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Plastic waste-to-fuel: What it is and how it works

09/22/2023 · 6 minute read

Plastic is part of our daily lives — it’s hard to imagine life without it. However, only 9% of plastic is recycled, with 12% incinerated and the remaining 79% landing in our oceans and landfills, where scientists predict it will take up to 450 years to biodegrade.

With the energy transition underway, the UK Government for the first time, in its upcoming Energy Bill, has enabled support of recycled carbon fuels, including those made from plastic waste. In this first instalment of a three-part series on plastic-to-fuel technology, we outline this new process and its challenges; future articles will examine the associated risks and how they can be mitigated.

Key ways to recycle plastics

There are several ways to recycle plastics, including:

Mechanical recycling: Plastic is crushed into granules that can then be used in another product, but its molecular structure is retained. This is a widely-used technique, but has limitations. For instance, sorting methods are not yet available at scale to differentiate food-grade plastics, which command higher prices. Plus, there are environmental health concerns relating to the release of particles during this process. Companies are currently repurposing plastics, using a variety of methods, into rugs, packaging, shoes, plastic jackets, skateboards, and construction materials.

Chemical recycling: There are currently two chemical processes for converting plastic waste to an energy carrier — pyrolysis and gasification (see figure 1). These methods break down plastic, remove any impurities, and convert it back to its chemical components. They have the potential to tackle the problem of plastic pollution while also providing an alternative source of energy.

UK plastic-to-fuel plants

  • 2022 West Dunbartonshire council approves plastics-to-hydrogen facility at Rothesay Dock on the river Clyde.
  • 2022 Cheshire West and Chester Council approves plastics recycling hub at Ellesmere Port that will produce hydrogen and have a hydrogen refuelling station.
  • 2022 Construction begins in Teeside on flagship plant to convert plastic waste into ultra-low sulphur fuels for the transport and heavy-machinery sectors. Nine similar plants planned for UK. 
  • 2023 Sunderland Council gives planning permission for plastic-to-oil recycling plant to be located on the Port of Sunderland.

Plastic-to-fuel process

Collection and sorting: Plastic waste is collected from sources such as households, industries, or recycling centres. It is sorted to remove any non-plastic materials, like paper or metal.

Shredding and pre-treatment: The sorted plastic waste is shredded into small pieces to increase the surface area and improve the efficiency of the subsequent processes. The shredded plastic may undergo pre-treatment processes — for example, washing or drying — to remove contaminants such as dirt or moisture.

Pyrolysis: The shredded plastic is subjected to high temperatures, typically in the range of 300°-500°C (572°-932°F), in an oxygen-free environment, a process known as pyrolysis. The plastic undergoes thermal decomposition and breaks down into simpler hydrocarbon molecules.

Vaporization and condensation: The vapors produced during pyrolysis are cooled, causing them to condense and form a liquid. This liquid consists of various hydrocarbon compounds, including impurities, which can be further refined to obtain usable fuels or chemical raw material components.

Refining: The condensed liquid is processed through further refining steps, such as fractional distillation and hydro-processing, to separate and purify the different hydrocarbon fractions. The resulting fuels can include gasoline, diesel, kerosene, or similar products.

By-product handling: Some by-products may also be generated during the process, such as char or residue. These may undergo additional treatment such as hydro-cracking, or be recycled or disposed of appropriately.

Gasification: In gasification, plastic waste reacts with a gasifying agent — such as steam, oxygen, or air — at high temperatures between 500°–1300 °C. This process produces synthesis gas, or syngas, that can be used to produce fuel for cells that can generate electricity.

One advantage of gasification compared to pyrolysis is the greater flexibility to jointly increase the value of plastics of different composition or mixtures or plastics mixed with other feedstock.

Figure 1

Source: American Chemical Society

An alternative to fossil fuel

The fundamental molecular components of plastics consist of hydrogen and carbon. Fuels produced from plastic waste can be tailored to meet a certain need, such as fuel for industrial, aeroplane, ship, locomotive, or diesel engines, and boilers. Plastics may also be processed to harvest hydrogen — a clean fuel that when consumed in a fuel cell, produces only water. As such, they are suitable substitutes for fossil fuels.

Advantages of converting plastic waste into fuel

There is much excitement about this relatively new technology worldwide — with visions that landfills could become the oil fields of the future. Several councils in the UK have already granted planning permission for plants that will convert plastic waste into fuels (see box), with other local authorities expected to follow suit. As well as in the UK, from India to Australia, plastic-to-fuel projects are underway. The benefits of creating fuel by using this technology include:

  • The fuels produced are better for the environment, as they have the properties of clean fuel, so can be burned with a lower carbon footprint than coal, oil, and natural gas.
  • Replaces the need for new carbon, as existing produced carbon and hydrogen molecules are utilised.
  • Reduces the amount of plastic incinerated in the UK and the carbon emissions resulting from that process.
  • Prevents hard-to-recycle or non-recyclable material from ending up in a landfill and reduces export of plastic waste from the UK (see figure 2).
  • The potential to develop the method to include other waste materials, including those that may not be easily recyclable, such as metal waste.
  • The chemical compounds produced can be used instead of fossil fuel-based alternatives in existing production lines.
  • The operational cost is relatively low once the plant is set up.
  • Oil and gas production has associated methane pollution, which is a large contributor to greenhouse gases. Less new carbon should result in less hydrocarbon production losses linked to flaring, methane leaks, and CO2 emissions from the chemical processes (some of which will come from cracking the plastic itself).

Figure 2

Source: National Packaging Waste Database (2020)

Challenges of plastic fuels

There are a number of environmental and health considerations associated with the chemical recycling of plastics due to the release of nitrous oxides, sulphur dioxides, particulate matter, and other harmful pollutants. Oil from plastic waste has more than a 20% lower flash point in comparison to regular diesel at under 40°C, increasing the opportunity of spontaneous ignition. The feedstock is variable (the raw products used in plastics, for example, vary from country to country). The different polymers that are fed into a pyrolysis reactor break along different patterns, which can pose challenges. In particular, molecules with high degrees of branching crack more easily than linear ones, which makes process control and reactor stabilization more difficult.

Once a plastic waste-to-fuel recycling plant is built, its costs of operation are comparatively low, but setting up the new unit can be costly. Lack of incentives and proper systems for waste collection can hinder the availability of waste plastic feedstock.

Additionally, the recycling industry is concerned that plastic waste-to-fuel will undermine the economy of other waste-to-fuel processes, such as solid waste-to-fuel. There is also the argument that the use of waste-to-fuel programmes does not resolve the issue of over reliance on plastics, but just increases their usefulness for the same amount of environmental impact.

The plastic recycling industry, however, is continuously evolving, and new technologies and innovations are being explored to improve the efficiency and sustainability of plastic-to-oil processes and enhance the quality of the end product.

Future articles in the series will explore the risks associated with plastic fuels and ways to mitigate them.

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Sanjeev Lakhera

Sanjeev Lakhera

Vice President, Energy and power

  • United Kingdom

Tom King

Tom King

Client Executive, Energy & Power

  • United Kingdom

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Andrew Herring

CEO, Energy and Power, Marsh Specialty UK

  • United Kingdom

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