Upcycling plastic waste into graphite provides possible alternative to landfills
Updated: Nov 28, 2022
UNIVERSITY PARK, Pa. — Upcycling plastic waste into graphite, used in electric vehicles and renewable energy storage, could positively contribute to the global economy, preserving resources, saving energy and reducing carbon dioxide emissions, according to Penn State researchers. Under a seed grant from the Materials Research Institute, the researchers will explore ways to take single-use plastic waste and turn it into high-quality graphite.
Plastics are an incredibly important element in U.S. consumerism due to their versatile and highly durable nature. They are used in everything from product packaging to construction to electronics and machinery. However, with growing demand comes the dark side of plastic consumption — millions of tons of non-recyclable plastic waste.
According to McKinsey & Company, approximately 37 million tons of plastic are used every year. Packaging and food service plastics represent about 16 million tons of that total, and these are typically “single-use” plastics that are used and then discarded. In fact, Americans consume roughly 100 pounds of packaging and food-service plastics per person, per year.
“We literally have mountains of plastic waste, millions of tons every year, and most of it is still going into the landfill,” said Randy Vander Wal, professor of energy and mineral engineering, materials science and engineering, and mechanical engineering at Penn State. “But what if we have the opportunity to take a waste product that has no destiny per se and turn that into graphite?”
The main types of plastic resin found in single-use packaging and food service applications are polyethylene terephthalate (PET), used in soft drink bottles; high-density polyethylene (HDPE), used in milk jugs; low-density polyethylene (LDPE), used in plastic bags, containers, films, and wraps; and polypropylene (PP), used in yogurt containers and bottle caps. Together, these plastic types make up approximately 85% of single-use volume, according to the EPA, and only about 12% of this material is recycled and 16% is burnt with municipal trash. The majority — more than 70%, or eleven million tons — is sent to landfills where it can take hundreds of years to break down.
Juxtaposed with an abundance of plastic waste is a forthcoming shortage in quality graphite.
“When everyone thinks of lithium-ion batteries, they think of lithium, which is a critical mineral, but quality carbon in the form of graphite is also needed in lithium-ion batteries,” Vander Wal said. “And there will be a huge shortfall in the graphite needed for batteries.”
In addition to lithium-ion batteries, certain industrial practices require graphite as well. For instance, in electrodes in aluminum refining and for electric arc furnaces used in steel manufacturing, among others.
“Every electric vehicle, like the Tesla Model 3, requires at least 70 kilograms of carbon,” Vander Wal said. “For every 1 million electric vehicles, a 10% increase of the current graphite market is projected.”
Currently, petroleum-derived cokes (a byproduct of the oil refining process), coal tar pitches (remnants from the distillation of coal tar) and mined graphite are the main sources of graphitic carbons used in energy storage methods such as lithium-ion batteries. Petroleum-derived cokes and coal tar pitches are nonrenewable resources and demand a lot of energy to produce. In addition, their production produces high emission levels of volatile organic compounds. Meanwhile, natural graphite is a limited resource, and the mining process is environmentally destructive.
The seed grant will allow Vander Wal and his team to take single-use plastic waste and turn it into high-quality graphite. To do this, they will use graphene oxide to provide the oxygen required for stabilization and an aromatic framework to guide the reconstruction of single-use plastics into a graphitic material. Compared to traditional catalysts, no purification or catalyst removal is required as the graphene oxide additive will have the same composition as the final graphite. Since low-density LDPE and PET plastics melt, they facilitate uniform mixing with the graphene oxide. During the heat treatment processing, the graphene’s chemical structure is imparted onto the surrounding plastic as it decomposes.
Furthermore, this graphitization heat treatment can be performed at varied scales and does not require significant infrastructure.
The researchers believe this work could create a new path for graphite manufacturing through the energy savings of a lower temperature process and the environmental benefits due to reduced carbon dioxide emissions. In addition, upcycling waste plastic into high-value graphitic carbons will lead to improved recycling economics, increased recycling infrastructure investment, and recycling workforce growth, while reducing greenhouse gas emissions. This becomes even more important as clean energy technology drives the demand for carbon as a material. In fact, lithium-ion battery production is expected to more than double by 2025, according to the Northern Graphite Corporation.
“We’re looking at a way to intersect a waste product with little commercial value and turn it into a commercial product with value but also facilitate the clean energy transition,” Vander Wal said.
Other researchers on this project include Ekaterina Bazilevskaya, staff scientist at the Penn State Materials Characterization Lab; Adri van Duin, professor of mechanical engineering at Penn State; Ramakrishnan Rajagopalan, associate professor of engineering at Penn State Dubois; and Carlos Leon y Leon, senior materials scientist at Morgan Advanced Materials.
The Pennsylvania Recycling Markets Center Corporation (RMC) is also contributing to this research, courtesy of Robert J. Bylone Jr., president and CEO. The RMC is an independent, Pennsylvania nonprofit corporation with a mission to reduce or eliminate barriers that lead to new expanded use of Pennsylvania’s recycled materials. The RMC has an affiliation with Penn State and is headquartered at Penn State Harrisburg with an office in Pittsburgh.
This article was originally published here.