Anode effects, PFCs, global warming, and the aluminum industry

Tabereaux, Alton T.

doi:10.1007/bf03222629

Cited by 51 publications

(33 citation statements)

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“…Production of c-C 4 F 8 for these uses, via the pyrolysis of HCFC-22 or perhaps from 1,2-dichlorotetrafluoroethane (CFC-114) (Siegemund et al, 2016), may cause emissions as well. While the two major atmospheric PFCs, tetrafluoromethane (CF 4 ) and hexafluoroethane (C 2 F 6 ), and the minor PFC octafluoropropane (C 3 F 8 ) are released during primary aluminum production (Holliday and Henry, 1959;Tabereaux, 1994;Fraser et al, 2013), no evidence for c-C 4 F 8 emissions from primary aluminum production has been presented so far. Cai et al (2018) presented evidence for negligible emissions of c-C 4 F 8 from the similar electrolytic production of rare earth elements in China.…”

Section: Introductionmentioning

confidence: 99%

Perfluorocyclobutane (PFC-318, c-C4F8) in the global atmosphere

Mühle¹,

Trudinger²,

Rigby³

et al. 2019

Preprint

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Abstract. We reconstruct atmospheric abundances of the potent greenhouse gas c-C4F8 (perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of ~&#8201;1&#8211;2&#8201;% reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66&#8201;ppt (parts per trillion dry-air mole fraction) in 2017. Global c-C4F8 emissions rose from near zero in the 1960s to ~&#8201;1.2&#8201;Gg&#8201;yr&#8722;1 in the late 1970s to late 1980s, then declined to ~&#8201;0.8&#8201;Gg&#8201;yr&#8722;1 in the mid-1990s to early 2000s, followed by a rise since the early 2000s to ~&#8201;2.2&#8201;Gg&#8201;yr&#8722;1 in 2017. These emissions are significantly larger than inventory based emission estimates. Estimated emissions from eastern Asia rose from 0.36&#8201;Gg&#8201;yr&#8722;1 in 2010 to 0.73&#8201;Gg&#8201;yr&#8722;1 in 2016 and 2017, 31&#8201;% of global emissions, mostly from eastern China. We estimate emissions of 0.14&#8201;Gg&#8201;yr&#8722;1 from Northern and Central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from North Western Europe and Australia are estimated to be small (&#8804;&#8201;1&#8201;% each). We conclude that emissions from China, India and Russia are likely related to production of polytetrafluoroethylene (PTFE, &#8220;Teflon&#8221;) and other fluoropolymers that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 (CHClF2) in which c-C4F8 is a known by-product. The semiconductor sector, where c-C4F8 is used, is estimated to be a small source. Without an obvious correlation with population density, incineration of waste containing fluoropolymers is probably a minor source, and we find no evidence of emissions from electrolytic production of aluminum in Australia. While many possible emissive uses of c-C4F8 are known, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to reduce c-C4F8 by-product were probably not in place in the early decades, explaining the increase in emissions. With the advent of by-product reporting requirements to the United Nations Framework Convention on Climate Change (UNFCCC) in the 1990s, concern about climate change and product stewardship, abatement, and perhaps the collection of c-C4F8 by-product for use in the semiconductor industry where it can be easily abated, it is conceivable that emissions in developed countries were stabilized and then reduced, explaining the observed emission reduction in the 1980s and 1990s. Concurrently, production of PTFE in China began to increase rapidly. Without emission reduction requirements, it is plausible that global emissions today are dominated by China and other developing countries, in agreement with our analysis. We predict that c-C4F8 emissions will continue to rise and that c-C4F8 will become the second most important emitted PFC in terms of CO2-equivalent emissions within a year or two. The 2017 radiative forcing of c-C4F8 (0.52&#8201;mW&#8201;m&#8722;2) is small but emissions of c-C4F8 and other PFCs, due to their very long atmospheric lifetimes, essentially permanently alter Earth's radiative budget and should be reduced. Significant emissions outside of the investigated regions clearly show that observational capabilities and reporting requirements need to be improved to understand global and country scale emissions of PFCs and other synthetic greenhouse gases and ozone depleting substances.

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Section: Introductionmentioning

confidence: 99%

Perfluorocyclobutane (PFC-318, c-C4F8) in the global atmosphere

Mühle¹,

Trudinger²,

Rigby³

et al. 2019

Preprint

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“…Therefore, based on the analysis of the gas molecule configuration, the characteristics of the products are better. Importantly, CF 4 , C 2 F 6 , C 3 F 6 , C 3 F 8 , C 4 F 10 , C 5 F 12 , and C 6 F 14 have a higher GWP value, 30,31 and its effect on the environment needs to be further assessed.…”

Section: Effect Of Micro-water On the Insulation Performance Of C 5 Fmentioning

confidence: 99%

Effects of micro-water on decomposition of the environment-friendly insulating medium C5F10O

Xiao

Zhang

et al. 2017

AIP Advances

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SF6 is widely used in all kinds of high-voltage electrical equipment because of its excellent insulation and arc-extinguishing performance. However, this compound leads to serious greenhouse effect, which harms the environment. Many research institutions are now actively in search of SF6 alternative gas. C5F10O has attracted much attention as an alternative gas with low global warming potential (GWP) and excellent dielectric strength. In this paper, we analyzed the possible decomposition paths of C5F10O under micro-water environment through density functional theory. We also evaluated the ionization parameters and toxicity of the decomposition products. The results show that OH• and H• produced by H2O exhibited a catalytic effect on the decomposition of C5F10O. CF4, C2F6, C3F6, C3F8, C4F10, C5F12, C6F14, C3F7COH, C3F7OH, CF3COH, C3F7H, and CF3OH were produced in the micro-water environment. Based on molecular configuration calculation, the ionization parameters of these products were inferior to perfluorocarbons, such as C3F8, leading to reduced insulation performance of the system. Moreover, CF2O and HF are hazardous to human health and equipment safety. Results will provide a basis for further study of the insulation characteristic of the C5F10O gas mixture under micro-water condition to guide the formulation of their relevant international standards prior to engineering applications.

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“…Tabereaux et al studied the anode effect gas and reported that the content of C 2 F 6 goes through a peak and drops to zero after 2-3 min; in some cases, no C 2 F 6 is found in Søderberg cells. 2,29 We consider the probable reason is attributed to the following automatic reaction:…”

Section: Resultsmentioning

confidence: 99%

“…The traditional view mentioned that fluorine ions react with carbon anodes to directly generate CF 4 and C 2 F 6 during the anode effect. 2,6,7 The formation of CF 4 and C 2 F 6 can be expressed by the following reactions: 4Na 3 AlF 6 + 3C = 12NaF + 4Al + 3CF4 E 1373K = 2.49 V [2] 2Na 3 AlF 6 + 2C = 6NaF + 2Al + C 2 F 6 E 1373K = 2.72 V [3] Moreover, CF 4 and C 2 F 6 coming from the decomposition of COF 2 has been suggested. [8][9][10][11] COF 2 is considered an intermediate product prior to the anode effect, then, it decomposes to form CF 4 and C 2 F 6 .…”

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confidence: 98%

Mechanism of Graphite Electrode Fluorinated in 2.4NaF/AlF₃–Al₂O₃Melt at 1373 K

Gong

Shi

Wang

et al. 2014

J. Electrochem. Soc.

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The electrochemical behavior of a graphite anode in 2.4NaF/AlF 3 -0.05wt%Al 2 O 3 molten salt was investigated via cyclic voltammetry (CV) and chrono-electrochemical techniques. Four oxidation current peaks, located at 1.42, 2.5, 3.1, and 3.94 V vs. Al/Al 3+ , were observed in CV curves, which may be attributed to the formation of CO 2 , CF 4 , graphite fluoride ((CF) n ), and F 2 , respectively. The anode effect occurred when the potential exceeded 3.5 V. Meanwhile, the mechanism of the electrode reaction of CO 2 and (CF) n formation was confirmed to be irreversible charge transfer followed by a chemical reaction. Therefore, we confirmed that the passivation of the graphite anode was due to the formation of (CF) n on the electrode surface, blocking the mass transfer. According to the number of the charge transfer and the characteristics of the electrode reactions, we discuss detailed reaction pathways for CF 4 and (CF) n formation. In addition, the presence of the small quantity of C 2 F 6 in the anode gas is discussed.In the primary aluminum production by the Hall-Héroult process, cryolite-alumina molten salt and a carbon anode are employed. The cell reaction under normal conditions isThe exit gas from the electrolysis cell consists of a mixture of CO 2 and CO, and the secondary reactions between CO 2 and aluminum yield CO. 1 However, a cell malfunction, known as the anode effect (AE), can easily occur when the alumina content in the electrolyte is less than 1 wt%. The anode effect results in not only the generation of perfluorocarbons (PFCs) CF 4 and C 2 F 6 but also a high consumption of energy for a higher cell voltage. 2 Owing to the high global warming potentials of CF 4 and C 2 F 6 3 and the fact that the primary aluminum industry is the major anthropogenic source of CF 4 and C 2 F 6 , 4 the Environmental Protection Agency and the primary aluminum producers have established the Voluntary Aluminum Industrial Partnership (VAIP) with the goal of substantially reducing PFC emission. 5 To gain a better understanding of the mechanism of CF 4 and C 2 F 6 generation, the anodic behaviors of carbonaceous electrodes have been widely studied in recent decades. The traditional view mentioned that fluorine ions react with carbon anodes to directly generate CF 4 and C 2 F 6 during the anode effect. 2,6,7 The formation of CF 4 and C 2 F 6 can be expressed by the following reactions:Moreover, CF 4 and C 2 F 6 coming from the decomposition of COF 2 has been suggested. 8-11 COF 2 is considered an intermediate product prior to the anode effect, then, it decomposes to form CF 4 and C 2 F 6 . The reactions are described as 2Na 3 AlF 6 + Al 2 O 3 + 3C = 3COF 2 + 6NaF + 4Al E 1373K = 1.81 V [4] 2COF 2 = CO 2 + CF 4 lg K 1373K = −0.176 [5] 3COF 2 + 2C = 3CO + C 2 F 6 lg K 1373K = −1.351 [6]

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Anode effects, PFCs, global warming, and the aluminum industry

Cited by 51 publications

References 0 publications

Perfluorocyclobutane (PFC-318, <i>c</i>-C<sub>4</sub>F<sub>8</sub>) in the global atmosphere

Perfluorocyclobutane (PFC-318, <i>c</i>-C<sub>4</sub>F<sub>8</sub>) in the global atmosphere

Effects of micro-water on decomposition of the environment-friendly insulating medium C5F10O

Mechanism of Graphite Electrode Fluorinated in 2.4NaF/AlF₃–Al₂O₃Melt at 1373 K

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Anode effects, PFCs, global warming, and the aluminum industry

Cited by 51 publications

References 0 publications

Perfluorocyclobutane (PFC-318, &lt;i&gt;c&lt;/i&gt;-C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;8&lt;/sub&gt;) in the global atmosphere

Perfluorocyclobutane (PFC-318, &lt;i&gt;c&lt;/i&gt;-C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;8&lt;/sub&gt;) in the global atmosphere

Effects of micro-water on decomposition of the environment-friendly insulating medium C5F10O

Mechanism of Graphite Electrode Fluorinated in 2.4NaF/AlF3–Al2O3Melt at 1373 K

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Perfluorocyclobutane (PFC-318, <i>c</i>-C<sub>4</sub>F<sub>8</sub>) in the global atmosphere

Perfluorocyclobutane (PFC-318, <i>c</i>-C<sub>4</sub>F<sub>8</sub>) in the global atmosphere

Mechanism of Graphite Electrode Fluorinated in 2.4NaF/AlF₃–Al₂O₃Melt at 1373 K