JP2024065743A - How to turn plastic into oil - Google Patents

Abstract

The present invention provides a method for converting used plastics into oil, which uses used plastics as a raw material for a decomposition reaction, does not produce oxygen-containing compounds, does not require wastewater treatment, and can produce oil with a high yield. The present invention provides a method for converting plastics into oil, which is characterized by decomposing plastics in the presence of aliphatic hydrocarbons in a subcritical or supercritical state to produce oil. [Selected Figures] None

Description

The present invention relates to a method for converting plastics into oil.

Petroleum-derived plastics are used for various purposes due to their excellent workability, heat resistance, electrical conductivity, transparency, and chemical resistance, while the amount of waste plastics is increasing year by year worldwide. Waste plastics are currently incinerated or landfilled after use, due to the fact that plastics with different properties are mixed together and are contaminated with foreign matter, with the exception of some plastics such as PET bottles for which material recycling has progressed. Therefore, recycling technology that can reuse and recycle waste plastics is required, and in particular, chemical recycling, which breaks down waste plastics to produce chemical raw materials such as decomposed oils or monomers, has been attracting attention in recent years. Chemical raw materials and monomerization are broadly divided into two technologies: gasification and oilification. Gasification generally requires high temperatures of over 600°C, which results in a large energy loss, so there is a demand for the development of oilification technology that can convert waste plastics into chemical raw materials at lower temperatures and with good energy efficiency.

One method for converting plastics into oil with high energy efficiency and yield is known to be a method in which plastics are mixed with a supercritical fluid as a processing medium and then thermally decomposed. For example, Non-Patent Document 1 focuses on supercritical water technology and discloses the action of water as a reactant in the decomposition of polyethylene in supercritical water. Non-Patent Document 1 describes that a characteristic of supercritical water is that hydrogen atoms and hydroxyl groups in the water molecules are added to the decomposition product radicals, suppressing the generation of coke (carbonized material), resulting in a higher oil yield than with normal thermal decomposition in the absence of water.

Non-Patent Document 2 also discloses a thermochemical decomposition process, and discloses a method of treating waste materials using a subcritical or supercritical treatment medium. Specifically, it discloses that polypropylene (PP), polystyrene (PS), polyurethane (PU) and mixtures of these are used as raw materials, and are thermally decomposed using supercritical toluene as the treatment medium to obtain oil. As an experimental example, it is described that PP, PS, PU and mixtures of these can be decomposed by heating them together with supercritical toluene to 300-400°C in a high-pressure vessel.

Polymer Journal, Vol. 58, No. 12, pp. 661-673 (Dec., 2001) Energy Conversion and Management: X13 (2022) 100158

The above-mentioned non-patent document 1 discloses the decomposition of polyethylene using supercritical water as a treatment medium, but the problem remains that the product contains oxygen-containing compounds such as alcohol and acid as impurities. For example, when separating the product from the treatment medium after the reaction, some water-soluble organic matter such as alcohol is mixed into the treatment medium, which requires wastewater treatment and increases costs. In addition, non-patent document 2 discloses the decomposition of polypropylene, polystyrene, polyurethane, and mixtures thereof using toluene in a supercritical state to obtain oil, but when polypropylene is used as a raw material, the decomposition reaction must be carried out at 400°C for 6 hours or more to obtain oil with a high yield. In addition, when the present inventors carried out a decomposition reaction at 400°C using polypropylene, it was suggested that a part of the toluene, which is the treatment medium, reacted, promoting the production of polycyclic aromatics.

The present invention aims to provide an oil-recovery method that uses used plastics as a raw material for a decomposition reaction under the above-mentioned circumstances, does not produce oxygen-containing compounds, does not require wastewater treatment, and can recover oil with a high yield containing fewer polycyclic aromatic compounds.

As a result of intensive research into solving the above problems, the inventors discovered that the above problems could be solved by decomposing plastics in the presence of aliphatic hydrocarbons in a subcritical or supercritical state, and thus completed the present invention.

That is, the present invention relates to the following.
[1] A method for converting plastics into oil, comprising decomposing plastics in the presence of aliphatic hydrocarbons in a subcritical or supercritical state to convert the plastics into oil.
[2] The method for producing oil from plastics described in [1] above, wherein the decomposition temperature is 300 to 550°C.
[3] The method for producing oil from plastics according to the above [1] or [2], wherein the decomposition pressure is 1 to 30 MPa.
[4] The method for producing oil from plastics according to any one of the above [1] to [3], wherein the plastics contain at least one selected from polyethylene, polypropylene, and polycarbonate.
[5] The method for converting plastics into oil according to any one of the above [1] to [4], wherein the aliphatic hydrocarbons contain components derived from decomposition products obtained by the decomposition.
[6] The method for converting plastics into oil according to any one of the above [1] to [5], wherein the aliphatic hydrocarbons are saturated hydrocarbons.

The present invention provides a method for converting used plastics into oil that uses used plastics as a raw material for a decomposition reaction, does not produce oxygen-containing compounds, does not require wastewater treatment, and can produce oil with a high yield.

FIG. 1 is a schematic diagram showing a plastic decomposition device.

The following describes in detail the embodiments of the present invention. Note that the following description is one example (representative example) of the embodiment of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist of the invention.

[Method of turning plastic into oil]
The method for converting plastics into oil of the present invention is characterized in that plastics are decomposed and converted into oil in the presence of an aliphatic hydrocarbon in a subcritical or supercritical state.

<Oil content>
Here, the term "oil" refers to a compound having a hydrocarbon skeleton and a mixture thereof that is liquid or greasy and has a viscosity of 1000 Pa·s or less at 60° C. under atmospheric pressure. The oil obtained in the present invention is not particularly limited as long as it fits the above definition, but examples of the oil include light oil, heavy oil, and asphalt.

<Processing medium>
By using aliphatic hydrocarbons in a subcritical or supercritical state as the treatment medium, plastics can be efficiently decomposed and oil can be obtained in a high yield. The advantages of using aliphatic hydrocarbons in a subcritical or supercritical state in the present invention include the following: 1) Subcritical or supercritical fluids have low interfacial tension and are less viscous and more diffusive than liquids, so they can penetrate plastics well. 2) Since the kinetic viscosity is smaller than that of gases and liquids, thermal convection due to slight temperature differences is likely to occur, so plastics can be heated uniformly and the generation of solids due to overheating can be suppressed. 3) Although aliphatic hydrocarbons are contained in oil, they can be easily separated from the oil by distillation or the like and can be recycled as a treatment medium. 4) Since aliphatic hydrocarbons do not contain oxygen atoms, they do not generate undesirable oxygen-containing compounds even when the treatment medium itself reacts, unlike when water or alcohol is used as the treatment medium. 5) Since aliphatic hydrocarbons are less stable when they become radicals, and unlike when aromatic hydrocarbons are used as the treatment medium, recombination between radicals is unlikely to occur, so the generation of undesirable polycyclic aromatic compounds can be suppressed.

The aliphatic hydrocarbon used as the treatment medium in the present invention is not particularly limited as long as the effects of the present invention can be achieved. For example, linear chain saturated hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, and heptadecane; linear chain unsaturated hydrocarbons such as pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, and octadecene; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, and cyclododecane. The aliphatic hydrocarbon may have a branched structure, and specific examples of the chain-type saturated hydrocarbon group constituting the branched structure include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, isobutyl, pentyl, tert-pentyl, isopentyl, hexyl, isohexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl, octadecyl, docosyl, and octacosanyl groups. Specific examples of the chain-type unsaturated hydrocarbon group include ethylene, propylene, butene, isobutene, isoprene, pentene, hexene, heptene, octene, nonene, decene, dodecene, tridecene, tetradecene, and octadecene groups. These may be introduced alone or in combination of two or more. The above aliphatic hydrocarbons can be used alone or as a mixture of two or more kinds. Furthermore, even if the hydrocarbon has 1 to 4 carbon atoms, such as methane or ethane, which is gaseous at room temperature, or the hydrocarbon has 18 or more carbon atoms, such as octadecane or nonadecane, which is solid at room temperature, it may be contained as long as it dissolves in the above aliphatic hydrocarbons that are liquid at room temperature and becomes liquid as a mixture. A liquid substance that is easy to handle is preferable. Among the above, from the viewpoint of ease of handling and availability, a carbon number of 5 to 30 is preferable, and a carbon number of 6 to 20 is more preferable. Furthermore, from the viewpoint of low reactivity of the treatment medium itself, saturated hydrocarbons are particularly preferable among the aliphatic hydrocarbons. From the viewpoint of recycling, aliphatic hydrocarbons other than the hydrocarbons with 5 to 12 carbon atoms used as the naphtha fraction may also be used as the supercritical fluid used for cracking.
Here, "hydrocarbons in a supercritical state" refers to hydrocarbons in a state where the pressure is equal to or higher than the critical pressure and the temperature is equal to or higher than the critical temperature. The critical pressure and critical temperature of a hydrocarbon vary depending on the type of hydrocarbon. Also, "hydrocarbons in a subcritical state" refers to hydrocarbons in a state where the pressure is equal to or higher than the critical pressure of the hydrocarbon and the temperature is slightly below the critical temperature, or hydrocarbons in a state where the pressure is slightly below the critical pressure of the hydrocarbon and the temperature is equal to or higher than the critical temperature, or hydrocarbons in a state where the temperature is below the critical temperature and the pressure is below the critical pressure but close to it.

(Ratio of aromatic hydrogen to alkyl group-derived hydrogen)
The present invention is characterized in that aliphatic hydrocarbons in a subcritical or supercritical state are used as the treatment medium, and the production of polycyclic compounds such as char is suppressed compared to the case where aromatic hydrocarbons in a supercritical state are used. This is because, as described in 5) above, the aliphatic hydrocarbon radicals derived from the treatment medium produced during the reaction are unstable compared to aromatic hydrocarbon radicals, and therefore the recombination reaction between radicals, i.e., the reaction of producing polycyclic aromatics, is unlikely to occur. The ratio of aromatic hydrogen to alkyl group-derived hydrogen is used as an indicator of the production of polycyclic compounds.
In the present invention, the ratio of aromatic hydrogen to alkyl hydrogen in the product oil is preferably 0.03 or less, more preferably 0.02 or less. If the ratio of aromatic hydrogen to alkyl hydrogen is 0.03 or less, the production of polycyclic compounds is suppressed, and the smaller the ratio, the more preferable.
In addition, the aliphatic hydrocarbon used as the treatment medium may contain cracked components derived from the cracked products. That is, the oil obtained by the method of the present invention or a part thereof may be used as the treatment medium. As described above, the oil obtained by the method of the present invention has a low content of aromatic compounds such as polycyclic compounds, so that the oil (product oil) can be used as the treatment medium. Therefore, as described in 3) above, it can be recycled as a treatment medium.

<Ingredients>
The plastics used as raw materials in the present invention are not particularly limited as long as they can produce the effects of the present invention, and examples thereof include polyolefins such as polyethylene, polypropylene, polybutene, polybutadiene, and poly4-methyl-1-pentene; addition polymerization polymers such as polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, and ethylene-vinyl alcohol copolymer resin; and polycondensation polymers such as polycarbonate, polyethylene terephthalate, polyamide, polyimide, polyurethane, polyether ketone, and polyether ether ketone. These plastics may be mixed, and may be in the form of a film, tube, or the like that is molded. Among these plastics, it is preferable to include at least one of polyethylene, polypropylene, and polycarbonate, which are often discharged as industrial and household waste, and it is more preferable to include either polyethylene or polypropylene. That is, it may include only polyethylene or polypropylene, or it may include polyethylene and polypropylene.

<Decomposition temperature>
The temperature at which plastics are decomposed is not particularly limited as long as it is within a range in which the effects of the present invention can be achieved, but is preferably in the range of 300 to 550°C. If the decomposition temperature is 300°C or higher, the decomposition reaction of plastics proceeds sufficiently. From the above viewpoints, the decomposition temperature is more preferably 350°C or higher, even more preferably 400°C or higher, and particularly preferably 430°C or higher. On the other hand, the upper limit is more preferably 500°C or lower, and even more preferably 475°C or lower, in terms of maintaining a high oil yield.

<Decomposition pressure>
The pressure for decomposing plastics is not particularly limited as long as it is within a range in which the effects of the present invention can be obtained, but is preferably in the range of 1 to 30 MPa. From the viewpoint of the yield of the produced oil, the pressure is more preferably in the range of 2 to 20 MPa, and even more preferably in the range of 2.5 to 10 MPa.

<Reaction time>
The reaction time when decomposing plastics in a batch process is not particularly limited as long as the effects of the present invention are achieved, but is preferably in the range of 1 to 300 minutes, more preferably 2 to 150 minutes, even more preferably 3 to 100 minutes, and particularly preferably 5 to 60 minutes. When the reaction time is in this range, excessive decomposition and recombination are suppressed, and a high yield of oil is maintained. Note that this preferred reaction time does not apply when using a process for decomposing plastics in a flow reaction.

<Apparatus>
The apparatus in the present invention may be of either a batch type or a flow type.

The present invention will be described in more detail in the following examples and comparative examples, but the present invention is not limited to these.

Example 1
The plastic decomposition device used was a batch-type decomposition device as shown in Figure 1. The pressure vessel used was a stationary Inconel vessel with an inner diameter of 30 mm, depth of 80 mm, capacity of about 56 mL, maximum operating temperature of 500°C, and maximum operating pressure of 50 MPa. When collecting gas, the cooling pipe after valve V02 was removed and a gas collection bag was connected.
6 g of low-density polyethylene (Sigma-Aldrich "LDPE", product number 428043) as the raw material and 10.8 g of n-octane (Fujifilm Wako Pure Chemical Industries, product number 153-00065) as the processing medium were placed in a pressure vessel and closed. The vessel was pressurized at the maximum pressure of the nitrogen gas cylinder, and after confirming that there was no pressure leakage, the vessel was slowly depressurized. The operation of pressurizing with nitrogen to 1 MPa, depressurizing and returning to normal pressure was repeated three times, and then gas was gently passed through the vessel at normal pressure for about 30 seconds to replace the internal atmosphere. All valves were closed, and the vessel was set in an electric furnace. The temperature was raised to a predetermined temperature (450 ° C) at a rate of 4 ° C per minute, and the temperature was held for a predetermined time from the point where the predetermined temperature was reached (holding time; 15 minutes). After the holding period was completed, the power to the electric furnace was stopped, the heat-insulating material was removed, and the vessel was removed from the electric furnace and cooled by blowing air. When the temperature inside the container became 40° C. or lower, the valve was slowly opened and the entire amount of gas was collected in a collection bag and weighed. The container was opened and the treated sample was taken out and weighed.
The recovered sample was liquid, and the yield of the oil content was calculated as 60.7% by the method described below. In addition, 0.995 g of the recovered sample was placed in a rotary evaporator, and low boiling components were removed under the following conditions. Furthermore, 1.174 g of n-octane (manufactured by Fujifilm Wako Pure Chemical Industries, product number 153-00065) was added and the same treatment (low boiling point component removal treatment) was performed again, and the residue was a dark brown liquid with a weight of 0.251 g. This residue was analyzed by GC-FID under the following conditions, and it was confirmed that the treatment medium components and components with a molecular weight of 140 or less had been removed. In addition, ¹ H-NMR analysis was performed under the following conditions, and the ratio of aromatic hydrogen to alkyl group-derived hydrogen was 0.014.

<Yield calculation of recovered sample>
Yield = 100 x (weight of recovered cracked oil) / (weight of input LDPE)
<Rotary evaporator>
Equipment: EYELA N-1300
Pressure: 20hPa
Rotation speed: 60 rpm
Water bath temperature: 40℃
Time: 1 hour <GC-FID analysis>
Apparatus: GC-2014 Shimadzu Corporation Column: DB-5 Agilent Technology
(60 m, 0.25 mm, 1.0 μm)
Column temperature conditions: hold at 40°C for 3 minutes, increase from 40°C to 325°C at 10°C/min, then hold at 325°C for 5 minutes. Flow rate: 1 mL/min
Detection: FID
Sample injection volume: 1 μL
< ^1H -NMR Analysis>
Equipment: JEOL 400HY
Resonance frequency: 400MHz
Flip angle: 45 degrees Measurement temperature: room temperature Sample: A mixture of 0.005 g of the residue obtained by rotary evaporator and approximately 5 mL of methylene dichloride (Kanto Chemical, product number: 21743-1A)

<Calculation method for the abundance ratio of aromatic hydrogen>
The peaks derived from aromatic hydrogen are observed at around 6.5 to 8.0 ppm. Meanwhile, the peaks derived from alkyl group hydrogen are observed at around 0.2 to 1.5 ppm. The abundance ratio of aromatic hydrogen to alkyl group hydrogen was calculated using the following formula.
Ratio of aromatic hydrogen to alkyl hydrogen = A/B
A is the integral value of the signal derived from aromatic hydrogen in the vicinity of 6.5 to 8.0 ppm.
B is the integral value of the signal derived from alkyl groups in the vicinity of 0.2 to 1.5 ppm.
A high ratio of aromatic hydrogen to alkyl group-derived hydrogen suggests that the oil contains a large amount of polycyclic aromatics.

Example 2
The reaction was carried out in the same manner as in Example 1, except that polypropylene (Sigma-Aldrich "PP", product number 182389) was used as the raw material instead of LDPE, the decomposition temperature was 400°C, and the reaction time was 180 minutes.
The recovered sample was liquid, and the yield was calculated in the same manner as in Example 1, and was 70.7%. 1.1542 g of the recovered sample was placed in a rotary evaporator, and low boiling components were removed in the same manner as in Example 1. Furthermore, 1.3848 g of n-octane (manufactured by Fujifilm Wako Pure Chemical Industries, product number 153-00065) was added and the same treatment (low boiling point component removal treatment) was performed again, and the residue was a yellow liquid and weighed 0.1798 g. This residue was analyzed by GC-FID in the same manner as in Example 1, and it was confirmed that the treatment medium components and components with a molecular weight of 140 or less had been removed. In addition, ¹ H-NMR analysis was performed in the same manner as in Example 1, and the ratio of aromatic hydrogen to alkyl group-derived hydrogen was 0.001.

Example 3
The reaction was carried out in the same manner as in Example 1, except that polycarbonate ("PC", product number 181625, manufactured by Sigma-Aldrich) was used instead of LDPE as the raw material.
The recovered sample was a liquid and a grease-like substance, and the yield was calculated to be 25.6% in the same manner as in Example 1. The viscosity of this grease-like substance was measured under the following conditions and found to be 71.8 Pa·s at 1 atmosphere and 60°C.
<Viscosity measurement>
Equipment: RHEOMETER DV3T BROOK FIELD
Spindle: CP-51
Measurement temperature: 60°C

Example 4
The reaction was carried out in the same manner as in Example 1, except that the treatment medium in Example 1 was changed from n-octane to n-hexadecane (Tokyo Chemical Industry Co., Ltd., product number H0066).
The recovered sample was a liquid, and the yield was calculated in the same manner as in Example 1 to be 51.7%.

Comparative Example 1
The reaction was carried out in the same manner as in Example 1, except that the treatment medium was changed from n-octane to toluene (manufactured by Fujifilm Wako Pure Chemical Industries, product number 207-15445).
The recovered sample was liquid, and the yield was calculated in the same manner as in Example 1 to be 68.1%. 1.2539 g of the recovered sample was placed in a rotary evaporator, and low boiling components were removed under the same conditions as in Example 1. Furthermore, 1.3668 g of n-octane (manufactured by Fujifilm Wako Pure Chemical Industries, product number 153-00065) was added and the same treatment (low boiling point component removal treatment) as in Example 1 was performed, and the residue was a dark brown liquid with a weight of 0.3071 g. This residue was analyzed by GC-FID in the same manner as in Example 1, and it was confirmed that the treatment medium components and components with a molecular weight of 140 or less had been removed. In addition, ¹ H-NMR analysis was performed in the same manner as in Example 1, and the ratio of aromatic hydrogen to alkyl group-derived hydrogen was 0.037.

Comparative Example 2
The reaction was carried out in the same manner as in Example 2, except that the treatment medium was changed from n-octane to toluene.
The recovered sample was liquid, and the yield was calculated in the same manner as in Example 1, and was 78.0%. 1.3475 g of the recovered sample was placed in a rotary evaporator, and low boiling components were removed under the same conditions as in Example 1. Furthermore, 1.3361 g of n-octane (manufactured by Fujifilm Wako Pure Chemical Industries, product number 153-00065) was added and the same treatment (low boiling point component removal treatment) was performed again, and the residue was a brown liquid and weighed 0.2030 g. This residue was analyzed by GC-FID, and it was confirmed that the treatment medium components had been removed. In addition, ¹ H-NMR analysis was performed in the same manner as in Example 1, and the abundance ratio of aromatic hydrogen to alkyl group-derived hydrogen was 0.13.

The results shown in Table 1 show that when a supercritical aliphatic hydrocarbon is used as the treatment medium, the ratio of aromatic hydrogen to alkyl group-derived hydrogen is small. On the other hand, when supercritical toluene is used as the treatment medium, the oil yield is high, but the ratio of aromatic hydrogen to alkyl group-derived hydrogen is large, suggesting the production of polycyclic compounds.

The results shown in Table 2 make it clear that plastics other than polyethylene and polypropylene can be converted into oil by using a supercritical aliphatic hydrocarbon as the processing medium. It also makes clear that plastics can be converted into oil when supercritical hexadecane is used as the processing medium.

According to the method for converting plastics into oil of the present invention, liquid hydrocarbons having the same carbon number as naphtha can be obtained in high yields using used plastics as a raw material. Since these liquid hydrocarbons do not contain oxygen-containing compounds, there is no need for purification or the like to remove the oxygen-containing compounds, and they can be used as they are as a raw material for a cracking device such as a naphtha cracker, from which olefins such as ethylene and propylene can be produced. In addition, the aliphatic hydrocarbons in a subcritical or supercritical state used as a processing medium can be easily separated and recovered by distillation after the cracking reaction is completed, and can be recycled.
As described above, the method for converting plastics into oil of the present invention can produce olefins from used plastics and is a technology that enables chemical recycling, and is therefore of great industrial value and is also extremely effective in terms of environmental conservation.

PG01; Pressure gauge V01, V02, V03; Valve

Claims (6)

A method for converting plastics into oil, which comprises decomposing plastics in the presence of aliphatic hydrocarbons in a subcritical or supercritical state to convert the plastics into oil. The method for converting plastics into oil according to claim 1, wherein the decomposition temperature is 300 to 550°C. The method for converting plastics into oil according to claim 1, wherein the decomposition pressure is 1 to 30 MPa. The method for producing oil from plastics according to claim 1, wherein the plastics include at least one selected from polyethylene, polypropylene, and polycarbonate. The method for converting plastics into oil according to any one of claims 1 to 4, wherein the aliphatic hydrocarbons contain decomposition components derived from decomposition products. The method for converting plastics into oil according to any one of claims 1 to 4, wherein the aliphatic hydrocarbons are saturated hydrocarbons.