What are tires made of? The composition of all tires includes four basic materials – natural or synthetic rubber, black carbon and quartz, metal and textile as reinforcing materials and components of other substances, such as filler oils.
The most commonly used rubber tires include natural rubber, styrene-butadiene rubber and butadiene rubber (on average 19% of the total amount of materials used in a tire). Black carbon and quartz are used to strengthen the rubber and contribute to its resistance to wear (22%). Filler oil, which is a mixture of aromatic hydrocarbons, serves to soften the rubber and improve its workability (25%). Tires also contain synthetic textile materials, sulphur, zinc oxide and stearic acid.
The good news – if several decades ago the only option for recycling these materials, except for steel, was burning, today all tire components can be recovered and recycled.
In general, waste tire recycling is divided into processes that focus on energy or material recovery.
Energy recovery or regeneration involves the thermal treatment of tires, converting used tires into thermal energy and thus replacing other energy sources.
In terms of material recovery, mechanical tire recycling or tire shredding is widely used in Europe. The process of mechanical tire recycling involves cutting the tire into small pieces or strips, reducing the space required for them and facilitating further processing, and removing the steel mesh. The tires are then shredded into different fractions.
However, the use of mechanical recycling technologies for used tires allows for very limited re-use. Namely, such recycled materials can be used for energy production, which is considered low added value processing, or for the production of products of a limited nomenclature, for example, coverings of sports fields, damping plates that absorb noise, acoustics and vibrations in industrial environments, or additives for asphalt bitumen mixtures.
Is it possible to recycle used tires more efficiently? Yes, using pyrolysis technology, which allows the breakdown of used tire material into separate substances.
What is pyrolysis? In simple words, pyrolysis means heating organic or inorganic material in an oxygen-free environment. Unlike burning, the pyrolysis process does not release heat.
The recycling of used tires using the pyrolysis process is a relatively new technology that is currently gaining more and more attention and is becoming one of the best alternatives to thermal recycling or burning of tires. It is considered the most economically attractive and viable technological way for tire recycling, because the materials obtained in the process – black coal, oil, gas and steel – have a very high reuse potential, which is especially important in times of fossil resource scarcity.
In the pyrolysis process, the temperature can vary between 200 and 450 °C, depending on the desired proportion of end products. At a lower temperature, a larger volume of pyrolysis oil is usually obtained, while at a higher temperature, a larger volume of gas is obtained, resulting in a very flexible process.
In general, the thermal efficiency of the pyrolysis process is about 70% and can increase to 90% if the gas obtained in the pyrolysis process is used as fuel for the pyrolysis process. The approximate amount of gas obtained by pyrolysis of tires is 10-30% of the weight of the recycled material (depending on the temperature of the pyrolysis process), while the heat capacity of the pyrolysis gas is sufficient to be used in energy.
The benefit of pyrolysis oil can reach 50% of the weight of recycled tires, the oil has a relatively high calorific value and can be used as fuel in industrial furnaces, power stations, as a raw material in the production of polymer products or added to petroleum products.
The benefit of black carbon is about 30% of the weight of recycled tires. The coal material obtained in the pyrolysis process can be used as a component of rubber and as a carbon additive in steel production, in water and air purification plants, as well as in the production of electric batteries.
In addition, an industrial and properly organized pyrolysis process allows to ensure not only the most efficient recycling of used tires, but also to exclude any associated risks of environmental pollution.