Method of recycling synthetic resin container

Abstract

To reuse a collected used synthetic resin container for cooking oil as a recycling material.SOLUTION: There is provided a recycling method, comprising: a pre-washing step of crushing a collected used synthetic resin container for cooking oil into flakes and washing the crushed resin flakes with water; a main-washing step of washing the resin flakes that is subjected to the pre-washing step in an aqueous solution containing a surfactant; a post-washing step of rinsing the resin flakes subjected to the main-washing step with water; a waste liquid pre-washing treatment step of separating oil from the pre-washing waste liquid containing the oil removed from the resin flakes in the pre-washing step; a waste liquid main-washing treatment step in which an inorganic salt is added to main-washing waste liquid containing the oil and surfactant removed from the resin flakes in the main-washing step, and the oil and surfactant are separated from the main-washing waste liquid by salting out; and a salting-out treatment liquid desalting treatment step for separating inorganic salts contained in treatment liquid subjected to salting out in the waste liquid main-washing treatment step from the treatment liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recycling synthetic resin containers. [Background technology]

[0002] Conventionally, containers made of synthetic resins, so-called plastic containers, have been widely used for various purposes. In recent years, in response to social demand, technology has been considered for recovering used and discarded containers and reusing them as recycled materials.

[0003] Regarding PET beverage bottles, recycling technology has become widespread, and a recycling technology called "bottle to bottle" is known, in which used PET bottles are collected and reused as recycled materials to manufacture PET bottles. For example, Patent Document 1 discloses a technology in which used plastic bottles are crushed and washed to generate resin flakes, contaminants contained in the resin flakes are decontaminated by volatilizing them by heating under vacuum, and then the resin flakes are supplied in a molten state through a filter to an injection molding machine to injection mold a preform. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-514728 Summary of the Invention [Problem to be solved by the invention]

[0005] However, recycling technology for synthetic resin containers for edible oils, such as salad oil, has not yet become as widespread as that for PET beverage bottles. This is thought to be partly because it is difficult to thoroughly remove the oil remaining in the collected containers by simply washing them with water. On the other hand, in light of the current social situation, it would be desirable for such cooking oil containers to also be widely utilized as recycled resources.

[0006] Therefore, the inventors of the present invention have conducted extensive research into a method for recycling synthetic resin containers in which collected synthetic resin containers for used edible oil are reused as recycled raw materials, and as a result have completed the present invention. [Means for solving the problem]

[0007] The method for recycling synthetic resin containers according to the present invention is a method for recycling synthetic resin containers in which collected used synthetic resin containers for cooking oil are reused as a recycling material, and includes a preliminary washing step in which the collected used synthetic resin containers for cooking oil are crushed into flakes and the crushed resin flakes are washed with water, a main washing step in which the resin flakes that have been subjected to the preliminary washing step are washed in an aqueous solution containing a surfactant, and a post-washing step in which the resin flakes that have been subjected to the main washing step are rinsed with water. The method includes a pre-washing waste liquid treatment step of separating the oil from the pre-washing waste liquid containing the oil removed from the resin flakes in the pre-washing step, a main washing waste liquid treatment step of adding an inorganic salt to the main washing waste liquid containing the oil removed from the resin flakes in the main washing step and the surfactant, and separating the oil and the surfactant from the main washing waste liquid by salting out, and a salting-out treatment liquid desalting treatment step of separating the inorganic salt contained in the treatment liquid salted out in the main washing waste liquid treatment step from the treatment liquid. Effect of the Invention

[0008] According to the present invention, a recycling method can be provided that, when reusing collected synthetic resin containers for used cooking oil as recycled raw materials, provides recycled raw materials with reduced residual oil and more suitable for reuse. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is an explanatory diagram showing steps of a recycling method according to an example of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0011] The method for recycling synthetic resin containers according to this embodiment makes it possible to reuse synthetic resin containers for edible oils, such as salad oil, as recycling materials (material recycling).

[0012] Generally, containers for edible oils are known that are made from thermoplastic resins such as polyolefin resins and polyester resins. A representative example of a container made from polyolefin resins is a polyethylene container. Also, a representative example of a container made from polyester resins is a PET bottle made from polyethylene terephthalate.

[0013] When such so-called plastic containers are used as containers for edible oil, in many cases oil remains or adheres to the inside of the used containers. Therefore, when collecting and reusing containers for edible oil, it is not preferable to subject the resin material that has been subjected to the same cleaning process as PET bottles used for beverages to material recycling, since the recycled product may have an unpleasant odor, a worsening of color, or a deterioration in physical properties due to insufficient removal of the oil.

[0014] In this embodiment, the collected used containers for cooking oil are washed in a preliminary washing process 11, a main washing process 12, and a post-washing process 13 to remove as much cooking oil remaining in the used containers as possible, and then the containers are pelletized, for example, to be used as raw materials for new resin products, thereby achieving material recycling. In this case, containers for other uses may be mixed in with the containers to be processed, but it is preferable to collect the containers for used cooking oil separately from the containers to be processed so that they can be recycled into the same containers for cooking oil.

[0015] In this embodiment, the waste liquid generated in each of the above washing steps 11, 12, and 13 is purified by a preliminary washing waste liquid treatment step 21, a main washing waste liquid treatment step 22, and a salting-out treatment liquid desalting treatment step 23 so that it can be reused in the above-mentioned washing steps 11, 12, and 13.

[0016] Each step will be described in detail below.

[0017] [Pre-cleaning process 11] In the preliminary washing step 11, the collected containers for used cooking oil are crushed into flakes, and the crushed resin flakes are washed with water. The water used for washing can be used without heating, and the temperature of the water can be room temperature (for example, 5 to 35°C). This makes it possible to remove residues adhering to the containers, and to enhance the washing effect in the main washing step 12 that is carried out next, even for substances that are difficult to remove, such as oil. The washed resin flakes are preferably dehydrated using a dehydrator to remove the washing liquid containing the residue adhering to the container, and then the resin flakes are subjected to the next step. The washing in the preliminary washing step 11 is carried out at least once, but it is preferable to carry out the washing a number of times after dehydration, since this allows for better removal of residues adhering to the collected containers.

[0018] For such washing, a known crushing and washing machine can be used. By simultaneously crushing and washing the collected containers using a crushing and washing machine, the processing time can be shortened and sufficient agitation can be performed during washing, which is preferable, but not limited to this. A known washing machine or dehydrator may also be used. In this case, it is preferable to use a washing machine that is configured to generate a water flow by agitation or the like from the viewpoint of obtaining an effective washing effect.

[0019] [Main cleaning step 12] In the main washing step 12, the resin flakes that have been subjected to the preliminary washing step 11 are washed in an aqueous solution containing a surfactant. The aqueous solution used for washing can be used without heating, and the temperature of the aqueous solution can be room temperature (for example, 5 to 35°C). This allows the oil adhering to the resin flakes to be effectively removed. The washed resin flakes are preferably dewatered using a dehydrator to remove the washing water containing oil and surfactant, and then subjected to the next step. The washing in the washing step 12 is carried out at least once, but it is preferable to carry out the washing a number of times after dehydration, since this makes it possible to more effectively remove oil adhering to the collected containers.

[0020] The surfactant is not particularly limited, but one that shows sufficient cleaning effect at room temperature can be preferably used. Specifically, a polyoxyethylene alkyl ether type nonionic surfactant can be preferably exemplified. It goes without saying that the concentration of the surfactant can be appropriately set according to the functional effect of the surfactant used and the amount of oil remaining in the collected container.

[0021] For such washing, a known washing machine can be used, and the mode is not particularly limited, but from the viewpoint of obtaining an effective washing effect, it is preferable to use a machine configured to generate a water flow by stirring or the like, as in the preliminary washing process 11. For example, a tank capable of storing an aqueous solution containing a surfactant and generating a water flow, specifically a washing tank having a cone-shaped bottom and a stirring blade, can be used. It goes without saying that the shape of the washing tank, the shape of the stirring blade, the installation of a baffle plate for promoting the stirring of the contents, etc. can be appropriately changed from the viewpoint of washing effect and efficiency.

[0022] [Post-cleaning process 13] In the post-cleaning step 13, the resin flakes that have been through the main cleaning step 12 are rinsed with water. The water used for rinsing can be used without heating, and the temperature of the water can be room temperature (e.g., 5 to 35°C). This allows the final removal of any residue adhering to the resin flakes, and the surfactant used in the main cleaning step 12 to be rinsed away. The washed resin flakes are preferably dehydrated using a dehydrator to remove the washing water containing the residue adhering to the container, and then the resin flakes are subjected to the next step. The washing in the post-washing step 13 is carried out at least once, but it is preferable to carry out the washing several times after dehydration, since this makes it possible to more effectively remove the residues and surfactant adhering to the resin flakes.

[0023] For such washing, a known washing machine and dehydrator can be used, and the mode is not particularly limited, as in the washing in the preliminary washing step 11. In addition, the resin flakes may be further crushed and washed using a known crushing and washing machine.

[0024] The post-cleaning step 13 may also include a drying step 14 in which the resin flakes are further dried in a dryer after being dehydrated.

[0025] The resin flakes that have been through each of the washing steps 11, 12, and 13 can be reused for manufacturing new synthetic resin containers, preferably after the drying step 14. When reusing the resin flakes, it is preferable to perform gravity separation in the post-washing step 13 to separate the recovered synthetic resin containers according to their materials. Such gravity separation may be performed in the preliminary washing step 11 or the main washing step 12. As mentioned above, containers for edible oils are known to be manufactured using thermoplastic resins such as polyolefin resins and polyester resins as raw materials, and depending on the collection route such as market collection, these may be mixed in the collected containers. In addition, if the collected containers are mixed with containers for other purposes, these containers may also be mixed with polyolefin resins and polyester resins. In addition, various resin materials may be mixed in caps, labels, etc. attached to products. In this way, if there is a risk that separate collection is not possible for each product or each raw material, it is preferable to separate the polyolefin resin resin flakes and the polyester resin resin flakes according to their specific gravity in at least one of the above-mentioned washing steps 11, 12, and 13. For example, as shown in the figure, the resin flakes can be separated into polyethylene resin flakes (PE) and polyethylene terephthalate resin flakes (PET) in a post-cleaning step 13 and then subjected to a subsequent step.

[0026] When gravity separation is performed, a known washing tank configured to enable gravity separation can be used as the washing tank, and the specific embodiment thereof is not particularly limited.

[0027] [Granulation process 15] In this embodiment, after the post-cleaning step 13, a granulation step 15 may be included in which the resin flakes are granulated into pellets in order to reuse the resin flakes as a recycled material.

[0028] In the granulation step 15, a known granulation device can be used, and is not particularly limited. For example, a granulation device equipped with a heating cylinder in which a plasticizing screw is arranged inside and a granulation die attached to the tip of the heating cylinder, and configured to cut the resin that is plasticized in the heating cylinder, melted and kneaded, and extruded in a strand shape from the granulation die into pellets, can be mentioned. In addition, it is more preferable to use a granulation device configured to decompress and suck gas phase components containing impurity components remaining in the granulation device through a vent port provided through the heating cylinder of the granulation device and discharge it outside the device. This makes it possible to further reduce the impurity components remaining in the plasticized resin.

[0029] [Pre-cleaning wastewater treatment process 21] In the pre-washing waste liquid treatment step 21, oil is separated from the waste liquid (pre-washing waste liquid) generated in the pre-washing step 11, which contains the oil removed from the resin flakes in the pre-washing step 11. The means for separating the oil from the pre-wash waste liquid is not particularly limited, but any known means such as filter filtration, reduced pressure distillation, centrifugation, and static separation can be used. The oil is separated through such a process, and the reclaimed water can be reused in the preliminary washing process 11 as shown in the figure. Similarly, the water can also be reused in the main washing process 12 and the post-washing process 13. The reclaimed water can also be disposed of in the sewer system without using a large-scale purification system. The oil separated in this process may be reused as a fuel or other resource.

[0030] [Main cleaning wastewater treatment process 22] In the main washing waste liquid treatment process 22, inorganic salts such as sodium chloride, magnesium chloride, calcium chloride, sodium carbonate, sodium sulfate, etc. are added to the waste liquid (main washing waste liquid) generated in the main washing process 12, which contains the oil and surfactant removed from the resin flakes in the main washing process 12, and the oil and surfactant are separated from the main washing waste liquid by salting out. For example, sodium chloride is added to the waste cleaning liquid, and the sodium chloride is dissolved by heating. The temperature of heating may be any temperature at which inorganic salt (sodium chloride) dissolves, and may be, for example, 50 to 60°C. This increases the salt concentration in the aqueous solution, attracting water molecules to salt ions, decreasing the amount of water molecules around the surfactant surrounding the oil, and strengthening the interaction between the oil and surfactant particles mixed in the water, thereby flocculating the oil and surfactant, and separating the oil and surfactant from the water. With such a separation means, the mixed layer of oil and surfactant is separated into the upper layer, and the water containing inorganic salt (sodium chloride) is separated into the lower layer.

[0031] Here, in the post-cleaning step 13 following the main cleaning step 12, the oil and surfactant remaining in the resin flakes that have been through the main cleaning step 12 are removed by rinsing, so that the waste liquid generated in the post-cleaning step 13 also contains the oil and surfactant. Therefore, it is preferable to mix the waste liquid generated in the post-cleaning step 13 with the main cleaning waste liquid and treat them together.

[0032] The inorganic salts used in this cleaning waste liquid treatment process 22 are not limited to those mentioned above. However, taking into consideration that the waste liquid will be regenerated and reused in each cleaning process 11, 12, and 13 later, and that the cleaned resin material will be used as a recycled raw material to manufacture new containers for food or edible oil, it is preferable to use inorganic salts that will cause few problems when used to clean containers for handling food.

[0033] The treatment tank for treating the cleaning waste liquid is not particularly limited, but is preferably one that can heat the tank to a temperature at which inorganic salts can be dissolved. Also, if the tank is capable of discharging the contents from the bottom, it is more preferable because when the water is separated to become the lower layer, only the water can be discharged from the tank.

[0034] The treated liquid from which the oil and surfactant have been separated by salting out in the cleaning waste liquid treatment step 22 contains inorganic salts and is therefore unsuitable for reuse in the above-mentioned cleaning steps 11, 12, and 13 in its current state. It is also undesirable to discharge the treated liquid containing a large amount of inorganic salts directly into the environment. In this embodiment, such treated liquid containing inorganic salts is subjected to the salting out treatment liquid desalting treatment step 23 described below. In addition, the oil and surfactant separated through this cleaning waste liquid treatment process 22 can be reused as resources, and for example, the oil and surfactant can be used in their mixed state to make soap, etc.

[0035] [Salting out solution desalting process 23] In the salting-out treatment liquid desalting treatment step 23, a desalting treatment is carried out to separate inorganic salts contained in the treatment liquid salted out in the main washing waste liquid treatment step 22 from the treatment liquid. For example, when sodium chloride is used in the main washing waste liquid treatment step 22, the treatment liquid is separated into water and concentrated sodium chloride water or solid salts. The desalination means can be appropriately selected depending on the running costs, installation environment, etc., and is not particularly limited. For example, electrodialysis, reverse osmosis, distillation, etc. can be used.

[0036] The water reclaimed through such treatment can be reused in the preliminary washing step 11 as shown in the figure. Similarly, it can also be reused in the main washing step 12 and the post-washing step 13. In addition, the reclaimed water can be disposed of in the sewer system without using a large-scale purification system. The inorganic salts separated in this step can be reused in the washing wastewater treatment step 22.

[0037] According to this embodiment, when the collected synthetic resin containers for used cooking oil are reused as a recycled raw material, a recycled raw material with reduced residual oil can be provided, and it is possible to reuse the recycled raw material (material recycling) as a recycled raw material with less risk of deterioration of physical properties. Furthermore, according to this embodiment, a good cleaning effect can be obtained even if the water and aqueous solution used for cleaning in the preliminary cleaning step 11, the main cleaning step 12, and the post-cleaning step 13 are cleaned at room temperature without heating, so that the extra cost associated with heating the water and aqueous solution used for cleaning can be reduced. Furthermore, according to this embodiment, the waste liquid and inorganic salts generated in each of the cleaning steps 11, 12, and 13 can also be reused, so that it is possible to provide a more environmentally friendly and sustainable recycling method when the collected synthetic resin containers for used cooking oil are reused. EXAMPLES

[0038] The present invention will now be described in more detail with reference to specific examples.

[0039] [Example 1] The cooking oil was filled into a polyethylene container, and then the container was drained to prepare a container for the used cooking oil. The container did not have a label.

[0040] Here, the amount of oil remaining in a 50 g used cooking oil container prepared in the same manner (residual oil amount) was measured, and the amount of residual oil was 5 g (10 wt%). The amount of residual oil was measured as follows. First, the prepared cooking oil container was cut and placed in a thermostatic bath at 50°C to which hexane had been added, and left to stand for 1 hour. Thereafter, the contents in the thermostatic bath were cooled to room temperature and suction filtered using a membrane filter with a pore size of 1.0 μm to obtain an extract. After drying the extract, the weight of the obtained extract was measured and used as the amount of residual oil.

[0041] Next, 50 g of a used cooking oil container, different from the one used for measuring the amount of residual oil described above, was placed in a crushing and washer, crushed into flakes, and washed with water to produce resin flakes. The water used for washing was not heated. The resin flakes were then dehydrated in a dehydrator (pre-washing step 11).

[0042] Next, the resin flakes were placed in a cylindrical tank and washed in an aqueous solution containing a surfactant while stirring for about 50 minutes (main washing step 12). The aqueous solution containing the surfactant was not heated. The surfactant used was a polyoxyethylene alkyl ether type nonionic surfactant ("Scorerol 700 Concentrate" manufactured by Kitahiro Chemical Co., Ltd.). The concentration of the surfactant in the washing tank was adjusted to 1.2% by weight.

[0043] The resin flakes were then placed in a crushing and washing machine, where they were crushed and washed with water, and then dehydrated. After dehydration, they were washed again with water, and then dehydrated. The water used for washing was not heated. The resin flakes were then dried using a dryer (post-washing process 13).

[0044] The resin flakes that had been through the preliminary washing step 11, the main washing step 12, and the post-washing step 13 were left to stand in a thermostatic chamber containing hexane in the same manner as described above, and the amount of residual oil was measured in the same manner as described above. The amount of residual oil in the resin flakes that had been through the preliminary washing step 11, the main washing step 12, and the post-washing step 13 was 0.09 g (0.18 wt %). It has been confirmed that by undergoing the cleaning process of this embodiment, when cooking oil containers are reused as recycled raw materials (material recycling), it is possible to remove oil to a degree that there is no risk of deterioration in the physical properties of the recycled product. In particular, when manufacturing food containers, the raw materials must meet certain standards, and therefore, oil must be thoroughly removed before reuse. Conventionally, it has been difficult to reuse collected food oil containers as recycled raw materials to manufacture new food oil containers, and the subsequent uses of the recycled resin material have been limited. However, according to this embodiment, it has been confirmed that it is possible to provide a resin material in a state in which new food oil containers can be manufactured from collected used food oil containers.

[0045] [Example 2] A main cleaning waste liquid was prepared by using the main cleaning step 12 three times in the same manner as in Example 1. Analysis of the components of this main cleaning waste liquid revealed that the concentration of n-hexane extract was 220 mg / L, the concentration of surfactant was 10,000 mg / L, the concentration of BOD (biochemical oxygen demand) was 10,000 mg / L, the concentration of COD (chemical oxygen demand) was 8,400 mg / L, and the concentration of TOC (total organic carbon) was 7,300 mg / L.

[0046] Sodium chloride was added to the prepared main cleaning waste liquid, and the liquid was left to stand for 2 to 3 hours while being heated to 50°C, and separated into a mixed layer of oil and surfactant and a water layer containing sodium chloride (main cleaning waste liquid treatment process 22). The sodium chloride was adjusted to a concentration of 20% by weight relative to the main cleaning waste liquid.

[0047] After treatment, the components of the water from which the oil and surfactant had been separated from the cleaning wastewater (the salted-out treated liquid) were analyzed. The concentrations of n-hexane extract were 1 mg / L, surfactants were 24 mg / L, BOD were 350 mg / L, COD were 210 mg / L, and TOC were 180 mg / L.

[0048] It was confirmed that the contamination of the wastewater can be almost completely removed by treating the cleaning wastewater in the cleaning wastewater treatment process 22. It was also confirmed that the water after treatment in the cleaning wastewater treatment process 22 falls below the sewage discharge standard value based on the provisions of the Sewerage Act.

[0049] Although the present invention has been described above by showing preferred embodiments, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0050] In the above-described embodiment, containers for edible oil have been used as an example of collected used containers, but it goes without saying that the present invention can also be preferably used for collected items, since oil can be removed in the same manner even if containers for other purposes, such as containers for food containing oil, are to be collected, or if containers for edible oil and containers for other purposes are mixed in the collected items. [Explanation of symbols]

[0051] 11 Pre-cleaning process 12. Cleaning process 13 Post-cleaning process 14 Drying process 15 Granulation process 21 Pre-cleaning waste liquid treatment process 22. Wastewater treatment process for cleaning 23 Desalination process of salting out solution

Claims

1. A method for recycling synthetic resin containers, which reuses collected used synthetic resin containers for cooking oil as recycling raw materials, comprising the steps of: A preliminary washing step of crushing the collected synthetic resin containers for used edible oil into flakes and washing the crushed resin flakes with water; a main washing step of washing the resin flakes that have been subjected to the preliminary washing step in an aqueous solution containing a surfactant; a post-cleaning step of rinsing the resin flakes that have been subjected to the main cleaning step with water; a pre-washing waste liquid treatment step of separating the oil from a pre-washing waste liquid containing the oil removed from the resin flakes in the pre-washing step; a main cleaning waste liquid treatment process in which an inorganic salt is added to the main cleaning waste liquid containing the oil and the surfactant removed from the resin flakes in the main cleaning process, and the oil and the surfactant are separated from the main cleaning waste liquid by salting out; a salting-out treatment liquid desalting treatment step for separating the inorganic salt contained in the treatment liquid salted out in the main washing waste liquid treatment step from the treatment liquid; A method for recycling synthetic resin containers, comprising:

2. 2. The method for recycling synthetic resin containers according to claim 1, wherein the processing liquid treated in the pre-cleaning waste liquid treatment step is reused in at least one of the pre-cleaning step, the main cleaning step and the post-cleaning step.

3. 2. The method for recycling synthetic resin containers according to claim 1, wherein the treatment liquid treated in the salting-out treatment liquid desalting treatment step is reused in at least one of the preliminary washing step, the main washing step and the post-washing step.

4. 2. The method for recycling synthetic resin containers according to claim 1, wherein the inorganic salt separated in the salting-out solution desalting treatment step is reused in the main cleaning waste liquid treatment step.

5. The method for recycling synthetic resin containers according to any one of claims 1 to 4, further comprising a granulation step of granulating the resin flakes into pellets after the post-cleaning step.

6. The method for recycling synthetic resin containers according to any one of claims 1 to 4, wherein the resin flakes are separated by gravity in the post-cleaning step.

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