Method for producing recycled non-hydrolyzable resin, and method for producing recycled polyolefin resin

Abstract

To provide a method for producing a recycled non-hydrolyzable resin and a method for producing a recycled polyolefin resin which can effectively use a resource by recycling, and can reduce energy consumption.SOLUTION: A method for producing a recycled non-hydrolyzable resin includes a production step of setting temperatures of a hydrolyzable resin and a non-hydrolyzable resin to be equal to or higher than a melting point of the hydrolyzable resin for 2 minutes or more under the condition of a temperature of 220 to 374°C and pressure of 0.1 to 22 MPa, decomposing at least a part of the hydrolyzable resin, and producing a recycled non-hydrolyzable resin containing the non-hydrolyzable resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a recycled non-hydrolyzable resin and a method for producing a recycled polyolefin resin. [Background technology]

[0002] Efforts to recycle polyethylene terephthalate (PET) bottles, polystyrene (PS) trays, and other items made from a single material are steadily progressing through mechanical recycling (material recycling). However, with mechanical recycling (material recycling), the quality of the resin deteriorates due to factors such as a decrease in molecular weight during recycling, so in many cases the material is recycled into something of lower value than the original product (cascade recycling).

[0003] Flexible packaging and molded container materials, which are made from composite materials containing multiple types of resin and metals, are not easy to recycle. There are cases where feedstock recycling (chemical recycling) such as oilification and gasification is being undertaken. For example, Patent Document 1 describes a method for decomposing resin waste, which is characterized by bringing the resin waste into contact with supercritical water containing a reaction accelerator to decompose the waste into low molecular weight components. Furthermore, Patent Document 2 describes a decomposition method in which a resin laminate is brought into contact with alcohol in a supercritical state to solvolyze a solvolyzable resin into monomers and / or oligomers. Patent Document 3 also describes a decomposition method in which shredded plastic multilayer molded articles consisting of condensation polymer film layers and addition polymer film layers are brought into contact with high-temperature, high-pressure water at a temperature that melts the addition polymer but does not decompose it, thereby decomposing the condensation polymer film layers into their monomer components and transferring the addition polymer film layers into the water as undecomposed solids. Furthermore, Patent Document 4 describes a selective hydrolysis and / or pyrolysis method for selectively hydrolyzing and / or pyrolyzing a natural or synthetic polymer compound using water in a supercritical or subcritical state as a solvent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-237215 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-126913 [Patent Document 3] Japanese Patent Application Publication No. 11-323006 [Patent Document 4] Japanese Patent Application Publication No. 5-31000 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional recycling methods involve the use of large amounts of energy to convert waste into oil or gas, and the conversion of waste into chemical products also requires the use of large amounts of energy. Patent Document 3 describes transferring an addition polymer film layer as an undecomposed solid. However, when a solid material made of an addition polymer is decomposed into oil by contacting it with high-temperature, high-pressure water at or above the decomposition temperature of the solid, a large amount of energy is required for the oil conversion or resynthesis. For this reason, reducing carbon dioxide (CO2) emissions, which contribute to global warming, has become an issue. Furthermore, when solid or liquid residues remain or adhere to plastic packaging, time-consuming pretreatment is required to expedite recycling.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a recycled non-hydrolyzable resin and a method for producing a recycled polyolefin resin that enable effective use of resources through recycling and reduce energy consumption. [Means for solving the problem]

[0007] The method for producing a recycled non-hydrolyzable resin of the present invention includes a production step of subjecting a hydrolyzable resin and a non-hydrolyzable resin to a temperature of 220 to 374°C and a pressure of 0.1 to 22 MPa, at least for 2 minutes, at a temperature equal to or higher than the melting point of the hydrolyzable resin, to decompose at least a portion of the hydrolyzable resin, thereby producing a recycled non-hydrolyzable resin containing the non-hydrolyzable resin.

[0008] The production method may further include a recovery step of recovering a decomposition product of the hydrolyzable resin as a gas or liquid. The hydrolyzable resin may contain a plurality of types of hydrolyzable resins, and in the recovery step, the decomposition products of the hydrolyzable resins may be recovered separately for each type of hydrolyzable resin. The plurality of types of hydrolyzable resins may include polyethylene terephthalate and nylon, and in the recovery step, decomposition products of polyethylene terephthalate and decomposition products of nylon may be recovered separately. In the manufacturing process, the recycled non-hydrolyzable resin may be recovered as a solid. The non-hydrolyzable resin may also contain a polyolefin. The method may further include a recovery step of recovering decomposition products of the hydrolyzable resin, and in the recovery step, the decomposition products of the hydrolyzable resin may be recovered as monomers or oligomers constituting the hydrolyzable resin.

[0009] The present invention also provides a method for producing a recycled polyolefin resin, which uses the method for producing a recycled non-hydrolyzable resin to produce a recycled polyolefin resin as the recycled non-hydrolyzable resin. [Effects of the Invention]

[0010] According to the present invention, resources can be effectively utilized through recycling, and energy consumption can be reduced. In particular, the molecular weight reduction of the non-hydrolyzable resin can be reduced, and the non-hydrolyzable resin can be extracted as a resin. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of an apparatus used in a method for producing a recycled non-hydrolyzable resin. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below based on preferred embodiments.

[0013] An example of an apparatus used in the method for producing recycled non-hydrolyzable resin is shown in Figure 1. This recycled non-hydrolyzable resin production apparatus 10 includes a raw material input section 11 into which raw material 21 containing a composite of non-hydrolyzable resin and hydrolyzable resin is input, a reactor 13 that decomposes the hydrolyzable resin by reaction, a liquid inlet section 14 that introduces a liquid 24 used to decompose the hydrolyzable resin into the reactor 13, a first outlet section 15 that discharges a first effluent 25 containing the non-hydrolyzable resin from the reactor 13, and a second outlet section 16 that discharges a second effluent 26 containing decomposition products of the hydrolyzable resin from the reactor 13.

[0014] The hydrolyzable resin decomposed in the reaction device 13 is contained in the raw material 21 introduced from the raw material introduction section 11. An example of the raw material introduction section 11 is a hopper. The raw material 21 is transported inside the device 12 and introduced into the reaction device 13. The state of the raw material 21 introduced from the raw material introduction section 11 is not particularly limited, and may be small pieces of packaging bags, packaging films, flakes, or the like. The raw material 21 does not need to be a molding material such as pellets, and may be waste after use, scraps from production, or the like.

[0015] Raw material 21 includes a composite of a non-hydrolyzable resin and a hydrolyzable resin, but may also include raw material 21 that does not include a hydrolyzable resin. For example, raw material 21 may include a composite of a non-hydrolyzable resin. An example of raw material 21 containing a non-hydrolyzable resin is mono-material packaging made of a non-hydrolyzable resin. Raw material 21 derived from mono-material packaging may include metals, inorganic substances, adhesives, etc. Examples of metals include metal foils such as aluminum, vapor deposition films, etc. Examples of inorganic substances include metal oxides such as silica and alumina, inorganic vapor deposition films, inorganic fillers, inorganic pigments, etc.

[0016] Reactor 13 performs a manufacturing process in which at least a portion of the hydrolyzable resin contained in raw material 21 is decomposed to produce a recycled non-hydrolyzable resin containing a non-hydrolyzable resin. In this manufacturing process, the hydrolyzable resin and the non-hydrolyzable resin are subjected to a temperature of 220 to 374°C and a pressure of 0.1 to 22 MPa, at a temperature equal to or higher than the melting point of the hydrolyzable resin, for at least 2 minutes. In this specification, the melting point refers to the crystalline melting temperature measured using a differential scanning calorimeter (DSC) at a heating rate of 20°C / min from 30°C to 300°C. In this specification, when multiple crystalline melting temperatures exist, the temperature equal to or higher than the temperature indicated by the apex of the crystalline melting peak with the largest area among the crystalline melting peaks in the DSC curve measured under the above conditions. This reduces the molecular weight reduction of the non-hydrolyzable resin, allowing it to be extracted as a resin. Furthermore, the recycled non-hydrolyzable resin maintains the original quality of the non-hydrolyzable resin before recycling. This allows for efficient use of resources and reduced energy consumption.

[0017] By using the above-described production method, it is possible to continuously produce a recycled non-hydrolyzable resin from the non-hydrolyzable resin contained in the first discharge 25. The non-hydrolyzable resin contained in the first discharge 25 may be a molten resin, but it can also be recovered as a solid resin.

[0018] Examples of non-hydrolyzable resins include addition polymerization resins such as polyolefins. Examples of polyolefins (PO) include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and polystyrene (PS). Examples of polyethylene (PE) include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). Examples of polypropylene (PP) include homo-PP, block PP, and random PP.

[0019] Furthermore, the production method can include a recovery step of recovering decomposition products of the hydrolyzable resin. The decomposition products contained in the second discharge 26 may be in any of a liquid phase, a solid phase, or a gas phase. However, it is preferable to condense gas phase components such as steam by cooling and recover the decomposition products as a gas or liquid. Moreover, the second discharge 26 may contain an excess amount of liquid 24. The decomposition products recovered as the second discharge 26 can also be used as a raw material for recycled resin. It is preferable to recover the decomposition products of the hydrolyzable resin as monomers or oligomers that constitute the hydrolyzable resin.

[0020] Examples of hydrolyzable resins include polyesters and polyamides. Examples of polyesters include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The polyester may be an aliphatic polyester or an aromatic polyester, a condensation polymer of a hydroxycarboxylic acid, a ring-opening polymer of a lactone, or a condensation polymer of a diol and a dicarboxylic acid. Examples of polyamides include nylon 6 (NY6) and nylon 66 (NY66). The polyamide may be nylon (NY) containing an aliphatic group, an aromatic aramid, a polymer of an aminocarboxylic acid, a ring-opening polymer of a lactam, or a condensation polymer of a diamine and a dicarboxylic acid.

[0021] Laminates of different resins that may be contained in raw material 21 include, but are not limited to, laminates made of polyethylene (e.g., 68.9 wt%), polyethylene terephthalate with an aluminum vapor deposition layer (e.g., 12.6 wt%), nylon 6 (e.g., 12.6 wt%), adhesive layers, etc. (e.g., 5.9 wt%).

[0022] The manufacturing method described above can be applied not only to a single type of plastic but also to a composite material made of two or more types of plastic as the raw material 21. Even if the name of the plastic substance is the same, resins that have different physical properties such as differential scanning calorimetry (DSC) curves, melt flow rates (MFR), and whether or not they are stretched are treated as different types of resins.

[0023] The liquid 24 used for decomposing the hydrolyzable resin may be a protic solvent such as water or alcohol. Examples of alcohol include methanol, ethanol, propanol, butanol, etc. These alcohols may be hydrous alcohols or bioalcohols. The liquid 24 may be one type of solvent or a mixed solvent of two or more types of solvents.

[0024] The pH of the liquid 24 is not particularly limited and may be neutral, acidic, or alkaline. However, using a neutral liquid 24 is preferable because it does not require the chemical resistance of the device to be increased. The decomposition reaction of the hydrolyzable resin can be accelerated by using appropriate heating and / or pressure conditions. An acid, base, catalyst, etc. may be added to the liquid 24.

[0025] The reaction conditions in the reactor 13 are equal to or higher than the temperature at which at least one of the hydrolyzable resins melts. In addition, the temperature and pressure do not necessarily have to be such that the decomposition liquid 24 reaches the supercritical state (supercritical conditions), and may be such that the liquid 24 does not reach the supercritical state (subcritical conditions).

[0026] The liquid 24 or its vapor contained in the second effluent 26 may be recovered from the second effluent 26 and reused for introduction through the liquid inlet 14. The vapor of the liquid 24 may be condensed while recovering heat. The liquid 24 recovered from the second effluent 26 may be purified using a filter, chemicals, or the like.

[0027] When the raw material contains two or more hydrolyzable resins, different decomposition conditions may be adopted depending on the respective hydrolyzable resins. Two or more reactors 13 may be used to accommodate the different decomposition conditions, and the reactor 13 may be divided into zones so that different decomposition conditions can be set.

[0028] When the hydrolyzable resin in the raw material 21 contains multiple types of hydrolyzable resins, the decomposition products of the hydrolyzable resins may be separated and collected according to the type of hydrolyzable resin in the decomposition product recovery step. For example, multiple second discharge sections 16 may be provided in the reaction device 13, and decomposition products with different compositions may be discharged from each second discharge section 16.

[0029] For example, if the raw material 21 contains polyester and polyamide, the reactor 13 may include a first section that mainly decomposes the polyester and discharges the polyester decomposition product, and a second section that mainly decomposes the polyamide and discharges the polyamide decomposition product. For example, if the multiple types of hydrolyzable resins contain polyethylene terephthalate and nylon, the polyethylene terephthalate decomposition product and the nylon decomposition product can be recovered separately. If the nylon is a ring-opening polymerization product of lactam, such as nylon 6, the decomposition product, such as lactam or aminocarboxylic acid, can be easily recovered.

[0030] A known single-screw, twin-screw, or multi-screw extruder may be used as the reaction device 13. There are various types of extrusion screw elements, making it easy to respond to various input materials.

[0031] A reactor equipped with a static mixer or the like as a stirring mechanism can also be used as the reaction device 13. The reaction device 13 may be equipped with a sintered filter in at least one or both of the liquid inlet 14 and the second outlet 16.

[0032] By using the method for producing a recycled non-hydrolyzable resin according to the above embodiment, a recycled non-hydrolyzable resin can be produced. In particular, a recycled polyolefin resin can be produced as the recycled non-hydrolyzable resin.

[0033] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments and various modifications are possible without departing from the spirit of the present invention. Modifications include addition, substitution, omission, and other changes to components in each embodiment. Furthermore, components used in two or more embodiments can be combined as appropriate. [Example]

[0034] The present invention will be specifically described below with reference to examples, but is not limited to these examples.

[0035] Example 1 The composite containing hydrolyzable and non-hydrolyzable resins contained polyethylene terephthalate resin and nylon 6 resin as the hydrolyzable resin, and polyethylene resin as the non-hydrolyzable resin. The composite was introduced into a twin-screw extruder, and while continuously injecting water, it was held at a temperature of 300°C and a pressure of 10 MPa for 10 minutes. The solid content was recovered from the tip of the twin-screw extruder, and the gas components were recovered from the side near the tip of the twin-screw extruder while being cooled. The solid matter recovered was a polyethylene resin, and it was confirmed using an infrared spectrophotometer that the purity of the polyethylene resin was 100% by mass and that no hydrolyzable resin was mixed in. The molecular weight distribution of the polyethylene resin recovered as a solid was measured. The weight average molecular weight and number average molecular weight before treatment were set at 100%, respectively, and it was found that the weight average molecular weight remained at 83% and the number average molecular weight remained at 69%. The recovered gas components were passed through a cooler and separated into solid, liquid, and gas phases under normal pressure and 25°C. From the liquid phase of the recovered gas components, monomers and oligomers of ε-aminocaproic acid, a decomposition product derived from nylon 6 resin, were recovered by vacuum distillation. From the solid phase of the recovered gas components, monomers and oligomers of ε-caprolactam derived from nylon 6 resin, and monomers of terephthalic acid and ethylene glycol derived from polyethylene terephthalate resin and their oligomers were recovered by extraction and vacuum distillation.

[0036] Example 2 The treatment was carried out in the same manner as in Example 1, except that the treatment conditions were a temperature of 330°C and a pressure of 12.9 MPa, and the treatment was maintained for 10 minutes. Solid matter was recovered from the tip of the twin-screw extruder, and gas components were recovered while being cooled from the side of the twin-screw extruder near the tip. The solid matter recovered was a polyethylene resin, and it was confirmed using an infrared spectrophotometer that the purity of the polyethylene resin was 100% by mass and that no hydrolyzable resin was mixed in. The molecular weight distribution of the polyethylene resin recovered as a solid was measured. The weight average molecular weight and number average molecular weight before treatment were set at 100%, respectively, and it was found that the weight average molecular weight remained at 82% and the number average molecular weight remained at 67%.

[0037] Examples 3 to 17 In Examples 3 to 17, the same procedures as in Example 1 were carried out except that the treatment conditions were changed as shown in Table 1.

[0038] [Table 1]

[0039] The results are summarized in Table 1. These results show that recycled non-hydrolyzable resin can be continuously produced with less energy consumption, by decomposing hydrolyzable resin into recycled resin raw material, and extracting non-hydrolyzable resin as recycled resin, while maintaining the original quality of the recycled resin. [Explanation of symbols]

[0040] 10...Regenerated non-hydrolyzable resin manufacturing apparatus, 11...Raw material input section, 12...Inside of the apparatus, 13...Reaction apparatus, 14...Liquid introduction section, 15...First discharge section, 16...Second discharge section, 21...Raw material, 24...Liquid, 25...First discharge product, 26...Second discharge product.

Claims

1. A method for producing recycled non-hydrolyzable resin, comprising a manufacturing step of subjecting a hydrolyzable resin and a non-hydrolyzable resin to a temperature of 220 to 374°C and a pressure of 0.1 to 22 MPa for 2 minutes or longer at a temperature equal to or higher than the melting point of the hydrolyzable resin, thereby decomposing at least a portion of the hydrolyzable resin and producing recycled non-hydrolyzable resin containing the non-hydrolyzable resin.

2. The method for producing a recycled non-hydrolyzable resin according to claim 1, further comprising a recovery step of recovering a decomposition product of the hydrolyzable resin as a gas or liquid.

3. 3. The method for producing recycled non-hydrolyzable resin according to claim 2, wherein the hydrolyzable resin contains a plurality of types of hydrolyzable resin, and in the recovery step, the decomposition products of the hydrolyzable resin are recovered separately according to the type of hydrolyzable resin.

4. 4. The method for producing recycled non-hydrolyzable resin according to claim 3, wherein the plurality of types of hydrolyzable resins include polyethylene terephthalate and nylon, and in the recovery step, decomposition products of polyethylene terephthalate and decomposition products of nylon are recovered separately.

5. The method for producing a recycled non-hydrolyzable resin according to claim 1 , wherein the recycled non-hydrolyzable resin is recovered as a solid in the production process.

6. The method for producing recycled non-hydrolyzable resin according to claim 1 , wherein the non-hydrolyzable resin contains a polyolefin.

7. 2. The method for producing recycled non-hydrolyzable resin according to claim 1, further comprising a recovery step of recovering decomposition products of the hydrolyzable resin, wherein the decomposition products of the hydrolyzable resin are recovered as monomers or oligomers constituting the hydrolyzable resin in the recovery step.

8. A method for producing a recycled polyolefin resin, comprising producing a recycled polyolefin resin as the recycled non-hydrolyzable resin using the method for producing a recycled non-hydrolyzable resin according to claim 1.

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