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I've seen some EPR experiments where they add gelatin to water with spin-probes in it, as it "hardens" it immobilizes the spin-probes so that you can check effect of tumbling rate on the EPR. Cool

I would like to do the same with asphaltene in crude oil.... So I'm looking for a chemical that I can add to oil that will turn it into a more-or-less solid black gooey mess. It shouldn't be something too reactive though, because I don't want it to change the chemical aspects of the asphaltene (e.g. not make it self-aggregate). Just lock it in place.

Thoughts?

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  • $\begingroup$ Asphaltene is too large and anisotropic to tumble effectively on an EPR timescale, isn't it? Anyway, can't you just vary the temperature? Crude oil should turn into a solid black mess at -20°C. $\endgroup$
    – Karl
    Commented Dec 7, 2020 at 19:52
  • $\begingroup$ Why single out asphaltenes ( which may or may not be in a crude oil ) of the myriad of components ? Crude may be anything from a water-like liquid , to something you can walk on ( at 20 C ). $\endgroup$
    – blacksmith37
    Commented Dec 7, 2020 at 21:34
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    $\begingroup$ Asphaltenes are usually the only paramagnetic component within crude oil. An individual molecule is about 1kDa but will get bigger if they self-aggregate, and they usually do!! For a recent oil that I was looking at, I got a good EPR match against EasySpin by using a tumbling rate of 45 nano-seconds. Hmmm. Only -20degC?? I had assumed much lower. Yes, I should check that. $\endgroup$
    – Tunneller
    Commented Dec 8, 2020 at 2:06
  • $\begingroup$ Heavy crudes are diluted with thinner oils or heated to be pumpable. $\endgroup$
    – blacksmith37
    Commented Dec 8, 2020 at 16:04

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Put your asphaltene source on a silica gel column and elute with hexane and then hexane/toluene mixture to remove paraffins (saturated compounds), aromatics, and resins (small polar compounds). At last, remove the asphaltenes (high molecular weight polar compounds) with pure toluene, evaporate to dryness (a brittle black solid), then with heat you can disolve/disperse the asphaltenes in a simple high molecular weight neutral material like petroleum jelly and let it cool. This will give a high and/or adjustable concentration of what you want to look at. https://en.wikipedia.org/wiki/Asphaltene

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  • $\begingroup$ Thanks for the feedback James. I worry that the spectrum of the asphaltene would change quite a bit if it was taken through that the extraction process. Indeed, there are papers which describe how that process creates spectra that depend on the solvent polarities used to create the standalone asphaltene. So my hope is to leave it somehow "unmolested" in the oil and then monitor the change in spectrum as the tumbling rate is frozen, and in such a way that I neither trigger self-aggragation nor destruction. $\endgroup$
    – Tunneller
    Commented Dec 8, 2020 at 17:19
  • $\begingroup$ In that case, you could add a wax, heat to dissolve, mix well, then cool. Waxes come in a wide range of melting points from petroleum jelly to paraffins (up to 60C mp) and microcrystalline waxes (up to 90C mp). Your comment suggests that some self-aggregation may be a natural condition. $\endgroup$
    – James Gaidis
    Commented Dec 9, 2020 at 15:47
  • $\begingroup$ Hi James, we had indeed arrived to the same conclusion, we are going to try candle wax this afternoon. Yes, some self-aggregation maybe unavoidable, indeed, I'm not exactly sure if I would know. But I'm excited about the idea of getting an EPR "powder" spectrum of the crude. It might tell me a lot. Mostly likely it will just confuse me though :-) $\endgroup$
    – Tunneller
    Commented Dec 9, 2020 at 18:30

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