Method and equipment for selectively recovering PBT resin component from waste containing PBT resin

Abstract

[Problem] To provide a method and a device for selectively recovering a PBT resin from a product containing a PBT resin. [Solution] A PBT resin recovery method and device in which waste containing a PBT resin is immersed in a tank containing an amount of 1,4-butanediol sufficient to immerse the waste, preferably at least five times the volume of the PBT resin fraction, and is heated while stirring at atmospheric pressure in a temperature range from 150℃ to the boiling point of the 1,4-butanediol to dissolve the PBT resin fraction, contaminants are removed by filtering the molten mixture, the 1,4-butanediol is separated and recovered from the filtered molten mixture by vacuum distillation, and the residual PBT resin fraction is recovered.

Description

Method and equipment for selectively recovering PBT resin components from waste containing PBT resin

[0001] The present invention relates to a method and equipment for separating and recovering polybutylene terephthalate (PBT) from waste containing polybutylene terephthalate (PBT) resin.

[0002] Polybutylene terephthalate (PBT) is a material that can easily be made into polymer blends and alloys. It is widely used as an engineering plastic in a variety of components, including automotive and industrial machinery parts, office equipment, home appliances, and housing materials. It enjoys the highest demand among engineering plastics in Japan. By incorporating glass fiber, PBT becomes a tough plastic with excellent abrasion resistance. It is also easily flame-retardant, and adding flame retardants makes it self-extinguishing. Furthermore, it is the newest engineering plastic, boasting long-term resistance to organic solvents and gasoline. While PBT has a short history, its excellent electrical insulation and high breakdown voltage have led to increased demand with the rapid adoption of electronic components in automobiles. Furthermore, as electric and hybrid vehicles become more common, PBT's uses are expected to expand further. This is because PBT can be produced by replacing ethylene glycol in recycled polyethylene terephthalate (PET) with 1,4-butylene glycol. However, a drawback of PBT resin is that it is not easy to recycle. Therefore, in view of the hydrolysis property of polybutylene terephthalate (PBT), only a method using a hydrolytic enzyme called "protease" has been proposed (Patent Document 1), and since it is not easy to recycle, most of it is disposed of as waste.

[0003] JP 2023-103426 A JP 2023-075033 A

[0004] Therefore, it is desirable to provide a recycling method and equipment that can efficiently and selectively extract PBT resin from waste containing PBT resin, instead of the inefficient enzymatic method.

[0005] A conventional method for producing polybutylene terephthalate (PBT) has been proposed for reusing recovered PBT resin, in which 1,4-butanediol is added as a depolymerization initiator in an amount of 0.7 to 2.0 times the molar amount of the PBT resin, and 0.01 to 0.1 wt % of an antioxidant is added, and the polybutylene terephthalate (PBT) is depolymerized and then repolymerized (Patent Document 2). However, such reuse is difficult when glass fiber or the like is added as a reinforcing agent, or when polybutylene terephthalate is used in combination with metal members. Therefore, the present inventors conducted extensive research to selectively separate and recover PBT resin from PBT products, rather than depolymerizing the PBT resin. As a result, they found that by using 1,4-butanediol as a dissolving agent, and boiling a sufficient amount of 1,4-butanediol, i.e., an amount sufficient to fully immerse the PBT resin, preferably at least five times the volume of the PBT resin, at atmospheric pressure at a temperature of 150°C or higher but lower than the boiling point, with stirring, only the PBT resin can be selectively dissolved in a short period of time and separated and recovered. The present invention was made based on such findings, and the gist of the present invention is that waste containing PBT resin is immersed in a tank containing 1,4-butanediol in an amount sufficient to immerse the waste, i.e., a volume large enough to immerse the PBT resin content, preferably at least five times the volume, and is stirred while being heated at atmospheric pressure within a temperature range of 150°C or higher but not exceeding the boiling point of the distilled PBT resin, thereby selectively dissolving the PBT resin content. The PBT molten mixture is then filtered to remove impurities and recovered, and the 1,4-butanediol is separated from the filtered molten mixture by distillation under reduced pressure under heating, and the PBT resin content is recovered.

[0006] According to the present invention, by heating a sufficient amount of 1,4-butanediol for immersion in a solution at a temperature range of 150°C or higher but below the boiling point, the PBT resin component can be dissolved from a PBT resin product, allowing the separation and recovery of only the PBT resin from a product containing PBT resin. The PBT resin is recovered in a dissolved state with 1,4-butanediol, but can be separated by evaporating the 1,4-butanediol and reused as a PBT resin solvent. The recovered PBT resin component may contain some 1,4-butanediol.

[0007] PBT resin is often used in combination with glass fiber, metal components, or other resins. In the former case, the PBT resin can be dissolved to separate the impurity glass fiber and metal components from the PBT resin, allowing the PBT resin to be recovered. The solvent can be recovered by distillation and reused. In the latter case, where other resins are included, the resins other than PBT can be dissolved and removed, and then the impurities and PBT resin can be separated in the same manner as in the former case.

[0008] This is a schematic diagram of a batch-type system for separating and recovering impurities and PBT resin from PBT products containing impurities. It is also a schematic diagram of a system for continuously performing the method shown in Figure 1. This is a photograph showing the state of a PBT resin dissolution experiment, showing that PBT resin dissolves and becomes transparent when heated to 210°C in 1,4-butanediol. This is a table showing the relationship between temperature and solubility for PBT resin to solvent ratios of 1:10, 1:20, and 1:30. This is a photograph of the process for recovering PBT resin from a wire containing both PVC and PBT resin. In the first step, the PVC resin is dissolved in a CHV, and the wire is recovered after PVC removal (Photo 3). In the second step, the recovered wire is placed in a PBT resin solvent (Photo 4). In the third step, the PBT resin is dissolved (Photo 5). Finally, in the fifth step, the PBT resin-containing solvent is separated from the copper wire, and the wire is recovered (Photo 6). These photographs show the process of separating and recovering PBT resin and glass fiber from glass fiber-reinforced PBT resin products. (a) shows PBT resin mixed with 30% glass fiber GF (Photo 1), and in the first step, it is poured into a solvent (Photo 2). In the second step, it is heated to 190-210°C for 21 minutes to dissolve (Photo 3). In the third step, the glass fiber and PBT resin are separated by decantation (Photo 4), and the 1,4-BG (liquid) containing the PBT resin is extracted. Photo 5 shows the solvent (liquid) containing PBT resin after extraction. When cooled, the 1,4-BG, which has a melting point of 19°C, solidifies at 21°C, as shown in (Photo 6). Photo 7 shows the recovered glass fiber GF, which has been washed with water, then with methanol, and then dried (Photo 8).

[0009] The present invention will be described below based on specific examples, but the present invention is not limited to these examples and those skilled in the art can carry out the invention based on the gist of the claims. The apparatus for carrying out the method of the present invention is divided into batch type and continuous type.

[0010] Figure 1 shows a conceptual diagram of a batch-type apparatus. The first dissolution tank V-01, which contains 1,4-butanediol as a solvent, contains a basket S-01, which filters the solvent and impurities after dissolving the PBT resin product in the solvent. The bottom of the first dissolution tank V-01 is connected to the heating tank V-02 via a solenoid valve. The heater EH-01 heats the 1,4-butanediol solvent to a temperature between 150°C and its boiling point, and the solvent is circulated to the dissolution tank via a circulation pump P-01. While the PBT solution is circulating, a portion of it is stored in an evaporation tank C-01, heated to above its boiling point under reduced pressure by a heater E-02, and evaporated 1,4-butanediol solvent is condensed and recovered in a condenser E-01. It is then temporarily stored in a solvent receiving tank V-03 and supplied to the dissolution tank V-01 via a transfer pump P-02. In this case, the PBT resin dissolved in the solvent remains in the evaporation layer C-01 and is recovered. While the entire solution containing the dissolved PBT resin may be recycled to the first dissolution tank V-01 after the PBT resin has been recovered, it is preferable to circulate a portion of the solution as is, as shown in the figure, while distilling the remainder under reduced pressure to recover 1,4-butanediol, which is then recycled. This is because 1,4-butanediol containing a portion of the dissolved PBT resin enhances the solubility of the PBT resin. The blending ratio of the dissolving agent that dissolved the PBT resin to the dissolving agent that recovered the PBT resin is maintained at at least 5:1, preferably 10:1 or greater, to prevent the PBT resin ratio in the dissolving agent in the first dissolution tank from becoming too high. The dissolution temperature is preferably adjusted to 150°C or higher, preferably 170°C or higher but below the boiling point (hereinafter, the PBT resin ratio and temperature control of the dissolving agent are the same in the continuous process).

[0011] Figure 2 shows an apparatus for continuously performing the recovery process, instead of the batch method described above. It comprises a first dissolution tank V-01 equipped with a horizontally moving first belt conveyor BC-1 and an inclined second dissolution tank V-02 equipped with a second belt conveyor BC-2 connected to it. The inlet of the first dissolution tank V-01 is equipped with a raw material inlet, and the raw material is introduced onto the first belt conveyor BC-1. The raw material is transported while immersed in the 1,4-butanediol solvent in the tank, and the PBT resin component of the PBT resin product dissolves in approximately 20 minutes at 210°C. In the second dissolution tank V-02, undissolved impurities are transported upward by the second belt conveyor BC-2 and are recovered at the top. The solvent that has dissolved the PBT resin is recovered at the junction between the first dissolution tank V-01 and the second dissolution tank V-02, and a portion of it is heated directly in heater EH-01 and circulated to the first dissolution tank V-01, while the remainder is stored in evaporation tank C-01, where the solvent is heated to its boiling point under reduced pressure in heater E-02. The evaporated solvent, 1,4-butanediol, is condensed and recovered in condenser E-01 and stored in solvent receiving tank V-03, and the solvent is supplied to the second dissolution tank V-01 via transfer pump P-02. Note that in the drawing, a portion of the recovered solution that has dissolved the PBT is circulated directly to the first dissolution tank V-01, but it is also possible to circulate all of the solution that has dissolved the PBT resin to the first dissolution tank V-01 after the PBT resin has been recovered.

[0012] Example 1: Dissolution Experiment of PBT Resin in 1,4-Butanediol A 300 ml separable flask was charged with the separating agent 1,4-butanediol. 100, 200, or 300 parts of solvent were added to 10 parts PBT resin by volume, and the mixture was heated at 210°C for 15 minutes, yielding the following results (Figure 3). In all cases, the PBT resin dissolved. When the liquid temperature was raised to 150°C, preferably 170°C, and more preferably 210°C, the viscosity was almost zero and the mixture became a transparent liquid. This demonstrates that PBT resin completely dissolves in 1,4-butanediol heated to a temperature above 150°C but below the boiling point. Since the viscosity increases as the temperature of the solvent decreases, a temperature and mixing ratio that are easy to work with should be selected.

[0013] Example 2: A PVC resin layer was formed on copper wire. Separation of PBT resin from a wire harness using PBT resin in the coupler section. 21.0 grams of the wire harness shown in Figure 5, Photo 1, was immersed in a container containing 117.3 grams of cyclohexanone and boiled at 150°C for 30 minutes to dissolve the PVC resin layer. 1.49 grams of solvent was evaporated to dryness, and 4.9 grams of PVC resin was recovered. The wire from which the PVC resin layer had been dissolved and removed is shown in Figure 4, Photo 4. This wire was then immersed in 112.7 grams of 1,4-butanediol (Figure 4, Photo 5) and boiled at 210°C for 15 minutes to dissolve and remove the PVC resin (Figure 4, Photo 6). The solvent was evaporated to dryness, and 4.3 g of PBT resin was recovered. The copper wire portion from which the PVC and PBT resin had been removed weighed 11.8 g (Figure 4, Photo 7).

[0014] Example 3: 22.6 g of reinforced plastic (PBC resin mixed with 30% glass fiber) (Fig. 6, Photo 1) was immersed in 156.4 g of 1,4-butanediol (solvent) (Fig. 6, Photo 2: 9.9 times the amount of PBT resin). This was then treated in the solvent heated to 210°C for 20 minutes (Fig. 6, Photo 3). The temperature was unstable, ranging from 190°C to 210°C. After treatment, the glass fiber GF was separated by decantation, as shown in Fig. 6, Photo 4, and the solvent (1,4-BG) containing the dissolved PBT resin was extracted (Fig. 6, Photo 5). It solidified upon cooling (Fig. 6, Photo 6). The recovered glass fiber GF (Fig. 6, Photo 7) was washed with water, washed with methanol, and dried, yielding a mass of 6.5 kg (Fig. 6, Photo 8). This demonstrates that the glass fiber GF was successfully separated and recovered from the glass fiber-reinforced plastic.

[0015] From the above examples, it can be seen that the PBT resin component can be selectively dissolved and recovered by heating the dissolving agent, 1,4-butanediol, to a temperature of 150° C. or higher and lower than the boiling point.

Claims

1. Immerse the waste containing PBT resin in a tank containing 1,4-butanediol in an amount equal to the volume of the PBT resin component sufficient for immersion, heat it while stirring within a temperature range of 150 °C or higher and its boiling point or lower under atmospheric pressure to dissolve the PBT resin component, filter the molten mixture to remove impurities, while separating and recovering 1,4-butanediol from the molten mixture after filtration, and recovering the remaining PBT resin component. A method for recovering PBT resin, characterized by the above steps.

2. The method for recovering PBT resin according to claim 1, wherein 1,4-butanediol in which PBT resin is dissolved as a PBT solvent and 1,4-butanediol from which PBT has been separated and recovered are mixed and used.

3. The method for recovering PBT resin according to claim 1 or 2, wherein when the waste containing PBT resin has a resin part other than PBT resin, the resin part other than PBT resin is removed by pretreatment.

4. An apparatus for implementing the method of claim 1, comprising: a first dissolution tank containing 1,4-butanediol, dissolving PBT resin, and having a filter therein for filtering and collecting impurities in the PBT resin product; a heating tank for recovering and heating a dissolution mixture of 1,4-butanediol in which PBT resin is dissolved; a branch path for circulating a part of the heated dissolution mixture to the first dissolution furnace while delivering the remaining part to an evaporation tank; an evaporation tank for heating the delivered remaining molten mixture and evaporating 1,4-butanediol under reduced pressure; a condenser for condensing the evaporated 1,4-butanediol; a receiving tank for storing the condensed and recovered 1,4-butanediol; and a path for circulating 1,4-butanediol from the receiving tank to the first dissolution tank. A batch-type PBT recovery apparatus.

5. An apparatus for implementing the method of claim 1, comprising: a first dissolution tank containing 1,4-butanediol, dissolving PBT resin, and incorporating a filter for filtering and collecting impurities in the PBT resin product; a heating tank for recovering and heating a dissolution mixture of 1,4-butanediol in which the PBT resin is dissolved; a branch path for delivering the heated dissolution mixture to an evaporation tank; an evaporation tank for heating the delivered molten mixture and evaporating 1,4-butanediol under reduced pressure; a condenser for condensing the evaporated 1,4-butanediol; a receiving tank for storing the condensed and recovered 1,4-butanediol; and a path for circulating 1,4-butanediol from the receiving tank to the first dissolution tank, the batch-type PBT recovery apparatus.

6. An apparatus for implementing the method of claim 1, comprising: a first dissolution tank containing 1,4-butanediol, dissolving PBT resin, and comprising a first belt conveyor for conveying the PBT resin product from an inlet to an outlet; a second dissolution tank communicating with the first dissolution tank and comprising a second belt conveyor for recovering undissolved matter from the PBT resin product; a branch path for recovering a dissolution mixture of 1,4-butanediol in which the PBT resin is dissolved from a connection portion between the first dissolution tank and the second dissolution tank and circulating it to the first dissolution tank via a heater, while delivering the remainder to an evaporation tank; an evaporation tank for heating the delivered molten mixture and evaporating 1,4-butanediol; a condenser for condensing the evaporated 1,4-butanediol; a receiving tank for storing the condensed and recovered 1,4-butanediol; and a path for circulating 1,4-butanediol from the receiving tank to the first dissolution tank, the continuous-type PBT recovery apparatus.

7. An apparatus for implementing the method of claim 1, comprising: a first dissolution tank containing 1,4-butanediol, dissolving PBT resin, and conveying a PBT resin product from an inlet to an outlet, and having a first belt conveyor; a second dissolution tank communicating with the first dissolution tank and having a second belt conveyor for recovering undissolved matter from the PBT resin product; a heating unit for recovering and heating a dissolution mixture of PBT resin dissolved in 1,4-butanediol from a connection part between the first dissolution tank and the second dissolution tank; an evaporation tank for heating the delivered molten mixture and evaporating 1,4-butanediol; an aggregator for aggregating the evaporated 1,4-butanediol; a receiving tank for storing the aggregated and recovered 1,4-butanediol; and a continuous PBT recovery apparatus having a path for circulating 1,4-butanediol from the receiving tank to the first dissolution tank.

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