JP7829816B2 - Method for producing olefins - Google Patents

Description

This disclosure relates to a method for producing olefins.

In order to realize a carbon-recycling society, attention is being drawn to technologies for chemically recycling waste plastics that were conventionally thermally recycled. As an example of such technology, a method for producing olefins is known, as shown in Patent Document 1, which includes a thermal decomposition step of thermally decomposing plastic to obtain a thermal decomposition gas, and a catalytic decomposition step of decomposing the obtained thermal decomposition gas in the presence of a catalyst to obtain a catalytic decomposition gas.

Brochure for International Application WO2023/047951

One aspect of this disclosure aims to improve the olefin yield in an olefin production process from plastics, which includes a two-stage pyrolysis treatment.

To solve the above problems, a method for producing an olefin according to one aspect of the present disclosure includes a first thermal decomposition step of thermally decomposing a plastic to obtain a first product, and a second thermal decomposition step of further thermally decomposing at least a portion of the first product, wherein the hydrocarbon contained in the first product satisfies all of the following conditions (i) to (iv):
(i) Let X [wt%] be the sum of the content [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product, then 5 ≤ X ≤ 35. (ii) Let Y [-] be 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, then 95 ≤ Y ≤ 240. (iii) Let Z [-] be the ratio of the sum of the content [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the content [wt%] of normal alkanes having 1 to 3 carbon atoms contained in the first product, then 0.30 ≤ Z ≤ 0.93. (iv) Let W [-] be 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, then 5 ≤ W ≤ 205.

According to one aspect of this disclosure, the olefin yield can be improved in an olefin production process from plastics that includes a two-stage pyrolysis treatment.

This flowchart shows an example of a method for producing an olefin according to Embodiment 1. This is a schematic diagram showing the main components of the manufacturing system according to Embodiment 1. This flowchart shows an example of a method for producing an olefin according to Embodiment 2. This is a schematic diagram of the experimental setup used in the demonstration test.

[Embodiment 1]
One embodiment of this disclosure will be described in detail below.

Hereinafter, a method for producing an olefin according to one embodiment of this disclosure will be described in detail with reference to the drawings, along with the manufacturing system used therein.

The olefin manufacturing method of this embodiment is a method for producing lower olefins that can be recycled as plastic raw materials using plastics such as waste plastics as raw materials. Figure 1 is a flowchart of an example of the olefin manufacturing method according to this embodiment. As shown in Figure 1, the olefin manufacturing method of this embodiment includes a pretreatment step S11, a first thermal decomposition step S12, a catalytic decomposition step S13, and a purification step S14. Each step will be described in detail below.

In this embodiment, as an example, the flowchart shown in Figure 1 and the olefin manufacturing system that realizes the manufacturing flow shown in the flowchart (Figure 2: manufacturing system 100) will be described. However, the systems described herein and in the drawings are merely typical examples and do not limit the scope of this disclosure in any way. This is also true in the following embodiments.

<Olefin manufacturing system (manufacturing system 100)>
First, an example of the configuration of the manufacturing system 100 will be explained using Figures 1 and 2. Figure 2 is a schematic diagram showing the main components of the manufacturing system 100 according to Embodiment 1.

The manufacturing system 100 of this embodiment is a system for decomposing plastics, particularly polyolefin-based plastics, to obtain an olefin-rich gas that is abundant in lower olefin gases. The plastic used as a raw material in the olefin manufacturing 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. 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.

As shown in Figure 2, the manufacturing system 100 of this embodiment is generally configured to include a pretreatment system 10, a pyrolysis apparatus 21, a catalytic cracking apparatus 22, a purification apparatus 30, and each of the pathways L1 to L6.

Plastics such as waste plastics are supplied to the pretreatment system 10 from route L1. The discharge port of the pretreatment system 10 and the supply port of the pyrolysis unit 21 are connected by route L2. The feed material M, which has been pretreated by the pretreatment system 10, is supplied to the pyrolysis unit 21 via route L2. The gas outlet 21O of the pyrolysis unit 21 and the supply port 22I of the catalytic cracking unit 22 are connected by route L3. The feed material M supplied to the pyrolysis unit 21 is pyrolyzed and supplied to the catalytic cracking unit 22 as pyrolysis gas G1 via route L3. Pyrolysis gas G1 is an example of the first product according to this disclosure. The catalytic cracking unit 22 and the purification unit 30 are connected by route L4. The pyrolysis gas G1 supplied to the catalytic cracking unit 22 is catalytically cracked and supplied to the purification unit 30 as catalytic cracking gas G2. The catalytic cracking gas G2 is purified by the purification unit 30, and the olefin-rich gas, which is rich in lower olefins, is discharged from path L5, while the liquid containing oil is discharged from path L6. Each device (system) is described in detail below.

The pre-treatment system 10 is a system that processes plastics such as waste plastics to make them suitable feed material M for decomposition treatment. In other words, the pre-treatment system 10 is a system that performs the pre-treatment process S11. The pre-treatment system 10 may include a plurality of devices that perform different treatments. For example, the pre-treatment system 10 may include one or more devices from among a sorting device, a crushing device, a washing device, a drying device, a melting device, or a dechlorination device. A sorting device is a device that sorts polyolefin plastics from raw materials such as waste plastics. As a sorting device, one or more devices such as an optical sorting device or a specific gravity separation device can be used. A crushing device is a device that crushes the sorted plastics. A washing device is a device that washes the crushed plastics. A drying device is a device that dries the washed plastics. A melting device is a device that heats the plastics to make them liquid. A dechlorination device is a device that removes chlorine contained in the plastics.

The pyrolysis apparatus 21 is a device that decomposes and vaporizes a substance by heating. In other words, the pyrolysis apparatus 21 is a device capable of carrying out the first pyrolysis step S12 of this embodiment. The pyrolysis apparatus 21 is a device that performs pyrolysis continuously, and can use, for example, an extruder, a stirring tank, a rotary kiln, or a fluidized bed. As the fluidized bed, an internal circulating fluidized bed or an external circulating fluidized bed can be used.

Furthermore, multiple of the above-described devices may be used as the pyrolysis apparatus 21, and the multiple reactors may be connected in parallel or in series. As the heat source required in the first pyrolysis step S12, heat obtained by burning one or more of the following can be used: the pyrolysis residue generated in the pyrolysis apparatus 21, the hydrocarbon-containing liquid and/or lower paraffin gas obtained in the purification step S14, or hydrocarbon fuels such as natural gas or kerosene. Alternatively, heat obtained by electric heating or microwave irradiation can also be used as a heat source. Alternatively, electric heating, microwave irradiation, and two or more of the heat obtained from the above-described combustion may be used in combination.

The heating method may be either direct heating or indirect heating. Direct heating involves holding a microwave-absorbing material (susceptor) within the device and supplying microwave energy to the waste plastic through it. Indirect heating methods include supplying heat obtained by burning an electric heater or hydrocarbon fuel through the heat transfer surface of the device, or preheating water vapor or an inert gas such as nitrogen or _CO2 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 mainly composed of iron, iron oxide, alumina, silica, etc., is preheated to a high temperature using a heat source before introducing it into the device. Preheating of gases or solid particles using a heat source may be performed in combination with the pyrolysis device 21, either in a portion of the pyrolysis device 21 or using a device similar to the pyrolysis device, circulating the gases or solids from these devices.

The catalytic cracking apparatus 22 is a device that decomposes a substance by bringing a pyrolysis gas G1 into contact with a catalyst. In other words, the catalytic cracking apparatus 22 is a device that carries out the catalytic cracking step S13. The catalytic cracking step S13 is an example of the second pyrolysis step according to this disclosure. The catalytic cracking apparatus 22 can use, for example, a fixed bed, a moving bed, or a fluidized bed. Multiple of these reactors as exemplified may also be used, and the multiple reactors may be connected in parallel or in series. As a heat source required in the catalytic cracking step S13, heat obtained by burning one or more of the following can be used: coke generated in the catalytic cracking apparatus 22 and adhering to the catalyst surface, a liquid containing hydrocarbons obtained in the refining step S14 and/or lower paraffin gas, or hydrocarbon fuels such as natural gas or kerosene. Alternatively, heat obtained by electric heating or microwave irradiation can also be used as a heat source. Alternatively, two or more of the following can be used in combination: electric heating, microwave irradiation, and the heat obtained from the aforementioned combustion.

The heating method may be either direct heating or indirect heating. Direct heating involves holding a microwave-absorbing material (susceptor) within the device and supplying microwave energy to the waste plastic through it. Indirect heating methods include supplying heat obtained by burning an electric heater or hydrocarbon fuel through the heat transfer surface of the device, or preheating water vapor or an inert gas such as nitrogen or _CO2 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 mainly composed of iron, iron oxide, alumina, silica, etc., is preheated to a high temperature using a heat source before introducing it into the device. The solid particles may also be the catalyst mentioned above. Preheating of the gas or solid particles using a heat source may be performed in a portion of the inside of the pyrolysis device 21 or using a device similar to the pyrolysis device, in combination with the pyrolysis device 21, circulating the gas or solid from these devices.

Alternatively, the pyrolysis gas G1 obtained by pyrolysis in the pyrolysis unit 21 may be separated into gaseous and liquid components using a cooling unit or purification unit, and some or all of the separated liquid component may be supplied to the catalytic cracking unit 22. In this case, the separated gaseous component may be supplied to the catalytic cracking unit 22 or to the purification unit 30 or later, bypassing the catalytic cracking unit 22. Alternatively, the gaseous component may be used as fuel in the manufacturing system 100 or as fuel in other manufacturing systems. The handling of the gaseous component is not limited to these.

The purification apparatus 30 is capable of separating the mixture supplied to the apparatus by known gas-liquid separation operations or distillation operations. In other words, the purification apparatus 30 is capable of carrying out the purification process S14 of this embodiment. The purification apparatus 30 can, for example, be a gas-liquid separation apparatus or a distillation apparatus. These apparatuses may also be combined, or multiple apparatuses may be connected together. In addition, a distillation apparatus may be optionally installed downstream of the purification apparatus 30 in order to increase the purity of the olefin obtained in the purification apparatus 30 to an olefin purity of a desired number of carbon atoms.

<Method for producing olefins>
The method for producing olefins 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 just one example and is not limited thereto. Each step in the method for producing olefins according to Embodiment 1 will be described in detail.

(Regarding the raw materials)
Before describing each process, the raw materials used in this 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 solid waste, etc. The plastic is preferably mainly composed of polyolefins such as polyethylene or polypropylene, but may also contain other plastics. 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. Furthermore, the waste plastic may also include unused mixed plastics or used mixed plastics.

(Pre-treatment step S11)
The pretreatment step S11 is a step of pretreatment of the plastic to obtain a feed material M to be used in the first pyrolysis step S12. The plastic can be supplied to the first pyrolysis step S12 as a feed material M mainly containing polyolefin-based plastics after the pretreatment step S11. Preferably, the polyolefin-based plastic content in the raw plastic is 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more after the pretreatment step.

(First pyrolysis step S12)
The first pyrolysis step S12 is a step of decomposing the feed material M by heating to obtain pyrolysis gas G1. More specifically, the first pyrolysis step S12 is a step of decomposing the olefin-based plastic contained in the feed material M by heating to produce pyrolysis gas G1. Through thermal decomposition in the first pyrolysis step S12, the carbon compounds contained in the feed material M are reduced in molecular weight and mainly decomposed into hydrocarbons with about 1 to 30 carbon atoms. The pyrolysis temperature (°C) in the first pyrolysis step S12 can be set based on the composition of the feed material M. A high temperature is desirable for a fast decomposition rate of the plastic, but if the temperature is too high, carbonization will occur, so for example, 400 to 800°C is desirable, preferably 435 to 595°C, and even more preferably 450 to 550°C. As for 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.

Furthermore, in the first pyrolysis step S12, a catalyst may be optionally used to accelerate decomposition. Examples of catalysts used in the first pyrolysis step S12 include, but are not limited to, silicate catalysts, preferably zeolite catalysts, and more preferably MFI-type zeolite catalysts. Silicate catalysts typically contain silicon atoms, aluminum atoms, oxygen atoms, and hydrogen atoms. Silicate catalysts 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.

In the first pyrolysis step S12, water vapor or an inert gas such as nitrogen gas or _CO2 gas may be present, and these gases may be used as the fluidizing gas in the fluidized bed. When a fluidized bed reactor is used in the first pyrolysis step S12, the more fluidizing gas there is, the lower the hydrocarbon concentration in the gas phase becomes, and the more easily the decomposed components tend to vaporize. The linear velocity of the fluidizing gas 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 (Nml/min) to the supply rate (g/min) of the feed material M supplied to the fluidized bed reactor is preferably 10 (Nml/g) or more and 2000 (Nml/g) or less, more preferably 50 (Nml/g) or more and 1500 (Nml/g) or less, and even more preferably 200 (Nml/g) or more and 1200 (Nml/g) or less. Furthermore, the ratio of the fluidizing gas supply rate (Nml/min) to the amount of fluidizing medium (g) present in the fluidized bed reactor is preferably 1.0 (Nml/g・min) or more and 100 (Nml/g・min) or less, more preferably 2.0 (Nml/g・min) or more and 50 (Nml/g・min) or less, and even more preferably 3.0 (Nml/g・min) or more and 25 (Nml/g・min) or less.

The inventors have found that the yield of olefins after catalytic cracking step S13 can be improved by having a characteristic hydrocarbon composition in the pyrolysis gas G1 obtained by the first pyrolysis step S12, as described below.

Specifically, in the method for producing olefins according to this disclosure, the pyrolysis gas G1 satisfies all of the following conditions (i) to (iv). In formulas (1) to (4) under the following conditions, CN (where N is a natural number) is the wt% content of N-carbon normal alkanes (chain saturated hydrocarbon compounds) in the pyrolysis gas G1, and CN' (where N is a natural number) is the wt% content of N-carbon alkenes (unsaturated hydrocarbon compounds) in the pyrolysis gas G1.

(i) Let X [wt%] be the sum of the content [wt%] of alkanes and alkenes with 3 or fewer carbon atoms in the pyrolysis gas G1, then 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)

(ii) If Y[-] is 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, then 95 ≤ Y ≤ 240, more preferably 120 ≤ Y ≤ 235, and even more preferably 150 ≤ Y ≤ 230. Specifically, Y can be calculated using the content [wt%] of each normal alkane by the following formula (2):
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)

(iii) If Z[-] is the ratio of the sum of the wt% content of C10-35 normal alkanes to the sum of the wt% content of C10-35 normal alkanes in the pyrolysis gas G1, then 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)

(iv) If W[-] is the ratio of the content of C1-3 alkanes [wt%] to the content of C35 normal alkanes [wt%] in the pyrolysis gas G1, 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).

The condition in (i) above is a provision that focuses on low molecular weight hydrocarbons contained in the pyrolysis gas G1. In this 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, it is thought that an excess of low molecular weight hydrocarbons may reduce the final olefin yield. Therefore, the condition in (i) above, which specifies the amount of low molecular weight hydrocarbons, is thought to contribute to improving the olefin yield.

The above condition (iii) is a provision that focuses on high molecular weight hydrocarbons contained in the pyrolysis gas G1. In this disclosure, high molecular weight hydrocarbons may be hydrocarbons having 10 or more carbon atoms. It is thought that high molecular weight hydrocarbons may not be decomposed to the desired olefins even after catalytic cracking in the catalytic cracking step S13 after the first pyrolysis step S12. Therefore, the above condition (iii), which specifies the amount of high molecular weight hydrocarbons, is thought to contribute to improving the olefin yield.

Furthermore, in the method for producing olefins according to this disclosure, the pyrolysis gas G1 satisfies all of the above conditions (i) to (iv), and preferably has a condensation ratio at 0°C of 39 wt% to 88 wt%, more preferably 45 wt% to 85 wt%, and even more preferably 55 wt% to 80 wt%.

(Catalytic cracking step S13)
Catalytic cracking step S13 is a step that can produce catalytic cracking gas G2, which is a hydrocarbon with approximately 1 to 20 carbon atoms, by decomposing the pyrolysis gas G1 in the presence of a catalyst and reducing its molecular weight. The decomposition temperature in catalytic cracking step S13 can be set based on the composition of the pyrolysis gas G1. The decomposition temperature is, for example, 400 to 800°C, preferably 450 to 650°C, and more preferably 500 to 600°C. The decomposition pressure in catalytic cracking step S13 is, for example, -80 to 1000 kPaG, preferably -10 to 300 kPaG, and more preferably 0 to 100 kPaG.

The catalyst used in the catalytic cracking step S13 is, for example, a silicate catalyst, preferably a zeolite catalyst, and more preferably an MFI-type zeolite catalyst, but is not limited to these. Silicate catalysts typically contain silicon atoms, aluminum atoms, oxygen atoms, and hydrogen atoms. Silicate catalysts 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. The weight-hourly space velocity [1/h] in the catalytic cracking step S13, which is the ratio of the mass flow rate [kg/h] of the pyrolysis gas G1 to the amount of catalyst [kg], 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].

In catalytic cracking step S13, water vapor or an inert gas such as nitrogen gas or _CO2 gas may be present, and these gases may be used as fluidizing gases for the fluidized bed.

(Purification step S14)
The purification step S14 is a step for separating and purifying the catalytic cracking gas G2. More specifically, the purification step S14 is a step that can separate the catalytic cracking gas G2 into a gas containing at least one type of hydrocarbon with a low number of carbon atoms (e.g., C1 to C4) and a liquid containing at least one type of hydrocarbon with a high number of carbon atoms (e.g., C5 or more). Furthermore, the gas may be an olefin-rich gas containing 90% by mass or more of lower olefins. The lower olefin may contain at least one type from ethylene, propylene, or butene. In addition, a purification step may be optionally added downstream of the purification step S14 in order to increase the purity of olefins with a specific number of carbon atoms in the olefin-rich gas obtained in the purification step S14.

By obtaining an olefin-rich gas containing abundant lower olefins, olefins can be produced with high efficiency without the use of hydrogen.

Furthermore, at least a portion of the hydrocarbon-containing liquid obtained in the purification step S14 may be supplied to the pyrolysis apparatus 21 or the catalytic cracking apparatus 22. This can further improve the yield of olefins.

Alternatively, the hydrocarbon-containing liquid and/or lower paraffin gas obtained in the purification step S14 may be burned and used as a heat source in any of the steps from the pretreatment step S11 to the purification step S14. This reduces the environmental impact of the entire olefin manufacturing system.

(Summary of Embodiment 1)
The first embodiment of the present disclosure is a method for producing an olefin, comprising a first pyrolysis step (S12) of pyrolyzing a plastic to obtain a first product (pyrolysis gas G1), and a second pyrolysis step (catalytic decomposition step: S13) of further pyrolyzing at least a portion of the first product, wherein the hydrocarbon contained in the first product satisfies all of the following conditions (i) to (iv).

(i) Let X [wt%] be the sum of the content [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product, then 5 ≤ X ≤ 35. (ii) Let Y [-] be 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, then 95 ≤ Y ≤ 240. (iii) Let Z [-] be the ratio of the sum of the content [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the content [wt%] of normal alkanes having 1 to 3 carbon atoms contained in the first product, then 0.30 ≤ Z ≤ 0.93. (iv) Let W [-] be 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, then 5 ≤ W ≤ 205.

With this configuration, the yield of olefins after the second pyrolysis step can be significantly improved.

Furthermore, the first product may satisfy all of the above-mentioned conditions (i) to (iv), and its condensation ratio at 0°C may be 39 wt% to 88 wt% of the pyrolysis gas G1. With such a configuration, the yield of olefins after the second pyrolysis step can be significantly improved.

Furthermore, by including a purification step after the second thermal decomposition step in the above-mentioned method for producing olefins, an olefin-rich gas containing abundant lower olefins can be obtained.

Furthermore, the method for producing an olefin according to Embodiment 1 of this disclosure may further include an analysis step for analyzing the composition of the pyrolysis gas G1, and a condition adjustment step for adjusting the pyrolysis conditions based on the analysis results in the analysis step.

Specifically, in the analysis step, the pyrolysis gas G1 may be sampled and its composition may be analyzed, for example, by 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 following may be adjusted: pyrolysis temperature, pyrolysis pressure, fluidizing gas linear velocity in the fluidized bed reactor, ratio of fluidizing gas supply rate to raw material supply rate, and ratio of fluidizing gas supply rate to amount of fluidizing medium present in the fluidized bed reactor.

For example, if the analysis reveals an excess of low molecular weight components, 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 an excess of low molecular weight components is found, 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 fluidized medium present in the fluidized bed reactor.

Conversely, if it is determined that there is an excess of high molecular weight components, adjustments may be made by increasing the thermal decomposition temperature, increasing the thermal decomposition pressure, or decreasing the linear velocity of the fluidizing gas in the fluidized bed reactor. Alternatively, if it is determined that there is an excess of low molecular weight components, adjustments may be made by reducing the ratio of the fluidizing gas supply rate to the raw material supply rate, or by reducing the ratio of the fluidizing gas supply rate to the amount of fluidizing medium present in the fluidized bed reactor.

By including analytical and condition adjustment steps, the conditions in the pyrolysis step can be set more appropriately, and the yield of olefins after the second pyrolysis step can be further improved.

[Embodiment 2]
Other embodiments of this disclosure are described below. For the sake of clarity, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

Figure 3 is a flowchart showing an example of an olefin manufacturing method according to Embodiment 2. The olefin manufacturing method according to Embodiment 2 can be carried out, for example, according to the flowchart shown in Figure 3. Note that the flowchart shown in Figure 3 is just an example and is not limited thereto.

The pretreatment step S21 and the first pyrolysis step S22 shown in Figure 3 may be the same steps as the pretreatment step S11 and the first pyrolysis step S12 of Embodiment 1, respectively.

The purification step S23 may be a step of separating low molecular weight gaseous components and heavy components from the first product obtained through the first pyrolysis step S22. By going through the purification step S23, a hydrocarbon mixture within the boiling point range of naphtha is obtained.

The hydrogenation step S24 may be a step that promotes the hydrogenation reaction of a hydrocarbon mixture obtained through the purification step S23, which is within the boiling point range of naphtha, and converts it into saturated hydrocarbons.

The cracking step S25 is an example of the second pyrolysis step according to this disclosure. The cracking step S25 may be a step in which a desired olefin is obtained by performing cracking using, for example, a naphtha cracker.

The method for producing an olefin according to Embodiment 2 of this disclosure includes a first thermal decomposition step (S22) of thermally decomposing a plastic to obtain a first product, and a second thermal decomposition step (cracking step: S25) of further thermal decomposing at least a portion of the first product, wherein the hydrocarbon contained in the first product satisfies all of the following conditions (i) to (iv). The second thermal decomposition step also includes cracking.

(i) If X [wt%] is the sum of the content [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product, then 5 ≤ X ≤ 35, more preferably 7 ≤ X ≤ 32, and even more preferably 9 ≤ X ≤ 28. (ii) If Y [-] is 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, then 95 ≤ Y ≤ 240, more preferably 120 ≤ Y ≤ 235, and even more preferably 150 ≤ Y ≤ 230. (iii) If Z[-] is the ratio of the sum of the wt% content of normal alkanes having 10 to 35 carbon atoms to the sum of the wt% content of normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms in the first product, then 0.30 ≤ Z ≤ 0.93, more preferably 0.40 ≤ Z ≤ 0.90, and even more preferably 0.50 ≤ Z ≤ 0.85. (iv) If W[-] is the ratio of the wt% content of alkanes having 1 to 3 carbon atoms to the wt% content of normal alkanes having 35 carbon atoms in the first product, then 5 ≤ W ≤ 205, more preferably 8 ≤ W ≤ 150, and even more preferably 12 ≤ W ≤ 100. With such a configuration, the yield of olefins after the second pyrolysis step can be significantly improved.

(Summary of implementations)
[1] A method for producing an olefin according to Embodiment 1 of the present disclosure includes a first thermal decomposition step of thermally decomposing a plastic to obtain a first product, and a second thermal decomposition step of further thermally decomposing at least a portion of the first product, wherein the hydrocarbon contained in the first product satisfies all of the following conditions (i) to (iv).

(i) Let X [wt%] be the sum of the content [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product, then 5 ≤ X ≤ 35. (ii) Let Y [-] be 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, then 95 ≤ Y ≤ 240. (iii) Let Z [-] be the ratio of the sum of the content [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the content [wt%] of normal alkanes having 1 to 3 carbon atoms contained in the first product, then 0.30 ≤ Z ≤ 0.93. (iv) Let W [-] be 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, then 5 ≤ W ≤ 205.

[2] In the method for producing an olefin according to Embodiment 2 of the present disclosure, in Embodiment 1, the first product is condensed at 0°C by an amount of 39 wt% to 88 wt% of the first product.

[3] In the method for producing an olefin according to aspect 3 of the present disclosure, in aspect 1 or 2 above, the second thermal decomposition step is a catalytic decomposition step using a catalyst.

[4] The method for producing an olefin according to aspect 4 of the present disclosure, wherein in aspect 1 or 2, the second pyrolysis step includes cracking.

[5] In any of the embodiments 1 to 4 described above, the method for producing an olefin according to embodiment 5 of the present disclosure is characterized in that the first pyrolysis step is carried out using a fluidized bed reactor and all of the following conditions (a) to (f) are satisfied.

(a) 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 fluidizing medium (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] A method for producing an olefin according to embodiment 6 of the present disclosure further includes, in any of embodiments 1 to 5 above, an analytical step of analyzing the composition of the first product, and a condition adjustment step of adjusting the thermal decomposition conditions based on the analytical results in the analytical step.

The present invention is not limited to the embodiments described above, 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 within the technical scope of the present invention.

[Demonstration Test]
The following describes the tests that demonstrated the method for producing the olefin related to this disclosure.

In this demonstration test, four experiments were conducted: Example 1 and Example 2 within the scope of this disclosure, and Comparative Example 1 and Comparative Example 2 as comparative examples. The results were then compared. Each experiment and its results are described in detail below. In this demonstration test, polyethylene (Sumitomo Chemical Co., Ltd.: Sumikasen® G201F), a polyolefin-based plastic, was used as the raw material.

(Experimental apparatus)
Figure 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 pyrolysis apparatus 21A, and a catalytic decomposition apparatus 22A. Apparatus 100A also includes an atmospheric discharge cooling trap 40, a sampling cooling trap 41, and a sampling gas bag 50.

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

The catalytic cracking apparatus 22A is a stationary 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 pre-filled with 1.0 g of MFI-type zeolite catalyst (catalyst 221), which was prepared by the method described in the examples of WO2022/039094A1. The catalyst 221 was adjusted using alumina balls so that it was filled in the center of the reactor in the vertical direction. The catalytic cracking apparatus 22A is equipped with an electric furnace 6 for heating the packed bed to a predetermined temperature.

The thermal decomposition conditions and catalytic decomposition conditions for Example 1, Example 2, Comparative Example 1, and Comparative Example 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 reached 500°C. The raw material, polyethylene, was supplied in a molten state to the pyrolysis apparatus 21A via the molten extruder 10A, and the pyrolysis process was carried out continuously. The pyrolysis conditions in the pyrolysis apparatus 21A are as shown in Table 1 and are within the scope of this disclosure.

The pyrolysis gas (first product) discharged from the top of the pyrolysis apparatus 21A was sent to the catalytic decomposition apparatus 22A through a transfer pipe heated by an electric jacket heater HT.

The pyrolysis gas composition was transferred to the sampling cooling trap 41 and sampling gas bag 50 without passing through the catalytic cracking apparatus 22A. The condensed oil was sampled in the ice-cooled sampling cooling trap 41, and the uncondensed gas was sampled in the sampling gas bag 50. The piping route for this sampling is not shown in the diagram.

Sampling began 80 minutes after the raw polyethylene material was supplied to the pyrolysis unit 21A, and sampling was performed for 10 minutes. During the period leading up to the start of sampling, the pyrolysis gas was sent to the atmospheric discharge cooling trap 40 for cooling. The composition of the sampled condensed oil and non-condensed gas was analyzed by GC-FID.

Specifically, the weight percentage of each component in the condensed oil was measured by dissolving the condensed oil with orthoxylene and then analyzing it using a Shimadzu gas chromatograph (GC-2010plus). The column used for gas chromatography was Agilent Technologies DB-1 123-1063, with a column temperature of 40°C to 280°C and an FID detector temperature of 280°C. The weight percentage of each component in the non-condensable gas was measured by analyzing it using a Shimadzu gas chromatograph (GC-2010). The column used for gas chromatography was Agilent Technologies HP-PLOT _{Al₂O₃KCl₁₀9091P} - _K33 , with a column temperature of 40°C to 180°C and an FID detector temperature of 200°C. The total weight of the sampled condensed oil and non-condensable gas was used as the basis for calculating the weight percentage of each component in the pyrolysis gas. The results of the compositional analysis of the pyrolysis gas are shown in Table 2 below.

The pyrolysis gas supplied to the catalytic cracking apparatus 22A was continuously catalytically cracked within the apparatus 22A. The catalytic cracking conditions in the catalytic cracking apparatus 22A are as shown in Table 1.

The composition of the catalytic cracking gas discharged from the catalytic cracking apparatus 22A was transferred to a sampling cooling trap 41 and a sampling gas bag 50. Condensed oil was sampled in the ice-cooled sampling cooling trap 41, and uncondensed gas was sampled in the sampling gas bag 50.

Sampling began 80 minutes after the thermal cracking gas was supplied to the catalytic cracking unit 22A, and sampling was performed for 10 minutes. Before sampling began, the catalytic cracking gas was sent to the atmospheric discharge cooling trap 40 for cooling. The composition of the sampled condensed oil and non-condensable gas was analyzed using the same method as for the thermal cracking gas. However, the condensed oil was analyzed by gas chromatography without dissolving it in orthoxylene. The results of the compositional analysis of the catalytic cracking gas are shown in Table 2 below.

(Example 2)
In Example 2, the thermal decomposition conditions in the thermal decomposition apparatus 21A and the catalytic decomposition conditions in the catalytic decomposition apparatus 22A were carried out under the conditions shown in Table 1. However, the thermal decomposition conditions in Example 2 are also within the scope of this disclosure.

The results of the compositional analysis of the pyrolysis gas and catalytic decomposition gas obtained in Example 2 are shown in Table 2 below.

(Comparative Examples 1 and 2)
In Comparative Examples 1 and 2, the pyrolysis conditions in the pyrolysis apparatus 21A and the catalytic decomposition conditions in the catalytic decomposition apparatus 22A were carried out under the conditions shown in Table 1. The pyrolysis conditions in Comparative Examples 1 and 2 are outside the scope of this disclosure.

The results of the compositional analysis of the pyrolysis gas and catalytic cracking gas obtained in Comparative Examples 1 and 2 are shown in Table 2 below.
(result)
As shown in Table 2, the hydrocarbons contained in the pyrolysis gases of Examples 1 and 2 all met the following conditions (i) to (iv).

(i) Let X [wt%] be the sum of the content [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the pyrolysis gas, then 5 ≤ X ≤ 35. (ii) Let Y [-] be 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, then 95 ≤ Y ≤ 240. (iii) Let Z [-] be the ratio of the sum of the content [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the content [wt%] of normal alkanes having 1 to 3 carbon atoms contained in the first product, then 0.30 ≤ Z ≤ 0.93. (iv) Let W [-] be 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, then 5 ≤ W ≤ 205.

Furthermore, Examples 1 and 2, which met the above conditions, showed a high yield of over 60% for the C2-C4 olefin, demonstrating that the results were significantly higher compared to Comparative Examples 1 and 2.

(2) In Examples 1 and 2, the pyrolysis gases had a condensation ratio of 39 wt% to 88 wt% 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% condenses at 0°C, the olefin yield of C2 to C4 showed a high yield of over 60%, which was demonstrated to be significantly higher than that of Comparative Examples 1 and 2.

100...Manufacturing system 10...Pretreatment system 21...Pyrolysis unit 22...Catalytic cracking unit 30...Purification unit G1...Pyrolysis gas (first product)
G2... Catalytic decomposition gas S11, S21... Pretreatment process S12, S22... First thermal decomposition process S13... Catalytic decomposition process (second thermal decomposition process)
S25... Cracking process (second thermal decomposition process)

Claims (6)

A first thermal decomposition step in which plastic is thermally decomposed to obtain a first product,
The process includes a second thermal decomposition step of further thermally decomposing at least a portion of the first product,
The hydrocarbon contained in the first product satisfies all of the following conditions (i) to (iv):
The aforementioned plastic has a polyolefin-based plastic content of 60% by mass or more.
The first thermal decomposition step is a method for producing olefins that satisfies all of the following conditions (a) to (c) :
(i) Let X [wt%] be the sum of the content [wt%] of alkanes and alkenes having 3 or fewer carbon atoms in the first product, then 5 ≤ X ≤ 35. (ii) Let Y [-] be the weight-average molecular weight calculated from the normal alkanes having 1 to 3 carbon atoms and 10 to 35 carbon atoms in the first product, then 95 ≤ Y ≤ 240. (iii) Let Z [-] be the ratio of the sum of the content [wt%] of normal alkanes having 10 to 35 carbon atoms to the sum of the content [wt%] of normal alkanes having 1 to 3 carbon atoms in the first product, then 0.30 ≤ Z ≤ 0.93. (iv) Let W [-] be 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 in the first product, then 5 ≤ W ≤ 205.
(a) The thermal decomposition is carried out continuously.
(b) The thermal decomposition temperature is between 435°C and 595°C.
(c) The thermal decomposition pressure is 0 kPaG or more and 100 kPaG or less . The method for producing an olefin according to claim 1, wherein at 0°C, 39 wt% to 88 wt% of the first product condenses. The method for producing an olefin according to claim 1, wherein the second thermal decomposition step is a catalytic decomposition step using a catalyst. The method for producing an olefin according to claim 1, wherein the second thermal decomposition step includes cracking. The first thermal decomposition step is carried out using a fluidized bed reactor and satisfies all of the following conditions ( d ) to (f), the method for producing the olefin according to claim 1 :
(d) The linear velocity of the fluidizing gas in the fluidized bed reactor is 0.1 cm/s or more and 100 cm/s or less. (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 more and 2000 (N ml/g) or less. (f) The ratio of the fluidizing gas supply rate (N ml/min) to the amount of fluidizing medium (g) present in the fluidized bed reactor is 1.0 (N ml/g・min) or more and 100 (N ml/g・min) or less. An analytical step for analyzing the composition of the first product,
A method for producing an olefin according to claim 1, further comprising a condition adjustment step of adjusting the thermal decomposition conditions based on the analysis results in the analysis step.