Depolymerization of crosslinked polyethylene

Abstract

The present disclosure relates to a process for producing a cracker feedstock by depolymerizing a plastic waste material comprising crosslinked polyethylene.

Description

Technical Field

[0001] This disclosure relates to a method for generating cracker feedstock by depolymerizing cross-linked polyethylene and / or multi-component materials containing polyolefins. Background Technology

[0002] Cross-linked polyethylene (commonly abbreviated as PEX, XPE, or XLPE) is primarily used in multi-component materials such as building service piping systems, liquid-circulating radiant heating or floor heating and cooling systems, domestic water pipes, and insulation for high-voltage cables. Cross-linked polyethylene is also used in natural gas and offshore oil applications, district heating, chemical transport, and wastewater and slurry transport, and more recently, in the mining industry.

[0003] The advantages of using cross-linked polyethylene (XLPE) include its flexibility, low cost, and ease of installation compared to, for example, copper pipes. XLPE also exhibits extended service life because it is not corrosion-resistant, has extremely high stress crack and abrasion resistance, and is therefore considered a suitable candidate for the gradual replacement of metal and thermoplastic pipes.

[0004] Although PEX tubing is expected to have a service life of 50 years, replacement will eventually be necessary, especially as the first generation of tubing installed 40 to 50 years ago comes to an end. However, recycling cross-linked polyethylene remains a challenge to date, as it may be shredded and compounded with non-cross-linked materials. The resulting material is unusable for standard applications because the ultra-high molecular weight of the cross-linked polymer chains prevents uniform mixing and causes the formation of large gels. Therefore, mechanical recycling, a standard procedure for plastic recycling, is not an option.

[0005] WO 2018 / 216031 relates to a system and method for reconverting plastics into various petrochemical liquids and gaseous hydrocarbons. The system mainly comprises a reactor, a combustion chamber, a feed unit, and a gas collection and cooling unit. For the reconversion method, granular plastic material is charged into the reactor along with 2% manganese sulfate as a catalyst and heated to first depolymerize, and then form a gaseous mixture of petrochemical compounds.

[0006] DE 198 22 568 proposes a method that should also be applied to cross-linked polyethylene for recycling plastics, wherein the plastic is contacted with a catalyst at an elevated temperature and the resulting gas phase of the reaction products is at least partially condensed.

[0007] US2017 / 0327663 discloses a system for continuously processing recycled polymer material, the system comprising: (a) a hopper configured to continuously feed the recycled polymer material into the system; (b) an extruder system configured to continuously rotate the recycled polymer material in a molten state; (c) a filter system configured to continuously filter the molten material; (d) a first reactor configured to continuously depolymerize the molten material into depolymerized molten material; (e) a heat exchanger configured to continuously cool the molten depolymerized material; and (f) a purifier system configured to continuously purify the molten material.

[0008] First methods for recycling cross-linked polyethylene are limited to laboratory settings, or cross-linked polyethylene can only be used to produce various waxes after depolymerization. Therefore, there is still a need for an efficient recycling method for cross-linked polyethylene materials that aims to restore waste materials to their molecular form for use as raw materials for new plastic materials.

[0009] This disclosure addresses this need by providing a method for generating cracker feedstock by depolymerizing cross-linked polyethylene. Summary of the Invention

[0010] In a first embodiment, this disclosure therefore provides a method for generating cracker feedstock by depolymerizing polymer waste material containing cross-linked polyethylene, the method comprising the following steps:

[0011] i) Introduce the waste material raw material into a pyrolysis reactor, preferably a reactor equipped with a screw conveyor;

[0012] ii) Mix the waste material with the depolymerization catalyst;

[0013] iii) Depolymerize the waste material in an oxygen-free atmosphere to obtain gaseous depolymerization products;

[0014] iv) Collect and condense at least a portion of the gaseous depolymerization products to obtain the desired cracker feedstock.

[0015] In a preferred embodiment, the catalyst is a particulate catalyst containing an acidic compound as an active component, the acidic compound of which is preferably deposited on a non-porous particulate support by means of a coating agent.

[0016] In a preferred embodiment, the nonporous microparticle support is selected from the group consisting of sand, glass beads, and metal particles.

[0017] In a preferred embodiment, the coating agent is selected from the group consisting of oils, inorganic hydrogels, and combinations thereof.

[0018] In a preferred embodiment, the acidic compound is selected from the group consisting of: Al / Si mixed oxides, Al2O3, aluminosilicates, silicon dioxide, and zeolites.

[0019] In one embodiment, the waste material also contains aluminum, and the method further includes the step of collecting aluminum from the waste material.

[0020] In a preferred embodiment, the cross-linked polyethylene in the polymer waste material is selected from the group consisting of: peroxide cross-linked polyethylene, silane cross-linked polyethylene, radiation cross-linked polyethylene, free radical cross-linked polyethylene, azo cross-linked polyethylene, UV-initiated free radical cross-linked polyethylene, and mixtures thereof.

[0021] In a preferred embodiment, the waste material is obtained from PEX pipes, PEX / Al / PEX pipes, Al / PEX pipes, and / or PEX / Al / PEX pipes.

[0022] In a preferred embodiment, the polymer waste material comprises or consists of shredded PEX pipe waste and a stream of plastic waste having a melt index (MFI, 21.6) greater than 10 g / 10 min, wherein the amount of the plastic waste stream is preferably at least 40% by weight, preferably from 40% to 80% by weight, based on the total weight of the waste material.

[0023] The polymer waste material according to this disclosure preferably contains a low amount, and particularly less than 12% by weight of the total dry weight of the polymer fraction of the waste material raw material, and even more preferably less than 10% by weight of a non-polyolefin component.

[0024] In a preferred embodiment, the gaseous depolymerization product is released from the reactor via a gas release unit placed along a screw conveyor.

[0025] In a preferred embodiment, the collection of the gaseous depolymerization products includes a hot gas filtration step.

[0026] In a preferred embodiment, the condensation of the gaseous depolymerization products is achieved by passing the gaseous depolymerization products successively through multiple condensation units.

[0027] In a preferred embodiment, the residence time of the waste material in the reactor does not exceed 60 minutes, preferably not more than 45 minutes.

[0028] In a preferred embodiment, the reactor operates at a temperature of 350°C to 650°C, preferably 400°C to 590°C, and more preferably 430°C to 500°C.

[0029] In a preferred embodiment, the reactor operates at 0.7 to 10 bar. g Pressure operation.

[0030] In one embodiment, the reactor is electrically heated.

[0031] In a preferred embodiment, at least a portion of any non-liquefiable depolymerization product and / or at least a portion of the catalyst is reintroduced into the reactor.

[0032] In a preferred embodiment, the method further includes monitoring the methane content in the collected gaseous depolymerization products.

[0033] In a preferred embodiment, based on the total weight of the depolymerization products, the collected depolymerization products contain more than 60% by weight of gaseous components, wherein, based on the total weight of the gaseous components, the gaseous components preferably contain more than 50% by weight of olefins.

[0034] In a preferred embodiment, the liquid depolymerization product comprises 35% to 45% by weight of a high-boiling fraction, 40% to 50% by weight of a medium-boiling fraction, and 15% to 25% by weight of a low-boiling fraction. Detailed Implementation

[0035] In one aspect, this disclosure relates to a method for generating cracker feedstock by depolymerizing polymer waste material containing cross-linked polyethylene using an acidic depolymerization catalyst.

[0036] In the first step of the method according to this disclosure, polymer waste material is introduced into a pyrolysis reactor, preferably a reactor equipped with a screw conveyor. It has been found that the screw conveyor, used in conjunction with a particulate catalyst, is particularly useful. This results in a homogeneous mixture of the waste material and the catalyst, thereby achieving uniform heating of the waste material (where the catalyst is considered to act as a heat carrier), while preventing the molten waste material from adhering to the screw.

[0037] To facilitate the efficient pyrolysis and depolymerization of polymer waste materials, the catalyst of this disclosure is preferably in particulate form. Particulate non-porous supports are preferably selected from the group consisting of sand, glass beads, and metal particles. The particulate non-porous supports can have any shape, such as spherical, cylindrical, or any non-uniform shape. In addition to being particulate, the supports used in the catalyst of this invention are also non-porous. Within the meaning of this disclosure, "non-porous" should be understood as impermeable to air, water, or other liquids.

[0038] The catalyst disclosed herein is specifically designed to be mixed with polymer waste materials undergoing depolymerization. To ensure adequate mixing, the catalyst preferably has an average particle size of 0.2 mm to 20 mm, preferably 0.5 mm to 10 mm, as determined by Coulter counter analysis according to ASTM D4438. The non-porous particulate support (preferably sand) has the following preferred particle size distribution.

[0039] Minimum maximum <3000μm 70％ 90％ >1400μm 40％ 80％ >1000μm 50％ 80％ <1000μm 0％ 20％

[0040] The acidic compound of the catalyst disclosed herein is preferably selected from the group consisting of: Al / Si mixed oxides, Al2O3, aluminosilicates, silica, and zeolites. Particularly preferred Al / Si mixed oxides in this disclosure refer to materials having a neutral structure comprising a mixture of Al2O3 and SiO2.

[0041] The zeolites mentioned in this disclosure should be understood as being composed of M having a general structure. n+ x / n [AlO2] - x (SiO2) y [+zH2O] co-angular SiO4 - and AlO4 - A crystalline microporous aluminosilicate composed of tetrahedra, where n is the charge of the cation M, which is typically an alkali metal, alkaline earth metal, or hydrogen ion, preferably an ion selected from the group consisting of: H + Na + Ca 2+ K + and Mg 2+ Furthermore, z defines the number of water molecules bound into this crystalline structure. Zeolites differ from mixed Al / Si oxides in that they define a pore structure and ionic properties. In a particularly preferred embodiment, the zeolite used as the acid compound is selected from the group consisting of zeolite Y, zeolite β, zeolite A, zeolite X, zeolite L, and mixtures thereof, particularly zeolite Y and zeolite β. The listed zeolites are known and commercially available. Zeolites in which the metal ion M is replaced by hydrogen are particularly preferred. Other specific examples of suitable zeolite-type components used in this disclosure include, but are not limited to, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, TS-1, TS-2, SSZ-46, MCM-22, MCM-49, FU-9, PSH-3, ITQ-1, EU-1, NU-10, silica zeolite-1, silica zeolite-2, boron zeolite-C, boron zeolite-D, BCA, and mixtures thereof.

[0042] In a particularly preferred embodiment, the acidic compound is an Al / Si mixed oxide. The composition of the Al / Si mixed oxide used as a support can be adjusted as needed. However, depolymerization is particularly effective when the acidic compound contains specific amounts of Al₂O₃ and SiO₂. Therefore, in a preferred embodiment, the acidic compound contains 20% to 99% Al₂O₃, preferably 30% to 80% by weight, and especially 40% to 70% by weight, based on the total weight of the acidic compound. Furthermore, based on the total weight of the acidic compound, the acidic compound preferably contains 1% to 80% by weight, preferably 20% to 70% by weight, and especially 30% to 60% by weight of SiO₂.

[0043] Surprisingly, it was found that if the acidic compound contains a slight excess of Al2O3, the results of the depolymerization process can be further improved. Therefore, in a preferred embodiment, the acidic compound comprises an excess of Al2O3. More preferably, the weight ratio of Al2O3 to SiO2 in the acidic compound is 99:1 to 30:70, preferably 9:1 to 3:2, and particularly embodiments of 4:1 to 3:2.

[0044] The SiO2 and Al2O3 contents of acidic compounds can be determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0045] The coating agent used in the catalyst disclosed herein is preferably selected from the group consisting of oil, inorganic hydrogel, or a combination thereof. As an inorganic hydrogel, a silica hydrogel is preferred. Regarding the oil used as the coating agent, a non-aromatic white mineral oil is preferred, and preferably based on isoparaffins. In a preferred embodiment, the oil used has a thickness of 140 to 180 mm at 20°C. 2 / s, preferably 150 to 170 mm 2 kinematic viscosity / s, and / or having a kinematic viscosity of 40 to 80 mm at 40°C. 2 / s, preferably 50 to 70 mm 2 kinematic viscosity / s, and / or having a kinematic viscosity of 5 to 15 mm at 100°C. 2 / s, preferably 7 to 10 mm 2 Kinematic viscosity per second. Kinematic viscosity can be determined according to ISO 3104.

[0046] In another preferred embodiment, the active compound is included in the catalyst disclosed herein in an amount of 0.5% to 6% by weight, preferably 2% to 4% by weight, based on the total weight of the catalyst.

[0047] The catalyst disclosed herein is preferably obtained by mixing a particulate nonporous support and a coating agent, and then adding an acidic compound in powder form to the resulting mixture. Optionally, the mixture may be heat-treated to obtain the catalyst. The heat treatment may be carried out, for example, at temperatures from 100°C to 600°C. In a preferred embodiment, the particulate nonporous support undergoes a drying step before being mixed with the coating agent.

[0048] In a preferred embodiment, the method of this disclosure is carried out in the presence of a catalyst, which is obtained by a method comprising the following steps:

[0049] a) Mixing the nonporous microparticle support with the coating agent; and

[0050] b) Add the acidic compound in powder form to the mixture from step a).

[0051] In a particularly preferred embodiment, the catalyst is characterized as follows:

[0052] • Sand as a non-porous support for microparticles;

[0053] • Al / Si mixed oxides or zeolites as acidic compounds; and

[0054] • Mineral oil or silica hydrogel used as a coating agent.

[0055] The preferred catalysts described above can be reactivated by heating, thus allowing for multiple uses and saving resources. Heat treatment is preferably carried out in an oxidizing atmosphere (such as air or oxygen) at a temperature of 500°C to 900°C, particularly 600°C to 900°C, alternatively 550°C to 850°C. The treatment time can be selected through experimental studies to find the optimal balance between catalyst activity and energy consumption. In this regard, the concentration of carbon residue on the catalyst is a parameter to consider. Preferably, the carbon residue on the regenerated catalyst is less than 20% by weight of the catalyst, more preferably less than 15%, more preferably less than 10%, and most preferably less than 5%. Treatment times of 0.5 hours to 100 hours, preferably 1 hour to 20 hours, and more preferably 2 hours to 10 hours are possible without excluding other treatment times.

[0056] This disclosure particularly relates to a method for treating waste cross-linked polyethylene. In particular, it is surprising to find that the method of this disclosure can be applied to different types of cross-linked polyethylene.

[0057] In a preferred embodiment, the cross-linked polyethylene in the polymer waste material is selected from the group consisting of: peroxide cross-linked polyethylene, silane cross-linked polyethylene, radiation cross-linked polyethylene, free radical cross-linked polyethylene, azo cross-linked polyethylene, UV-initiated free radical cross-linked polyethylene, and mixtures thereof.

[0058] In some key application areas, particularly pipes and cables (e.g., high-voltage cables), cross-linked polyethylene (XLPE) is used in conjunction with multi-component materials that may also contain polyolefins. These types of pipes and cables typically consist of multiple layers, with XLPE being one of them. Other materials include metals (particularly aluminum), adhesives, and other polymers such as EVOH. Although waste recycling is a common practice in pipe and cable production, the focus to date has been on Al recovery and limited to waste accumulated during the production process. Surprisingly, it has been found that even multi-component materials containing XLPE can be effectively used as waste material feedstocks in the methods of this disclosure. Therefore, in a preferred embodiment, polymer waste material is obtained from multi-component materials containing XLPE, particularly high-voltage cables, PEX pipes, PEX / Al / PEX pipes, PEX / Al / PE-RT pipes, and / or PEX / Al / PE pipes. Thus, the methods of this disclosure directly address the need for recycling processes for XLPE pipes.

[0059] In a particularly preferred embodiment, the waste material comprises or consists of at least one of the following:

[0060] i) 5-layer pipe: PEX / Ad / Alu / Ad / PEX

[0061] ii) 5-layer pipe: PEX / Ad / Alu / Ad / PE

[0062] ii) 5-layer tube: PEX / Ad / Alu / Ad / PERT

[0063] iv) 5-layer tube: PEX / Ad / EVOH / Ad / PEX

[0064] v) 5-layer pipe: PEX / Ad / EVOH / Ad / PE

[0065] vi) 5-layer tube: PEX / Ad / EVOH / Ad / PERT

[0066] vii) 3-layer tube: PEX / Ad / EVOH

[0067] viii) 3-layer tubing: Stainless steel / Ad / PEX

[0068] ix) 3-layer tube: copper / Ad / PEX

[0069] PEX describes the cross-linked polyethylene layer, Ad represents the adhesive, Alu represents aluminum, PE-RT represents polyethylene for elevated temperature applications, PE represents polyethylene, and EVOH represents ethylene-vinyl alcohol.

[0070] In another preferred embodiment, the polymer waste material comprises or consists of a blend comprising: shredded PEX pipe waste and a stream of plastic waste having a melt index (MFI / 21.6) greater than 10 g / 10 min, wherein the amount of plastic waste stream is preferably at least 40% by weight, preferably 40% to 80% by weight, based on the total weight of the waste material.

[0071] It constitutes the provision of this disclosure having at least 150 g / cm³ 3 A preferred embodiment of the polymer waste material with a bulk density of [specific value]. It has been found that the aforementioned bulk density value greatly facilitates a continuous, flow-free depolymerization method and prevents feed line blockage and reactor fouling. Furthermore, it contributes to obtaining low residue levels and enhanced depolymerization, thereby increasing the yield of the desired product. Preferably, the polymer waste material has a bulk density of 200 to 700 g / cm³, as determined according to DIN 53466. 3 Preferably, 200 to 600 g / cm³ 3 More preferably 250 to 550 g / cm³ 3 The packing density.

[0072] The polymer waste material is preferably shredded tube with a particle size of <50 mm, preferably <30 mm, more preferably <20 mm, and most preferably <15 mm.

[0073] In another preferred embodiment, the polymer waste material has a concentration of at least 300 g / cm³. 3 Shredded pipe with a bulk density and a particle size of <20mm and an organic content of at least 90% PE+PP.

[0074] To further enhance the sustainability of cross-linked polyethylene (XLPE) pipes (especially those containing aluminum), the method of this disclosure employs XLPE waste material raw materials that also contain aluminum. In this regard, in a preferred embodiment, the method of this disclosure further includes the step of collecting aluminum from the waste material raw material.

[0075] The method of this disclosure is characterized by generating liquid depolymerization products that can be used as feedstock for crackers in ethylene production. Therefore, a preferred embodiment of this disclosure involves releasing gaseous depolymerization products from a screw reactor via a gas release unit positioned along a screw conveyor, which then condenses into the desired liquid depolymerization product. In this way, different vapor fractions can be released sequentially along the screw and can be collected individually.

[0076] Surprisingly, the method of this disclosure produces highly selective depolymerization products. The specific combination of the screw reactor and particulate catalyst used in this disclosure further improves selectivity. Selectivity can be further improved by hot gas filtration, which can be advantageously combined with the collection of gaseous depolymerization products. Therefore, in a preferred embodiment, the collection of gaseous depolymerization products includes a hot gas filtration step.

[0077] In the method of this disclosure, the gaseous depolymerization products are at least partially condensed to produce liquid depolymerization products, which can be further processed into cracker feedstock. In a preferred embodiment of the method of this disclosure, the condensation of the gaseous depolymerization products is achieved by passing the gaseous depolymerization products sequentially through multiple condensation units. The condensation units can operate at different temperatures to facilitate the separation of high-boiling fractions, medium-boiling fractions, and high-boiling fractions of the depolymerization products.

[0078] In addition to exhibiting high selectivity, it has been surprisingly found that the method of this disclosure also allows for a relatively short residence time of the waste material in the reactor. Therefore, one embodiment of this disclosure is preferred, wherein the residence time of the waste material does not exceed 60 minutes, preferably not more than 45 minutes.

[0079] Surprisingly, the method disclosed herein can be carried out at advantageous low temperatures, which, combined with the short residence time of waste materials in the reactor, allows for the saving of valuable energy and a reduction in the carbon footprint. In a preferred embodiment, the reactor is therefore operated at a temperature of 350°C to 650°C, preferably 400°C to 590°C, and more preferably 430°C to 500°C. In another preferred embodiment, the reactor is operated at 0.7 to 10 bar. g Pressure operation.

[0080] In a preferred embodiment, the reactor is electrically heated. This heating method (particularly in conjunction with the successive release of different vapor fractions along the screw conveyor) is considered to further support detailed quality and thermal equilibrium of the depolymerization process, thereby allowing for high selectivity of the method disclosed herein.

[0081] The depolymerization products obtained by the methods of this disclosure may contain non-liquefiable fractions. In a preferred embodiment, these non-liquefiable fractions are reintroduced into the reactor to minimize the generation of unusable depolymerization waste. Furthermore, it has been found that the catalyst used in this method can be used in more than one cycle and can be reactivated due to activity loss. Therefore, in a preferred embodiment, at least a portion of the catalyst is reintroduced into the reactor.

[0082] During the process of this disclosure, it was discovered that the methane content in the gaseous depolymerization products can be used as an indicator of depolymerization progress. Therefore, in a preferred embodiment, the methane content in the collected gaseous depolymerization products is monitored.

[0083] The method disclosed herein produces depolymerization products with particular selectivity. In a preferred embodiment, the obtained liquid depolymerization product comprises 35% to 45% by weight of a high-boiling fraction, 40% to 50% by weight of a medium-boiling fraction, and 15% to 25% by weight of a low-boiling fraction.

[0084] The method disclosed herein surprisingly produces almost no to no carbon. Therefore, in a preferred embodiment, the residue from the depolymerization process of this disclosure has a carbon content of less than 5% by weight, preferably less than 2% by weight, based on the total weight of the product.

[0085] The obtained liquid depolymerization products can be further separated. Therefore, the method of this disclosure also includes the step of distilling the liquid depolymerization products.

[0086] It has also been found that the method of this disclosure produces depolymerization products with high gas content. In a preferred embodiment, based on the weight of the polymer fraction of the polymer waste material, the gas content in the depolymerization product after step iv) is preferably greater than 30% by weight of the gaseous component, more preferably greater than 50% by weight, particularly greater than 60% by weight, and especially greater than 70% by weight, and based on the total weight of the gaseous component, the gaseous component preferably contains greater than 50% by weight of olefins.

[0087] The gaseous fraction of the depolymerization products is further characterized by a high content of monomeric olefinic C2-C4- compounds, which are particularly useful for further processing, for example, for the production of polymers. Due to the large amount of these compounds generated during depolymerization, the gaseous depolymerization products can also be used directly as feedstock in cracking processes and subsequent polymerization. The gaseous products, containing light olefins and light alkanes, can be transferred, for example, through an oven to a downstream cracker to produce a polymerization-grade monomer stream. Other byproducts such as ethane, propane, and butane will be cracked in the oven. Thus, the step of processing the depolymerization products to obtain the desired monomers, which would normally be necessary, can be bypassed, saving valuable energy and reducing CO2 output.

[0088] i) Liquid depolymerization products

[0089] The obtained liquid depolymerization product preferably has a low content of aromatic compounds, especially low content of polycyclic aromatic compounds and asphaltane. Therefore, the liquid depolymerization product obtained by the method of this disclosure is characterized by low content of aromatic and olefinic components and high purity.

[0090] Preferably, the content of aromatic compounds in the obtained liquid depolymerization product is less than 10 mol%, preferably less than 5 mol%, and particularly not more than 3 mol%. The content of aromatic components is measured as follows: 1 The content of aromatic protons, expressed in mol%, as determined by H-NMR spectroscopy.

[0091] Furthermore, the liquid depolymerization products obtained by the depolymerization method of this disclosure are characterized by low content of olefins. Based on the total number of hydrocarbon protons, the content of olefins in the liquid depolymerization products is preferably less than 5 mol%, more preferably less than 3 mol%, even more preferably less than 1.5 mol%, and particularly not more than 1 mol%. The content of olefins is based on, as described by... 1 The content of olefinic protons is determined by H-NMR spectroscopy.

[0092] Another measure of the double bond content in a given sample is the bromine value (BrNo.), which indicates the degree of unsaturation. In a preferred embodiment, the liquid depolymerization product obtained by the method of this disclosure has a bromine value (expressed as g bromine / 100 g sample) of less than 25, preferably 0.1 to 20, more preferably 0.2 to 15, even more preferably 0.3 to 10, and particularly 0.5 to 5, as determined according to ASTM D1159-01.

[0093] The liquid depolymerization product obtained by the method of this disclosure preferably has a boiling point range of 30°C to 650°C, more preferably 50°C to 250°C. By separation techniques such as distillation, the depolymerization product can be separated into hydrocarbon fractions with different boiling point ranges, such as light naphtha fractions mainly containing C5 and C6 hydrocarbons with a boiling point range of 30°C to 130°C, and fractions mainly containing C6 to C6 hydrocarbons with a boiling point range of 130°C to 220°C. 12 Heavy naphtha fraction of hydrocarbons, mainly containing C9 to C6 hydrocarbons with boiling points ranging from 220°C to 270°C. 17 Hydrocarbons can be separated into kerosene fractions or other high-boiling fractions, such as diesel fuel, fuel oil, or wax oil.

[0094] Surprisingly, the liquid depolymerization products contain little to no solid residues typically found in common depolymerization processes. In a preferred embodiment, the residue content of the liquid depolymerization products upon evaporation, as determined by ASTM D381, does not exceed 5 ppm (w).

[0095] ii) Gaseous depolymerization products

[0096] The obtained gaseous depolymerization product preferably has a low content of low-molecular-weight hydrocarbons, such as methane or ethane. As mentioned above, the gaseous depolymerization product preferably contains a large amount of higher olefins, such as ethylene, propylene, and butene, which are generally required for polyolefin production. Therefore, the gaseous depolymerization product obtained by the method of this disclosure is characterized by: a high content of any one of ethylene, propylene, and butene and / or a low content of saturated low-molecular-weight hydrocarbons, particularly those of the general formula C n H 2n+2 The hydrocarbon, where n is a real number ranging from 1 to 4.

[0097] Therefore, in a preferred embodiment, the gaseous depolymerization products of the method of this disclosure are characterized by a methane content of up to 5% by weight, preferably up to 4% by weight, more preferably up to 3% by weight, most preferably up to 2% by weight, and especially up to 0.5% to 1.5% by weight, based on the total weight of the gaseous depolymerization products after step iv) of the method of this disclosure.

[0098] Surprisingly, the gaseous depolymerization products obtained by the method disclosed herein contain a large amount of low-molecular-weight olefins, especially C. n H 2n The gaseous fractions can therefore be used directly as feedstock for further processing downstream of the cracker (e.g., feed gas compressor) to obtain a purified monomer stream, and subsequently used for polymer production, thereby allowing bypassing the typically energy-intensive flow cracker while reducing CO2 output. Thus, in a preferred embodiment, the gaseous depolymerization products of the method of this disclosure are characterized by: based on the total weight of the gaseous depolymerization products after step iv) of the method of this disclosure, at least 50% by weight, preferably at least 60% by weight, more preferably at least 65% by weight, most preferably at least 70% by weight, and especially at least 75% by weight of the general formula C n H 2n The content of compounds of (olefins) (where n = 2-4).

[0099] The gaseous depolymerization products may contain small amounts of HCl, HCN, H2S, H2O, NH3, COS, etc., which may optionally be separated in the refining step before being introduced into the downstream section of the steam cracker.

[0100] The methods of this disclosure will be explained in more detail with reference to the following embodiments, which should in no way be construed as limiting the scope and spirit of this disclosure.

[0101] The following analytical methods were used:

[0102] 1) GC MS is used for liquid and gas analysis.

[0103] 2) After decoking the reactor residue at 800℃, the carbon residue is determined based on mass balance.

[0104] 3) The liquid content was characterized using SimDist analysis according to ASTM D 7213:2012.

[0105] 4) The total content of unsaturated components in liquid condensates is characterized by bromine value determination using an 848 Titrino Plus (Metrohm AG, Herisau, Switzerland) equipped with a dual PT wire electrode with an integrated PT1000 temperature sensor and a 10 ml burette, according to ASTM D1159-01 (as described in Metrohm Application Bulletin 177 / 5e, December 2018). The bromine value (BrNo.) represents the amount of bromine absorbed by 100 grams of sample (in grams).

[0106] 5) 1 H-NMR analysis was performed by dissolving the liquid condensate sample in CDCl3 and characterizing the sample using proton NMR spectroscopy. Aromatic, alkene, and aliphatic protons were designated according to the chemical shifts summarized in Table 1.

[0107] Table 1- 1 Integral region in H-NMR spectrum

[0108] Peak attribution <![CDATA[ 1 H chemical shift (ppm) <![CDATA[I1 (Aromatic protons)]]> 8.25–7.27 <![CDATA[CDCl3 - Solvent]]> 7.26 <![CDATA[I2 (aromatic protons)]]> 7.25–6.60 <![CDATA[I3 (olefinic proton - type 2)]]> 6.60–5.95 <![CDATA[I4 (olefinic proton - type 1)]]> 5.95–5.67 <![CDATA[I5 (olefinic proton - type 2)]]> 5.67–5.35 <![CDATA[I6 (olefinic proton - type 3)]]> 5.35–5.15 <![CDATA[I7 (olefinic proton - type 1)]]> 5.15–4.85 <![CDATA[I8 (olefinic proton - type 4)]]> 4.85–4.40 <![CDATA[I9…(Protons of alkanes)]]> 4.40–0.25

[0109] Assume that the listed types of olefinic protons correspond to the following structures:

[0110]

[0111] The amounts of aromatic, alkene, and aliphatic protons can be determined based on the peak integral of the distribution according to the following equation:

[0112] Aroma proton Mol% = [(I1+I2) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0113] 1 Mol% of alkene proton types = [(I4+I7) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0114] 2 Mol% of alkene proton types = [(I3+I5) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0115] 3 Mol% of alkene proton types = [(I6) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0116] 4 Mol% of alkene proton types = [(I8) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0117] Alkane protons Mol% = [(I9) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)]%

[0118] 6) The water content of the catalyst was determined using Sartorius MA45 (Sartorius AG, Göttingen, Germany) at 180°C on samples ranging from 0.5 g to 1 g.

[0119] 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.

[0120] 8) Determine the particle size distribution of the particulate nonporous support and catalyst using Coulter counter analysis according to ASTM D4438.

[0121] 9) The characteristics of the organic waste materials used were determined as follows:

[0122] Since the composition of waste materials can vary, samples of waste materials ranging from 20g to 100g are ground and analyzed. Alternatively, granulated samples of polymer waste are analyzed.

[0123] Use the following methods:

[0124] i) Total volatile matter (TV) is measured as the weight loss of a 10g sample after 2 hours at 100°C and 200 mbar.

[0125] ii) Determine water content by Karl Fischer titration using a device equipped with a PT100 indicator electrode for volumetric KF titration from Metrohm 915KF Ti-Touch, conforming to ASTM E203 and Metrohm Application Bulletin 77 / 3e.

[0126] iii) IR spectroscopy is used for qualitative identification of various polymers (PP, PE, PS, PA, PET, PU, ​​polyester) and additives such as CaCO3.

[0127] iv) Standard elemental analysis is 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).

[0128] v) 1 H-NMR is used to determine substances that are soluble in sufficient quantities for recording. 1 Composition of polymers in solvents in H-NMR spectra: PE / PP equilibrium (including copolymers), PET, PS

[0129] vi) Determine the ash content of plastics at 800°C according to DIN EN ISO 3451-1 (2019-05).

[0130] vii) Determine the bulk density of polymer waste according to DIN 53466.

[0131] viii) The corrosivity was determined by measuring the pH of the aqueous solution (5g sample in 50ml of distilled water) after 3 hours of contact.

[0132] ix) Inductively coupled plasma atomic emission spectrometry (ICP-AES) is used for quantitative elemental determination (total chlorine content, Si or metal content).

[0133] Various catalysts were prepared and tested in the depolymerization of different polymer waste materials.

[0134] The particulate nonporous support used as the catalyst is sand with a particle size distribution as summarized in Table 2.

[0135] Table 2: Particle Size Distribution

[0136] sand weight % >1400μm 40,55％ >1400μm->1000μm 55,30％ <1000μm 4,15％

[0137] 99% of the particles were smaller than 3 mm. The sand was pre-dried at 80°C for 24 hours in a drying oven with circulating air.

[0138] Catalyst #4:

[0139] The acidic compound was mixed with 25 kg of sand to obtain the catalyst shown in Table 4.

[0140] Catalyst #3:

[0141] 25.0 kg of sand was placed in a 60 L steel drum fitted with a nut and equipped with a Teflon insert. 350 ml of mineral oil was added (corresponding to 1.4 wt% relative to the sand). The drum was placed on a rotary ring mixer and rotated for 1 hour (approximately 100 rpm). 24.5 kg of the resulting mixture was placed in another drum, and 500 g of the corresponding acidic component (corresponding to a 2 wt% loading) was added. The drum was placed on a rotary ring mixer and rotated for 1 hour (approximately 100 rpm). At the end of the mixing process, a free-flowing catalyst was obtained, in which the acidic component particles were uniformly distributed on the surface of the sand particles.

[0142] Because it uses Ondina X 432 mineral oil, which is commercially available from Shell, it has the following characteristics:

[0143] Table 3:

[0144] nature method Shell Ondina X 432 <![CDATA[Kinematic viscosity at 20 °C, unit: mm 2 / s]]> ISO 3104 165 <![CDATA[Kinematic viscosity at 40 °C, unit: mm 2 / s]]> ISO 3104 59 <![CDATA[Kinematic viscosity at 100 °C, unit: mm 2 / s]]> ISO 3104 9.0

[0145] Preparation of catalysts #1 to #2

[0146] The catalyst using silica hydrogel as a coating agent disclosed herein is prepared as follows:

[0147] 25.0 kg of sand was placed in a 60 L steel drum fitted with a nut and equipped with a Teflon insert. 500 ml of water was added (corresponding to 2.0 wt% relative to the sand), and the drum was placed on a rotary ring mixer and rotated for 1 hour (approximately 100 rpm). 24.5 kg of the resulting mixture was placed in another drum, and 1000 g of a 1:1 milled, free-flowing mixture of silica hydrogel and acidic compound was added (corresponding to a 2 wt% loading). The drum was placed on a rotary ring mixer and rotated for 1 hour (approximately 100 rpm). At the end of the mixing process, a free-flowing catalyst was obtained, in which the acidic compound particles were uniformly distributed on the surface of the sand particles. The resulting mixture was vacuum dried at 120 °C for 6 hours.

[0148] Silica hydrogels were prepared according to Example 1 of EP1290042. The solids content of the hydrogel sample was 20% by weight. According to ASTM D4438, the D50 of the milled mixture of silica hydrogel and acidic component was between 80 μm and 100 μm.

[0149] Table 4 summarizes the catalysts used, with the amount of acidic compounds given as a percentage of weight relative to sand.

[0150] Table 4

[0151] catalyst# Coating acidic compounds Amount of acidic compounds 1 silica hydrogel Zeolystβ 2 2 silica hydrogel Zeolyst ZSM-5 2 3 Oil Zeolystβ 2 4 none Zeolystβ 2

[0152] Acidic compounds:

[0153] Zeolyst ZSM-5 and Zeolystβ (CP811E-75) are commercially available from PQ Corporation, Malvern, PA, USA.

[0154] raw material:

[0155] The following organic waste materials are used as raw materials:

[0156] A) Shredded multilayer PEX pipe waste with an aluminum layer (particle size <20mm)

[0157] B) Shredded PEX pipe waste with EVOH (particle size <20mm)

[0158] C) Shredded PEX pipe waste with an aluminum layer (particle size <20mm)

[0159] D) Shredded single-layer PEX pipe waste (particle size <20mm)

[0160] E) Shredded cross-linked waste from high-voltage cables (particle size <20mm)

[0161] F) Mixed plastic waste from shredded and granulated household packaging (comparison)

[0162] G) A 1:1 mixture of raw material D) and post-consumer recycled material with MFR(21,6) of 20 g / 10 min is blended at 190 °C to obtain extrudable pellets with MFR(21,6) of 15 g / 10 min.

[0163] The average characteristics of the raw materials from the analysis of the three samples are summarized in Table 5.

[0164] Table 5:

[0165]

[0166] Ash content: Ash content

[0167] TV: Total Volatile Matter

[0168] BD: Bulk Density

[0169] CL: Total chlorine content

[0170] PE: Polyethylene content

[0171] PP: Polypropylene content

[0172] PET: Content of polyethylene terephthalate

[0173] PS: Polystyrene content

[0174] PA: Polyamide content

[0175] Other contents: content of other pollutants

[0176] The feedstock and catalyst were introduced into a reactor at 450°C with a screw conveyor, and the residence time was 30 minutes. The product composition of the depolymerization process is summarized in Table 6. The obtained gaseous fraction was further separated into liquid and gaseous depolymerization products by condensation. The amounts of the obtained fractions are also given in Table 6.

[0177] Table 6: Process Parameters and Quality Balance

[0178] run# catalyst# raw material <![CDATA[Wax % 1 > <![CDATA[Liquid % 2) > <![CDATA[H2O%]]> gas% Residue % loss% 1 1 A 0 11.7 0.7 60.3 28.4 -1.1 2 1 B 0 20.3 0.9 82 0 -3.2 3 1 C 0 13.2 0.6 77.4 12.1 -3.3 4 1 D 0 18.5 0.8 81.7 1.9 -2.9 5 1 E 0 16.6 0.9 74.4 7.2 0.9 C6 1 F 0 36.2 - 52.9 8.9 1.9 C7 4 F (0) <![CDATA[46.7 *) ]]> - 32.4 10.1 10.7 C8 Catalyst-free F (0) <![CDATA[52.4 *) ]]> - 29 18 1

[0179] 1) It is a solid at room temperature; 2) It is a liquid at room temperature.

[0180] *): Pale yellow particles are visible after cooling, and the liquid fraction becomes a suspension containing wax.

[0181] Runs #1-5 demonstrate highly efficient depolymerization of cross-linked plastic waste, generating over 70% gas with a hydrocarbon content greater than 95%. The resulting HC liquid exhibits low viscosity and appears brown / red. In contrast, the HC liquid obtained from runs #C7-C8 is black, with high viscosity and visible wax particles. It is also noteworthy that the small amounts of methane, CO, and CO2 obtained in the inventive runs #1-5 indicate high selectivity of the employed catalyst for olefins.

[0182] Run #4 was repeated with raw material G. As expected, very similar results were obtained as with raw material D.

[0183] During operation #C7, significant losses due to reactor scaling were observed.

[0184] The resulting residue / sand mixture from runs #1 and #3 is sieved on a 2 mm grid. This effectively separates the aluminum layers from the sand / residue mixture, allowing for further recycling of the PEX tubes to an aluminum content of up to 90% of the total Al content, even with simple sieving.

[0185] Specifically, based on starting material A, 18% of the Al yield can be recovered in operation #1 and 9% of the Al yield can be recovered in operation #3.

[0186] The bulk density tests were also conducted in the same reactor apparatus at densities of 60 and 150 g / cm³. 3 The operation of polymer waste materials was compared. Repeated blockages in the feed line and reactor scaling negatively impacted operation, making it cumbersome.

[0187] Table 7 shows the mass balance of the gaseous depolymerization products obtained in runs #1-8.

[0188] Table 7: Mass Balance of Gaseous Depolymerization Products

[0189] run 1 2 3 4 5 C6 C7 C8 raw material A B C D E F F F catalyst# 1 1 1 1 1 1 4 Catalyst-free Components weight% weight% weight% weight% weight% weight% weight% weight% <![CDATA[H2]]> 0 0.1 0.1 0.1 0.1 0.0 0.0 0.0 CO 0.6 0 0 0.0 0.0 11.4 11.3 6.4 <![CDATA[CO2]]> 3.7 0.6 0.5 0.5 2.0 22.6 22.3 36.5 <![CDATA[CH4]]> 0.5 0 0 0.0 0.6 5.5 5.4 3.6 <![CDATA[C2H6]]> 0.4 0.6 0.7 0.5 0.4 7.6 7.5 5.8 <![CDATA[C2H4]]> 1.1 1.4 1.5 2.0 1.6 6.8 6.7 5.1 <![CDATA[C3H8]]> 3.4 2.7 3.2 3.4 0.7 7.1 7.0 4.4 <![CDATA[C3H6]]> 34.6 28.8 28.3 29.6 32.1 15.1 14.9 15.6 butane 27.9 23.4 22.6 23.2 22.5 3.6 3.5 1.8 Butene 27.7 42.4 43.2 40.7 40.0 8.9 8.9 10.8 the remaining 0 0 0 0.0 0.0 11.4 12.5 10.2 Olefins 63.4 72.6 73.0 72.3 73.7 30.8 30.5 31.4 Total HC 95.6 99.3 99.5 99.4 97.9 54.6 54.0 46.9 Olefins / HC 66.3 73.1 73.4 72.7 75.3 56.3 56.4 66.9

Claims

1. A method for generating cracker feedstock by depolymerizing a polymer waste material comprising cross-linked polyethylene (PEX), the method comprising the following steps: i) Introduce the waste material raw material into the pyrolysis reactor; ii) Mix the waste material with a depolymerization catalyst containing an acidic compound; iii) The waste material is depolymerized in an oxygen-free atmosphere at a temperature ranging from 400°C to 590°C to obtain gaseous depolymerization products; iv) Collect and condense at least a portion of the gaseous depolymerization products to obtain the desired cracker feedstock. The polymer waste material is shredded pipe or shredded high-voltage cable cross-linked waste with a particle size of <20 mm.

2. The method according to claim 1, characterized in that, The acidic compound of the catalyst is deposited on the non-porous support of the microparticles by means of a coating agent.

3. The method according to claim 2, characterized in that, The acidic compound is selected from the group consisting of: Al / Si mixed oxides, Al2O3, aluminosilicates, silicon dioxide, and zeolites.

4. The method according to claim 2, characterized in that, The non-porous microparticle support is selected from the group consisting of sand, glass beads and metal particles, and the coating agent is selected from the group consisting of oil, inorganic hydrogels and combinations thereof.

5. The method according to claim 1, characterized in that, The waste material also contains aluminum, and the method further includes the step of collecting aluminum from the waste material.

6. The method according to claim 1, characterized in that, Based on the total weight of the dry weight polymer fraction of the waste material raw material, the polymer waste material contains less than 12% by weight of non-polyolefin components in the polymer fraction.

7. The method according to claim 1, characterized in that, According to DIN 53466, the polymer waste material has a content of at least 150 g / cm³. 3 The packing density.

8. The method according to claim 1, characterized in that, The cross-linked polyethylene in the polymer waste material is selected from the group consisting of: peroxide cross-linked polyethylene, silane cross-linked polyethylene, radiation cross-linked polyethylene, free radical cross-linked polyethylene, azo cross-linked polyethylene, and mixtures thereof.

9. The method according to claim 8, characterized in that, The free radical cross-linked polyethylene is UV-initiated free radical cross-linked polyethylene.

10. The method according to claim 1, characterized in that, The polymer waste material is obtained from PEX pipes, PEX / Al / PEX pipes, PEX / Al / PE-RT pipes, and / or PEX / Al / PE pipes.

11. The method according to claim 1, characterized in that, The polymer waste material comprises or consists of the following: shredded PEX pipe waste and a stream of plastic waste having a melt index (MFI / 21.6) greater than 10 g / 10 min, wherein the amount of the plastic waste stream is at least 40 g based on the total weight of the waste material.

12. The method according to claim 1, characterized in that, The method is carried out in a reactor with a screw conveyor, and the gaseous depolymerization products are released from the reactor through a gas release unit placed along the screw conveyor.

13. The method according to claim 12, characterized in that, The residence time of the waste material in the reactor shall not exceed 60 minutes.

14. The method according to claim 1, characterized in that, The reactor operates at 0.7 to 10 bar. g Pressure operation.

15. The method according to claim 1, characterized in that, Based on the weight of the polymer fractions of the polymer waste material, the collected gaseous depolymerization products contain more than 30% by weight of gaseous components, wherein, based on the total weight of the gaseous components, the gaseous components contain more than 50% by weight of olefins.

16. The method according to claim 1, characterized in that, The depolymerized liquid product comprises 35 wt% to 45 wt% of a high-boiling fraction, 40 wt% to 50 wt% of a medium-boiling fraction, and 15 wt% to 25 wt% of a low-boiling fraction, wherein the high-boiling fraction has a boiling point range of 220°C to 270°C, the medium-boiling fraction has a boiling point range of 130°C to 220°C, and the low-boiling fraction has a boiling point range of 30°C to 130°C.

17. The method according to claim 1, characterized in that, The pyrolysis reactor is a reactor equipped with a screw conveyor.

18. The method according to claim 2, characterized in that, The acidic compounds consist of the group consisting of zeolite Y, zeolite β, zeolite A, zeolite X, zeolite L, and mixtures thereof.

19. The method according to claim 2, characterized in that, The acidic compounds consist of the group consisting of zeolite Y and zeolite β.

20. The method according to claim 1, characterized in that, Based on the total weight of the dry weight polymer fraction of the waste material raw material, the polymer waste material contains less than 10% by weight of non-polyolefin components in the polymer fraction.

21. The method according to claim 1, characterized in that, According to DIN 53466, the polymer waste material has a content of 200 to 700 g / cm³. 3 The packing density.

22. The method according to claim 1, characterized in that, According to DIN 53466, the polymer waste material has a content of 200 to 600 g / cm³. 3 The packing density.

23. The method according to claim 1, characterized in that, According to DIN 53466, the polymer waste material has a content of 250 to 550 g / cm³. 3 The packing density.

24. The method according to claim 1, characterized in that, The polymer waste material comprises or consists of the following: shredded PEX pipe waste and a stream of plastic waste having a melt index (MFI / 21.6) greater than 10 g / 10 min, wherein the amount of the plastic waste stream present is 40% to 80% by weight based on the total weight of the waste material.

25. The method according to claim 12, characterized in that, The residence time of the waste material in the reactor shall not exceed 45 minutes.

26. The method according to claim 1, characterized in that, Based on the weight of the polymer fractions of the polymer waste material, the collected gaseous depolymerization products contain more than 50% by weight of gaseous components, wherein, based on the total weight of the gaseous components, the gaseous components contain more than 50% by weight of olefins.

27. The method according to claim 1, characterized in that, Based on the weight of the polymer fractions of the polymer waste material, the collected gaseous depolymerization products contain more than 60% by weight of gaseous components, wherein, based on the total weight of the gaseous components, the gaseous components contain more than 50% by weight of olefins.

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