How Does How to Get Fuel Oil from Waste Plastic Pyrolysis Work?

In the energy transition, diversifying power sources is often seen as a necessary step on the route to net zero. According to the International Energy Agency, if we are going to meet zero emissions by the middle of the century, then a “dramatic transformation” of our energy system is needed, and the inclusion of new energy sources is necessary. 

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While renewable electricity generation shows promising growth, much existing energy infrastructure was designed for liquid or gas fuels. Industries such as shipping, construction and manufacturing still rely heavily on crude oil and natural gas. For consumers, much of our global energy infrastructure and pipelines, notably in the global south, was designed for the transportation of crude products. Decarbonising these liquid fuels provides a cheaper route to net-zero for these consumers, even if it only fills a gap on the way to renewables. 

As such, some have looked into producing alternative liquid fuels from a variety of sources, from plants and organic matter to waste material. Plastic, which is originally produced using crude oil, can also be used to produce synthetic oil and gas through a process called pyrolysis.  

Through pyrolysis, the plastic is heated to extremely high temperatures, between 300⁰C and 900⁰C, with a lack of oxygen. This causes it to break down into smaller molecules and transforming it into pyrolysis oil or gas. This product can then be used as a fuel or to create new, second-life plastic products. 

Supporters of pyrolysis claim that it holds the answer to the dual challenge of plastic waste and excessive fossil fuel consumption.  Pyrolysis company Stellar 3 has developed a “particular pyrolysis technology that is the most flexible and efficient with the highest quality outputs”, CEO Dan Nienhauser says. However, the process is not without its detractors. 

An emerging technology  

Plastic degradation, through pyrolysis, uses differing types of plastic, such as polyethylene or polystyrene, to produce a variety of liquid gas fuel products. Plastics can be added individually or as a mix in order to produce a diverse range of products. Differing types of catalysts are used to improve the pyrolysis process, including ZSM-5, zeolite, Y-zeolite, FCC, and MCM-41. While high temperatures are used, pyrolysis avoids incinerating its feedstock, instead reforming it into fuels. 

Many pyrolysis facilities produce a liquid oil with a high heating value which resembles conventional diesel. This product can be used to power vehicles and machinery after it is refined and blended with conventional fuels. As such, fuels produced through pyrolysis could offer a lower carbon solution for hard-to-abate industries. 

Stellar 3 has developed a pyrolysis process which can recycle plastics including PVC. “PVC is typically avoided because it has a chlorine in it, so we have designed, developed and built a chlorine extraction pre-pyrolysis unit. What that does is it keeps the plastic to a temperature that where the plastic is still liquid, and then the chlorine evaporates, that chlorine is captured and condensed into a 30% hydrochloric acid into a special container, and then the rest of the plastic goes through the regular pyrolysis process”. 

Pyrolysis is not a form of incineration, Nienhauser adds, as when burning waste an amount of energy is lost in the process. 

“You’re eliminating all the carbon footprint of taking oil out of the ground, shipping it to a refinery and then shipping it all the way to importing countries. Some of that can be replaced with a blend-ready diesel, produced locally based on the plastics that are there”. 

Local energy production 

For Nienhauser one of the major benefits of pyrolysis technology is that the plants are small enough to accommodate fuel production on a local level which is then transported in liquid form. Stellar 3 builds facilities which take in 30 tonnes of waste material per day, the equivalent plastic waste production of 250,000 people per day. 

Alongside others globally, the company manages a processing facility located in the Philippines. “Because of the island location, one of the challenges is that you don’t have extra room for landfill. So, once it’s filled, you put extra plastic on the top of the landfill, and it rolls down into a river that ends up in an ocean. Our objective by is to have the capacity to take 500 tonnes of landfill waste per day and use it in a waste transformation facility,” Nienhauser adds. 

The problem of plastic pollution 

With the increased consumption and urbanisation of our society comes more plastic waste. Around 12 million tonnes of plastic makes its way into the world’s oceans every year. Environmentalists and NGOs are calling for better waste management of plastics. Currently, 9% of plastics are recycled and an additional 22% are mismanaged. Much of the plastic we used is currently either heads to landfill or the oceans. 

Pyrolysis has the potential to increase the demand for second-life plastics turning them into a useful product. However, while pyrolysis offers a potential waste solution critics argue that it is not the fix-all green solution for both plastic waste and fossil fuel use. 

How green is pyrolysis? 

Producing a fuel from a hydrocarbon product means that when that product is burned, it will produce carbon dioxide and other greenhouse gases. As such, they can only reduce emissions from their suppliers, not their consumers. Synthetic fuels that make use of pre-existing oil and gas infrastructure could also delay the infrastructure overhaul need to transform our energy system. Detractors argue that whether it is oil and gas pipelines or vehicle engines, at some point our infrastructure and technologies will have to change. 

Additionally, pyrolysis is not a perfect science. When producing a product from waste, it is difficult to ensure the exact same product every time when the input material varies. Critics say that given the variety in plastic types, in reality only a fraction of it is recycled effectively in pyrolysis. 

But for Nienhauser, recycling any plastic should be counted as a positive. “When you put something into a system and you turn it into a gas, you can’t change what it is from a from a molecular structure standpoint. That said, the developing world is very excited about ways of reducing waste.” 

Stellar 3 is also developing recycling facilities that handle only one type of material. “We’ve done a pilot facility looking at end-of-life tires. Frequently, there are these very large facilities where their only purpose is to shred tires. We have a new plant that, instead of taking the shredded material, takes a whole tire and puts it into a vacuum sealed environment where the rubber and petroleum-based part is melted off it. You leave the steel and the fabric on top of a sieve and then you have the liquid that proceeds into the pyrolysis chamber.” 

“In addition to providing a petroleum and carbon black product that can be put back into the tire industry, and you can create around 60% of a new tire if you have the right efficiencies in your system for from an old tire. And that for us is very exciting where we start to really cut back on those raw virgin materials”. 

How much energy does pyrolysis need? 

Any kind of recycling requires large amounts of energy, especially when heating materials to high temperatures. However, recycling remains more energy efficient than producing a product from original materials. 

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“It’s part of pyrolysis’ reputation, because there’s a lot of companies that have done it less efficiently in the past,” says Nienhauser. But pyrolytic facilities are innovating: Stellar 3, for example, burns excess synthetic gas produced from the process to produce the necessary heat. “Once it’s operational, the process needs a low level of external power which can be provided from renewables.” 

For Nienhauser is “the year of chemical recycling”. “This is really a time where the circular economy starts to have economic legs, as opposed to being something that we do because we really have to. With all the climate challenges going on today, I think anything we can do, even if it’s flawed compared to what we may envisage as a perfect scenario, it’s something we should start doing as soon as possible,” he concludes. 

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.

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°– °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 ()

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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