Imagine a world where post-consumer plastic did not have to be placed in a landfill or incinerated. Imagine if all the negative environmental impacts associated with landfilling and incineration, such as contamination from leaching, ingestion of microplastics, and increased carbon emissions, could be virtually eliminated… forever. Additionally, wouldn’t it be a better planet if the amount of fossil fuels needed to supply the world with plastics were also reduced? This type of future is possible. In fact, we are now in the early days of plastic manufacturing technology that will one day take us to an even better, cleaner, and healthier future for the environment and all living things.
Mechanical Recycling has Dominated
Until recently, the only way to recycle post-consumer waste plastic and reuse it to make new resin was through the process of mechanical recycling. In this recycling process plastic waste is sorted, washed, shredded, and heated back into resin pellets, with the actual molecular structure remaining intact. This process has limitations because it requires a raw material that is as clean and pure as possible. Moreover, there is an increased risk that the recycled plastic resin may contain contaminants. Additionally, color may vary by batch because the original plastic pigmentation is not removed. Lastly, plastic cannot be mechanically recycled indefinitely. With each cycle, the technical properties of the plastic degrades until it can no longer be used to make resin. Not all plastic is compatible with this process. Although plastic resin produced from this method is not considered virgin, it does have the benefit of reducing the plastic waste that is incinerated or ends up in landfills.
Fossil Fuels Drive Plastic Production
In today’s world, fossil fuels, specifically petroleum and natural gas, are refined to create the primary feedstocks for plastic production. Feedstocks, or the specific chemical ingredients that go into the process, are what get converted into plastics via chemical reactions at the plastic manufacturing plant. Ethane, obtained from natural gas, or Naphtha, obtained from crude oil, are processed into ethylene. Ethylene is a small, two-carbon molecule which is the primary hydrocarbon feedstock for making polyethylene plastic.
Plastics are made of polymers, which are molecules that contain many repeating carbon units. These long chain molecules are arranged in formations that give plastics many of the qualities that make it so versatile. Flexibility, malleability, and strength are examples of the qualities resulting from the chemical structure of plastic.
To make these polymers, and ultimately plastic itself, the refinement process first subjects the ethane or naphtha to “cracking”, a heat-intensive process which produces the ethylene. This process then continues as the ethylene is subjected to chemical reactions which grow the number of carbon atoms each molecule possess until the correct length polymer is formed.
Plastics made from fossil feedstocks are often called synthetic plastics. Beyond that, there are bioplastics which are made from ethanol feedstock derived from sustainable crops, such as corn or sugarcane. This bioplastic is chemically and physically identical to petroleum-based plastic because the feedstock both sources supply produce the exact same ethylene molecules which then create the same virgin plastic during the manufacturing process. However, because the bioplastic is made from sustainable materials we all can decrease the carbon footprint by using plastics generated from renewable sources.
A New Way to Recycle Plastics
Advanced recycling is a game-changing process that allows post-consumer plastic waste to be recycled into new virgin plastics. Advanced recycling is an umbrella term that encompasses several technologies, such as: pyrolysis, methanolysis, gasification, etc. One of the key benefits of Advanced recycling is that it offers a solution to transform difficult-to-recycle plastic waste into molecular building blocks or feedstocks that can be used by the petrochemical industry to create virgin plastics. Those plastics include polyethylene, polypropylene, polystyrene, PET, and more.
One of the more common and commercial technologies of Advanced recycling is “pyrolysis” – particularly efficient to recycle polyethylene, polypropylene and polystyrene. During the pyrolysis process post-consumer plastic waste is broken down on a molecular level into a liquid called “pyrolysis oil”. By processing the pyrolysis oil in crackers or refineries, and consequently backing out of fossil feedstock – petrochemical companies are able to create circular ethylene and other circular by-products. This circular ethylene is indistinguishable from fossil- or bio-based ethylene, since it has the exact same molecular composition (four hydrogen atoms bound to a pair of carbon atoms). By polymerizing this ethylene, a circular or recycled polyethylene can be created, again identical to virgin.
There are major differences between advanced recycling and mechanical recycling. Mechanical recycling is a downward spiral. First, plastic degrades over time due ultraviolet light and other environmental conditions. Additionally, as plastic is ground and melted during mechanical recycling, the polymer chains are partially broken down. Both of these factors reduce its tensile strength and viscosity, making it more difficult to process. This lower grade plastic can only be recycled a limited number of times before its altered physical properties make it unusable for plastic product containers. At some point, without emerging technologies such as advanced recycling, mechanically recycled plastic will end up in a landfill or be incinerated.
Advanced recycling is an infinite loop. Plastic recycled this way can be processed over and over again without any reduction in physical properties. This is because the waste is not just being cleaned and reheated, but it is being used as feedstock into a chemical process which transforms it back to ethylene molecules and then ultimately into the exact same specified plastic used for the original package. This allows for tremendous scaling potential. Instead of rejecting some plastics because they are the wrong color or made of composite materials, advanced recycling can utilize all types of plastic as its engine to becoming the ultimate recycling system. This moves us to a circular economy, where we can continuously use waste as raw materials for new plastic containers
The Pyrolysis Process is the Key to Advanced Recycling
Pyrolysis is a process which breaks down matter by heating it in an environment without oxygen. When feedstocks, such as waste plastic, are heated without oxygen they do not burn. Instead, they break down into a variety of simpler hydrocarbons. Controlling the process conditions, such as temperature and pressure, affect the type and mix of the resulting hydrocarbons. The mixture is known as “pyrolysis oil”, a liquid substance that is a complex blend of molecules which can be further upgraded through petrochemical facilities to create the ethylene needed for plastic production.
Pyrolysis is not a new technology. However, because of its tremendous potential to create an absolute circular recycling model it has caused companies to begin investing in building the infrastructure to support large scale pyrolysis production. Industrial-scale pyrolysis reactors are coming on-line with plans to create billions of pounds of plastic within the next 5 to 10 years. Pyrolysis oil offers us a pathway to a sustainable solution that has the potential to eliminate plastic waste from the environment. We are only in the beginning stages of this journey.
Summarizing the Processes
The graphic above summarizes the plastic production processes which support polyethylene production as have been discussed.
- The traditional pathway to create plastic resin which involves using customary fossil fuel feedstocks, such as petroleum and natural gas, as the source for the ethylene needed to create plastic.
- Bio-based sustainable resources, such as sugarcane or corn, can be grown for use as a feedstock for plastic resin production.
- Advanced recycling is the emerging sustainable method to produce plastic resin by transforming post-consumer waste plastic into a pyrolysis oil feedstock.
- Post-consumer waste plastic can be sorted, washed, cleaned, ground, and heated to produce a mechanically recycled resin that can be reprocessed a limited number of times.
Advanced recycling offers the potential to create a circular economy, where we can continuously use plastic waste as raw materials. Keeping waste plastics out of landfills and incinerators, along with eliminating the need for fossil fuels as feedstocks for plastic production, are all within reach with this technology.
Mass Balancing For Feedstock Accounting
At this time, virgin polyethylene plastic resin production can use fossil fuels, bio-based materials, or pyrolysis oil as feedstocks. The same plastic resin manufacturing plant can make plastic resin using a combination of these feedstocks. Currently the vast majority of the polyethylene plastic resin produced is from 100% fossil fuel feedstock. There have been plastic resins made from 100% bio-based materials on the market, but the quantity is very limited. So, how will the pyrolysis oil be used? The answer to this question is that plastic resin will be made from multiple feedstocks, and the feedstock content will be managed by an accounting technique known as Mass Balancing.
Mass Balancing is an approach developed to trace the flow of materials through a complex value chain. The Mass Balancing methodology provides rules for how to allocate the bio-based and/or recycled content to different products. This is accomplished by documenting and tracking recycled content from the plastic resin manufacturer to the plastic package manufacturer, to the consumer product manufacturer through to final delivery to consumers. This is not a new concept. In fact, Mass Balancing has been used for years in the energy sector to account for wind, water, and fossil feedstocks used in energy generation.
Mass Balancing is essentially a certification trail that allows companies to accurately and consistently claim how much of the content is bio-based or recycled-based. This is needed as, chemically, there is no way to identify the circular content since the resulting resin is the same as virgin. Over time, the expectation is that the plastic resin industry will reduce the amount of fossil feedstock being used, until blends of pyrolysis oil and bio-based materials are used as feedstocks exclusively. Until then, Mass Balancing will allow customers to know what percentage of plastic resin is generated from advanced recycled or bio-based feedstocks.
Several organizations are leading the effort to certify the amount of recycled and bio-based materials in the Mass Balancing model. One such emerging organization, the ISCC System GmbH in Cologne, Germany, is seeing widespread global adoption. For each batch of resin that is sold, the purchaser of the resin receives both a certificate of assurance and credits. The certificate that contains the circular or recycled content claim is called the Sustainability Declaration. The credits, derived from Mass Balancing, communicate how many pounds or metric tons of the specific batch were produced using recycled or bio-based materials. This system serves the dual purpose of assuring resin producers provide accurate information and delivering information to consumers to validate the quantity of recycled and bio-based materials. You can learn more about the International Sustainability and Carbon Certification at www.iscc-system.org.