Environment & Energy
Showing Original Post only (View all)Defluorinating Branched Perfluoroalkanes with Cobalt Catalysts. [View all]
Recently in this space I decried what I called "The Worst Idea In Energy" with the caveat that possibly, based on the likelihood of it actually happening, the idea of lead perovskite solar cells was potentially worse.
My remarks were based on this paper:
Comparison of Linear and Branched Molecular Structures of Two Fluorocarbon Organosilane Surfactants for the Alteration of Sandstone Wettability (Ivan Moncayo-Riascos* and Bibian A. Hoyos, Energy Fuels, 2018, 32 (5), pp 57015710)
The paper was all about using recalcitrant perfluoroalkane species as a surfactant in "fracking" operations.
Not two days later, I came across a paper that suggested that people are already doing something very much like it. It's this paper:
Reductive Defluorination of Branched Per- and Polyfluoroalkyl Substances with Cobalt Complex Catalysts (Timothy J. Strathmann et al, Environ. Sci. Technol. Lett., 2018, 5 (5), pp 289294)
From the text:
Despite having received much less attention than linear PFASs have received, branched PFASs (Figure 1) have also been extensively applied and detected in the environment. For example, perfluoro-3,7-dimethyloctanoic acid (PFMe2OA) serves, along with linear PFASs, as an ingredient of well treatment fluids.22 This compound is also on the STANDARD 100 by OEKO-TEX list, indicating its wide application in textile production,23 and it has been detected in European water bodies.24 Perfluoroethylcyclohexanesulfonate (PFECHS)25 also contains two branched carbons on the cyclic structure, and its detection in Canadian Arctic lakes has been attributed to its use in aircraft anti-erosion fluid.26 Industrial PFOS products often contain variable fractions of branched isomers, which have been detected in both environmental waters and human tissues.27,28
The added bold is mine.
The authors propose a cobalt catalyst - a porphyrin catalyst - to defluorinate these recalcitrant and possibly toxic compounds.
The structure of the catalyst is shown in the cartoon in the header of the paper:
Here are the structures of the target compounds they seek to address:
Biochemists will note that the catalyst has certain similarities to the structure of vitamin B12, which the authors also note, pointing to it in another graphic:
The caption:
It appears from the paper that vitamin B12 - as is explored in the text as well as in the graphic - also can carry out this defluorination reaction, albeit on a very long time scale, which is displayed in the graphic as well. This of course is somewhat good news, although each fluorine removal results in an alternate toxicology I would suspect. Note the timeline for defluorination is not short, on the order of days, not minutes.
Another graphic gives the bond energies of some of these compounds calculated by DFT:
The caption:
These are very strong bonds, which accounts for the persistence of these molecules in the environment and in human, animal and plant flesh, as well as in water supplies.
Unbelievable.
Cobalt, as I note when criticizing the less than satisfying hype surrounding Elon Musk, hero of electric car cultists, is a conflict metal, mined under appalling conditions in many places on earth. It's role in Vitamin B12 also makes it an essential element for human health, albeit in tiny amounts.
Preparation of the cobalt species is not given in the paper, but I'd imagine an industrial scale synthesis would be, um, interesting and expensive.
When the best tool with which one is familiar is a hammer, everything looks like a nail. Radiolysis with gamma rays would do this job much better and much more completely, but well, I think that what will be done about these wells is nothing.
Have a nice "hump day."