## 4 Discussion  
This paper assesses the content of sulfur and nitrogen in contaminated foils and plastics obtained from the recycling process of used vehicles and in the products of their pyrolysis (with the final temperature of 425 \({}^{\circ}\)C). A mass balance was also carried out for these elements. The high migration potential of sulfur and nitrogen was shown for the waste subjected to the pyrolysis process. Sulfur: for homogeneous foils and mixed plastics, most of the sulfur is immobilized in oil, while for foils it is clear oil (in proportions of 57% to 43%), and for recycled plastics mainly in turbid oil (in proportions of 22% to 78%). The sulfur content of char for both types of plastics is practically the same (about 13%). Slight differences occur for pyrolytic gases (approx. 3% for foils and approx. 6% for recycled plastics). The phenomenon of sulfur migration is described, for example, in [10]. Waste fires were tested there and the pyrolysis process was carried out at temperatures ranging from 600 \({}^{\circ}\)C to 800 \({}^{\circ}\)C. The tests were carried out for small samples and with fast heating in a flow screw reactor. The results of these studies confirm the sulfur migration possibilities presented in this article. There, the sulfur content in the oil varies from 20% to 10% when the process temperature changes from 600 \({}^{\circ}\)C to 800 \({}^{\circ}\)C, respectively (it decreases with increasing temperature), for \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type of** & **Input** & **Char** & **Clear** & **Pyolytic Oil** & **Pyolytic** & **Gyrolytic** \\
**Plastic** & **[\%]** & **[\%]** & **Pyolytic Oil** & **[\%]** & **Turbid** & **Gas** \\  & & & & **[\%]** & **[\%]** & **[\%]** \\ \hline Soft foils & 100.0 & 43.31 & 22.84 & 15.94 & 17.91 \\ Mixed & 100.0 & 29.24 & 7.02 & 11.53 & 52.22 \\ materials & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Nitrogen migration in products. Figure 3: Migration of nitrogen in pyrolysis products: (**a**) for contaminated foils; (**b**) for mixed plastics. char--the change ranges from 70% to 50% (decreases with increasing temperature), for gas--change is in the range from 11% to 30% (increases with temperature increase). Nitrogen: for homogeneous foils and mixed plastics, nitrogen migration is different. For homogeneous foils, most nitrogen is immobilized in char (approx. 43%), then in pyrolytic oil (39%); the remainder is transferred to gas (approx. 18%). For mixed plastics, most of the nitrogen is immobilized in pyrolytic gas (over 52%), the remainder goes to char (nearly 30%) and pyrolytic oil (over 18%). The phenomenon of nitrogen migration is described, for example, in [23]. There, waste rigid polyurethane foam was tested and the pyrolysis and gasification processes were carried out. Similarly, migration of nitrogen between the pyrolysis products was observed. In addition, greater nitrogen migration to gas was observed with the increase in process temperature (and in the presence of a catalyst) and the possibility of nitrogen conversion to pure nitrogen dioxide was demonstrated. The results of research and analysis will allow the identification of possible ways of managing the problematic waste, which consists of contaminated and mixed, non-recyclable plastics. For example, when energy recycling is chosen, sulfur and nitrogen form sulfur dioxide and fuel oxides of nitrogen, respectively--knowing the contents of these elements, the flue gas treatment process can be designed accordingly [5]. Substances obtained as a result of the pyrolysis process can be used in many ways. Pyrolysis gas can be used in the combustion process and the released energy can be directed to the pyrolysis process. Pyrolysis oil can be used to produce new plastics. The obtained char can be subjected to another thermal treatment in order to produce activated carbon. At each of these stages, the presence of sulfur and nitrogen should be kept in mind [6; 15].