Many companies and brands have been trying to reduce the amount of plastic they use for their products and packaging for a number of years. Now, the introduction of Plastic Packaging Tax (PPT) in the UK is further accelerating these efforts as companies seek to avoid the impact of higher prices in an already volatile market. While the desire to reduce the use of plastic labels is admirable, many ask how this can be possible while still ensuring sufficient quality, durability and suitability for their products and use-cases. Luckily, more and more sustainable label materials are now available which are not subject to the plastic packaging tax which still maintain plastic-like properties.
Pyrolysis Processes
In September, Dow declared a milestone in its effort to mitigate the flow of plastic waste. The big chemical company and Mura Technology took the wraps off a project in Böhlen, Germany, to build a plant based on Mura’s supercritical steam process. The facility will convert mixed plastic waste into hydrocarbon liquids that Dow will load into its ethylene cracker at the site for conversion back into new plastics.
The plant will be the largest of its kind in Europe, diverting 120,000 metric tons (t) of waste per year from incinerators. It will be six times the size of Mura’s first plant, still under construction in Teesside, England. “Böhlen is sort of a base case, and it will just get larger from there,” Oliver Borek, Mura’s chief commercial officer, said during a press conference. An executive from the engineering firm KBR, which is licensing the process beyond Dow and Mura, noted that his firm is already designing three plants in South Korea and one in Japan.
Petrochemical makers are fully behind the broad array of pyrolysis processes, like Mura’s, under development around the world. Nearly every large chemical company—Dow, BASF, Shell, ExxonMobil, LyondellBasell Industries, Sabic, Ineos, Braskem, and TotalEnergies, to name some—either has joined hands with a smaller firm developing a process or is creating its own.
The Argument
These firms argue that pyrolysis can make up for the shortcomings of mechanical recycling, the familiar process of washing and repelletizing the plastics that consumers drop into blue bins. Only two polymers—the polyethylene terephthalate (PET) found in soda and water bottles and the high-density polyethylene in milk jugs and other such containers—are widely recycled at an appreciable scale. And it is difficult to get even these relatively homogeneous materials up to the contamination specifications needed for food-contact use. In all, mechanical recycling manages to capture only about 9% of plastics in the US, according to the US Environmental Protection Agency.
Too Good to be True
Recyclers can tackle a few more resins with depolymerization processes that break down polymers into their chemical precursors. For example, methanolysis can be used to recycle PET products like fibers and sheets that aren’t amenable to mechanical methods. And firms have been breaking down nylon using hydrolysis for many years. But the bulk of the plastics we use—the candy wrappers, stand-up pouches, potato chip bags, protective packaging, single-use cups, frozen food bags, razors, toothpaste tubes, cotton swabs, and other objects of our daily lives—defy both mechanical recycling and depolymerization.
These items are constructed from multiple plastics that are nearly impossible to separate. Plus they are mostly made of polyolefins like polyethylene and polypropylene, which have strong carbon-carbon bonds that resist depolymerization. For these mixed plastics, pyrolysis is the industry’s only currently viable tool for recovering raw materials and making new polymers.
But a pyrolysis reactor isn’t a magic box that can make the plastics industry’s waste problems vanish. The process is superficially simple: using high temperatures in the absence of oxygen to break down plastics into a mixture of smaller molecules known as pyrolysis oil. Yet converting the different kinds of plastics that can end up as waste into an uncontaminated feedstock—such as the C5–C12 paraffins that would be an ideal naphtha feedstock for an ethylene cracker—poses considerable challenges. Plastics companies will need to overcome these challenges if they are to debunk environmentalists’ objections and meet their own goals for reducing waste and carbon emissions.
According to a review paper by University of Minnesota Twin Cities bioproduct and biosystem engineer Roger Ruan and other scientists, polypropylene decomposes at 378–456 °C, while low-density polyethylene breaks apart at 437–486 °C, and high-density polyethylene at 452–489 °C. As a result, firms processing mixed plastic waste must select a temperature—normally over 500 °C—at which all the polymers they take in on a given day will break down.
However, temperature affects the composition of a pyrolysis unit’s output. Pyrolysis yields useful liquids, such as naphtha and diesel. But it also creates less-desirable waxes that might need to be broken down further. And pyrolysis makes lighter gases that are typically burned as fuel in the reactor. High temperatures and long reactor residence times might cut wax output and yield more naphtha, but they also create gases that have limited utility.
High temperatures can also lead to dehydrogenation, cyclization, aromatization, and Diels-Alder reactions, thereby creating more aromatics. “For fuels and so on, it’s fine,” Ruan says. “But sometimes we want naphtha feedstock for new plastics production; we don’t want a lot of aromatics.” And feeding the wrong plastics into pyrolysis reactors creates inefficiency and can contaminate the output. PET contains oxygen and tends to form carbon dioxide, Ruan says. Polyvinyl chloride (PVC) yields chlorinated compounds. Additionally, some plastics have a lot of inorganic additives, such as carbon black, carbonate, and clay. They lead to the formation of char, which pyrolysis operators must dispose of as solid waste.
The Critics
Environmentalists loathe pyrolysis. And a growing number of jurisdictions, such as California, don’t consider it recycling at all. One critic is Jan Dell, a chemical engineer who founded and heads the Last Beach Cleanup, an environmental organization. She has helped larger environmental groups, such as the Natural Resources Defense Council and Greenpeace, prepare reports on the practice. For presentations, Dell has compiled 16 pages of objections.
One of Dell’s primary complaints is that pyrolysis facilities can’t actually accept the mixed plastic waste they claim they can. The residual PVC, PET, and other materials in the stream gum up the process too much. “There’s too many types,” Dell says. “There are too many additives. You can’t recycle them all together, and separating them out defies the second law of thermodynamics. It is just impossible to reorder—like Humpty Dumpty—all these plastics once they’ve been put into a bin.”
A second charge is that pyrolysis is really incineration, even though pyrolysis reactors operate in the absence of oxygen. “If you look at just the pyrolysis vessel itself, no, there’s no burning. I have to agree with that,” Dell says. “But here’s the deal: How do you heat that pyrolysis vessel to the 900 to 1,500 °F you need? You heat it by incinerating the gas that comes off of it.” Dell points to the pyrolysis company Brightmark, which disclosed to the EPA that 70% of the output from a plant it is building in Ashley, Indiana, will be gases that it plans to use for energy or flare. Brightmark now says those figures were submitted in error. Such gases represent only about 18% of the output, the firm says, and it is submitting the updated figure to the EPA.
Another critique has to do with scale. Dell says that roughly 120,000 t per year of pyrolysis and other chemical recycling capacity is currently onstream in the US. This represents a minuscule fraction of the overall plastics production of about 56 million t in North America in 2021, according to the American Chemistry Council. Just one new polyethylene plant has about 500,000 t of annual capacity.
To critics like Dell, pyrolysis is a greenwashing scheme meant to fool the public into thinking plastics are recycled more than they actually are. She points out that the industry, under similar pressure in the early 1990s, built up a lot of recycling capacity, only to shutter it when the projects proved unworkable and public attention faded. The industry is now repeating this pattern, Dell says.
A plethora of recent reports in the US have raised concerns about the environmental impact of chemical recycling. Earlier this year, US NGO the Natural Resources Defense Council (NRDC) conducted in-depth research on eight chemical recycling facilities in the country. It concluded that the facilities are “generating hazardous waste and exacerbating environmental injustices under the false guise of recycling”. It said most facilities are not producing or planning to produce new plastic but are performing “a kind of plastic incineration – turning plastic into dirty fuel using energy-intensive processes”.
Many people may consider totally removing labels from their packaging, instead focusing on pre-printed cartons, boxes or containers. This may be a solution in some situations, however this introduces various challenges related to inventory management, plus the generally much higher costs of pre-printed packaging versus printing labels. In addition, we must keep in mind the recycling issues of packaging and not just labels. Labels are already a complicated subject, and factors such as the Plastic Packaging Tax and general sustainability desires are only making navigation of the industry even more challenging.
While the debate rages on, one thing is clear: the US needs a solution to its plastic waste crisis. National and state governments, as well as governments across the globe, must ensure investment is funnelled where it can be most effective. Advocates of chemical recycling say investment is needed to encourage technological innovation, but green groups counter that this should only happen if and when robust data is available. Whether the chemical recycling revolution takes off may well depend on this.
