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Thermal Decomposition Mechanism and Fire-Extinguishing Performance of trans -1,1,1,4,4,4-Hexafluoro-2-Butene: A Potential Candidate for Halon Substitute
Abstract
In view of the appropriate physicochemical characteristics and environmental friendliness of trans-1,1,1,4,4,4-Hexafluoro-2-Butene (HFO-1336mzz(E)) substance, the thermal-decomposition mechanism, as well as the fire-extinguishing mechanism and performance of this agent were systematically studied by employing both the experimental and theoretical methods in this work. We found that the HFO-1336mzz(E) agent not only has promising thermal stability at room temperature, but also exhibits pronounced fire-extinguishing performance, which is comparable to the HFC-236fa and even better than that of HFC-125 extinguishant. Additionally, the promising fire-extinguishing performance of HFO-1336mzz(E) may result from the physical and chemical extinguishing effect of its thermal-decomposition products including HFO-1336mzz(Z), HC≡CCF3, CF3C≡CCF3 and CF3H, which make a significant contribution to capturing the free radicals in the flame, as well as cooling and diluting the combustible fuel-air mixture. Both the experimental and theoretical results suggest that the HFO-1336mzz(E) agent is a highly recommendable candidate for Halon extinguishant, which is worthy of further investigation and evaluation of its practical applicability in fire-suppression utilizations.
... Out of many potential Halon substitutes, hydrofluorocarbons (HFCs), and perfluoro-2-methyl-3-pentanone (PFMP) have been extensively researched and have shown promise as clean fire suppression agents. 55 2-Bromo-3,3,3-Trifluoro Propane (2-BTP).-With a much lower environmental impact than Halon, 2-BTP is well-suited for electronic and battery fire applications. Being fluorinated, it breaks the combustion chain and quickly extinguishes the flames. ...
The rising energy density and widespread use of lithium-ion batteries (LIBs) pose a growing safety challenge, marked by the potential for fires and explosions. Given the unique combustion characteristics of LIBs, the need for efficient and prompt fire suppression is paramount. Here we explore the mechanisms and characteristics of LIBs fires, emphasizing the critical design principles for effective fire-extinguishing agents and evaluating various agents, including gaseous, dry powders, water-based, aerosol-based, and composite-based fire-extinguishing agents, elucidating their mechanisms and effectiveness in suppressing LIBs fires. Noteworthy agents such as C6F12O and water-based solutions are highlighted for their superior extinguishing and cooling capabilities. Water-based fire-extinguishing agents show promise, exhibiting superior cooling capacity and anti-flash properties. Despite certain limitations, the review underscores the necessity of identifying an ideal fire-extinguishing agent that is thermally conductive, electrically insulating, cost-effective, non-toxic, residue-free, and capable of absorbing toxic gases. We conclude by discussing perspectives and outlooks, emphasizing the synergy between the ideal agent and innovative extinguishing strategies to ensure the high safety standards of current and future LIB-based technologies.
... Considering the similar dielectric strength of both, the content of HFO-butene in the gas mixture (using CO2 or N2 as the buffer gas) could reach to higher level for GIE application. [17][18][19] HFO-butene has a lethal concentration (LC50) of 25400-49000ppm, which is larger than that of C4F7N (10000-15000 ppm) and C5F10O (20000 ppm). Thus, the application of HFO-butene gas mixture is more secure. ...
HFO-1336mzz(E) (HFO-butene) is regarded as a promising eco-friendly insulating gas to replace the sulfur hexafluoride (SF 6 ) used in medium-voltage gas insulated equipment (MV-GIE). In this paper, we systematically explored the partial discharge properties of HFO-butene/CO 2 gas mixture by revealing the partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV), and phase resolved partial discharge (PRPD) pattern under different mixing ratio, gas pressure conditions. Meanwhile, the action and influence mechanism of "space charge layer" on the PD distribution properties of HFO-butene/CO 2 was proposed for the first time. We found that the PDIV of HFO-butene/CO 2 demonstrated linear-saturation increase trend with the mixing ratio and gas pressure, which is equivalent to that of SF 6 as the HFO-butene content reaches 25%∼30%. In addition, there existed "double peak" phenomenon in the n-φ spectrum of the HFO-butene/CO 2 with low HFO-butene content and gas pressure, which is ascribed to the shielding effect of the stable "space charge layer" nearby the needle electrode that improves the non-uniformity of the electric field. The corresponding results revealed the PD characteristics of HFO-butene/CO 2 gas mixture and brought guidance to the development of brought guidance based MV-GIE.
... Even so, the system used toxic and flammable isobutane as the working fluid of ORC, posing certain safety risks [17]. After continuous exploration, a batch of excellent ORC working fluids, for instance, R1336mzz (Z), R1233zd (E), R1224yd (Z), and R1336mzz (E), came into the investigators' view [18][19][20]. For the cycle layout of ORC, there are two primary types: subcritical cycle and trans-critical cycle [21]. ...
In spite of the fact that the solar power tower system is considered as one of the most valuable power generation facilities, it still faces challenges such as insufficient utilization of the solar salt temperature range and the dependence on high solar radiation intensity. To address this issue, an integrated recompression Brayton cycle and trans-critical regenerative organic Rankine cycle in parallel layout is proposed. The comparison with other literature shows that the specific work of the integrated system (147.8 kW/kg) outperforms the partial cooling Brayton cycle (130.1 kW/kg) under the same solar salt temperature range. In order to forecast future electricity generation and serve as a reference for plant operation, a power prediction strategy using neural networks is developed. Findings indicate that the integrated system can increase power production and maximize solar salt temperature utilization by adjusting the physical constraint strategy based on the changing temperature interval. Its equivalent work and thermal efficiency reach 12.7 MW and 38.36%, respectively, and it can recover the cost in 8 years. These results suggest that the proposed integrated system is a promising solution to enhance the performance of solar power tower systems with significant economic benefits.
... R1336mzz(E) is the isomer of R1336mzz(Z) and is also referred to as DR-12, HFO-1336mzz(E), or trans-1,1,1,4,4,4hexafluoro-2-butene with the CAS No. 66711-86-2. R1336mzz(E) is a novel, non-flammable, low GWP working fluid that was recently introduced for various potential applications, including HTHPs (Kontomaris and Simoni 2016;Juhasz 2017;Akei et al. 2018;Hamacher 2019;Mateu-Royo et al. 2021;Jesper et al. 2021;Drofenik et al. 2022), chillers (Kontomaris 2015), as fire-extinguishing agent (Zhang et al. 2020), and as drop-in replacements to R245fa for ORC processes (Juhasz and Simoni 2015;Kontomaris and Simoni 2016;Juhasz 2017;Yang et al. 2019). The main difference in the molecular structure of the two stereoisomers Z-and E-CF 3 CH=CHCF 3 (i.e., R1336mzz(Z) and R1336mzz(E)) can be seen in Figure 1. ...
Electrically driven high-temperature heat pumps (HTHP) are an attractive technology for decarbonizing industrial process heat. A key factor for HTHP performance and market acceptance are natural and synthetic refrigerants with low global warming potential (GWP). This paper extends previously presented studies on hydrofluoroolefin (HFO) and hydrochlorofluoroolefin (HCFO) refrigerants in a 10-kW heating capacity laboratory HTHP up to a heat sink outlet temperature of 150 °C. Here, we present experimental test results with the new refrigerant isomer R1336mzz(E), intended for waste heat recovery applications by HTHP and organic Rankine cycles (ORC). R1336mzz(E) benefits from a high volumetric heating capacity, non-flammability (safety class A1), and a low GWP. The working fluid has a critical temperature of 130.4 °C, allowing condensation at about 120 °C. There are only a few theoretical comparisons with the (Z) and (E) isomers, and almost no experimental results have been published for heat pumps. In this study, R1336mzz(E) is tested over a range of 70 °C to 130 °C heat sink outlet temperatures while using a waste heat source between 30 °C and 80 °C. In addition, the experimental results in the laboratory HTHP system are compared with previous tests using R1336mzz(Z), R1233zd(E), R1224yd(Z), and R245fa and with theoretical simulation studies. R1336mzz(E) results show COPs in a comparable range as the previously tested refrigerants, but the heating capacity at the reference condition of W60/W110 was 117% and 18% higher than R1336mzz(Z) and R245fa, respectively. Furthermore, the experimental results align closely with cycle simulations.
... According to previous research [31] as well as breakdown test results that were obtained in this experiment, it could be inferred that a tiny amount of HFO1336mzz(E) underwent a carbonisation reaction to form carbon due to the extreme heat being released at the moment of breakdown after multiple breakdowns, which is attached to the electrodes surface. ...
Abstract The emissions of SF6 have been restricted owing to 3400 years of atmospheric lifetime and high global warming potential (GWP) as an insulating gas in gas‐insulated electrical equipment. In this study, HFO‐1336mzz(E) and N2/CO2 mixtures are proposed as SF6 substitutes for their short atmospheric lifetime, low GWP and superior insulation performance. The GWP of HFO‐1336mzz(E) is only 18 and its atmospheric lifetime is days to weeks. The breakdown voltage of 25% HFO‐1336mzz(E) and N2/CO2 mixtures is about 85% that of pure SF6 under alternating current. The self‐recovery ability of HFO‐1336mzz(E) and CO2 mixtures is superior to that of HFO‐1336mzz(E) and N2 mixtures. The decomposition characteristic of HFO‐1336mzz(E) shows that a tiny amount of its gas might initiate a carbonisation reaction to form carbon after multiple breakdown tests, which is verified by observations using energy dispersive X‐rays spectroscopy and scanning electron microscope. The acute toxicity test of HFO‐1336mzz(E) indicates that the gas is non‐toxic. The results show that HFO‐1336mzz(E) and N2/CO2 mixtures are potential substitutes for SF6 in electrical applications.
... In contrast, the properties of HFO-1336mzz(E) have been less studied. HFO-1336mzz(E)(trans-1,1,1,4,4,4-hexafluoro-2-butene) is a non-flammable compound with a favorable safety profile [15]. It has been considered as a substitute for HFC-245fa, a type of working fluid in high-temperature heat pumps and Organic Rankine Cycle Systems by Katsuyuki Tanaka and co-studiers [16]. ...
As a strong greenhouse gas, sulfur hexafluoride used in electrical equipment has been advocated to be replaced. HFO-1336mzz(E), an eco-friendly insulation alternative medium with excellent insulation performance and environmental effect, deserves studied deeply. In this paper, the decomposition mechanism of HFO-1336mzz(E) is studied by density functional theory calculations. The effect of trace water on the decomposition properties is also considered and studied. Besides, multiple linear regression models are used to assess the insulation properties of main decomposition products that came from HFO-1336mzz(E). The results show that more than 15 molecules are formed in the decomposition process of HFO-1336mzz(E), among which CF3CH=C=CF2, CF2=CF-CH=CF2, C2F6, and HF are the most abundant products. Besides, C2F4, CF2=CFH, and C2H2 could be taken as typical products for diagnosing the serve fault degree that occurred in the electrical equipment. In terms of insulation properties, CF3CH=C=CF2 and CF2=CF-CH=CF2, two of the main products, with big volumes have excellent insulation strength that is slightly less than that of HFO-1336mzz(E). Small molecules with low dielectric strength such as CF3H, CF3OH, COF2, and HF, etc can also be produced in the presence of micro humidity. Luckily, the yield of these small molecules is small so that they will not have a significant impact on the insulation properties of the overall system. Remarkably, the presence of micro humidity will make it easier to generate toxic gas products such as COF2 and HF. Given these conditions, the acceptable moisture content in the power equipment is expected to propose before any application in the electrical industry. Relative studies on the decomposition mechanism of HFO-1336mzz(E)/H2O in this paper may be helpful to understand the subsequent scientific experimental research.
... According to the thermal decomposition study of HFO-1336mzz(E) by Zhang 16 , considering the convergence of decomposition rate at 10s and the short time of fire extinguish process, the residence time of 10s is selected for thermal decomposition analysis. Considering the low molecular weight of CF 3 I, its decomposition into organic products is difficult, and the decomposition temperature should be relatively high. ...
The urgent desire for Halon substitution propels the exploration of potential alternatives, because of the severe damage of Halons to the stratospheric ozone layer. In this paper, the thermal decomposition mechanism, as well as fire-extinguishing mechanism and performance of Trifluoroiodomethane (CF3I) were studied by density functional theory (DFT) calculation and experimental measurements, to analyze the practicability of this proposed Halon substitute. The thermal decomposition products of CF3I can react with active OH· and H· radicals to achieve the purpose of rapidly fire-extinguishing. Besides, through DFT calculation and reaction kinetics analysis, the fire-extinguishing radicals CF3· and I· are more easily generated during the interaction between CF3I and flame, which indicates the chemical- extinguishing mechanism and pronounced fire-extinguishing performance of CF3I. To explore its actual fire-extinguishing effect, the fire-extinguishing concentration (FEC) of CF3I was measured in cup burner. The FEC value of this proposed Halon substitute is 3.42vol% for extinguishment of methane-air flame, which is smaller than those of three HFCs and HFO-1336mzz(Z) and is comparable to that of Halon 1301. These findings suggest the promising applicability of CF3I in practical Halon replacement and the necessity of further evaluation.
... There have been many attempts in the literature to develop approaches that address the HF generation mechanism during fire suppression. The main emphasis of available researches are focused on HF yield amount [15] and mechanism of CF 3 H [16], thermal decomposition mechanism of CHF 2 CF 3 [17,18] and other Halon alternatives [19], HF production of CF 3 CHFCF 3 [20], thermal decomposition of trans-CF 3 CH = CHCF 3 [21], HF pyrolysis of CF 2 H 2 [22], thermal decomposition of CF 3 CBrH = CH [23] and so on. Although the yield of corrosive gases has been reported to impact potential damage on the surface of materials [24], the comprehensive study of the influence of HF on the color change of wooden materials is still unavailable. ...
Many wooden Chinese historic buildings are destroyed due to the ravages of frequent fire disasters. The fire risk of historic buildings are highly enlarged since a long-time weathered wooden structures in the natural environment. The clean fire-extinguishing technology using fluorinated chemical gases to put out a historic building fire rapidly at the initial stage is highly recommended and widely used. However, the gaseous hydrogen fluoride (HF) yielded during the fire suppression process could be a potential method to result in secondary damage due to its corrosiveness. Nowadays, experiments were employed to clarify the effect of fire suppression on the surface of historic wooden buildings. Five traditional fluorinated chemical gases, H-37, FK-5-1-12, H-1323, H-2402, and H-1301, are used to suppress a fixed flame. The wooden samples, including a Dao Talisman board, a painting paper, and wooden chips, are placed in a chamber. Wooden chips consist of traditional and weathered samples (acting as the Chinese historic buildings). The concentration of gaseous products yielded from fire suppression are monitored by a gas-FTIR from ABB, and the surface analysis is conducted by a Quanta FEG SEM–EDX from FEI. It is observed that flame enhancement happens at the early stage of fire suppression and varies with fire agents. The amount of F-deposited on the wooden surface is positively correlated with a total amount of gaseous HF. The color change mechanism of the wooden surface is comprehensive, although the amount of HF is a leading factor. The influence of HF on color change depends on the amount of both gaseous H2O and HF. It is concluded that the value of L* of the traditional chip is much easier to be reduced comparing with weathered samples with the same wood grain. The reduction of b∗\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{b}}^{*}$$\end{document} value of weathered samples is much larger than the traditional ones. It suggests the weathered chips show a color shift toward blue because of fire suppression. The present study hopes to provide a basic acknowledgment for the comprehensive understanding of secondary damage caused by fire suppression.
... A recent work measured the HFO-1336mzz(E) concentration in glass tubes originally containing neat HFO-1336mzz(Z) after aging at 448 K and 473 K for 14 days in the presence of carbon steel, copper and aluminum [6]. However, the stereo isomerization of HFO-1336mzz(Z) to HFO-1336mzz(E) was extremely little, and the experimental results reported by Kontomaris shows that the concentrations of HFO-1336mzz-E were 0.004 and 0.011 at 448 K and 473 K. HFO-1336mzz(E) is a potential candidate for Halon Substitutes based on experimental and theoretical results of Zhang [29].This team found that The isomerization reaction of HFO-1336mzz(E) occurs after the environmental temperature increases to above 773 K, and HFO-1336mzz(Z) could be produced in this endothermal reaction. HFO-1336mzz(Z) and HFO-1336mzz(E) are cis-trans isomerism and this isomerization reaction was shown with the conversion between (a) and (b) in Figure 3. ...
A series of thermal decomposition experiments were conducted over a temperature range of 873–1073 K to evaluate the thermal stability of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)) and the production of hydrogen fluoride (HF). According to the detected products and experimental phenomena, the thermal decomposition of HFO-1336mzz(Z) could be divided into three stages. Our experimental results showed that HF concentration gradually increased with the elevation of thermal decomposition temperature. In this present study, a total of seven chemical reaction pathways of HFO-1336mzz(Z) pyrolysis were proposed to explore the generated mechanism on products through density functional theory (DFT) with M06-2X/6-311++(d,p) level theory. The thermal decomposition mechanism of pure HFO-1336mzz(Z) was discussed and the possible formation pathways of HF and other main products were proposed.
Thermal runaway is of great concern for developing high-performance Li-ion batteries (LIBs) and is accelerated by melting a separator at the elevated temperature during the battery failure. Here, we report...
HFO-butene (HFO-1336mzz(E)) has been explored as eco-friendly gas insulating medium to replace the most greenhouse gas sulfur fluoride (SF
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) for the power industry. At present, studies on the stability and decomposition mechanism of HFO-butene mainly focus on neutral molecules or radicals. However, the discharge induced decomposition will generate positive and negative ions, which significantly affect the physicochemical properties of gas composition. Meanwhile, experimental evaluation of the partial discharge (PD) induced decomposition characteristics of HFO-butene is lacking. In this paper, the decomposition mechanism of HFO-butene considering free radicals and ions is systematically explored for the first time. The molecular structure, ionization and attachment properties of HFO-butene are revealed, and the reaction enthalpy analysis of the decomposition and by-product generation pathways are explored. The long-term PD experiments on HFO-butene/CO
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gas mixture are conducted combined with gas composition analysis under different applied voltage, gas pressure and mixing ratio conditions. Relevant results provide an important reference for understanding the PD decomposition characteristics of HFO-butene.
Eco-friendly HFO-1336mzz(E) is promising as an insulating gas in medium-voltage equipment. However, the surface flashover characteristics of epoxy resin in HFO-1336mzz(E) /buffer-gas mixtures, significantly influencing the insulation performance and operational safety, have gained little academic attention by far. This article has studied the effects of typical buffer gas (N2 and CO2), pressure, and mixing ratio on the surface flashover characteristics under negative dc voltage. The results show that more solid by-products have been generated after several flashovers in the HFO-1336mzz(E) /N2 gas mixtures, leading to a lower tolerance than HFO-1336mzz(E) /CO2 gas mixtures. The surface flashover voltage of HFO-1336mzz(E) /CO2 gas mixtures increases with gas pressure or mixing ratio, and there is a positive synergistic effect between HFO-1336mzz(E) and CO2. The available concentration of HFO-1336mzz(E) gas in the mixtures depends on the limiting liquefaction temperature and gas pressure. When the liquefaction temperature is limited to −15 °C, the HFO-1336mzz(E)/CO2 gas mixtures with 4%–6% HFO-1336mzz(E) at 0.40 MPa and 6%–10% HFO-1336mzz(E) at 0.30 MPa can be used to replace pure SF6 at 0.13 MPa in medium-voltage equipment. This article can provide an essential reference for its engineering application.
This work combined high-level quantum chemistry calculations with RRKM/master-equation simulations to gain insight into reactions between C6F12O and hydrogen radical under combustion conditions. The energetics for all stationary points on potential energy surface were determined at CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) level of theory. RRKM/master-equation calculations were utilized to simulate the title reaction over a wide range of temperatures and pressures, i.e. 300-3000 K and 0.01-100 atm. Kinetic and mechanistic analyses demonstrate that hydrogen addition to initial adduct C2F5CFCOH(CF3)2 and two dissociations from adduct (CF3)2CFCHOC2F5 to CF3CF2COH + CF3CFCF3 and (CF3)2CFCOH) + CF3CF2 conjointly dominate the overall kinetics over the investigated temperatures and pressures.
Due to the serious destruction of Halon to the ozone layer, it is significant to explore the fire‐extinguishing agent with zero ozone depletion potential (ODP). At the molecular structure level, Octafluoro‐2‐butene has a special arrangement of fluorine atoms, endowing itself with better potential to replace Halon than the reported perfluoroalkanes and hydrofluoroethylenes (HFOs). However, as a new Halon substitute, the fire‐extinguishing mechanism of Octafluoro‐2‐butene has not been studied. In this paper, the thermal decomposition and fire‐extinguishing mechanism of Octafluoro‐2‐butene were studied by density functional theory (DFT) and the rate constants of each reaction path were calculated for the first time. The calculation results show that Octafluoro‐2‐butene produces a large number of fire extinguishing groups and the rate constants of the main fire extinguishing paths are fast. Noteworthy, there is no combustion radical produced during extinguishing. In addition, the thermal decomposition of Octafluoro‐2‐butene mostly produced halogenated alkane with the better ability to react with chain radicals. The theoretical results show that Octafluoro‐2‐butene is a promising Halon substitute, and its practicability can be further studied and comprehensively evaluated. The possible decomposition pathways, BDEs and rate constants were studied to explore the decomposition mechanism of Octafluoro‐2‐butene. The energy barriers, reaction paths and reaction rate constants of Octafluoro‐2‐butene and its decomposition products with H∙ and OH· were studied to analyze the extinguishing mechanism of Octafluoro‐2‐butene. Specifically, Octafluoro‐2‐butene can decompose into CF3H and CF4 those can be recycled to consume chain free radicals. Theoretical calculations demonstrate that Octafluoro‐2‐butene has the potential to replace Halon.
Since halon fire‐extinguishing agents are forbidden to be used due to environmental concerns, it is necessary to explore new environmentally friendly fire‐extinguishing agents. Perfluorotriethylamine (N(CF2CF3)3) with good physicochemical properties is a potential substitute for halons. To evaluate its practicability as the halon substitute, the thermal decomposition performance and mechanism of N(CF2CF3)3 were systematically investigated by combining experiment and theory in this study. The initiation reaction of N(CF2CF3)3 thermal decomposition was calculated by density functional theory. The reactive molecular dynamics simulations based on the reactive force field were used to investigate the thermal decomposition process of N(CF2CF3)3 at different temperatures, including the intermediates, decomposition temperature, and product distribution. To examine the actual fire‐extinguishing performance of N(CF2CF3)3, its fire‐extinguishing concentration in the n‐heptane‐air flame was measured by the cup‐burner method. Finally, the chemical fire‐extinguishing mechanism of N(CF2CF3)3 was proposed. N(CF2CF3)3 was pyrolyzed during the interaction with flame, producing the fire extinguishing radical CF3∙, which further consumed the active H∙ and OH∙ radicals by reactions. N(CF2CF3)3 is considered to be a very promising halon replacement extinguishing agent with excellent physicochemical properties and environmental friendliness. In this paper, the fire extinguishing concentration was measured by the cup‐burner method，and the thermal decomposition and fire extinguishing mechanisms were investigated using ReaxFF MD simulation and density functional theory methods.
This paper investigates the AC insulation properties and explores the influence of electric field inhomogeneity on the breakdown voltage of HFO-1336mzz(E)/CO
2
gas mixture. The electrical field sensitivity of HFO-1336mzz(E)/CO
2
and SF
6
is further compared. It is found that the insulation performance of HFO-1336mzz(E)/CO
2
mixture with 25–30% HFO-1336mzz(E) can reach up to 75-85% of SF
6
under the quasi-uniform electric field and there is a favorable positive synergistic effect between HFO-1336mzz(E) and CO
2
. The breakdown voltage of HFO-1336mzz(E)/CO
2
gas mixture demonstrates a “hump” effect with gas pressure under the highly non-uniform electric field and its sensitivity to the electric field inhomogeneity is significantly lower than that of SF
6
. The insulation performance of HFO-1336mzz(E)/CO
2
with HFO-1336mzz(E) content higher than 20% reaches 0.99–1.05 times that of SF
6
under highly non-uniform electric field. The AC breakdown voltage of HFO-1336mzz(E)/CO
2
gas mixture and SF
6
decreases first and then increases with the electric field inhomogeneity (f), demonstrating a “U-shaped” like curve and finally tends to be stable. The related results of this paper systematically reveal the AC insulation properties of HFO-1336mzz(E)/CO
2
gas mixture and provide an important reference for its engineering application.
The gas sensing technique based on the differential pressure principle is quite suitable to evaluate the effectiveness of gas fire extinguishing system. This paper is focused on the study of the change rule of its response fluctuation that is critical to the concentration measuring accuracy. The variation of response fluctuation and sensing performance with sensing structure and constant temperature was explored. Results show that it will often enlarge the response fluctuation when promoting the response/sensitivity or response rate by changing the sensing structure, which can cover the improvement in sensitivity causing the decrease in measuring precision, especially for high concentration. However, the increase of temperature will reduce the response fluctuation while improving the response/sensitivity and response rate, which is a good way to promote sensing performance. The research in the paper can provide suggestions for the optimization design of the sensor.
As Halon extinguishers impose severe damage to the stratospheric ozone layer, Halon substitutions are urgently desired and explored. In this paper, the thermal decomposition mechanism, the fire‐extinguishing performance and mechanism were experimentally and theoretically investigated for Trifluoroiodomethane (CF3I). The theoretical results direct that CF3I and its main decomposition products (CF3· and I·) can react with OH· and H· to block the combustion chain reactions. Besides, reaction kinetics analysis also direct that CF3· and I· are more easily generated during the interaction between CF3I and the flame. And the minimum fire‐extinguishing concentration (MEC) of CF3I in extinguishing methane‐air flames is 3.42 vol%, which is lower than those of representative HFCs and HFO‐1336mzz(E) and even comparable to that of Halon 1301. Both the experimental and theoretical results suggest the promising applicability of CF3I in practical Halon replacement and the necessity of its further evaluation. The fire‐extinguishing performance of CF3I was studied by high temperature cracking and the cup burner experiments. The theoretical calculations based on density functional theory show that CF3I itself and its main products I· and CF3· can react with active radicals in the burning flames. And the MEC of CF3I on methane‐air flame is 3.42 vol%, which is lower than those of representative hydrofluorocarbons and HFO‐1336mzz(E) and even comparable to that of Halon 1301.
The cis‐1,1,1,4,4,4‐hexafluoro‐2‐butene (DR‐2 or HFO‐1336mzz(Z)) is a novel environmentally friendly working fluid with appropriate physicochemical characteristics. The present work firstly investigated the decomposition mechanism and thermal stability of DR‐2 in a oxygen (O2)‐containing atmosphere at high temperature experimentally. The oxidative degradation features of DR‐2 were explored at the temperature of 473–1073 K and the products were monitored by GC–MS and IC. The experimental and ReaxFF‐based molecular dynamics results demonstrated the promotion effects of O2 on the DR‐2 decomposition. The participation of O2 molecules was supposed to lower the initial thermal decomposition temperature by 240 K approximately and increase the number of products such as hydrogen fluoride (HF), but the enhancement effect was weakened by the increasing reaction temperature. The reasonable Arrhenius parameters were calculated from the first‐order kinetic analyses‐based reactive molecular dynamics (RMD) simulations. Combined with the density functional theory, the pathways of initial oxidation decomposition product firstly observed in the experiment and RMD simulations were proposed in this study. These results may pave the way for further study of DR‐2 as a working fluid with lower global warming potential. The promoting effect of O2 molecules on DR‐2 was investigated experimentally and theoretically at high temperature in this study. HF was one of the main products of thermal decomposition of DR‐2 with O2, and the ReaxFF MD simulation were in good agreement with the experimental results. And the process of O2 molecule attacking DR‐2 to form the oxidation products was deduced in combination with the DFT method.
Chinese historic buildings are characterized by a wooden structure, which has caused serious results due to the ravages of frequent fire disasters. After the weathering by the natural environment, the fire risk of wood is highly enlarged. Fluorinated chemical gases are widely used for fire suppression at the early stage of a historic building fire. However, the effects of hydrogen fluoride (HF) released during fire suppression on historic buildings are unavailable. Presently, experiments were performed to study HF effects on the weathered timbers. Five traditional fluorinated chemical gases, H-37, FK-5-1-12, H-1323, H-2402, and H-1301, are employed to suppress a fixed flame. The weathered timber chips, acting as historic building materials, are located in the chamber to detail the influence of HF on the surface. The characteristic of gas production and elements variety of wood surface are discussed by FTIR and SEM-EDX, respectively. It is observed that flame enhancement takes place at the early stage of fire suppression and various types of fire agents. The total amount of HF during 50 min is highly dependent on the physical parameters of fluorinated chemical gases. The SEM results of weathered timber suggest the surface of the wood is porous, resulting in a strong gas absorption performance. The amount of deposited F on the wood surface is found to be positively correlated with the total amount of HF yielded during fire suppression.
The mechanism of thermal decomposition and fire suppression, and the fire-extinguishing performance of HFO-1234yf, HCFO-1233xf and 2-BTP agents were investigated by using both experimental and theoretical methods. The different halogen atoms connected with the middle carbon atom result in the varied strength of C-X (X = F, Cl, Br) bonds, and thus different thermal stability of these agents, which could further affect the pyrolysis mechanism/products and the fire-extinguishing mechanism/performance of these agents. Owing to the generation of CF3˙, Cl˙ and Br˙ radicals, as well as some unsaturated small molecules produced by their pyrolysis, the HFO-1234yf, HCFO-1233xf and 2-BTP agents have minimum extinguishing concentrations (MECs) of 9.80 vol%, 7.28 vol% and 2.92 vol% (9.80 vol%, 7.28 vol% and 2.56 vol%) for suppressing propane-air (methane-air) flame, respectively, which are comparable to or even better than those of other hydrofluoroolefin (HFO) and hydrofluorocarbon (HFC) agents. Despite the contribution of directly produced Br˙ radicals, which have the lowest energy barrier and the highest efficiency in capturing free radicals, the Br˙ and CF3˙ radicals produced by the follow-up reactions with OH˙/H˙ radicals may also contribute a lot to the best fire-suppressing performance of 2-BTP. Due to the high reactivity of these unsaturated halogenated olefins and their pyrolysis products, exothermic reactions could occur between the original agents (or their pyrolysis products) and the OH˙/O: radicals, thus leading to the combustion-promotion effect of the HFO-1234yf, HCFO-1233xf and 2-BTP agents. The slightest combustion-promotion effect of the 2-BTP extinguishant may result from the easier generation and best performance of the Br˙ radicals, as well as the lowest energies released by the exothermic reactions.
CF3CBrCH2 (2-bromo-3,3,3-trifluoropropene, 2-BTP) is a potential replacement for CF3Br; however, it shows conflicted inhibition and enhancement behaviors under different combustion conditions. To better understand the combustion chemistry of 2-BTP, a theoretical study has been performed on its reactions with OH and H radicals. Potential energy surfaces were exhaustively explored by using B3LYP/aug-cc-pVTZ for geometry optimizations and CCSD(T)/aug-cc-pVTZ for high level single point energy refinements. Detailed kinetics of the major pathways were predicted by using RRKM/master-equation methodology. The present predictions imply that the –C(Br)=CH2 moiety of 2-BTP is most likely to be responsible for its fuel-like property. For 2-BTP + OH, the addition to the initial adduct (CF3CBrCH2OH) is the dominant channel at low temperatures, while the substitution reaction (CF3COHCH2 + Br) and H abstraction reaction (CF3CBrCH + H2O) dominates at high temperatures and elevated pressures. For 2-BTP + H, the addition to the initial adduct (CF3CBrCH3) also dominates the overall kinetics at low temperatures, while Br abstraction reaction (CF3CCH2 + HBr) and β-scission of the adduct forming CF3CHCH2 + Br dominates at high temperatures and elevated pressures. Compared to 2-BTP + OH, the 2-BTP + H reaction tends to have a larger effect on flame suppression, given the fact that it produces more inhibition species.
We present the GMTKN55 benchmark database for general main group thermochemistry, kinetics and noncovalent interactions. Compared to its popular predecessor GMTKN30 [Goerigk and Grimme J. Chem. Theory Comput, 2011, 7, 291], it allows assessment across a larger variety of chemical problems — with 13 new benchmark sets being presented for the first time — and it also provides reference values of significantly higher quality for most sets. GMTKN55 comprises 1505 relative energies based on 2462 single-point calculations and it is accessible to the user community via a dedicated website. Herein, we demonstrate the importance of better reference values, and we re-emphasise the need for London-dispersion corrections in density functional theory (DFT) treatments of thermochemical problems, including Minnesota methods. We assessed 217 variations of dispersion-corrected and -uncorrected density functional approximations, and carried out a detailed analysis of 83 of them to identify robust and reliable approaches. Double-hybrid functionals are the most reliable approaches for thermochemistry and noncovalent interactions, and they should be used whenever technically feasible. These are, in particular, DSD- BLYP-D3(BJ), DSD-PBEP86-D3(BJ), and B2GPPLYP-D3(BJ). The best hybrids are ωB97X-V, M052X-D3(0), and ωB97X-D3, but we also recommend PW6B95-D3(BJ) as the best conventional global hybrid. At the meta-generalised-gradient (meta-GGA) level, the SCAN-D3(BJ) method can be recommended. Other meta-GGAs are outperformed by the GGA functionals revPBE-D3(BJ), B97-D3(BJ), and OLYP-D3(BJ). We note that many popular methods, such as B3LYP, are not part of our recommendations. In fact, with our results we hope to inspire a change in the user community’s perception of common DFT methods. We also encourage method developers to use GMTKN55 for cross-validation studies of new methodologies.
Due to the environmental problems caused by the existing Halon substitutes, it is essential to explore new extinguishants with better environmental friendliness. In this study, in order to evaluate the practicability of cis‐1,1,1,4,4,4‐hexafluoro‐2‐butene (HFO‐1336mzz(Z)) as a potential Halon substitution product, the thermal decomposition mechanism and fire‐extinguishing performance of HFO‐1336mzz(Z) were studied by using density functional theory calculation and experimental analysis. The computational results show that thermal decomposition of HFO‐1336mzz(Z) would result in some products that can further react with active OH˙ and H˙ radicals, which are indispensable reactants in the flame and combustion. Moreover, during the interaction between HFO‐1336mzz(Z) and flame, the fire‐extinguishing radical CF3˙ would be produced, indicating the chemical‐extinguishing mechanism and the pronounced fire‐extinguishing performance of HFO‐1336mzz(Z). To explore its actual fire‐extinguishing effect, the fire‐extinguishing concentration (FEC) of HFO‐1336mzz(Z) on methane‐air flame was measured in cup‐burner. The FEC value of HFO‐1336mzz(Z) is 6.84% in volume, which is lower than those of HFC‐125 and HFC‐116, and is slightly higher than that of HFC‐236fa. Both the experimental and theoretical results suggest that HFO‐1336mzz(Z) can be a promising candidate for Halon substitute. The theoretical and experimental investigations on fire‐extinguishing mechanism and extinguishing performance of environmentally friendly HFO‐1336mzz(Z) suggest that it is a promising candidate for Halon substitute.
Cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)) conforms the most of necessary requirements as an environment-friendly extinguishant. However, its fire suppression performance has not been investigated. In this study, the fire suppression effectiveness of HFO-1336 was evaluated by a cup burner apparatus. The extinguishing concentration indicates nonpositive correlation with the fuel flow. On the other hand, to characterize the heat release of the reaction kernel, the temperature of the flame base was measured. The results showed that the temperature increased with HFO-1336 loading in the range of 2–5 %, while decreased as the concentration exceeded 5 %. In addition, the thermal decomposition properties of HFO-1336 were investigated over a temperature range of 100–800 ℃ and the products were analyzed by GC–MS. According to the detected products, the possible decomposition pathways were proposed and the extinguishing mechanism were discussed.
The pρT (pressure–density–temperature) properties of HFO-1336mzz(E) (trans-1,1,1,4,4,4-hexafluoro-2-butene) is measured by the isochoric method. A total of 154 pρT property data points are obtained at temperatures from 323 to 523 K and pressures up to 10 MPa along 19 isochores at densities from 84 kg·m–3 to 1212 kg·m–3. The Benedict–Webb–Rubin–Starling equation of state is used to correlate the present data. Saturated temperatures are analytically determined at 15 state points by extrapolating the isochores to intersect with the vapor pressure curve.
The thermodynamic properties of HFO-1336mzz(E) (trans-1,1,1,4,4,4-hexafluoro-2-butene) were determined. The critical point was ascertained by visual observation of the meniscus disappearance within an optical cell. The critical temperature, critical density, and critical pressure were determined to be 403.37 ± 0.03 K, 515.3 ± 5.0 kg m⁻³, and 2766.4 ± 4.5 kPa, respectively. Vapor pressures were also measured at temperatures ranging from 323 K (50 °C) to the critical temperature, and were correlated using the Wagner-type equation. The acentric factor and normal boiling point were determined to be 0.4053 and 280.58 K (7.43 °C), respectively, using the vapor pressure correlation. Based on the critical parameters and the acentric factor, saturated vapor densities and liquid densities were estimated using the Peng–Robinson equation and the Hankinson–Thomson equation, respectively. The heat of vaporization was also calculated from the Clausius–Clapeyron equation.
Twenty-two chemical reaction pathways of thermal decomposition of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf, CF3CF[dbnd]CH2) are proposed to investigate the formation mechanism of some possible products (CF3H, CF4, HF, H2) by using density function theory (DFT) simulations with M06-2X/6–311++(d,p) level of theory. The results point out that the ground state CF3CF[dbnd]CH2 will excite into the lowest triplet state CF3CF-CH2 favorably in the first step with an energy barrier of 264.67 kJ mol⁻¹ and pathway 5 is the most preferred route of homolytic cleavage reactions with the lowest energy barrier of 205.70 kJ mol⁻¹. F radical is hard to generate during thermal decomposition processes because of its higher energy barrier. H radical and CF3 radical play a dominant role in thermal decomposition of HFO-1234yf. H-abstraction and F-abstraction reactions are proposed in subsequent radical attacking chain reactions. CF3H and H2 are easier to be generated due to their lower energy barriers. Our work presents the mechanism of thermal decomposition of HFO-1234yf from the molecule level and provides a reference for studying the thermal stability of other working fluids.
This paper investigates the thermal decomposition properties of pentafluoroethane (HFC-125) fire extinguishing agent, which is regard as the ideal replacement of HCFC and PFC, due to its good environmental performance and low-toxicity, on the pyrolysis properties within 600 ∼ 850 °C, although the physical-chemical properties and extinguishing characteristics of HFC-125 have been widely reported, its decomposition mechanism is still unclear. With the help of analysis methods of gas chromatography (GC), ion chromatography (IC), gas chromatography–mass spectrometry (GC–MS) together with theoretical calculation, thermal decomposition details of HFC-125 is investigated, as well as possible thermal decomposition mechanism. The results show that the pyrolysis of HFC-125 occurs above 700 °C, the exhaust of HFC-125pyrolysis products mainly contains CF2 = CFCF3, CHF3, CF2 = CF2, CF3CHCF2, HF, CF2 = C(CF3)2 and the component concentrations vary with pyrolysis temperature and residence time. What’s more, a possible decomposition mechanism is also proposed, according to the activation energy of being calculated by using the first order reaction kinetics model and the detail dissociation pathways and gaseous products are deduced using the density functional theory. By combining the experimental results and theoretical calculation, characteristics involved in the decomposition of HFC-125 are given for the first time. It is expected that these investigation results would be of great help to the further study of the fire suppression of HFC-125.
The un-stretched burning velocities and Markstein lengths of premixed CH4– and C3H8–air flames with added C3H2F3Br (2-BTP) or CF3Br (Halon 1301), have been studied experimentally and numerically. For CF3Br flame inhibition, the un-stretched burning velocities, predicted using a recently updated kinetic model for CF3Br flame inhibition, were in excellent agreement with the experimental results over a range of fuel-air equivalence ratio and CF3Br loading. For C3H2F3Br flame inhibition, the un-stretched burning velocities predicted using a recently developed kinetic mechanism were in good agreement with the experimental results for most of the equivalence ratios tested; nonetheless, for very lean flames approaching the flammability limit, model predictions differed by up to 25%, even for uninhibited flames. The influence of inhibitor on the flame response to stretch and susceptibility to instabilities was examined through consideration of the measured burned gas Markstein lengths. Markstein lengths were very large, leading to large stretch effects on the flame stability after ignition, and flame wrinkling during explosion tests, greatly increasing the rate of pressure rise. The influence of stretch with regard to flame inhibitor effectiveness is discussed.
As a new kind of Halon replacement, 2-bromo-3,3,3-trifluoropropene (BTP) is highly effective at fire suppression with an extinguishment concentration lower than that of Halon 1301. Although the physical properties and extinguishing characteristics of BTP have been widely reported, there are relatively few studies on its thermal pyrolysis and extinguishing mechanisms. In this study, the thermal decomposition of BTP was studied over a temperature range of 25-800 degrees C and the decomposition products were analyzed by GC and GC-MS. Experimental results showed that the decomposition products were mainly trifluoropropyne (CF3CCH) and/or bromotrifluoromethane (CF3Br). The calculated apparent activation energies for the thermal pyrolysis of BTP by first order reaction approximation were in excellent agreement with the theoretical calculation results by Gaussian 03. Furthermore, by analyzing decomposition products and their chemical inhibition effect, thermal decomposition mechanism of BTP and its chemical extinguishing mechanism at high temperature were then proposed.
In order to clarify the chemical suppression mechanisms of CF3H, experimental and theoretical studies were conducted respectively in this paper. Firstly, the combustion species in low pressure laminar premixed flat methane flames with CF3H addition is measured by synchrotron radiation molecular beam mass spectrometry (SR-MBMS) experimentally. Fire suppression chemistry of CF3H is investigated by selective detection of combustion radicals and intermediates in experimental process. Secondly, quantum chemistry calculations are performed to calculate the potential energy surfaces (PES) for the CF3H unimolecular dissociation reaction and reactions of CF3H with free radical OH and H at the B3LYP/6-311++G** and QCISD(T)/6-311++G** levels. Finally, the chemical suppression mechanism of CF3H was discussed by comparing the theoretical calculation with experimental measurement.
In an earlier paper [A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], Kohn–Sham density‐functional calculations of the total atomization energies of the 55 molecules of the Gaussian‐1 database of Pople and co‐workers [J. Chem. Phys. 90, 5622 (1989); 93, 2537 (1990)] were reported. We found that the local‐spin‐density exchange‐correlation approximation with a ‘‘gradient correction’’ for exchange gave an average deviation from experiment of only 3.7 kcal/mol. In the present work we assess the role of gradient corrections for dynamical correlation, and we enlarge our earlier survey to include 42 atomic and molecular ionization potentials and 8 proton affinities as well. We conclude that gradient corrections for correlation do not improve atomization energies, but are vitally important in electron nonconserving processes such as ionization.
The kinetics of pyrolysis of CF3CHFCF3 have been studied in dilute mixtures (0.5 and 3 mol %) in argon in a single-pulse shock tube over the temperature range of 1200−1500 K, residence times behind the reflected shock of between 650 and 850 μs, and pressures between 16 and 18 atm. Fluorinated products were quantified with gas chromatography and Fourier transform infrared spectroscopy; identification of unknown fluorocarbons and hydrofluorocarbons was performed with gas chromatography−mass spectrometry. The most significant products detected were C2F6, CF2CHF, C2F4, C3F6, cyclo-C3F6, and CF3CHFCF2H. Traces of CF3H, CF4, C2F5H, C3F8, C4F6, and isomers of C4F8 were also identified. A detailed kinetic reaction scheme is presented to model the experimental reactant and product yield profiles as a function of temperature. The results of modeling showed that the major initiation reaction was the C−C bond fission reaction. The abstraction of the secondary H atom by F atoms was also predicted to be important, whereas 1,2-HF elimination was slower. From experiments and modeling, the following initiation rate constants were obtained: CF3CHFCF3 → CF3 + CF3CHF (k37 = 1015.9 exp(−355.6 kJ mol-1/RT) s-1), CF3CHFCF3 → C3F6 + HF (k38 = 1012.9 exp(−291.2 kJ mol-1/RT) s-1), and CF3CHFCF3 + F → CF3CFCF3 + HF (k39 = 1013.6 exp(−10.1 kJ mol-1/RT) cm3 mol-1 s-1).
One of the fastest steps in the initial decomposition of HFCs under combustion conditions is hydrogen atom abstraction by hydroxyl radicals. We have utilized ab initio quantum mechanics and transition-state theory (TST) to calculate the temperature dependence of rate constants for the reactions of OH with CH4, CH3F, CH2F2, and CHF3. Rate constants calculated using HF/6-31G(d) frequencies and MP2(full)/6-31G(d) structures to evaluate reactant and transition-state partition functions and the Hartree−Fock imaginary frequency, ωi, to compute Eckart tunneling factors, Γ, yielded rate constants that were substantially greater than experiment. Adjustment of the energy barrier to effect agreement between experimental and calculated rate constants at 298 K gave Arrhenius plots that exhibited markedly greater curvature than measured rate constants. When the imaginary frequency and barrier height were calculated by fitting high-level (G2) energies along the reaction path with a semiempirical Eckart function, it was found that the calculated imaginary frequency is a factor of 2.5 lower than the HF/6-31G(d) value, indicating that the energy barrier is considerably broader than predicted by the latter frequency. When the new imaginary frequencies and barrier heights were used to calculate rate constants, it was found that kTST < kexpt but that lowering the barrier height (by an average of 4.7 kJ/mol for the four reactions) yields calculated rate constants that are in excellent agreement with experiment at all temperatures.
The rate constants for the reactions of OH radicals with the fluorinated alkenes containing one Br atom (CFBr=CF2, CHBr=CF2, CH2=CBr-CF3, CH2=CBr-CF2-CF3, and, CH2=CH-CF2-CF2Br), as well as CF2=CF2, were measured using the flash photolysis resonance fluorescence technique over the temperature range 250-370 K to give the following Arrhenius expressions: k(C2F3Br)(T) = (2.02(-0.12)(+0.12)) X 10(-12) exp{(396 +/- 18)/T} cm(3) molecule(-1) s(-1); k(C2HF2Br)(T) = (1.30(-0.18)(+0.22)) X 10(-12) exp{(370 +/- 47)/T} cm(3) molecule(-1) s(-1); k(C3H2F3Br)(T) =(1.36(-01.14)(+0.17)) X 10(-12) exp{(317 +/- 34)/T} cm(3) molecule(-1) s(-1); k(C4H2F5Br)(T) = (0-98(-0.26)(+0.35)) X 10(-12) exp{(369 +/- 90)/T} cm(3) molecule(-1) s(-1); k(C4H3F4Br)(T) (0.85(-0.12)(+0.15)) X 10(-12) exp{(201 +/- 46)/T} cm(3) molecule(-1) s(-1); kC2F4(T) = (3.39(-0.12)(+0.22)) X 10(-12) exp{(323 +/- 11)/T} cm(3) molecule(-1) s(-1). Ultraviolet absorption spectra of these brominated fluoroalkanes and bromoethene were measured between 164 and 276 nm. On the basis of these results, the atmospheric lifetimes were estimated to be 1.4, 2.4, 2.8, 3.2, 7.0, and 1.1 days, respectively. The general pattern of haiolalkene reactivity toward OH is discussed.
HFC-227ea (CF3CHFCF3;1, 1, 1, 2, 3, 3, 3-heptafluoropropane) is an effective replacement for Halon 1301 in fire suppression systems, providing rapid extinguishment of flames through a combination of physical and chemical mechanisms. The vast majority of applications for HFC-227ea involve the protection of Class A hazards, which are characterized by low fuel loadings and low energy output, with fire sizes often in the range of 5–10 kW. Mid- and large-scale testing has demonstrated that HFC-227ea, at its minimum design concentration of 7.0% v/v, is effective at extinguishing fires typical of those expected to occur in electronic data processing (EDP) facilities, telecommunication facilities and anechoic chambers. The levels of HF produced following extinguishment of typical Class a fires with HFC–227ea were well below the estimated mammalian LC50 and the human Dangerous Toxic Load (DTL), and do not appear to present a threat to electronic equipment.
The performance of a recently introduced hybrid of density functional theory and Hartree—Fock theory, the B—LYP/HF procedure, has been examined with a variety of basis sets. We have found that even the relatively small 6-31G* basis set yields atomization energies, ionization potentials and proton affinities whose mean absolute error, compared with a large body of accurate experimental data, is only 6.45 kcal/mol. We have also found that the addition of a “higher-level correction” (of the type used in G2 theory) to the B—LYP/HF total energies reduces the mean absolute error to 4.14 kcal/mol.
Perfluorinated carboxylic acids are widely distributed in the environment, including remote regions, but their sources are not well understood. Perfluoropropionic acid (PFPrA, CF(3)CF(2)C(O)OH) has been observed in rainwater but the observed amounts can not be explained by currently known degradation pathways. Smog chamber studies were performed to assess the potential of photolysis of perfluoro-2-methyl-3-pentanone (PFMP, CF(3)CF(2)C(O)CF(CF(3))(2)), a commonly used fire-fighting fluid, to contribute to the observed PFPrA loadings. The photolysis of PFMP gives CF(3)CF(2)C·(O) and ·CF(CF(3))(2) radicals. A small (0.6%) but discernible yield of PFPrA was observed in smog chamber experiments by liquid chromatography-mass spectrometry offline chamber samples. The Tropospheric Ultraviolet-Visible (TUV) model was used to estimate an atmospheric lifetime of PFMP with respect to photolysis of 4-14 days depending on latitude and time of year. PFMP can undergo hydrolysis to produce PFPrA and CF(3)CFHCF(3) (HFC-227ea) in a manner analogous to the Haloform reaction. The rate of hydrolysis was measured using (19)F NMR at two different pHs and was too slow to be of importance in the atmosphere. Hydration of PFMP to give a geminal diol was investigated computationally using density functional theory. It was determined that hydration is not an important environmental fate of PFMP. The atmospheric fate of PFMP seems to be direct photolysis which, under low NO(x) conditions, gives PFPrA in a small yield. PFMP degradation contributes to, but does not appear to be the major source of, PFPrA observed in rainwater.
Neutrals CCCO, CC13CO, CCCS and CC13CS have been prepared by one-electron vertical (Franck–Condon) oxidation of the precursor anion radicals (CCCO)−˙, (CC13CO)−˙, (CCCS)−˙ and (CC13CS)−˙ respectively in collision cells of a reverse sector mass spectrometer. Ionisation of the neutrals to decomposing cations shows the neutrals to be stable for the microsecond duration of the neutralisation–ionisation (−NR+) experiment. No rearrangement of the label in energised CC13CO or CC13CS occurs during these experiments. In contrast, minor rearrangement of (CC13CO)+˙ is observed [(CC13CO)+˙
→
(OCC13C)+˙], while significant rearrangement occurs for (CC13CS)+˙
[(CC13CS)+˙
→
(SCC13C)+˙]. Theoretical calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory show that the cationic rearrangements occur by stepwise processes via key rhombic structures. Overall, the degenerate processes result in O and S migration from C-3 to C-1. The cations (CCCO)+˙ and (CCCS)+˙ require excess energies of ≥ 516 and ≥ 226 kJ mol−1 respectively to effect rearrangement.
Aircraft cargo MPS test of FK-5-1-12
- J W Reinhardt
Assessment of the Fire Suppression Mechanics for HFC-227ea Combined with NaHCO3
- R R Skaggs