Process for depolymerizing plastics material

Abstract

The present invention relates to a process for depolymerizing plastics material (1), the process comprising: - heating the plastics material (1) to form a plastic melt (3), - processing a pyrolysis feed (8) comprising the plastic melt (3) and an external solvent (5) in a pyrolysis reactor (9) to generate a pyrolysis product (10), - withdrawing a recycling stream (6) from the pyrolysis product (10) and including at least a portion of said recycling stream (6) in the pyrolysis feed (8), wherein the external solvent (5) comprises at least 10 wt% of compounds comprising an n-paraffinic hydrocarbon chain and having a boiling point of at least 285 °C.

Description

[0001] Process for depolymerizing plastics material

[0002] The present invention relates to a process for depolymeri zing plastics material .

[0003] Plastics materials have become integral to both industrial and consumer applications , resulting in the generation of substantial volumes of waste . A signi ficant portion of this waste is incinerated, contributing to the release of large amounts of carbon dioxide ( C02) , which exacerbates the environmental impact and highlights the pressing need for more sustainable recycling methods .

[0004] While mechanical recycling is widely practiced, it has inherent limitations . This process typically involves the physical reprocessing of plastics without altering their chemical structure . Steps such as sorting, cleaning, shredding, melting, and re-extruding are typically employed to convert waste plastics into new products . However, with each recycling cycle , the quality of the plastic deteriorates due to thermal and mechanical stress , leading to a reduction in material properties and ultimately limiting the number of times plastics can be mechanically recycled .

[0005] Chemical recycling has emerged as a promising alternative . Chemical recycling involves breaking down plastics at the molecular level , typically through depolymeri zation, to produce monomers or other valuable chemicals . This method can accommodate mixed or contaminated plastic waste streams that mechanical recycling struggles to handle , and it has the potential to recycle plastics multiple times without signi ficant loss in quality . As a result , chemical recycling represents a key pathway toward closing the loop in plastic waste management .

[0006] One of the primary approaches to chemical recycling is pyrolysis , which involves the thermal decomposition of plastics at high temperatures , typically between 400 and 600 ° C, to produce hydrocarbon products commonly referred to as "pyrolysis oils" , " synthetic crude oils" or " syncrudes" . These pyrolysis oils have a range of potential applications , including the use as alternative fuels or as feedstock for the production of new chemicals and materials . A notable advancement in pyrolysis-based recycling is described in WO 2012 / 149590 Al , which outlines a process where plastics material is melted and mixed with a crude oil fraction as an external solvent . The resulting mixture is then processed in a pyrolysis reactor . The use of an external solvent reduces the viscosity of the mixture , enhancing heat trans fer ef ficiency within the reactor . This reduction in viscosity helps minimi ze temperature gradients across the reactor, thereby reducing the risk of locali zed overheating and coking .

[0007] Nevertheless , despite such developments , there is still an urgent need to develop more ef ficient and economically viable processes for depolymeri zing plastics material , to promote their widespread adoption . Thus , new and improved processes for depolymeri zing plastics material are needed, in particular processes that address at least some of the limitations of the prior art and that enable the ef ficient recycling of plastics material . It is an obj ect of the present invention to provide such processes .

[0008] Therefore , the present invention provides a process for depolymeri zing plastics material , the process comprising :

[0009] - heating the plastics material to form a plastic melt ,

[0010] - processing a pyrolysis feed comprising the plastic melt and an external solvent in a pyrolysis reactor to generate a pyrolysis product ,

[0011] - withdrawing a recycling stream from the pyrolysis product and including at least a portion of said recycling stream in the pyrolysis feed, wherein the external solvent comprises at least 10 wt% compounds comprising an n-paraf finic hydrocarbon chain and having a boiling point of at least 285 ° C .

[0012] The addition of external solvents to plastic pyrolysis feeds , as disclosed in WO 2012 / 149590 Al , was a signi ficant advancement for processes for depolymeri zing plastics material . As used herein, the "external solvent" can also be referred to as "diluent" or "reaction medium" . As mentioned above , the use of an external solvent reduces the viscosity of the pyrolysis feed, enhancing heat trans fer ef ficiency within the reactor, minimi zing temperature gradients across the reactor and reducing the risk of locali zed overheating and coking . As regards the type of external solvent , WO 2012 / 149590 Al suggests using a heavy oil with a content of aromatic hydrocarbons of at least 25% .

[0013] In the context of the present invention, it was surprisingly found that while the viscosity-reducing ef fects sought after in WO 2012 / 149590 Al can be achieved with a variety of di f ferent solvents , the ef ficiency of these processes can be improved by selecting speci fic types of solvents , that are not typically used in such processes . Speci fically, it was found that when the external solvent comprises compounds with n-paraf finic hydrocarbon chains and boiling points of at least 285 ° C, the consumption of the external solvent can be signi ficantly reduced, making the overall process more ef ficient and more economical .

[0014] According to the inventor, without wishing to be bound to a particular theory, this reduced consumption of external solvent is due to the fact that n-paraf finic compounds are more stable under pyrolysis conditions than iso-paraf finic or even olefinic or aromatic compounds . Thus , in a process that involves a recycling stream from the pyrolysis product to the pyrolysis feed, such compounds can remain in circulation longer, and even accumulate in circulation, thus reducing the amount of fresh external solvent that has to be added to the process .

[0015] During the pyrolysis of plastics materials , the decomposition typically occurs through radical mechanisms or p-elimina- tion, leading to the formation of smaller molecular fragments . The chain scission preferentially occurs at branch points or other energetically favorable positions within the polymer , p- elimination results in the removal of hydrogen (H2) and the formation of double bonds , which can further react to form dienes , polyenes , and ultimately aromatic compounds . As a result of this process , compounds can undergo progressive aromati zation, eventually forming highly condensed aromatic systems , such as asphaltenes . Under conditions of prolonged thermal exposure , these systems can lose additional side chains , leaving behind a pure carbon framework, commonly referred to as coke .

[0016] The inventive process exploits the stability of n-paraf finic compounds in comparison to iso-paraf finic, olefinic, and aromatic compounds . In the case of n-paraf finic hydrocarbon chains , the absence of branching reduces the likelihood of cracking through p-elimination, as this process is energetically less favorable in straight-chain hydrocarbons . On the other hand, isoparaf finic compounds , with their branched structures , are more prone to crack at the branch points , generating radicals that can propagate further decomposition .

[0017] Olefinic compounds , due to their unsaturation, are even more reactive under pyrolysis conditions . They are already one step closer to coke formation than paraf finic compounds . In particular, they can undergo cycli zation reactions , such as Diels-Alder reactions , resulting in the formation of ring structures . These rings , particularly cyclohexadienes , are often thermally and kinetically unstable and can further decompose , releasing hydrogen or breaking of f side chains . The continued aromati zation of these systems reduces the hydrogen content while increasing the carbon content , ultimately leading to the formation of coke .

[0018] Compared to olefinic compounds , aromatic compounds are yet another step closer to coke formation . Additionally, they can lead to the formation of phenyl and benzyl radicals . Phenyl radicals are highly reactive , while benzyl radicals exhibit resonance stabili zation, making them more stable . The presence of these aromatic radicals can promote the formation of polyaromatic structures , which, under the high-temperature conditions typical of cracking processes , can lead to the accumulation of coke .

[0019] For these reasons it was found that when the external solvent contains a higher proportion of n-paraf finic compounds , a greater amount of the external solvent can withstand the pyrolysis conditions and remain in the process through the recycling stream . In this context , it is particularly advantageous i f the n-paraf finic compounds have a high boiling point , as this facilitates separating them from lighter cracking products , which can be obtained as the desired end product of the process in the form of synthetic crude oil . The n-paraf finic compounds can accumulate within the recycling stream, continuing to function similarly to the external solvent , thereby reducing solvent consumption and enhancing process ef ficiency .

[0020] As mentioned above , WO 2012 / 149590 Al suggests using heavy oils having high contents of aromatic compounds as external solvents . However, in contrast to the teaching of

[0021] WO 2012 / 149590 Al , it was found in the context of the present invention that low aromatic contents can of fer signi ficant advantages . More speci fically, for the reasons outlined above , it was found that reducing the content of aromatic compounds can lead to higher stability of the external solvent under pyrolysis conditions and signi ficantly reduce coke formation .

[0022] Additionally, it was found that when the plastics material used as a feedstock contains high amounts of polyolefins , in particular polyethylene and / or polypropylene , using an external solvent with a low aromatic content can be better suited for solubili zing these polymers . Without wishing to be bound to a particular theory, the inventor speculates that when the external solvent is more aliphatic in nature , it is chemically more similar to polyolefins and therefore better at solubili zing them, leading to an overall more ef ficient process .

[0023] Therefore , it is preferred that the external solvent comprises less than 35 wt% aromatic compounds , preferably less than 25 wt% , more preferred less than 20 wt% , more preferred less than 15 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred less than 3 wt% , more preferred less than 2 wt% , more preferred less than 1 wt% . Preferably, the content of aromatic compounds is determined according to ASTM D6591- 19 or ASTM D5134-21 , especially ASTM D6591- 19 .

[0024] It is further preferred preferred that the external solvent comprises at least 20 wt% , preferably at least 40 wt% , more preferred at least 60 wt% , more preferred at least 80 wt% compounds comprising an aliphatic hydrocarbon chain . As mentioned above , aliphatic hydrocarbons are chemically more similar to polyolefins and therefore particularly well suited for feedstocks of plastics material containing high amounts of polyolefins .

[0025] Preferably, the external solvent has a Conradson Carbon Residue ( CCR) of less than 15 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred less than 2 wt% , more preferred less than 1 wt% , more preferred less than 0 . 5 wt% . Providing an external solvent with a lower CCR reduces the amount of coke formation within the process, decreasing maintenance costs and increasing the efficiency of the process.

[0026] For the reasons outlined above, it has been found to be highly advantageous, when the external solvent comprises n- paraffinic compounds, as such compounds are better able to withstand the conditions during pyrolysis and remain in circulation for a longer period of time, thus reducing consumption of the external solvent. Of note, already moderate amounts, such as 10 wt%, of compounds comprising n-paraffinic hydrocarbon chains are highly advantageous, as it was found that due to their stability under pyrolysis conditions, these compounds can accumulate in the recycling stream, so that their concentration in the pyrolsis feed increases over time. Nevertheless, these advantageous effects are even more pronounced when higher amounts of such compounds are present. Therefore, the external solvent comprises at least 10 wt% compounds comprising an n-paraffinic hydrocarbon chain, preferably at least 15 wt%, more preferred at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%. As used herein, the wt% are based on the total weight of the external solvent, i.e., the external solvent comprises at least X wt% compounds comprising an n- paraffinic hydrocarbon chain based on the total weight of the external solvent.

[0027] As also mentioned above, it is highly preferred that the compounds comprising an n-paraffinic hydrocarbon chain have a high boiling point. This allows easily separating said compounds from shorter chain hydrocarbons obtained from depolymerizing the plastics material, which may be collected as the end product of the process in the form of synthetic crude oil. In this way, the compounds comprising an n-paraffinic hydrocarbon chain can be preferentially kept in the process as part of the recycling stream.

[0028] Therefore, the compounds comprising an n-paraffinic hydrocarbon chain have a boiling point of at least 285 °C, preferably at least 315 °C, more preferred at least 340 °C, more preferred at least 365 °C, more preferred at least 390 °C, more preferred at least 410 °C, more preferred at least 430 °C. Thus, preferably, the external solvent comprises at least 10 wt%, preferably at least 15 wt%, more preferred at least 20 wt%, more preferred at least 30 wt%, more preferred at least

[0029] 40 wt%, more preferred at least 50 wt% compounds comprising an n-paraffinic hydrocarbon chain, wherein said compounds have a boiling point of at least at least 285 °C, preferably at least

[0030] 315 °C, more preferred at least 340 °C, more preferred at least

[0031] 365 °C, more preferred at least 390 °C, more preferred at least

[0032] 410 °C, more preferred at least 430 °C. For clarification, this does not exclude that in addition to the indicated wt% of such compounds, the external solvent may also comprise further n- paraffinic compounds having lower boiling points.

[0033] On the other hand, it is preferred that the compounds comprising an n-paraffinic hydrocarbon chain have a boiling point that is not too high. It was found that when the external solvent comprises a larger proportion of lighter compounds, it can have a better solubilizing effect. Without wishing to be bound to a particular theory, it is assumed that smaller solvent molecules may diffuse more easily into the plastic polymers and disrupt the interactions therein through intercalation.

[0034] Therefore, it is preferred that the compounds comprising an n-paraffinic hydrocarbon chain have a boiling point of at most 800 °C, more preferred at most 750 °C, more preferred at most 700 °C, more preferred at most 650 °C, more preferred at most 600 °C. Preferably, the compounds comprising an n-paraffinic hydrocarbon chain have a boiling point between 285 °C and 800 °C, more preferred between 340 °C and 775 °C, more preferred between 365 °C and 750 °C, more preferred between 390 °C and 700 °C, more preferred between 410 °C and 650 °C, more preferred between 430 °C and 600 °C.

[0035] In a preferred embodiment, the compounds comprising an n- paraffinic hydrocarbon chain have an n-paraffinic C16+- hydrocarbon chain, preferably n-paraffinic Cl 8+-hydrocarbon chain, more preferred an n-paraffinic C20+-hydrocarbon chain, more preferred an n-paraffinic C22+-hydrocarbon chain. For the reasons mentioned above, providing heavier compounds having longer hydrocarbon chains allows to more easily keep these compounds in the process as part of the recycling stream. On the other hand, for ensuring a particularly good solubilization, as explained above, it is preferred that the hydrocarbon chains are not too long. Therefore, the compounds comprising an n-paraffinic hydrocarbon chain preferably have an n-paraffinic Cl 6-C12 O-hydrocarbon chain, preferably an n- paraffinic Cl 8-C8 O-hydrocarbon chain, more preferred an n- paraffinic C20-C65-hydrocarbon chain. Thus, preferably, the external solvent comprises at least 10 wt%, preferably at least 15 wt%, more preferred at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt% compounds comprising an n-paraffinic Cl 6-C120-hydrocarbon chain, preferably an n-paraffinic Cl 8-C80-hydrocarbon chain, more preferred an n-paraffinic C20-C65-hydrocarbon chain. For clarification, this does not exclude that in addition to the indicated wt% of such compounds, the external solvent may also comprise further compounds having shorter or longer n-paraffinic hydrocarbon chains .

[0036] In the context of the inventive process, any suitable types of compounds comprising n-paraffinic hydrocarbon chains may be used. Preferably, the compounds comprising an n-paraffinic hydrocarbon chain are selected from n-paraffins, aliphatic carboxylic acids, aliphatic alcohols, and derivatives thereof. Aliphatic carboxylic acids may include fatty acids and waxy acids, preferaby having chain lengths as defined above. Similarly, aliphatic alcohols may include fatty alcohols and waxy alcohols, preferaby having chain lengths as defined above. Suitable types of derivates include, but are not limited to, esters, amides, anhydrides and ethers. It is particularly preferred that the compounds comprising an n-paraffinic hydrocarbon chain are n-paraffins. As used herein, "n-paraffins" may also be referred to as "n-alkanes".

[0037] For the reasons outlined above, it is preferred that the external solvent comprises a high amount of paraffinic compounds, especially compared to olefinic and aromatic compounds. While n- paraffinic compounds are particularly preferred, any types of paraffinic compounds can provide advantages over conventional solvents typically used in plastic pyrolysis processes, which are often highly aromatic. Therefore, it is preferred that the external solvent comprises at least 20 wt% compounds comprising a paraffinic hydrocarbon chain, preferably at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred at least 98 wt%, more preferred at least 99 wt%, more preferred 100 wt%.

[0038] All embodiments specified above for the compounds comprising an n-paraffinic hydrocarbon chain are also preferred for the compounds comprising a paraffinic hydrocarbon chain. Thus, preferably, the compounds comprising a paraffinic hydrocarbon chain have a boiling point of at least 285 °C, preferably at least 315 °C, more preferred at least 340 °C, more preferred at least 365 °C, more preferred at least 390 °C, more preferred at least 410 °C, more preferred at least 430 °C. Preferably, the compounds comprising a paraffinic hydrocarbon chain have a boiling point of at most 850 °C, preferably at most 800 °C, more preferred at most 750 °C, more preferred at most 700 °C, more preferred at most 650 °C, more preferred at most 600 °C. Preferably, the compounds comprising a paraffinic hydrocarbon chain have a boiling point between 285 °C and 850 °C, more preferred between 315 °C and 850 °C, more preferred between 340 °C and 800 °C, more preferred between 365 °C and 750 °C, more preferred between 390 °C and 700 °C, more preferred between 410 °C and 650 °C, more preferred between 430 °C and 600 °C.

[0039] In a preferred embodiment, the compounds comprising a paraffinic hydrocarbon chain have a paraffinic Cl 6+-hydrocarbon chain, preferably a paraffinic Cl 8+-hydrocarbon chain, more preferred a paraffinic C20+-hydrocarbon chain, more preferred a paraffinic C22+-hydrocarbon chain. The compounds comprising a paraffinic hydrocarbon chain preferably have a paraffinic C16- C120-hydrocarbon chain, preferably a paraffinic C18-C80- hydrocarbon chain, more preferred a paraffinic C20-C65- hydrocarbon chain.

[0040] Preferably, the compounds comprising a paraffinic hydrocarbon chain are selected from paraffins, fatty acids, fatty alcohols, and derivatives thereof. Suitable types of derivates include, but are not limited to, fatty acid esters, fatty ester amides, fatty acid anhydrides, and fatty acid ethers . While it is preferred that the external solvent comprises a high amount of paraffinic compounds, n-paraffinic compounds are preferred over iso-paraffinic compounds, for the reasons specified above. In particular, their branched structures make isoparaffinic compounds more prone to radical formation and thus to breakdown under pyrolysis conditions. Therefore, it is preferred that the external solvent comprises less than 60 wt%, preferably less than 50 wt%, more preferred less than 40 wt%, more more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% compounds comprising an iso-paraffinic hydrocarbon chain. It is particularly preferred that the external solvent comprises less than 60 wt%, preferably less than 50 wt%, more preferred less than 40 wt%, more more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% iso-paraffins.

[0041] In a preferred embodiment, the external solvent contains compounds comprising an n-paraffinic hydrocarbon chain and compounds comprising an iso-paraffinic hydrocarbon chain at a mass ratio of at least 1:1, more preferred at least 2:1, more preferred at least 4:1, more preferred at least 6:1, more preferred at least 8:1, more preferred at least 10:1.

[0042] As outlined above, it has been found in the context of the invention that olefinic compounds contained in the external solvent can be more prone to unfavorable reactions under pyrolysis conditions than paraffinic compounds. On the one hand, double bonds can stabilize radicals and thus promote radical formation. On the other hand, they can lead to diene formation and undergo cyclization reactions resulting in the formation of ring structures and ultimately leading to the formation of coke.

[0043] Therefore, it is preferred that the external solvent comprises less than 60 wt%, preferably less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% compounds comprising an olefinic hydrocarbon chain. Preferably, the external solvent comprises less than 60 wt%, preferably less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% olefins.

[0044] In a preferred embodiment, the external solvent contains compounds comprising a paraffinic hydrocarbon chain and compounds comprising an olefinic hydrocabon chain at a mass ratio of at least 1:1, more preferred at least 2:1, more preferred at least 4:1, more preferred at least 6:1, more preferred at least 8:1, more preferred at least 10:1. It is especially preferred that the mass ratio between compounds comprising an n-paraffinic hydrocarbon chain and compounds comprising an olefinic hydrocabon chain is at least 1:1, more preferred at least 2:1, more preferred at least 4:1, more preferred at least 6:1, more preferred at least 8:1, more preferred at least 10:1.

[0045] Preferably, the external solvent has a bromine number of less than 100 g Br2 / 100 g, more preferred less than 90 g Br2 / 100 g, more preferred less than 80 g Br2 / 100 g, more preferred less than 70 g Br2 / 100 g, more preferred less than 60 g Br2 / 100 g, more preferred less than 50 g Br2 / 100 g, less than 40 g Br2 / 100 g, more preferred less than 30 g Br2 / 100 g, more preferred less than 20 g Br2 / 100 g, more preferred less than 15 g Br2 / 100 g, more preferred less than 10 g Br2 / 100 g, more preferred less than 5 g Br2 / 100 g, more preferred less than 3 g Br2 / 100 g, more preferred less than 2 g Br2 / 100 g, more preferred less than 1 g Br2 / 100 g, more preferred less than 0.5 g Br2 / 100 g. The bromine number, preferably determined according to ASTM D1159-07 (2017 ) , can be considered as a sum parameter for all unsaturated components contained in the external solvent.

[0046] In addition to the above-described advantageous effects of the n-paraffinic compounds contained in the external solvents having a high boiling point, it was found to also be advantageous when the external solvent as a whole has a high boiling range. When the external solvent has a higher boiling range, less pressure is required to keep the solvent liquid at high temperatures. Thus, a higher boiling range of the external solvent allows keeping the process pressure lower, increasing safety and reducing the demands on the equipment used.

[0047] Therefore, in a preferred embodiment, the external solvent has a boiling range with an IBP (initial boiling point) of at least 150 °C, preferably at least 180 °C.

[0048] It is further preferred that the external solvent has a boiling range with an FBP (final boiling point) of at most 800 °C, more preferred at most 750 °C, more preferred at most 700 °C, more preferred at most 650 °C, more preferred at most 600 °C.

[0049] Moreover, it is preferred that the external solvent has a boiling range with a T10 (temperature at 10% volume distilled) of at least 200 °C, more preferred at least 225 °C, more preferred at least 250 °C, more preferred at least 275 °C. Preferably the T10 is between 200 °C and 500 °C, more preferred between 225 °C and 400 °C, more preferred between 250 °C and 300 °C.

[0050] It is further preferred that the external solvent has a boiling range with a T50 (temperature at 50% volume distilled) of at least 285 °C, more preferred at least 315 °C, more preferred at least 350 °C, more preferred at least 380 °C, more preferred at least 400 °C. Preferably the T50 is between 285°C and 600 °C, more preferred between 315 °C and 600 °C, more preferred between 350 °C and 550 °C, more preferred between 380 °C and 500 °C, more preferred between 400 °C and 450 °C.

[0051] It is further preferred that the external solvent has a boiling range with a T90 (temperature at 90% volume distilled) of at most 850 °C, more preferred at most 750 °C, more preferred at most 650 °C, more preferred at most 600 °C. Preferably, the T90 is between 350 °C and 850 °C, more preferred between 375 °C and 750 °C, more preferred between 400 °C and 650 °C, more preferred between 430 °C and 600 °C.

[0052] In a further preferred embodiment, the external solvent has a Hydrogen / Carbon (H / C) ratio of at least 0.10, preferably at least 0.12, more preferred at least 0.14, more preferred at least 0.15, more preferred at least 0.16, more preferred at least 0.17. As used herein, the H / C ratio refers to the ratio of the external solvent's hydrogen content in wt% divided by the carbon content in wt%. A higher H / C ratio thus indicates a higher proportion of hydrogen relative to carbon. This was found to be advantageous, as in this case higher amounts of hydrogen are available during cracking, which can improve pyrolsis and reduce coke formation. A high H / C ratio can be achieved, e.g. by limiting the amount of unsaturated hydrocarbons in the external solvents. Preferably, the external solvent has an H / C ratio between 0.10 and 0.20, more preferred between 0.12 and 0.19, more preferred between 0.14 and 0.19, more preferred between 0.15 and 0.19, more preferred between 0.16 and 0.19, more preferred between 0.17 and 0.18.

[0053] The plastics material used in the inventive process preferably comprises polyethylene (PE) , polypropylene (PP) , polystyrene (PS) , polyvinyl chloride (PVC) , polyethylene terephthalate (PET) , polyamide (PA) , styrene acrylonitrile (SAN) and / or acrylonitrile butadiene styrene (ABS) . Preferably, the plastics material may be plastic waste, especially pre-consumer, post-consumer and / or post-industrial plastics. Preferably, the plastics material comprises polyolefins, preferably selected from polyethylene and polypropylene, and / or polystyrene.

[0054] The inventive process has been found to be particularly well suited for recycling polyolefin (PO) -based plastics material. In particular, it has been found that when the external solvent contains a high amount of paraffinic compounds, PO-based plastics material can be particularly well solubilized. Thus, it is preferred that the plastics material comprises PO, preferably selected from PE and / or PP. Preferably, the plastics material comprises at least 20 wt% PO, more preferred at least 50 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%.

[0055] In the inventive process, the plastics material is heated to form a plastic melt, wherein the pyrolysis feed comprises the plastic melt. Preferably, the plastics material is heated in a mixer, especially in an extruder. This allows the subsequent pyrolysis to be carried out more energy-ef f iciently and in a shorter amount of time. In the mixer, especially the extruder, the plastics material can preferably also be degassed. This allows producing a uniform mass without gas inclusions, ensuring that a homogeneous pyrolysis product can be obtained through the subsequent pyrolysis.

[0056] Preferably, the plastics material is heated to a temperature of at least 80 °C to form the plastic melt, preferably at least 100 °C. Preferably, the plastics material is heated to a temperature between 80 °C and 450 °C, more preferred between 100 °C and 350 °C. Preferably, the plastics material is heated to the said temperature at a pressure of 10 to 30 bar, preferably 15 to 25 bar.

[0057] In a preferred embodiment, the pyrolysis feed contains the plastic melt and the external solvent at a weight ratio of between 1:1 and 200:1, more preferred between 2.5:1 and 100:1, more preferred between 5:1 and 20:1 (plastic melt : external solvent) . It has been found that providing such a ratio between the plastic melt and the external solvent allows to effectively solubilize the plastic melt and decrease the viscosity of the pyrolysis feed.

[0058] Similarly, it is further preferred that the pyrolysis feed contains the external solvent and the recycling stream at a weight ratio of between 1:2000 and 1:10, more preferred between 1:1500 and 1:20 (external solvent : recycling stream) .

[0059] In a preferred embodiment of the inventive process, the external solvent is mixed with the recycling stream to form a diluent stream, wherein said diluent stream is added to the plastic melt .

[0060] At the timepoint when the diluent stream is added to the plastic melt, the plastic melt preferably has a temperature of at least 80 °C, preferably at least 120 °C, more preferred at least 150 °C, more preferred at least 200 °C. Preferably, the plastic melt has a temperature between 80 °C and 450 °C, preferably between 120 °C and 450 °C, more preferred between 150 °C and 400 °C, more preferred between 200 °C and 350 °C. Alternatively or in addition, the diluent stream can preferably be heated to a temperature of at least 80°C, preferably at least 120°C, more preferred at least 150 °C, more preferred at least 200 °C before being added to the plastic melt. Preferably the diluent stream has a temperature between 80 °C and 450 °C, preferably between 120 °C and 450 °C, more preferred between 150 °C and 400 °C, more preferred between 200 °C and 350 °C. By increasing the temperature of the plastic melt and / or the diluent stream, the mixing can proceed more quickly and efficiently. This can also allow the subsequent pyrolysis to be carried out more efficiently. In a preferred embodiment, the plastics material is depolymerized in the pyrolysis reactor at a temperature of at least 360 °C. However, even higher temperatures may be preferred to allow for more efficient and / or faster depolymerization. Thus, it is preferred if the plastics material is depolymerized at a temperature of at least 400 °C, more preferred at least 440 °C. Preferably the plastics material is depolymerized at a temperature between 360 °C and 510 °C, more preferred between 400 °C and 500 °C, more preferred between 440 °C and 480 °C.

[0061] The depolymerization of the plastics material may be by thermal cracking, without the addition of a catalyst, and / or by catalytic cracking. Thermal cracking is preferred. The depolymerization can be carried out under a substantially oxygen-free atmosphere, particularly under an inert atmosphere, such as under nitrogen. By limiting or excluding oxygen, complete combustion can be prevented more effectively.

[0062] In a preferred embodiment of the inventive process, the pyrolysis product is separated into a heavy product and a light product, preferably wherein the recycling stream is withdrawn from the heavy product.

[0063] The pyrolysis product may be separated into the heavy product and the light product using any suitable method known to the skilled person. For instance, it may be separated in a separation vessel, preferably wherein the separation vessel is a liquid-gas separation vessel, especially a cyclone. A particularly suitable type of separation vessel is disclosed in WO 2023 / 036751 Al.

[0064] Preferably, the light product has a boiling range with an FBP (final boiling point) below 250 °C, more preferred below 230 °C, more preferred below 210 °C. However, it is also preferred that the FBP is not too low, as this may reduce the amount of the final hydrocarbon product obtained through the process. Therefore, the light product preferably has a boiling range with a FBP above 150 °C, more preferred above 170 °C, more preferred above 190 °C. It is particularly preferred, if the light product has a boiling range with a FBP between 150 and 250 °C, more preferred between 170 and 230 °C, more preferred between 190 and 210 °C. The heavy product preferably has a boiling range with an IBP (initial boiling point) of at most 250 °C, more preferred at most 230 °C, more preferred at most 210 °C. Preferably, the IBP is between 150 °C and 250 °C, more preferred between 170 °C and 230 °C, more preferred between 190 °C and 210 °C. Similarly, it is preferred that the heavy product has a boiling range with an T10 (temperature at 10% volume distilled) of at most 250 °C, more preferred at most 230 °C, more preferred at most 210 °C. Preferably, the T10 is between 150 °C and 250 °C, more preferred between 170 °C and 230 °C, more preferred between 190 °C and 210 °C. When the heavy product has a boiling range with such a low IBP and / or T10, this helps ensure that a large proportion of compounds originating from the external solvent that survive the pyrolysis conditions, especially of the compounds comprising an n-paraffinic hydrocarbon chain, end up in the heavy product. This is particularly advantageous when the recycling stream is withdrawn from the heavy product, because in this case, a larger proportion of these compounds remains in circulation, reducing external solvent consumption.

[0065] For the same reasons, the recycling stream preferably has a boiling range with an IBP (initial boiling point) of at most 250 °C, more preferred at most 230 °C, more preferred at most 210 °C. Preferably, the IBP is between 150 °C and 250 °C, more preferred between 170 °C and 230 °C, more preferred between 190 °C and 210 °C. Similarly, it is preferred that the recycling stream has a boiling range with an T10 (temperature at 10% volume distilled) of at most 250 °C, more preferred at most 230 °C, more preferred at most 210 °C. Preferably, the T10 is between 150 °C and 250 °C, more preferred between 170 °C and 230 °C, more preferred between 190 °C and 210 °C. As explained above, this helps ensure that the recycling stream can comprise a large proportion of compounds originating from the external solvent having survived the pyrolysis conditions.

[0066] Unless specified otherwise, all parameters as used herein correspond to parameters at IUPAC SATP-conditions („Standard Ambient Temperature and Pressure") , in particular a temperature of 25 °C and a pressure of 101.300 Pa.

[0067] Percentages (indicated as "%", "wt%" and the like) as used herein correspond to weight per weight (w / w) unless specified otherwise . Similarly, ratios used herein correspond to weight ratios (w / w) unless speci fied otherwise .

[0068] References to percentages of a given component in any composition refer to the weight percent relative to the total weight of the respective composition unless speci fied otherwise . Thus , when it is speci fied that a certain composition comprises X wt% compound A, this means that compound A constitutes X wt% of said composition, i . e . , that said composition contains X wt% compound A based on the total weight of said composition . For instance , i f it is stated that "the external solvent comprises at least 10 wt% compounds comprising an n-paraf finic hydrocarbon chain" , this means that compounds comprising an n-paraf finic hydrocarbon chain constitute at least 10 wt% of the external solvent .

[0069] As used herein, the phrase "at least a portion of" or similar phrases refer to any subset of a speci fied material , component , or stream, which may include part or all of the speci fied entity . This definition is intended to encompass not only partial quantities but also the entirety of the material , component , or stream in question . Consequently, whenever "at least a portion of" a stream or other entity is mentioned, it is also preferred to use the entire stream or entity . For instance , when it is mentioned that at least a portion of the recycling stream is included in the pyrolysis feed, it is also preferred that the recycling stream ( as a whole ) is included in the pyrolysis feed .

[0070] As used herein, the term "compounds comprising an n-paraffinic hydrocarbon chain" preferably refers to chemical entities that include at least one unbranched, saturated alkyl chain . Such compounds are herein also referred to as "n-paraf finic compounds" . In addition, the "compounds comprising an n-paraf finic hydrocarbon chain" can also be referred to as "compounds comprising a linear alkyl group" . Preferably, these compounds comprise a linear C12+-alkyl group, preferably a linear C14+-alkyl group, more preferred a linear C16+-alkyl group, more preferred a linear C18+-alkyl group .

[0071] Similarly, the term "compounds comprising an iso-paraf finic hydrocarbon chain" preferably refers to chemical entities that include at least one branched, saturated alkyl chain . Such compounds are herein also referred to as " iso-paraf finic compounds". In addition, the "compounds comprising an iso-paraf- finic hydrocarbon chain" can also be referred to as "compounds comprising a branched alkyl group". Preferably, these compounds comprise a branched C12+-alkyl group, preferably a branched C14+-alkyl group, more preferred a branched C16+-alkyl group, more preferred a branched C18+-alkyl group.

[0072] The term "paraffinic hydrocarbon chain", as used herein, preferably encompasses both n-paraffinic and iso-paraffinic hydrocarbon chains. Compounds comprising a paraffinic hydrocarbon chain may also be referred to as "paraffinic compounds".

[0073] The term "olefinic hydrocarbon chain", as used herein, preferably refers to a hydrocarbon chain containing at least one carbon-carbon double bond (C=C) . Compounds comprising an olefinic hydrocarbon chain may also be referred to as "olefinic compounds" .

[0074] Any hydrocarbon chain referred to herein, such as an n-par- affinic-, iso-paraffinic-, paraffinic-, or olefinic hydrocarbon chain, preferably refers to a hydrocarbon chain comprising at least 12 carbon atoms, preferably at least 14, more preferred at least 16, more preferred at least 18 carbon atoms.

[0075] As used herein, the term "Cx-hydrocarbon chain" refers to hydrocarbon chains having the number of carbon atoms represented by the number "x". The term "Cx+-hydrocarbon chain" refers to hydrocarbon chains having x or more carbon atoms. The term "Cx- Cy-hydrocarbon chain" refers to hydrocarbon chains having from x to y carbon atoms. Thus, for instance, a "Cl 6+-hydrocarbon chain" refers to a hydrocarbon chain having at least 16 carbon atoms, i.e., an alkyl group having at least 16 carbon atoms. A "Cl 6-C12 O-hydrocarbon chain" refers to a hydrocarbon chain having from 16 to 120 carbon atoms, i.e., an alkyl group having from 16 to 120 carbon atoms.

[0076] Carbon number distributions referred to herein are preferably determined according to ASTM D5442-17 (2021 ) , unless specified otherwise.

[0077] Pressures given in "bar" indicate absolute pressures ("bara") , unless specified otherwise.

[0078] Quantities given in "ppm" refer to parts per million on a weight basis (ppmw) , unless indicated otherwise. Thus, 1 ppm as used herein corresponds to 0.0001 wt%.

[0079] Boiling ranges mentioned herein are preferably determined according to ISO 3924:2019, in particular, Procedure A or Procedure B as defined in said standard, or ASTM D86-23ae; preferably ASTM D86-23ae.

[0080] Contents of aromatic compounds are preferably determined according to the standard ASTM D6591-19. Alternatively or in addition, they can also be determined according to ASTM D5134- 21.

[0081] Conradson Carbon Residue (CCR) , as specified herein, is preferably determined according to ISO 10370:2014 or ASTM D189- 06(2019) , preferably ASTM D189-06(2019) .

[0082] Bromine numbers, as specified herein, are preferably determined according to ASTM D1159-07 (2017 ) .

[0083] Hydrogen / carbon (H / C) ratios, as specified herein, are preferably determined as the ratio of the hydrogen wt% and the carbon wt%, wherein the hydrogen and carbon wt% are preferably determined according to ASTM D5291-21.

[0084] Figure 1 shows a process flow diagram of an embodiment of the process for depolymerizing plastics material.

[0085] Figure 2 shows a thermogravimetric analysis (TGA) of vegetable oils.

[0086] Figure 3 shows a TGA of plastics polymers.

[0087] In the embodiment shown in Figure 1, plastics material 1 is supplied to an extruder 2, in which the plastics material is compacted, molten and / or degassed. The resulting plastic melt 3 is mixed with a diluent stream 4, which comprises an external solvent 5, and a recycling stream 6 comprising a fraction of depolymerized plastics material. The external solvent 5 comprises at least 10 wt% compounds comprising an n-paraffinic hydrocarbon chain and having a boiling point of at least 285 °C. The plastic melt 3 is mixed with the diluent stream 4 in a static mixer 7 to form a pyrolysis feed 8. The pyrolysis feed 8 is processed in a pyrolysis reactor 9 at a temperature between 360 °C and 510 °C, whereby the plastics material 1 contained in the pyrolysis feed 8 is depolymerized through thermal cracking, yielding a pyrolysis product 10. At least a portion of the compounds comprising an n-paraffinic hydrocarbon chain remain intact under the conditions in the pyrolysis reactor 9 and are found in unaltered form in the resulting pyrolysis product 10.

[0088] Next, the pyrolysis product 10 is conveyed to a separation vessel 11, wherein the pyrolysis product 10 is separated into a heavy product 12 and a light product 13. The light product 13 may be post-treated, e.g., by washing and / or hydrotreating, and may be used as a synthetic crude oil for further applications such as the production of alternative fuels or new chemicals and materials. The heavy product 12 comprises the compounds comprising an n-paraffinic hydrocarbon chain that withstood the pyrolysis process. At least a part of the heavy product 12 comprising these compounds is withdrawn as the recycle stream 6, which is recycled and added to the plastic melt 3 as part of the diluent stream 4. In this way, the compounds comprising n-paraffinic hydrocarbon chains originating from the external solvent 5 accumulate in the recycle stream 6 over time, reducing the amount of external solvent 5 that needs to be supplied to the process.

[0089] Example 1: Stability of n-paraffins and iso-paraffins under pyrolysis conditions.

[0090] Experiments were conducted to investigate the stability of different types of paraffins under pyrolysis conditions. Specifically, the stability of different n-paraffins and iso-paraffins was tested. As n-paraffins, octadecane and icosane were tested. As iso-paraffins, pristane and squalane were tested. To simulate cracking conditions , a stainless-steel reactor with a glass inlet was filled with 10 g of the desired compound . The reactor was flushed three times with N2and was disposed with 5 bar N2pressure at room temperature . The reactor was heated to 460 ° C for 1 h (heating rate 250 ° C / h) , then cooled to room temperature and the overpressure was released . All phases were separated ( liquid, solid) , balanced for the yield factors and analyzed .

[0091] The following mass balances were obtained based on 10 g starting material :

[0092] Additionally, as a further stability parameter, the bromine number of the liquid phases was measured . A higher bromine number is indicative of a higher content of double bonds or reactive aromatic compounds formed under pyrolysis conditions .

[0093] The above results demonstrate the n-paraffins octadecane and ico- sane were significantly more stable under pyrolysis conditions than the iso-paraffins pristane and squalane .

[0094] Example 2 : TGA analysis of vegetable oils . To determine which types of compounds would be most stable under pyrolysis conditions and thus most suitable for incorporation into the external solvent for the purposes of the invention, thermogravimetric analyses (TGA) of different types of compounds were carried out.

[0095] In a first experiment, two vegetable oils were tested as potential external solvents, specifically coconut oil and partially hydrogenated sunflower oil. Both oils had similar boiling ranges (T50 in the range of 380 °C to 420 °C) . However, due to the hydrogenation of the sunflower oil, they differed in the amount of olefinic hydrocarbon chains. Specifically, the following amounts of unsaturated fatty acids were determined in the two oils:

[0096] Thus, the coconut oil contained significant amounts of a variety of compounds containing olefinic hydrocarbon chains, including 7.3 wt% octadecenoic acid. Such compounds were not detected for the partially hydrogenated sunflower oil, whose main component was determined as octadecanoic acid (76.2 wt%) , i.e., a compound having an n-paraffinic hydrocarbon chain. The difference in olefinic content was also reflected in the bromine numbers of the two oils. For the coconut oil, a bromine number of 3.7 g Br2 / 100g was determined, while for the partially hydrogenated sunflower oil the bromine number was only 2.9 g Br2 / 100g.

[0097] Both oils were tested in TGA experiments, the results of which are shown in Figure 2. These results clearly show that the partially hydrogenated sunflower oil, containing a higher proportion of compounds having n-paraffinic hydrocarbon chains, was significantly more stable than the coconut oil having a higher proportion of compounds having olefinic hydrocarbon chains.

[0098] Example 3: TGA analysis of different types of plastic polymers.

[0099] In a further TGA experiment, different types of plastic polymers were compared, namely high-density polyethylene (HDPE) , low-density polyethylene (LDPE) , polypropylene (PP) , and polystyrene (PS) . This experiment served to confirm how different degrees of branching and aromatic content in hydrocarbon chains affect the stability of such chains under pyrolysis conditions.

[0100] Out of the materials tested, HDPE has the highest amount of unbranched saturated (i.e., n-paraf f inic) hydrocarbon chains. LDPE polymers contain more branched (i.e., iso-paraffinic) hydrocarbon chains. PP is made from propylene monomers meaning that every other carbon atom in the backbone has a methyl group attached, introducing regular side groups and thus a very high degree of branching along the chain. PS polymers contain phenyl side groups and are thus highly aromatic.

[0101] The results of the TGA analysis are shown in Figure 3. They show a clear trend of HDPE being the most stable, followed by LDPE, PP, and PS. This demonstrates that unbranched carbon chains are more stable than branched chains (HDPE > LDPE > PP) and that higher aromatic contents result in even lower stability (PS) .

[0102] Example 4: Impact of aromatic content on coke formation.

[0103] To determine the impact of the aromatic content on coke formation during pyrolysis, the polyaromatic content of various different types of external solvents was determined and compared to the Conradson Carbon Residue (CCR) . Aromatic contents were determined according to ASTM D6591-19. CCR was determined according to ISO 10370:2014.

[0104] In a first experiment, the CCR of solvents consisting of various amounts of terphenyl in n-heptane were determined. The following results were obtained:

[0105] These results show a clear correlation between the amount of aromatic compounds added and the CCR .

[0106] In a further experiment , a heavy distillate having a boiling range between 210 ° C and 480 ° C was tested as external solvent , once without and once with hydrogenation . Hydrogenation reduced the polyaromatic content , which was found to also reduce the CCR, as shown in the following table :

Claims

25Claims :

1. A process for depolymerizing plastics material (1) , the process comprising:- heating the plastics material (1) to form a plastic melt (3) ,- processing a pyrolysis feed (8) comprising the plastic melt(3) and an external solvent (5) in a pyrolysis reactor (9) to generate a pyrolysis product (10) ,- withdrawing a recycling stream (6) from the pyrolysis product (10) and including at least a portion of said recycling stream (6) in the pyrolysis feed (8) , wherein the external solvent (5) comprises at least 10 wt% of compounds comprising an n-paraffinic hydrocarbon chain and having a boiling point of at least 285 °C.

2. The process according to claim 1, wherein the external solvent (5) comprises less than 35 wt%, preferably less than 25 wt% aromatic compounds.

3. The process according to any one of the claims 1 and 2, wherein the compounds comprising an n-paraffinic hydrocarbon chain have an n-paraffinic Cl 6+-hydrocarbon chain.

4. The process according to any one of claims 1 to 3, wherein the compounds comprising an n-paraffinic hydrocarbon chain are selected from n-paraffins, aliphatic carboxylic acids, aliphatic alcohols, and derivatives thereof.

5. The process according to any one of claims 1 to 4, wherein the external solvent (5) contains compounds comprising an n- paraffinic hydrocarbon chain and compounds comprising an isoparaffinic hydrocarbon chain at a mass ratio of at least 1:1, preferably at least 2:1.

6. The process according to any one of claims 1 to 5, wherein the external solvent (5) contains compounds comprising a paraffinic hydrocarbon chain and compounds comprising an olefinic hydrocabon chain at a mass ratio of at least 1:1, preferably at least 2:1.

7. The process according to any one of claims 1 to 6, wherein external solvent (5) has a bromine number of less than 100 g Br2 / 100 g, preferably less than 90 g Br2 / 100 g.

8. The process according to any one of claims 1 to 7, wherein the external solvent (5) has a boiling range with a T50 (temperature at 50% volume distilled) between 315 °C and 600 °C.

9. The process according to any one of claims 1 to 8, wherein the plastics material (1) comprises polyethylene (PE) , polypropylene (PP) , polystyrene (PS) , polyvinyl chloride (PVC) , polyethylene terephthalate (PET) , polyamide (PA) , styrene acrylonitrile (SAN) and / or acrylonitrile butadiene styrene (ABS) .

10. The process according to any one of claims 1 to 9, wherein the plastics material (1) comprises at least 50 wt% polyolefins(PO) .

11. The process according to any one of claims 1 to 10, wherein the pyrolysis feed (8) contains the plastic melt (3) and the external solvent (5) at a weight ratio of between 1:1 and 200:1, preferably 2,5:1 and 100:1 (plastic melt : external solvent) .

12. The process according to any one of claims 1 to 11, wherein the pyrolysis feed (8) contains the external solvent (5) and the recycling stream (6) at a weight ratio of between 1:2000 and 1:10, preferably 1:1500 and 1:20 (external solvent : recycling stream) .

13. The process according to any one of claims 1 to 12, wherein the external solvent (5) is mixed with the recycling stream (6) to form a diluent stream (4) , and wherein said diluent stream(4) is added to the plastic melt (3) .

14. The process according to any one of claims 1 to 13, wherein the plastics material (1) is depolymerized in the pyrolysis reactor (9) at a temperature of at least 360 °C.

15. The process according to any one of claims 1 to 14, wherein the pyrolysis product (10) is separated into a heavy product (12) and a light product (13) , wherein the recycling stream (6) is withdrawn from the heavy product (12) .

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