Method for producing olefin

Abstract

This method for producing an olefin includes a first thermal decomposition step (S12) for thermally decomposing a plastic and obtaining a first product and a second thermal decomposition step (S13) for further thermally decomposing at least a part of the first product. The hydrocarbons contained in the first product satisfy all the following conditions (i) to (iv): (i) the sum of the content of C3 or fewer alkanes and alkenes is 5≤X≤35 (wt%). (ii) The weight-average molecular weight calculated from C1-3 and C10-35 normal alkanes is 95≤Y≤240. (iii) The ratio of the sum of the content of C10-35 normal alkanes to the sum of the contents of C1-3 and C10-35 normal alkanes is 0.30≤Z≤0.93. (iv) The ratio of the content of C1-3 alkanes to the content of C35 normal alkanes is 5≤W≤205.

Description

Olefin production process

[0001] The present disclosure relates to a process for producing olefins.

[0002] In order to realize a carbon-recycling society, attention is being focused on technology for chemically recycling waste plastics, which have traditionally been thermally recycled. As one such technology, for example, as shown in Patent Document 1, a method for producing olefins is known, which includes a thermal cracking step in which plastics are thermally decomposed to obtain a thermal cracking gas, and a catalytic cracking step in which the obtained thermal cracking gas is decomposed in the presence of a catalyst to obtain a catalytic cracking gas.

[0003] International Application No. WO2023 / 047951 Pamphlet

[0004] One aspect of the present disclosure is directed to improving the olefin yield in a process for producing olefins from plastics that involves a two-stage pyrolysis process.

[0005] In order to solve the above-mentioned problems, a method for producing an olefin according to one embodiment of the present disclosure includes a first pyrolysis step of pyrolyzing a plastic to obtain a first product, and a second pyrolysis step of further pyrolyzing at least a portion of the first product, wherein the hydrocarbons contained in the first product satisfy all of the following conditions (i) to (iv): (i) when the sum of the contents [wt %] of alkanes and alkenes having 3 or less carbon atoms in the first product is X [wt %], 5≦X≦35; (ii) when the weight average molecular weight calculated from normal alkanes having 1 to 3 carbon atoms and normal alkanes having 10 to 35 carbon atoms in the first product is Y [-], 95≦Y≦240. (iii) When the ratio of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms contained in the first product to the sum of the contents [wt%] of normal alkanes having 1 to 3 carbon atoms and normal alkanes having 10 to 35 carbon atoms contained in the first product is defined as Z[-], the ratio satisfies 0.30≦Z≦0.93. (iv) When the ratio of the content [wt%] of alkanes having 1 to 3 carbon atoms to the content [wt%] of normal alkanes having 35 carbon atoms contained in the first product is defined as W[-], the ratio satisfies 5≦W≦205.

[0006] According to one aspect of the present disclosure, the olefin yield can be improved in a process for producing olefins from plastics, which includes a two-stage pyrolysis process.

[0007] Fig. 1 is a flowchart showing an example of an olefin production method according to embodiment 1. Fig. 2 is a system diagram schematically showing the main configuration of a production system according to embodiment 1. Fig. 3 is a flowchart showing an example of an olefin production method according to embodiment 2. Fig. 4 is a schematic diagram of an experimental apparatus used in a demonstration test.

[0008] First Embodiment Hereinafter, one embodiment of the present disclosure will be described in detail.

[0009] Hereinafter, an olefin production method according to an embodiment of the present disclosure will be described in detail together with a production system used therein, with reference to the drawings.

[0010] The olefin production method of this embodiment is a method for producing lower olefins that can be recycled as a plastic raw material using plastics such as waste plastics as a raw material. FIG. 1 is a flowchart showing an example of the olefin production method of this embodiment. As shown in FIG. 1, the olefin production method of this embodiment includes a pretreatment step S11, a first thermal cracking step S12, a catalytic cracking step S13, and a purification step S14. Each step will be described in detail below.

[0011] In this embodiment, the flowchart shown in Figure 1 and an olefin production system (Figure 2: production system 100) that realizes the production flow shown in the flowchart will be described as an example. However, the systems described in this specification and drawings are merely typical examples and do not limit the scope of the present disclosure in any way. This also applies to the other embodiments described below.

[0012] <Olefin Production System (Production System 100)> First, an example of the configuration of the production system 100 will be described with reference to Fig. 1 and Fig. 2. Fig. 2 is a system diagram schematically showing the main configuration of the production system 100 according to the first embodiment.

[0013] The production system 100 of this embodiment is a system that decomposes plastics, particularly polyolefin-based plastics, to obtain an olefin-rich gas that is rich in lower olefin gases. The plastic used as a raw material in the olefin production method of this embodiment can be, for example, waste plastic. Furthermore, the plastic used as a raw material is preferably a polyolefin-based plastic such as polyethylene or polypropylene. Furthermore, the polyolefin-based plastic content in the raw material plastic is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0014] As shown in FIG. 2, the production system 100 of this embodiment is generally configured to include a pretreatment system 10, a thermal cracking device 21, a catalytic cracking device 22, a refining device 30, and each of the paths L1 to L6.

[0015] Plastics such as waste plastics are supplied to the pretreatment system 10 via a path L1. A path L2 connects the exhaust port of the pretreatment system 10 to the supply port of the thermal cracking device 21. A feed material M pretreated by the pretreatment system 10 is supplied to the thermal cracking device 21 via the path L2. A path L3 connects the gas outlet 21O of the thermal cracking device 21 to the supply port 22I of the catalytic cracking device 22. The feed material M supplied to the thermal cracking device 21 is thermally decomposed and supplied to the catalytic cracking device 22 via the path L3 as a thermal cracking gas G1. The thermal cracking gas G1 is an example of a first product according to the present disclosure. A path L4 connects the catalytic cracking device 22 and the purification device 30. The thermal cracking gas G1 supplied to the catalytic cracking device 22 is catalytically cracked and supplied to the purification device 30 as a catalytic cracking gas G2. The catalytic cracking gas G2 is purified by a purification unit 30, and an olefin-rich gas containing a large amount of lower olefins is discharged from a line L5, and a liquid containing oil is discharged from a line L6. Each unit (system) will be described in detail below.

[0016] The pretreatment system 10 processes plastics, such as waste plastics, to produce a feedstock M suitable for decomposition. In other words, the pretreatment system 10 is a system that performs the pretreatment step S11. The pretreatment system 10 may include multiple devices that perform different processes. For example, the pretreatment system 10 may include one or more devices selected from a sorting device, a crushing device, a cleaning device, a drying device, a melting device, and a dechlorination device. The sorting device is a device that separates polyolefin-based plastics from raw materials, such as waste plastics. The sorting device may include one or more devices, such as an optical sorting device or a gravity separator. The crushing device is a device that crushes the sorted plastics. The cleaning device is a device that cleans the crushed plastics. The drying device is a device that dries the cleaned plastics. The melting device is a device that heats the plastics to liquefy them. The dechlorination device is a device that removes chlorine from the plastics.

[0017] The pyrolysis device 21 is a device that decomposes and vaporizes a substance by heating. That is, the pyrolysis device 21 is a device that can perform the first pyrolysis step S12 of this embodiment. The pyrolysis device 21 is a device that continuously performs pyrolysis, and for example, an extruder, a stirring tank, a rotary kiln, or a fluidized bed can be used. The fluidized bed can be an internal circulating fluidized bed or an external circulating fluidized bed.

[0018] Furthermore, a plurality of the above-described devices may be used as the thermal decomposition device 21, and the plurality of reactors may be connected in parallel or in series. The heat source required in the first thermal decomposition step S12 can be heat obtained by burning one or more of the following: the thermal decomposition residue generated in the thermal decomposition device 21, the hydrocarbon-containing liquid and / or lower paraffin gas obtained in the refining step S14, or a hydrocarbon fuel such as natural gas or kerosene. Alternatively, heat obtained by electrical heating or microwave irradiation can also be used as a heat source. Alternatively, two or more of electrical heating, microwave heating, and the heat obtained from the above-described combustion may be used in combination.

[0019] The heating method may be either direct or indirect. Direct heating involves holding a microwave-absorbing substance (susceptor) inside the device and supplying microwave energy to the waste plastic through it. Indirect heating involves supplying heat obtained by burning an electric heater or hydrocarbon fuel through the heat transfer surface of the device, or using steam, nitrogen gas, or CO ２ One method is to heat an inert gas such as a gas to a high temperature using a heat source before introducing it into the device. Another method is to preheat a solid containing iron, iron oxide, alumina, silica, or the like as a main component to a high temperature using a heat source before introducing it into the device. Preheating of the gas or solid particles using a heat source may be performed using a part of the interior of the thermal decomposition device 21 or a device similar to the thermal decomposition device, combined with the thermal decomposition device 21, and circulating the gas or solid from these devices.

[0020] The catalytic cracking unit 22 is a unit that cracks substances by bringing the pyrolysis gas G1 into contact with a catalyst. That is, the catalytic cracking unit 22 is a unit that performs the catalytic cracking step S13. The catalytic cracking step S13 is an example of the second thermal cracking step according to the present disclosure. The catalytic cracking unit 22 can be, for example, a fixed bed, a moving bed, or a fluidized bed. Furthermore, a plurality of these exemplified reactors may be used, and the plurality of reactors may be connected in parallel or in series. The heat source required in the catalytic cracking step S13 can be heat obtained by burning one or more of the following: coke generated in the catalytic cracking unit 22 and adhering to the catalyst surface; hydrocarbon-containing liquid and / or lower paraffin gas obtained in the refining step S14; or hydrocarbon fuels such as natural gas or kerosene. Alternatively, heat obtained by electrical heating or microwave irradiation can also be used as a heat source. Alternatively, two or more of electrical heating, microwave heating, and the heat obtained from the combustion described above may be used in combination.

[0021] The heating method may be either direct or indirect. Direct heating involves holding a microwave-absorbing substance (susceptor) inside the device and supplying microwave energy to the waste plastic through it. Indirect heating involves supplying heat obtained by burning an electric heater or hydrocarbon fuel through the heat transfer surface of the device, or using steam, nitrogen gas, or CO ２ One method involves heating an inert gas such as a gas to a high temperature using a heat source before introducing it into the device. Alternatively, a method may be used in which a solid whose main component is iron, iron oxide, alumina, silica, or the like is preheated to a high temperature using a heat source before introducing it into the device. The solid particles may be the catalyst. Preheating of the gas or solid particles using a heat source may be performed using a part of the interior of the thermal decomposition device 21 or a device similar to the thermal decomposition device, combined with the thermal decomposition device 21, and circulating the gas or solid from these devices.

[0022] Furthermore, the pyrolysis gas G1 obtained by pyrolysis in the pyrolysis device 21 may be separated into gas components and liquid components using a cooling device or a purification device, and some or all of the separated liquid components may be supplied to the catalytic cracking device 22. In this case, the separated gas components may be supplied to the catalytic cracking device 22 or to the purification device 30 and subsequent devices, bypassing the catalytic cracking device 22. Alternatively, the gas components may be used as fuel in the production system 100 or as fuel for other production systems. The handling of the gas components is not limited to this.

[0023] The purification device 30 is a device capable of separating the mixture supplied thereto by a known gas-liquid separation operation, distillation operation, or the like. In other words, the purification device 30 is a device capable of performing the purification step S14 of this embodiment. The purification device 30 can be, for example, a gas-liquid separation device or a distillation device. These devices may also be combined, or a plurality of these devices may be connected. Note that, in order to increase the purity of the olefins obtained in the purification device 30 to an olefin with a desired carbon number, a distillation device may be optionally installed downstream of the purification device 30.

[0024] <Olefin Production Method> The olefin production method according to embodiment 1 is carried out, for example, according to the flowchart shown in Figure 1. Note that the flowchart shown in Figure 1 is an example and is not intended to be limiting. Each step in the olefin production method according to embodiment 1 will be described in detail.

[0025] (Regarding Raw Materials) Prior to describing each process, the raw materials used in the present disclosure will be described. Plastic can be used as the raw material supplied to the pretreatment system 10. The plastic may be waste plastic contained in municipal waste or the like. The plastic is preferably primarily composed of polyolefins such as polyethylene or polypropylene, but may also contain other plastics. The other plastics may include, for example, chlorinated plastics (such as chlorinated polyethylene), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), non-chlorinated plastics (such as polyethylene, polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate, polystyrene, nylon 66, etc.), or mixtures thereof. The waste plastic may also include virgin mixed plastics or post-consumer mixed plastics.

[0026] (Pretreatment step S11) The pretreatment step S11 is a step of pretreating the plastic to obtain a feed M to be supplied to the first pyrolysis step S12. The plastic can be supplied to the first pyrolysis step S12 as a feed M containing mainly polyolefin-based plastics after passing through the pretreatment step S11. The pretreatment step preferably results in a polyolefin-based plastic content of 80% by mass or more in the raw plastic, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0027] (First Pyrolysis Step S12) The first pyrolysis step S12 is a step of decomposing the supply M by heating to obtain a pyrolysis gas G1. More specifically, the first pyrolysis step S12 is a step of decomposing the olefin-based plastic contained in the supply M by heating to generate a pyrolysis gas G1. By the thermal decomposition in the first pyrolysis step S12, the carbon compounds contained in the supply M are decomposed into lower molecular weight compounds, mainly into hydrocarbons having approximately 1 to 30 carbon atoms. The pyrolysis temperature (°C) in the first pyrolysis step S12 can be set based on the composition of the supply M. The pyrolysis temperature is preferably a high temperature at which the decomposition rate of the plastic is rapid, but if the temperature is too high, carbonization will occur. Therefore, for example, a temperature of 400 to 800°C is desirable, preferably 435 to 595°C, and more preferably 450 to 550°C. Regarding the pressure in the first pyrolysis step S12, a low pressure is desirable because the decomposition reaction is a reaction in which the number of moles increases. The pressure in the first pyrolysis step S12 is, for example, −80 to 1000 kPaG, preferably −10 to 300 kPaG, and more preferably 0 to 100 kPaG.

[0028] In addition, in the first thermal decomposition step S12, a catalyst may be optionally used to promote decomposition. Examples of the catalyst used in the first thermal decomposition step S12 include, but are not limited to, silicate catalysts, preferably zeolite catalysts, and more preferably MFI-type zeolite catalysts. The silicate catalyst may typically contain silicon atoms, aluminum atoms, oxygen atoms, and hydrogen atoms. The silicate catalyst may also contain atoms such as sodium atoms, titanium atoms, chromium atoms, manganese atoms, iron atoms, cobalt atoms, nickel atoms, copper atoms, ruthenium atoms, rhodium atoms, palladium atoms, silver atoms, iridium atoms, platinum atoms, boron atoms, nitrogen atoms, magnesium atoms, phosphorus atoms, zinc atoms, and gallium atoms.

[0029] In the first pyrolysis step S12, water vapor or nitrogen gas, CO ２An inert gas such as a nitrogen gas may be allowed to coexist, and such a gas may be used as a fluidizing gas for the fluidized bed. When a fluidized bed reactor is used in the first pyrolysis step S12, the greater the amount of fluidizing gas, the lower the hydrocarbon concentration in the gas phase, and therefore the more likely the cracked components are to be vaporized. The fluidizing gas linear velocity in the fluidized bed reactor is preferably 0.1 cm / s or more and 100 cm / s or less, more preferably 0.5 cm / s or more and 75 cm / s or less, and even more preferably 0.8 cm / s or more and 20 cm / s or less. Furthermore, the ratio of the fluidizing gas supply rate (N ml / min) to the supply rate (g / min) of the feed material M supplied to the fluidized bed reactor is preferably 10 (N ml / g) or more and 2000 (N ml / g) or less, more preferably 50 (N ml / g) or more and 1500 (N ml / g) or less, and even more preferably 200 (N ml / g) or more and 1200 (N ml / g) or less. The ratio of the fluidizing gas supply rate (N ml / min) to the amount (g) of bed material present in the fluidized bed reactor is preferably 1.0 (N ml / g min) or more and 100 (N ml / g min) or less, more preferably 2.0 (N ml / g min) or more and 50 (N ml / g min) or less, and even more preferably 3.0 (N ml / g min) or more and 25 (N ml / g min) or less.

[0030] The inventors have discovered that the hydrocarbon composition contained in the pyrolysis gas G1 obtained by the first pyrolysis step S12 has a characteristic structure as described below, which makes it possible to improve the olefin yield after passing through the catalytic cracking step S13.

[0031] Specifically, in the olefin production method according to the present disclosure, the pyrolysis gas G1 satisfies all of the following conditions (i) to (iv): In the formulas (1) to (4) under the following conditions, CN (N is a natural number) is the content [wt %] of normal alkanes (chain saturated hydrocarbon compounds) having a carbon number N in the pyrolysis gas G1, and CN′ (N is a natural number) is the content [wt %] of alkenes (unsaturated hydrocarbon compounds) having a carbon number N in the pyrolysis gas G1.

[0032] (i) When the sum of the contents [wt %] of alkanes and alkenes having 3 or less carbon atoms in the pyrolysis gas G1 is X [wt %], 5≦X≦35, more preferably 7≦X≦32, and even more preferably 9≦X≦28. Specifically, X can be calculated using the following formula (1): X=C1+C2+C3+C2′+C3′ (1)

[0033] (ii) When the weight average molecular weight calculated from the normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the pyrolysis gas G1 is Y[-], 95≦Y≦240 is satisfied, more preferably 120≦Y≦235, and even more preferably 150≦Y≦230. Specifically, Y can be calculated by the following formula (2) using the content [wt %] of each normal alkane: Y=(16.04×C1+30.07×C2+44.10×C3+142.28×C10+156.31×C11+170.33×C12+184.36×C13+198.39×C14+212.41×C15+226.44×C16+ 240.47×C17+254.49×C18+268.52×C19+282.55×C20+296.57×C21+310.60×C22+324.63×C23+338.65×C24+352.68×C25+366.71×C2 6+380.73×C27+394.76×C28+408.79×C29+422.81×C30+436.84×C31+450.87×C32+464.89×C33+478.92×C34+492.95×C35)÷(C1+C2 +C3+C10+C11+C12+C13+C14+C15+C16+C17+C18+C19+C20+C21+C22+C23+C24+C25+C26+C27+C28+C29+C30+C31+C32+C33+C34+C35) (2)

[0034] (iii) If the ratio Z[-] of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms contained in the pyrolysis gas G1 to the sum of the contents [wt%] of alkanes having 1 to 3 carbon atoms and normal alkanes having 10 to 35 carbon atoms contained in the pyrolysis gas G1 is 0.30≦Z≦0.93, more preferably 0.40≦Z≦0.90, and even more preferably 0.50≦Z≦0.85. Specifically, Z can be calculated using the following formula (3): Z = (C10 + C11 + C12 + C13 + C14 + C15 + C16 + C17 + C18 + C19 + C20 + C21 + C22 + C23 + C24 + C25 + C26 + C27 + C28 + C29 + C30 + C31 + C32 + C33 + C34 + C35) / (C1 + C2 + C3 + C10 + C11 + C12 + C13 + C14 + C15 + C16 + C17 + C18 + C19 + C20 + C21 + C22 + C23 + C24 + C25 + C26 + C27 + C28 + C29 + C30 + C31 + C32 + C33 + C34 + C35) (3)

[0035] (iv) If the ratio of the content [wt %] of alkanes having 1 to 3 carbon atoms contained in the pyrolysis gas G1 to the content [wt %] of normal alkanes having 35 carbon atoms contained in the pyrolysis gas G1 is W [-], then 5≦W≦205, more preferably 8≦W≦150, and even more preferably 12≦W≦100. Specifically, W can be calculated using the following formula (4): W=(C1+C2+C3) / C35 (4).

[0036] The above condition (i) is a provision that focuses on the low molecular weight hydrocarbons contained in the pyrolysis gas G1. In the present disclosure, low molecular weight hydrocarbons may be hydrocarbons having 1 to 3 carbon atoms. Since low molecular weight hydrocarbons can become aromatic compounds through catalytic cracking in the catalytic cracking step S13 after the first pyrolysis step S12, an excess of low molecular weight hydrocarbons is thought to have the potential to reduce the final olefin yield. Therefore, the above condition (i), which defines the amount of low molecular weight hydrocarbons, is thought to contribute to improving the olefin yield.

[0037] The above condition (iii) is a specification that focuses on the high molecular weight hydrocarbons contained in the pyrolysis gas G1. In the present disclosure, high molecular weight hydrocarbons may be hydrocarbons having 10 or more carbon atoms. It is considered that high molecular weight hydrocarbons may not be cracked to the desired olefins even after catalytic cracking in the catalytic cracking step S13 after the first pyrolysis step S12. Therefore, it is considered that the above condition (iii), which specifies the amount of high molecular weight hydrocarbons, contributes to improving the olefin yield.

[0038] Furthermore, in the olefin production method according to the present disclosure, the pyrolysis gas G1 satisfies all of the above-mentioned conditions (i) to (iv), and the condensation ratio at 0°C of the pyrolysis gas G1 is preferably 39 wt% or more and 88 wt% or less, more preferably 45 wt% or more and 85 wt% or less, and even more preferably 55 wt% or more and 80 wt% or less.

[0039] (Catalytic cracking step S13) The catalytic cracking step S13 is a step in which the thermal cracking gas G1 is cracked in the presence of a catalyst to produce a catalytic cracking gas G2 in which the molecular weight of the gas has been reduced to hydrocarbons having a carbon number of about 1 to 20. The cracking temperature in the catalytic cracking step S13 can be set based on the composition of the thermal cracking gas G1. The cracking temperature is, for example, 400 to 800°C, preferably 450 to 650°C, and more preferably 500 to 600°C. The cracking pressure in the catalytic cracking step S13 is, for example, -80 to 1000 kPaG, preferably -10 to 300 kPaG, and more preferably 0 to 100 kPaG.

[0040] Examples of catalysts used in the catalytic cracking step S13 include, but are not limited to, silicate catalysts, preferably zeolite catalysts, and more preferably MFI-type zeolite catalysts. The silicate catalyst typically contains silicon, aluminum, oxygen, and hydrogen atoms. The silicate catalyst may also contain atoms such as sodium, titanium, chromium, manganese, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, iridium, platinum, boron, nitrogen, magnesium, phosphorus, zinc, and gallium. The weight hourly space velocity (WHSV) [1 / h], which is the ratio of the mass flow rate [kg / h] of the pyrolysis gas G1 to the amount of catalyst [kg] in the catalytic cracking step S13, is, for example, 0.1 to 100 [1 / h], preferably 1.0 to 50 [1 / h], and more preferably 2.0 to 20 [1 / h].

[0041] In the catalytic cracking step S13, steam or nitrogen gas, CO ２ An inert gas such as a gas may be present in the fluidized bed, and such a gas may be used as a fluidizing gas for the fluidized bed.

[0042] (Purification step S14) The purification step S14 is a step of separating and purifying the catalytic cracking gas G2. More specifically, the purification step S14 is a step of separating the catalytic cracking gas G2 into a gas containing at least one hydrocarbon having a low carbon number (e.g., C1-4) and a liquid containing at least one hydrocarbon having a high carbon number (e.g., C5 or higher). Furthermore, the gas may be an olefin-rich gas containing 90% by mass or more of lower olefins. The lower olefins may contain at least one of ethylene, propylene, or butene. Note that, in order to increase the purity of olefins of a desired carbon number in the olefin-rich gas obtained in the purification step S14, an optional purification step may be added downstream of the purification step S14.

[0043] By obtaining an olefin-rich gas that is rich in lower olefins, olefins can be produced with high efficiency without using hydrogen.

[0044] At least a portion of the hydrocarbon-containing liquid obtained in the refining step S14 may be supplied to the thermal cracking unit 21 or the catalytic cracking unit 22. This can further improve the olefin yield.

[0045] Alternatively, the hydrocarbon-containing liquid and / or lower paraffin gas obtained in the refining step S14 may be combusted and used as a heat source in any of the steps from the pretreatment step S11 to the refining step S14, thereby reducing the environmental load of the entire olefin production system.

[0046] (Summary of Embodiment 1) The method for producing olefins according to embodiment 1 of the present disclosure includes a first pyrolysis step (S12) of pyrolyzing plastic to obtain a first product (pyrolysis gas G1), and a second pyrolysis step (catalytic cracking step: S13) of further pyrolyzing at least a portion of the first product, and hydrocarbons contained in the first product satisfy all of the following conditions (i) to (iv):

[0047] (i) When the sum of the contents [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product is X [wt%], 5≦X≦35 is satisfied. (ii) When the weight average molecular weight calculated from the normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Y [-], 95≦Y≦240 is satisfied. (iii) When the ratio of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the contents [wt%] of normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Z [-], 0.30≦Z≦0.93 is satisfied. (iv) When the ratio of the content [wt%] of alkanes having 1 to 3 carbon atoms to the content [wt%] of normal alkanes having 35 carbon atoms contained in the first product is W [-], 5≦W≦205 is satisfied.

[0048] According to this configuration, the olefin yield after the second pyrolysis step can be significantly improved.

[0049] The first product may satisfy all of the above conditions (i) to (iv) and have a condensation ratio of 39 wt % to 88 wt % of the pyrolysis gas G1 at 0° C. According to this configuration, the olefin yield after the second pyrolysis step can be significantly improved.

[0050] Furthermore, by including a purification step after the second thermal cracking step in the above-mentioned olefin production process, an olefin-rich gas containing a large amount of lower olefins can be obtained.

[0051] Furthermore, the olefin production method according to the first embodiment of the present disclosure may further include an analysis step of analyzing the composition of the pyrolysis gas G1, and a condition adjustment step of adjusting the pyrolysis conditions based on the analysis results in the analysis step.

[0052] Specifically, in the analysis step, the pyrolysis gas G1 may be sampled and its composition may be analyzed by, for example, gas chromatography with a flame ionization detector (GC-FID). Then, in the condition adjustment step, the pyrolysis conditions in the first pyrolysis step S12 may be adjusted based on the results of the composition analysis. More specifically, in the first pyrolysis step S12, one or more of the pyrolysis temperature, pyrolysis pressure, fluidizing gas linear velocity in the fluidized-bed reactor, ratio of the fluidizing gas supply rate to the raw material supply rate, and ratio of the fluidizing gas supply rate to the amount of bed material present in the fluidized-bed reactor may be adjusted.

[0053] For example, if the analysis indicates that the low-molecular-weight components are excessive, adjustments may be made such as lowering the pyrolysis temperature, lowering the pyrolysis pressure, or increasing the linear velocity of the fluidizing gas in the fluidized-bed reactor. Alternatively, if the analysis indicates that the low-molecular-weight components are excessive, adjustments may be made such as increasing the ratio of the fluidizing gas supply rate to the raw material supply rate, or increasing the ratio of the fluidizing gas supply rate to the amount of bed material present in the fluidized-bed reactor.

[0054] Conversely, if it is determined that the high molecular weight component is excessive, adjustments may be made such as increasing the pyrolysis temperature, increasing the pyrolysis pressure, or decreasing the linear velocity of the fluidizing gas in the fluidized bed reactor. Alternatively, if it is determined that the low molecular weight component is excessive, adjustments may be made such as decreasing the ratio of the fluidizing gas supply rate to the raw material supply rate, or decreasing the ratio of the fluidizing gas supply rate to the amount of bed material present in the fluidized bed reactor.

[0055] By including the analysis step and the condition adjustment step, the conditions in the thermal cracking step can be set more appropriately, and the olefin yield after the second thermal cracking step can be further improved.

[0056] [Embodiment 2] Another embodiment of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0057] Fig. 3 is a flowchart showing an example of the olefin production method according to embodiment 2. The olefin production method according to embodiment 2 can be carried out, for example, according to the flowchart shown in Fig. 3. Note that the flowchart shown in Fig. 3 is an example and is not limiting.

[0058] The pretreatment step S21 and the first pyrolysis step S22 shown in FIG. 3 may be the same steps as the pretreatment step S11 and the first pyrolysis step S12 of the first embodiment, respectively.

[0059] The refining step S23 may be a step of separating low molecular weight gas components and heavy components from the first product obtained through the first thermal cracking step S22. Through the refining step S23, a hydrocarbon mixture having a boiling point in the range of approximately that of naphtha is obtained.

[0060] The hydrogenation step S24 may be a step of promoting a hydrogenation reaction of the hydrocarbon mixture having a boiling point in the range of approximately that of naphtha obtained through the refining step S23, and converting it into saturated hydrocarbons.

[0061] The cracking step S25 is an example of a second thermal cracking step according to the present disclosure. The cracking step S25 may be a step of obtaining desired olefins by cracking using, for example, a naphtha cracker.

[0062] The olefin production method according to a second embodiment of the present disclosure includes a first pyrolysis step (S22) of pyrolyzing a plastic to obtain a first product, and a second pyrolysis step (cracking step: S25) of further pyrolyzing at least a portion of the first product, wherein hydrocarbons contained in the first product satisfy all of the following conditions (i) to (iv): The second pyrolysis step includes cracking.

[0063] (i) When the sum of the contents [wt %] of alkanes and alkenes having 3 or less carbon atoms in the first product is X [wt %], 5≦X≦35, more preferably 7≦X≦32, and even more preferably 9≦X≦28. (ii) When the weight average molecular weight calculated from normal alkanes having 1 to 3 carbon atoms and normal alkanes having 10 to 35 carbon atoms contained in the first product is Y [−], 95≦Y≦240, more preferably 120≦Y≦235, and even more preferably 150≦Y≦230. (iii) When the ratio of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms contained in the first product to the sum of the contents [wt%] of normal alkanes having 1 to 3 carbon atoms and normal alkanes having 10 to 35 carbon atoms contained in the first product is Z[-], the ratio is 0.30≦Z≦0.93, more preferably 0.40≦Z≦0.90, and even more preferably 0.50≦Z≦0.85. (iv) When the ratio of the content [wt%] of alkanes having 1 to 3 carbon atoms to the content [wt%] of normal alkanes having 35 carbon atoms contained in the first product is W[-], the ratio is 5≦W≦205, more preferably 8≦W≦150, and even more preferably 12≦W≦100. According to such a configuration, the yield of olefins after the second thermal cracking step can be significantly improved.

[0064] (Summary of embodiments) [1] A method for producing olefins according to aspect 1 of the present disclosure includes a first pyrolysis step of pyrolyzing a plastic to obtain a first product, and a second pyrolysis step of further pyrolyzing at least a portion of the first product, wherein hydrocarbons contained in the first product satisfy all of the following conditions (i) to (iv):

[0065] (i) When the sum of the contents [wt%] of alkanes and alkenes having 3 or less carbon atoms in the first product is X [wt%], 5≦X≦35 is satisfied. (ii) When the weight average molecular weight calculated from the normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Y [-], 95≦Y≦240 is satisfied. (iii) When the ratio of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the contents [wt%] of normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Z [-], 0.30≦Z≦0.93 is satisfied. (iv) When the ratio of the content [wt%] of alkanes having 1 to 3 carbon atoms to the content [wt%] of normal alkanes having 35 carbon atoms contained in the first product is W [-], 5≦W≦205 is satisfied.

[0066] [2] In the olefin production method according to Aspect 2 of the present disclosure, in Aspect 1, 39 wt % to 88 wt % of the first product is condensed at 0° C.

[0067] [3] A method for producing an olefin according to a third aspect of the present disclosure is the method according to the first or second aspect, wherein the second thermal cracking step is a catalytic cracking step using a catalyst.

[0068] [4] A fourth aspect of the present disclosure provides a method for producing an olefin, in the first or second aspect, wherein the second pyrolysis step includes cracking.

[0069] [5] A method for producing an olefin according to a fifth aspect of the present disclosure is any one of the first to fourth aspects, wherein the first thermal cracking step is carried out using a fluidized bed reactor, and the following conditions (a) to (f) are all satisfied:

[0070] (a) The pyrolysis is carried out continuously. (b) The pyrolysis temperature is 435°C or higher and 595°C or lower. (c) The pyrolysis pressure is 0 kPaG or higher and 100 kPaG or lower. (d) The fluidizing gas linear velocity in the fluidized bed reactor is 0.1 cm / s or higher and 100 cm / s or lower. (e) The ratio of the fluidizing gas supply rate (N ml / min) to the raw material supply rate (g / min) is 10 (N ml / g) or higher and 2000 (N ml / g) or lower. (f) The ratio of the fluidizing gas supply rate (N ml / min) to the amount of bed material (g) present in the fluidized bed reactor is 1.0 (N ml / g min) or higher and 100 (N ml / g min) or lower.

[0071] [6] The olefin production method according to Aspect 6 of the present disclosure, in any one of Aspects 1 to 5, further includes an analysis step of analyzing the composition of the first product, and a condition adjustment step of adjusting thermal cracking conditions based on the analysis results in the analysis step.

[0072] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0073] [Demonstration Test] The following describes a test that demonstrated the olefin production method according to the present disclosure.

[0074] In this demonstration test, four experiments were conducted: Example 1 and Example 2 within the scope of the present disclosure, and Comparative Examples 1 and 2 as comparative examples, and the results were compared. Each experiment and its results are described in detail below. In this demonstration test, polyethylene (Sumikathene (registered trademark) G201F manufactured by Sumitomo Chemical Co., Ltd.), a polyolefin plastic, was used as the raw material.

[0075] 4 is a schematic diagram of the experimental apparatus (hereinafter referred to as apparatus 100A) used in this demonstration test. Apparatus 100A includes a melt extruder 10A, a thermal cracking apparatus 21A, and a catalytic cracking apparatus 22A. Apparatus 100A also includes an atmospheric discharge cooling trap 40, a sampling cooling trap 41, and a sampling gas bag 50.

[0076] The pyrolysis apparatus 21A is a fluidized bed pyrolysis reaction apparatus having a stainless steel reactor with an inner diameter of 21 mm. In the pyrolysis apparatus 21A, silica sand 212 with a median diameter of 90 μm was placed as a fluidizing medium on a dispersion plate 211 installed in the reactor. Nitrogen was used as the fluidizing gas. The nitrogen was preheated in advance by an electric jacket heater HT and supplied to the pyrolysis apparatus 21A. The pyrolysis apparatus 21A is equipped with an electric furnace 210 that heats the fluidized bed to a predetermined temperature.

[0077] The catalytic cracking apparatus 22A is a fixed-bed catalytic cracking reactor having a stainless steel reactor with an inner diameter of 13 mm. The reactor of the catalytic cracking apparatus 22A was packed with 1.0 g of an MFI zeolite catalyst (catalyst 221) prepared in advance by the method described in the examples of WO 2022 / 039094 A1. The catalyst 221 was adjusted using alumina balls so that it was packed in the center of the reactor in the vertical direction. The catalytic cracking apparatus 22A is equipped with an electric furnace 6 that heats the packed bed to a predetermined temperature.

[0078] The thermal cracking conditions and catalytic cracking conditions for Examples 1 and 2, and Comparative Examples 1 and 2 are shown in Table 1 below. Example 1 In Example 1, the output of the electric furnace 210 was adjusted so that the fluidized bed temperature was 500°C. Polyethylene, the raw material, was supplied in a molten state to the thermal decomposition device 21A via the melt extruder 10A, and continuous thermal decomposition treatment was carried out. The thermal decomposition conditions in the thermal decomposition device 21A were as shown in Table 1, and are within the range of the present disclosure.

[0079] The pyrolysis gas (first product) discharged from the top of the thermal cracking unit 21A was sent to the catalytic cracking unit 22A through a transfer pipe heated by an electric jacket heater HT.

[0080] The pyrolysis gas composition was transferred to the sampling cooling trap 41 and the sampling gas bag 50 without passing through the catalytic cracking unit 22A. Condensed oil was sampled in the ice-cooled sampling cooling trap 41, and uncondensed gas was sampled in the sampling gas bag 50. The piping routes for the sampling are not shown in the figure.

[0081] Sampling began 80 minutes after the feed polyethylene started to be supplied to the thermal cracking apparatus 21A, and continued for 10 minutes. Until sampling began, the pyrolysis gas was sent to the atmospheric exhaust cooling trap 40 and cooled. The compositions of the sampled condensed oil and non-condensable gas were analyzed by GC-FID.

[0082] Specifically, the weight percentage of each component contained in the condensed oil was measured by dissolving the condensed oil in orthoxylene and then analyzing it using a gas chromatograph (GC-2010plus) manufactured by Shimadzu Corporation. The column used in the gas chromatography was DB-1 123-1063 manufactured by Agilent Technologies, the column temperature was 40°C to 280°C, and the FID detector temperature was 280°C. The weight percentage of each component contained in the non-condensed gas was measured by analysis using a gas chromatograph (GC-2010) manufactured by Shimadzu Corporation. The column used in the gas chromatography was HP-PLOT Al manufactured by Agilent Technologies. ２ O ３ The column temperature was 40°C to 180°C, and the FID detector temperature was 200°C. The content of each component in the pyrolysis gas was calculated in weight percent based on the total weight of the sampled condensed oil and non-condensed gas. The results of the composition analysis of the pyrolysis gas are shown in Table 2 below.

[0083] The thermal cracking gas supplied to the catalytic cracking unit 22A was continuously catalytically cracked in the catalytic cracking unit 22A. The catalytic cracking conditions in the catalytic cracking unit 22A are as shown in Table 1.

[0084] The composition of the catalytic cracking gas discharged from the catalytic cracking unit 22A was transferred to the sampling cooling trap 41 and the sampling gas bag 50. The ice-cooled sampling cooling trap 41 sampled condensed oil, and the sampling gas bag 50 sampled uncondensed gas.

[0085] Sampling began 80 minutes after the start of supplying the thermal cracking gas to the catalytic cracking unit 22A, and was continued for 10 minutes. Until sampling began, the catalytic cracking gas was sent to the atmospheric exhaust cooling trap 40 for cooling treatment. The compositions of the sampled condensed oil and non-condensed gas were analyzed using the same method as for the analysis of the thermal cracking gas. However, the condensed oil was analyzed by gas chromatography without being dissolved in ortho-xylene. The results of the composition analysis of the catalytic cracking gas are shown in Table 2 below.

[0086] Example 2 In Example 2, the thermal cracking conditions in the thermal cracking apparatus 21A and the catalytic cracking conditions in the catalytic cracking apparatus 22A were set as shown in Table 1. However, the thermal cracking conditions in Example 2 are also within the scope of the present disclosure.

[0087] The results of the composition analysis of the thermal cracking gas and catalytic cracking gas obtained in Example 2 are shown in Table 2 below.

[0088] (Comparative Examples 1 and 2) In Comparative Examples 1 and 2, the thermal cracking conditions in the thermal cracking apparatus 21A and the catalytic cracking conditions in the catalytic cracking apparatus 22A were set as shown in Table 1. The thermal cracking conditions in Comparative Examples 1 and 2 were outside the scope of the present disclosure.

[0089] The results of the composition analysis of the thermal cracking gas and catalytic cracking gas obtained in Comparative Examples 1 and 2 are shown in Table 2 below. (Results) From the results in Table 2, in Examples 1 and 2, the hydrocarbons contained in the pyrolysis gas satisfied all of the following conditions (i) to (iv).

[0090] (i) When the sum of the contents [wt%] of alkanes and alkenes having 3 or less carbon atoms in the pyrolysis gas is X [wt%], 5≦X≦35 is satisfied. (ii) When the weight average molecular weight calculated from the normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Y [-], 95≦Y≦240 is satisfied. (iii) When the ratio of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the contents [wt%] of normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Z [-], 0.30≦Z≦0.93 is satisfied. (iv) When the ratio of the content [wt%] of alkanes having 1 to 3 carbon atoms to the content [wt%] of normal alkanes having 35 carbon atoms contained in the first product is W [-], 5≦W≦205 is satisfied.

[0091] Furthermore, Examples 1 and 2, which satisfied the above conditions, exhibited a high yield of C2 to C4 olefins exceeding 60%, and it was demonstrated that this result was significantly higher than that of Comparative Examples 1 and 2.

[0092] (2) The pyrolysis gas in Examples 1 and 2 has a condensation ratio of 39 wt % to 88 wt % of the pyrolysis gas at 0° C. When the pyrolysis gas satisfies the above conditions (i) to (iv) and has a composition in which 39 wt % to 88 wt % of the pyrolysis gas condenses at 0° C., the C2 to C4 olefin yield is high, exceeding 60%, and it has been demonstrated that this result is significantly higher than that of Comparative Examples 1 and 2.

[0093] 100... Production system 10... Pretreatment system 21... Thermal cracking apparatus 22... Catalytic cracking apparatus 30... Purification apparatus G1... Thermal cracking gas (first product) G2... Catalytic cracking gas S11, S21... Pretreatment process S12, S22... First thermal cracking process S13... Catalytic cracking process (second thermal cracking process) S25... Cracking process (second thermal cracking process)

Claims

1. A method for producing olefins, comprising: a first pyrolysis step of pyrolyzing plastics to obtain a first product; and a second pyrolysis step of further pyrolyzing at least a portion of the first product, wherein the hydrocarbons contained in the first product satisfy all of the following conditions (i) to (iv): (i) when the sum of the contents [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product is X [wt%], 5≦X≦35; (ii) when the weight average molecular weight calculated from normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms contained in the first product is Y [-], 95≦Y≦240; and (iii) when the ratio of the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the contents [wt%] of normal alkanes having 10 to 35 carbon atoms contained in the first product is Z [-], 0.30≦Z≦0.

93. (iv) When the ratio of the content [wt %] of alkanes having 1 to 3 carbon atoms contained in the first product to the content [wt %] of normal alkanes having 35 carbon atoms contained in the first product is W [-], 5≦W≦205.

2. The method for producing olefins according to claim 1, wherein the first product is condensed at 0°C in an amount of 39 wt% to 88 wt%.

3. The method for producing olefins according to claim 1, wherein the second thermal cracking step is a catalytic cracking step using a catalyst.

4. The method for producing olefins according to claim 1, wherein the second pyrolysis step comprises cracking.

5. The method for producing olefins according to claim 1, wherein the first thermal cracking step is carried out using a fluidized bed reactor and satisfies all of the following conditions (a) to (f): (a) the thermal cracking is carried out continuously; (b) the thermal cracking temperature is 435°C or higher and 595°C or lower; (c) the thermal cracking pressure is 0 kPaG or higher and 100 kPaG or lower; (d) the fluidizing gas linear velocity in the fluidized bed reactor is 0.1 cm / s or higher and 100 cm / s or lower; (e) the ratio of the fluidizing gas supply rate (N ml / min) to the raw material supply rate (g / min) is 10 (N ml / g) or higher and 2000 (N ml / g) or lower; and (f) the ratio of the fluidizing gas supply rate (N ml / min) to the amount of bed material (g) present in the fluidized bed reactor is 1.0 (N ml / g min) or higher and 100 (N ml / g min) or lower.

6. The method for producing an olefin according to claim 1, further comprising: an analyzing step for analyzing the composition of the first product; and a condition adjusting step for adjusting thermal cracking conditions based on the analysis results in the analyzing step.

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