Plastic pollution is a pressing global issue. According to data collected from the University of Oxford at Our World in Data[i], an average of over 300 million tons of plastic is being made every year since 2000. For reference, that is equal to 15 million semi-trucks full of plastic, which if you parked those trucks end to end would wrap around the world almost seven times! Close to half of that total is intended to be single-use plastic. This means that close to 150 million tons of plastic every year is destined to be discarded almost immediately after it is purchased, before it makes its way to a landfill. Not all those 150 million tons make it all the way to the landfill either. Plastic Oceans estimates that about 10 million tons of plastic every year finds its way into our rivers and oceans, where it has a detrimental impact on the ecosystem[ii]. The science world has been constantly working on finding a solution to the global plastic pollution problem ever since the discovery of the Great Pacific Garbage Patch in 1997. One solution that has gained a lot of traction as of late has been the pyrolysis of plastics.
The Benefits of Plastic
Polyethylene and polypropylene are essential global materials because of how versatile they are compared to other materials that have tried to replace them. Polyethylene is sought after because of high durability and tensile strength. Flexible plastic is able to last far longer than other materials because it will not crack or erode as easily[i]. Polypropylene has similar advantages, as well as being extremely lightweight and cost efficient, which significantly reduces transportation expenses. Polypropylene, or PP, is more rigid than polyethylene and can withstand a high amount of stress without any permanent deformation. PP is popular in the electrical industry because it is a great insulator thanks to its high heat tolerability and is used to protect all sorts of electric components. The biggest use for PP is in the food industry; because it is FDA approved material, it is a common plastic used in all food packaging products.
The plastic industry constantly receives backlash because of its environmental impact and the growing global plastic waste problem. In reality, the use of plastic is reducing greenhouse gas emissions if you compare it to the waste that other replacement materials would create. Plastic is lighter, cheaper, and more versatile than any other material. Every major industry uses plastic because of its great properties. Since it is so much lighter, cars use significantly less fuel when traveling as plastic can weigh half as much as alternative materials, according to the American Chemistry Council[ii]. Plastic insulation in houses makes heating and cooling systems more energy efficient. Plastic is a necessity in the medical field as it allows medical devices to be more precisely made from plastic molds as well as using plastic packaging to assure the user that the devices are unused and sterile. This reduces infection rates and costs for not only hospitals, but also for patients[iii]. The plastic industry is constantly researching pathways that can lead to better recycling methods so that plastic can continue to offer these benefits at a lower cost. Plastic pyrolysis provides a pathway to ensure the plastic in these industries can be 100% recyclable.
The Process of Plastic Pyrolysis
Plastic pyrolysis is heating plastic in an oxygen free environment to break down long-chain hydrocarbons into smaller hydrocarbon groups. A common misconception of plastic pyrolysis is that it is burning or incinerating plastic, which is harmful to both humans and the environment. Burning, or combusting, any material is physically and chemically impossible without oxygen present.
The absence of oxygen in the process prevents the plastic from burning and instead allows it to thermally decompose. Thermal energy from the reaction “cracks” the plastic molecules through thermal decomposition into a vapor comprised of smaller hydrocarbon chains that are chemically like naphtha or diesel distillates. When cooled, this vapor will condense into synthetic crude oil. This synthetic crude oil is also known as Circular Polymer Feedstock™ or CPF. The components of CPF can be broken down into monomers such as ethylene and propylene using a steam cracker. Through a process called polymerization, the monomers are “added” back together to form the final polymer products, polypropylene and polyethylene.
Developing "circular" polyethylene and polypropylene from CPF can be advantageous when compared to conventional production methods that utilize traditional feedstocks. CPFs are already more chemically similar to ethylene and propylene than traditional fossil-based feedstocks, which facilitates monomer production, and typical polymer feedstocks such as fossil fuels are obtained through carbon-intensive methods such as hydraulic fracturing or conventional drilling and pumping. With plastic pyrolysis we can decrease the energy input and carbon footprint of creating plastic significantly and begin turning a greener page in the world of plastic.