Cleaning method for polyethylene terephthalate chemical recycling equipment

Abstract

To provide a cleaning method for polyethylene terephthalate (PET) chemical recycling equipment that realizes efficient removal of deposits in the PET chemical recycling equipment.SOLUTION: A cleaning method for PET chemical recycling equipment is for cleaning sites on which materials originating from PET products are deposited in PET chemical recycling equipment, where blast cleaning is performed by employing a medium consisting of one or more selected from PET and bis-2-hydroxyethyl terephthalate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for cleaning a polyethylene terephthalate (PET) chemical recycling facility, and more particularly to a method for cleaning areas in a PET chemical recycling facility where substances derived from PET products and their raw materials are adhered. [Background technology]

[0002] As consumption of PET products such as PET bottles expands, recycling is also progressing. For example, PET bottles are recycled through horizontal recycling, known as "bottle-to-bottle," in which used bottles are used as raw materials to manufacture similar products again.

[0003] As a method for recycling PET bottles, mechanical recycling is known, in which collected used PET bottles are crushed, washed, and dried to obtain flakes, which are then pelletized as necessary and used to manufacture PET bottles as recycled PET resin. Chemical recycling is also used, in which collected used PET bottles are crushed, washed, and dried to obtain flakes, which are then depolymerized into raw materials or intermediate raw materials for PET resin, refined, and then repolymerized to produce new PET resin, which is used to manufacture PET bottles.

[0004] One known method of chemical recycling is to add ethylene glycol in a depolymerization step to produce bis-2-hydroxyethyl terephthalate (BHET), an intermediate raw material for PET resin (see, for example, Patent Document 1). In this method, after the depolymerization step, the crude BHET is decolorized and metal ions are removed in a purification step, and purified BHET is obtained through BHET crystallization, solid-liquid separation, BHET concentration, and molecular distillation. PET resin is then obtained by polymerizing this purified BHET. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-53802 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned chemical recycling, unreacted materials and crude products during depolymerization are likely to adhere as fouling to the inner walls of reactors and piping, which are subject to particularly large heat and pressure loads, in the depolymerization and purification steps, and this is one of the factors reducing the productivity of purified BHET. Furthermore, in order to remove such deposits, particularly solid deposits, it has been necessary to periodically shut down the operation of the facility and perform cleaning of the reactor and piping.

[0007] As a cleaning method, high-pressure washing using water or a cleaning liquid, which is commonly used, is not preferred because it is desirable to prevent water from entering the reactor as much as possible. In addition, dry ice blast cleaning, which is known as a cleaning method that does not use water and does not contaminate the system with a cleaning medium, is not effective in removing the attached materials because the hardness of the dry ice medium is lower than the adhered materials to be removed. In the end, the adhered materials had to be peeled off manually, which required a lot of time and effort, resulting in a decrease in productivity.

[0008] The present invention has been made under these circumstances, and an object of the present invention is to provide a cleaning method for PET chemical recycling equipment that can efficiently remove stuck-on materials in PET chemical recycling equipment. [Means for solving the problem]

[0009] The present invention is based on the discovery that by using PET or its intermediate raw material BHET as media in blast cleaning, it is possible to efficiently remove solid objects in the system during the depolymerization and purification processes without introducing foreign objects into the PET chemical recycling facility.

[0010] The present invention provides the following means. [1] A method for cleaning areas in chemical recycling facilities where polyethylene terephthalate products and substances derived from its raw materials have adhered, comprising blast cleaning using media consisting of one or more selected from polyethylene terephthalate and bis-2-hydroxyethyl terephthalate, in a cleaning method for chemical recycling facilities for polyethylene terephthalate. [2] The method for cleaning a polyethylene terephthalate chemical recycling facility according to [1], wherein the polyethylene terephthalate product is a PET bottle. [3] The method for cleaning a polyethylene terephthalate chemical recycling facility according to [1] or [2], wherein the areas to which the polyethylene terephthalate products and substances derived from its raw materials are adhered are the inner walls of reactors and piping. Effect of the Invention

[0011] According to the present invention, it is possible to efficiently remove stuck materials in PET chemical recycling facilities. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The cleaning method for PET chemical recycling equipment of the present invention is a method for cleaning areas in PET chemical recycling equipment where substances derived from PET products and their raw materials are adhered, and is characterized by blast cleaning using media consisting of at least one type selected from PET and BHET. Blast cleaning using PET and / or BHET, the raw materials used in the production of PET, can efficiently remove stuck-on materials in PET chemical recycling facilities without introducing foreign matter from the cleaning agent that would become impurities in PET products into the chemical recycling facilities.

[0013] As described above, in the chemical recycling of PET, heat loads and pressure loads are applied in the depolymerization and purification processes, and these loads are particularly large on the inner walls of the reactors and piping in the chemical recycling facilities. For this reason, substances derived from the PET products and their raw materials, such as unreacted materials and crude products during depolymerization, tend to adhere to the inner walls of the reactors and piping as dirt, and further remain as solids. In chemical recycling of PET, in order to regenerate PET with high purity and efficiently, it is necessary to periodically clean the chemical recycling equipment to remove such adhered substances, and in the method of the present invention, PET and / or BHET are used for the cleaning by blast cleaning. Either PET or BHET may be used alone, or both may be used in combination. PET is preferably used.

[0014] PET and BHET are raw materials and intermediate materials used in the manufacture of PET products such as plastic bottles. In the chemical recycling of PET, the solidified materials remaining in the chemical recycling equipment are also substances derived from PET and its raw materials. Therefore, by using media of similar materials for blast cleaning, the chemical recycling equipment can be cleaned without damaging the areas in the chemical recycling equipment where solidified materials remain and the surrounding parts. Furthermore, even if PET and / or BHET used as media remain in the chemical recycling equipment after blast cleaning, they do not become impurities in PET products.

[0015] Furthermore, PET and BHET have a higher grinding effect on resin materials than silica sand, walnut shells, dry ice, and other media commonly used in blast cleaning, and can exert a good blast cleaning effect on the adhered matter. Furthermore, unlike silica sand, they do not generate dust when colliding with the adhered matter during blast cleaning. Therefore, blast cleaning using PET and / or BHET as a media can efficiently remove the adhered matter and efficiently clean PET chemical recycling equipment.

[0016] The blast cleaning of the present invention is applied to areas in PET chemical recycling facilities where substances derived from PET products and their raw materials are adhered, specifically, for example, inner walls of reactors and pipes.

[0017] The particle size of the PET and / or BHET that is the media in the blast cleaning of the present invention is not particularly limited, but from the viewpoint of efficient removal of the adhered matter, it can be, for example, in the range of 0.5 to 2.0 mm. The particle size referred to here is a value based on sieving with a specified mesh size.

[0018] The particle shape of the PET and / or BHET media is not particularly limited, and may be spherical, elongated spheroidal, or polyhedral.

[0019] The ejection pressure of the media in the blast cleaning is not particularly limited, but from the viewpoint of efficient removal of the adhered matter, it can be set to, for example, in the range of 0.3 to 0.7 MPa. EXAMPLES

[0020] The present invention will be described based on the following examples, but the present invention is not limited to these examples.

[0021] [Blast test] PET or polyethylene test panels were used as simulative samples of areas where substances derived from PET products, etc. have adhered, and blast tests (simulative cleaning tests) were conducted using the following media. (Media used) ·PET: particle size 1.0~1.9mm, specific gravity 1.39 Silica sand: Ube silica sand Shintoku No. 5A, particle size 0.2-1.6mm (catalog value), specific gravity 2.56 Walnut shells: particle size 1.5-2.0mm (catalog value), specific gravity 0.53 Dry ice: particle size 2.0-3.0mm (catalog value)

[0022] (Test Method) A test plate (PET or polyethylene; 200mm x 200mm, approximately 5mm thick) with an iron plate on its back was fixed vertically at a position 300mm away from the tip of the nozzle (7mm diameter) of the blast machine, and the blast test was performed by spraying each medium from the nozzle vertically against the surface of the test plate for 10 seconds. The spray pressure was 0.5MPa for PET, silica sand and walnut shells, and 1.2MPa for dry ice. After the test, the thickness before the test (a) and the minimum thickness after the test (b) were measured with a digital caliper from the cross-sectional image of the test plate at the location where the media hit. The thickness reduction (ab) was taken as the grinding depth to evaluate the blasting performance of the media. The evaluation results are shown in Table 1.

[0023] [Table 1]

[0024] As can be seen from Table 1, when PET was used as the media, the grinding depth of the test plate was greater than when other media were used, and the grinding depth of the PET test plate was the greatest. In addition, during the blast test, almost no dust was generated when PET was used as the media. Therefore, it can be said that blast cleaning using PET as a medium can efficiently remove stuck substances originating from PET products in PET chemical recycling facilities.

Claims

1. A method for cleaning the areas where polyethylene terephthalate products and substances derived from its raw materials remain as adherents in a chemical recycling facility, comprising the steps of: A cleaning method for chemical recycling equipment for polyethylene terephthalate, which comprises blast cleaning using a medium which is polyethylene terephthalate and / or bis-2-hydroxyethyl terephthalate.

2. 2. The method for cleaning a chemical recycling facility for polyethylene terephthalate according to claim 1, wherein the polyethylene terephthalate product is a PET bottle.

3. 3. The method for cleaning a chemical recycling facility for polyethylene terephthalate according to claim 1 or 2, wherein the locations to which the polyethylene terephthalate products and substances derived from the raw materials thereof are adhered are the inner walls of a reactor and piping.

Images