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The IBM researchers turned to organic catalysts, whose design is similar to biological enzymes.
"Organic catalysts have traditionally been heavily criticized because they have low activity and large amounts of them are required" to help a reaction along, says Hedrick. "We found families of catalysts that are as active as metallic catalysts," some of which are good for working with insulating materials for chips, and some of which can work with PET. The IBM researchers collaborated with a computational chemistry group within the company to model the activity of the catalysts, and have demonstrated them experimentally in the lab.
The PET-recycling catalyst, a type of molecule called a carbene, was inspired by vitamin B1, says Stanford chemistry professor Robert Waymouth. The Stanford and IBM researchers guessed that a similar organic small molecule might be good at catalyzing reactions that string esters together to make long polymers.
The IBM researchers will now collaborate with researchers at the King Abdulaziz City for Science and Technology in Saudi Arabia to test the chemical recycling of PET on a larger scale. "We need to see if what we discovered on the lab bench can work in big reactors," says Waymouth. In initial tests, they will focus on breaking down the polymer into its constituents. However, the company has also had good results using its organic catalysts to depolymerize PET to make specialized materials such as feedstocks for high-strength plastics that are more valuable but are expensive to make using other pathways. "You start with trash, and build it back up into higher value materials," says Robert Allen, senior manager of advanced materials chemistry at IBM Almaden.
The DOE funds a company that recycles plug-in vehicle batteries.
The company hopes to develop powerful, lightweight lithium-air batteries.
De-polymerization and re-polymerization - one or two steps?
This was a really interesting article. This type of catalyst, modeling biological processes, will transform the chemical and synthetic materials industries, making them less energy intensive and less dependent on non-renewable feedstocks. There were a couple of items in the article, however, that got me a bit confused.
The article states:
"The Stanford and IBM researchers guessed that a similar organic small molecule might be good at catalyzing reactions that string esters together to make long polymers."
(i.e., polymerization) But the article also states:
"the company has also had good results using its organic catalysts to depolymerize PET to make specialized materials such as feedstocks...."
So, are there one or two catalysts involved in the process? (one for de- and one for re-polymerization)
Also: "The catalyst works in an ethylene glycol solution. When cut up water bottles are placed in the solution, the catalyst causes the organic acid in the plastic to react with the ethylene glycol in solution to make PET that is of the same quality used to make the bottle initially."
It sounds like the organic acid (which is terephthalic acid (TPA)) is released from the PET (by catalyst induced de-polymerization) and is re-polymerized with ethylene glycol to form new PET in the same reactor. This seems like a messy business. How can the same catalyst work for both de-polymerization and re-polymerization? Is it possible that a two-step process is used, i.e., that they separate the TPA from the solution and purify it, prior to re-polymerizing? To produce a “like new” polymer, they would want to control the molecular weight distribution of the new polymer carefully and reformulate with a new package of additives. I expect that it would be difficult to control the polymerization reaction precisely when you are depolymerizing in the same reaction vessel. They would also want to avoid any contamination from the original additives or any degradation products in the original polymer.
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mkogrady
423 Comments
Can you clarify
Katherine Bourzac - the article states PET is not reused for new bottles or containers, but can the discarded plastic be remelted and then formed into a non-food related product such as green house panels, or non food application like giant bio reactors for algae farms.
If the plastic is damaged by UV rays, then periodically replacing them and remelting the old PET may offer some means to keep continuous recycling.
A simple argument may be that "X amount" of petroleum is used in making "Y number or pounds" of PET, so anything we can do to reuse this stuff makes financial sense.
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