A new way to degrade plastics that turns them into fuel

A new way to degrade plastics that turns them into fuel
A novel chemical process converts post-consumer polyethylene plastic bottles, bags, and films into liquid fuels and waxes. Credit: Jia et al. Science Advances (2016). DOI: 10.1126/sciadv.1501591

(Phys.org)—A combined team of researchers from the Chinese Academy of Sciences and University of California has found a way to degrade ordinary plastics in a way that allows for fuel to be created from plastic trash. In their paper published in the journal Science Advances, the team describes their technique and their hopes for scaling it up to allow for it to be used in actually reducing plastic trash.

Most people know that modern life is filled with plastics, from packaging, to bags and soda bottles—the world has been inundated with them since they became a cheaper alternative to many other products. The problem is, of course, that they break down very slowly, which means they are piling up in landfills and serving as the source material in artificial island creation in our seas. Scientists have been looking for good ways to degrade plastics, particularly polyethylene, the most common kind produced, but until have not been able to find a means for doing so that is both inexpensive and scalable. In this new effort, the researchers report on successes they have achieved in the former and their hopes for the latter.

The method by the team involves mixing the plastics with an organometallic catalyst, which was made by mixing readily available molecules that were then doped with metal iridium. The reaction caused the bonds holding the plastic together to weaken, allowing them to be more easily torn apart—after doing, so, the team was able to use the broken down material to create a diesel-like which they claim could be used to power vehicles and other motors—they report that burning the fuel is also cleaner than burning other combustible materials.

The team claims that the process is inexpensive and not very difficult, though it is still not clear if it is scalable. The ratio of to catalyst is currently approximately 30 to1, which is not nearly good enough for commercial purposes. Their goal is 10,000 to 1. The team is also looking for something to use as part of the catalyst instead of iridium, because it is both difficult to get in large quantities and too expensive. The team is cautiously optimistic however that they will be able to find a way to change their technique to allow for use in commercial applications, which could mean, future energy seekers might be looking in landfills for a source material, rather than beneath our feet.

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More information: X. Jia et al. Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions, Science Advances (2016). DOI: 10.1126/sciadv.1501591

Polyethylene (PE) is the largest-volume synthetic polymer, and its chemical inertness makes its degradation by low-energy processes a challenging problem. We report a tandem catalytic cross alkane metathesis method for highly efficient degradation of polyethylenes under mild conditions. With the use of widely available, low-value, short alkanes (for example, petroleum ethers) as cross metathesis partners, different types of polyethylenes with various molecular weights undergo complete conversion into useful liquid fuels and waxes. This method shows excellent selectivity for linear alkane formation, and the degradation product distribution (liquid fuels versus waxes) can be controlled by the catalyst structure and reaction time. In addition, the catalysts are compatible with various polyolefin additives; therefore, common plastic wastes, such as postconsumer polyethylene bottles, bags, and films could be converted into valuable chemical feedstocks without any pretreatment.

Press release

Journal information: Science Advances

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User comments

Jun 20, 2016
Very interesting and no doubt relevant in our times. I'd like to ask how is this better than pyrolysis- an already developed and working concept with actual functional plants having been built (and not requiring exotic materials for catalysis)? If anyone could briefly provide some hint's, that would be great.

Jun 20, 2016
Personally I would rather see the stuff melted down and extruded into housing materials like framing boards and other building materials.

Jun 20, 2016
PE dissolves into benzene and acetone. You could pretty much blend a small amount of dissolved plastic bags into fuels, or just burn it as it is, or evaporate the solvent and spin it into fibers and fabric.

It also works as a sort of glue.

Jun 20, 2016
So much plastics go into landfills where it takes an enormous amount of time to break down. Processing it into fuel for future vehicle use sounds good.

Jun 20, 2016
Personally I would rather see the stuff melted down and extruded into housing materials like framing boards and other building materials.
- 24volts
Composite lumber already exists, which is made from a combination of wood fiber, plastic and a binding agent. It's good stuff and is great for patio decks, but it's kind of more expensive than pressure-treated lumber

Jun 20, 2016
Any idea how many Walmart bags it takes to make a stud length 2x4?
A LOT....

OS, I stick with cedar.

Jun 20, 2016
OS, I agree, it is more expensive but it might not be so expensive if more were made out of the stuff. It's not like there is any lack of it.

Jun 26, 2016
The Blest Company in Japan offers a range of pyrolizers to turn plastics into fuel or chemical feedstocks. These devices use tuned microwaves to break down the plastics. No rare iridium or other catalyst is needed.

Their desktop sized machine turns 1 kg of plastic into about 0.8 kg of diesel-like liquids.
And 0.2 kgs of CO2, I think. That's not good, but burning the fuel also creates a certain amount of CO2.


Jun 26, 2016
Here is a video about Blest Co.s devices


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