Thermal and Catalytic Pyrolysis of Real Plastic Solid Waste as a Sustainable Strategy for Circular Economy

ABSTRACT The management of plastic waste is a serious environmental problem, therefore numerous strategies have been explored to reuse/recover these materials, avoiding their disposal in landfills. In particular, research has focused on thermochemical conversion processes and especially on pyrolysis processes. Therefore, in this study, a real Plastic Solid Waste (PSW) from COREPLA (Italian national consortium for collection, recycling, and recovery of plastic packaging), deprived of PET, PVC, and PTFE was used as feedstock for batch thermal and catalytic pyrolysis tests. The experiments were performed in a micro-reactor under nitrogen flow, using ɣ-alumina as catalyst. The effects of a variation in pyrolysis temperature (450–650°C) on the gaseous, condensable, and solid products were assessed. The thermal and catalytic pyrolysis tests of LDPE at 550°C were also investigated, as a representative surrogate of the plastics materials found in PSW. Preliminary results highlight that gas and condensate yields increase with pyrolysis temperature (with or without γ–alumina). The condensate products of all experiments were an oily wax made up mainly of long-chain aliphatic hydrocarbons (mostly diesel-like fraction, C12-C20). The qualitative composition of gaseous and condensable products differs between thermal and catalytic tests. However, the alumina leads to a higher formation of aromatic hydrocarbons.


Introduction
Versatility, lightness, and strength along with economy and design flexibility are the properties of plastic materials that have made these polymers of particular interest in a wide range of applications, going, for example, from use at high temperatures to corrosion-resistant devices, civil engineering, the medical field (Rodríguez-Luna, Bustos-Martínez, and Valenzuela 2021) with a dominant role played by the goods and food packaging sector, which absorbs almost 40% of the total production (Plastics -The Facts 2018).For these reasons, there is an increasing worldwide interest in the use of these polymers.In 2018, in fact, global plastic production reached 359 million tons (Plastics -The Facts 2019), with an expected increase in the years to come, driven by the development of new applications.In this contest, High and Low-Density Polyethylene (HDPE and LDPE) are among the most widely used polymers.
However, it is estimated that only about 50% of the plastic produced is available for collection and recycling, as a result, most of this material is wasted with a negative impact on the environment.In particular, every year more than 60 million tons of PE are disposed of, and only one-third is recycled or reused (Onwudili, Insura, and Williams 2009;Rodríguez-Luna, Bustos-Martínez, and Valenzuela 2021).
Management of post -consumer plastic waste, mainly of the packaging, poses therefore a serious environmental problem, and several strategies were devised to reuse/recover these materials, mainly with the aim of obtaining useful materials and avoiding landfilling (Ragaert, Delva, and Van Geem 2017;Singh et al. 2017).
An approach commonly adopted in many EU countries, to deal with this kind of waste, consists in recovering the most valuable fractions from the stream of discarded plastic packaging, such as polyethylene terephthalate (PET) bottles, and heavy polypropylene (PP) containers.The remaining fraction is used for producing Solid Recovered Fuel (SRF), a secondary fuel made in accordance with CEN -EN15359 (European Committee for Standardization 2011) and mainly used in cement kilns.The "raw material" for SRF production is a mixture of mostly polyolefinic plastics with many impurities, and the SRF production process essentially consists of a sequence of size reduction and purification operations, mainly aimed at reducing the amount of non -plastic impurities and of chlorine containing contaminants, mainly polyvinyl chloride (PVC), which are highly undesired in the combustion process.
However, SRF utilization poses some problems, mainly related to the relatively low number of cement kilns able to accept it in partial substitution of traditional fossil fuels.With respect to Italy, from an overall amount of plastic wastes of roughly 1 million ton/year, 450,000 ton/year were left over from the recovery of the most valuable fractions as polyolefinic mixture, roughly half of it being sent to cement kilns while the residual is either incinerated or landfilled (Corepla 2018).Furthermore, more and more country legislations support waste recycling (i.e., transformation in useful materials) over waste utilization as fuel (Amending Directive 2008/98/EC on Waste 2018).In consideration of this, some alternative strategies must therefore be considered for plastic waste utilization, and among them, pyrolysis processes, that are aimed at producing useful products (i.e., liquid fuels for use in endothermic engines and chemicals), can play a significant role.Moreover, the gasoline produced during this process could be a renewable feedstock for new plastic production in the petroleum industry so that this finding might provide a new insight for a circular economy (Dai et al. 2021).
Plastic waste pyrolysis processes, either thermal or catalytic, were the subject of considerable attention during the last few decades, mainly because process operating variables can be optimized so as to enhance the yield of the desired products, e.g., liquid oil yield up to 80% wt was reported by Sharuddin et al. (2016).The use of a catalyst, for example, allows making the process more efficient not only in terms of required temperatures but also in improving the liquid oil and gas quality (Miandad et al. 2016).Several kinds of catalysts can be used for this purpose (such as ZSM-5, HZSM-5, FCC, Al 2 O 3 , Red Mud, and NZ), and in general, their acidity and porosity affect the amount of gas and liquid products.In particular, the microporosity and the acidity promote the production of the gaseous species (Miandad et al. 2016).The cost of the catalysts and their regeneration are the main limitations to the application of catalytic processes, and the main challenges are the development of cheaper catalysts and stable to the regeneration process (Miandad et al. 2016).In the literature, there are a number of reviews presenting the results obtained so far (Al-Salem et al. 2017;Armenise et al. 2021;Lopez et al. 2017;Miandad et al. 2017;Sharuddin et al. 2016), but only a relatively minor fraction of the papers published so far dealt with real municipal plastic waste "as is."The large majority discusses the pyrolysis of either single-component feedstocks (e.g., polyethylene rather than polystyrene) or of simulated plastic wastes, made of premixed mixtures of virgin polymers, but in real plastic waste the impurities, remaining despite economically viable pre-treatments, unavoidably complicates the process and affects the range of products that can be obtained from pyrolysis.
In the present paper, to overcome some of the limitations mentioned above, a real Plastic Solid Waste (PSW) was used as feedstock for the pyrolysis process.More specifically, the PSW material was provided by COREPLA (the Italian national consortium for collection, recycling, and recovery of plastic packaging), after being depleted in polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE) (polymers more suitable for recycling).Thermal (non-catalytic) and catalytic experiments were carried out, in order to analyze the effect of temperature and of a cracking catalyst on the quality and yield of the pyrolysis products (gas, condensable, and solid products).In particular, in the catalytic tests, a high surface γalumina was used as catalyst.Several studies have already reported the adoption of this type of catalyst for the pyrolysis processes of plastic solid waste.The larger pores of γalumina (Al 2 O 3 ) catalyst, in fact, allow polymers or long-chain hydrocarbons present in the pyrolysis vapors to enter the pores for cracking into lighter hydrocarbons (Al-Salem et al. 2017;Dai et al. 2021).Moreover, it is not expensive and has good thermal stability up to 1000°C which can be a useful feature during the regeneration phase.
Thermal and catalytic pyrolysis tests of low-density polyethylene (LDPE) were also carried out in order to understand if there was a synergistic effect among the different plastic components of the PSW which could affect the obtained products.LDPE, in fact, is one of the main constituents of PSW, as reported by Onwudili, Insura, and Williams (2009), who claim that there are six main component plastics in Municipal Solid Waste, which are high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET), of which LDPE and HDPE make up over 40% of the total plastic content, and it is largely used as model compound to simulate plastic feedstock (Onwudili, Insura, and Williams 2009).
Experiments were carried out in a batch mode in a quartz micro-reactor under pure nitrogen flow.Pyrolysis tests of PSW were performed at three different temperatures, namely 450°C, 550°C, and 650°C, to identify the optimal pyrolysis temperature, while the pyrolysis tests of LDPE were carried out only at 550°C, identified as the most suitable temperature among the three selected.

Materials and methods
The pyrolysis experiments were carried out using as feedstock a real Plastic Solid Waste (PSW), made up of plastic materials (mainly deriving from plastic packaging) not suitable for recycling processes.More specifically, the plastic sample, supplied by P.R.T. of Sarno (Napoli, Italy), was deprived of PET, PTFE, and PVC.It was produced by grinding and purification of a mixed polyolefinic waste, in turn deriving from the removal of valuable materials from the plastic waste originating from the differentiated collection in the Campania region of Italy.
Virgin low-density polyethylene plastic pellets (LDPEs) were provided from Sigma -Aldrich Ltd.
Figure 1a shows an image of the plastic waste sample, in which fragments of plastic wrapping and bags and some polystyrene packaging can be identified.There are also several pieces of rigid plastics, along with fabric and wood residues.Figure 1b, instead, reports the adopted LDPE pellets.
The elemental analyses of the PSW and LDPE ground samples were carried out using a LECO CHN 628 (ASTM D5373) and LECO CS144 (UNI 7584), whereas the proximate analyses were performed by means of a LECO TG701 according to UNI 9903.The determination of the High Heating Value (HHV) was carried out using a PARR 6200 Isoperibol Oxygen Bomb Calorimeter (ASTM D5865).The determination of the chlorine content was performed using an 883 Basic IC plus ion chromatography by Metrohm (UNI 9903).
Table 1 shows the main properties of the feedstocks used in this paper, such as average values of triplicate analyses.
The main difference in the composition of the LDPE and the real plastic solid waste was the presence of small amounts of ashes in the latter, probably deriving from additives present in the different kinds of plastic that make up PSW, and the presence of heteroatoms such as N, Cl, and S that can influence the pyrolysis behavior and the nature of the products.Small differences in the elemental composition in terms of C and H were observed, although the PSW C/H molar ratio is slightly higher than LDPE one (0.52 and 0.50 respectively).The presence of oxygen in PSW can be associated with the presence of ashes.

Experimental
Both thermal and catalytic pyrolysis experiments were carried out in batch-mode, under a pure nitrogen flow (60 Nl/h) at three different temperatures, 450°C, 550°C, and 650°C, for PSW samples, whereas the pyrolysis tests of LDPE were carried out adopting only the temperature of 550°C.The tests have been carried out using a fixed bed quartz microreactor (length of 0.40 m and ID of 0.026 m), in a horizontal configuration, as reported in Figure 2.
The catalyst used for the tests was a commercial mesoporosus γ-alumina (SASOL) characterized by a particle diameter of 1 mm, a high surface area (160 m 2 /g), and high mechanical strength.To ensure the maximum conversion of gas phase, an excess of catalyst was used (catalyst to PSW weight ratio of about 6).
The feedstock was pre-loaded in a basket of metal net and successively inserted coaxially into the quartz reactor.This configuration has been selected to avoid the dragging of lighter components and the clogging of the section due to solids melting.
During catalytic tests, as shown in Figure 2, the γ-alumina particles were placed downstream of the metal basket containing the sample, and a metal support net was inserted into the outlet duct in order to avoid dragging phenomena.
The reactor was placed into a furnace, and a heating rate of 30°C/min was set in all experiments.When the set point value was reached, the temperature was kept constant until no further gas production was detected, i.e., until the entire sample was completely converted.
At the exit of the reactor, gases pass through the condensation train made up of four flasks in series, the first one kept at room temperature and the other three refrigerated at a temperature of −12°C, to enhance the condensation of the vapor evolved during the pyrolysis process.The non-condensable gases leaving the condensation train go across a set of ABB on-line analyzers to continuously measure the concentration of O 2 , CH 4 , CO, CO 2 , and H 2 .Further analyses of the gas products were performed by collecting batches of the gas downstream of the gas analyzers in inert Tedlar Ⓡ sampling bags, at different reaction times.The content of the bags was analyzed by means of a micro-gas chromatograph (micro-GC) Agilent 3000 for the determination of light hydrocarbons (C 1 -C 6 ) in addition to H 2 , CH 4 , CO, and CO 2 .The condensate, recovered in the condensation train, was first solubilized in dichloromethane (DCM Sigma-Aldrich), then separated from the bigger insoluble waxy solid fraction and finally filtered to eliminate undissolved suspended residues with hydrophobic PTFE Millipore filters (0.45 µm pore size and 47 mm diameter membrane).
The fraction soluble in DCM was analyzed by means of an Agilent 7890A GC (column HP35 of phenyl-ethyl-methyl siloxane) equipped with a mass spectrometer 5975C-VLMSD.The temperature ramp chosen for the analysis provides that the column was heated first up to 50°C for 5 min, then up to 200°C with a speed of 5°Cmin −1 , then up to 270°C with a speed of 10°Cmin −1 and finally up to 310°C with a speed of 5°Cmin −1 for 15 min.Chromatographic peaks were identified using the NIST11 mass spectral data library, and a semi-quantitative approach was adopted to determine the relative content of each oil component.
The bigger waxes not solubilized in DCM were characterized by means of a simultaneous TGA-DSC using a Perkin Helmer STA 6000 thermogravimetric analyzer (30°C/min from room temperature up to 700°C, under a nitrogen flow 40 mL/min) and by a LECO CHN 628, as previously reported for the determination of C, H, and N.
At the end of the tests, the reactor was cooled at room temperature under nitrogen flow.The solid residues were discharged, weighted, and characterized by means of a LECO CHN 628 analyzer to evaluate the C, H, and N composition (each analysis was repeated three times).

Gas composition
Table 2 compares the quality of gas obtained during the different tests in terms of the mass of the produced gaseous species calculated by the integration of the concentration profiles obtained by means of online analyzers.The total gas production, in good agreement with data reported in the literature (Al-Salem et al. 2017), increases with temperature increase.Catalyst affects not only the amount of total gas produced but also their quality.In particular, both H2 concentration and CH 4 production were higher than those observed in thermal tests, likely as a consequence of the cracking activity of alumina.Even the production of CO 2 is strongly enhanced by the presence of the catalyst, which promotes the further oxidation of hydrocarbon products, following the WGS reaction that occurs between the hydroxyl groups (OH − ) of the Al 2 O 3 and CO x on the alumina surface, with consequent production of CO 2 and H 2 in accordance with that reported by Ammendola et al. (2011).A lower amount of gas was produced using LDPE as feedstock, as a consequence of different amounts of volatiles characterizing this material made up of different plastic materials and probably also to the activity of the ashes present in the real plastic mixture.
In line with the data from online analyzers, the results of the micro-GC analyses (Table 3) showed a greater production of CH 4 and light hydrocarbons in catalytic tests, thus confirming the cracking activity of the catalyst.For the catalytic PSW tests, the optimal temperature for the maximization of gaseous hydrocarbons production was 550°C, because at 650°C the increase in the total gas production has been associated with a decrease in the total amount of hydrocarbons.
In general, a higher production of hydrocarbons is found for the LDPE also in the absence of catalyst, suggesting a potential role of the ashes in real plastic waste in the formation of CO x .
In the thermal test at the temperature level of 550°C among the gaseous products, the dominant species in the PSW pyrolysis tests are the alkenes (0.22%), on the contrary in the LDPE experiments the alkanes are the most abundant species (0.56%).
Exactly the opposite occurs in the catalytic pyrolysis tests at 550°C, since in the PSW tests alkanes (0.58%) are slightly more abundant than alkenes (0.54%), while in the LDPE tests alkenes are the most detected species (0.67%).

Condensate composition
The main product of all thermal and catalytic pyrolysis experiments, using both PSW and LDPE as feedstock, was an oily wax consisting mainly of aliphatic compounds with long chains, in line with what was reported in the literature (Onwudili, Insura, and Williams 2009).Qualitative analysis, in fact, showed that the fraction of the oily wax soluble in DCM was made up mainly of long linear hydrocarbons, both saturated and unsaturated, with a carbon number between C 9 and C 22 .As stated by Westerhout  1998), the wide distribution of aliphatic chains in condensed products is due to the thermal decomposition of LDPE which, during the primary cracking process, follows a random scission mechanism.This type of alkenes is highly required in the petrochemical industry where they are used as chemical feedstock for plastic and detergent manufacture, whereas the alkanes could be utilized as paraffin wax or further processed to extract some of the beneficial components for industry and could be upgraded to produce lighter fuel fractions or gasified to hydrogen to make it more commercially beneficial.In detergent industries, the aliphatic fractions from C 12 to C 18 as well as alpha-olefins are highly desired feedstocks for the manufacture of raw materials such as alkyl benzene sulfonic acid (ABSA) and sodium lauryl ether sulfate (SLES) (Onwudili, Insura, and Williams 2009).
The results of the semi-quantitative analyzes of the adopted feedstocks in both thermal and catalytic pyrolysis tests, at different temperature levels (450, 550, and 650°C for PSW tests and 550°C for LDPE tests), are shown in the supplementary.For an easier understanding of the data, the compounds have been divided into three compound classes: aliphatic hydrocarbons (n-alkanes and n-alkenes), aromatics, and cyclic aliphatic along with non-detected compounds, as shown in Table 4.
The data highlight that the dominant class was constituted by aliphatic hydrocarbon compounds.In the thermal tests, the condensate products of both feedstocks were dominated by alkenes followed by alkanes, while in the catalytic tests the alkanes were the more abundant compound, especially when LDPE was used as feedstock.Cyclic aliphatic compounds were mostly detected in LDPE thermal tests.
No significant levels of aromatic compounds were found in all pyrolysis experiments, and more specifically, they were mainly produced in catalytic processes.This trend is in line with the cracking activity of the alumina leading to the formation of cyclic and aromatic hydrocarbons in agreement with the findings of Ateş and Işikdaǧ (2009).An acid catalyst, such as alumina, shows excellent performance for catalytic reforming of plastic pyrolysis vapors, mainly producing C 5 -C 23 olefins that are the important precursors to form aromatics via Diels-Alder reaction, or through oligomerization, and deoxygenation occurring on the active acidic sites of the catalyst (Dai et al. 2021;Miandad et al. 2017).The extent to which each of these reactions takes place depends strongly on the nature of the catalyst, the composition of the alkanes, and the operating conditions.The aromatization of hydrocarbons, from a thermodynamic point of view, is favored at high temperature and low pressure (Mériaudeau and Naccache 1997).In the oils collected in the PSW thermal and catalytic pyrolysis tests, there were a large amount of compounds not detected by GC-MS.This was perhaps due to the fact that the maximum temperature of the ramp used on the GC-MS (310°C) was not sufficient to vaporize and therefore identify the heavier compounds present in the condensate samples and maybe these compounds were generated by the thermal degradation of plastic materials different from LDPE, for which more than 90% of the compounds were identified by GC-MS (Chan et al. 2020).However, most of the compounds identified in PSW oils were also present in LDPE oil, suggesting a poor interaction of the different kinds of plastics present in the PSW.
The identified compounds were also divided into three classes, based on the number of carbon atoms: a Gasoline -like fraction (C 5 -C 11 ), a Diesel -like fraction (C 12 -C 20 ), and a higher hydrocarbon fraction (C > 20).The percentage areas of the peaks of the chromatogram were calculated in order to compare the results of different tests (Table 5).
Results highlighted that in each test for both feedstocks the diesel fraction was the most abundant.In the PSW experiments, it was not possible to recognize a trend with the increasing temperature, because of the heterogeneous composition of the sample (Lopez-Urionabarrenechea et al. 2012).
Nevertheless, from a comparison between thermal and catalytic tests, a reduction of the fractions (gasoline, diesel, and C > 20 fractions) can be observed in the presence of γ-alumina.This fact demonstrates the effect of the catalyst on the conversion of vapors into lighter hydrocarbons, which appears to be higher in the PSW tests carried out at 450 and 550°C, rather than in the one at 650°C.The only exception was the diesel-like fraction in the test conducted at 550°C, which in the presence of the catalyst increases considerably compared to the corresponding thermal test.A different behavior was assumed instead in the LDPE tests, in which the C > 20 fraction halves in favor of the gasoline and diesel fractions which increase significantly compared to tests performed in the absence of the catalyst.
The results of the elemental analysis (CHN) carried out on waxes not dissolved in DCM, recovered during both thermal and catalytic experiments, are reported in Table 6 (Nitrogen was not reported because the values were below the instrument's detection limits).It should be noted that the values of the C/H ratio for the waxes were typical values of olefins (C n H 2n ).Moreover, the values of the C/H ratio for the waxes (5.9 < C/H < 6.2) were very similar to the one obtained for the PSW (C/H = 6.2) and LDPE (C/H = 6.0) samples.
Higher values were observed only in the tests carried out at 450°C (C/H = 8.1 for thermal and C/H = 7.5 for catalytic tests).In the PSW catalytic tests performed at 450 and 650°C, the C/H ratio was slightly lower than the value obtained in the corresponding thermal experiment, while it was the same for the PSW tests carried out at 550°C and for LDPE tests.The results of the thermogravimetric analysis, carried out on waxes under nitrogen flow, are reported in Figure 3.
For the waxes originating from thermal tests, the weight loss was complete at 500°C.This suggests that almost all ashes, originally present in the PSW, were retained in the solid residue of the pyrolysis process.The TG curves of the wax recovered at lower temperature in the catalytic tests not differs from the thermal ones, suggesting that the catalyst is not active at 450°C, while a shift of TG curves to lower temperatures was observed for the catalytic tests carried out at 550°C and 650°C suggesting the formation of lighter component due to the activity of catalyst.This was a confirmation of the different characteristics of the waxes produced in thermal and catalytic pyrolysis, and it was in line with their elemental analysis.

Solid composition
With respect to the composition of solid products, it was evident that almost all the ashes initially present in the PSW sample were retained into the solid residue.
The results of the elemental analysis (CHN) performed on solid products recovered during both thermal and catalytic experiments, are reported in Table 7.The solid product 13.9 C/H 8.1 5.9 6.2 5.9 7.5 5.9 5.9 5.9 was obviously enriched in carbon; therefore, mainly in thermal experiments, it presented C/ H ratios up to eight times higher than the original PSW sample.

The catalyst
The alumina recovered after the catalytic tests highlights coke deposition on particles surface, as shown in Figure 4a.Consequently, an evaluation of the amount of the coke deposited on the catalyst was carried out by means of thermogravimetric analyses performed on the exhaust alumina under air flow (temperature ramp of 30°C/min up to 900°C).
The combustion of coke deposited on the alumina was also confirmed by the presence of an exothermic peak in the DSC analysis simultaneously performed during the TG test.This treatment allowed achieving the complete removal of the coke, suggesting that the complete regeneration of catalyst can be obtained.

Conclusion
This work investigated the preliminary pyrolysis process of a real Plastic Solid Waste (PSW) provided by COREPLA resulting from the recycling and recovery of plastic packaging.Both, thermal and catalytic experiments were performed to analyze the effects of temperature and utilization of a cracking catalyst (namely, γ-alumina) on product yield (gas, condensable, and solid products).The catalytic and non-catalytic (thermal) pyrolysis tests of low-density polyethylene (LDPE) were also investigated as a representative surrogate of the plastic materials commonly found in PSW and to evaluate possible synergies coming from the presence of different kinds of plastic.Pyrolysis tests were carried out in batch mode in a fixed bed quartz micro-reactor under nitrogen flow.The PSW experiments were performed at three different temperatures (450°C, 550°C, and 650°C), whereas LDPE experiments only at 550°C.
The pyrolysis products were characterized in terms of their chemical composition by several analytical techniques.The use of a high surface catalyst such as γ-alumina allowed having gaseous products as well as condensed compounds with a qualitatively different composition with respect to thermal tests.
The total gas production was in good agreement with data reported in the literature and in particular, its production increased with the temperature rising.In the catalytic pyrolysis experiments, a higher fraction of light hydrocarbons and hydrogen was observed.
In both thermal and catalytic tests, the gas composition obtained by PSW pyrolysis was strongly different from that obtained by LDPE one.This suggests that the ashes present in the real plastic can play a role in the transformation of gaseous species produced during the pyrolysis.
The main product of all thermal and catalytic pyrolysis experiments, using both PSW and LDPE, was an oily wax consisting mainly of aliphatic compounds with long chains, although the amount of waxes produced under catalytic tests is visibly lower.From the GC-MS analysis of the condensates solubilized in DCM, it emerged that most of the compounds identified in the PSW oils were detected in the LDPE oil too, demonstrating that this was a major contributor to the PSW and suggesting that a not high interaction of the different plastic occurs.
In each test and for both feedstocks, the diesel fraction is the most abundant one in terms of area%.A reduction of the gasoline-like, diesel-like, and C > 20 fractions was observed in the presence of γ-alumina, except for the diesel-like fraction in the PSW test conducted at 550°C, when a considerable increase in catalytic tests was recorded compared to the corresponding thermal test.On the contrary, in the LDPE catalytic tests the C > 20 fraction halves in favor of the gasoline and diesel fractions.However, the catalytic action of the alumina also led to the higher formation of cyclic and aromatic hydrocarbons that were, instead, less detected in thermal pyrolysis tests.
A coke deposition was observed on the catalyst, but an air treatment totally removed the coke allowing the catalyst regeneration.
It can therefore be concluded that this closed-batch system can be used to effectively degrade PSW to produce chemical-rich oils (especially alkanes and alkenes) that can be used in the industrial field.However, the reaction conditions must be optimized to improve the quality of the products obtained.

Figure 1 .
Figure 1.a) Image of PSW; b) Image of LDPE.

Figure 2 .
Figure 2. Schematic representation of the experimental apparatus.

Figure 3 .
Figure 3. TG curves of waxes obtained in thermal and catalytic PSW pyrolysis tests.

Figure 4 .
Figure 4. Image of alumina a) after pyrolysis test and b) after regeneration (the thermogravimetric analysis).

Table 1 .
Results of proximate and ultimate analysis of the PSW and LDPE.

Table 2 .
Mass of permanent gases produced during thermal and catalytic pyrolysis tests.

Table 3 .
The average concentration of the gaseous species, determined by means of micro-GC, in both thermal and catalytic pyrolysis tests.

Table 4 .
Compound classes obtained in the oils of the PSW and LDPE pyrolysis tests.

Table 5 .
Fractions of compounds obtained in the PSW and LDPE pyrolysis tests.

Table 6 .
The results of elemental analysis (CHN) performed on the waxes fraction not dissolved in DCM.

Table 7 .
The results of elemental analysis (CHN) performed on solid products.