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From waste to circular products: Tire pyrolysis oil analysis and properties

9 minutes for read

Tire pyrolysis oil is the most abundant product from recycling end-of-life tires with pyrolysis.

As a circular product, its properties allow it to be used as an eco-friendly alternative to several industrial manufacturing commodities. This article will conduct a tire pyrolysis oil analysis, review the properties, and shed more light on this valuable product.

What is Tire Pyrolysis Oil?

Tire pyrolysis oil (TPO) is the liquid fraction produced by the pyrolysis of end-of-life tires (ELTs). According to Martinez 2023, TPO can make up between 40 and 50 per cent by weight of the pyrolytic products depending on the process and temperature.

TPO is a thick, viscous dark brown or black liquid that can be semi-solid in cooler temperatures. It’s a complex mixture of hydrocarbon families with varying carbon numbers of C5 – C50. These consist of 49.54 per cent aliphatic compounds and 16.65 per cent aromatic compounds, like xylene, etc. The hydrocarbons have a wide range of boiling points from 70 ºC to 450 ºC (Pilusa 2013).

TPO composition will depend on tire types, pyrolysis technology, and conditions. However, the average TPO composition (Pilusa et al., 2013) is as follows:

  • Carbon: 83 per cent by weight
  • Hydrogen: 6.6 per cent by weight
  • Oxygen: 8.6 per cent by weight
  • Nitrogen: 0.3 per cent by weight
  • Sulphur: 1 per cent by weight

The various components of TPO will influence the oil’s physical and chemical properties and behaviour (Jammel 2018). 

Let’s look at some of these properties more closely.

What are the properties of tire pyrolysis oil?

Other tire pyrolysis oil analyses have found that it has critical properties and characteristics similar to some fossil fuels, allowing it to be used as an eco-friendly alternative.

However, TPO does have disadvantages, such as a higher sulphur content and a lower flash point than fossil fuels. To determine whether TPO is an appropriate alternative feedstock instead of fossil-based petroleum products for producing chemicals or use as fuel, its viscosity, flash point, calorific values, and corrosivity must be analysed.

1. Viscosity

Viscosity refers to how easily oil can flow. The viscosity of oil changes with temperature and pressure: oil becomes thinner as the temperature rises and its viscosity decreases. At 40oC, TPO from ELTs has medium viscosity and is 10 centistokes (cSt) at 40oC, whereas fossil–based diesel, which TPO could replace, has a viscosity of 2.58 cSt at 40oC (cSt) (Pilusa 2013). 

2. Density

Viscosity is connected to density, which is the relation of the weight of a substance with its volume.

At higher temperatures, oil’s density decreases. TPO from ELTs has a high energy density of 920 kg/m3@15oC. In comparison, petrol and diesel have a density of 740 and 822 kg/m3@15oC, respectively (Pilusa 2013).

3. Calorific value

The calorific value indicates the energy or heat a substance produces when completely burnt.

A high calorific value indicates a substance will be suitable as a fuel. TPO’s Gross Calorific Value is 41-44  MJ/Kg, that is, burning one kilo of it produces 41-44 megajoules of energy. In comparison, the Gross Calorific Value of diesel and petrol are 43.8 and 46.0 MJ/kg, respectively, according to Pilusa.

4. Flash point

TPO, like other fossil fuels, produces vapours.

The flashpoint of oil is the temperature at which its vapour will burn when a small flame is applied. When there is little vapour and more air, there is no combustion. When the mix of air and vapour is correct, even a small spark can cause it to burn. The pressure created from burning has produced violent explosions that can destroy storage tanks and lead to oil spills and major fires. TPO has a low flashpoint below 65°C, which is one of its disadvantages (Pilusa 2013).

5. Corrosivity

Like other crude oils, TPO is corrosive due to contaminants, like a high content of oxygen and acids.

Corrosivity in oils can affect metal pipes and storage tanks. Raw TPO can be very corrosive to metals like steel and other alloys with low chromium content. Containers at 50°C develop cracks when TPO is stored for a few hundred hours (Keiser 2011).

Why is recovered Tire Pyrolysis Oil important?

Industries are looking to increase the use of secondary products in their manufacturing processes to improve circularity. TPO is a circular and sustainable product whose range of potential applications positions it as a valuable secondary raw material.

The high carbon content of TPO makes it an interesting raw material for producing high-value carbon products. TPO is also called bunker oil or black liquor because of its composition and properties that are similar to petroleum products. It could be used in place of diesel for internal combustion engines, after distillation and removing undesirable chemicals like sulphur and nitrogen using existing refinery facilities.

Moreover, heavy aromatic compounds make TPO suitable for producing carbon black (CB) by replacing fossil fuel feedstocks, which make up 60 per cent of the manufacturing costs of CB (Martinez et al., 2023). Xylene in TPO also has several applications in the chemical industry.

It’s possible to increase the value TPO can bring to industries by introducing standards and regulations for the tire pyrolysis industry. Creating demand will also stabilise supply and prices to reduce raw material bottlenecks.

Conventional ELT recycled products like rubber crumbs have reached market saturation. TPO’s high value and wide range of applications in the circular economy can also make pyrolysis upcycling of ELTs profitable, more sustainable, and attractive globally. Though ELT recycling is high in the EU, it is very low in several regions worldwide.

Environmental reasons

The environmental benefits of TPO are another reason to consider using it instead of conventional fuels and feedstocks.

Pyrolysis, a thermo-chemical process, is the most environmentally friendly method of recycling ELTs. The process produces little or no pollutants, has a low carbon footprint, and can be made operationally safe. TPO’s carbon footprint as fuel is competitive compared to biofuels (Martinez et al., 2023).

Contec’s TPO

Contec’s protected and innovative tire pyrolysis process has integrated design and engineering features to make the process safe for its staff and the environment.

The company has measured its process’s carbon emissions, and ConPyro, Contec’s TPO, has a low carbon footprint of only 399.75 kg CO2e/1t.

Contec has designed and operates one of Europe’s few tire pyrolysis plants to solve the ELT problem and produce circular products for tire manufacturing, plastics, and other industries. Promoting tire pyrolysis oil uses helps to support the circular economy and sustainability goals. Find out more about Contec’s circular TPO, ConPyro.

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