**Figure 2.** Composition of oil and distillate fractions.

**Figure 3.** Energy dispersive X-ray fluorescence (EDXRF) results and water concentration analysis of oil and distillate fractions.

**Figure 4.** Fractions obtained by fractional distillation.

### **4. Discussion**

The pyrolysis of WEEE or flame-retarded polymers contained in WEEE with and without catalyst has been conducted in a number of recent works [2,6,9,10,15,20–23,30,32,76,77]. Furthermore, mixed WEEE residues can vary widely in terms of composition, strongly depending on their origin [1] (pp. 209–212) [2,3,7,9].

On average, the thermal conversion of WEEE at different temperatures yields 36 wt.% condensate, 39 wt.% gas, and 25 wt.% solid residue [6]. Recent works yielded 71–91 wt.% condensate, 3–21 wt.% solid residue and 2–8 wt.% gas from thermal pyrolysis of real mixed WEEE at 600 ◦C in a laboratory scale [76,78]. The iCycle® process applied for this work yielded 29 wt.% condensate, 32 wt.% solid residue, and 39 wt.% gas on a demonstration scale plant. The converted WEEE contained around 40% metals and inorganics, which explains the comparatively high amount of solids. Due to the operating temperature of 650 ◦C, the production of 39 wt.% gas is in an expectable range. However, the distribution of the products is, aside from operational parameters and scale, also highly dependent on the composition of the input material. Similar results (40 wt.% condensate, 30 wt.% solid residue, 12.5 wt.% tar, and 13.5 wt.% gas) were found by Vasile et al. [77] throughout the pyrolysis of mixed WEEE in a temperature range of 430–470 ◦C in a smaller demonstration scale plant. The produced oil (condensate) comprised a comparable content of 62.75 vol% aromatics as BTEX, styrene, and phenol derivatives. The condensate produced throughout the present work was also very rich in monocyclic aromatic compounds (including BTEX aromatics, styrene, phenol, and cresols), representing 76.81 area% in the pretreated pyrolysis oil. Condensates by Santella et al. [76] contained less than 20 wt.% aromatic compounds and mostly styrene. The pyrolysis oil produced from mixed WEEE by Hall et al. [78] consisted mainly of phenol, isopropyl phenol (30.2 wt.%), and styrene (5.9 wt.%), indicating major differences in the composition of the investigated feedstock. However, Hall et al. [78] found a similar chemical composition of the liquid pyrolysis product from waste refrigerators; bromine and chlorine contents of the condensate were 0.3 % and 0.1 %, respectively.

The current investigation showed that the pretreatment of the condensate in terms of filtration and phase separation is capable of removing roughly 10 wt.% of substances as solids and water that are undesired for further upgrading of the oil, as they are likely to disturb the refinement processes to produce other materials, e.g., bulk chemicals or fuels. Hence, the pretreatment technologies are crucial in terms of condensate processing, and they need to be conducted before further upgrading.

The chlorine and bromine concentrations of the investigated pyrolysis oil amount to roughly 5000 ppm chlorine and 2000 ppm bromine. Other related works found less than 600 ppm chlorine and less than 900 ppm bromine in the pyrolysis oil from mixed WEEE [78]. This confirms the enormous differences in WEEE composition [7,72] and manifests the need of the dehalogenation of pyrolysis oil in order to upgrade them to fuels or chemicals.

By means of fractional distillation, pure BTEX fractions and concentrated monocyclic aromatic fractions were produced:


The results evidenced that the pyrolysis of WEEE shredder residues and subsequent distillation of the condensate might be applied to produce high purity chemical fractions which can be used as a feedstock in the chemical industry and in polymer synthesis to produce virgin grade chemical products and polymers and also to substitute crude oil consumption.

The chlorine and bromine concentrations were significantly reduced by up to 99% in the distillate fractions. The EDXRF analysis showed that bromine accumulates in the distillation residue where chlorine concentration is decreased in all fractions, including the residue. The decrease in chlorine concentration in all fractions promote the assumption that chlorine (in the form of HCl) was dissolved in the oil and released throughout distillation [77].

In the first three fractions (RT–140 ◦C), bromine concentrations do not exceed 20 ppm, which represents a reduction of 99% in relation to the crude condensate and can already be sufficient debromination for the industrial application of the produced chemicals. Fractions 4–7 comprise bromine concentrations roughly between 200 ppm and 400 ppm, representing a significant reduction from the initial oil (2151 ppm).

Fractions 1, 2, 4, and 6 chlorine concentrations were reduced to roughly 250–470 ppm from 4843 ppm in the initial oil. Fraction 3 and 5 still comprise 913 ppm and 1914 ppm chlorine, respectively. Further dehalogenation is needed in order to reuse such fractions for industrial applications [77].

Beside the chemicals, the solid fraction is also suitable for recycling. It can be supplied to copper smelters, where metals are recovered. The gas can be used for energy recovery after treatment as described in Figure 1. The water phase, however, needs to be treated as hazardous waste as it contains metal compounds, organic, and halogen residues.

Several studies in the field of chemical recycling of WEEE have investigated the production of fuels, which is less valuable as a product compared to high-purity monocyclic aromatic fractions. Furthermore, the chemical recycling to valuable basic chemicals and monomers has a positive environmental impact in terms of climate change and fossil resource depletion compared to the productions of fuels. Thus, the conversion of WEEE to valuable chemicals has great potential to close the loop of the nonmetal fraction of WEEE as it will be mainly kept in the material cycle where the production of fuels entails the release of the nonmetal fraction (especially in the form of carbon dioxide) to the atmosphere [79,80].

### **5. Conclusions**

A significant amount of more than 200 kg real WEEE shredder residues from a German recycling company were treated in a demonstration scale pyrolysis plant and the subsequent fraction was distillated, in order to produce basic chemicals with high purity. Such treatment of liquid pyrolysis products from WEEE shredder residues to produce pure chemical fractions have not been reported yet. Thus, a new approach for recovering valuable chemicals like aromatics from pyrolysis oil was investigated and was successfully proven in a demonstration scale plant.

From the conducted experiments, it can be concluded that:


Current results revealed that a combination of filtration followed by fractional distillation is suitable for the reduction of halogen content. The halogen content was reduced up to more than 99% in the obtained fractions. Therefore, the recovered aromatics have great potential to be used as feedstock in chemical industry.

Estimations made by Fraunhofer UMSICHT suggest that the pyrolysis of WEEE for the recovery of metals is already economically viable in a scale >250 kg/h. The recovery of aromatics from WEEE nonmetal fraction instead of energetic utilization, however, enables significant improvement of both economic and ecologic aspects of WEEE recycling.

Further research works need to be conducted on higher halogen reduction and are part of our current projects. The development and scale-up of the presented technologies are the next steps to implement the recovery of aromatic compounds from different plastic waste streams in industry.

**Author Contributions:** Conceptualization, A.H. (Alexander Hofmann); methodology, T.R. and V.P.; software, T.R. and V.P.; formal analysis, V.P.; data curation, J.C.O. and T.R.; writing—original draft preparation, T.R.; writing—review and editing, A.H. (Alexander Hofmann), M.F. and V.P.; visualization, T.R.; supervision, A.H. (Andreas Hornung), A.H. (Alexander Hofmann), V.P. and T.R.; project administration, A.H. (Alexander Hofmann), V.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** The authors are grateful to Jan Grunwald and Martin Nieberl for technical support and discussion.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

