*3.1. Waste Tyre Conversion Using Pyrolysis*

Due to its nature and fewer processing steps, the pyrolysis process, such as other similar thermochemical processes, is thought to be the most environmentally friendly [39]. The process involves the decomposition of the solid at a considerably inflated temperature of around 300–900 ◦C in an environment that is free of oxygen and as a result produces producing char, oil, and gas [54–58]. The important products of pyrolysis gas in most cases are H2, CO, CO2, CH4, whereas the liquid consists of mainly CH3OH, CH3COOH, and H2O. The rest of the solid products consist of carbon and ash [58–60]. The steps of the waste tyre pyrolysis process are depicted in Figure 3.

**Figure 3.** Waste tyre pyrolysis process.

Yield outcomes of the pyrolysis process depend on the different operating conditions and reactor settings [57,61]. There are three main kinds of pyrolysis: (i) slow pyrolysis process, (ii) fast pyrolysis process, and (iii) flash pyrolysis process. Slow pyrolysis, also known as conventional pyrolysis, is commonly used to produce wood charcoal from wood biomass. Fast and flash pyrolysis, on the other hand, is used to produce bio-fuel [59,62]. The main configurations of bio-fuel are esters, organic acids, phenols, alkenes, furfurals, and certain inorganic species. These products are easier to transport and store than solid biomass, which is converted into valuable biofuels and chemicals [63].

The pyrolysis processes depend on factors such as temperature, material size, residence period, etc [54,60]. Different types of pyrolysis reactors were developed and examined in recent years to produce waste tyre for oil, char, and gas. Pyrolysis production yields depend on the feedstock's preparation, reactor types, and pyrolysis reaction condition [57,61]. However, temperature is the main factor to control the configuration of the pyrolysis process [64].
