Developments in Depolymerization
Plastic pollution has proven detrimental to the environment and has the potential to cause serious health issues. Despite their well documented environmental and anticipated health impacts, a rise in the consumption of plastics is expected (Wright 2017). Plastics are everywhere: polyethylene terephthalate (PET) is the plastic base for soda bottles; polyester is a common fabric in clothing; and polyvinyl chloride (PVC) is often used for making water pipes. This ubiquity is not an issue on its own. In fact, plastics have been crucial in advancements in medicine and technology; however, both the disposal and production of plastic are harmful to Earth. We can be sure that plastics will continue to be made; the methods by which we dispose of plastics, however, are likely to change.
The linear nature of the plastic economy serves few, and will ultimately hurt us all. The innovation of chemical recycling, which breaks plastic into monomers, is a product of increasing regulatory pressure on companies, at least in part. Companies are beginning to be held accountable for the plastic they use with legislation such as Extended Producer Responsibility (EPR) bills. Three states have passed EPR bills and more are expected to follow suit in the coming years (Snarnoff 2023). These bills reflect the public opinion that something must be done about the plastic problem, and can be viewed as an encouraging sign in combating plastic waste. The overall volume of plastic being recycled is expected to increase, and new methods, like pyrolysis and depolymerization, are expected to grow in prominence (Hundertmark 2018). Chemical recycling, specifically depolymerization, offers exciting solutions to many of the shortcomings associated with current practices.
The majority of plastics are not recyclable in America (Hocevar 2020). Single use plastics vastly outnumber plastics that have the capability of being recycled. Recycling plants can only accept certain types of plastics, and the rest are discarded into landfills or burned. Our landfills are overflowing, and the burning of plastics emits carbon dioxide, a harmful greenhouse gas. The Great Pacific Garbage Patch (GPGP) is a mass of floating plastic about the size of Texas (Pyrek 2016). Plastics take around five hundred years to decompose if untreated, drastically affecting the environment into which they are discarded (Siahaan 2007). Because they are not made with naturally occurring pieces, plastics will not readily decompose on their own in a timely manner. Most of the plastics we dispose of are not reused, instead seeping into our environment, either directly, through littering, or through the way in which they are processed – landfills and incineration. Because most plastics do not degrade naturally, almost every piece made in history still exists today. We already have too much plastic waste and we do not show signs of slowing down further production or consumption (Geyer 2017).
The way we make most plastics presents an issue as well. Common plastics are petroleum based which means we need to obtain oil to make them. Crude oil is extracted from oil deposits before being transported to industrial plants. Heat breaks down the crude oil into petroleum and the petroleum into a number of monomers, the building blocks of polymers. These monomers undergo polymerization to create a long chain of repeating monomers. These polymers undergo additional treatment, such as plasticization, specified for their intended use. This is the general process by which plastics are created. It is, by all accounts, not an eco-friendly process. Bio-based plastics, or bioplastics, are intended to decrease the strain on natural resources while reducing the time it takes for plastics to degrade (Pilla 2011). Because the ingredients of bioplastics are naturally occurring, there is a natural method by which these plastics can be broken down and returned to nature without producing harmful emissions. Bioplastics, unfortunately, are not the silver bullet to a greener tomorrow. They are often less recyclable than petroleum based plastics, and undergo degradation at the same rate as petroleum based plastics in water, which is where much of plastic waste ends up. Bioplastics have been able to lessen the need for oil in plastic production, but their promise has yet to be realized to its fullest extent. The shortcomings of bioplastics have ensured that petroleum based plastics will continue to be the main type of plastic being produced.
Having a basic understanding of the issues surrounding the creation and disposal of plastics illustrates why depolymerization, the conversion of polymers to monomers, is such an appealing concept—it has the capability to reduce both the amount of crude oil we use and the amount of waste we create. Two types of recycling exist: mechanical and chemical. Most recycling plants currently employ some method of mechanical recycling (Ragaert 2017). This process involves heating up plastic and reshaping it. Unfortunately, not all plastics can be repurposed this way. The few types of plastics that can undergo mechanical recycling require virgin plastic to form a final product. The limits of mechanical recycling have led to developments in the field of depolymerization.
We can, under the right conditions, break down any plastic into its monomer substituents. A wide array of methods of depolymerization exist and more are being developed (Miao 2021). Many startups are creating new catalysts in the hope to innovate our handling of plastic waste. Finding the methods that make depolymerization time and cost effective is crucial for implementing depolymerization on a large scale. Several companies believe they have such a method and are opening or plan on opening industrial depolymerization plants soon.
Carbios is a French company that has designed an enzymatic solution to the plastic problem. They secured their funding through L’instrument Financier Pour L’Environnement (L.I.F.E.), an EU program that sponsors scientific endeavors with industrial implications. Their process boasts an entirely recycled plastic product that is 100% recyclable. This development is groundbreaking as current methods of recycling require virgin plastic and produce a less recyclable product. Carbois’s enzymatic solution was found to depolymerize PET at a higher rate than other similar enzymes (Tourneir 2020). Eager to scale up their product to an industrial level, they opened a plant in 2021, which has been producing clear plastic bottles since opening. Carbois has developed an outstanding product with great promise and will be looking to expand their production moving forward.
Another company worth highlighting is Samsara. Samsara, a term which refers to the cyclic nature of life, claims to have created a method that will yield pure, recyclable plastic from used plastic. Samsara has enhanced enzymes to break down plastics at low temperatures and recover the water they use during the process. Their plants do not require high heat and have a low rate of carbon emission, in accordance with green chemistry ideals. They are currently developing ways to harness the power of similar enzymes to break down plastic textiles, like polyester. Polyester recycling represents a largely unexplored field. Samsara claims that their first plant, scheduled to open in 2024, will be instantly profitable.
Pyrowave implements a different technique to depolymerize plastics. Microwave assisted polymerization uses heat to break down the polymer into its monomer constituents. This differs from mechanical recycling because it transforms the polymer into monomer building blocks. Whereas Carbois and Samsara have taken a biochemical approach to depolymerizing PET, Pyrowave uses their patented microwave technology to break down styrofoam. Their process relies on electricity, which is harnessed sustainably through wind farms or solar panels. This is different from many of the mechanical recycling companies, which use fossil fuels. They have a recycling plant in Canada that is estimated to produce around 30,000 tons of recycled plastic per year.
A large implementation of depolymerization is expected in the future (Collins 2022). This growth would reflect a shift away from a markedly linear plastic sector to a more circular one. With old plastics being the necessary components to make new plastics, the motivation to remove plastic from the environment could lead to a mass cleanup. Perhaps methods to remove microplastics from soil will be implemented, or ocean clean-up like Clear Blue Sea, which makes robots that collect marine plastic, may be better funded, or there could be increased legislation surrounding plastic disposal and all plastic used will be recycled. Or, perhaps less drastic changes will occur. The extent to which developments in depolymerization will change the world remains to be seen, but that’s exciting. A desire to better the world has led to innovative solutions in the field of chemical recycling and suggest that a circular plastic economy is on the horizon.
References
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Carbois’s Website