What Is Pyrolysis? Questions & Answers on Pyrolysis and Plastic Recycling


If you follow progress on plastic recycling, you may have heard mention of an age-old technology that is being applied today to used plastic: pyrolysis. While the basic technology is old, pyrolysis’ use in plastic recycling is new. So people are asking questions. What is pyrolysis? What does pyrolysis have to do with plastic recycling? Can pyrolysis help increase plastic recycling rates?

Here are some answers. And some links to further information along the way.

What is pyrolysis?

Pyrolysis is a thermal conversion or decomposition technology that has been used for thousands of years to create multiple materials, such as charcoal, roasted coffee, biofuels, chemicals and coke. (Pyrolysis was even used in ancient Egypt to create embalming fluid from cedar wood.)

Pyrolysis is the application of heat to a material in the absence of oxygen, which prevents the material from burning. It differs from combustion in that it does not involve oxygen. The process converts one material into a different, typically more valuable material.

Pyrolysis examples:

Wood becomes charcoal, biomass becomes fuel, plastic fibers become carbon fiber, coal becomes coke, petroleum products become chemicals, natural gas becomes hydrogen and so on.

(BTW: Pyrolysis also occurs when roasting, baking, toasting and grilling, typically only on the outer layer of food after it dries out.)

How is pyrolysis used in plastic recycling?

The use of pyrolysis for plastic recycling is quite new and continues to evolve as companies innovate. During pyrolysis, used plastic otherwise destined for disposal is typically converted into “pyrolysis oil” (often called “pyoil”) using heat and no oxygen.

Pyrolysis is one of several technologies under an umbrella term, “advanced” or “chemical” recycling, that convert used plastic into raw materials that can be reused to make new plastic and other materials.

Where does pyoil go? What is it used for?

Pyoil most often is sent to petrochemical manufacturing facilities where it is used to make multiple materials. It typically is mixed with other “hydrocarbons” derived from fossil fuels. These combined materials are then processed to separate the various fractions (materials of different molecular weight) for use in making plastic, chemicals, waxes, lubricants and other materials.

Pyoil can be used similarly to how oil or natural gas is used, thus reducing the need to pull more resources out of the ground.

Once the pyoil is mixed with other materials, how can we figure out how much used plastic goes into new plastic?

Pyoil molecules are essentially the same as fossil-derived hydrocarbons (in other words, the two are fungible when mixed), so it’s not practical to follow where pyoil molecules go when mixed together.

Then how do we figure out how much pyrolysis-derived recycled material is in a plastic product?

A longstanding accounting method called “mass balance” is used to help make sure that only the appropriate amount of pyoil-derived recycled plastic is claimed as recycled material in products. Mass balance is used widely in many industries to account for the origins of raw materials, such as those used in biofuels, chocolate, coffee , forestry products and energy distribution. The system accounts for the amount of an input (e.g., pyoil, wind energy, certified coffee, etc.) used in goods or services to increase transparency and help make sure that input is accurately reflected and not double counted.

For example, an electricity provider may want to communicate how much of its electricity is derived from solar power. The provider may be distributing energy from multiple sources, such as coal, natural gas, biomass, wind power and solar power. It may not be possible to say exactly how much electricity at a specific time is derived from solar power, but the provider can measure how much solar power it uses over time and then identify a data-backed allocation of its electricity that is derived from solar power.

As the Rainforest Alliance says, “All major international sustainability initiatives use mass balance in one form or another.”

Similarly with plastic, by accounting for the pyoil used to create plastic, companies can claim a specific percentage of recycled input used to create plastic products. In other words, the mass balance approach measures the amount of plastic building block materials made from pyoil that are being mixed with traditional materials to create new products.

Rather than following every individual molecule from origin to destination, the mass balance approach measures the amount of used plastic that enters recycling processes and makes certain that claims of recycled materials in the resultant products do not exceed that amount.

Using this approach, companies can help track and communicate the use of materials derived from recycling in their finished products.

What are the benefits of mass balance?

For decades, mass balance has demonstrated the ability to drive advances in sustainability, such as increased use of solar or wind power. The added value of “improved sustainability” helps drive company and consumer choices toward more sustainable goods and services.

And third-party organizations certify sustainability claims, which provides greater certainty in the marketplace and for consumers.

For plastic recycling, companies want to measure – and tell their customers – how much recycled material is in the final products that they make, sell or use. This measurement is a key component in many companies’ sustainability goals, so it must be based on transparent, widely accepted and trustworthy standards.

Broad global adoption of mass balance accounting for outputs from pyrolysis (and advanced plastic recycling technologies overall) provides guidance to brands and the value chain to support data-backed marketing claims. It also removes some barriers to investment, leading to greater market and consumer acceptance. This will help enable more rapid growth of pyrolysis recycling businesses, more collection of used plastic and more demand for the outputs of pyrolysis — all leading to a more circular economy for plastics and helping companies and consumers contribute to sustainability.

What’s the motivation for using pyrolysis to recycle plastic?

Simple answer: improved sustainability. Company leaders and employees want to contribute to a brighter, more sustainable future. And from a business perspective, brand companies (and their consumers) want to see more recycled materials in their products. It’s a win-win for everyone.

Plastic recycling through pyrolysis is in line with the United Nation’s Sustainable Development Goals (SDGs), particularly SDG-12 that promotes sustainable consumption and production.

Simply put, a barrel of pyoil replaces the need for a barrel of fossil-derived resources, helping reduce the need for extraction of oil and natural gas.

Pyoil and other similar technologies can reduce the environmental footprint of making and using plastics.

Pyrolysis significantly increases the types and amount of plastic that can be recycled. This allows our society to use our natural resources more efficiently. It also contributes to a circular economy for plastic, in which plastic is reused instead of discarded.

Can pyrolysis help increase the recycling rates for plastic?

As noted above, pyrolysis and other advanced recycling (or chemical recycling) technologies can help significantly increase the types and amounts of plastic that can be recycled.

Conventional mechanical plastic recycling is great for some things, but it has limited ability to tackle certain plastic products. Plastic bottles and containers are widely recycled in mechanical recycling facilities around the country, but other items – foams, pouches, bags, films, tubes – present challenges at these facilities. Pyrolysis and other advanced recycling technologies can more readily handle these items.

More info on advanced recycling for plastic here.