Tire pyrolysis is the thermal transformation of materials at high temperatures in an inert atmosphere. Tire pyrolysis can be achieved through either thermal or catalytic routes. Pyrolysis is known for its high operating temperature, reaction time and low oil quality. To overcome the difficulties associated with pyrolysis, catalytic pyrolysis of used tires using catalysts has been developed. In fact, 60% to 80% of used tires can be converted into pyrolysis oil, which is very similar to diesel, by catalytic pyrolysis. As a result, the pyrolysis oil produced is of higher quality and can produce useful compounds that can be used as feedstocks for chemical processes and energy-related applications such as power generation, transportation fuels and heat sources.
Parameters Affecting the Yield of Tire Pyrolysis Products
The distribution of pyrolysis products in the gaseous, liquid and solid phases and their physical and chemical properties are mainly affected by temperature. Other important variables include:
- Heating rate,
- Particle size,
- Feedstock composition,
- Pyrolysis time,
- Tire residence time,
- Carrier gas flow rate and volatile residence time,
- Atmospheric pressure and
- Type of tire (including the presence of steam in the carrier gas)
- Presence of catalyst.
We will discuss temperature and catalyst parameters in detail. Because it plays a very important role in the tire pyrolysis process.
Tire Pyrolysis Temperature
In order to pyrolyze tires, the pyrolysis temperature must be high enough; however, higher temperatures and longer gas residence time in the reactor hot zone will cause the oil to volatilize into gas. Therefore, there is an optimal temperature to maximize oil production. Since oil is the most valuable product, the goal is usually to maximize oil production.
Studies have shown that the optimal temperature range for tire pyrolysis oil production is 425°C to 720°C, with maximum yields ranging from 38% to 60%. Variations in heating rate, gas residence time, reactor type, tire mass flow rate, and tire particle size can be the cause of significant variations in the ideal temperature and maximum yield. These secondary variables can especially affect secondary reactions that convert liquid chemicals to gas or solid compounds to gas.
Catalysts used in tire pyrolysis
Catalysts can increase pyrolysis rate, oil quality, oil yield, and the yield of chemicals such as aromatic hydrocarbons used in chemical synthesis. Dung et al. (2009) used ITQ-21 and ITQ-24 as additives to commercial HMOR zeolites to catalytically pyrolyze waste tires to improve the pyrolysis rate and oil quality. They showed how the ratio of catalyst to tire affected the ability of the pyrolysis oil to produce gasoline, kerosene, and asphaltene.
Kar (2011) heated expanded perlite (a volcanic rock composed primarily of silica and alumina) to 850–1000 °C to form a porous catalyst support. Metals were then added to the support to act as catalysts. The ratio of perlite to waste tire was 0.10. Oil yield increased from 60.0 to 65.1 weight percent. The calorific value, density, viscosity, and elemental composition of the produced fuel were comparable to standard petroleum fuels. Ates et al. (2005) used 10% activated alumina and increased oil yield and the aromatic content of the oil. Williams and Brindle (2003) used Y zeolite catalysts (CBV-400 and CBV-780) and zeolite ZSM-5 to increase the concentration of aromatics, naphthalene and alkylated naphthalene.
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