Turning Trash Into Liquid Gold

June 20, 2016 | Joanne Kennell

Plastic garbage
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Scientists have discovered a way to break down plastic into hydrocarbon fuel.

Humanity needs a solution to our plastic waste problem. Although it is easy to shout that everyone should just recycle, a lot of people don’t have access to recycling facilities, while others, let’s be honest, are just plain lazy.

What this means is that a lot of our plastic garbage ends up in landfills where it lasts for hundreds to thousands of years, or in the oceans — either breaking down to teeny-tiny bits that are eaten by marine life or floating in the sea for a very, very long time. So we need a practical solution, and we need one fast. Luckily for us and the environment, it may have just arrived.

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Scientists have come up with a new way to turn plastic waste into liquid fuel, and it uses less energy than previous methods and even produces a higher quality end product. The process breaks down polyethylene, the most abundant plastic in the world — around 110 million tons of it is produced every year — and spits out fuel.

There is no better way to encourage people to eliminate plastic waste than by converting it into a usable commodity. Given that polyethylene is made up of hydrogen and carbon — the main components of fuel — why not transform it into something we can burn?

This is not a new idea. Researchers have been working on creating hydrocarbon fuel for some time, but the difficulty is breaking the plastic back into its basic parts — hydrogen and carbon. Unfortunately, even though polyethylene is made from fossil fuels, it is a really stable chemical compound, so it doesn’t want to be separated.

Without treatment, polyethylene will continue to exist as is. Previous attempts to break it down involved heating it to very high temperatures — 400 degrees Celsius (752 degrees Fahrenheit) — but given the cost and unpredictable final products, that’s not practical.

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"[I]f you try to heat them at more than 400 degrees Celsius (which some methods do), they collapse into all kinds of combinations, resulting in a messy mix of gas, oil, wax and char that’s not especially useful," explained Amina Khan from the Los Angeles Times.

The team, consisting of researchers from the University of California, Irvine and the Shanghai Institute of Organic Chemistry, designed a process that uses chemical catalysts that are normally used to produce polymers, and instead, sets them to break down polymers.

The first catalyst breaks apart the hydrogen atoms from the carbon ones, causing the carbon atoms to form bonds with each other. Since the newly bonded carbon atoms form double, rather than single, bonds, a second catalyst is introduced to break them. Then, the separated hydrogen atoms are added back into the mix, and the process is repeated several times.

As a result, the team can produce either a diesel fuel or a wax that can be used for industrial purposes. What’s more, because the process requires heating at only 175 degrees Celsius (347 degrees Fahrenheit) to break down the plastic, it uses a lot less energy. However, the process does have some downsides.

"For starters, the catalysts break down polyethylene slowly, over the course of a day or more. They are also expensive and decompose after breaking apart just a few thousand polymer chains, far less than the millions carried out by most commercial catalysts," explained Robert Service of Science Magazine.

The research team is now trying to figure out how to make their technique even more efficient. Hopefully this means we will be able to say goodbye to a lot of our plastic waste.

The study has been published in the journal Science Advances.

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