Here is what you’ll learn in this story:
- Plastic is littering the entire planet, and scientists are trying to turn it back into a usable fuel source by heating it to very high temperatures.
- The process is not efficient enough to be feasible at large scales though. For the first time, scientists have discovered a promising method for creating the fuel.
- If current hurtles are overcome, then large-scale production of “bio-fuel” could supplement or even replace fossil fuels eventually, scientists hope.
When we say “plastic is everywhere,” that isn’t an exaggeration.
Almost 30 years ago, a Japanese underwater ROV spotted a plastic bag floating along the depths of the Mariana Trench, the deepest point in all of the world’s oceans. The oil-based product is now embedded in Earth’s geologic layer as a new sedimentary rock known as “plastistone.” And the average adult human brain likely contains up to a spoon’s worth of microplastic. The global scourge of plastic is so dire that the United Nations is currently developing a plastics treaty.
Due to our ongoing failure to control the proliferation of this oil-based menace, some scientists—as well as the oil and plastics industries at large—have turned to a controversial method to help alleviate the problem: Converting the plastic back into usable oil. If it’s scaled up efficiently, scientists say the “bio-oil” from plastic could feed directly into energy-hungry technologies that require fuel to produce heat and electricity, such as boilers, furnaces, and turbines, as well as diesel for trucks, trains, and ships. This is a global effort, and scientists working on the problem hope to create an innovative process that will satisfy multiple petroleum-based needs—and encourage less reliance on fossil fuels that are wrecking the environment. However, the current method is arguably inefficient and still needs to be proven.
Recently, researchers from Yale University may have made a dent in that inefficiency. They successfully tested a novel way to produce more bio-oil at less cost. It shows promise for scaling up production in the future, which is a crucial step for making plastic trash a viable source of energy.
The chief method of pulling off this chemical wizardry starts with pyrolysis, which applies heat to a material in the absence of oxygen. When the dial is turned up to 900 degrees Celsius (1,652 degrees Fahrenheit) plastic’s polymer chains break down into hydrocarbon molecules. These are organic compounds made mainly of carbon and hydrogen atoms and are the basic molecule required for creating fuel energy. Results vary, but pyrolysis usually turns about 60 percent of plastic into bio-oil.
Various bio-oil production methods exist, but they typically use a catalyst, such as the mineral zeolite, to enhance the breakdown of materials and increase yields. The new Yale study discovered a method that boosts the yield to roughly 66 percent—without the need for a catalyst at all. This could be a huge cost saver, said materials engineer Liangbing Hu, Ph.D., in a Yale University press statement. “Whenever you talk about catalysts, they’re very expensive and you have a lifetime issue because catalysts will eventually die by different means,” he said. Hu co-authored a paper detailing the process in the journal Nature Chemical Engineering earlier this summer.
The key to this innovation was creating a three-section 3D-printed carbon column reactor, with each section containing a different pore size. As chemicals passed through the reactor, the differing pore sizes—1 millimeter, 500 micrometer, and 200 nanometer—could effectively control the progress of the reaction. Next, the researchers planned how to scale up the process. So they experimented with constructing their reactor using readily available carbon felt, a high-temperature resistant, flexible material. Even without determining ideal pore sizes, they still achieved a high yield, of around 56 percent. Their work so far shows that advanced recycling via pyrolsis still has room for sustainability and efficiency improvement.
While increasing yields of bio-oil and making pyrolysis cost effective is important, scaling up also comes with some problems of its own that scientists must overcome. The most obvious one is the immense amount of energy the current technology uses, which means more carbon dioxide in the atmosphere as well as other waste products. Experts speaking with the independent, investigative nonprofit news organization ProPublica called the broader pyrolysis concept “a fairy tale,” a convenient story often touted by oil companies and plastic producers so they can keep relying on fossil fuels. At least for the foreseeable future, pyrolysis isn’t a cure-all for our plastic problem.
However, as scientists continue to pursue creative innovations, like Hu and his team’s, they could one day turn this “fairy tale” into a real solution to the world’s ever-growing plastic crisis. With the world is producing more single-use plastic than ever before, it’s clear that—at least for now—the best kind of plastic is still one that’s never made in the first place.
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.