This blog is my attempt to reconnect with the world of chemistry. I have a PhD in Inorganic Chemistry and make a living doing research for a large company in Michigan. As times have changed, that company has changed its focus and I no longer have as much chance to do the basic, fundamental research which I most enjoy. Through this blog, I am hoping to recapture the magic which I felt during my graduate (and undergraduate) days in college. Expect topics on chemistry and alchemy along with some non-chemistry related items which I think might be interesting.

"The chymists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasure among smoke and vapour, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I would change places with the Persian King."

Johann Joachim Becher (phlogistonist)
Acta Laboratorii Chymica Monacensis, seu Physica Subterranea, (1669).

Wednesday, April 15, 2009

PAHs -- Not Found at Your Local Health Food Store

Yesterday, my family and I returned from a five day visit with my parents in southwestern Missouri. This, of course, means I’ll be spending most of today actually recovering from the “vacation”. You have to love how that works. The travel part of the trip went smoothly, thankfully. No one got sick, the plane was on time, and there were no traffic problems; so we arrived in Springfield at the appointed time – only two hours before the tornadoes passed through. Ah, the joys of traveling!

Several of the houses in our neighborhood (not mine) have asphalt driveways. They’re a popular option since they cost less to build than concrete driveways, but they require a yearly application of sealant for protection from the elements. Apparently, that sealant contains polycyclic aromatic hydrocarbons (PAHs). PAHs (sometimes referred to as polynuclear aromatics or PNAs) consist of three or more fused aromatic rings (anthracene is one example), and as you might guess, are not always the most healthy of chemicals. And according to a recent study, the PAHs from these sealants are making their way into the water system. Since many PAHs are carcinogenic, you can kind of understand the concern.

As an inorganic chemist, I never really had much contact with PAHs, but I did run into them a few years ago while working on reforming catalysts. These catalysts convert air and hydrocarbons (like gasoline or diesel fuel) into CO and H2, along with smaller amounts of methane. I began to notice the buildup of an orange/yellow/brown solid all throughout my vent lines, sometimes as far as 10 feet away from the reactor. This necessitated not only the periodic replacement of these lines, but also, to my great joy, a massive clean out of my mass spectrometer. An NMR revealed this solid to be a mixture of PAHs. A little research revealed that under hot (700C), reducing conditions, methane forms PAHs quite happily. A little more research revealed that PAHs have been found responsible for the higher than usual rates of testicular cancer among workers in the metal cutting industry. Cutting fluids contain PAHs, and wearing clothes which are constantly soaked with them was found to be a bad idea.

I elected to start wearing gloves. Anybody else have any interesting stories about carcinogenic materials with which they’ve worked?

On the lighter side, David Bradley has managed to convince a few people to reveal some of the more stupid things they have done in the lab. .

I’ve decided to add a verification check in the comments section. I apologize for the inconvenience, but this blog seems to have been targeted by a bot which feels the need to leave garbage in the comments section and I’m getting tired of deleting it. Hopefully I’ll be able to drop it again in a couple of weeks.


John Fetzer said...

PAHs in my work? Try "PAHs were my work". The sealants for asphalt driveways differ. The cheap ones are made out of coar tar pitch, which means lots of PAHs. Plasticied sealants are not laden with PAHs.

Your reformer story is interesting. Reforming is high energy, very active catalyst processing. That means not only lots of PAHs, the thermodynamic sink of all hydrocarbon chemistry, but lots of variety in those PAHs. If you had done GC or HPLC of the deposit, it would have been extremely complex, akin to coal tar pitch without the heterocyclic analogues.

But lots of glowy components. Your deposit ought to have fluoresced bright blue or greenish.

Elliott Broidy said...

Yea, I couldn't find it either!