KR20210067749A - Chemically recycling method of waste polyethylene terephthalate by depolymerization using fibrous perovskite catalyst - Google Patents

Abstract

The present invention relates to a fibrous perovskite catalyst represented by general formula: A_χA'_(1-χ)B_(1-y)B'_yO_(3-δ), a method for manufacturing the fibrous perovskite catalyst, and PET depolymerization applications providing high yields. Since a perovskite catalyst of the present invention has a large surface are to volume, it is advantageous for the reaction, and can be used in the depolymerization of waste PET to provide a high yield of BHET.

Description

Chemical recycling method of waste polyethylene terephthalate by depolymerization using fibrous perovskite catalyst

The present invention relates to a method for chemical recycling of waste polyethylene terephthalate (hereinafter abbreviated as 'waste PET') through depolymerization using a perovskite catalyst. Specifically, it relates to an improved method of recycling waste PET, which can obtain high yield of BHET by using the perovskite catalyst according to the present invention in a conventional waste PET glycolysis depolymerization reaction.

Polyester has excellent physical properties such as thermal stability, transparency, and strength compared to its price, and is widely used because it has many utility in various fields such as films, beverage bottles, and textiles. The total world production of polyester was between 25 and 3,000 tonnes in 2000. This value increased to 55 million tonnes in 2012, mostly composed of polyethylene terephthalate (PET).

High demand for textile applications as well as food packaging and bottle markets for glass fiber solids has led to a significant increase in polyester consumption in textiles and molding resins.

As consumption has increased tremendously, it is very important to economically recycle polyester in terms of resources and the environment, as the most practical solution for sustainability.

There are four ways to recycle PET (primary recycling, secondary material recycling, tertiary chemical recycling, and quaternary thermal energy recovery). Among these approaches, the most suitable method from the perspective of sustainability is tertiary (chemical) recycling. . This is because this process produces the monomers from which the polymer was originally prepared.

Conventional PET chemical recycling method is divided into oligomer recovery method glycolysis (glycolysis), monomer recovery method methanolysis (methanolysis), hydrolysis (hydrolysis). Specifically, in order to chemically recycle PET, the PET polymer chain is decomposed through decomposition reactions such as glycolysis by glycol-based compounds, methanolysis by methanol, and hydrolysis by water, and then through a separation and purification process. Monomers or polyester oligomers such as MEG, DMT, and PTA were obtained. The materials thus obtained can be used to synthesize polyesters.

In particular, the glycolysis depolymerization reaction has the advantage that depolymerization is performed under a lower temperature and pressure compared to other chemical recycling processes and the treatment process is simple. The glycolysis depolymerization reaction is specifically a method of recovering BHET (bis-hydroxyethyl terephthalate) and EG through the reaction of PET and EG (ethylene glycol). Under pressure, BHET and oligomers are produced using an excess of glycol, usually EG, in the temperature range of 180 to 240°C. The resulting BHET must be purified using melt filtration, usually under pressure, before it can be used to produce new PET polymers. Depolymerization is usually carried out in the presence of a transition metal acetate catalyst such as zinc acetate or lithium acetate, or a zinc-based catalyst. However, these conventional catalysts have a problem of low yield.

Accordingly, there is a need to develop a catalyst for obtaining BHET in high yield by a waste PET glycolysis depolymerization method instead of a conventional transition metal acetate catalyst or a zinc-based catalyst.

One object of the present invention is to provide a novel fibrous perovskite catalyst that can be used as a high-efficiency catalyst leading to BHET production in high yield in the glycolytic depolymerization reaction of waste PET.

Another object of the present invention is to provide a method for preparing a novel perovskite catalyst according to the present invention.

This will be described in detail as follows. Meanwhile, each description and embodiment disclosed in the present invention may be applied to each other description and embodiment. That is, all combinations of the various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be considered that the scope of the present invention is limited by the specific descriptions described below.

As a first aspect of the present invention, in order to achieve the above object, the present invention provides a fibrous perovskite catalyst having a chemical composition represented by the following general formula (1):

[General formula 1]

A _χ A' _(1-χ) B _(1-y) B' _y O _3-δ

where A and A' are each independently Li, Na, Mg, K, Ca, Sc, Mn, Fe, Co, Cu, Zn, Rb, Sr, Y, Mo, Tc, Cd, In, Te, Cs , Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Hg, Tl, Pb, Bi, Po, Ra, Th , Pa, U, Np, and an element differently selected from the group consisting of Pu, and B and B' are each independently Li, Be, Al, Si, P, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi, Po, At, Th, Pa, Elements differently selected from the group consisting of U, Np and Pu, where x is 0.01 to 0.99, y is 0.01 to 0.99, and δ represents oxygen deficiency.

As a second aspect of the present invention, in order to achieve the above object, the present invention comprises a first step of dissolving an inorganic compound sample containing a transition metal element in a solvent to prepare a catalyst precursor solution;

a second step of preparing a mixed solution of a catalyst precursor and a polymer by adding a polymer to the catalyst precursor solution and stirring;

a third step of preparing a fibrous catalyst by electrospinning the mixed solution; and

A fourth step of calcining the electrospun fibrous catalyst to remove residual polymer and nitrate in the catalyst; provides a method for producing a perovskite catalyst having a chemical composition represented by Formula 1, including a.

Hereinafter, the present invention will be described in more detail.

As used herein, the term "perovskite (Perovskite)" is a cubic crystal structure represented _{by the formula ABR 3 .} One chemical unit (ABR ₃ ) is included in the unit cell. R is usually oxygen or a halogen element such as Cl, Br, or I. B is usually a metal ion with a coordination number of 6. A is a large atom with a coordination number of 12, and metals such as Ca, K, Na, Pb, and Sr are used. Whether a particular perovskite material is stable is predicted by a tolerance factor (t). It is known that the perovskite structure is stable when t is 0.8~1.0. Depending on the composition, it exhibits various functions such as ferroelectricity, semiconductivity, superconductivity, mixed conductivity, electro-optical effect, and catalytic function.

As used herein, the term "transition metal" is also referred to as a transition element, and includes all elements from Groups 3 to 12 of the periodic table.

As used herein, the term "depolymerization" refers to a phenomenon in which natural or synthetic polymers are decomposed into units. This corresponds to the reverse reaction of the polymerization reaction. When it is decomposed by heating, a unit is produced. Like polymerization, this reaction is also used industrially.

Chemical decomposition of polyester refers to PET depolymerization, and PET depolymerization is classified into glycolysis, methanolysis, hydrolysis, ammonolysis, and the like.

As used herein, the term "glycolysis" is the simplest and oldest PET (poly(ethyleneterephthalate)) depolymerization method. Compared to other processes, PET depolymerization is carried out under a relatively stable temperature and pressure, and the process is simple. As shown in Reaction Scheme 1 below, ethylene glycol (EG) is usually used, and is performed in the presence of a catalyst. PET reacts with EG to recover bis(hydroxyethyl terephthalate) (BHET), a monomer of PET. BHET is widely used in the synthesis of many polymers such as unsaturated polyester, PET, and polyurethane.

[Scheme 1]

Since the perovskite catalyst of the present invention has a large surface area to volume ratio, it is advantageous for the reaction and can be used in PET glycolysis depolymerization to obtain BHET in high yield.

In the first aspect of the present invention, x and y in General Formula 1 are preferably, x is 0.15 to 0.85, and y may be 0.25 to 0.75, but is not limited thereto.

As a preferred perovskite catalyst of the first aspect of the present invention, a catalyst having a chemical composition of the following formula (1) may be exemplified, but is not limited thereto.

[Formula 1]

La _0.8 Ce _0.2 Ti _0.7 Ni _0.3 O ₃

According to the second aspect of the present invention, the method for preparing a fibrous perovskite catalyst includes a first step of dissolving an inorganic compound sample containing a transition metal element in a solvent to prepare a catalyst precursor solution;

a second step of preparing a mixed solution of a catalyst precursor and a polymer by adding a polymer to the catalyst precursor solution and stirring;

a third step of preparing a fibrous catalyst by electrospinning the mixed solution; and

A fourth step of calcining the electrospun fibrous catalyst to remove residual polymer and nitrate in the catalyst; may include.

Specifically, the inorganic compound containing the transition metal element of the first step is La(NO₃)₃6H₂O, Ce(NO₃) ₃ , Sr(NO ₃ ) ₂ , Ni(NO ₃ ) _{2 ,} titanium isopropoxide (Titanium) (IV) isopropoxide), or Cerium (III) nitrate hexahydrate (Ce(NO ₃ ) ₃ ·6H ₂ O), but is not limited thereto.

Specifically, the solvent of the first step is, for example, N,N-dimethylformamide (N,N-Dimethylformamid (DMF)), ethyl alcohol (Ethyl alcohol), DI-water, dimethylacetamide (Dimethylacetamide (DMAc) )), tetrahydrofuran (Tetrahydrofuran (THF)) and the like may be included, but is not limited thereto.

Polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polysulfone (PSF), etc. can be used, but is not limited thereto.

The polymer additive in the second step may be added in an amount of 1 to 99% by weight based on the total weight of the catalyst precursor solution, but if necessary, the amount of the polymer additive added (mixed) may be adjusted to adjust dispersibility and/or viscosity. can be changed appropriately for

The stirring of the second step may be performed, for example, at 10 to 30° C. for 1 hour to 12 hours, but if necessary, the stirring conditions may be changed so that the precursor and the polymer additive are well dispersed.

The electrospinning of the third step may be performed at 0% RH to 60% RH, but is not limited thereto.

When the humidity exceeds 60% RH during electrospinning, since the solvent is not evaporated, it is not electrospun in the form of a fiber, so it may be difficult to prepare a catalyst in the form of a nanofiber.

Preferably, it may be carried out at 10 Kv to 30 kV, 0.5 ml/h to 2.0 ml/h, 10% RH to 50% RH, and 30° C. to 40° C. conditions.

The sintering in the fourth step may be performed under conditions of 500° C. to 1400° C. for 1 hour to 50 hours, but the conditions may be changed if necessary.

When the calcination temperature is less than 500 ℃, since all the polymer is not removed, a pure catalyst cannot be obtained, and when it exceeds 1400 ℃, some precursor elements are melted, thereby destroying the structure of the catalyst.

Preferably, the sintering may be performed for 5 to 7 hours, 700 to 900° C. 1° C./min temperature rise condition.

Since the perovskite catalyst of the present invention has a large surface area to volume ratio, it is advantageous for the reaction, and can be used in the depolymerization of waste PET to provide a high yield of BHET.

1 is a schematic diagram showing the inside of a microwave reactor used in the PET depolymerization reaction.
2 is a graph showing the results of FT-IR analysis of PET, BHET, and products produced after PET depolymerization.
3 is a graph showing the results of TGA analysis of PET, BHET, and products produced after depolymerization of PET.
4 is a schematic diagram showing a PET depolymerization reaction.
5 is a SEM photograph showing the fibrous perovskite catalyst of the present invention.

Hereinafter, the present invention will be described in more detail through examples. These Examples are for explaining the present invention in more detail, and the scope of the present invention is not limited by these Examples.

Preparation Example 1: Method for preparing nanofibrous perovskite catalyst

A perovskite type (ABO ₃ ) nanofibrous catalyst was prepared.

Specifically, lanthanum nitrate hexahydrate (La(NO₃)₃6H₂O)), nickel nitrate (Ni(NO ₃ ) ₂ )), cerium nitrate hexahydrate (Cerium(III) nitrate hexahydrate (Ce(NO ₃ )) ₃ 6H ₂ O)), titanium isopropoxide (Titanium(IV)isopropoxide) was _{calculated according to the stoichiometric ratio (La 0.8} Ni _0.3 Ce _0.2 Ti _0.7 O ₃ ) N,N-dimethylform A catalyst precursor solution was prepared by dissolving 12 wt% in 7 g of amide (N,N-Dimethylformamid (DMF)) solvent.

1 g of polyvinylpyrrolidone (PVP, MW = 1,300,000)) was added to the prepared catalyst precursor solution as a polymer additive and stirred at room temperature for 3 hours to prepare a uniform precursor-polymer additive mixed solution. The prepared precursor mixed solution was ^{electrospun under 18 kV, 1.2 mL h -1} feed flow conditions. The tip size used was 30G (0.15 mm, inner diameter), and the length between the tip and the drum collector was adjusted to 15 cm. In addition, 30% RH (relative humidity) and 35 ℃ atmosphere was maintained during electrospinning. Residual PVP and nitrate were removed from the electrospun fibrous catalyst and calcined at 800° C. for 6 hours to form a perovskite structure. The fibrous perovskite catalyst (La _0.8 Ce _0.2 Ni _0.3 Ti _0.7 O ₃ ) was obtained.

As shown in FIG. 5 , the fibrous perovskite catalyst prepared in Preparation Example 1 was confirmed.

Example 1: Glycolytic Depolymerization of PET

0.1 g of polyethylene terephthalate (PET) was dispersed in 30 g of ethylene glycol, and the fibrous perovskite catalyst prepared in Preparation Example 1 was added in an amount of 0.1% compared to PET, and sonication was performed. ) to disperse. Then, a reflux condenser was connected to the microwave reactor as shown in FIG. 1, and a depolymerization reaction using a microwave/catalyst was performed for 30 minutes under the conditions of 1000 W and 196° C. while stirring at 500 rpm with a magnetic bar.

After reacting for 30 minutes for the above reaction time, the mixture is first filtered using hot water, the filtered liquid phase is stirred for 6 hours under normal temperature and atmospheric pressure conditions, and then the monomer is recrystallized in a refrigerator 2℃ atmosphere for 48 hours. did. The resulting monomer crystals were subjected to a secondary filter using cold water and dried in an oven at 60° C. to obtain BHET (Bis(2-Hydroxyethyl) terephthalate) (yield = 88%).

The yield of the obtained BHET monomer was calculated using Equation (1) below.

Test Example 1: FT-IR analysis

In order to confirm the generation of BHET monomer according to PET depolymerization through microwave/catalytic reaction, a comparative analysis was performed on PET before the reaction, the product of Example 1 that was secondarily filtered, and Sigma-Aldrich's BHET reagent as a control.

As shown in Figure 2, it was confirmed that the spectrum of PET and the spectrum of the product after depolymerization were significantly different, ^{and 3500 cm -1} _{corresponding to the -OH group, which was not seen in PET, and -CH 2} OH corresponding to the end of BHET. It was confirmed that the corresponding 3000 cm ^-1 peaks were generated. It was confirmed that this was the same as the BHET reagent measured comparatively as a control. It was confirmed that PET was decomposed into BHET monomers through the microwave/perbroshite catalyzed depolymerization reaction of Example 1.

Test Example 2: TGA analysis

The product BHET monomer of Example 1 was also confirmed by TGA (thermogravimetric analysis).

As shown in Figure 3, in the case of the product after the microwave / perbroskite catalyzed depolymerization reaction, whereas PET is thermally decomposed at about 450 ° C, thermal decomposition in two sections around 230 ° C and 450 ° C was confirmed. did. It was confirmed that this is the same pyrolysis section as the BHET reagent.

Test Example 3: BHET yield analysis comparison

The yield of BHET monomers according to the microwave/perbroskite catalyzed depolymerization reaction was analyzed and shown in Table 1 below.

BHET yield (%) Non-catalyst - Zinc-based commercial catalyst 76 Perovskite-type nanofibrous catalyst of the present invention 88

As shown in Table 1, it was confirmed that the BHET yield when using the perovskite-type nanofibrous catalyst of the present invention was about 88%. Compared to the BHET yield of about 76% when using a Zinc-based commercial catalyst used for conventional microwave/catalytic depolymerization, it can be seen that the catalyst of the present invention exhibits a high yield.

Summarizing the results of Test Examples 1 to 3 of the present invention, since the fibrous perbroskite catalyst of the present invention can provide a wide catalytic reaction surface in its structure, it is advantageous for the reaction, resulting in a high waste PET decomposition rate and significantly improved BHET yields can be provided. Therefore, the fibrous perovskite catalyst of the present invention is expected to have great industrial application in the field of chemical recycling of waste plastics.

From the above description, those skilled in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof. In this regard, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention should be construed as being included in the scope of the present invention, rather than the above detailed description, all changes or modifications derived from the meaning and scope of the claims described below and their equivalents.

Claims (10)

As a fibrous perovskite catalyst having a chemical composition represented by the following general formula 1,
[General formula 1]
A _χ A' _(1-χ) B _(1-y) B' _y O _3-δ
where A and A' are each independently Li, Na, Mg, K, Ca, Sc, Mn, Fe, Co, Cu, Zn, Rb, Sr, Y, Mo, Tc, Cd, In, Te, Cs , Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Hg, Tl, Pb, Bi, Po, Ra, Th , Pa, U, Np, and an element differently selected from the group consisting of Pu, and B and B' are each independently Li, Be, Al, Si, P, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi, Po, At, Th, Pa, Elements differently selected from the group consisting of U, Np and Pu, wherein x is 0.01 to 0.99, y is 0.01 to 0.99, and δ represents oxygen deficiency.
According to claim 1,
The catalyst is a PET depolymerization use, the perovskite catalyst.
According to claim 1,
The perovskite catalyst is a perovskite catalyst comprising the following formula (1):
[Formula 1]
La _0.8 Ce _0.2 Ti _0.7 Ni _0.3 O _3.
A first step of preparing a catalyst precursor solution by dissolving an inorganic compound sample containing a transition metal element in a solvent;
a second step of adding a polymer additive to the catalyst precursor solution and stirring to prepare a mixed solution of the catalyst precursor and the polymer additive;
a third step of preparing a fibrous catalyst by electrospinning the mixed solution; and
A method for producing a fibrous perovskite catalyst according to claim 1, comprising a; a fourth step of calcining the electrospun fibrous catalyst to remove residual polymer additives and nitrates in the catalyst.
5. The method of claim 4,
The solvent is N,N-dimethylformamide (N,N-Dimethylformamid (DMF)), the method for producing a fibrous perovskite catalyst.
5. The method of claim 4,
The polymer additive is polyvinylpyrrolidone (PVP), a method for producing a fibrous perovskite catalyst.
5. The method of claim 4,
The polymer additive is added in an amount of 1 to 99% by weight based on the total weight of the precursor solution.
5. The method of claim 4,
The stirring is carried out for 1 hour to 12 hours at 10 to 30 ℃, the method for producing a fibrous perovskite catalyst.
5. The method of claim 4,
The electrospinning method of producing a fibrous perovskite catalyst, which will be carried out in a humidity condition of 0% RH to 60% RH.
5. The method of claim 4,
The method for producing a fibrous perovskite catalyst, wherein the calcination is carried out at 500 ℃ to 1400 ℃ conditions for 1 to 50 hours.

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