The tyre-to-oil process, often executed in a tyre to oil plant, is an increasingly important method for converting waste tyres into valuable resources such as oil, carbon black, and gas. The process utilizes thermal decomposition, known as pyrolysis, to break down the complex hydrocarbons in tyres into simpler products. This conversion not only addresses the environmental challenge of tyre waste but also produces usable byproducts that have significant economic and industrial value. A critical aspect of understanding this process lies in analyzing the material changes that occur as tyres undergo pyrolysis.
Tyres are primarily composed of rubber, steel, and synthetic fibers, with varying amounts of other additives to enhance performance. The rubber in tyres consists mostly of natural rubber (polyisoprene) and synthetic rubbers, such as styrene-butadiene rubber (SBR) and butadiene rubber (BR). These materials are combined with oils, resins, and carbon black to enhance strength, flexibility, and durability. The steel components in tyres reinforce their structural integrity, while synthetic fibers (such as polyester and nylon) are used to provide additional strength.
In their initial form, these components make tyres highly resistant to degradation, which presents significant challenges for their disposal. However, the high carbon content and complex molecular structure of tyres also make them ideal candidates for the pyrolysis process.
In the tyre to oil machine, tyres are subjected to elevated temperatures in an oxygen-free environment. This process, known as pyrolysis, decomposes the complex materials in the tyres into simpler compounds. The temperatures typically range from 400°C to 800°C, with the exact temperature depending on the desired output and the feedstock's characteristics.
During pyrolysis, the rubber undergoes a process called depolymerization, where the long-chain molecules in the rubber break apart into smaller molecules, producing various gases, oils, and solid residues. The breakdown of the synthetic rubbers and natural rubber results in the formation of a complex mixture of hydrocarbons, which can then be condensed into liquid oil. The specific composition of the oil depends on the operating conditions of the pyrolysis reactor, including temperature, pressure, and the feedstock used.
The first major material change in a tyre pyrolysis reactor is the production of gaseous byproducts. These gases primarily consist of hydrocarbons, such as methane, ethylene, acetylene, and carbon monoxide, which are released during the pyrolysis process. Some of these gases can be used as fuel for the pyrolysis plant itself, improving the overall energy efficiency of the operation. These gases can also be captured and processed for other uses, such as in the production of synthetic fuels or chemicals.
The second major product of the tyre pyrolysis process is the liquid oil, which is the key goal of many tyre-to-oil plants. This pyrolysis oil is composed of a range of hydrocarbons, with lighter fractions such as gasoline, diesel, and kerosene, and heavier fractions such as lubricating oils and waxes. The exact composition of the pyrolysis oil depends on the feedstock, temperature, and other operating parameters. However, it typically contains a high percentage of aromatic compounds, such as benzene, toluene, and xylene, which are valuable for use in petrochemical industries.
The third material change is the formation of carbon black, a solid residue that remains after the volatile compounds have been removed. Carbon black is a valuable byproduct in various industries, including the production of rubber, plastics, and inks. The quality and quantity of carbon black produced during pyrolysis depend on the temperature and pressure within the pyrolysis reactor. In general, higher temperatures and longer reaction times lead to higher yields of carbon black, although this must be balanced with the desired quantity of oil and gas.
While the rubber in tyres undergoes significant chemical changes during pyrolysis, the steel and synthetic fibers present in the tyres also undergo transformation, but to a lesser degree. Steel wires, which are used to reinforce the structure of the tyre, do not decompose during the pyrolysis process. Instead, they remain in their metallic form, and they can be recovered and recycled for further industrial use. The steel wires typically account for around 15-20% of the total weight of a tyre.
The synthetic fibers, such as polyester or nylon, also do not fully decompose during pyrolysis. These fibers can either be partially converted into gases or remain as non-degradable residues, which may require additional processing or disposal. The amount of fiber remaining in the reactor after pyrolysis depends on the type of feedstock and the conditions under which the pyrolysis is carried out.
Understanding the material changes that occur during the tyre-to-oil process is crucial for optimizing the pyrolysis process to maximize the recovery of valuable byproducts. The ability to produce oil, gas, and carbon black from waste tyres not only helps mitigate environmental pollution but also provides a viable economic model. The pyrolysis oil, for instance, can be used as a substitute for conventional fossil fuels, reducing dependence on petroleum-based products.
Additionally, the carbon black produced during pyrolysis has several industrial applications, including its use in the production of new tyres, rubber goods, and even as a reinforcing agent in plastics. This creates a circular economy where waste tyres are transformed into valuable materials that can be reused in manufacturing.
