Olefin production process

Abstract

The present invention addresses the problem of providing a method for producing olefins that can sufficiently remove polyamides from waste plastics. [Solution] The method for producing olefins according to the present invention includes a thermal decomposition step of thermally decomposing a waste plastic raw material containing polyolefins and polyamides to obtain a hydrocarbon stream, a separation step of separating a thermal decomposition product of the polyamides from the hydrocarbon stream that has undergone the thermal decomposition step, and a catalytic cracking step of catalytically cracking the hydrocarbon stream that has undergone the separation step in the presence of a catalyst containing zeolite to obtain olefins.

Description

[Technical Field]

[0001] The present invention relates to a process for producing olefins. [Background technology]

[0002] In recent years, the regeneration and reuse of plastics has been attracting attention from the perspective of resource recycling. For example, processes such as reuse, material recycling, and chemical recycling are being carried out to recycle waste plastics. In particular, chemical recycling has the potential to overcome the limitations of performance degradation caused by recycling, as it can chemically decompose plastics and regenerate them into petrochemical raw materials.

[0003] As one of the chemical recycling techniques, for example, Patent Document 1 discloses a method in which a raw material is thermally decomposed, and then polyolefins are catalytically decomposed in the presence of a catalyst containing zeolite to obtain lower olefins. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2022 / 039094 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, waste plastics contain several percent of polyamides, such as nylon. It has been known that catalytic cracking of waste plastics containing polyamides poisons the catalyst, resulting in a decrease in the yield of lower olefins. Therefore, polyamides are removed from waste plastics by visual manual sorting, mechanical separation using a vibrating screen, flotation utilizing their buoyancy in water, electrostatic separation utilizing differences in surface charge, and other methods. However, removing polyamides from waste plastics using the above-mentioned methods is extremely difficult, and the accuracy of removal is poor. Therefore, catalytic cracking of waste plastics is currently carried out while polyamides are still present.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing olefins that can sufficiently remove polyamides from waste plastics. [Means for solving the problem]

[0007] The method for producing olefins according to the present invention includes a thermal decomposition step of thermally decomposing a waste plastic raw material containing polyolefins and polyamides to obtain a hydrocarbon stream, a separation step of separating a thermal decomposition product of the polyamides from the hydrocarbon stream that has undergone the thermal decomposition step, and a catalytic cracking step of catalytically cracking the hydrocarbon stream that has undergone the separation step in the presence of a catalyst containing zeolite to obtain olefins. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing an olefin that can sufficiently remove polyamide from waste plastics. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0010] The olefin production method according to this embodiment includes a thermal decomposition step in which a waste plastic raw material containing polyolefins and polyamides is thermally decomposed to obtain a hydrocarbon stream, a separation step in which a thermal decomposition product of the polyamide is separated from the hydrocarbon stream that has undergone the thermal decomposition step, and a catalytic cracking step in which the hydrocarbon stream that has undergone the separation step is catalytically cracked in the presence of a catalyst containing zeolite to obtain olefins.

[0011] (pyrolysis process) The waste plastic raw material refers to a plastic product that has been used for some final purpose, and includes at least a polyolefin and a polyamide.

[0012] Specific examples of polyolefins contained as the waste plastic raw material include polyolefin-based plastics such as polyethylene, polypropylene, polybutene, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, and ethylene-α-olefin copolymer, as well as mixtures of two or more of these. Among these, the polyolefins contained as the waste plastic raw material are preferably polyethylene, polypropylene, or ethylene-propylene copolymer.

[0013] In addition to the polyolefins and polyamides, the waste plastic raw materials may contain other components such as polystyrene, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyurethane, polyester, polymethyl methacrylate, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, natural rubber, and synthetic rubber.

[0014] The waste plastic raw materials may include, for example, industrial products such as molded articles produced using the above-mentioned polyolefins, polyamides, and other components. Specific examples of industrial products include plastic containers and packaging collected under the Container and Packaging Recycling Law.

[0015] The waste plastic raw material may be in a solid state like the above-mentioned molded body. The waste plastic raw material may be the above-mentioned solid industrial product converted into a liquid and / or gaseous state, and may be, for example, a liquid and / or gaseous mixture of the above-mentioned polyolefin, polyamide, and other components.

[0016] Examples of polyamides contained in the waste plastic raw material include aliphatic polyamides such as nylon 6, nylon 66, nylon 11, and nylon 12; and aromatic polyamides such as polymetaxylene adipamide. The polyamide may be at least one selected from the group consisting of nylon 6 and nylon 66.

[0017] The content of polyamide contained in the waste plastic raw material is not particularly limited, and is usually 0.01% by mass or more and 30% by mass or less.

[0018] The hydrocarbon stream may include hydrocarbons, oxygen-containing compounds, nitrogen-containing compounds, sulfur-containing compounds, chlorine-containing compounds, and the like.

[0019] Examples of the hydrocarbon include alkanes such as methane, ethane, and propane; diolefins such as butadiene; aromatic hydrocarbons such as benzene, toluene, and xylene; and cycloalkanes such as cyclohexane.

[0020] Examples of the oxygen-containing compounds include organic compounds having an oxygen functional group such as a carboxyl group, a hydroxyl group, or an ether group, carbon dioxide, and carbon monoxide. Examples of the nitrogen-containing compounds include organic compounds having a nitrogen functional group such as an amino group or an isocyanate group, nitrogen ring compounds, nitric oxide, and nitrogen dioxide. Examples of the sulfur-containing compounds include organic compounds having a sulfur functional group such as a thiol group, a thioether group, or a sulfonyl group, sulfur ring compounds, and hydrogen sulfide. Examples of the chlorine-containing compounds include chlorine-containing alkanes such as methyl chloride and chloroform, and chlorine-containing aromatic compounds.

[0021] In the pyrolysis step, virgin plastic raw materials containing polyolefins may be further pyrolyzed. The virgin plastic raw materials refer to polymers produced by a process including a polymerization step, resin compositions containing the polymers, or plastic products using the polymers or resin compositions, which have not been used for any end use. The polyolefins contained in the virgin plastic raw materials are the same as the polyolefins contained in the waste plastic raw materials.

[0022] The pyrolysis temperature is usually 350°C or higher and 550°C or lower, preferably 400°C or higher and 500°C or lower, from the viewpoint of improving the yield of the hydrocarbon stream.

[0023] The thermal decomposition pressure is usually 0 MPaG or more and 5 MPaG or less, and preferably 0 MPaG or more and 0.5 MPaG or less.

[0024] In the thermal decomposition step, an inert gas such as water vapor, nitrogen gas, or CO2 gas may be present.

[0025] The pyrolysis step can be carried out using any suitable conventionally known reaction vessel, for example, quartz glass, carbon steel, stainless steel, Inconel alloy, Hastelloy alloy, Incoloy alloy, Monel alloy, etc.

[0026] The hydrocarbon stream obtained by the thermal cracking step usually contains hydrocarbons having about 1 to 50 carbon atoms, hydrogen, and the like, which may be in a liquid state, a gaseous state, or a mixture thereof.

[0027] (separation process) The hydrocarbon stream that has undergone the thermal decomposition step contains a thermal decomposition product of the polyamide. In the separation step, the thermal decomposition product of the polyamide is separated. Specifically, the gaseous thermal decomposition product of the polyamide can be separated as a gas from the reaction vessel, and the solid thermal decomposition product of the polyamide can be separated as a solid from the reaction vessel. The thermal decomposition product of the polyamide may contain at least one selected from the group consisting of ammonia and amines.

[0028] The olefin production method according to this embodiment may further include a removal step of removing the thermal decomposition product of the polyamide separated in the separation step.

[0029] In one embodiment, the removal step is carried out by contacting the polyamide pyrolysate with a liquid. Specifically, the removal step is carried out by contacting the polyamide pyrolysate with the liquid filled in a container. The liquid is preferably at least one selected from the group consisting of water and an acidic aqueous solution, and more preferably water. Examples of the acidic aqueous solution include hydrochloric acid, sulfuric acid, nitric acid, acetic acid, phosphoric acid, oxalic acid, and citric acid. From the viewpoint of efficiently removing the polyamide pyrolysate, the acidic aqueous solution is preferably hydrochloric acid or sulfuric acid.

[0030] The temperature at which the polyamide is brought into contact with the liquid is preferably 5° C. or more and 60° C. or less, more preferably 10° C. or more and 50° C. or less, from the viewpoint of efficiently removing pyrolysis products of the polyamide. The time for which the polyamide is brought into contact with the liquid is preferably 1 second or more and 10 hours or less, more preferably 10 seconds or more and 1 hour or less, from the viewpoint of efficiently removing pyrolysis products of the polyamide.

[0031] In another embodiment, the removal step is carried out by contacting the polyamide pyrolysate with an adsorbent. Specifically, the removal step is carried out by contacting the polyamide pyrolysate with the adsorbent filled in a container. Examples of adsorbents include activated carbon, zeolite, silica gel, ion exchange resins, and activated alumina.

[0032] The temperature for contact with the adsorbent is preferably 5° C. or more and 60° C. or less, more preferably 10° C. or more and 50° C. or less, from the viewpoint of efficiently removing the thermal decomposition products of the polyamide. The time for contact with the adsorbent is preferably 1 second or more and 10 hours or less, more preferably 10 seconds or more and 1 hour or less, from the viewpoint of efficiently removing the thermal decomposition products of the polyamide.

[0033] (catalytic cracking process) Examples of zeolites used in the catalytic cracking step include beta zeolite, faujasite zeolite, L zeolite, ferrierite zeolite, mordenite zeolite, and MFI zeolite. The zeolite is preferably MFI zeolite, i.e., has an MFI structure. The sodium content in the zeolite is less than 0.1% by mass. From the viewpoint of improving the yield of the target olefin, the sodium content in the zeolite is preferably less than 0.05% by mass.

[0034] The zeolite may typically contain silicon atoms, aluminum atoms, oxygen atoms, and hydrogen atoms as atoms other than sodium atoms, and may also contain atoms such as 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.

[0035] Here, the ratio of the number of moles of silicon atoms to the number of moles of aluminum atoms in the zeolite (Si / Al ratio) is preferably 100 or more, more preferably 300 or more, from the viewpoint of improving the yield of the target olefin.

[0036] The sodium content and Si / Al ratio in the zeolite can be calculated by analyzing the zeolite according to a conventionally known ICP emission spectrometry method.

[0037] Here, MFI type zeolite means a crystalline aluminosilicate having an MFI structure according to the structure code of the International Zeolite Association (IZA). Specific examples of MFI type zeolite include H + -ZSM-5, NH4 + -ZSM-5, Na + -ZSM-5, Ca 2+ MFI type zeolite can be prepared by any suitable method known in the art, and commercially available H + ZSM-5 may also be used. The identification of MFI type zeolite can be carried out by analysis using X-ray diffraction analysis.

[0038] A method for producing the zeolite will be described below. The zeolite can be produced by a production method including the steps of preparing a mixture containing a silicon source, an aluminum source, a template, and an alkali metal source, and crystallizing the mixture to obtain the zeolite. Here, the "template" refers to a substance that imparts a pore structure to the zeolite.

[0039] As the silicon source, any known silicon source used in the production of various zeolites can be used, including tetraethyl orthosilicate, colloidal silica, silica gel dry powder, silica hydrogel, and sodium silicate.

[0040] As the aluminum source, any known aluminum source used in the production of various zeolites can be used. Specific examples of the aluminum source include aluminum nitrate, aluminum chloride, sodium aluminate, aluminum hydroxide, and aluminum alkoxide. Among these, the aluminum source is preferably aluminum nitrate or sodium aluminate.

[0041] The type of the template is not particularly limited. Conventional templates, such as organic ammonium salts and amines, commonly used in the synthesis of zeolites can be used as the template. Specific examples of the template include tetrapropylammonium salt, tetraethylammonium salt, tetramethylammonium salt, benzyltrimethylammonium salt, tetrabutylammonium salt, propanolamine, ethanolamine, n-propylamine, morpholine, 1,5-diaminopentane, 1,6-diaminohexane, dipropylenetetramine, and triethylenetetramine. Among these, the template is preferably tetrapropylammonium salt (tetrapropylammonium hydroxide).

[0042] Examples of the alkali metal source include alkali metal hydroxides, alkali metal chlorides, alkali metal bromides, alkali metal sulfides, etc. Specific examples of alkali metals include sodium and potassium.

[0043] When the alkali metal is sodium, specific examples of the sodium source include sodium hydroxide, sodium nitrate, sodium chloride, sodium bromide, sodium sulfate, sodium silicate, sodium aluminate, and compounds containing sodium as a counter cation.

[0044] When the alkali metal is potassium, specific examples of the potassium source include potassium hydroxide, potassium nitrate, potassium chloride, potassium bromide, potassium sulfate, potassium silicate, potassium aluminate, and compounds containing potassium as a counter cation.

[0045] In the mixture, the ratio of the number of moles of silicon atoms to the number of moles of aluminum atoms (Si / Al ratio) is preferably 100 or more, and more preferably 300 or more. The ratio may be 10,000 or less, and is preferably 2,500 or less.

[0046] Furthermore, it is preferable that the ratio of the number of moles of each component in the mixture to the number of moles of silicon atoms satisfies the following requirements. Molding agent: 0.02 or more, 5.0 or less Alkali metal source: 0.01 or more, 0.2 or less Water: 2 or more, 100 or less

[0047] Furthermore, it is more preferable that the ratio of the number of moles of each component in the mixture to the number of moles of silicon atoms satisfies the following requirement. Molding agent: 0.05 or more, 2.0 or less Alkali metal source: 0.04 or more, 0.3 or less Water: 5 or more, 50 or less

[0048] Specific steps will be described below. First, the above components (mixture) are stirred at room temperature for 1 hour to 48 hours (for example, 18 hours), and the resulting mixture is placed in a sealed pressure vessel (autoclave). The mixture is then treated in the autoclave at a temperature of 100°C to 200°C for 1 hour to 120 hours, thereby preparing a zeolite precursor.

[0049] After the crystallization is completed, the mixture (suspension) containing the prepared zeolite precursor is thoroughly cooled with ice water or the like, and after cooling is completed, the mixture is subjected to solid-liquid separation (e.g., centrifugation) to remove the supernatant, and the mixture is further washed with a sufficient amount of pure water to perform solid-liquid separation. This process is repeated until the pH of the removed supernatant becomes 8 or less.

[0050] Next, it is dried at a temperature of 100°C to 150°C (for example, 120°C) for 1 hour to 48 hours (for example, 8 hours), and then may be fired at a temperature of about 400°C to 700°C (for example, 550°C) for 1 hour to 48 hours (for example, 7 hours).

[0051] Zeolite (for example, MFI type zeolite) can be obtained by the above steps.

[0052] The zeolite prepared as described above contains a relatively large amount of sodium or potassium contained in the alkali metal source, and therefore, in order to obtain the zeolite, it is usually necessary to remove the alkali metal from the zeolite.

[0053] As a method for removing the alkali metal from the zeolite, a method of contacting the zeolite with an aqueous solution of an ammonium salt can be mentioned.

[0054] Examples of ammonium salts include ammonium salts of inorganic acids such as ammonium sulfate, ammonium hydrogen sulfate, ammonium carbonate, ammonium hydrogen carbonate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, ammonium hydrogen pyrophosphate, ammonium pyrophosphate, ammonium chloride, and ammonium nitrate, and ammonium salts of organic acids such as ammonium acetate, etc. Among these, the ammonium salt is preferably ammonium sulfate, ammonium chloride, or ammonium nitrate.

[0055] Specifically, this step involves mixing an aqueous solution of an ammonium salt with zeolite and contacting them at a temperature of 50°C to 200°C for 1 to 48 hours, and repeating this step one or more times as necessary, thereby adjusting (reducing) the alkali metal content (e.g., sodium atom content) to a desired content.

[0056] Next, the solid is allowed to cool sufficiently to separate it into solid and liquid, washed with a sufficient amount of pure water, and dried at any temperature between 60°C and 150°C.

[0057] Thereafter, it is preferable to carry out firing at a temperature of about 400° C. to 700° C. (for example, 550° C.) for 1 hour to 48 hours (for example, 5 hours).

[0058] By preparing the zeolite as described above, the amount of sodium atoms, which is an alkali metal, can be reduced, and the zeolite having a sodium content of less than 0.1 mass % can be obtained.

[0059] The catalytic cracking temperature is usually 400°C or higher and 700°C or lower, and preferably 450°C or higher and 650°C or lower.

[0060] The catalytic cracking pressure is usually 0 MPaG or more and 5 MPaG or less, and preferably 0 MPaG or more and 0.5 MPaG or less.

[0061] The residence time required for the catalytic cracking step is preferably 1 second or more and 10,000 seconds or less, more preferably 10 seconds or more and 1,000 seconds or less, from the viewpoint of reducing the proportion of unreacted hydrocarbon flow.

[0062] In the catalytic cracking step, an inert gas such as water vapor, nitrogen gas, or CO2 gas may be present.

[0063] The catalytic cracking step can be carried out using any suitable conventionally known reactor, and examples of the material for the reactor include quartz glass, carbon steel, stainless steel, Inconel alloy, Hastelloy alloy, Incoloy alloy, and Monel alloy.

[0064] The olefin obtained by the catalytic cracking step is preferably at least one selected from the group consisting of ethylene, propylene, butene, and pentene.

[0065] The olefin production method according to this embodiment comprises a thermal decomposition step of thermally decomposing a waste plastic raw material containing polyolefins and polyamides to obtain a hydrocarbon stream, a separation step of separating the polyamide pyrolysate from the hydrocarbon stream resulting from the thermal decomposition step, and a catalytic cracking step of catalytically cracking the hydrocarbon stream resulting from the separation step in the presence of a zeolite-containing catalyst to obtain olefins. The olefin production method includes the separation step of separating the polyamide pyrolysate from the hydrocarbon stream resulting from the thermal decomposition step, thereby enabling the polyamide in the waste plastics to be sufficiently removed. As a result, catalyst poisoning in the catalytic cracking step can be suppressed, and the olefin yield can be improved.

[0066] In the olefin production method according to this embodiment, the polyamide may be at least one selected from the group consisting of nylon 6 and nylon 66. The olefin production method can suitably remove polyamides having such a structure.

[0067] In the olefin production method according to the present embodiment, the polyamide pyrolysate may contain at least one selected from the group consisting of ammonia and amines. The olefin production method can suitably separate the pyrolysate having such a composition.

[0068] The olefin production method according to the present embodiment may further include a removal step of removing the thermal decomposition products of the polyamide separated in the separation step. With such a configuration, the olefin production method can remove the thermal decomposition products of the polyamide from the system.

[0069] In one aspect of the olefin production method according to the present embodiment, the removing step is carried out by contacting the polyamide with a liquid. With this configuration, the olefin production method can efficiently remove the thermal decomposition products of the polyamide.

[0070] In the olefin production method according to the present embodiment, the liquid is preferably at least one selected from the group consisting of water and an acidic aqueous solution, which allows the olefin production method to more efficiently remove the thermal decomposition products of the polyamide.

[0071] In another aspect of the olefin production method according to the present embodiment, the removing step is carried out by contacting the polyamide with an adsorbent. With this configuration, the olefin production method can efficiently remove the polyamide thermal decomposition products.

[0072] In the olefin production method according to the present embodiment, the olefin is preferably at least one selected from the group consisting of ethylene, propylene, butene, and pentene. The olefin production method can efficiently produce olefins having such a structure.

[0073] In the olefin production method according to this embodiment, the zeolite preferably has an MFI structure. With this configuration, the olefin production method can produce olefins in a high yield.

[0074] The present invention includes the following aspects. [1] A pyrolysis step of pyrolyzing a waste plastic raw material containing polyolefins and polyamides to obtain a hydrocarbon stream; a separation step of separating a pyrolysis product of the polyamide from the hydrocarbon stream that has been subjected to the pyrolysis step; a catalytic cracking step in which the hydrocarbon stream that has been subjected to the separation step is catalytically cracked in the presence of a catalyst containing a zeolite to obtain olefins; A method for producing an olefin, comprising: [2] The method for producing an olefin according to [1], wherein the polyamide is at least one selected from the group consisting of nylon 6 and nylon 66. [3] The method for producing an olefin according to [1] or [2], wherein the thermal decomposition product of the polyamide contains at least one selected from the group consisting of ammonia and amines. [4] The method for producing an olefin according to any one of [1] to [3], further comprising a removal step of removing a thermal decomposition product of the polyamide separated in the separation step. [5] The method for producing an olefin according to [4], wherein the removing step is carried out by contacting with a liquid. [6] The method for producing an olefin according to [5], wherein the liquid is at least one selected from the group consisting of water and an acidic aqueous solution. [7] The method for producing an olefin according to [4], wherein the removal step is carried out by contacting the olefin with an adsorbent. [8] The method for producing an olefin according to any one of [1] to [7], wherein the olefin is at least one selected from the group consisting of ethylene, propylene, butene, and pentene. [9] The method for producing an olefin according to any one of [1] to [8], wherein the zeolite has an MFI structure.

[0075] The olefin production method according to the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. In addition, the configurations, methods, etc. of the embodiments other than those described above may be arbitrarily adopted and combined.

Claims

1. a pyrolysis step of pyrolyzing a waste plastic raw material containing polyolefins and polyamides to obtain a hydrocarbon stream; a separation step of separating a pyrolysis product of the polyamide from the hydrocarbon stream that has been subjected to the pyrolysis step; a catalytic cracking step in which the hydrocarbon stream that has been subjected to the separation step is catalytically cracked in the presence of a catalyst containing a zeolite to obtain olefins; A method for producing an olefin, comprising:

2. 2. The method for producing an olefin according to claim 1, wherein the polyamide is at least one selected from the group consisting of nylon 6 and nylon 66.

3. The method for producing an olefin according to claim 1, wherein the thermal decomposition product of the polyamide contains at least one selected from the group consisting of ammonia and amines.

4. The method for producing an olefin according to claim 1, further comprising a removing step of removing the thermal decomposition product of the polyamide separated in the separating step.

5. The method for producing an olefin according to claim 4, wherein the removing step is carried out by contacting with a liquid.

6. The method for producing an olefin according to claim 5, wherein the liquid is at least one selected from the group consisting of water and an acidic aqueous solution.

7. The method for producing an olefin according to claim 4, wherein the removing step is carried out by contacting the olefin with an adsorbent.

8. The method for producing an olefin according to claim 1, wherein the olefin is at least one selected from the group consisting of ethylene, propylene, butene, and pentene.

9. The method for producing olefins according to claim 1, wherein the zeolite has an MFI structure.