A review of the pyrolysis process of used tyre as a method of producing an alternative energy source is presented in this paper. The study reports the characteristics of used tyre materials and methods of recycling, types and principles of pyrolysis, the pyrolysis products and their composition, effects of process parameters, and kinetic models applied to pyrolysis. From publications, the proximate analysis of tyre rubber shows that it is composed of about 28.6 wt.% fixed carbon, 62 wt.% volatile material, 8.5 wt.% ash, and 0.9 wt.% moisture. Elemental analysis reveals that tyre rubber has an estimated value of 82 wt.% of C, 8 wt.% of H, 0.4 wt.% of N, 1.3 wt.% of S, 2.4 wt.% of O, and 5.9 wt.% of ash. Thermogravimetry analysis confirms that the pyrolysis of used tyre at atmospheric pressure commences at 250°C and completes at 550°C. The three primary products obtained from used tyre pyrolysis are solid residue (around 36 wt.%), liquid fraction or biocrude (around 55 wt.%), and gas fraction (around 9 wt.%). Although there is variation in the value of kinetic parameters obtained by different authors from the kinetic modeling of used tyre, the process is generally accepted as a first order reaction based on Arrhenius theory.

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This paper reports the investigation of zeolite NaY synthesized from kaolin, a locally abundant soil material found in the Benin City metropolis, Nigeria, as a suitable catalyst and its effect on the properties of pyrolytic oil produced from used tires. The pyrolysis process was conducted from a range of 1 to 10 wt.% of catalyst concentration to the used tire at an operating temperature of 600°C, heating rate of 15°C/min, and particle size of 6 mm. An increase in the catalyst weight gave a maximum yield of catalytic pyrolytic oil (CPO) of 21.3 wt.% at a catalyst-to-tire ratio of 7.5 wt.%. Although this was lower than the noncatalyzed pyrolytic oil yield (34.40 wt.%), the quality in terms of chemical composition and hydrocarbon fuel range varied from that of the noncatalyzed pyrolytic oil, as indicated by the FT-IR, NMR, and GC-MS analyses. From the GC-MS result, the CPO gave a benzene yield higher than that of noncatalyzed pyrolytic oil. The CPO benzene yield can be ranked as CPO (5 wt.%) > CPO (1 wt.%) > CPO (10 wt.%) > CPO (7.5 wt.%) > noncatalyzed pyrolytic oil. The catalyst also improved the yield of other valuable chemicals such as ethylbenzene, o- and p-xylene, styrene, toluene, quinoline, pyrene, thiophene, P-cresol, phenol, and limonene in the pyrolytic oil. For hydrocarbon range, the catalyst displayed the potential to increase the yield of carbon range (C6–C15), which is similar to gasoline (C6–C12) and kerosene (C11–C14), with a lower yield of diesel and fuel oils (C11–C20) when compared to the noncatalyzed pyrolytic oil.

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