Upcycling Plastics: Turning Garbage into Gold
Written by Nikolai Haines and Robert Trapnell
Earth’s population is growing faster than ever before, and with more people comes even more waste. Recycling, even at its best, reduces energy consumption by about 66%. Although a promising step in the right direction, “only around 16% of plastic is actually recycled and usually ends up being ‘downcycled’ into lower-value materials with diminished properties” (Román-Leshkov). Most single-use plastics are thrown away into general trash cans to be emptied into landfills or end up in the Great Pacific Garbage Patch, both of which are detrimental to our environment. After being deposited in a landfill, the average plastic water bottle takes around 450 years to fully decompose. Recently, however, a group of chemists have identified a way to “convert plastics used in bottles and other packaging into fuels and chemical feedstock” using a ruthenium-carbon catalyst and mild, low-energy reactions conditions (American Chemical Society). Their findings suggest promising avenues of exploration for the decomposition of waste.
Before going into their discoveries, it is best to provide some context for those unfamiliar with the riveting topic of plastic degradation. Most common use plastics are polyolefin polymers such as polyethylene and polypropylene, and are typically produced by the polymerisation of oil and natural gas. These polymers are abundant and inexpensive, which is why they are being produced all over the world. Polymerisation is the process of joining monomer molecules together in a chemical reaction to create polymer chains. These long chains made of carbon and hydrogen atoms make the plastics very difficult to degrade. Carbon-hydrogen bonds create some of the least reactive molecules on our planet, which is why polyolefin polymers do not break apart easily. Under normal conditions, there are 4 plastic degradation methods: photodegradation, thermo oxidative degradation, hydrolytic degradation and biodegradation by microorganisms. Ultraviolet light from the sun allows oxygen atoms to be incorporated into the polymer, which causes the plastic to be slowly broken up “until the polymer chains reach sufficiently low molecular weight to be metabolised by microorganisms” (Webb). These processes take hundreds of years to fully transform our population’s plastic waste, leaving us stuck with mountains of plastic in the meantime.
So, the question becomes, can the scientists’ new method be effective enough to reduce the plastic crisis into something manageable and sustainable? The short answer is yes. Through the process of chemical reactions using a catalyst, the hydrocarbon chains can be broken down into smaller, less complex compounds that can be used for other purposes such as fuels and chemical feedstock. Using a catalyst reduces the energy needed to break down plastics and creates a much more effective and efficient process. In an experiment conducted by the discoverers, the scientists found that ruthenium-carbon nanoparticles “converted over 90% of the hydrocarbons into shorter compounds at 392 F” (American Chemical Society). In essence, that means that we could reduce plastic waste by around 90 percent, while simultaneously producing valuable alkanes that can be used as fuel. Even when testing the method on polyolefins with a more robust and complicated structure, such as the ones used in plastic water bottles, the researchers found that they could break down these chemical structures into other liquid and gas products. This process can be edited and fine tuned to produce liquid alkanes or natural gases.
To truly utilize this strategy of waste reduction, we must first create the technology to purify the alkanes and gases created. Further studies on the effects of moisture and decreasing the formation of light alkanes will need to be done before this process can be fully industrialized. That being said, while there is still progress to be made before this can become a fully effective process, it is a major step forward in reducing the plastic waste that is constantly flowing into landfills around the world.
Further Reading:
The battle to break plastic’s bond — BBC News
Selective bacterial colonization processes on polyethylene waste samples in an abandoned landfill site — Nature.com Scientific Reports