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Sun Dec 24, 2017, 10:53 AM

Accumulation of a very potent greenhouse gas has stopped.

Recently I was going through some papers I downloaded on the subject of the gas oxygen difluoride, OF2, which is of interest to me because of some ideas I've had about electrochemical/fluoride volatility approaches to the recovery of valuable materials from used nuclear fuels, specifically the elements ruthenium, rhodium, technetium, molybdenum, plutonium, neptunium and uranium.

To my surprise, one of the papers found by my Google scholar search and collected by me was this one: Identifying the Molecular Origin of Global Warming (Lee, Berra and Francisco, J. Phys. Chem. A, 2009, 113 (45), pp 12694–12699) which, it seemed to me, has nothing to do with nuclear fuel reprocessing or even the chemistry of OF2.

But for some reason, the gas OF2 appears in table 1 the paper with a list of gases with global warming potential, their atmospheric lifetimes, global warming potential, etc.

The atmospheric lifetime of OF2 is not listed, which is not surprising, it should be as close to zero as it can be without actually being zero. OF2 is one of the few molecules known in which a positive charge resides on the extremely electronegative atom oxygen. As such it is one of the most powerful oxidants known; it will rapidly and quantitatively oxidize water: OF2 + H2O -> 2HF + O2.

Possibly it was included because it is a powerful fluorinating agent and thus may be utilized in the production of some of the gases that are utilized to make gases like the perfluoroalkanes and hydrofluoroalkanes (HFCs) that have replaced ozone depleting chloroflouroalkanes (CFCs) banned under the Montreal Protocol in refrigeration systems, HFC's being gases that are not ozone depleting but are nonetheless global warming forcing gases.

Otherwise, almost all of the other gases in the table were familiar to me, varieties of the aforementioned CFC's and HFCs, nitrous oxide, N2O (a potent ozone depleting gas as well as a global warming forcing gas), SF6 which replaced polychlorobiphenyls (PCBs) in electronic equipment as is also used in "green" thermally insulating windows in "environmentally aware" McMansions and office buildings meeting LEED certifications...blah...blah...blah.

In contrast to the situation with oxygen, most bonds to fluorine are extremely stable, notably in the case of carbon fluorine bonds, nitrogen fluorine bonds and sulfur flourine bonds, and as a result these compounds can persist for a very long time and are only destroyed by exposure to high energy radiation, far UV, x-rays and gamma rays.

Then there in table 1 was one gas of which I'd never heard, and about which I knew zero, pentafluorosulfuryltrifluoromethane, SF5CF3.

I asked myself, what the hell is that and why is it there and what the hell do they use that for?

In the table, it is listed as the most potent global warming potential gas, said potential being 22,800 on a scale in which the dangerous fossil fuel waste carbon dioxide is defined as having a value of 1.

As for "what the hell do they use that for?" the answer is, apparently, "nothing." The gas was discovered in atmospheric samples in Antarctica in the year 2000 and reported in the journal Science: A Potent Greenhouse Gas Identified in the Atmosphere: SF5CF3 (Sturges et al Science ol. 289, Issue 5479, pp. 611-613) Since there was no known use for the gas, the authors speculated that the gas was being created in the high field electronic equipment in which SF6 was utilized by reaction with teflon components. (The HTML version of the paper is open sourced, the PDF is not.)

It turns out that the authors were wrong and cheerfully admitted as much: Emissions halted of the potent greenhouse gas SF5CF3 (Sturges et al, Atmos. Chem. Phys., 12, 3653–3658, 2012) This paper is also open sourced as a PDF, but I'll excerpt it anyway.

Immediately following publication of our article, however, an open letter to the publishing journal from the company 3M stated that “one source of this compound is as a by-product of the manufacture of certain 3M fluorochemicals” (Santoro et al., 2000). It transpired that the relevant process was electrochemical fluorination for the production of perfluorooctanyl sulphonate, (PFOS) and other fluorosurfactants, used in the manufacture of foams and stain-resist coatings.

They went on to note that these production operations were to be imminently curtailed in the USA. In a subsequent personal communication, their bottom-up emission estimates were evidently close to the global emission rate that we had deduced from observations. We have updated the time series of atmospheric measurements from our original publication, and find that SF5CF3 has ceased to increase in the atmosphere, whereas the abundance of SF6 has continued to rise unabated. This clearly demonstrates that our original supposition that SF5CF3 originates from the degradation of SF6 was incorrect, and that all evidence now points to 3M being correct in their earlier assertion and that, as they predicted, emissions of this greenhouse gas have subsequently reduced to the point where they are no longer distinguishable by observation from zero.

PFOS is a serious persistent pollutant in its own right with a seriously long lifetime. I have written quite a bit about this compound which is also only degraded by high energy radiation, more or less, although some metabolism into potentially worse pollutants has been observed. PFOS can be pretty much detected in every living thing on the planet, particularly in lipids. 3M sold it until early 2000 in the product Scotch Guard which was very popular for protecting furniture.

(Other very persistent pollutants are also related to furniture as well, the flame retardants known as PBDE's, polybromodiphenyl ethers: These are also being phased out in furniture and clothing. They are also highly stable and only degraded radiochemically.)

To the credit of 3M, once they became aware of the persistence problem they voluntarily stopped making the product, which was a big seller, rather than manufacture ersatz "science" proving it was harmless - the Exxon approach.

They also immediately and voluntarily "'fessed up" about the source of SF5CF3, as noted by authors.

It does seem, happily, that this gas will not be growing in the atmosphere, even if most greenhouse gases will continue to rise unabated because, basically, we just don't care.

Have a happy holiday season.

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Reply Accumulation of a very potent greenhouse gas has stopped. (Original post)
NNadir Dec 2017 OP
delisen Dec 2017 #1
Igel Dec 2017 #2
eppur_se_muova Dec 2017 #3
NNadir Dec 2017 #4

Response to NNadir (Original post)

Sun Dec 24, 2017, 10:58 AM

1. Reminder:never just rail at the "corporate culture" -the differences

in how corporation behave can mean life or death for us and the planet.

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Response to delisen (Reply #1)

Sun Dec 24, 2017, 01:22 PM

2. Ultimately, corporations are legal fiction.

Behind corporations are people. Often they make decisions based on simply not getting in trouble, not getting fired (on the one hand) or showing how great they are and that they *can* do something outrageous, brave, or daring (on the other).

It's really hard to say, "If I do this, I'll lose my job, but it's the ethical thing." It's much easier to say, "I don't want to lose my job, so I'll find a way to view this as ethical." In so doing, we sell out our ethics. The group you're afraid of offending will proclaim that you've "grown" or "evolved" or "repented"; the group you don't care about will say bad things about you, and you simply won't care because they're not responsible for keeping you employed.

Pretty much the same for thrill-seekers. Those who push the edge for greater income, attention, doing things that might be harmful just because they think they can and they'll be considered important.

Sniveling or risk-seekers, both extremes are harmful, and corporations like pretty much every organization winds up emphasizing each.

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Response to NNadir (Original post)

Mon Dec 25, 2017, 02:02 AM

3. I could have sworn I first read about SF5CF3 (CF3SF5 to most organic chemists, rules be damned) ...

... here at DU, but I can't find the post. I remember thinking about unintended consequences ... and some chemistry I was interested in doing.

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Response to eppur_se_muova (Reply #3)

Mon Dec 25, 2017, 10:51 AM

4. It didn't come from me. I never heard of this molecule, unless I forgot about doing so.

I am an old man, and sometimes I forget things.

I'd imagine that it would be a useful methylating reagent, maybe less toxic than dimethylsulfate and cheaper than methyl iodide or bromide.

Methylating agents, all of them, are fairly toxic because they methylate tyrosines and thus screw with any and all kinase substrates, but it's always useful to have methylating agents, and it seems that this molecule might fit somewhere in a "tunable" set of such agents.

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