the experimental data. The low activation energy is explained by the hydrogen-bond interactions between the −OH group of the acid and the F atom of the CF 2 O. First-principles calculations at the G4MP2 level of theory were carried out to understand the dynamics of the decomposition. Thermodynamic activation values found for this reaction are as follows: ΔH ⧧ = 105.6 ± 6.4 kJ mol −1 , ΔS ⧧ = −88.6 ± 9.7 J mol −1 K −1 , and ΔG ⧧ = 153.7 ± 13.5 kJ mol −1. The comparison between theory and experimental results showed excellent similarities, thus strengthening the proposed mechanism. 1. INTRODUCTION Carbonyl fluoride (CF 2 O) and trifluoroacetic acid (TFA) could account for almost a third of the inorganic fluorinated compounds in the atmosphere, 1−4 and it is expected that their concentrations will increase in the future. 5−7 This is due to the current widespread use of replacements, that is, hydrofluorocarbons and hydrofluoroethers, as well as the past use of chlorofluorocarbons. 8−13 Though their concentrations are still far from becoming an environmental problem (its mutual reaction has not yet become an environmental issue), the reaction is of interest from the point of view of fluorine as well as physical chemistry. It affords a new fluorooxygenated compound to be synthesized and characterized and allows fundamental kinetic parameters to be known. It is widely accepted that perfluorinated carbonyl compounds have proved to be valuable tools in the study of radical reactions of atmospheric species. 14−17 Gangloff et al. 18 studied the thermal decomposition of CF 2 O. The only probable reaction path is the C−F bond scission. The activation energy for this reaction is 323 ± 13 kJ mol −1. Modica et al. 19 proposed that CF 2 O may react with CO to produce covalent organic framework radicals, but this reaction is completely displaced toward reagents. Ashworth et al. studied the thermal decomposition of CF 3 C(O)OH in the gas phase by Fourier transform infrared (FTIR) spectroscopy, with a stainless steel IR gas cell equipped with silver chloride 49 windows. The main products found for this reaction were 50 CF 3 H and CO 2. 20 51 The reactions of Cl/F and OH with CF 3 C(O)OH were 52 studied by Wallington and Hurley, 21 concluding that these 53 reactions constitute a minor atmospheric fate of CF 3 C(O)OH 54 and that the major atmospheric removal mechanism would be 55 wet and dry deposition, which probably occurs on a time scale 56 of the order of several weeks. 5,22,23 However, little is known 57 about the reaction of the acid with other stable molecules that 58 have longer lifetimes than the radicals mentioned. 59 Our group has extensive experience in the synthesis of 60 fluorocarbooxygenated molecules. 24−27 In particular, studies 61 have been carried out on thermal reactions in the gas phase 62 that afforded new species that have been characterized by 63 different techniques and rigorously verified by the kinetic 64 mechanisms proposed. 28−30 65 We hereafter present a thorough study of the thermal 66 reaction between CF 3 C(O)OH and CF 2 O at different 67 temperatures and pressures, which was also supported by 68 high-level ab initio calculations. The results from the kinetic 69 study are discussed with respect to the characterization of 70 CF 3 C(O)OC(O)F by FTIR spectroscopy.

Journal of Physical Chemistry A, 2019

The thermal decomposition of trifluoroacetic acid and carbonyl fluoride (CF 2 O) has been extensively studied because of their importance in the oxidation of hydrochlorofluorocarbons in the atmosphere. We hitherto present the study of the thermal reaction between these two molecules. The reaction mechanism was studied using Fourier transform infrared spectroscopy in the temperature range of 513-573 K. The reaction proceeds homogeneously in the gas phase through the formation of a reaction intermediate, here characterized as CF 3 C(O)OC(O)F (detected for the first time in this work), the major final products being CF 3 C(O)F, HF, and CO 2 . We demonstrate that the reaction is first-order respect to each reagent, second-order global and the mechanism consists of two steps, the first being the rate-determining one. The E a = 110.1 ± 6.1 kJ mol -1 and A = (1.2 ± 0.2) × 10 -12 cm 3 molec -1 s -1 values were obtained from the experimental data. The low activation energy is explained by the hydrogen-bond interactions between the -OH group of the acid and the F atom of the CF 2 O. First-principles calculations at the G4MP2 level of theory were carried out to understand the dynamics of the decomposition. Thermodynamic activation values found for this reaction are as follows: ΔH ⧧ = 105.6 ± 6.4 kJ mol -1 , ΔS ⧧ = -88.6 ± 9.7 J mol -1 K -1 , and ΔG ⧧ = 153.7 ± 13.5 kJ mol -1 . The comparison between theory and experimental results showed excellent similarities, thus strengthening the proposed mechanism. Gangloff et al. studied the thermal decomposition of CF 2 O. The only probable reaction path is the C-F bond scission. The activation energy for this reaction is 323 ± 13 kJ mol -1 . Modica et al. proposed that CF 2 O may react with CO to produce covalent organic framework radicals, but this reaction is completely displaced toward reagents. Ashworth et al. studied the thermal decomposition of CF 3 C(O)OH in the gas phase by Fourier transform infrared (FTIR) spectroscopy, with a stainless steel IR gas cell equipped with silver chloride 49 windows. The main products found for this reaction were 50 CF 3 H and CO 2 . 20 51 The reactions of Cl/F and OH with CF 3 C(O)OH were 52 studied by Wallington and Hurley, 21 concluding that these 53 reactions constitute a minor atmospheric fate of CF 3 C(O)OH 54 and that the major atmospheric removal mechanism would be 55 wet and dry deposition, which probably occurs on a time scale 56 of the order of several weeks. 5,22,23 However, little is known 57 about the reaction of the acid with other stable molecules that 58 have longer lifetimes than the radicals mentioned. 59 Our group has extensive experience in the synthesis of 60 fluorocarbooxygenated molecules. 24-27 In particular, studies 61 have been carried out on thermal reactions in the gas phase 62 that afforded new species that have been characterized by 63 different techniques and rigorously verified by the kinetic 64 mechanisms proposed. 28-30 65 We hereafter present a thorough study of the thermal 66 reaction between CF 3 C(O)OH and CF 2 O at different 67 temperatures and pressures, which was also supported by 68 high-level ab initio calculations. The results from the kinetic 69 study are discussed with respect to the characterization of 70 CF 3 C(O)OC(O)F by FTIR spectroscopy.

The motivation behind the study is that reaction of CHF 3 with CH 4 provides a possible route for synthesis of CH 2 =CF 2 (C 2 H 2 F 2 ). Experiments are carried out in a plug flow, isothermal αalumina reactor at atmospheric pressure over the temperature range of 973 to 1173 K. Under all conditions studied for the reaction of CHF 3 and CH 4 , the major products are C 2 F 4 , C 2 H 2 F 2 and HF. The initial step is the gas-phase unimolecular decomposition of CHF 3 , producing CF 2 and HF. It is proposed that CF 2 decomposes on the surface of α-alumina, producing F radicals that are responsible for the activation of CH 4 . A reaction scheme developed on the basis of the existing NIST HFC and GRI-Mech 3.0 mechanisms is used to model the reaction of CHF 3 with CH 4 . Generally satisfactory agreement between experimental and modelling results is obtained on the conversion levels of CHF 3 and CH 4 and rates of formation of major products.