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The most abundent large PAH? July 25, 2008

Posted by fetzthechemist in PAHs, Speculation.
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In my research, I discovered an important reaction in petroleum processing that creates a specific large PAH. The process known as hydrocracking converts a heavy saturated-hydrocarbon stream, in the range of the oil in motor oil or lubricating oil or light wax into the much smaller fuel hydrocarbons. Hydrocrackers are common, with hundreds of units in refineries throughout the world. One common problem is buildup of a reddish deposit in the pipes that take the oil from the catalytic chamber to areas of further processing, such as the distillation tower where the light fuels are removed. This red material plugs the lines and production has to stop to remove it. There are usually 100 or more kilograms in each deposit. A deposit buildup might happen as often as once a quarter, but usually once a year. Thus, worldwide tens of thousands of kilograms of the red material are produced every year.

My research isolated this material by removing the entrained oil and any inorganics (rust, catalyst fines, etc.). Mass spec and fluorescence showed it to be the condensed dimer of coronene, fifteen rings with a six-memberred bridging ring. The deposits were often > 95 % of this coronene dimer, trivially called dicoronylene. So, dicoronylene has been produced for over 50 years in these amount. About a million kilograms, as a ballpark number, for one specific large PAH.

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1. A-non-y-mous - August 28, 2008

And no one has found a use for this yet? My impression from talking with the few petrochemists I’ve met is that nothing is wasted. So what happens to these tons of red crap – mold it into bricks?

2. fetzthechemist - August 28, 2008

Petrochemists like to think that, but it depends on where something is made. A refinery is an interlinked series of processes. Waste happens – like flares on stacks, burning that “excess
methane, ethane, and propane. It is only excess because the design does not allow for collection at that point.

The same here. This compound is very heavy, in a petroleum sense of being high-boiling (it sublimes at 300 C under ultrahigh vacuum). It is produced at the clean end where the processes are designed to give motor fuels and clean base oil for lubricating oil use. No design for heavy waste.

The law say you cannot dump that into the residuum used as asphalt unless it is an approved additive. So it gets dumped.

Nobody has come up with a use. It is produced here and there in 100 to 500 kg amounts, sporadically – each refinery makes it at whatever pace the process design and chemistry result in. It might be a good base for an organic semiconductor or to make unique carbon composite, but nobody has researched it. A materials scientist needs to hook up with a refiner to get large amounts and just play with it.

3. Rhenium - October 27, 2008

Is it soluble in anything?

4. fetzthechemist - October 27, 2008

It is sparingly soluble, a few tens of parts-per-million, in 1,2,4-trichlorobenzene and 1-methylnaphthalene. Max Zander recrystallized some in boiling pyrene, but that is the only reference of that being used as a solvent. It is less soluble in nitrobenzene and you can get a part-per-billion or so into dichloromethane.


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