Chemical mechanism and atmospheric degradation of C₄F₉N initiated by OH radical: Ab initio kinetic exploration

Abstract

This work presents a thoroughgoing theoretical study on the OH-initiated combustion chemical kinetics and atmospheric degradation mechanism of C 4 F 9 N by employing high-level quantum chemical methods and RRKM/master-equation theory. Stationary points on potential energy surface were cautiously investigated at B3LYP/6-311++G(d,p) level for geometry optimizations, and thereby their singlepoint energies were refined by applying CCSD(T)/6-311++G(d,p) method. Based on quantum calculations, kinetics and branching ratios for the major channels were predicted within 300-3000 K and 0.01-100 atm by solving the RRKM/master-equations. The OH addition to C 4 F 9 N generating M1 dominates the overall kinetics at low temperatures. Subsequently, its two β-scission channels of C C bonds to CF 3 CF 2 N CF(OH) + CF 3 and CF 2 NCF(OH)CF 3 + CF 3 become competitive and play a lead role in whole C 4 F 9 N + OH system at the corresponding high temperatures and elevated pressures. The CF 3 radical generated prompts these two routes to potentially have the significant contribution to flame inhibition in actual applications.Additionally, the complex degradation pathways of C 4 F 9 N were also looked into by successively reacting with various oxides, including OH, O 2 , NO, and HO 2 , to finally generate the removal products CF 3 CF 2 N(OOH)CF(OH)CF 3 , CF 3 CFO, and CF 3 CF 2 NO. The atmospheric lifetime of C 4 F 9 N was evaluated as 49 years regarding to the kinetic for one step addition of OH radical.addition, atmospheric degradation, C 4 F 9 N, fire extinguishing mechanism, kinetics | INTRODUCTIONBrominated halons, that is, CF 3 Br (Halon 1301), CF 2 FBr (Halon 1211), and CF 2 BrCF 2 Br (Halon 2402), have been the predominant gaseous fire extinguishing mediums for their high inhibition efficiencies [1,2]. Since they have displayed the strongly adverse effects on the depletion of stratospheric ozone and global warming as greenhouse gases, severe restrictions have been imposed within the Montreal Protocol and subsequent amendments to regulate their use and even phase out them [3,4]. Concerns about the environment protection drive the ongoing researches to search for new alternatives with low global warming potential (GWP) and short atmospheric lifetime (ALT). Given by the significant role of halons in practical application, the ideal alternatives with high extinguishing ability and environmentally friendly are anticipated. Bromine-free fluorinated hydrocarbons, that is, perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs), are among considered as the replacements. But, they have the fairly higher GWPs and longer ALTs [5]. Given this, halogenated nitriles (FNs) are introduced as the potential climate friendly replacements [3,6,7].Additionally, although without a bromine atom, several specific perfluoroalkylamines can exhibit a good fire-fighting ability that can compare to HFCs [7,8]. Takahashi et al. [7] tried to investigate the inhibition effects of several polyfluoroalkylamines, including (CF 3 CF 2 ) 3 N, (CF 3 ) 2 NCF 2 CF 3 ,

A comparative on the thermal decomposition and fire‐extinguishing performance of C5F8 and C5F7Cl

“…The Gaussian 16 code [15] was used for the theoretical study of C 5 F 8 and C 5 F 7 Cl decomposition and radical reaction. The geometric structures of all reactants, intermediates, transition states and products were optimized by density functional theory at B3LYP/6-311++G(d, p) level [12,[16][17][18][19]. The convergence condition of optimized geometry and optimized geometry of transition state was shown in Table S1 and Figures S1-S6.…”