High performance catalysts for degradation of eva from waste solar panels

Abstract

The invention relates to improved catalysts and methods for the degradation of ethylene vinyl acetate (EVA). Particularly, the invention may relate to thermal recycling of solar panels at the end of their useful life.

Description

[0001] HIGH PERFORMANCE CATALYSTS FOR DEGRADATION OF EVA FROM WASTE SOLAR PANELS

[0002] This application claims priority from Australian Provisional Patent Application No. 2024902790 filed 4 September 2024, the content of which is incorporated herein by reference in its entirety.

[0003] FIELD

[0004] The invention relates to improved catalysts and methods for the degradation of ethylene vinyl acetate (EVA). The invention will be described in the context of thermal recycling of solar panels at the end of their useful life, however, it will be appreciated that the invention is not limited to such use but may also be used more generally in the degradation of EVA and related materials.

[0005] BACKGROUND

[0006] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0007] Due to the increase in the harnessing of solar energy in recent years, the number of installed photovoltaic (PV) panels in recent years has soared. Consequently, there has been a rapid rise in the amount of PV waste due to the relatively short 25-30 year operational lifespan of solar panels. The end- of-life (EOL) PV mass is estimated to reach 60-70 million tonnes by 2050. Due to the drastic environmental threats stemming from the direct dumping of EOL PV panels into landfills, the recycling of solar panel waste is an important step in the overall PV lifecycle.

[0008] In order to recycle PV panels at EOL, they must first be delaminated to separate their components. The delamination process is conventionally conducted via mechanical, thermal, or chemical methods, of which thermal methods are considered the most efficient and feasible. In these thermal methods, the crushed PV panels are combusted or pyrolysed under high-temperature conditions. The aim of these conditions are to fully remove the EVA encapsulating layers from the glass, back sheet, and solar cells. EVA makes up around 6.5 wt% of a typical PV panel.

[0009] At temperatures above 500 °C, thermal treatment of PV waste in the absence of oxygen for 1 hr leads to the degradation of >99% of polymeric layers, including EVA. Between 400 to 500 °C, 75% of the polymeric substances are degraded. Degradation of polymeric layers at 500 °C under controlled oxidising conditions can enable proper separation of components. Keeping PV panels at 500 °C (773 k) for 30 mins has been shown to effect complete removal of plastic materials. While it is possible that the EVA layers can fully get degraded at temperatures over 500 °C, the conventional temperature for the non-catalytic PV waste pyrolysis is 600°C.

[0010] Thermal methods for recycling PV panels are very energy-intensive. Further, a major proportion of EVA in these thermal processes gets converted to condensable gases, which condense in the form of sticky liquid products (tar) when the temperature drops. Tar brings operational challenges for the downstream equipment if not handled properly. Analysis of the pyrolysis of EVA shows that thermal decomposition of EVA leads to the formation of 10% permanent gas, 89.9% condensate, and 0.1 % coke.

[0011] A further concern arising from the thermal treatment of plastic wastes is the generation of harmful emissions containing CO, hydrocarbons (HCS), VOCs and NOXthat can pollute the environment and give rise to a variety of detrimental consequences. Even though all these hurdles make the use of thermal methods so very challenging, they are still among the most employed approaches to dealing with solar panel waste.

[0012] Reducing the process temperature and energy consumption of thermal PV recycling, enhancing the EVA-to-gas conversion ratio, and handling the off-gas emitted from the process would make it more economically and environmentally feasible and drastically increase the efficiency of the thermal PV recycling methods.

[0013] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0014] It is an object of at least one preferred form of the present invention to provide a method of degrading EVA with improved efficiency. It is an object of further preferred forms of the present invention to a method of degrading EVA with improved economic and / or environmental viability. It is an object of yet further preferred forms of the present invention to a method of degrading EVA with reduced decomposition temperature.

[0015] SUMMARY

[0016] According to a first aspect the invention provides a method for thermal degradation of ethylene vinyl acetate (EVA) to a non-condensible gas during photovoltaic device recycling, comprising the step of heating EVA containing material in the presence of a HBeta zeolite as catalyst.

[0017] H-Beta catalysts are an advanced family of acidic zeolites characterized by their three-dimensional porous structure, composed of interconnected SiO4and AIO4tetrahedra, making them highly effective catalysts in hydrocarbon conversion processes. Their unique Beta structure features uniform, interconnected channels and cages capable of accommodating relatively large hydrocarbon molecules, enhancing the conversion of heavier hydrocarbons into lighter fractions. This makes HBeta catalysts particularly ideal for the cracking of bulky molecules. The pore sizes of Hbeta catalysts typically range from 5 to 7 A (angstroms) and can be optimized for catalyzing reactions involving molecules of varying sizes.

[0018] One of the key advantageous features of HBeta catalysts is the presence of strong Bnansted acid sites, which significantly enhance catalytic activity in acid-catalyzed reactions such as cracking, alkylation, isomerization, and dehydration. Compared to catalysts like HZSM-5, which has a 10-membered ring pore structure with straight and zigzag channels, Hbeta catalysts possess a 12-membered ring pore system — with both straight and sinusoidal channels — allows for greater flexibility and efficiency in catalyzing reactions involving bulkier molecules.

[0019] HBeta's thermal stability is another critical factor that sets it apart. Capable of withstanding temperatures up to 700°C, HBeta catalysts maintain their structural integrity even in high-temperature reactions. This contrasts with MCM-41 , which has lower thermal stability and whose mesoporous structure may collapse under similar conditions. While MCM-41 is a mesoporous material with larger pore diameters (2 to 10 nm), its relatively low acidity and weaker acid sites limit its catalytic effectiveness.

[0020] Moreover, HBeta catalysts exhibit a balanced distribution of both Bnansted and Lewis acid sites, with moderate to high acidity depending on the Si / AI ratio, providing superior catalytic versatility. In contrast, HZSM-5, although known for its strong Bnansted acidity, generally has a higher Si / AI ratio, leading to lower overall acidity compared to Hbeta catalysts. MCM-41 , being predominantly siliceous, inherently possesses weaker acidity, further underscoring the superior catalytic potential of Hbeta catalysts.

[0021] In summary, HBeta catalysts excel in stability, acidity, and activity, particularly in reactions involving bulky molecules, positioning it as a superior catalyst compared to both HZSM-5, which is better suited for smaller molecules, and MCM-41 , which lacks the thermal and acidic robustness of HBeta.

[0022] Overall, what distinguishes HBeta catalysts in comparison to other catalysts such as HZSM-5 and MCM-41 , are their moderate pore size (which allows proper accessibility to acid sites and reduces the likelihood of coke deposition), high inherent acidity (from both Bnansted and Lewis acid sites), and, most importantly, their uniform, interconnected channels and cages that can accommodate relatively large hydrocarbon molecules.

[0023] As used herein, the term “HBeta” refers to any member of the HBeta zeolite family possessing the above properties. Examples of suitable HBeta catalysts include those available from ACS material (pore diameter -0.5-0.7 nm; SiC AbOs Molar ratio 40-150; SSA 500 m2 / g; Na2O (%) <0.1 ; crystallinity >95%), from Tosoh (Pore diameters ~0.6 nm; SiC AbOs Molar ratio 27-500; SSA 450-600 m2 / g), from Clariant (pore diameters ~0.7 nm; SiC AbOs Molar ratio 25-150; SSA >500 m2 / g) orthose available from Zeolyst International.

[0024] In some embodiments, the temperature of thermal degradation may be greater than 400°C and / or less than 500°C. Advantageously, the temperature of thermal degradation does not exceed 450°C. In some embodiments, the temperature of thermal degradation may be about 400°C to about 450°C, about 450°C to about 500°C, about 500°C to about 550°C, or about 550°C to about 600°C.

[0025] In some embodiments, the temperature of thermal degradation may be about 300°C to about 350°C, about 350°C to about 400°C, about 400°C to about 450°C, or about 450°C to about 500°C.

[0026] In some embodiments, the temperature of thermal degradation may be about 400°C to about 420°C, about 420°C to about 440°C, about 440°C to about 460°C, about 460°C to about 480°C, or about 480°C to about 500°C.

[0027] In some embodiments, the temperature of thermal degradation does not exceed 500°C, 490°C, 480°C, 470°C, 460°C, 450°C, 440°C, 430°C, 420°C, 410°C, or 400°C.

[0028] In one embodiment, the method of the present invention is carried out under non-oxidative conditions, such as under a nitrogen atmosphere. In that case, the non-condensible gas may be provided in a yield of at least 74% by weight or greater. For example, the non-condensible gas may be provided in a yield of at least 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, or 98%.

[0029] In some embodiments, the non-condensible gas may comprise CnHmin an amount of 90% or greater by volume, for example, about 90% to about 91 %, about 91 % to about 92%, about 92% to about 93%, about 93% to about 94%, about 94% to about 95%, about 95% to about 96%, about 96% to about 97%, about 97% to about 98%, or about 98% to about 99%.

[0030] In some embodiments, the non-condensible gas may comprise CO2 in an amount of 5% or less by volume, for example, about 0.1 % to about 0.5%, about 0.5% to about 1 %, about 1 % to about 2%, about 2% to about 3%, about 3% to about 4%, or about 4% to about 5%.

[0031] In some embodiment, the tar yield may be 25% by weight or less, for example, about 1 % to about 5%, about 5% to about 10%, about 10% to about 15%, about 15% to about 20%, or about 20% to about 25%.

[0032] In an alternative embodiment, the method of the present invention is carried out under oxidative conditions, such as under an air atmosphere. In that case, the non-condensible gas may be provided in a yield of at least 45% by weight or greater, for example, at least 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0033] In some embodiments, the non-condensible gas may comprise CnHmin an amount of 35% or greater by volume, for example, about 35% to about 40%, about 40% to about 45%, about 45% to about 50%, about 50% to about 55%, about 55% to about 60%, about 60% to about 65%, or about 65% to about 70%. In some embodiments, the non-condensible gas may comprise CO2 in an amount of 21 % or less by volume, for example, about 1 % to about 5%, about 5% to about 10%, about 10% to about 15%, about 15% to about 20%, or about 20% to about 21 %.

[0034] In some embodiments, the non-condensible gas may comprises CO in an amount of 40% or less by volume, for example, about 1 % to about 5%, about 5% to about 10%, about 10% to about 15%, about 15% to about 20%, about 20% to about 25%, about 25% to about 30%, about 30% to about 35%, about 35% to about 40%.

[0035] In some embodiments, the tar yield may be 55% by weight or less, for example, about 1 % to about 5%, about 5% to about 10%, about 10% to about 15%, about 15% to about 20%, about 20% to about 25%, about 25% to about 30%, about 30% to about 35%, about 35% to about 40%, about 40% to about 45%, about 45% to about 50%, or about 50% to about 55%.

[0036] In either the non-oxidative or oxidative embodiments above, the amount of char is low, for example about 0% by weight, or about 1 %, about 2%, about 3%, about 4%, or about 5% by weight.

[0037] In the present invention, the catalyst may be used in an amount of 5-20% by weight, for example 10- 20% by weight, based on the amount of EVA. Alternatively, the catalyst may be used in an amount of greater than 20% by weight based on the amount of EVA. For example, the catalyst may be used in an amount about 5% to about 10%, about 10% to about 15%, about 15% to about 20%, about 20% to about 25%, about 25% to about 30%, about 30% to about 35%, about 35% to about 40%, about 40% to about 45%, or about 45% to about 50%, based on the amount of EVA.

[0038] In another aspect the invention provides method according to the preceding aspect further including the step of treating the non-condensible gas with a reforming catalyst under oxidising conditions at an elevated temperature.

[0039] In some embodiments, the reforming catalyst may be for example Pt / AI2C>3.

[0040] In some embodiments, the oxidising conditions may comprise air, oxygen enhanced air, or oxygen at 50%-100% by volume, for example, about 50% to about 60%, about 60% to about 70%, about 70% to about 80%, about 80% to about 90%, about 90% to about 100% by volume.

[0041] In one embodiment of this aspect, the elevated temperature is 250-450°C (for example about 300°C) thereby to produce CO2, for example, about 250°C to about 270°C, about 270°C to about 290°C, about 290°C to about 310°C, about 310°C to about 330°C, about 330°C to about 350°C, about 350°C to about 370°C, about 370°C to about 390°C, about 390°C to about 410°C, about 410°C to about 430°C, or about 430°C to about 450°C.

[0042] In an alternative embodiment of this aspect, the elevated temperature is 450°C (for example about 500°C) or above thereby to produce syngas (CO + H2), for example, about 450°C to about 500°C, about 500°C to about 550°C, about 550°C to about 600°C, about 600°C to about 650°C, or about 650°C to about 700°C.

[0043] DEFINITIONS

[0044] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

[0045] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0046] As used herein, the phrase “consisting of’ excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of’ (or variations thereof) appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase “consisting essentially of’ limits the scope of a claim to the specified elements or method steps, plus those that do not materially affect the basis and novel characteristic(s) of the claimed subject matter.

[0047] With respect to the terms “comprising”, “consisting of’, and “consisting essentially of’, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not otherwise explicitly recited, any instance of “comprising” may be replaced by “consisting of’ or, alternatively, by “consisting essentially of’.

[0048] Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, “%” will mean “weight %”, “ratio” will mean “weight ratio” and “parts” will mean “weight parts”.

[0049] The term ‘substantially’ as used herein shall mean comprising more than 50% by weight, where relevant, unless otherwise indicated.

[0050] The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1 , 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0051] Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0052] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

[0053] It must also be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0054] As used herein, with reference to numbers in a range of numerals, the terms “about,” “approximately” and “substantially” are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to +1 % of the referenced number, most preferably -0.1 % to +0.1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth.

[0055] Although exemplary embodiments of the disclosed technology are explained in detail herein, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the disclosed technology be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The disclosed technology is capable of other embodiments and of being practiced or carried out in various ways.

[0056] DESCRIPTION OF THE DRAWINGS

[0057] Figure 1A summarises the effect of various catalysts on EVA decomposition behaviour under a) non- oxidative b) oxidative conditions. Figure 1 B shows the TGA profile of the reaction.

[0058] Figure 2A summarises the effect of catalyst weight on EVA decomposition behaviour under a) non- oxidative b) oxidative conditions. Figure 2B shows the TGA profile of the reaction.

[0059] Figure 3 shows a): EVA product yields under various atmospheres (T=500 °C, gas flow rate=20 mL / min), b): effect of different catalysts (catalyst content 10%) on EVA product yields (T=500 °C, atmosphere=Air+N2, gas flow rate=20 mL / min)

[0060] Figure 4 shows the effect of atmosphere on a HBeta catalyst (catalyst weight 10%) performance for EVA conversion (T=500 °C, gas flow rate=20 mL / min) Figure 5 shows the effect of a HBeta catalyst amount for EVA conversion under a, b): non-oxidative atmosphere (T=500 °C, atmosphere= N2, gas flow rate=20 mL / min) and c, d): oxidative atmosphere (T=500 °C, atmosphere=Air, gas flow rate=20 mL / min)

[0061] Figure 6 shows the effect of lowering process temperature on EVA conversion and a HBeta catalyst performance under a): non-oxidative atmosphere (atmosphere=N2, gas flow rate=20 mL / min) and b): oxidative atmosphere (atmosphere=Air, gas flow rate=20 mL / min)

[0062] Figure 7 shows the effect of a): reforming catalyst amount in the downstream reactor (Ti=450 °C, T2=500 °C, atmosphere^ air, gas flow rate=20 mL / min, sample- EVA+10% HBeta, catalyst in second reactor= Pt / AkOs) b): downstream reactor temperature (Ti=450 °C, atmosphere^ air, gas flow rate=20 mL / min, sample^ EVA+10% HBeta, catalyst amount in second reactor= 100 mg) on the off-gas composition.

[0063] Figure 8 shows a):Effect of gas flow rate on the off-gas composition after gas treatment (T1 =450 °C, T2=300 °C, atmosphere= air, sample= EVA+10% HBeta, catalyst in second reactor=100 mg P AI2O3) b):off-gas composition after gas treatment under various oxidative condition (Ti=450 °C, T2=300 °C, gas flow rate=10 mL / min, sample= EVA+10% HBeta, catalyst in second reactor= 100 mg P AI2O3)

[0064] Figure 9 is a schematic of the gasification / pyrolysis setup used in this study.

[0065] Figure 10 is a schematic for an alternative EVA catalytic degradation process.

[0066] DETAILED DESCRIPTION

[0067] Zeolite-based catalysts like Y-zeolite, p-zeolite, HZSM-5, and AI-MCM-41 have been extensively used for improving the degradation of different polymers, including for both reducing the degradation temperature or increasing the product quality and value. While degradation of polymers, in general, requires a high-temperature condition and leads to the formation of a wide range of products, using a catalyst can be a useful way to lower the decomposition temperature and time and improve the selectivity toward the desired products. Another merit of using a catalyst can be an increasing in the gas yield and a reduction in the liquid oil yield compared with the non-catalytic process under the same temperature.

[0068] The performance of zeolite catalysts depends on its attributes, such as acidity, particle size and volume, pore size, and specific surface area and the ultimate catalyst selection must be made carefully based on the system’s requirements.

[0069] Catalytic oxidation is a thermally and economically efficient process that is used to convert harmful gas products into CO2 and water. Oxidation catalysts mainly comprise a precious metal like platinum (Pt) or palladium (Pd) on alumina support and can oxidise the harmful species at relatively low temperatures. Pt-based catalysts are widely employed among different oxidation catalysts due to their decent activity and stability. Although CO2, the main product of catalytic oxidation treatment, is one of the main contributors to global warming, it is less toxic and harmful than CO, HCS, VOCs, and NOX. Further, if harnessed and managed properly, CO2 can be used as a low-cost raw material for producing fuels and value-added chemicals like urea and methanol via carboxylation or reduction routes.

[0070] Although the thermal treatment of PV panel waste to decompose EVA layers has been investigated by others, there remain no attempts in the literature to find catalytic solutions to reduce the process temperature and enhance EVA-to-gas ratio.

[0071] The present inventors have studied the effect of a number of commercial zeolite-based catalysts, including p-zeolites, HZSM-5, and AI-MCM-4, on the degradation behaviour of neat EVA sheets under oxidative and anaerobic conditions.

[0072] While the introduction of zeolite catalysts such as MCM-41 , HZSM-5 and HBeta, is found to effectively lower the temperature at which EVA degrades, surprisingly it has been found that HBeta catalysts are particularly effective, especially when oxygen is absent. In addition, beyond enhancing the degradation behaviour of EVA, the use of Hbeta catalysts increases the conversion of EVA into gases and substantially reduces tar production. Further, it has been found that HBeta catalysts enables the process temperature to be lowered to 450°C without loss of effectiveness when nitrogen is used as the decomposition medium, Additionally, employing Pt / AfeOs as an oxidation catalyst in a separate reactor for gas treatment effectively converts carbon monoxide (CO) and hydrocarbons into carbon dioxide (CO2), with almost 95 vol%, thereby mitigating harmful emissions during EVA’s thermal decomposition significantly. Lower temperatures, a controlled flow of carrier gas, and higher oxygen concentrations are advantageous for a more efficient CO / hydrocarbon-to-C02 conversion.

[0073] The use of a HBeta catalyst to reduce the EVA decomposition temperature, along with gas treatment using an oxidation catalyst, offers a promising approach to make the thermal recycling of photovoltaic panels more economically and environmentally viable.

[0074] As mentioned above, the present inventors have studied the effect of a number of commercial zeolitebased catalysts, p-zeolite, HZSM-5, and AI-MCM-4, on the degradation behaviour of neat EVA sheets under oxidative and anaerobic conditions.

[0075] Thermogravimetric analysis (TGA) is a useful tool to study the degradation behaviour of material against temperature and has been used in developing the present invention. Among data obtained from the TGA test, Tonset, at which degradation starts; Tmax, at which the degradation rate is maximum; and Tend, at which the decomposition of material ends, are the appropriate criteria to see how changing the condition can affect the decomposition pattern. Fig. 1 A. gives information about the Tonset, Tmax, and Tend of EVA and EVA mixed with three different catalysts under nitrogen and air atmospheres. This information is extracted from the TGA and DTG curves in the Fig. 1 B. Under nitrogen, the Tonset and Tend for EVA are 290 and 497 °C, respectively. Fig.l B. shows that EVA decomposes in two primary stages. In the first stage, the vinyl acetate (VA) group decomposes, and in the second stage the PE hydrocarbon chains start decomposing. Using a catalyst affects EVA’s decomposition behaviour noticeably and makes the decomposition peaks wider regardless of the catalyst type. Widening of the decomposition peaks is mainly due to changes in the decomposition mechanism and the emergence of a wider array of different intermediates in the presence of a catalyst compared with direct thermal decomposition. For HZSM-5, the Tonset is not affected significantly compared with neat EVA, but the Tmax drops 462 to 432.5 °C, and EVA decomposition finishes at 467 °C. Replacing HBeta with HZSM-5 does not affect the Tmax. It reduces Tonset and Tend significantly, and the decomposition starts at 165 °C and finishes at 455 °C. While the MCM-41 catalyst reduces the Tonset to 160 °C, the Tmax and Tend are not enhanced, and the maximum degradation happens at 449 °C, and decomposition ends at 470 °C.

[0076] The effectiveness of adding catalysts in enhancing the thermal decomposition of polymers depends on the acidity, pore size, external surface area, and topology of catalyst crystals. Polymeric chain cracking starts at the catalyst’s outer surface and the pore mouth. Still, the active acidic sites of zeolite-catalysts are located inside the pores, and pore size significantly determines the accessibility of acid sites. If the pore size is smallerthan the molecular diameter of intermediate reactants, they cannot enter and access the acid sites; thus, leading to a poor catalytic efficiency. Without wishing to be bound by theory, it is believed that the lower catalytic activity of HZSM-5 relative to HBeta and MCM-41 , particularly at the first decomposition stage, is mostly due to its small pores hindering the mass transfer and access of bulky intermediates formed at the external surface of the catalyst to active sites. HZSM-5 also has a low surface area and the high SiO2 / Al2C>3 ratio (low acidity).

[0077] Among the catalysts tested, MCM-41 had the highest acidity, largest pore size, and highest surface area and therefore would be expected to perform better than its counterparts. Surprisingly, however, compared with HBeta, despite its good performance in reducing the Tonset, MCM-41 shows higher Tmax and Tend, indicating reduced catalytic activity which is thought to be due to poor mass transfer after finishing the first decomposition step. It is noteworthy that too small pores and low acidity bring their demerits. On the other hand, too large pores and high acidity promote coke deposition inside the catalyst channels, reducing the catalyst performance, which could be a reason for the non-convincing performance of MCM-41 despite its favourable physical characteristics. Among studied catalysts, HBeta demonstrated superior performance in enhancing EVA thermal decomposition’s first and second stages. Compared with MCM-41 , HZSM-5 and HY zeolites, HBeta zeolite unexpectedly exhibited greater activity due to its overall morphology, acidity, and surface area.

[0078] Looking at Fig. 1 B, EVA degradation under air shows different behaviour and comprises three peaks. Compared with the nitrogen atmosphere, the degradation of EVA under air is more accelerated, although the overall decomposition range is broader, and decomposition finishes at a higher temperature. For catalytic EVA decomposition, regardless of the type of catalyst, the degradation behaviour under oxidative conditions is noticeably different from the non-oxidative atmosphere, which confirms the more complex EVA degradation process under air. For HZSM-5, HBeta, and MCM-41 catalysts, the Tonset is 241 , 200, and 160 °C, respectively. While using these catalysts can improve the onset temperature of EVA with 260 °C, looking at Fig. 1., it can be seen that these catalysts fail to enhance the Tmax. Also, the catalytic degradation finishes at higher temperatures than neat EVA under air. A good explanation for these observations is that in the presence of oxygen, the employed catalysts get deactivated quickly due to the formation of stable oxygenated intermediates blocking the catalyst channels and reducing the mass transfer significantly. Among the studied catalysts for EVA degradation under air, HBeta shows better performance in terms of Tmax and Tend ; however, the degradation rate of neat EVA under air is much higher compared with samples containing catalysts, indicating that the use of catalyst is inhibiting the EVA decomposition rate under oxidative condition.

[0079] Fig. 2A. shows TGA data for EVA and EVA / HBeta catalyst at various catalyst loading under nitrogen and air atmospheres. TGA and DTG curves are shown in Fig. 2B. Under nitrogen, increasing the loading of HBeta shows a positive effect on improving EVA degradation. The increase in catalyst loading increases the number of acid sites facilitating polymer cracking. Also, high catalyst loading is reported to promote secondary cracking reactions. While at 10% HBeta, the degradation is much better compared with 5% HBeta and neat EVA, increasing the catalyst weight to 20% does not indicate significant improvements in Tonset, Tmax, and Tend. Based on these results, it can be concluded that under nitrogen for EVA degradation, increasing the catalyst loading, to a certain level, can be beneficial for accelerating the degradation process. Under oxidative conditions, 5% HBeta improves Tonset and Tend and reduces Tmax marginally. However, increasing the catalyst weight to 10% and 20% does not affect the Tmax and merely reduces the Tonset. Further, the Tend at the presence of a higher amount of catalyst under air shifts to higher temperatures. This shows again that the presence of oxygen reduces the activity of the catalyst severely.

[0080] From the TGA results and discussions, it can be recapped that the catalytic degradation of EVA can be more efficient than neat EVA thermal degradation, providing that the process is conducted under a non- oxidative atmosphere and the suitable catalyst with a proper mixing ratio are selected. In the current study, using 10% HBeta under nitrogen atmosphere can significantly improve EVA degradation among the evaluated catalysts. Consequently, the degradation of EVA with this approach can be performed at lower temperatures compared with the normal degradation temperature of EVA, which is between 500 to 600 °C.

[0081] Fig. 3a. illustrates the gas composition and product yields from EVA thermochemical conversion at 500 °C under nitrogen, diluted air, and air atmospheres. Under non-oxidative conditions, the gas released from EVA degradation comprised 20.6 % CO2, 3.9 % CO, 3.7 % CH4, 5.8 % H2, and 66 vol% hydrocarbons (CnHm) ranging from C2 to C7 species. Changing the atmosphere and increasing the oxygen concentration increases the CO concentration significantly; however, it impacts the CO2 and CH4 concentrations slightly. The most noticeable effect of increasing oxygen concentration is on the CnHm. Compared with the anaerobic environment, oxidising conditions diminish the CnHmconcentration profoundly. The CnHmconcentrations for diluted air and air environment are 21.8 and 18.6 vol%, respectively. The observation is due to the promotion of hydrocarbons’ partial and complete oxidation in the presence of air.

[0082] Regarding the product yields, it can be mentioned that the char yield is zero irrespective of the employed atmosphere, indicating that all EVA gets converted to gas and tar through the process at 500 °C for 90 mins. Compared with oxidising conditions, the nitrogen environment produces less tar and more gas and changing nitrogen with air increases tar yield from 68.9 to 83.8 wt% and reduces gas yield from 31.2 to 16.3 wt%. The higher tar yield under air is due to more complex reactions leading to the formation of oxygenates and heavier products, which can be condensed easily when the temperature drops, resulting in a greater tar content.

[0083] Fig. 3b. compares the performance of three catalysts in terms of gas composition and product yields for EVA conversion at 500 °C. Under the same condition, when HZSM-5 is used, the gas comprises 37.5% CO, 2.3% CH4, 19.5% CO2, 2.1 % H2, and 38.8% CnHmhydrocarbons. The CH4and H2concentrations are in the same range for other catalysts. The CO and CO2concentrations for HBeta are 30.8 and 18.9%, respectively, and 34 and 29.8% for the MCM-41 catalyst. The CnHmconcentrations for HBeta and MCM-41 are 47.6 and 31 .9, respectively. It should be noted that hydrocarbon formation is due to the decomposition of longer polymeric chains (tar species), and a higher concentration of CnHmindirectly implies more tar decomposition through the process. Concerning the product yields, it can be noted that using HBeta produces less tar and more gas than HZSM-5 and MCM-41 . While the tar yield for HBeta is 49.5 wt%, it rises to 73.1 and 59.6 wt% for MCM-41 and HZSM-5, respectively. As a result, the lower tar yield and higher CnHmconcentration in the gas phase show that the EVA-to-gas conversion is much better from the HBeta catalyst than its counterparts.

[0084] These observations and differences in the performance of various catalysts are mostly due to the physical structures and characteristics of employed catalysts. It is reported that high amounts of heavy products from the thermocatalytic decomposition of polymers can signal the catalyst’s inefficiency. The selection of catalysts with high acidity, particularly high Bnansted acid sites, and proper pore size are approaches to enhance the gas yield and avoid the operational challenges stemming from high tar formation. While the main mechanism for medium to low acidity catalysts is random-chain cracking, high acidity (low SiO2 / AI2C>3) promotes end-chain cracking, leading to higher gas selectivity. This point should not be neglected that too high zeolite acidity conversely increases the probability of coke deposition inside pores.

[0085] The pore size of the catalyst defines its shape selectivity as well. Too small pores restrict the access of large polyolefin molecules to the active sites, forming heavy products. The large pores make the active sites more accessible for polymeric chains. However, when the pores are too large, it increases the residence time of heavy intermediates in channels, leading to the emergence of a hydrocarbon pool mechanism, which increases the probability of side reactions like decarbonylation, decarboxylation, oligomerisation, isomerisation, Diels-Alder, and coke formation. The promotion of secondary reactions has two consequences: 1) the shape selectivity of the catalyst is shifted to coke and heavier liquid products rather than non-condensable gases, and 2) fast catalyst deactivation due to pore blocking phenomena.

[0086] The performance of a catalyst is not just defined with its pore size and acidity. The high stability and convincing performance of HBeta may be attributed to its morphology and bent pores limiting the probability of carbon deposition. Catalysts with higher BET surface area are also likely to improve the polymer decomposition and raise the gas yield. All points discussed above can be accountable for a better performance of HBeta with its intermediate properties between those of HZSM-5 and MCM-41 zeolites.

[0087] Looking at TGA results and based on the catalyst screening conducted for EVA thermocatalytic conversion, it was demonstrated that HBeta performs better under the same condition in terms of lowering the degradation temperature and enhancing the EVA-to-gas conversion. In this part, the performance of HBeta under various conditions is assessed for a better understanding of its effectiveness for EVA degradation. Fig. 4. gives information about the performance of HBeta under different atmospheres. When EVA mixed with HBeta is processed under an anaerobic environment, the released gas comprises 1 .2% CO, 1 .2% H2, 6.3% CO2 and 91 .2% CnHmand an insignificant amount of CH4. Under a diluted air atmosphere, the CO increases to 30.8%, and the CO2 concentration is 18.9%. Further, the CnHmconcentration drops significantly to 47.6% due to the promotion of partial and complete oxidation reactions of hydrocarbons. When air is used as the carrier gas, the CO and CO2 concentrations are 39.4 and 21 .2%, respectively, and the CnHmconcentration drops to 36.1 %. In association with the product yields, regardless of the employed environment, the char yield is almost zero for all cases. However, the tar yield under nitrogen is 26.4 wt%, which increases remarkably to

[0088] 54.4 wt% when air is used. The gas yield for nitrogen, diluted air, and air atmosphere is 74.1 , 50.5, and

[0089] 45.5 wt%, respectively. Based on the results, the HBeta catalyst shows better efficiency in EVA gasification when the process is conducted in the nitrogen environment, and it is due to its fast deactivation under an oxidative atmosphere, as discussed earlier.

[0090] Fig. 5. presents information about the effect of HBeta loading on the gas composition and product yields under non-oxidative and oxidative atmospheres. Fig. 5a. shows that under nitrogen, compared with the gas released from neat EVA, using 5% HBeta increases the CnHmconcentration from 66% to 90% and reduces the CO2 concentration noticeably, from 20.6 to 3.4%. When the catalyst weight is increased to 20%, it can be seen that the changes in gas composition are not conspicuously affected. However, looking at Fig 5b. it can be noted that increasing the catalyst weight positively affects the EVA-to-gas conversion by reducing the tar yield. Under nitrogen, the tar yield at 20% catalyst is almost half of the 5% catalyst, and one-third of the tar remained from neat EVA degradation under the same operating condition. Another point worth mentioning is that the differences between using 10% and 20% catalysts are much less noticeable compared with 5% and 10% catalysts. This shows that due to zeolites’ saturating effect, increasing the catalyst weight to a level can enhance the process, after which adding more catalysts may not bring any improvements. These findings are in good agreement with the TGA results presented earlier. The production of more hydrocarbons and reduction in tar yield is mainly due to the promotion of secondary cracking reaction at a higher catalyst loading. Also, increasing the loading is a way to enhance the catalyst acidity (instead of reducing SiOz / AbOs), which facilitates the cracking of liquids then larger amounts of hydrocarbons are produced.

[0091] Fig. 5c. demonstrates that using the catalyst and increasing the catalyst weight under air affects the gas composition significantly. Compared with neat EVA, using 5% HBeta reduces the concentrations of CO, CO2, CH4, and H2 and conversely increases CnHmconcentration. This trend is the same when the weight of the catalyst is increased. Furthermore, looking at Fig. 5d., it can be observed that the tar yield shows a decreasing trend against catalyst weight and drops from 84 wt% for neat EVA to 44 wt% when 20% HBeta is employed. These observations indicate that increasing the catalyst weight can enhance the EVA conversion under an air atmosphere. However, comparing the efficiency of adding HBeta for improving the EVA conversion, it is clear that the nitrogen environment is more suitable for using the catalyst potentials to the fullest. The desired results can be met at lower catalyst weights in a non- oxidative environment.

[0092] Compared with thermal pyrolysis, the catalytic process can be performed at a lower temperature since catalysts promote cracking of polymeric chains. Based on the TGA results, it was indicated that using HBeta significantly improves the degradation behaviour of EVA by reducing the onset, end and maximum degradation temperatures. To pinpoint how reducing the processing temperature can affect the gas composition and product yields, the pyrolysis / gasification of EVA and EVA containing 10% HBeta are performed at 400 and 450 °C, and the results are compared with 500 °C in Fig. 6.

[0093] Under nitrogen, reducing the process temperature to 400 °C increases tar yield, and the rise in char yield shows an incomplete EVA degradation, which indicates that 400 °C is not a sufficient temperature for running the process. At 450 °C, the EVA is almost fully converted. Regardless of the atmosphere used, the presence of the catalyst exacerbates the condition and increases the char yield at 400 °C. This observation is probably due to the mass and heat transfer limitations imposed by catalyst particles. While at 400 °C the char yield for EVA under air is a bit lower than in nitrogen, using an oxidative environment for the catalytic process at the same temperature results in a profound increase in the char yield. The char yield for EVA+10% HBeta at 400 °C under nitrogen and air is 8.2 and 39.3 wt%, respectively. The higher char yield of the catalytic process under air is due to the formation of coke and heavy oxygenated intermediates in the presence of the oxidising agent, reducing the catalyst activity profoundly.

[0094] For neat EVA, reducing the temperature causes a rise in tar yield and a reduction in gas yield. At lower temperatures, the cracking of C-C bonds is hindered, producing long-chain hydrocarbons. Also, at a lower temperature, the probability of random chain scission is higher than chain-end scission, causing heavier hydrocarbon formation. However, in the presence of HBeta under nitrogen, reducing the process temperature does not affect the product yields significantly. Further, from the insignificant changes in the CnHmconcentration, it can be concluded that lowering the process temperature to at least 450 °C does not negatively affect EVA-to-gas efficiency under nitrogen. Table 1 gives information about the complete gas composition at lower temperatures, and from Table 1 , it can be seen that under nitrogen, the gas composition is negligibly affected at lower temperatures.

[0095] Table 1 Effect of lowering process temperature on EVA conversion and HBeta catalyst performance under non-oxidative atmosphere (atmosphere=N2, gas flow rate=20 mL / min) Contrary to the nitrogen atmosphere, under air, even in the presence of the catalyst, reducing the temperature unfavourably increases the tar yield. Moreover, under an oxidative condition, the CnHmconcentration drops at lower temperatures for both catalytic and non-catalytic processes. This implies that tar destruction reactions are inhibited under air at a lower temperature, and then less hydrocarbons are generated. Table 2 below shows that lowering the temperatures reduces CnHmconcentration and increases CO concentration, while CO2, H2, and CH4 concentrations are slightly affected.

[0096] Table 2 Effect of lowering process temperature on EVA conversion and HBeta catalyst performance under oxidative atmosphere (atmosphere=Air, gas flow rate=20 mL / min)

[0097] From these results presented in Fig. 6., it can be deduced that while 400 °C is insufficient for EVA full decomposition, the process can be conducted efficiently at 450 °C, providing the environment is kept non-oxidative.

[0098] As discussed, the gas released from the thermocatalytic conversion of EVA is composed of CO, CO2, CH4, H2, and a broad range of hydrocarbons. Due to the low concentration of combustible species and impurities, the quality of the off-gas is improper and cannot be utilised directly as a source of energy or feedstock of a downstream unit. Furthermore, releasing these gases into the atmosphere results in severe environmental repercussions. Thus, the utmost priority is to deal with this issue and convert the off-gas to a product with the least environmental harm. While CO2 is a big environmental threat, it can be considered a feedstock for producing value-added chemicals through chemical processing if harnessed and utilised properly. The following evaluates the effectiveness of using a gas treatment reactor with a reforming catalyst, Pt / AhOs, to convert the emissions mostly to CO2.

[0099] Fig. 7. gives information about the effects of treatment and catalyst weight in the second reactor and its temperature on the gas composition. It should be noted that for all experiments here, the gas generated in the primary reactor from the decomposition of EVA mixed with 10% HBeta under air passes the reforming reactor continuously. Looking at Fig. 7a., comparing with gas composition without any treatment, which consists of 46.8% CO, 1 .9% CH4, 23.4% CO2, 26.5% CnHm, and 1 .5% H2, the employment of the treatment reactor affects the gas composition significantly. When the load of Pt / AhCh is 100 mg, and the temperature of the reforming reactor is kept at 500 °C, the CO and CnHmconcentrations drop to 11.7% and 15.2%, respectively. Also, CO2 and H2 concentrations increase significantly and reach 57.5% and 13.8%, respectively. The changes in CH4 concentration are negligible after the gas treatment.

[0100] It is believed that in the presence of the oxidative catalyst, the CO oxidation (CO + 0.5 O2-> CO2), hydrogen oxidation (H2+ 0.5 O2-> H2O), water-gas shift (CO + H2O CO2+ H2), hydrocarbons oxidation reforming (CnHm+ 2n H2O -> (2n + m / 2) H2+ n CO2) reactions are accelerated. The promotion of CO and H2 oxidation reactions increase the CO2 and H2O concentrations. When H2O increases, the water-gas shift reaction shifts toward products consuming more CO and forming more CO2 and H2. Further, hydrocarbons are depleted in oxidation and reforming reactions, leading to reduced CnHmconcentration and a rise in CO2 and H2. It can be a good explanation for changes in the gas composition after oxidative treatment. Further rise in the load of the reforming catalyst to 200 mg and 300 mg under the same condition does not show significant changes in the gas composition; it merely leads to a marginal reduction in CnHmconcentration and slight increases in CO and CF .

[0101] The catalytic oxidation depends on temperature to a large extent, and it is very limited kinetically if the temperature drops below 250 to 280 °C. Thus, here, the effect of temperature over 300 °C is studied to see how changing temperature can affect gas treatment efficiency. Fig. 7b shows that compared with 500 °C, a rise in the temperature to 600 °C reduces CO2 to 43.2% and increases CO and H2 to 22.8 and 18.1 %, respectively. Also, a rise in temperature leads to a better conversion of hydrocarbons; as a result, CnHm drops. However, when the temperature of the reforming process is reduced, less CO and H2 are produced, and the off-gas consists mainly of CO2 (68.7%) and CnHm(20%) at 300 °C. At 300 °C, CO, CH4, and H2 concentrations are 8, 1 .2, and 2%, respectively. A rise in CO at a higher temperature is due to the promotion of exothermic CO oxidation and water-gas shift reaction in the reverse direction. While H2 is expected to drop at higher temperatures because of its consumption in reverse water-gas shift reaction, the promotion of endothermic hydrocarbon conversion reactions leads to a rise in H2 and reduces CnHm. Also, exothermic H2 oxidation reaction is hindered at a highertemperature, causing more H2 production.

[0102] From these observations, it can be concluded that reducing the reforming process temperature is more favourable for converting the off-gas to CO2. However, if the priority is converting the off-gas to syngas (CO+H2), the reforming process should be performed at higher temperatures.

[0103] While the off-gas after treatment at 300 °C consists mainly of CO2, the presence of 8% CO and 20% hydrocarbons can be considered an unfavourable condition because these species are impurities when CO2 is supposed to be used as a feedstock in the downstream CO2 utilisation units. Thus, the following assesses more approaches for improving the conversion of CnHmand CO to CO2. Fig. 8. indicates the effects of reducing the gas flow rate and increasing oxygen concentration on the off-gas composition following the catalytic treatment. Based on the information from Fig. 8a., lowering the carrier gas flow rate to 10 mL / min increases the CO2 concentration to 76.5% and reduces the CO and CnHmconcentrations to 3 and 16.1 %, respectively. This observation is due to increased gas residence time in the reforming zone when the carrier gas flow rate is reduced. At a higher residence time, more CnHmdestruction is expected, and CO has more time to react with the excess available oxygen, leading to a rise in CO2 and a reduction in CO concentrations. The effects of changing the carrier gas flow rate on H2 and CH4 concentrations are insignificant.

[0104] Fig. 8b. shows what happens to the off-gas composition if the oxygen concentration in the carrier gas is enhanced. As can be seen, increasing the oxygen concentration in the carrier gas causes a rise in the CO2 concentration and reduces the percentage of CnHm. Compared with the condition that air is used as the carrier gas, under diluted oxygen (50% O2), the CO2 rises to 87.4% from 76.5%, and CnHmdrops to 7.4% from 16.1 %. The CO2 and CnHmfor pure oxygen are 95 and 1.9%, respectively. Also, CO, CH4 and H2 drop to 0.8, 0.6, and 2%, respectively, when pure oxygen is replaced with air. Table 3 gives more information about the gas composition under each of these oxidative conditions.

[0105] Table 3 off-gas composition after gas treatment under harsh oxidative condition (Ti=450 °C, T2=350 °C, gas flow rate=10 mL / min, sample= EVA+10% HBeta, catalyst in second reactor= 100 mg Pt / AI2O3)

[0106] Concerning the reasons, it can be mentioned that a rise in the oxygen concentration promotes the partial and complete oxidation reactions of hydrocarbons, leading to a noticeable increase in the amount of generated carbon dioxide. Further, at a higher oxygen availability, carbon monoxide partial combustion and hydrogen combustion reactions are promoted, reducing CO and H2 concentrations.

[0107] The importance of choosing the proper atmosphere for better catalyst performance in the primary reactor has been discussed earlier. As mentioned, regardless of the process temperature, the thermocatalytic conversion of EVA is more efficient (i.e., more gas and less tar) under nitrogen than oxidative conditions. However, as illustrated earlier, if the gas treatment reactor with the reforming catalyst is supposed to be employed due to its advantages, it is necessary to keep the oxygen concentration of the carrier gas as high as possible. This contradictory situation can be addressed satisfactorily if some changes and modifications are applied to running the process. For this purpose, keeping the environment of the primary EVA catalytic conversion non-oxidative may be preferred and mixing the released gas with an oxidative agent (air or oxygen) before passing the gas through the reforming reactor for treatment may also be preferred. This may be found in the process illustrated in Fig. 10.

[0108] EXAMPLES

[0109] The plastic feedstocks used in this study was EVA sheet used in the solar panel structures, and the EVA sheets were used as received. The used EVA sheet contains 28% vinyl acetate based on the technical information provided by the supplier. In this study, three catalysts, HZSM-5, HBeta, and MCM- 41 , are used for the thermocatalytic degradation process, and one catalyst Pt / AhOs is used for downstream off-gas treatment. The HZSM-5 nano zeolite powder (CAS No.: 1318-02-1) with particle size of 250-300 nm, pore size of 5 A0, SiC^ / AhOs ratio of 52, and specific surface area of 362 m2 / g, and Beta zeolite (HBeta, CAS No.: 1318-02-1) with particle size of 20-30 nm, pore size of 0.55-0.7 nm, SiO2 / Al2C>3 ratio of 40, and specific surface area of 500 m2 / g were purchased from ACS material (Pasadena, CA, USA). Aluminosilicate, mesostructured (MCM-41 hexagonal, CAS No.:1318-02-1) with particle size of 4.5-4.8 nm, pore size of 2-4 nm, SiC AhOs ratio of 32, and specific surface area of 900- 1100 m2 / g and platinum 5wt % on alumina (Pt / AhOs powder) were purchased from Sigma-Aldrich. To prepare the EVA / catalysts mixtures, the desired weight ratio was heated at 80 °C for one hr until the EVA had softened sufficiently to stir both components manually to give a homogenous mixture. The blended sample was then cut into small pieces and used for experiments. In all experiments, the weight of EVA is kept constant at 300 mg. For samples containing catalyst, for instance, EVA+5% catalyst, 300 mg EVA is mixed with 15 mg catalyst. For samples with 10% and 20% catalysts, the used catalyst is 30 mg and 60 mg, respectively.

[0110] Pyrolysis experiments were conducted within a quartz tube reactor with a length of 55 cm, an internal diameter of 15 mm, and a wall thickness of 1 mm. The pyrolysis system utilised in this study is visually represented in Fig. 9. A quartz sample holder measuring 8 cm in length and 8 mm in width was employed to load pellets for each experiment. After inserting the sample, the system was sealed and purged with nitrogen for 30 minutes before initiating the experiment. An electric furnace facilitated the heating process with a total length of 25 cm and a heating zone extending 10 cm. A thermocouple was connected to a temperature controller to regulate the temperature. Initially, the system was heated to 150°C within five minutes and maintained at this temperature for an additional five minutes. Subsequently, the sample underwent a controlled heating rate of 20°C per minute until reaching the desired temperature, where it was held for 90 minutes. To collect condensates and tar species produced during the gasification process, the downstream end of the quartz tube was packed with quartz wool. Non-condensable products were directed into a gas bubbler submerged in an ice bath, enabling the recovery of additional volatile organic compounds (VOCs). The gas exiting the bubbler was gathered in a multi-layered Tedlar bag for quantitative analysis using a gas chromatograph (GC). For gas treatment, a quartz tube reactor with a length of 50 cm, an internal diameter of 4 mm, and a wall thickness of 1 mm was used. The heating process was done by an electric furnace, with a length of 30 cm and a heating zone of 10 cm.

[0111] The gas composition of the sample collected in a Tedlar bag was examined offline using a programmable GC (Shimadzu GC-2010) equipped with a methaniser / flame ionisation detector (FID) and a thermal conductivity detector (TCD). The GC employed an HP-PlotQ column with specific dimensions (30 m length, 0.32 mm inner diameter, and 20-micron film thickness). Helium was used as the carrier gas at a flow rate of 20 mL / min. The GC column temperature was initially set at 50 °C for five minutes and then ramped up to 220 °C at a rate of 10 °C / min, where it remained for 10 minutes. The methaniser / FID setup allowed for the detection of gases such as CO, CO2, CH4, C2H4, C2H6, C3H6, CsHs, and heavier hydrocarbons up to C7. Quantification of these species was accomplished through an external standard method, and calibration curves for each component were generated using a premix gas cylinder.

[0112] Additionally, H2 produced during the gasification process was measured separately using a different GC (YL instrument, GC6500) with a CarboPLOT P7 column (25 m length, 0.53 mm diameter, and 25-micron thickness) and a TCD, where argon served as the carrier gas.

[0113] To investigate the thermal decomposition behaviour of both EVA and EVA / catalyst blends, thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) analysis were conducted using a Q5000 instrument from TA Instruments. These tests were performed under both air and nitrogen atmospheres at a constant flow rate of 20 mL / min. The analysis involved heating the samples from room temperature up to 1000 °C at a rate of 20 °C / min, with each sample weighing approximately 15 mg.

[0114] The study here defines gas composition on a volumetric basis and product yields as the performance indicators are described below:

[0115] Ysyngas (mL) — Si Vi — VH2+ Vco+ VCH4+ VC02+ VCtlHmrij =Vix 100

[0116] Vsyngas

[0117] Where Vtotalrepresents the overall gas volume within the Tedlar bag, xj signifies the volume proportion of each gas component (where i can be H2, CO, CH4, CO2, CnHm(where n and m >1)) obtained from calibration curves. V, indicates the quantity of each specific gas present in the Tedlar bag, and Vsytlgasdenotes the amount of produced syngas after excluding nitrogen content, nj is the volumetric concentration of each gas component after removing nitrogen. The total gas volume generated and collected during the process (Vtotal) was determined using an internal helium standard. After the gasification process, a known quantity of helium (VHe) was introduced into the gas bag, and the resulting helium fraction (xHe) was employed to estimate the total gas volume (VHe= xHex Vtotal). To ensure the reliability and reproducibility of the system, selected experiments were randomly duplicated.

[0118] The tar product yield was determined by weighing the collected tar, while the char yield was calculated as the difference in weight of the sample holder before and after gasification. The gas yield was computed using the equations shown below:

[0119] > T ,ar yi .e ild i (wt .% / \) = — weight of collected Tar (mg) . weigh —t o —f th -e samp ,le (mg) x 100 L / \ weight of collected Char (mg) .

[0120] Char yield (wt%) = — weight of the samp ,lez(mg) X 100

[0121] Gas yield (wt%) = 100 — Tar (wt%) — Char (wt%)

[0122] The present invention thus provides an effective method for the thermocatalytic degradation of EVA, such as that found in the encapsulating layers in PV panels. As shown by TGA, the degradation of neat EVA under air was more accelerated, but its overall decomposition finished at a higher temperature than the nitrogen. The use of catalysts mutated the decomposition behaviour of EVA noticeably. Among assessed catalysts, HBeta unexpectedly performed better than its counterparts in reducing Tmax, Tonset and Tend, thus potentially the energy-efficiency of the process. The performance of all catalysts was better under nitrogen than air in increasing the gas / tar ratio of the products. Increasing HBeta loading positively improved EVA degradation, particularly under nitrogen.

[0123] Based on the results presented, regardless of the used atmosphere, the gas emitted from neat-EVA decomposition contained high concentrations of CO and hydrocarbons (over 75 vol%). Tar yields from neat-EVA decomposition under nitrogen was 68.9 wt%. Compared with neat EVA, the use of catalysts affected the gas composition and, most importantly, tar yield, which dropped noticeably (from 68.9 to 26.5 wt%). Again, among the catalysts investigated, HBeta performed better in reducing tar yield and enhancing EVA-to-gas conversion. Further, HBeta showed better efficiency under non-oxidative conditions, and the presence of oxygen inhibited the catalyst performance possibly through the formation of oxygenated intermediates that could block the zeolite pores. Moreover, the HBeta- catalysed EVA decomposition process can be conducted effectively (i.e., fully decomposed) at a lower temperature (450 °C).

[0124] Additionally, treatment of the off-gas from the thermocatalytic degradation of EVA using PVAI2O3 in a separate reactor was an effective approach to mitigate the harmful gas products from upstream EVA’s thermal decomposition. Following the treatment, CO and hydrocarbons were mostly converted, and the gas mainly comprised CO2. The performance of the downstream reactor was almost independent of the catalyst loading while reducing the reactor temperature and the carrier gas flow and increasing the oxygen concentration all led to a noticeable improvement in CO2 concentration (up to 95 %). In conclusion, the present invention illustrates that the HBeta-catalysed gasification of EVA, both with and without oxygen, coupled with off-gas treatment, emerges as a promising and versatile strategy which can not only reduce energy input but also allow for the refinement of product distributions tailored to specific requirements in the recycling and treatment of PV materials.

[0125] Other embodiments of the present invention as described herein are defined in the following paragraphs:

[0126] 1 . A method for thermal degradation of ethylene vinyl acetate (EVA) to a non-condensible gas during photovoltaic device recycling, comprising the step of heating EVA containing material in the presence of a HBeta zeolite.

[0127] 2. The method according to paragraph 1 wherein the temperature of thermal degradation is greater than 400°C.

[0128] 3 The method according to any one or more of the preceding paragraphs wherein the temperature of thermal degradation is less than 500°C.

[0129] 4. The method according to any one or more of the preceding paragraphs wherein the temperature of thermal degradation does not exceed 450°C.

[0130] 5. The method according to any one or more of the preceding paragraphs when carried out under non-oxidative conditions.

[0131] 6. The method according to any one or more of the preceding paragraphs wherein the non- oxidative conditions comprise a nitrogen atmosphere.

[0132] 7. The method according to any one or more of the preceding paragraphs wherein the non- condensible gas is provided in a yield of at least 74% by weight or greater.

[0133] 8. The method according to any one or more of the preceding paragraphs wherein the non- condensible gas comprises CnHmin an amount of 90% or greater by volume.

[0134] 9. The method according to any one or more of the preceding paragraphs wherein the non- condensible gas comprises CO2 in an amount of 5% or less by volume.

[0135] 10. The method according to any one or more of the preceding paragraphs wherein the tar yield is 25% by weight or less.

[0136] 11 . The method according to any one or more of the preceding paragraphs when carried out under oxidative conditions. 12. The method according to any one or more of the preceding paragraphs wherein the oxidative conditions comprise an air atmosphere.

[0137] 13. The method according to any one or more of the preceding paragraphs wherein the noncondensible gas is provided in a yield of at least 45% by weight or greater.

[0138] 14. The method according to any one or more of the preceding paragraphs wherein the noncondensible gas comprises CnHmin an amount of 35% or greater by volume.

[0139] 15. The method according to any one or more of the preceding paragraphs wherein the noncondensible gas comprises CO2 in an amount of 21 % or less by volume.

[0140] 16. The method according to any one or more of the preceding paragraphs wherein the noncondensible gas comprises CO in an amount of 40% or less by volume.

[0141] 17. The method according to any one or more of the preceding paragraphs wherein the tar yield is 55% by weight or less.

[0142] 18. The method according to any one or more of the preceding paragraphs wherein the char yield is about 0% by weight.

[0143] 19. The method according to any one or more of the preceding paragraphs wherein the catalyst is used in an amount of 5-20% by weight based on the amount of EVA.

[0144] 20. The method according to any one or more of the preceding paragraphs wherein the catalyst is used in an amount of 10-20% by weight based on the amount of EVA.

[0145] 21 . The method according to any one or more of the preceding paragraphs wherein the catalyst is used in an amount of greater than 20% by weight based on the amount of EVA.

[0146] 22. The method according to any one or more of the preceding paragraphs further including the step of treating the non-condensible gas with a reforming catalyst under oxidising conditions at an elevated temperature.

[0147] 23. The method according to any one or more of the preceding paragraphs wherein the reforming catalyst is Pt / AI2C>3.

[0148] 24. The method according to any one or more of the preceding paragraphs wherein the oxidising conditions comprise air.

[0149] 25. The method according to any one or more of the preceding paragraphs wherein the oxidising conditions comprise oxygen enhanced air. 26. The method according to any one or more of the preceding paragraphs wherein the oxidising conditions comprise oxygen at 50%-100% by volume.

[0150] 27. The method according to any one or more of the preceding paragraphs wherein the elevated temperature is 250-450°C thereby to produce CO2 28. The method according to any one or more of the preceding paragraphs wherein the elevated temperature is about 300°C

[0151] 29. The method according to any one or more of the preceding paragraphs wherein the elevated temperature is 450°C or above thereby to produce syngas (CO + H2)

[0152] 30. The method according to any one or more of the preceding paragraphs wherein the elevated temperature is about 500°C

Claims

CLAIMS1 . A method for thermal degradation of ethylene vinyl acetate (EVA) to a non-condensible gas during photovoltaic device recycling, comprising the step of heating EVA containing material in the presence of a HBeta zeolite.

2. The method according to claim 1 wherein the temperature of thermal degradation is greater than 400°C.3 The method according to claim 1 wherein the temperature of thermal degradation is less than 500°C.

4. The method according to claim 1 wherein the temperature of thermal degradation does not exceed 450°C.

5. The method according to any one of claims 1 to 4 when carried out under non-oxidative conditions, preferably the non-oxidative conditions comprise a nitrogen atmosphere.

6. The method according to claim 5 wherein the non-condensible gas is provided in a yield of at least 74% by weight or greater.

7. The method according to claim 5 or claim 6 wherein the non-condensible gas comprises CnHmin an amount of 90% orgreater by volume, and / or the non-condensible gas comprises CC>2 in an amount of 5% or less by volume.

8. The method according to any one of claims 5 to 7 wherein the tar yield is 25% by weight or less.

9. The method according to any one of claims 1 to 4 when carried out under oxidative conditions, preferably the oxidative conditions comprise an air atmosphere.

10. The method according to claim 9 wherein the non-condensible gas is provided in a yield of at least 45% by weight or greater.11 . The method according to claim 9 or claim 10 wherein the non-condensible gas comprises CnHmin an amount of 35% orgreater by volume, and / or the non-condensible gas comprises CC>2 in an amount of 21 % or less by volume, and / or the non-condensible gas comprises CO in an amount of 40% or less by volume.

12. The method according to any one of claims 9 to 11 wherein the tar yield is 55% by weight or less.

13. The method according to any one of claims 5 to 12 wherein the char yield is about 0% by weight.

14. The method according to any one of the preceding claims wherein the catalyst is used in an amount of 5-20% by weight based on the amount of EVA, or in an amount of 10-20% by weight based on the amount of EVA, or in an amount of greater than 20% by weight based on the amount of EVA.

15. The method according to any one of the preceding claims further including the step of treating the non-condensible gas with a reforming catalyst under oxidising conditions at an elevated temperature.

16. The method according to claim 15 wherein the reforming catalyst is Pt / AI2C>3.

17. The method according to claim 15 or 16 wherein the oxidising conditions comprise air, preferably oxygen enhanced air.

18. The method according to claim 15 or 16 wherein the oxidising conditions comprise oxygen at 50%- 100% by volume.

19. The method according to claim any one of claims 15 to 18 wherein the elevated temperature is 250-450°C thereby to produce CO2, preferably about 300°C.

20. The method according to any one of claims 15 to 18 wherein the elevated temperature is 450°C or above thereby to produce syngas (CO + H2), preferably about 500°C.

Images