# Valorization of Waste Tires by Pyrolysis and Activation Processes
## 3 Results and Discussion
### Liquid Fraction Qualitative Characterization  
The qualitative composition of the liquid fraction (Table 4) varied mainly with the presence of chemical activation; physical activation did not have a significant effect on its composition. L1 and L3, which are formed during processes that did not involve a chemical activation, reported the presence of compounds like D-limonene and benzene. On the other hand, naphthalene and its derivatives are compounds found in L2 and L4. The compounds presented on the liquid fraction have also been reported by other au  
Figure 7: Analysis of the conductivity results: (**a**) surface area effect and (**b**) pore size effect on the electrical conductivity. thors [10]. Among the complex composition of the liquid fraction, limonene is a major and valuable compound that increases the economic potential of these pyrolytic fractions [47]. It has been reported that limonene concentration significantly decreased at high pyrolysis temperatures [39, 47, 48], as it is decomposed or transformed into aromatic compounds at higher temperatures (>450 \({}^{\circ}\)C) [39, 48]; however, some studies have reported the presence of limonene at temperatures above 700 \({}^{\circ}\)C [39, 47]. In this study, the dominant presence of limonene may be associated with the transient conditions of the pyrolysis system and the vapor residence time. The high heating rate might also be an important factor [47]. The influence of the pyrolysis temperature on the limonene concentration has been amply investigated, while the effect of the heating rate [47] and pressure [48] have received significantly less attention. Moreover, the influence of chemical activations on the feedstock previous pyrolysis has been even less studied. Table 4 shows a clear effect of the chemical activations on limonene yield: D-limonene was not presented on the liquid fraction from acid-treated waste tire (L2 and L4), while it was the main compound on the liquid fraction from nonactivated waste tire (L1 and L3). These results are possibly associated with the decrease on the volatile matter content from 67.16% to 47.04% observed on the acid-treated waste tire (Table 1). As the volatile matter of a tire is mainly constituted by rubbers [49] and limonene is derived from rubber [50], a decrease of the limonene yield was expected on the acid-treated waste tire, which is in agreement with TGA and proximal analysis results. Liquid fractions from all processes present sulfur-based compounds such as benzothiazole, commonly used during the vulcanization process [51]. The undesirable sulfur content is an obstacle for its utilization as fuel for its environmental pollution potential [4]; therefore, further effort focused on the reduction of its content must be made [39]. Desulfurization processes have been studied by some researchers [52]. Compounds were assigned to major categories, which are depicted in Figure 8. The percentage of aliphatic and aromatic compounds changed considerably depending on whether or not the waste tire was chemically activated. The lower content of aliphatic and higher content of aromatic in L2 and L4 may be attributed to aromatization reactions such as Diels-Alder, converting aliphatic into aromatic compounds. It has been reported that pyrolysis temperatures >600 \({}^{\circ}\)C favor aromatic formation reactions [39, 47].