Conversion of plastic waste to hydrocarbons using transition metal oxides.

Abstract

a) contacting plastic waste with steam and a hydrogen control material comprising at least one transition metal and / or an oxide thereof, where the transition metal is not in its highest oxidation state, thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, and oxidizing said hydrogen control material to an oxidized hydrogen control material; and x) A step of extracting the mixture of hydrocarbons in gaseous form. 1. A method for producing a mixture of hydrocarbons from plastic waste, comprising:

Description

[Technical Field]

[0001] The present invention relates to the field of polymer recycling, in particular the recycling of polymers into their monomeric fraction. Even more specifically, the present invention relates to the recycling of polymers by steam cracking. [Background technology]

[0002] The use of fluidized bed technology to break down plastic waste into chemicals has been thoroughly investigated since the 1970s, as outlined, for example, in U.S. Pat. No. 3,985,820. Much effort has been directed toward the production of oils and other heavier chemicals as a means of treating plastic waste. However, these methods suffer from the drawback of not being able to directly access the monomer portion of the polymer. However, access to such technology is desirable because it would completely close the cycle of polymer recycling.

[0003] Recent developments have therefore also targeted the recovery of monomers, particularly olefins, from plastic waste, although with varying degrees of success. International Publication No. 2020 / 169888 outlines a method for producing hydrocarbons, particularly olefins, by vaporizing plastic waste in the presence of sand and Ca-containing species. However, a significant fraction of heavy compounds is still produced in addition to the olefin fraction. The advantage of these methods is the lack of multifunctional catalysts, which are highly sensitive to the various contaminants present in the waste stream. However, the product distribution in these methods is generally controlled by the peak cracking temperature. Therefore, these methods are purely thermally controlled. Furthermore, higher selectivity to the monomer portion of the process output is generally achieved using higher temperatures (i.e., higher severity), making the process energetically unfavorable.

[0004] Therefore, polymer cracking processes using catalytically active fluidized bed materials have been developed. These catalytically active fluidized bed materials interact with the radical pool in the reaction zone, causing a change in the product distribution. Steam cracking of long-chain saturated hydrocarbons proceeds via a free radical reaction mechanism. The initial hydrocarbon chain undergoes random scission by C-C bond cleavage, forming two free radicals. [ka]

[0005] This first step forms a primary radical, which can undergo intramolecular H-atom migration (backbiting) to generate more stable secondary or tertiary radicals. [ka]

[0006] Thus, the initial distribution of hydrogen atoms along the carbon chain is altered by intramolecular H atom transfer. Further reactions of these radicals result in the formation of unstable free radicals with H / C ≠ 2, such as the methyl free radical. These unstable free radicals can in turn remove H atoms from surrounding molecules and free radicals, a process known as intermolecular H atom transfer. Intermolecular H atom transfer further disrupts the distribution of H atoms and can lead to the removal of H atoms from stable molecules such as ethylene. [ka]

[0007] H atom transfer results in the formation of products with H / C ratios varying from 0 to 4. Thus, the products obtained from steam cracking of naphtha-like hydrocarbons, such as polyethylene, can be divided into two groups: 1. H / C=2 (same as the H / C ratio of the initial polyethylene molecule) 2. H / C≠2 (formed due to H atom migration)

[0008] Table 1 shows the products that belong to each category. [Table 1]

[0009] In the absence of H-atom transfer, the products of steam cracking are expected to have the same H / C ratio as the feed. Steam cracking of polymers such as poly(methyl methacrylate) (PMMA) and polystyrene (PS) preserves not only the H / C ratio but also the molecular structure. Random scission of PMMA and PS molecules leads to the formation of tertiary free radicals, which are relatively more stable than primary free radicals. Furthermore, the presence of functional groups -COOCH3 and -C6H5 provides steric hindrance, preventing the detachment of H atoms from the hydrocarbon chain.

[0010] Thus, H-atom transfer is important in the steam cracking of polymeric (e.g., polyolefin) hydrocarbons, as it prevents the production of light monomers (e.g., olefins: ethylene and propylene) and contributes to the production of less valuable hydrocarbons (methane, carbon oxides, aromatics, etc.). This is particularly relevant since H-atom transfer during the steam cracking of polyolefins is unavoidable due to the absence of tertiary carbon atoms and the lack of steric hindrance along the polymer chain.

[0011] As a solution, the prior art offers a hydrocracking process. During the hydrocracking process, cracked hydrocarbon molecules are immediately hydrogenated under high hydrogen partial pressure. The catalysts used in these processes are bifunctional catalysts with cracking and hydrogenation functions. The hydrogenation function works on the principle of activating the catalyst by adsorbing hydrogen under very high pressure (greater than 200 bar). The adsorption of hydrogen atoms onto the surface of platinum (hydrocracking catalyst) is shown in Figure 1. Without the adsorption of hydrogen atoms under high pressure, hydrogen molecules behave chemically inertly due to their high bond dissociation energy (436 kJ / mol).

[0012] However, compared to the steam cracking process described above, the hydrocracking process has the drawback of requiring significantly higher pressures to operate, which leads to the usual disadvantages of high energy consumption, high demands on the equipment used, and potential explosion hazards. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Patent No. 3,985,820 [Patent Document 2] International Publication No. 2020 / 169888 Summary of the Invention [Problem to be solved by the invention]

[0014] It is therefore an object of the present invention to find a process for steam cracking polymers, in particular polyolefins, which has low energy requirements, high safety standards and high selectivity to the monomer portion of the polymer, in particular the olefins. It is a further object of the present invention to provide such a steam cracking process which can be carried out continuously. [Means for solving the problem]

[0015] Surprisingly, the above objectives are: a) contacting plastic waste with steam and a hydrogen-control material comprising at least one transition metal and / or its oxide, wherein said transition metal is not in its highest oxidation state, thereby producing a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, and oxidizing said hydrogen-control material to an oxidized hydrogen-control material; and x) A step of extracting the hydrocarbon mixture in gaseous form It has been found that this can be achieved by a method for producing a mixture of hydrocarbons from plastic waste, comprising: [Brief explanation of the drawings]

[0016] [Figure 1] Figure 1 is a schematic diagram of hydrogen activation by a hydrocracking catalyst. [Figure 2] Figure 2 is a schematic diagram of hydrogen activation from water molecules by transition metals. [Figure 3] FIG. 3 is a schematic diagram of the hydrogenation and recycling mechanism of the hydrogen control material of the present invention. [Figure 4] FIG. 4 is a schematic diagram of a typical dual fluidized bed (DFB) system configuration. [Figure 5] FIG. 5 is a schematic diagram of the configuration of a dual fluidized bed system of the present invention. [Figure 6] FIG. 6 is a schematic diagram of the reactor setup used in the comparative and inventive examples. [Figure 7] Figure 7 shows the hydrogen concentration profile during oxidation of reduced bauxite in steam at 800°C. [Figure 8] FIG. 8 is a diagram showing the yield of light olefins in comparison between the comparative example (CE) and the example of the present invention (IE). [Figure 9] Figure 9 is a backscattered electron micrograph of 2Fe / Al2O3 particles. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a method of contacting steam with plastic waste and a hydrogen control material comprising at least one transition metal and / or its oxide that is not in its highest oxidation state.

[0018] In this way, hydrogen control materials help prevent intramolecular H atom migration, which can lead to the formation of secondary or tertiary free radicals and thereby cause the generation of other undesirable by-products of the desired monomer portion of the polymer.

[0019] Any transition metal and / or its oxide can be used as the hydrogen control material, as long as the transition metal is not in its highest oxidation state. In other words, the transition metal is in an oxidation state that can reduce HO to H under the specified conditions. Preferably, the transition metal of the hydrogen control material is selected from the list consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. However, the selection of the hydrogen control material generally depends on the minimum process temperature. For example, of all transition metals, Cr, Mn, Zn, and Fe can be oxidized by steam (at a pressure of at least 1 bar) at temperatures above 100°C, preferably in the range of 500-1200°C, more preferably in the range of 700-1000°C, and most preferably in the range of 700-900°C. Therefore, more preferably, the transition metal of the hydrogen control material is selected from the list consisting of Cr, Mn, Zn, and Fe. Most preferably, the transition metal of the hydrogen control material is Fe.

[0020] The hydrogen control material is preferably an oxide of a transition metal. Preferably, the transition metal has the second highest oxidation state. Most preferably, the transition metal has the lowest oxidation state.

[0021] In a specific embodiment, the hydrogen control material comprises a non-oxidized transition metal, such as iron in the zero oxidation state.

[0022] In another specific embodiment, the hydrogen control material comprises a transition metal oxide such as iron(II) oxide and / or iron(III) oxide, particularly iron(III) oxide. More specifically, the hydrogen control material comprises iron(III) oxide (i.e., FeO).

[0023] In a further specific embodiment, the hydrogen control material is selected from reduced bauxite or Al2O3 particles coated (at least partially) with iron (III) oxide, preferably in an amount equivalent to 2 wt. % atomic iron ("2Fe / Al2O3").

[0024] To carry out the reactions described below, it is particularly necessary that the hydrogen control material be in direct contact with the steam.

[0025] Without being bound by theory, it is believed that transition metals that are not in their highest oxidation state split water molecules into hydrogen and oxygen: [ka]

[0026] Because water molecules react on the transition metal surface, the hydrogen generated on the metal surface can be likened to hydrogen adsorbed on a hydrocracking catalyst (Figure 1). Figure 2 shows the decomposition of water molecules on such a transition metal surface.

[0027] Thus, when used in the steam cracking of hydrocarbons, hydrogen-control materials hydrogenate the free radicals produced while simultaneously decomposing the polymer chains. The H atoms required for hydrogenation are provided by the decomposition of water molecules on the surface of these materials, while the oxygen atoms of the water molecules oxidize the transition metal (e.g., M to MeO).

[0028] The hydrogen oxide control material is preferably recycled to the process after reduction with a suitable reducing agent. Such reducing agent is preferably selected from the list consisting of carbon monoxide, methane, and hydrogen. Such a recycling process is depicted in Figure 3.

[0029] Plastic waste generally contains a polymer backbone composed of uninterrupted C-C chains. Therefore, plastic waste preferably contains polymers such as polyolefins and halogenated polymers such as PVC and PTFE. More preferably, plastic waste contains polyolefins such as polyolefins. Plastic waste may contain one or more polyolefins selected from polyethylene homopolymers, polyethylene copolymers, polypropylene homopolymers, and polypropylene copolymers. Most preferably, plastic waste contains polyethylene. It is preferred that plastic waste be substantially free of additives such as fillers, antioxidants, and common additives.

[0030] The mixture of hydrocarbons preferably includes a monomer that can be used to polymerize one of the polymers in the plastic waste, and more preferably includes at least one of ethene, propene, and butene.

[0031] The temperature of step a) of the method of the present invention depends on the transition metal of the hydrogen control material used. In general, the method of the present invention can usually be carried out at room temperature. Nevertheless, higher temperatures increase the reaction rate. Therefore, preferably, step a) of the method of the present invention is carried out at a temperature above 500°C. More preferably, step a) of the method of the present invention is carried out at a temperature above 700°C. Typically, step a) of the method of the present invention is carried out at a temperature below 1000°C.

[0032] Preferably, step a) of the process of the present invention is carried out at atmospheric or reduced pressure, more preferably at a pressure at which steam can exist in a subcritical state at the temperature used in process step a).

[0033] Preferably, step a) of the method of the present invention is carried out as a fluidized bed process, with steam forming part of the carrier gas and at least the hydrogen control material forming part of the fluidized bed material. It is essential to the present invention that the hydrogen control material be in contact with the steam and the plastic waste. Therefore, the hydrogen control material can be located anywhere in the fluidized bed material, but it must be ensured that it is in at least partial direct contact with the steam and the plastic waste. Preferably, in such a case, at least a portion of the hydrogen control material is located on at least a portion of the surface of the fluidized bed material. This is necessary to allow the steam and the plastic waste to come into contact with said hydrogen control material. Preferably, more than 50% of the surface of the fluidized bed material is covered by the hydrogen control material, and more preferably, more than 80% of the surface of the fluidized bed material is covered by the hydrogen control material. Preferably, the remainder of the fluidized bed material is chemically inert to the hydrogen activation reaction. More preferably, the remainder of the fluidized bed material is capable of transferring heat. Even more preferably, the remainder of the fluidized bed material is a metal oxide satisfying the aforementioned two properties. Therefore, even more preferably, such a metal oxide is selected from the list consisting of SiO2, Al2O3, and MgO. Most preferably, the fluidized bed material is reduced bauxite.

[0034] In one embodiment, step a) of the process is carried out as a fluidized bed process, wherein the fluidized bed material comprises particles of a metal oxide selected from SiO, AlO, and MgO, the particles being at least partially coated with a hydrogen control material.

[0035] In another embodiment, step a) of the process is carried out as a fluidized bed process, the fluidized bed material comprising particles of a metal oxide selected from SiO, AlO, and MgO, the particles being at least partially coated with at least one transition metal, the transition metal not being in its highest oxidation state, the transition metal being selected from the list consisting of Cr, Mn, Zn, and Fe.

[0036] In another embodiment, step a) of the process is carried out as a fluidized bed process, the fluidized bed material comprising particles of a metal oxide selected from SiO, AlO, and MgO, the particles being at least partially coated with iron(III) oxide.

[0037] In a specific embodiment, step a) of the method is carried out as a fluidized bed process, the fluidized bed material comprising particles of Al2O3, the particles being at least partially coated with iron(III) oxide.

[0038] In another specific embodiment, step a) of the process is carried out as a fluidized bed process, and the fluidized bed material comprises particles of reduced bauxite.

[0039] As mentioned above, the hydrogen control material needs to be reduced again after the decomposition and hydrogenation reactions have occurred. Therefore, to enable the method to be carried out continuously, the hydrogen control material also needs to be continuously reduced and reintroduced into step a). This can be done by any means known to those skilled in the art. A preferred method for achieving this purpose is described below.

[0040] Preferably, the process of the present invention, in which step a) is carried out as a fluidized bed process, is modified in that the fluidized bed material containing the hydrogen control material is continuously or batchwise removed from the fluidized bed without interfering with the operation of the fluidization process. This can be achieved by any means known to those skilled in the art. Preferably, it is achieved by a non-mechanical valve called a loop seal (LS). The loop seal allows the transport of the fluidized bed material without gas exchange between the two reactors. Typically, these loop seals are fluidized to prevent agglomeration of the hot fluidized bed material. In steam cracking processes, the loop seal is usually fluidized using steam.

[0041] The removed fluidized bed material contains a certain amount of hydrogen oxide control material because it has already been used to promote the steam cracking and hydrogenation reactions. Therefore, after being removed from the fluidized bed, the steam used to fluidize the loop seal is at least partially replaced with a reducing agent, which reduces the hydrogen oxide control material back to hydrogen control material. Preferably, the reducing agent is selected from the list consisting of carbon monoxide, methane, and hydrogen. After the reduction step, the fluidized bed material containing the hydrogen control material is reintroduced into the fluidized bed in step a).

[0042] Therefore, the method of the present invention preferably comprises: b) removing at least a portion of the hydrogen oxide control material from the fluidized bed of step a); d) reducing the hydrogen oxide control material with a reducing agent, thereby forming a hydrogen control material; e) reintroducing the hydrogen control material into step a). Further includes:

[0043] Even more preferably, the hydrogen oxide control material reduction step is combined with a heat supply step. A heat supply step is typically required in industry to maintain high heat levels in the steam cracking reactor. The steam cracking reaction is endothermic and requires a continuous supply of thermal energy. This is provided by heating the reactor or by introducing hot materials into the reactor. This configuration is defined as a dual fluidized bed (DFB) system. The most common industrial process that can be compared to this DFB system is the fluidized catalytic cracking (FCC) process. Hot fluidized bed material is recirculated between two interconnected fluidized beds: a combustor and a steam cracker (Figure 4). The overall reaction on the combustor side is exothermic, while the reaction on the cracker side is endothermic. The heat generated on the combustor side is transported to the cracker side by the fluidized bed material to satisfy the endothermic heat demand. This type of configuration allows the production of two separate gas streams: flue gas from the combustor and product gas from the cracker.

[0044] In a DFB system, the fluidized bed material is continuously circulated between two interconnected fluidized beds (Figure 4). The fluidized bed material is fully oxidized in the combustor (in the presence of air) and partially reduced in the cracker (in the presence of a hydrocarbon feed). The partially reduced fluidized bed material leaves the cracker along with the unreacted solids and enters the combustor, where the unreacted solids are oxidized along with the fluidized bed material.

[0045] In the DFB system, the two fluidized beds are preferably interconnected by a non-mechanical valve called a loop seal (LS). The loop seal allows the transport of fluidized bed material between the two reactors without gas exchange. Typically, these loop seals are fluidized to prevent agglomeration of the hot fluidized bed material. Such a configuration is shown in Figure 5. This system is modified according to the previously described embodiment. After being removed from the fluidized bed of the steam cracker, the steam used to fluidize the loop seal (LS2) is at least partially replaced by a reducing agent, which reduces the oxidized hydrogen control material back to the hydrogen control material. Preferably, the reducing agent is selected from the list consisting of carbon monoxide, methane, and hydrogen. After the reduction step, the hydrogen control material is reintroduced into the fluidized bed of step a).

[0046] Therefore, even more preferably, the method of the present invention comprises: b) removing at least a portion of the hydrogen oxide control material and at least a portion of the condensed hydrocarbon mixture from the fluidized bed of step a); c) oxidizing the condensed hydrocarbon mixture, thereby forming a flue gas and a heated hydrogen oxide control material; d) reducing the heated hydrogen oxide control material with a reducing agent, thereby forming a hydrogen control material; e) reintroducing the hydrogen control material into step a). Further includes:

[0047] Preferably, step c) of the process of the present invention is carried out at a temperature of 500 to 1200° C., preferably 700 to 1000° C., most preferably 800 to 900° C. Likewise, preferably, step c) of the process of the present invention is carried out at a pressure below atmospheric pressure, preferably above −0.5 bar(g), preferably in the range of −0.8 to −2 kPa.

[0048] Also preferably, step d) of the process of the present invention is carried out at a temperature of 500 to 1200° C., preferably 700 to 1000° C., most preferably 800 to 900° C. Likewise preferably, step d) of the process of the present invention is carried out at a pressure below atmospheric pressure, preferably above −0.5 bar(g), preferably in the range of −0.8 to −2 kPa.

[0049] Preferably, the movement of the hydrogen control material in the method of the preferred embodiment is accomplished by moving a fluidized bed of material containing the hydrogen control material. The initial disclosure of this specification encompasses at least the following aspects. [1] a) contacting plastic waste with steam and a hydrogen-control material comprising at least one transition metal and / or its oxide, wherein the transition metal is not in its highest oxidation state, thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, and oxidizing the hydrogen-control material to an oxidized hydrogen-control material; x) A step of extracting the hydrocarbon mixture in gaseous form A method for producing a hydrocarbon mixture from plastic waste, comprising: [2] The method according to [1], wherein the transition metal is selected from the list consisting of Cr, Mn, Zn and Fe, and preferably the transition metal is Fe. [3] The method according to [1], wherein the hydrogen control material comprises iron(II) oxide and / or iron(III) oxide, particularly iron(III) oxide. [4] The hydrogen control material is reduced bauxite or Al coated with iron (III) oxide in an amount corresponding to 2% by weight of atomic iron. 2 O 3 Particles (“2Fe / Al 2 O 3 The method according to any one of [1] to [3], wherein the method is selected from the group consisting of [5] The method according to any one of [1] to [4], wherein the plastic waste contains one or more polyolefins. [6] The method according to [5], wherein the polyolefin is selected from polyethylene homopolymer or copolymer, polypropylene homopolymer or copolymer. [7] The method according to any one of [1] to [6], wherein step a) is carried out at a temperature higher than 500°C, preferably at a temperature of 700°C or higher. [8] The method according to any one of [1] to [7], wherein step a) is carried out at normal pressure. [9] The method according to any one of [1] to [8], wherein step a) is carried out as a fluidized bed process, the steam forming part of the carrier gas, and at least the hydrogen-control material forming part of the fluidized bed.

[10] b) removing at least a portion of the hydrogen oxide control material and at least a portion of the condensed hydrocarbon mixture from the fluidized bed of step a); c) oxidizing the condensed hydrocarbon mixture, thereby forming a flue gas and a heated, oxidized hydrogen control material; d) reducing the heated and oxidized hydrogen control material with a reducing agent, thereby forming said hydrogen control material; e) reintroducing the hydrogen control material into step a). The method according to [8], further comprising:

[11] The method according to [9], wherein the reducing agent is selected from the list consisting of carbon monoxide, methane, and hydrogen.

[12] The method according to any one of [8] to

[10] , wherein step c) is carried out at a temperature of 500 to 1200°C.

[13] The method according to any one of [8] to

[11] , wherein step c) is carried out at a pressure lower than atmospheric pressure.

[14] The method according to any one of [8] to

[12] , wherein step d) is carried out at a temperature of 500 to 1200°C.

[15] The method according to any one of [8] to

[13] , wherein step d) is carried out at a pressure lower than atmospheric pressure.

[16] The method according to any one of [8] to

[14] , wherein step c) is carried out as a fluidized bed process. [Example]

[0050] [Measurement method] Fluidized bed material analysis To confirm the presence of Fe in the Al2O3 particles, SEM-EDS was performed. Figure 9 shows the backscattered electron (BSE) signal from a cross-section of an Al2O3 particle coated with iron(III) oxide, where the atomic iron weight percentage is 2% based on the total weight of the coated Al2O3 particle. The contrast in the BSE results from differences in average atomic weight; that is, pixel brightness increases as the atomic weight of the scanned element increases. Thus, the epoxy, which is composed of light elements, appears black, while the particles appear lighter in color. Because Fe is heavier than Al, the relative Fe content of the particles can be determined from the BSE contrast; brighter particles contain more Fe.

[0051] Devolatization gas analysis The sampled gases are analyzed for their H, CO, CO, and CH concentrations (vol %) using a SICK GMS 820 permanent gas analyzer. These gases are continuously monitored to determine the total devolatization time and ensure that no volatile gases remain after a sampling time of 120 seconds.

[0052] Comprehensive Gas Analysis For comprehensive analysis of other devolatilized species, the remainder of the sampled gas is passed through a coil condenser maintained at -5°C. The gas exiting the coil condenser is collected in a 0.5 L Tedlar gas bag. The gas bags collected during each experiment are analyzed using an Agilent 490 Micro GC system to determine their composition. The Agilent micro-GC is equipped with four different columns, each with a TCD detector. An overview of the gases measured by the micro-GC system is shown in Table 2.

[0053] [Table 2]

[0054] 〔material〕 The PE pellets used in this study have a bulk density of 945 kg / m 3 The bed materials, with a pellet size of 2.5 mm, were supplied by Borealis AB. Fluidized bed materials with different iron oxide contents were investigated for their hydrogenation capabilities. The chemical compositions of the bed materials used in this study are listed in Table 3 (wt. % based on the total weight of the material).

[0055] [Table 3]

[0056] Bauxite is obtained directly from natural ores, while Al2O3 is a synthetic material obtained from Sigma Aldrich. 2Fe / Al2O3 is prepared by impregnating Al2O3 with a solution of iron nitrate nonahydrate (Fe(NO3)3·9H2O). Fe2O3 forms on the surface of Al2O3 via the following reaction: [ka]

[0057] The 2Fe / Al2O3 material is calcined at 700°C. Therefore, it can be assumed that the majority of the iron (Fe) is in the form of Fe2O3 and is therefore in oxidation state +3, i.e., iron(III) oxide. Therefore, "2Fe / Al2O3" is defined herein as Al2O3 coated with iron(III) oxide, where the weight % of atomic iron is 2% based on the total weight of the coated Al2O3 particles.

[0058] Reactor Setup The experimental setup used for the comparative and inventive examples is shown in Figure 6. The main reactor is a stainless steel tube with an internal diameter (ID) of 88.9 mm and a height of 1305 mm. It is a bubbling fluidized bed reactor, similar to a cracker in a DFB system. Fluidizing gas is fed from the bottom of the reactor through a wind box and a distribution plate. The fluidizing gases are fed separately and mixed uniformly in the wind box before entering the reactor through the gas distribution plate. The flow rate of the fluidizing gas is controlled by a mass flow controller (MFC).

[0059] The reactor is externally heated by an electric oven. The temperature along the height of the reactor is continuously measured and recorded by a thermocouple at the rear of the reactor. The fluidized bed material is introduced into the top of the reactor before the reactor oven is turned on. A split stream of gas exiting the reactor is sampled through one of the gas sampling ports: h1-h5.

[0060] A gas sampling probe is inserted into the reactor through one of the ports, and the remaining ports are sealed to prevent bed material from entering the ports. The port height is selected according to the bed height. The probe is heated to 350 °C with an electric heating band to prevent condensation of hydrocarbons and vapors. The sampled gas is divided into two parts, one of which is passed through a gas conditioning system and the other through a coil condenser.

[0061] The gas conditioning system includes an isopropanol wash of the sampled gas, followed by drying with silica gel beads and glass wool. The gas conditioning system is immersed in a water bath, as shown in Figure 6. The cold, dried gas is analyzed using a SICK GMS 820 permanent gas analyzer. The coil condenser used in this study is a 4.5 m long PTFE tubing coil maintained at -5°C. The sampled gas is collected through the coil condenser into a 0.5 L Tedlar gas bag.

[0062] Comparative Example 1 g of PE pellets per batch was directly charged into the high-temperature fluidized bed. The experimental conditions and procedures for each set are summarized in Tables 4 and 5, respectively.

[0063] Helium is used as one of the fluidizing gases during the devolatization and char combustion stages of each experiment. A known volume of helium is used as a tracer gas to determine the volume of gas produced during devolatization and char combustion.

[0064] Before each batch of PE pellets is added, the fluidized bed material is exposed to an oxidizing environment at the same reaction temperature. Oxidation of the fluidized bed material is accomplished by fluidizing the bed material with air, as described in the previous section.

[0065] A slipstream of gas exiting the reactor was sampled through sampling port h5 and continuously analyzed for O2 concentration (vol %). Complete oxidation was considered when the O2 concentration leaving the fluidized bed matched the ambient O2 concentration of 20.9 vol %. To simulate the conditions of a DFB system, the fluidized bed material was fully oxidized before each batch of experiments. The fluidized bed material entered the cracker after being fully oxidized in the combustor.

[0066] The conditions used in the comparative examples are shown in Tables 4 and 5.

[0067] [Table 4]

[0068] [Table 5]

[0069] During the steam cracking of polyethylene, a portion of the sampled gas is analyzed for its H, CO, CO, and CH concentrations (volume %) by a continuous gas analyzer. These gases are continuously monitored to determine the total devolatization time and ensure that no volatile gases remain after the sampling time of 120 seconds.

[0070] Micro-GC analysis was performed to analyze the full spectrum of products in the resulting product gas.

[0071] [Example of the invention] The simultaneous hydrogenation of hydrocarbon species produced from the steam cracking of polyethylene is achieved by the decomposition of water molecules on the surface of a fluidized bed material containing reduced transition metals. To reduce the iron oxides present in the fluidized bed material, the fluidized bed material is fluidized with a CO / N2 gas mixture. The fluidized bed material is fluidized with a CO / N2 gas mixture until the concentration of CO2 leaving the reactor is 0% by volume. The iron oxide content of the fluidized bed material decreases according to the following equation: [ka]

[0072] The fluidizing gas is then switched to 100% N2 for 2 minutes to purge the reactor and create an inert environment. After the CO concentration reaches 0%, steam is added to the fluidized bed as the fluidizing gas. The steam added to the reactor is converted to hydrogen by the fluidized bed material according to the following reaction: [ka]

[0073] The polyethylene pellets are directly added to the fluidized bed immediately after adding steam to the reactor. This ensures that the steam cracking and hydrogen generation reactions occur simultaneously. The concentration profile of hydrogen produced during the process using bauxite as the fluidized bed material is shown in Figure 7. The reaction time marked "PE feed" in Figure 7 is the time when the polyethylene pellets were fed into the fluidized bed. The experimental procedure is shown in Tables 4 and 6.

[0074] [Table 6]

[0075] 〔result〕 The yields of gaseous products obtained for comparative and inventive examples of steam cracking of polyethylene in the presence of bauxite and 2Fe / Al2O3 are shown in Table 7.

[0076] [Table 7]

[0077] The yield of the light olefins, ethylene and propylene, increases significantly when using transition metals that are not in their highest oxidation state, i.e., reduced. A comparison of the yields of light olefins from both hydrogen-control materials is shown in Figure 8. The results clearly demonstrate that hydrogen generated by the decomposition of water molecules on the surface of the reduced transition metal inhibits the free radical pool generated during the steam cracking of polyethylene. Because this example was carried out at atmospheric pressure, it was possible to demonstrate that high selectivity to the light monomer portion of the polymer is possible at low pressures in a steam cracking process.

[0078] Furthermore, in bauxite, Fe2O3 is not located only on the surface of the Al2O3 particles, but is uniformly distributed throughout the Al2O3 material as individual particles. In contrast, in 2Fe / Al2O3, the Al2O3 has an Fe2O3 layer on its surface. Figure 9 shows a scanning electron microscope (SEM) image of 2Fe / Al2O3. Hydrogen donation works well with both fluidized bed materials. However, the difference in olefin yield is significantly greater with 2Fe / Al2O3.

Claims

1. a) contacting plastic waste with steam and a hydrogen-control material comprising at least one transition metal and / or its oxide, wherein said transition metal is not in its highest oxidation state, thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons and oxidizing said hydrogen-control material to an oxidized hydrogen-control material, wherein step a) is carried out as a fluidized bed process, wherein said steam forms part of the carrier gas and at least said hydrogen-control material forms part of the fluidized bed; b) removing at least a portion of the hydrogen oxide control material and at least a portion of the condensed hydrocarbon mixture from the fluidized bed of step a); c) oxidizing the condensed hydrocarbon mixture, thereby forming a flue gas and a heated, oxidized hydrogen control material; d) reducing the heated and oxidized hydrogen control material with a reducing agent, thereby forming said hydrogen control material; e) reintroducing the hydrogen control material into step a); x) removing the hydrocarbon mixture in gaseous form; A method for producing a hydrocarbon mixture from plastic waste, comprising:

2. 2. The method of claim 1, wherein the transition metal is selected from the list consisting of Cr, Mn, Zn and Fe, preferably the transition metal is Fe.

3. The method of claim 1 , wherein the hydrogen control material comprises iron (II) oxide and / or iron (III) oxide, in particular iron (III) oxide.

4. The hydrogen control material is preferably reduced bauxite or Al coated with iron (III) oxide in an amount equivalent to 2 wt. % atomic iron. ２ O ３ Particles (“2Fe / Al ２ O ３ 10. The method of claim 1, wherein the hydroxyl group is selected from the group consisting of hydroxyl groups.

5. The method of claim 1 , wherein the plastic waste comprises one or more polyolefins.

6. 6. The method of claim 5, wherein the polyolefin is selected from polyethylene homo- or copolymer, polypropylene homo- or copolymer.

7. 2. The method according to claim 1, wherein step a) is carried out at a temperature above 500°C, preferably at a temperature of 700°C or higher.

8. 10. The method of claim 1, wherein step a) is carried out at atmospheric pressure.

9. 10. The method of claim 1, wherein the reducing agent is selected from the list consisting of carbon monoxide, methane, and hydrogen.

10. The method of claim 1, wherein step c) is carried out at a temperature of 500 to 1200°C.

11. 10. The method of claim 1, wherein step c) is carried out at subatmospheric pressure.

12. 10. The method of claim 1, wherein step d) is carried out at a temperature of 500 to 1200°C.

13. 10. The method of claim 1, wherein step d) is carried out at subatmospheric pressure.

14. 10. The process of claim 1, wherein step c) is carried out as a fluidized bed process.

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