Catalytic fluorination of 1,1,1-trifluoro-2-chloro-ethane in the presence of oxygen over chromium based catalyst doped or not by zinc supported over partially fluorinated alumina

International audienc

Catalytic Fluorination of Various Chlorinated Hydrocarbons by HF and a Chromium Based Catalyst: Effect of the Presence of Zinc

International audienceThe Cl/F exchange of chlorinated hydrocarbons with HF was carried out in the gas phase (P = 1 atm. and T = 380 A degrees C) on chromium catalysts doped with zinc. A promoting effect of zinc has been found for various chlorinated hydrocarbons. This positive effect was more significant for CF(3)CH(2)Cl than for CF(3)CHCl(2) or CH(2)Cl(2). CF(3)CH(2)Cl was less reactive than the two other reactants. The promoting effect observed for an atomic ratio Zn/(Zn + Cr) = 0.15 was higher with a low (Zn + Cr) content, which corresponds to a better dispersion of the different elements on the surface. The presence of zinc is supposed to promote the dispersion of chromium and to favour its fluorination to form the centers which are active in Cl/F exchange and were characterized in XPS by energies corresponding to the presence of "CrOF" and "Cr-F" species

Synthesis of vinylidene fluoride via reaction of chlorodifluoromethane (HCFC-22) with methane

The gas-phase reaction of CH₄ and CHC1F₂ (HCFC-22, R22) has been studied in an alumina tubular reactor at atmospheric pressure and in the temperature range of 673−1073 K. The motivation of the investigation is to assess this process as a potential route for the treatment of CHC1F₂, as well as a technology for the synthesis of CH₂═CF₂ (vinylidene fluoride, VDF). Under the conditions studied, the major products are C₂F₄, CH₂═CF₂, HF, and HCl. Minor products detected include C₂HF₃, C₂H₂, CHF₃, C₂H₃F, C₂H₂F₄, CH₂F₂, C₃F₆, CH₃Cl. A mechanistic interpretation of the results is proposed, including the reactions involved in the initial decomposition of CHClF₂, those contributing to the activation of CH₄ and developing the pathways leading to the formation of product species. The result of changing feed ratio experiments is consistent with the reaction mechanism developed. The introduction of small amounts of O₂ improves the conversion of CH₄ and formation of CH₂═CF₂ markedly

An experimental and kinetic modeling study of the reaction of CHF₃ with methane

The gas-phase reaction of CHF₃ with CH₄ has been studied experimentally and computationally. The motivation behind the study is that reaction of CHF₃ with CH₄ provides a possible route for synthesis of CH₂=CF₂ (C₂H₂F₂). Experiments are carried out in a plug flow, isothermal α-alumina reactor at atmospheric pressure over the temperature range of 973-1173 K. To assist in understanding the reaction mechanism and the role of the reactor material involved in the reaction of CHF₃ with CH₄, the reaction of CHF₃ with CH₄, pyrolysis of CH₄, and pyrolysis of CHCIF₂ have been studied in the presence of α-alumina or α-AIF₃ particles under various conditions. Under all conditions studied for the reaction of CHF₃ and CH₄, the major products are C₂F₄, C₂H₂F₂, and HF. Minor products include C₂H₂, C₂H₄, C₂H₃F, C₂HF₃, C₃F₆, CO₂, and H₂. C₂H₆, CH₂F₂, and CHF₂CHF₂ are detected in trace amounts. The initial step is the gas-phase unimolecular decomposition of CHF₃, producing CF₂ and HF. It is proposed that CF₂ decomposes on the surface of α-alumina, producing F radicals that are responsible for the activation of CH₄. 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 CHF₃ with CH₄. Generally satisfactory agreement between experimental and modeling results is obtained on the conversion levels of CHF₃ and CH₄ and rates of formation of major products. Using the software package AURORA, the reaction pathways leading to the formation of major products are elucidated