Magnetically recoverable superparamagnetic nanocatalyst for polyester depolymerization

Abstract

The present invention relates to a magnetically recoverable superparamagnetic nanocatalyst for polyester depolymerization. A zinc-containing ferrite nanocatalyst for depolymerization can be used in polymer decomposition to reduce the energy required for a process and the energy required for separation, can be reused following separation, and provides large environmental and economic advantages when reused.

Description

Magnetically recoverable superparamagnetic nanocatalyst for polyester depolymerization

[0001] The present invention provides a superparamagnetic nanocatalyst for polyester depolymerization that can be recovered by a magnet.

[0002] The vast amount of plastic waste generated globally is generally disposed of through landfilling and incineration, and these disposal methods have adverse environmental impacts and result in resource loss. Among plastic waste, polyester, represented by PET (polyethylene terephthalate), is recovered separately and processed through mechanical recycling. However, mechanical recycling has problems such as a narrow range of raw materials and degradation of physical properties.

[0003] Various studies have been conducted to address the problems associated with the processing of such polyesters. Chemical recycling is a method that involves decomposing the polymer down to its raw monomers and then repolymerizing them; this not only prevents resource loss but also theoretically ensures no degradation of physical properties. Depending on the type of solution used, chemical recycling of polyester includes hydrolysis, methanol decomposition, and glycol decomposition, with glycol decomposition offering the mildest process conditions among the various methods. Nevertheless, chemical recycling has limitations, such as requiring significant energy due to high reaction temperatures and pressures. To overcome these issues, it is necessary to develop catalysts that lower the process temperature of the glycol decomposition of polyester.

[0004] Conventional technology includes a method of lowering the process temperature using a zinc acetate catalyst. This method lowers the process temperature to 196°C for the glycol decomposition of polyester using a homogeneous catalyst containing zinc. However, this methodology has the limitation that it is difficult to separate the catalyst from the reactants after the process. Another conventional technology involves the glycol decomposition of polyester using a heterogeneous catalyst utilizing ZnMnO2 nanoparticles. Although separation is possible due to the characteristics of the heterogeneous catalyst, the separation process is more complex compared to the method using magnets.

[0005] Accordingly, there is a need to develop polyester glycol decomposition catalysts that exhibit high activity and are easy to separate with a magnet.

[0006] The objective of the present invention is to provide a catalyst composition for polyester depolymerization comprising nanoparticles as an active ingredient.

[0007] Another objective of the present invention is to provide a nanoparticle catalyst for polyester depolymerization comprising nanoparticles as an active ingredient.

[0008] Another objective of the present invention is to provide a method for purifying bis-2-hydroxyethyl terephthalate (Bis(2-hydroxylethyl)terephthalate; BHET) using a nanoparticle catalyst for polyester depolymerization containing the nanoparticles as an active ingredient.

[0009] To achieve the above objective, the present invention provides a catalyst composition for polyester depolymerization comprising nanoparticles represented by the following chemical formula 1 as an active ingredient.

[0010] [Chemical Formula 1]

[0011] Zn x Fe 3-x O4

[0012] The above x is 0.25 to 2.

[0013] In addition, the present invention provides a nanoparticle catalyst for polyester depolymerization comprising a nanoparticle represented by the above chemical formula 1 as an active ingredient.

[0014] In addition, the present invention provides a method for purifying bis-2-hydroxyethyl terephthalate (Bis(2-hydroxylethyl)terephthalate; BHET), characterized by comprising: a first step of preparing a nanoparticle catalyst for polyester depolymerization; and a second step of depolymerizing in the presence of the prepared catalyst.

[0015] The present invention relates to a superparamagnetic nanocatalyst for polyester depolymerization that can be recovered by a magnet. The magnetically recoverable zinc-containing ferrite depolymerization nanocatalyst can be used for polyester decomposition to reduce the energy required for the process and separation, and can be reused after separation, offering significant advantages from an environmental and economic perspective.

[0016] Figure 1 shows a schematic diagram of the nanocatalyst manufacturing process.

[0017] Figure 2 shows the analysis results according to transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS).

[0018] Figure 3 shows the structure and structural schematic diagram through XRD.

[0019] Figure 4 shows data confirming whether the ligand of the nanocatalyst was replaced through FT-IR.

[0020] Fig. 5 shows Zn x Fe 3-x O4 nanoparticles were used as a PET decomposition catalyst, and a schematic diagram of separation by magnet is shown.

[0021] Figure 6 shows data confirming the magnetic moment of the nanocatalyst.

[0022] Figure 7 shows data confirming the yield of BHET according to the catalyst composition.

[0023] Figure 8 shows a schematic diagram of the depolymerization of PET according to the ester exchange reaction mechanism.

[0024] Figure 9 shows data confirming whether the product obtained through the nano-catalyst is identical to BHET.

[0025] The present invention will be described in more detail below.

[0026]

[0027] The present invention provides a catalyst composition for polyester depolymerization comprising nanoparticles represented by the following chemical formula 1 as an active ingredient.

[0028] [Chemical Formula 1]

[0029] Zn x Fe 3-x O4

[0030] The above x is 0.25 to 2.

[0031] The above Zn and Fe can form a spinel structure.

[0032] The above nanoparticles may have an average particle size of 4 to 20 nm.

[0033] The above nanoparticles can be capped with citric acid ions.

[0034] The above polyester may be any one of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), PTT (Polytrimethylene terephthalate), PEN (Polyethylene naphthalate), polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipice (PEA), polybutylene succinate (PBS), and PHBV (Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)).

[0035] The above composition has superparamagnetism, so polyester can be separated by a magnet.

[0036]

[0037] In addition, the present invention provides a nanoparticle catalyst for polyester depolymerization comprising a nanoparticle represented by the above chemical formula 1 as an active ingredient.

[0038]

[0039] In addition, the present invention provides a method for purifying bis-2-hydroxyethyl terephthalate (Bis(2-hydroxylethyl)terephthalate; BHET), characterized by comprising: a first step of preparing a nanoparticle catalyst for polyester depolymerization; and a second step of depolymerizing in the presence of the prepared catalyst.

[0040] After the second step above, a third step of separating the catalyst; and a fourth step of purifying the generated monomer from impurities using an ion exchange resin may be additionally included.

[0041]

[0042] Hereinafter, to aid in understanding the present invention, examples and the like will be described in detail. However, the following examples and the like are merely illustrative of the content of the present invention and the scope of the present invention is not limited to the following examples and the like. The examples and the like of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0043]

[0044] [Example 1] Zn x Fe 3－x Synthesis method of O4 nanoparticles

[0045] 1) Fe(acac)3, Zn(acac)2, 1,2-hexadecanediol, oleic acid, and oliloramine were weighed and added to a solvent (benzyl ether), and moisture was removed under vacuum at 70°C for 1 hour. (10 minutes required for 25°C > 70°C)

[0046] 2) After switching to an argon (Ar) atmosphere, the temperature was raised to 200 ℃ and heated for 2 hours. (70 ℃ > 200 ℃ takes 30 minutes)

[0047] 3) After raising the temperature to 300 ℃, heated for 1 hour. (200 ℃ > 300 ℃ took 40 minutes)

[0048] 4) After removing the heat source and cooling to room temperature, the process was carried out using ethanol and toluene.

[0049]

[0050] [Example 2] Ligand replacement method

[0051] 1) The nanoparticles obtained in Example 1 above were mixed with tetrahydrofuran (THF) at a ratio of 5 g / L.

[0052] 2) The above mixed solution and 0.1 M sodium citrate buffer solution were mixed in a 2:1 ratio and heated at 65°C for 15 minutes.

[0053] 3) Afterwards, the mixture was centrifuged at 12,000 rpm for 2 to 3 minutes and dispersed in ethanol.

[0054] 4) The obtained nanoparticles were dispersed in ethylene glycol at a concentration of 1 mg / ml.

[0055]

[0056] [Example 3] Polyethylene Terephthalate Decomposition Experiment Method

[0057] To 1 g of polyethylene terephthalate (hereinafter referred to as PET), 1 wt% of the nanoparticles of Example 1 or 2 and 20 ml of ethylene glycol were added, and moisture was removed under vacuum at 200 rpm and 70°C for 1 hour. Subsequently, the mixture was reacted at 175-195°C under an argon atmosphere with stirring at 500 rpm. The heating rate was 2°C / min. After the reaction was complete, the catalyst was separated from the product using a magnet for one day, and the yield was calculated using HPLC. The PET that did not undergo the reaction was filtered through filter paper, dried, and used for the conversion calculation.

[0058] - PET conversion (%) = (m PET,i -m PET,t) / m PET,i *100

[0059] - PET Yield (%) = (m BHET / M BHET ) / (m PET / M PETrepatingunit )*100

[0060]

[0061] [Example 4] Device and measurement method

[0062] Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) analysis was performed using a Thermo Fisher Scientific Talos F200S instrument operating at an acceleration voltage of 200 kV.

[0063] X-ray diffraction (XRD) (D2 Phaser, Bruker, Germany) was operated in reflection mode with Cu-Ka radiation (k = 0.1524 nm) at angles ranging from 15 to 80 degrees for 2 hours.

[0064] Vibrational Sample Magnetography (VSM) (Lake Shore 7407-S, USA) was performed to obtain the magnetization loops of nanoparticles at room temperature in magnetic fields up to 10 kOe. Fourier Transform Infrared Spectroscopy (ATR FT-IR) measurements were performed using a VERTEX 70 FT-IR spectrometer (Bruker).

[0065] 1 H and 13 C nuclear magnetic resonance (NMR) spectra were obtained using a JEOL ECZ500R / S1 500 MHz instrument. Chemical shifts were given in ppm (d) for tetramethylsilane (TMS) using DMSO-d6 as an internal standard.

[0066] The thermal properties of the material were measured by thermogravimetric analysis (TGA) in a nitrogen atmosphere using a Mettler Toledo TGA / DSC 1 instrument. Measurements were taken under a nitrogen atmosphere at a heating rate of 10 °C / min.

[0067] High performance liquid chromatography (HPLC) was performed using an Agilent 1260 Infinity II LC system with a flow rate of 0.5 mL / min, a sample injection volume of 10 μl, and a detector of 254 nm, with methanol and water mixed in a 7:3 ratio as the solvent.

[0068]

[0069] [Experimental Example 1] Zn x Fe 3-x Synthesis of O4 nanoparticles

[0070] Zn x Fe 3-x O4 nanoparticles were synthesized using the heat-up method described earlier, and the synthesized Zn x Fe 3-x The size and composition of O4 nanoparticles were confirmed through TEM and EDS, and the exact composition ratio was confirmed through ICP. TEM data showed that the nanoparticles were synthesized with a uniform size of 6-7 nm, and EDS confirmed that iron and zinc were synthesized in a uniformly distributed state without clumping together (Fig. 2).

[0071] Synthesized Zn x Fe 3-x The structure of O4 nanoparticles was analyzed using XRD. XRD data was obtained as shown in Figure 3, and 29.7 o , 34.8 o , 42.4 o , 53.2 o , 56.5 o , 70.9 o , 73.5 o and 74.3 o A peak occurred at Zn x Fe 3-xO4 nanoparticles have a spinel structure, and it was confirmed that the diffraction patterns are shown in the (200), (311), (400), (422), (511), (440), (620), and (533) planes of the structure (Fig. 3). In addition, in Fig. 3, the structure in the (100) direction of the spinel structure, in the form of AB2O4, the bright element represents the A site and the dark element represents the B site.

[0072] Zn x Fe 3-x The O4 nanoparticles were replaced from an oleate ligand to a citrate ligand through Example 2 above, and the ligand replacement was confirmed via FT-IR (Fig. 4). As the ligand changed from the existing oleate ligand to citrate, 3370 cm⁻¹ -1 Wavelength and 895 cm -1 A peak corresponding to the -OH group of the wavelength appeared. 1529 cm⁻¹ of oleate -1 At this wavelength, the C=C peak disappeared, and the peak of the OCO resonance structure, 1600 cm⁻¹, was reached. -1 and 1395 cm -1 It originated at. In addition, the common CH2 peak is 2922 cm. -1 And 2850 cm -1 Silver is visible in both sets of data and is 580 cm⁻¹, a bond between metal and oxygen. -1 All the peaks at were also visible.

[0073]

[0074] [Experimental Example 2] Zn x Fe 3-x Confirmation of use of O4 nanoparticles as PET decomposition catalyst and separation by magnet (Fig. 5)

[0075] Zn x Fe 3-xThe magnetism of O4 nanoparticles was measured using VSM, and it was confirmed that they exhibit superparamagnetism. The bulk spinel structure of ZnFe2O4 contains Zn 2+ Occupying this A site, Fe 3+ Ga occupies site B, so Fe 3+ The Hall spins were completely canceled out by antiferromagnetic coupling, so no magnetism was observed. However, when ZnFe2O4 reaches the nanoscale, a change in cation distribution occurs, and Zn 2+ Part of is at site B, Fe 3+ A portion of it exists at the A site, and as a result, in nanoscale spinel ZnFe2O4, Fe 3+ It was confirmed that a significant number of hole spins did not cancel each other out, resulting in a ferrimagnetic spin configuration. Since the nanocatalyst has a small particle size of several nanometers, the thermal energy at room temperature becomes greater than the magnetic anisotropic energy, causing it to possess superparamagnetism. Accordingly, the nanocatalyst exhibited high dispersibility without clumping due to residual excitation in solution, as no residual excitation was observed at an external magnetic field of zero. Meanwhile, due to its superparamagnetism, the nanocatalyst exhibited a high magnetization of approximately 50 emu / g at a magnetic field of 1T, which was attributed to the high magnetic moment of the nanocatalyst (Fig. 6). The nanocatalyst possessing these superparamagnetic properties could be easily separated using a magnet after the PET depolymerization reaction.

[0076]

[0077] [Experimental Example 3] Zn x Fe 3-x Application of O4 nanocatalysts as glycolysis depolymerization catalysts

[0078] BHET (bis(2-hydroxyethyl terephthalate)) was obtained by reacting PET with ethylene glycol as a solvent in the presence of a catalyst at 180 °C for 2 hours. High yields of over 95% were observed for all compositions, and the yield increased as the Zn content increased, indicating that Zn 0.75 Fe 2.25 In the case of the O4 catalyst, a very high yield of 99.28% was observed (Fig. 7).

[0079]

[0080] [Experimental Example 4] Zn x Fe 3-x PET depolymerization results of O4 nanocatalyst

[0081] The depolymerization of PET occurred via the ester exchange reaction mechanism shown in Fig. 8. Zn 2+ Increases the rate of the ester exchange reaction in the presence of Zn 2+ It acts as a Lewis acid and receives electrons from the carbonyl oxygen of PET, which leads to an electron deficiency on the carbonyl carbon and promotes a nucleophilic attack, thereby strengthening the ester exchange reaction by ethylene glycol.

[0082] The carboxylate group of the citrate used as a ligand in this nanocatalyst increased the rate of nucleophilic attack of ethylene glycol. The carboxylate of the citrate formed hydrogen bonds with the hydrogen of ethylene glycol, weakening the bond between the oxygen of the hydroxyl group and the hydrogen. The ester exchange reaction is a reaction in which the lone pair of electrons on the oxygen of the hydroxyl group of ethylene glycol attacks the carbonyl carbon of PET, causing the ester to detach. As the oxygen of the hydroxyl group became more electron-rich, its nucleophilicity increased, strengthening the nucleophilic attack and promoting the breakdown of the ester bond.

[0083] The obtained results were HNMR and C 13 Structural analysis was performed using NMR and FT-IR, and it was found to be identical to BHET. TGA analysis also revealed that the thermal properties were identical (Fig. 9).

[0084]

[0085] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0086] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

1. A catalyst composition for polyester depolymerization comprising nanoparticles represented by the following chemical formula 1 as an active ingredient: [Chemical Formula 1] Zn x Fe 3-x O4 The above x is 0.25 to 2.

2. A catalyst composition for polyester depolymerization according to Claim 1, characterized in that the Zn and Fe have a spinel structure.

3. A catalyst composition for polyester depolymerization according to claim 1, characterized in that the nanoparticles have an average particle size of 4 to 20 nm.

4. A catalyst composition for polyester depolymerization according to claim 1, characterized in that the nanoparticles are capped with citric acid ions.

5. A catalyst composition for polyester depolymerization according to claim 1, wherein the polyester is any one of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), PTT (en: Polytrimethylene terephthalate), PEN (en: Polyethylene naphthalate), polyglycolide (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipic acid (PEA), polybutylene succinate (PBS), and PHBV (Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)).

6. A catalyst composition for polyester depolymerization according to claim 1, characterized in that the composition has superparamagnetism and can separate polyester with a magnet.

7. A nanoparticle catalyst for polyester depolymerization comprising nanoparticles represented by the following chemical formula 1 as an active ingredient: [Chemical Formula 1] Zn x Fe 3-x O4 The above x is 0.25 to 2.

8. A first step of preparing a nanoparticle catalyst for polyester depolymerization according to Claim 7; and A method for purifying bis-2-hydroxyethyl terephthalate (Bis(2-hydroxylethyl)terephthalate; BHET), characterized by comprising a second step of depolymerizing in the presence of the prepared catalyst.

9. A method for purifying bis-2-hydroxyethyl terephthalate (Bis(2hydroxylethyl)terephthalate; BHET) according to claim 8, further comprising: a third step of separating the catalyst after the second step; and a fourth step of purifying the generated monomer from impurities using an ion exchange resin.

Images