Thermal process for converting plastic waste to olefins.

Abstract

A process for the depolymerization of polymer waste is disclosed, which is specifically designed for directly converting polymer waste into olefins via depolymerization reaction, as it is characterized by a high yield of gaseous depolymerization products.

Description

[Technical field]

[0001] The present disclosure relates to the depolymerization of waste polymers. More specifically, the present disclosure relates to a process for directly converting waste polymers into olefins via a depolymerization reaction. [Background technology]

[0002] Plastics include a variety of synthetic and semi-synthetic materials that use polymers as their main components. Their plasticity allows them to be molded, extruded, or pressed into solid objects of various shapes. This adaptability, combined with a variety of other properties such as light weight, durability, and low production costs, has led to their widespread use. The production of plastics has increased dramatically over the past decades. At the same time, the increase in the amount of plastics poses environmental problems, since most plastics are resistant to natural degradation processes. As such, the material can persist for centuries or more, filling up landfills and even appearing in the food chain as microplastics.

[0003] Therefore, efforts are being made to improve the recycling of polymer waste. Current recycling procedures mainly include mechanical recycling and chemical recycling. In mechanical recycling, plastics are mechanically transformed without changing their chemical structure, making them available for the production of new materials. The general mechanical recycling process includes collecting the polymer waste, sorting the polymer waste into different types of plastics and colors, pressing or crushing the polymer waste, washing and drying to baling the plastic waste, and agglomerating, extruding, cooling and reprocessing the plastic waste into pellets to obtain recycled raw materials that can then be molded into new articles.

[0004] Chemical recycling generally involves recovering plastic waste and then heating it to break down the polymers into smaller organic molecules that are recycled in the petrochemical industry.

[0005] Typically, the main output from a pyrolysis process is a liquid stream, also called pyrolysis oil, which can either be refined and used as a fuel or subjected to a further steam cracking process to produce a gaseous fraction composed of C2-C4 olefins.

[0006] The pyrolysis stage can be carried out in the presence of a catalyst, which helps to accelerate the cracking of the hydrocarbon chains. However, the use of catalysts also has some drawbacks. In particular, although the overall yield of the depolymerization product may be increased, the composition of the gaseous depolymerization product may result in a too high content of oxygenated products such as CO and CO2. These oxygenated gases must be removed beforehand, as they prevent the gaseous depolymerization product containing olefins from being fed directly to the back-end separation section of the cracker. Furthermore, the generation of CO2 partially jeopardizes attempts to reduce the CO2 footprint of plastic waste processing. In addition, the use of catalysts in the depolymerization also increases costs and makes the process more complex, as equipment for handling and feeding the catalyst must be added to the plant design. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, it would be important to develop a pure thermal treatment process that directly converts plastic waste into olefins with low CO and CO2 gas emissions.

[0008] In one aspect, the present disclosure provides a process for converting plastic waste to olefins, comprising:

[0009] Depolymerizing a plastic scrap feedstock at a temperature in the range of -480 to 700°C, the plastic scrap feedstock comprising more than 80% by weight polyolefins based on the polymer content of the plastic scrap feedstock;

[0010] - recovering the gaseous fraction generated during pyrolysis;

[0011] - separating the recovered gaseous fraction to obtain a gaseous depolymerization product and a liquid depolymerization product, wherein the amount of the gaseous depolymerization product is higher than 40 wt. % based on the total polyolefin content, while in the gaseous depolymerization product, the amount of C2-C4 olefins is 50 wt. % or more based on the total amount of hydrocarbons. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Preferably, the plastic scrap feedstock is characterized by: (a) a polyolefin content, in particular the combined polypropylene (PP) and polyethylene (PE) content, of more than 85 wt.-%, more preferably more than 90 wt.-%, in particular more than 95 wt.-%, based on the total weight of the polymer scrap feedstock.

[0013] Preferably, the upper limit of the polyolefin content is 99% by weight, more preferably 98% by weight, especially 97% by weight, based on the total amount of plastic waste feedstock.

[0014] In another preferred embodiment, the weight ratio PE / PP in the polymer waste raw material is 3.5 or more, more preferably 5 or more, and particularly preferably 6 or more.

[0015] Furthermore, the total ash content of the plastic scrap feedstock is preferably less than 10% by weight, more preferably less than 5% by weight, and most preferably less than 3% by weight, measured as the residue after heating the polymer scrap feedstock at 800° C. in air for 120 hours. Preferably, the plastic waste raw material is characterized in that (i) it has a bulk density of 70-500 g / L, preferably 100-450 g / L, if the polymer waste raw material is present in shredded form, or 300-700 g / L, if the polymer waste raw material is in pellet form, the bulk density being determined according to DIN 53466, respectively. It has been found that the above bulk density values ​​are of great help in realizing a continuous flowless depolymerization process and in preventing clogging of the feed lines and fouling of the reactor. Furthermore, it also helps in reducing the amount of residues and intensifying the depolymerization reaction, leading to a higher yield of the desired product. Preferably, the polymer waste is obtained from shredded pipes with a particle size of less than 50 mm, preferably less than 30 mm, more preferably less than 20 mm, most preferably less than 15 mm.

[0016] In a preferred embodiment, the plastic waste feedstock is additionally characterized by: (i) a total volatiles (TV) content of less than 4%, preferably less than 3%, measured as the weight loss of a 10 g sample after 2 hours at 100°C and 200 mbar.

[0017] In addition to the polyolefin components described above, the polymer scrap feedstock used in the process of the present disclosure can include essentially any polymeric material, especially polymeric materials formed from synthetic polymers. Non-limiting examples include polyolefins other than PE and PP, such as polybutene-1 and ethylene-propylene elastomers, polystyrene, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyamides, polycarbonates, polyurethanes, polyesters, natural and synthetic rubber, tires, filled polymers, composites and plastic alloys, plastics dissolved in solvents, and the like.

[0018] However, in accordance with the present disclosure, which is directed to maximizing the production of light gas olefins, the plastic feedstock preferably consists primarily of polyolefins, and non-polyolefin polymer materials may only be present in amounts less than 10%, preferably less than 5%, based on the total amount of plastic scrap feedstock.

[0019] As mentioned above, the polymer waste feedstock may consist of one type of polyolefin waste or may be a mixture of two or more different types of polymer waste. Particularly preferred is an embodiment in which the polyolefin waste consists entirely of polyethylene (PE).

[0020] The polymer waste raw material may be provided in a variety of different forms. In smaller scale operations, the polymer waste raw material may be in the form of a powder. In larger scale operations, the polymer waste raw material may be in the form of pellets with a particle size of 1-2 mm, preferably 2-10 mm, more preferably 2-8 mm, or in the form of chopped flakes and / or film pieces with a particle size of 1-20 mm. In the context of this disclosure, a particle size within a defined range means that 90% by weight of the particles have a particle size within the defined range. Particle size may be measured by sieving or using a Beckman Coulters LS13320 laser diffraction particle size analyzer.

[0021] The plastic waste materials disclosed above are mainly composed of plastic materials and are usually named after the type of polymer that forms the main component of the polymer waste material.Preferably, the plastic waste materials used as raw materials in the process of the present disclosure contain more than 50% by weight of polymer material of its total weight, preferably more than 6% by weight, more preferably more than 70% by weight.Other components in the polymer waste raw materials may be additives such as fillers, reinforcing agents, processing aids, plasticizers, pigments, light stabilizers, lubricants, impact modifiers, antistatic agents, inks, antioxidants, etc.

[0022] In certain embodiments, the polymer waste materials used in the process of the present disclosure preferably include polyolefins and polystyrene, such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), ethylene-propylene-diene monomer (EPDM), polypropylene (PP), and polystyrene (PS). Plastic waste materials including mixtures of polyolefins and polystyrene are particularly preferred.

[0023] Other non-polyolefin polymer waste materials such as polyamides, polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polyurethane (PU), acrylonitrile-butadiene-styrene (ABS), nylon, fluorinated polymers, etc., can also be used in the process of the present disclosure. If present in the polymer waste material, it is preferred that such polymers are present in an amount of less than 10%, especially less than 5%, of the total weight of the polymer waste feedstock on a dry weight basis.

[0024] Preferably, the polymer waste is essentially free of thermosetting polymers, where substantially free means that the thermosetting polymer content is less than 10% by weight, more preferably less than 5% by weight, based on the polymer waste feedstock.

[0025] The polymer waste material used in the process of the present disclosure is preferably selected from the group consisting of single plastic waste, mixed plastic waste, rubber waste. Single plastic waste, off-spec single virgin plastic, mixed plastic waste, rubber waste, or mixtures thereof are preferred. Off-spec single virgin plastic, mixed plastic waste, or mixtures thereof are particularly preferred.

[0026] The polymer waste may contain limited amounts of non-pyrolyzable components as foreign matter such as water, glass, stones, metals, etc. By "limited amounts" it is preferably meant an amount less than 15% by weight, more preferably less than 10% by weight of the total weight of the dry polymer waste feedstock.

[0027] The polymer waste can be extruded if necessary before being used as a raw material in the process of the present disclosure. In a preferred embodiment, the plastic waste is pelletized and the pellets are used as a raw material in the process of the present disclosure. In another preferred embodiment, the polymer waste is used in a molten state, for example at a temperature of 200°C to 300°C.

[0028] Particularly preferred types of polymer waste materials used as raw materials in the process of the present disclosure are characterized by the following features:

[0029] i) The polyolefin content in the polymer waste, in particular the polypropylene (PP) and / or polyethylene (PE) content, is greater than 80% by weight, preferably greater than 85% by weight, more preferably greater than 90% by weight, in particular greater than 95% by weight, based on the total weight of the polymer waste raw material.

[0030] ii) The polymer waste is shredded, optionally compressed, polymer waste and has a bulk density of 70-500 g / L, preferably 100-450 g / L, or the polymer waste is in pellet form and has a bulk density of 300-700 g / L, the bulk density being measured according to DIN 53466.

[0031] iii) The total content of volatiles (TV), measured as the weight loss of a 10 g sample after 2 hours at 100°C and 200 mbar pressure, is less than 5%, preferably less than 3%, more preferably less than 2%, in particular less than 1%.

[0032] iv) The amount of polar polymeric impurities in the waste polymer is less than 5% by weight, more preferably less than 3% by weight, based on the total weight of the waste polymer.

[0033] v) The amount of cellulose, wood and / or paper in the polymer waste is less than 5% by weight, more preferably less than 3% based on the total weight of the polymer waste.

[0034] vi) The total chlorine content is less than 1.0 wt.%, preferably less than 0.5 wt.%, and more preferably less than 0.1 wt.%, based on the total weight of the polymer waste.

[0035] vii) The total ash content of the polymer waste raw material is less than 10% by weight, more preferably less than 5% by weight, and most preferably less than 3% by weight, measured as the residue after heating the polymer waste in air at 800° C. for 120 hours. In another preferred embodiment, the ash content is between 0.01 and 2% by weight, preferably between 0.02 and 1.5% by weight, and even more preferably between 0.05 and 1.0% by weight.

[0036] In a preferred embodiment of the present disclosure, the waste polymer material used as raw material in the process of the present disclosure is defined by upper limits of trace components, constituents or impurities expressed in weight percent. The lower limits of the amount of these components, constituents or impurities in the preferred waste polymer material are preferably below the detection limit, or the lower limit is 0.001% by weight or 0.01% by weight or 0.1% by weight, respectively.

[0037] Many techniques are known for separating materials in polymer waste streams. Moving beds, drums, screens, and air separators are used to fractionate materials according to size, weight, and density. Advanced sorting of plastic waste by spectroscopy (MIR, NIR [near infrared]), X-ray, or fluorescence spectroscopy provides high quality plastic waste streams with high polyolefin content.

[0038] Automated sorting technologies for waste plastics include dry sorting technology, electrostatic sorting technology, mechanical sorting methods (including centrifugal force, specific gravity, elasticity, particle shape, selective crushing, and mechanical properties), wet sorting technology (e.g., sinking and flotation sorting method), and chemical sorting methods.

[0039] Suitable feedstocks for use in the processes of the present disclosure may be obtained by applying any of the known sorting techniques, for example as summarized in B. Ruj et al: Sorting of plastic waste for effective rexycling, Int. J. Appl. Sci. Eng. Res 4, 2015, 564-571.

[0040] Depolymerization

[0041] According to the present disclosure, the process for depolymerization of plastic waste comprises pyrolysis of the plastic waste at a temperature of 480-700°C, preferably 500-650°C, more preferably 500-600°C, in particular 500-580°C.

[0042] The gaseous effluent from the pyrolysis reactor is then (a) recovered and (b) separated into a gaseous depolymerization product and a liquid depolymerization product.

[0043] The recovered gaseous fraction is separated by condensation into a liquid depolymerization product and a gaseous depolymerization product, which may then be further processed.

[0044] The process of the present disclosure may produce little or no char. Thus, in a preferred embodiment, the residue of the depolymerization process of the present disclosure has a char content of less than 5 wt.%, preferably less than 2 wt.%, based on the total weight of the product.

[0045] The resulting liquid depolymerization product may be further separated. Thus, the process of the present disclosure may further comprise a step of distilling the liquid depolymerization product.

[0046] The process of the present disclosure results in a depolymerized product with high gas content, in a preferred embodiment, the gas content in the depolymerized product is preferably greater than 45 wt%, more preferably greater than 50 wt%, especially greater than 65 wt%, based on the initial total weight of polyolefins in the plastic waste feed.

[0047] In addition, the gaseous fraction of the depolymerization products may be particularly useful for further processing, such as the production of monomeric olefin-based C 2~C4 It is further characterized by a high content of olefinic C2-C4 compounds, in particular the amount of which is at least 55%, preferably higher than 60%, in particular higher than 65%, based on the total amount of hydrocarbons.

[0048] In a particular embodiment, the proportion of ethylene relative to the total olefinic C2-C4 compounds is higher than 28% by weight, preferably higher than 30% by weight.

[0049] The amount of C2-C4 hydrocarbons in the gaseous fraction of the depolymerization product is preferably higher than 80%, preferably higher than 85%, in particular higher than 90%, based on the total amount of hydrocarbons. Due to the high amount of such compounds produced during depolymerization, the gaseous depolymerization product may be used directly as a feedstock for a cracking process and subsequent polymerization. The gaseous product, including light olefins and light alkanes, can be transferred to a downstream cracker, for example by passing through an oven, to produce a polymerization grade monomer stream.

[0050] Other by-products such as ethane, propane, and butane can be cracked in an oven, eliminating the normally required step of processing the product obtained after depolymerization to obtain the desired monomers, thus saving valuable energy and reducing CO2 emissions.

[0051] The depolymerization process according to the present disclosure can be carried out in a reactor comprising: (a) a feeding device for introducing polymer waste and a catalyst into the reactor; (b) a pyrolysis device equipped with a heating unit, a gas discharge unit and a solid discharge unit; and (c) a condensation device.

[0052] Preferably, gas discharge units are distributed throughout the pyrolysis device and are provided with an outlet for discharging the gaseous fraction of the depolymerization and an inlet for introducing a wash gas into the pyrolysis device.

[0053] In a preferred embodiment, the reactor may comprise two or more pyrolysis units.

[0054] The polymer waste raw material and, if used, the catalyst are introduced into the pyrolysis unit via at least one feeder and then heated to achieve depolymerization. The gaseous fraction produced during depolymerization is discharged from the outlet of the gas discharge unit and conveyed to a condensation unit for further processing. The solid residue of the depolymerization, if any, is discharged via a solid discharge unit. A washing gas for washing the gas discharge unit and the pyrolysis unit may be introduced through the inlet of the gas discharge unit.

[0055] In a preferred embodiment, the gas discharge unit is equipped with a filter membrane to ensure that the gaseous fraction is free of solids after being discharged from the pyrolysis device. The gas discharge unit is preferably made of metal or ceramic particle or fiber material.

[0056] The pyrolyzer is preferably further equipped with a screw for uniformly mixing the polymer waste in the pyrolyzer throughout the depolymerization. The residence time of the solids in the pyrolyzer could be clearly defined by adjusting the rotation speed of the screw.

[0057] The gaseous fraction discharged from the depolymerization is conveyed to a condenser to obtain a liquid depolymerized product and a gaseous depolymerized product. In a preferred embodiment, the condenser includes a plurality of condensers preferably operated at different temperatures. The temperature of the condenser may be set according to the boiling point of the condensate.

[0058] depolymerization products

[0059] The gaseous fraction produced during pyrolysis is separated, for example by condensation, into liquid and gaseous depolymerization products.

[0060] The process of the present disclosure results in depolymerized products with surprisingly high selectivity for gaseous fractions.

[0061] liquid depolymerization products

[0062] The resulting liquid depolymerization product exhibits a surprisingly low content of aromatics, particularly polyaromatics and asphaltanes, especially when carried out in the presence of a catalyst. Thus, the liquid depolymerization product obtained by the process of the present disclosure is characterized by a low content of aromatics and olefinic components and a high purity.

[0063] Preferably, the content of aromatics in the obtained liquid depolymerization product is less than 10 mol %, preferably less than 5 mol %, in particular equal to or less than 3 mol %, the content of aromatic components being measured as the content in mol % of aromatic protons determined by H-NMR spectroscopy.

[0064] In addition, the liquid depolymerized product obtained by the depolymerization process of the present disclosure is characterized by a low content of olefinic compounds. The content of olefinic compounds in the liquid depolymerized product is preferably less than 7 mol%, more preferably less than 5 mol%, and even more preferably less than 3 mol%, based on the total number of hydrocarbon protons, and the content of olefinic compounds is determined based on the content of olefinic protons determined by 1H-NMR spectroscopy.

[0065] Another measure of the content of double bonds in a given sample is the Bromine Number (BrNo.), which indicates the degree of unsaturation. In a preferred embodiment, the liquid depolymerized product obtained by the process of the present disclosure has a Bromine Number, expressed as grams of bromine per 100 grams of sample, of less than 150, preferably 10-100, more preferably 15-80, even more preferably 20-70, and especially 25-100, measured according to ASTM D1159-01.

[0066] The liquid depolymerization product obtained by the process of the present disclosure preferably has a boiling point range of 30 to 650° C., more preferably 50 to 250° C. By separation techniques such as distillation, the depolymerization product can be separated into hydrocarbon fractions of different boiling point ranges, for example, a light naphtha fraction mainly containing C5 and C6 hydrocarbons with a boiling point range of 30° C. to 130° C., a C6 to C8 hydrocarbon fraction with a boiling point range of 130° C. to 220° C., and a light naphtha fraction mainly containing C5 and C6 hydrocarbons with a boiling point range of 130° C. to 220° C. 12 Heavy naphtha fraction containing mainly hydrocarbons, C9-C with a boiling point range of 220℃-270℃ 17 It may be separated into a kerosene fraction containing primarily hydrocarbons, or other higher boiling fractions such as diesel fuel, fuel oil, hydrowax, etc.

[0067] Even more surprisingly, it has been found that the liquid depolymerization product contains little or no solid residue, and in a preferred embodiment, the liquid depolymerization product upon evaporation has a residue content of 5 ppm(w) or less, as measured according to ASTM D381.

[0068] Gaseous depolymerization products

[0069] The resulting gaseous depolymerization product exhibits a surprisingly low content of low molecular weight hydrocarbons such as methane or ethane. Rather, it has been surprisingly found that the gaseous depolymerization product contains unusually high amounts of higher olefins such as ethylene, propylene, and butenes, which are typically desired for polyolefin production.

[0070] As described above, the amount of olefinic C2-C4 compounds is 55% or more, preferably higher than 60%, and particularly higher than 65%, based on the total amount of hydrocarbons in the gaseous depolymerization product. Therefore, the gaseous depolymerization product obtained by the process of the present disclosure has a high content of any one of ethylene, propylene, and butene, and also has a high content of saturated low molecular weight hydrocarbons, particularly those represented by the general formula C n H 2n+2 (wherein n is a real number in the range of 1 to 4) is characterized by a low content of hydrocarbons.

[0071] In a preferred embodiment, the gaseous depolymerization product of the disclosed process is characterized by a CO content of at most 2 wt.-%, preferably at most 1 wt.-%, more preferably at most 3 wt.-%, most preferably at most 2 wt.-%, in particular at most 0.1-0.5 wt.-%, based on the total weight of the gaseous depolymerization product after step (e) of the disclosed process.

[0072] In a preferred embodiment, the gaseous depolymerization product of the disclosed process is characterized by a CO content of up to 5 wt.-%, preferably up to 3 wt.-%, more preferably up to 2 wt.-%, based on the total weight of the gaseous depolymerization product after step (e) of the disclosed process.

[0073] Due to its very high olefin content, the gaseous fraction can be used directly as feedstock for further processing in downstream crackers, e.g. feed gas compressors to obtain purified monomer streams which can then be used to produce polymers, thus avoiding the energy-intensive stream cracking ovens normally required and at the same time reducing CO2 emissions.

[0074] Gaseous depolymerization products include small amounts of HCl, HCN, H2S, and H 2O、NH3 , COS, etc., which can be separated as needed in a refining stage before being introduced into the downstream segments of the steam cracker.

[0075] The present disclosure is further illustrated with reference to the following figures and examples. EXAMPLES

[0076] The following analytical methods were employed:

[0077] 1) GC MS was used for the analysis of liquids and gases.

[0078] 2) After decoking the reactor residue at 800°C, the char residue is determined by mass balance.

[0079] 3) The liquid content is characterized using simulated distillation (SimDist) analysis according to ASTM D7213:2012. The final boiling point (FBP), boiling temperature at 50%, and initial boiling point (IBP) are obtained from SimDist.

[0080] 4) The total content of unsaturated components in the liquid condensate was characterized by bromine number measurements using an 848 Titrino Plus (Metrohm AG, Herisau, Switzerland) equipped with a double PT wire electrode with integrated PT1000 temperature sensor and a 10 mL burette according to ASTM D1159-01 as described in Metrohm Application Bulletin 177 / 5e of December 2018. Bromine number (BrNO.) expresses the amount of bromine in grams absorbed by 100 grams of sample.

[0081] 5) 1H-NMR analysis was performed by dissolving a sample of the liquid condensate in CDCl3 and characterizing the sample using proton NMR spectroscopy. Aromatic, olefinic, and aliphatic protons were assigned according to the chemical shifts summarized in Table 1.

[0082] [Table 1]

[0083] The olefinic proton types listed are assumed to correspond to the following structures: [ka]

[0084] The amounts of aromatic, olefinic and aliphatic protons may be determined based on the assigned peak integrals according to the following formula:

[0085] Mole% of aromatic protons = [(I1+I2) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0086] Mole% of olefin proton type 1=[(I4+I7) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0087] Mole% of olefin proton type 2=[(I3+I5) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0088] Mole% of olefin proton type 3=[(I6) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0089] Mole% of olefin proton type 4=[(I8) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0090] Molar % of paraffin protons = [(I9) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0091] 6) The water content of the catalyst was measured at 180 °C on 0.5–1 g samples using a Sartorius MA45 (Sartorius AG, Goettingen, Germany).

[0092] 7) To determine the pH value of the hydrodepolymerization product, a liquid sample of the hydrodepolymerization product was extracted with water at a water:sample volume ratio of 1:5, and the pH value of the aqueous solution was measured.

[0093] 8) The characteristics of the organic waste raw materials used were determined as follows:

[0094] Because the composition of organic waste materials can vary, 20-100 g samples of polymer waste were ground and analyzed. Alternatively, pelletized samples of polymer waste were analyzed. Use the following method:

[0095] i) Total volatiles (TV) was determined as the weight loss of a 10 g sample after 2 hours at 100° C., 200 mbar.

[0096] ii) Water content was determined by Karl Fischer titration using a Metrohm 915 KF Ti-Touch instrument equipped with a PT100 indicator electrode for volumetric KF titrations according to Metrohm Application Bulletin 77 / 3e in accordance with ASTM E203.

[0097] iii) IR spectroscopy was used to qualitatively identify different polymers (PP, PE, PS, PA, PET, PU, ​​polyester) and additives such as CaCO3.

[0098] iv) Standard elemental analysis methods were used to determine the weight % of H, C, N (DIN 51732:2014-07) and S (tube furnace, ELTRA GmbH, Haan, Germany, DIN 51724-3:2012-07).

[0099] v) 1H-NMR was used to determine the composition of polymers soluble in solvents suitable for recording 1H-NMR spectra, i.e. PE / PP balance (including copolymers), PET, PS.

[0100] vi) The ash content analysis of plastics was determined at 800 °C according to DIN EN ISO 3451-1 (2019-05).

[0101] vii) The bulk density of the polymer waste was determined according to DIN 53466.

[0102] viii) Corrosivity was determined as the pH value of the aqueous solution after a contact time of 3 hours (5 g of sample in 50 mL of distilled water).

[0103] ix) Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) was used for quantitative determination of elements (total chlorine content, Si or metal content).

[0104] x) Determine the ash content of liquid feedstocks such as pyrolysis oil in accordance with ASTM D482-19.

[0105] Raw materials:

[0106] Some of the following organic waste materials were used as raw materials:

[0107] A: Pelletized agricultural and industrial packaging films.

[0108] The raw material properties, averaged over the three samples, are summarized in Table 2.

[0109] [Table 2]

[0110] *) Other contents include inorganic, polymeric or organic foreign matter and volatile constituents.

[0111] Ash: Ash content

[0112] TV: Total Volatile Matter

[0113] BD: Bulk density

[0114] Cl: Total chlorine content

[0115] PE: Polyethylene content

[0116] PP: Polypropylene content

[0117] PET: Polyethylene terephthalate content

[0118] PS: Polystyrene content

[0119] PA: Polyamide content

[0120] Other Content: Content of other impurities

[0121] The raw materials were introduced into a reactor apparatus equipped with a heating unit, a gas discharge unit, a solid discharge unit, a condenser, and a screw for homogeneously mixing the reactor contents (plastic waste and sand) during depolymerization. The depolymerization conditions carried out are summarized in Table 6. The gaseous fraction obtained was further separated into liquid and gaseous depolymerization products by condensation. The amounts of the fractions obtained are also shown in Table 3.

[0122] [Table 3]

[0123] (a) Any amount less than 100% is due to losses. (b) A large amount of wax suspended in a heterogeneous liquid. +) The liquid is a mixture of all fractions and may contain waxy solid particles and agglomerates, which disappear when heated above 50°C.

[0124] Experiment #2 was carried out with only Plastic Waste A without any sand.

[0125] The above data show that the catalysts of the present disclosure are capable of producing a large amount of gaseous depolymerization products and maintaining good performance even when the feedstock is loaded with heterogeneous materials. The analysis results of the gaseous depolymerization products are summarized in Table 4.

[0126] [Table 4]

[0127] *) Catalysts that maintained good selectivity after three consecutive runs were then regenerated by heating in air to 800°C and sieving off smaller particles (ash) below 500 μm.

[0128] HC: Hydrocarbons

[0129] Olefins: Sum of ethylene, propylene and butenes

[0130] Olefins / HC: Ratio of total olefins to total hydrocarbons

[0131] As can be seen from Table 4, the process of the present disclosure resulted in a gaseous depolymerization product containing a large amount of monomers useful as feedstock for polymerization after purification. Any gaseous saturated hydrocarbons can be treated in the usual manner and returned to the steam cracker oven.

[0132] Bulk density 60g / cm 3 Comparative experiments with polymer waste were also carried out with the same reactor setup. The experiments were repeatedly affected by plugging of the feed lines and fouling of the reactor, which made the experiments difficult.

Claims

1. 1. A process for converting plastic waste into olefins, comprising: Depolymerizing a plastic scrap feedstock at a temperature in the range of -480 to 700°C, the plastic scrap feedstock comprising more than 80% by weight polyolefins based on the polymer content of the plastic scrap feedstock; - recovering the gaseous fractions generated during pyrolysis; - separating the recovered gaseous fraction to obtain a gaseous depolymerization product and a liquid depolymerization product, the amount of the gaseous depolymerization product being greater than 40 wt. % based on the total polyolefin content, and in the gaseous depolymerization product, ２ ~C ４ the amount of olefins is 50 wt% or more based on the total amount of hydrocarbons.

2. 2. The process according to claim 1, wherein the plastic scrap feedstock is characterized in that (a) the polyolefin content, in particular the total content of polypropylene (PP) and polyethylene (PE), is greater than 85% by weight, based on the polymer content of the plastic scrap feedstock.

3. 3. The process according to claim 1 or 2, wherein the upper limit of the polyolefin content is 99 wt.%, more preferably 98 wt.%, especially 97 wt.%, based on the total amount of plastic waste feedstock.

4. 4. The process according to any one of claims 1 to 3, wherein in the polymer content of the plastic waste feedstock, the weight ratio PE / PP is equal to or greater than 3.

5.

5. 5. The process according to claim 4, characterized in that the plastic waste raw material has a bulk density of 70-500 g / L, preferably 100-450 g / L, if the polymer waste raw material is present in shredded form, or a bulk density of 300-700 g / L, if the polymer waste raw material is in pellet form, said bulk density being determined in each case according to DIN 53466.

6. 6. The process according to any one of claims 1 to 5, wherein the polymer content of the plastic waste feedstock is composed entirely of Polyethylene (PE).

7. The process according to any one of claims 1 to 6, wherein the depolymerization reaction is carried out at a temperature in the range of 500 to 650°C.

8. 8. The process of claim 7, wherein the depolymerization reaction is carried out at a temperature in the range of 500 to 600°C.

9. 9. The process of claim 8, wherein the gas content in the depolymerized product is greater than 45 wt%.

10. In the gaseous depolymerization product, ２ ~C ４ The process of any one of claims 1 to 9, wherein the amount of olefins is 55 wt% or more based on the total amount of hydrocarbons.

11. In the gaseous depolymerization product, ２ ~C ４ 11. The process of claim 10, wherein the amount of olefins is 60 wt% or greater based on the total amount of hydrocarbons.

12. In the gaseous depolymerization product, olefinic C ２ ~C ４ The process according to any one of claims 1 to 11, wherein the proportion of ethylene relative to the total amount of compounds is higher than 28% by weight, preferably higher than 30% by weight.

13. CO ２ is at most 5 wt.-%, preferably at most 3 wt.-%, more preferably at most 2 wt.-%, based on the total weight of the gaseous depolymerization product.

14. 14. The process according to any one of the preceding claims, wherein the content of CO is at most 2 wt.-%, preferably at most 1 wt.-%, more preferably at most 3 wt.-%, most preferably at most 2 wt.-%, in particular at most 0.1-0.5 wt.-%, based on the total weight of the gaseous depolymerization product.

15. C in the gaseous fraction of the depolymerization product ２ ~C ４ A process according to any one of the preceding claims, wherein the amount of hydrocarbons is preferably higher than 80%, preferably higher than 85%, in particular higher than 90%, based on the total amount of hydrocarbons.

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