# Characterization and Use of Char Produced from Pyrolysis of Post-Consumer Mixed Plastic Waste
## 3 Results and Discussion
### Effect of the Operating Temperature on the Properties of the Produced Solids
#### 3.3.1 Elemental Analysis, Thermal Decomposition, Immediate Analysis, HHV and Surface Properties
[6] showed similar results for the immediate analysis of the solid residue resulting from the pyrolysis of different waste mixtures at a temperature of 440 \({}^{\circ}\)C. Specifically, for the film-rich mixture, a low percentage of moisture (5%) and high ash content (57.7%) were obtained, although it should be noted that these results are on a wet basis and were also carried out together with the catalyst, as it was impossible to separate it from the resulting solid. [PERSON] et al. [3], working with HDPE waste and PE bags, also obtained quite low values for fixed carbon content (between 8.59% and 25.88%) and a high content of volatile matter (35.29-58.56%) and ash (27.33-49.47%). They also obtained similar values for moisture content, around 1%. [PERSON] et al. [18], who used different mixtures of biomass waste, tires and plastic waste in different proportions, carry out pyrolysis at 420 \({}^{\circ}\)C obtaining solid products with a fixed carbon content varying between 41.4% and 55%, a volatile material content between 28.5% and 53.3%, a low ash content (2.02-7.77%) and a low moisture content (1.03-3.94%). These results revealed that the introduction of biomass waste and used tires improves the properties of the carbonaceous solid obtained by pyrolysis. In another research by the same authors [1], the carbonaceous solids reached fixed carbon content values of 94.7%, and very  
low volatile matter and ashes contents (2.18% and 3.16%, respectively). The investigation of the pyrolysis of HDPE plastic waste by [PERSON] et al. [19] revealed that the solid product presented an immediate analysis similar in terms of volatile material (51.4%) and moisture (2.41%), but presented a higher amount in fixed carbon (46.03%), and lower ash content (0.16%). Regarding the results of the HHV (also reported in Table 4), the three solid samples analyzed showed a low HHV that decreased significantly with increasing pyrolysis temperature. This is mainly due to the decarbonization of the sample as the pyrolysis temperature increases and the increase in oxygen content, which results in a lower heating value of the material. [PERSON] et al. [45] indicate the same decreasing in HHV value with increasing pyrolysis temperature, with very similar results ranging from 20.4 to 11.2 MJ/kg from 400 to 700 \({}^{\circ}\)C.  
Finally, Table 4 includes the results obtained from the surface analysis of the solid products (char) obtained at the different pyrolysis temperatures. It can be concluded that the pyrolysis temperature directly affects the properties of the solid product, in this case pyrolysis at a higher temperature being favorable in order to obtain a solid with a higher specific surface area. An increase of 100 \({}^{\circ}\)C in the pyrolysis temperature results in a solid product with approximately 250 times more specific surface area. The same conclusion was reached by [PERSON] et al. [10] whose specific surface area values are very similar (between 0.1 m\({}^{2}\)/g and 58.9 m\({}^{2}\)/g). This increase in specific surface area may be due to the fact that the higher the temperature, the greater the breakage of the polymer chains, favoring the production of volatile compounds and increasing the specific surface area. However, an increase in temperature above 650 \({}^{\circ}\)C could destroy adjacent pore walls, leading to a decrease in the specific surface area. On the other hand, [PERSON] et al. [10] also point out the influence of the composition of the mixture to be pyrolyzed on the specific surface area due to the variation in the chemical and physical properties of the different plastics. Similar results were obtained by [PERSON] et al.