Method for solvent-free catalytic degradation recycling of polyethylene terephthalate

Abstract

The present application relates to a method for solvent-free catalytic degradation recycling of polyethylene terephthalate, and belongs to the technical field of catalytic degradation recycling of polyethylene terephthalate. The polyethylene terephthalate is mixed with a catalyst, and then heated to degrade the polyethylene terephthalate to obtain an intermediate product, bisvinyl terephthalate. The bisvinyl terephthalate is then soaked in an alkali solution to hydrolyze the bisvinyl terephthalate to obtain terephthalate and ethylene glycol. The white solid obtained after filtration is the recovered catalyst. An acid solution is added to the filtrate to react the terephthalate to obtain terephthalic acid solid. The terephthalic acid is recycled after solid-liquid separation. The ethylene glycol is obtained after distillation of the filtrate, and the ethylene glycol is recycled. The present application does not use organic solvents, has low cost, short degradation time, fast reaction speed, low reaction temperature, high yield, and the catalyst can be recycled and reused. The whole reaction is carried out at normal pressure without the need for a protective gas.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalytic degradation and recycling of polyethylene terephthalate (PET), and more particularly, relates to a method for solvent-free catalytic degradation and recycling of polyethylene terephthalate, and especially relates to a method for converting waste PET into its monomers using aluminum, titanium and manganese compounds, and recycling the catalyst. BACKGROUND

[0002] Plastics have the advantages of abundant sources, good processability, low density, good durability and low price, and are widely used in important fields of national economy such as building, automobile manufacturing, packaging, medical devices, etc. PET is a typical thermoplastic plastic obtained by polycondensation of terephthalic acid and ethylene glycol, or prepared by ester exchange reaction of dimethyl terephthalate and ethylene glycol, and has the advantages of non-toxic, odorless, light weight, high transparency, good mechanical properties, etc., and is widely used in fibers, packaging and engineering plastics, etc. As one of the most widely used commercial plastics, the global annual output of PET is about 700 million tons. However, the recycling rate of waste PET is very low, only 14%. A large amount of waste PET is scattered in the natural environment, which has a difficult to reverse impact and damage on the ecological environment and human health, and also causes serious resource waste. At present, efficient recycling and utilization of PET has become one of the hot issues widely concerned at home and abroad. Common treatment methods of waste plastics include incineration, landfill, mechanical recycling and chemical recycling.

[0003] Landfill has the advantages of short-term effectiveness, simplicity and ease of implementation. However, due to the characteristics of small density and difficult degradation of waste plastics, the landfill method has a large impact on land resources. Microplastics also change the physical and chemical properties of soil and affect the normal growth of plants. Incineration is a method of treating non-degradable waste plastics by incineration to recover heat energy and generate electricity. Incineration has the advantage of simple operation, but it produces a variety of toxic gases including polycyclic aromatic hydrocarbons, and also produces a large amount of dust and smoke, which seriously pollutes the atmospheric environment. Mechanical recycling is to reprocess the waste polyester into plastic products, which has the advantages of simple process and low cost. However, PET is prone to decomposition to produce acetaldehyde during high-temperature blow molding and stretching, so the regenerated products may have excessive acetaldehyde content, limiting their use. Chemical recycling is a method of converting waste plastics into chemicals, which is an important step towards green chemical economy, and is attracting widespread attention from the scientific research community and industry. Compared with physical recycling, chemical recycling has the advantages of wider applicability, higher product application value and flexible treatment method. Common PET chemical recycling methods include alcoholysis, hydrolysis, aminolysis, enzymatic hydrolysis and catalytic cracking, etc.

[0004] The alcoholysis method refers to a method in which PET and an alcohol solvent undergo a transesterification reaction under the action of a catalyst at 180°C to 250°C, 1.4 MPa to 2.0 MPa to obtain a corresponding ester compound or an oligomer and ethylene glycol. The PET alcoholysis reagent is various, and a monohydric alcohol and ethylene glycol are generally used. The electrogativity of the metal ion in the catalyst (for example, stannous chloride and zinc acetate) promotes the reaction of the metal acetate and the alcohol to generate a metal alcoholate, and at the same time, acetic acid is produced. Then, the metal on the metal alcoholate provides an empty orbital to combine with the lone pair of electrons of the carbonyl oxygen in PET, and the transesterification is completed. The alcoholysis method has simple operation process, good degradation effect, but the product is not easy to purify, the separation and purification cost is high, and the reaction condition is harsh. The hydrolysis method refers to a method in which PET is depolymerized to terephthalic acid and ethylene glycol in an acidic, alkaline or neutral aqueous solution under high temperature and high pressure. PET can be hydrolyzed and depolymerized to terephthalate or terephthalic acid and ethylene glycol under acidic, alkaline or neutral conditions by using the hydrolysis of an ester group. Alkaline hydrolysis usually refers to the depolymerization of PET in an NaOH or KOH aqueous solution at 200°C to 250°C and 1.4 MPa to 2.0 MPa. The reaction is relatively complete, and the product components are few, but the waste alkali solution after hydrolysis needs to be treated. Acidic hydrolysis usually refers to the catalytic depolymerization of PET by using concentrated sulfuric acid, nitric acid or phosphoric acid and the like. This process produces a large amount of waste acid, and the post-treatment cost is high, and the concentrated acid corrodes the equipment. Neutral hydrolysis is generally carried out in water or steam, and the reaction temperature is 200°C to 280°C. The use of an ester exchange catalyst such as calcium acetate can reduce the reaction temperature. This process has no acid and alkali equipment corrosion problem, but the hydrolysis product has many impurities, and the separation and purification process is relatively complex. Compared with the alcoholysis method and the hydrolysis method, the amineolysis method and the enzymatic hydrolysis method are less studied. The amineolysis method generally refers to the amineolysis of PET in a primary amine solution to prepare terephthalic acid diamide. The disadvantages of the amineolysis method are that the raw material is expensive, a large amount of organic solvent is needed, the product purification process is complicated, and the cost is high. The enzymatic hydrolysis method generally uses PET hydrolytic enzyme to degrade PET into terephthalic acid, ethylene glycol or other incomplete hydrolysis products. However, this method has slow reaction speed, many degradation products, and the price of the enzyme is expensive, which is not suitable for large-scale use.

[0005] Compared with alcoholysis, hydrolysis and the like, catalytic cracking has the advantages of fast reaction speed and no need to use a large amount of organic solvent. Catalytic cracking includes high-temperature catalytic cracking and low-temperature catalytic cracking. High-temperature catalytic cracking is a method for preparing small molecular compounds such as aromatic hydrocarbons by catalyzing waste PET to degrade at 500-900 DEG C under a nitrogen atmosphere by using a metal compound catalyst. The disadvantages of this technology are high reaction temperature, easy deactivation of the catalyst, high energy consumption, high requirement for equipment, and wide product distribution, with dozens of types of products being difficult to separate and purify. Low-temperature catalytic cracking is a method for preparing small molecular products such as terephthalic acid and ethylene by catalyzing waste PET to degrade at 200-500 DEG C under a hydrogen atmosphere. Yosi Kratish et al. prepared a carbon-supported molybdenum dioxide catalyst, and PET was depolymerized into terephthalic acid and ethylene at 260 DEG C under a hydrogen atmosphere (Yosi Kratish, et al. Polyethylene terephthalate deconstruction catalyzed by a carbon-supported single-site molybdenum-dioxo complex. Angewandte Chemie International Edition, 2020, 59(45): 19857-19861). The advantages of this technology are low reaction temperature, low energy consumption, and non-deactivation of the catalyst, and no use of organic solvent. The disadvantages are low yield under a nitrogen atmosphere, need for a pure hydrogen atmosphere, expensive catalyst, high cost, and difficulty in large-scale application. In a recent patent (application number 202110360655.X), researchers proposed using zinc oxide or a compound that can be decomposed into zinc oxide by heating as a catalyst to prepare terephthalic acid and ethylene glycol from waste PET. This technology realizes low-temperature controllable degradation of waste PET, but needs to use a large amount of hydrochloric acid to dissolve the residual catalyst, and a large amount of alkali to regenerate the catalyst. The catalyst recovery process is complicated, and the cost of the catalyst is high.

[0006] From the above analysis, the ideal PET low-temperature controllable catalytic degradation technology needs to meet the following conditions: no need to use organic solvent, low reaction temperature, reaction gas is air, and no need for nitrogen or hydrogen protective gas; the raw material of the catalyst is easy to obtain, low cost, non-toxic, and stable during the reaction. Based on this, there is an urgent need for a green and environmentally friendly method that does not use organic solvent, has low cost, short degradation time, low temperature, high yield, simple post-treatment, the catalyst can be separated and recycled, and the whole process is under atmospheric pressure, so as to promote the high value-added conversion and reuse of a large amount of municipal and industrial waste PET. SUMMARY

[0007] The application provides a method for preparing terephthalic acid and ethylene glycol by catalytic degradation of waste PET at low temperature, which comprises the following steps: using aluminum, titanium and manganese oxides as catalysts, or metal compounds capable of generating aluminum or manganese oxides during heating, such as trimanganese tetroxide, dimanganese trioxide, aluminum trioxide, titanium dioxide, manganese carbonate, aluminum hydroxide and manganese hydroxide, then activating the RCOOR' bond (i.e. ester bond) in the PET macromolecular chain by the catalyst (for example, the manganese ion in the trimanganese tetroxide catalyst activates the C=O double bond and the O in the C-O single bond in the ester bond), to generate bisvinyl terephthalate, and then generate terephthalic acid and ethylene glycol through hydrolysis. The method solves the problem of recycling of industrial and urban waste PET, provides a new green way for recycling of a large amount of waste PET, and provides a new simple method for preparing important chemical raw material terephthalic acid and ethylene glycol, which has important significance for environmental protection, resource recycling and sustainable development. The application fully meets the needs of waste PET recycling, and can realize ecological development of the industry, and provide strong support for the operation of the current waste PET recycling industry.

[0008] According to the purpose of the application, a method for solvent-free catalytic degradation and recycling of polyethylene terephthalate is provided, which comprises the following steps:

[0009] (1) mixing polyethylene terephthalate fragments with a catalyst to obtain a mixture, wherein the catalyst is aluminum oxide, titanium oxide or manganese oxide, or a metal compound capable of generating aluminum or manganese oxides during heating;

[0010] (2) heating the mixture obtained in step (1) to make the catalyst degrade the polyethylene terephthalate to obtain an intermediate product bisvinyl terephthalate; then soaking the intermediate product in an alkaline solution to make the bisvinyl terephthalate hydrolyze to obtain terephthalate and ethylene glycol; filtering to obtain white solid, which is the recycled catalyst; then adding an acid solution to the filtrate to make the terephthalate react to obtain terephthalic acid solid, and realizing the recycling of terephthalic acid after solid-liquid separation; and distilling the filtrate to obtain ethylene glycol, realizing the recycling of ethylene glycol.

[0011] Preferably, the aluminum oxide is aluminum trioxide; the titanium oxide is titanium dioxide; and the manganese oxide is trimanganese tetroxide or dimanganese trioxide.

[0012] Preferably, the metal compound capable of generating aluminum oxides during heating is aluminum hydroxide.

[0013] Preferably, the metal compound capable of generating manganese oxides during heating is manganese carbonate or manganese hydroxide.

[0014] Preferably, the heating temperature is 200℃-340℃, and the heating time is 5min-120min.

[0015] Preferably, the polyethylene terephthalate is waste polyethylene terephthalate.

[0016] Preferably, the waste polyethylene terephthalate is at least one of waste polyethylene terephthalate bottles, waste polyethylene terephthalate packaging sheets, waste polyethylene terephthalate films, waste polyethylene terephthalate fibers, and waste polyethylene terephthalate textiles.

[0017] Preferably, the mass ratio of the polyethylene terephthalate to the catalyst is (1-100):10.

[0018] Preferably, the heating rate is 2℃ / min-100℃ / min.

[0019] Preferably, in step (1), the polyethylene terephthalate fragments and the catalyst are added to a ball mill, and stirred and mixed at a rotation speed of 30r / min-600r / min for 3min-30min to obtain a mixture.

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0021] (1) The present application is green and environmentally friendly, does not produce polluting gases, does not use organic solvents, has low cost, short degradation time, fast reaction speed, low reaction temperature, high yield, and the catalyst can be recycled and reused, and the entire reaction is carried out at normal pressure without the need for protective gases (such as nitrogen and hydrogen).

[0022] (2) The present application requires water vapor to change the reaction intermediate divinyl terephthalate into a transition state of diethylene glycol terephthalate. Due to the presence of this diethylene glycol terephthalate, ammonia solution or sodium hydroxide solution can be added directly to obtain a mixture of terephthalate and ethylene glycol, which is then directly distilled to obtain ethylene glycol, and the catalyst is separated by filtration, and acid is added to obtain terephthalic acid.

[0023] (3) The present application prepares high-yield and high-purity terephthalic acid and ethylene glycol by catalytic degradation of PET, not only providing a new strategy for resource recycling of PET, but also providing a new method for preparing terephthalic acid and ethylene glycol, which has important practical significance and broad application prospects.

[0024] (4) The catalyst used in the application is low in price, and can be recycled by simple separation, and is used repeatedly, for example, when using trimanganese tetroxide as the catalyst, the crystal structure of the catalyst after 10 times of use has no change, and the catalytic efficiency is not reduced.

[0025] (5) Preferably, the waste PET is used as the raw material, which not only simplifies the operation process of the waste PET degradation and recovery product, but also makes the degradation process green and environmentally friendly, and no organic solvent is used in the reaction process. Compared with the traditional catalytic degradation which is often carried out under high temperature and high pressure, the application can realize efficient catalytic depolymerization of waste PET under low temperature and normal pressure, and no oligomer by-products such as dimers or polymers are generated, and high-purity and high-yield terephthalic acid and ethylene glycol are obtained. The application turns waste PET into treasure, fundamentally realizes permanent closed-loop circulation of PET, and will produce great social and economic benefits, and has very obvious industrialization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 For example 1, the X-ray diffraction spectrum of terephthalic acid prepared by degrading waste PET at 220 DEG C with titanium dioxide as the catalyst.

[0027] Figure 2 For example 2, the nuclear magnetic carbon spectrum of terephthalic acid prepared by degrading waste PET at 280 DEG C with dimanganese trioxide as the catalyst.

[0028] Figure 3 For example 2, the nuclear magnetic carbon spectrum of ethylene glycol prepared by degrading waste PET at 280 DEG C with dimanganese trioxide as the catalyst.

[0029] Figure 4 For example 3, the X-ray diffraction spectrum of terephthalic acid prepared by degrading waste PET at 260 DEG C with manganese carbonate as the catalyst.

[0030] Figure 5 For example 4, the X-ray diffraction spectrum of terephthalic acid prepared by degrading waste PET at 260 DEG C with aluminum trioxide as the catalyst.

[0031] Figure 6 For example 5, the nuclear magnetic hydrogen spectrum of terephthalic acid prepared by degrading waste PET at 240 DEG C with aluminum hydroxide as the catalyst.

[0032] Figure 7 For example 6, the infrared spectrum of terephthalic acid prepared by degrading waste PET at 200 DEG C with manganese hydroxide as the catalyst.

[0033] Figure 8X-ray diffraction patterns of fresh and recycled manganese tetroxide catalysts after degradation of waste PET at 300℃ with manganese tetroxide as catalyst in Example 7. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0035] The present application provides a method for preparing terephthalic acid and ethylene glycol by catalytic low-temperature controllable degradation of waste PET using oxides of aluminum, titanium and manganese as catalysts. Specifically, the waste PET material is washed and cut to obtain waste PET fragments with a size of 1mm-10mm; then the waste PET fragments are mixed with the catalyst at a certain mass ratio, and the mixture is heated to a reaction temperature and kept for a period of time. After the reaction is completed, the reaction product is post-treated, the catalyst is recovered, and high-purity and high-yield terephthalic acid and ethylene glycol are obtained.

[0036] The specific process steps are as follows:

[0037] (1) The waste PET is washed and cut to obtain waste PET fragments with a size of 1mm-10mm;

[0038] (2) The waste PET fragments obtained in step (1) and the catalyst are mixed uniformly to obtain a mixture of waste PET and catalyst;

[0039] (3) The mixture obtained in step (2) is heated at 200℃-340℃ for 5min-120min. After cooling to room temperature, the solid product is a mixture of catalyst and terephthalic acid divinyl ester. After hydrolysis, separation and washing, the solid product is the catalyst, which can be recovered and directly used again; the filtrate is sodium terephthalate and ethylene glycol. After adding acid, sodium terephthalate becomes terephthalic acid solid, which can be obtained by filtration. The filtrate is distilled to obtain ethylene glycol.

[0040] The reaction general formula of the present application is:

[0041]

[0042] In some embodiments, the waste PET material is at least one of PET bottles, PET packaging sheets, PET films, PET fibers and PET textiles.

[0043] In some embodiments, the catalyst is an oxide of aluminum, titanium and manganese, or a metal compound that generates the corresponding oxide of aluminum, titanium and manganese during heating, such as trimanganese tetraoxide, dimanganese trioxide, aluminum trioxide, titanium dioxide, manganese carbonate, aluminum hydroxide, manganese hydroxide, and the like.

[0044] In some embodiments, the heating temperature is 200℃-340℃.

[0045] In some embodiments, the heating rate is 2℃ / min-100℃ / min.

[0046] In some embodiments, the holding time after the temperature is raised to the reaction temperature is 5min-120min.

[0047] In some embodiments, the waste PET pieces and the catalyst are added to a ball mill, stirred and mixed at a rotation speed of 30r / min-600r / min for 3min-30min to obtain a mixture of the waste PET and the catalyst.

[0048] In some embodiments, the mass ratio of the waste PET to the catalyst is 1:10-10:1.

[0049] The following are specific embodiments

[0050] Embodiment 1

[0051] (1) The waste PET bottles are cleaned, dried, and then crushed in a crusher to obtain waste PET pieces with a size of 1mm-10mm.

[0052] (2) 3.5g of the waste PET pieces and 3.5g of titanium dioxide are weighed and put into a ball mill, stirred and mixed at a rotation speed of 60r / min for 10min to obtain a uniform mixture of the two.

[0053] (3) The mixture obtained in step (2) is transferred to a tubular reactor, which is placed in a heating table, and set to heat at a heating rate of 10℃ / min, to a reaction temperature of 220℃, and held at this temperature for 40min.

[0054] (4) After the heating table is naturally cooled, the solid product of the tubular reactor is obtained. The solid product of the tubular reactor is soaked in 0.1mol / L ammonia solution for 1h, and then separated by filtration. The white filtrate is washed, dried to obtain recovered titanium dioxide. White precipitate is obtained after 0.5mol / L hydrochloric acid solution is added to the filtrate. The filtrate is separated by filtration, washed and dried to obtain terephthalic acid with a yield of 98wt%, and the filtrate is distilled to obtain ethylene glycol with a yield of 98wt%.

[0055] The prepared terephthalic acid product was a white powder, and the X-ray diffraction spectrum is shown in Figure 1 The prepared terephthalic acid and the commercial terephthalic acid (purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., purity > 99wt%) were almost completely consistent in crystal form, which confirmed that the product was terephthalic acid.

[0056] Example 2

[0057] The catalyst in the above Example 1 was replaced with manganese trioxide, the reaction temperature was changed to 280℃, and the other steps were unchanged, obtaining colorless liquid ethylene glycol and white powder terephthalic acid, with yields of 95wt% and 95wt% respectively. The prepared terephthalic acid and ethylene glycol nuclear magnetic carbon spectrum are shown in Figure 2 and Figure 3 respectively, which shows that the purity of the prepared terephthalic acid and ethylene glycol is very high, close to 100%.

[0058] Example 3

[0059] (1) The waste PET bottles were cleaned, dried and then crushed in a crusher to obtain waste PET fragments with a size of 1mm-10mm.

[0060] (2) 5.5g of waste PET fragments and 7.8g of manganese carbonate were weighed and placed in a ball mill, and stirred and mixed at a speed of 100r / min for 15min to obtain a uniform mixture of the two.

[0061] (3) The mixture obtained in step (2) was transferred to a tubular reactor, and the tubular reactor was placed in a heating table, and the heating rate was set to 20℃ / min, and the reaction temperature was raised to 260℃, and the temperature was kept for 90min.

[0062] (4) After the heating table was naturally cooled, the solid product of the tubular reactor was obtained. The solid product of the tubular reactor was soaked in 0.1mol / L ammonia solution for 1h, and then filtered and separated. The white filtrate was washed, dried to obtain the recovered manganese carbonate. After adding 0.5mol / L hydrochloric acid solution to the filtrate, a white precipitate was obtained. The filtrate was filtered, washed and dried to obtain terephthalic acid with a yield of 97wt%, and the filtrate was distilled to obtain ethylene glycol with a yield of 97wt%.

[0063] The X-ray diffraction spectrum of the prepared terephthalic acid product is shown in Figure 4 which shows that the prepared terephthalic acid and the commercial terephthalic acid (purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., purity > 99wt%) are almost completely consistent in crystal form, which confirms that the product is terephthalic acid.

[0064] Example 4

[0065] The catalyst in the above Example 3 was replaced by aluminum oxide, and other steps were unchanged, to obtain ethylene glycol colorless liquid and terephthalic acid white powder, with yields of 95wt% and 95wt%, respectively.

[0066] The X-ray diffraction spectrum of the prepared terephthalic acid product is shown in Figure 5 The X-ray diffraction spectrum of the prepared terephthalic acid product is shown in

[0067] Example 5

[0068] (1) The waste PET bottles were cleaned, dried and then crushed in a crusher to obtain waste PET fragments with a size of 1mm-10mm.

[0069] (2) 8.6g of the waste PET fragments and 5.1g of aluminum hydroxide were weighed and put into a ball mill, and stirred and mixed at a speed of 200r / min for 10min to obtain a uniform mixture of the two.

[0070] (3) The mixture obtained in step (2) was transferred to a tubular reactor, which was placed in a heating table and set to heat at a temperature increasing rate of 15℃ / min, to a reaction temperature of 240℃, and maintained at this temperature for 60min.

[0071] (4) After the heating table was naturally cooled, the solid product of the tubular reactor was obtained. The solid product of the tubular reactor was soaked in 0.1mol / L ammonia solution for 1h, and then separated by filtration. The white filtrate was washed and dried to obtain recovered aluminum hydroxide. White precipitate was obtained after 0.5mol / L hydrochloric acid solution was added to the filtrate. The filtrate was separated by filtration, washed and dried to obtain terephthalic acid, with a yield of 96wt%, and ethylene glycol was obtained after distillation of the filtrate, with a yield of 96wt%.

[0072] The nuclear magnetic resonance spectrum of the terephthalic acid prepared by degradation of waste PET is shown in Figure 6 The nuclear magnetic resonance spectrum of the terephthalic acid prepared by degradation of waste PET is shown in

[0073] Example 6

[0074] (1) The waste PET bottles were cleaned, dried and then crushed in a crusher to obtain waste PET fragments with a size of 1mm-10mm.

[0075] (2) 4.9g of the waste PET fragments and 15.8g of manganese hydroxide were weighed and put into a ball mill, and stirred and mixed at a speed of 300r / min for 5min to obtain a uniform mixture of the two.

[0076] (3) The mixture obtained in step (2) was transferred into a tube reactor, which was placed in a heating stage, and set to heat at a temperature increasing rate of 10°C / min, to a reaction temperature of 200°C, and kept at this temperature for 80 min.

[0077] (4) After the heating stage was naturally cooled, the solid product of the tube reactor was obtained. The solid product of the tube reactor was soaked in 0.1 mol / L ammonia solution for 1 h, and then separated by filtration. The white filtrate was washed and dried to obtain recovered manganese hydroxide. White precipitate was obtained after 0.5 mol / L hydrochloric acid solution was added dropwise into the filtrate. The filtrate was separated by filtration, washed and dried to obtain terephthalic acid, with a yield of 98 wt%, and the filtrate was distilled to obtain ethylene glycol, with a yield of 99 wt%.

[0078] The infrared spectrum of terephthalic acid prepared from waste PET is shown in Figure 7 , which confirms that the product is terephthalic acid.

[0079] Example 7

[0080] (1) The waste PET bottles were cleaned and dried, and then crushed in a crusher to obtain waste PET fragments with a size of 1 mm to 10 mm.

[0081] (2) 4.5 g of waste PET fragments and 8.9 g of manganese trioxide tetraoxide were weighed and placed in a ball mill, and stirred and mixed at a speed of 300 r / min for 5 min to obtain a uniform mixture of the two.

[0082] (3) The mixture obtained in step (2) was transferred into a tube reactor, which was placed in a heating stage, and set to heat at a temperature increasing rate of 20°C / min, to a reaction temperature of 300°C, and kept at this temperature for 10 min.

[0083] (4) After the heating stage was naturally cooled, the solid product of the tube reactor was obtained. The solid product of the tube reactor was soaked in 0.1 mol / L ammonia solution for 1 h, and then separated by filtration. The brown-red filtrate was washed and dried to obtain recovered manganese trioxide tetraoxide. White precipitate was obtained after 0.5 mol / L hydrochloric acid solution was added dropwise into the filtrate. The filtrate was separated by filtration, washed and dried to obtain terephthalic acid, with a yield of 96 wt%, and the filtrate was distilled to obtain ethylene glycol, with a yield of 97 wt%.

[0084] The manganese trioxide tetraoxide was recycled and used for 10 times in total, and the yield of terephthalic acid was maintained at more than 95 wt%. The X-ray diffraction spectrum of Mn304 after repeated use is shown in Figure 8The recovered Mn304 is completely consistent with the crystal structure of Mn304 before the reaction. This shows that Mn304 is easy to recover, and the crystal structure of the Mn304 catalyst before and after the reaction does not change at all, and can be directly used again.

[0085] Those skilled in the art will easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for solvent-free catalytic polyethylene terephthalate degradation recycling, characterized by, The method comprises the following steps: (1) mixing polyethylene terephthalate fragments with a catalyst to obtain a mixture, wherein the catalyst is aluminum oxide, titanium oxide or manganese oxide, or a metal compound capable of generating aluminum oxide or manganese oxide during heating; (2) heating the mixture obtained in step (1) at a temperature of 200-340 DEG C, wherein the catalyst activates the ester bond in the polyethylene terephthalate polymer chain during heating, and the catalyst degrades the polyethylene terephthalate to obtain an intermediate product bisvinyl terephthalate; then the bisvinyl terephthalate is soaked in an alkaline solution to hydrolyze the bisvinyl terephthalate to obtain terephthalate and ethylene glycol; the white solid obtained after filtration is the recovered catalyst; then an acid solution is added to the filtrate to react the terephthalate to obtain terephthalate solid, and the terephthalate is recovered after solid-liquid separation; the filtrate is distilled to obtain ethylene glycol, and the ethylene glycol is recovered.

2. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, The aluminum oxide is aluminum trioxide; the titanium oxide is titanium dioxide; and the manganese oxide is trimanganese tetroxide or dimanganese trioxide.

3. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, The metal compound capable of generating aluminum oxide during heating is aluminum hydroxide.

4. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, The metal compound capable of generating manganese oxide during heating is manganese carbonate or manganese hydroxide.

5. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to any one of claims 1 to 4, characterized in that, The heating time is 5 min-120 min.

6. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, The polyethylene terephthalate is waste polyethylene terephthalate.

7. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 6, wherein The waste polyethylene terephthalate is at least one of waste polyethylene terephthalate bottles, waste polyethylene terephthalate packaging sheets, waste polyethylene terephthalate films, waste polyethylene terephthalate fibers and waste polyethylene terephthalate textiles.

8. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, The mass ratio of the polyethylene terephthalate to the catalyst is (1-100):

10.

9. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, The heating rate is 2 DEG C / min-100 DEG C / min.

10. The method for solvent-free catalytic degradation recycling of polyethylene terephthalate according to claim 1, wherein, In step (1), the polyethylene terephthalate fragments and the catalyst are added to a ball mill, and stirred and mixed at a rotation speed of 30 r / min-600 r / min for 3 min-30 min to obtain the mixture.

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