Via the New York Times, quite the picture in this interesting profile of the new Shell cracker being built outside Pittsburgh:
...The plant Ms. Mercer has come here to build is “as big as you get,” she said. When finished, Shell’s cracker plant — named for the chemical reaction of “cracking” gas molecules into the building blocks of plastic — will consume vast quantities of ethane pumped from wells across Pennsylvania into an enormous furnace. The superheated gas is then cooled, forming solid pellets about the size of arborio rice. The process takes about 20 hours....
Never quite thought about polyethylene being like arborio rice, but I suppose that's reasonably accurate (also, I've never held the raw pellets in my hand.)
And just think, all of that polethylene will be plastic nanoparticles in the ocean, one day. The plant could be a target for an eco-terrorist.
ReplyDelete"superheated gas is then cooled, forming solid pellets about the size of arborio rice" - Not accurate. The cracker simply makes small molecules from slightly larger hydrocarbons. Slightly more accurate: the superheated gas is cooled, the ethylene produced is separated and fed to a polyethylene reactor and made into "fluffy" plastic particles. The plastic particles are fed into a giant extruder that melts and mixes the polymer which is fed out as strands (picture a giant meat grinder) and chopped into pellets. These plastic pellets are the size and shape of Arborio rice. Not the description I would have immediately thought of, but is reasonably accurate.
ReplyDelete- Polyolefin Research Chemist (large petrochemical company)
I've never quite understood why the extrusion process results in strands that are then cut up - undoubtedly this is a question that was answered by polymer engineers in the 1950s!
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