Process method for preparing glycollic acid based on catalytic conversion of waste plastic PET

Abstract

The invention discloses a process method for preparing glycollic acid based on catalytic conversion of waste plastic PET (Polyethylene Terephthalate). The process method comprises the following steps: adding a composite catalyst and alkali liquor into a reaction kettle, adding waste plastic PET, replacing with high-purity oxygen, filling oxygen to 0.5-2 MPa, sealing the reaction kettle, carrying out a depolymerization-oxidation cascade reaction, and separating and purifying after the reaction is finished to obtain glycollic acid, wherein the composite catalyst is a supported catalyst loaded with noble metal elements. According to the process method, waste plastic polyethylene glycol terephthalate (PET) is successfully and efficiently converted into glycollic acid through a thermal catalytic depolymerization-oxidation cascade technology, solid waste recycling and high-value utilization are achieved, meanwhile, a one-pot method is adopted in the whole process method, operation is easy and convenient, the requirement for equipment is low, and the process method has the advantages of being environmentally friendly, efficient, capable of saving energy and the like and has wide application prospects. A new thought is provided for low-cost and large-scale production of glycollic acid.

Description

Technical Field

[0001] The present invention relates to the field of resource recycling and green chemical synthesis. More specifically, it relates to a process for catalytic conversion of waste plastic PET to prepare glycolic acid. Background Art

[0002] Glycolic Acid (C2H4O3), as the smallest molecular structure of α-hydroxy carboxylic acid, has the characteristics of both hydroxyl and carboxyl bifunctional groups and is the core monomer for synthesizing the biodegradable polymer material polyglycolic acid (PGA). Due to the excellent mechanical strength (tensile strength ≥ 100 MPa) and controllable degradation characteristics (hydrolysis half-life adjustable to 30 - 90 days) of PGA, it has been approved by the FDA for biomedical materials (such as surgical sutures, bone fixation devices) and environmentally friendly packaging fields. Therefore, the preparation of its upstream raw material glycolic acid has always been a key concern for researchers.

[0003] Polyethylene terephthalate (PET) is a common polymer material. Due to its high strength, stiffness, good thermal stability and chemical stability, it is widely used in packaging, fiber and film fields. It is statistically shown that 70 million tons of PET plastics are produced globally every year, but less than 20% of them are recycled. Most of the waste PET plastics are landfilled or discarded, which may not only cause serious environmental problems but also result in waste of resources.

[0004] In recent years, some researchers have focused on the technical route of preparing glycolic acid by electrocatalytic conversion of waste PET plastics. This not only solves the problems of environmental pollution and resource waste caused by waste PET plastics but also realizes the reuse of solid waste. The applicant has also conducted certain in-depth research on the above process before. For example, CN114959749A discloses a method for electrocatalytic glycol or electrocatalytic reforming of waste plastic PET to prepare glycolate. In an electrolytic cell system, an alkaline electrolyte containing glycol can be oxidized to glycolate at the anode, while water is reduced to hydrogen at the cathode. CN116283559A discloses a method for purification and recovery of the anode product - glycolic acid from PET electrocatalytic reforming. This purification and recovery method mainly relies on the compound distribution in the anode electrolyte and combines the characteristics of vacuum distillation, solubility and acidification of various compounds to achieve the separation and purification of the main product glycolic acid, the preparation of high-purity glycolic acid crystals, and the recovery and utilization of by-products. However, in the above electrochemical catalytic route, it is necessary to first pre-depolymerize waste PET in strong alkali, which takes a long time, generally more than 12 hours. After depolymerization, the glycol alkaline hydrolysis solution needs to be separated and electrolyzed to obtain glycolic acid. The operation process is complex, and the entire preparation cycle is long due to the limitation of the depolymerization time, which is not suitable for large-scale industrial production. Therefore, there is still a need to develop a simpler and more efficient production route for glycolic acid. Summary of the Invention

[0005] To solve the problems existing in the prior art, the object of the present invention is to provide a process for the catalytic conversion of waste plastic PET to glycolic acid. This process successfully converts waste plastic polyethylene terephthalate (PET) into glycolic acid in one step through a thermal catalytic depolymerization-oxidation cascade technology, realizing the resource utilization and high-value utilization of solid waste. At the same time, the whole process is easy to operate, the reaction conditions are mild, the requirements for equipment are low, and it has the characteristics of being green, efficient, and energy-saving.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a process for the catalytic conversion of waste plastic PET to glycolic acid, which comprises the following steps:

[0008] Add a composite catalyst and an alkali solution into a reaction kettle, add waste plastic PET, replace it with high-purity oxygen, fill oxygen to 0.5 - 2 MPa and seal the reaction kettle, and carry out a depolymerization-oxidation cascade reaction. After the reaction is completed, glycolic acid is obtained through separation and purification.

[0009] Among them, the composite catalyst is a supported catalyst loaded with noble metal elements.

[0010] In the present invention, the catalytic conversion of waste plastic PET to glycolic acid is carried out by a one-pot method. By selecting an efficient composite catalyst (rich in noble metal elements), the waste plastic PET is efficiently converted in a sealed oxygen-filled environment. The whole reaction process is relatively mild, the reaction temperature is relatively low (≤160 °C), and the reaction pressure is also relatively low (≤2 MPa). Therefore, the requirements for equipment are low, the operation safety is high, the reaction rate is fast, the operation process is simple, and it is suitable for large-scale industrial production.

[0011] The catalyst provided by the present invention is a supported catalyst with noble metal elements as the active component and loaded on a conventional carrier. Of course, noble metal element-noble metal element alloys, noble metal element-non-noble metal element compositions, etc. as the active component are also equally applicable to the catalytic system of the present invention.

[0012] Further, the waste plastic PET is derived from at least one of waste PET plastic bottles, waste PET fibers, waste PET packaging boxes, and waste PET foams.

[0013] Further, the noble metal element is selected from one or more of Pt, Pd, and Au;

[0014] The catalyst carrier is selected from one or more of activated carbon, carbon black, graphene, carbon nanotubes, carbon nitride, TiO2, SiO2, CeO2, ZrO2, Fe2O3, Co3O4, and Al2O3.

[0015] As an example, a preparation method of a composite catalyst is provided as follows, and the specific steps are as follows:

[0016] Disperse the catalyst support in an aqueous solution, add a soluble noble metal salt, and stir for 6 - 24 h to obtain a mixed solution A;

[0017] Evaporate the water from the mixed solution A at 50 - 100 °C to obtain a solid. Grind the solid and then calcine it in a muffle furnace, and then reduce it in a hydrogen / argon atmosphere to obtain the product.

[0018] Further, the soluble noble metal salt is selected from one or more of chloroplatinic acid and its salts (such as H2PtCl6, Na2PtCl6, K2PtCl6), platinum nitrate, platinum sulfate, chloroauric acid and its salts (such as HAuCl4, NaAuCl4, KAuCl4), palladium chloride, palladium nitrate, palladium acetate, potassium tetrachloropalladate.

[0019] Further, the concentration of the catalyst support in the mixed solution A is 10 - 100 mg / mL. Exemplarily, the concentration of the catalyst support can be 10 mg / mL, 20 mg / mL, 30 mg / mL, 40 mg / mL, 50 mg / mL, 60 mg / mL, 70 mg / mL, 80 mg / mL, 90 mg / mL, 100 mg / mL, etc.

[0020] Further, calculated by the content of the noble metal element, the mass ratio of the noble metal element to the catalyst support is 0.1 - 10 wt%. Exemplarily, the mass ratio of the noble metal element to the catalyst support can be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc.

[0021] Further, the calcination temperature is 300 - 500 °C, and the calcination time is 1 - 10 h;

[0022] The reduction temperature is 200 - 500 °C, and the reduction time is 1 - 5 h.

[0023] Further, the mass ratio of the composite catalyst to the waste plastic PET is 0.1 - 1:1 - 5. Exemplarily, the mass ratio of the composite catalyst to the waste plastic PET can be 0.1 - 0.2:1 - 5, 0.1 - 0.3:1 - 5, 0.1 - 0.4:1 - 5, 0.1 - 0.5:1 - 5, 0.1 - 0.2:1 - 2, 0.1 - 0.3:1 - 2, 0.1 - 0.4:1 - 2, 0.1 - 0.5:1 - 2, 0.1 - 0.2:1 - 3, 0.1 - 0.3:1 - 3, 0.1 - 0.4:1 - 3, 0.1 - 0.5:1 - 3, etc.

[0024] Further, the lye is selected from potassium hydroxide solution and / or sodium hydroxide solution, and its concentration is 0.5 - 2 mol / L. Exemplarily, its concentration can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc.

[0025] Further, the mass - volume ratio of the waste plastic PET to the lye is 1 - 5 g:50 mL.

[0026] Further, the reaction temperature of the depolymerization - oxidation cascade reaction is 80 - 160 °C, preferably 80 - 140 °C, the reaction time is 1 - 12 h, preferably 1 - 3 h, and the stirring speed is 100 - 1000 rpm, preferably 100 - 500 rpm.

[0027] Further, the separation and purification includes the following steps:

[0028] Filter the reaction solution obtained after the depolymerization - oxidation cascade reaction to obtain a filter cake and a filtrate. The filter cake mainly contains the composite catalyst and unreacted PET, and the filtrate contains the required reactants. Collect the filtrate and adjust the pH value of the filtrate to 2 - 3. Hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc. can be added for acidification, and precipitation will occur. The precipitate is terephthalic acid. Filter and collect the filtrate. The filtrate is an aqueous solution containing sodium salts, ethylene glycol, and glycolic acid. Concentrate the filtrate under reduced pressure. As the water evaporates, glycolic acid and sodium salts gradually crystallize out. When the filtrate is concentrated to 1 / 8 - 1 / 15 of the original volume, filter and collect the filter cake, so that the liquid ethylene glycol can be removed to obtain sodium salts and glycolic acid. Since glycolic acid has good solubility in ethanol and acetone, while sodium salts are almost insoluble in ethanol and acetone, the filter cake is dispersed with ethanol and / or acetone, filtered, and a filtrate rich in glycolic acid is obtained. After drying, glycolic acid is obtained.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention provides a process method for catalytic conversion of waste plastic PET to prepare glycolic acid, which realizes the resource utilization and high - value utilization of solid waste. In the present invention, by using a supported catalyst loaded with noble metal elements as the active substance, waste plastic PET is catalytically converted to glycolic acid under relatively low oxygen pressure, completely solving the problems existing in the traditional synthesis route, such as high process toxicity (involving highly toxic raw materials), large environmental load (high emissions of three wastes), and harsh reaction conditions (high temperature and high pressure). The whole process method is simple to operate, the reaction conditions are mild, the requirements for equipment are low, and it has the characteristics of green, high - efficiency, and energy - saving, providing a new idea for low - cost and large - scale production of glycolic acid.

[0031] Under the catalytic system provided by the present invention, the conversion rate of waste plastic PET can reach as high as 99%, and the glycolic acid yield can reach as high as 91%, with relatively high catalytic efficiency. At the same time, the separation and purification process of the product glycolic acid after the reaction is relatively simple, and the amount of waste liquid generated is significantly reduced. Description of the Drawings

[0032] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0033] Figure 1 The TEM image of the Pt / AC catalyst prepared in Example 1 of the present invention is shown.

[0034] Figure 2 The 1H NMR spectrum of the glycolic acid crystal obtained in the present invention is shown.

[0035] Figure 3 The 13C NMR spectrum of the glycolic acid crystal obtained in the present invention is shown. Specific Embodiments

[0036] To more clearly illustrate the present invention, the following further describes the present invention with reference to preferred embodiments and the accompanying drawings. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0037] In addition, unless otherwise specified, the raw materials used in the present invention can be obtained through commercial purchase, and any range described in the present invention includes the end values and any numerical values between the end values, as well as any sub-ranges formed by any numerical values between the end values or the end values.

[0038] Example 1: Preparation of Pt / AC Catalyst

[0039] Weigh 2 g of activated carbon support and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / AC.

[0040] From Figure 1 the TEM image, it can be seen that Pt nanoparticles are evenly distributed on the surface of the activated carbon.

[0041] Example 2: Preparation of Pt / C Catalyst

[0042] Weigh 2 g of carbon black and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / C.

[0043] Example 3: Preparation of Pt / G catalyst

[0044] Weigh 2 g of graphene and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / G.

[0045] Example 4: Preparation of Pt / CN catalyst

[0046] Weigh 2 g of carbon nanotubes and disperse them in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / CN.

[0047] Example 5: Preparation of Pt / C3N4 catalyst

[0048] Weigh 2 g of C3N4 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / C3N4.

[0049] Example 6: Preparation of Pt / TiO2 catalyst

[0050] Weigh 2 g of TiO2 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / TiO2.

[0051] Example 7: Preparation of Pt / SiO2 catalyst

[0052] Weigh 2 g of SiO2 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / SiO2.

[0053] Example 8: Preparation of Pt / CeO2 catalyst

[0054] Weigh 2 g of CeO2 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / CeO2.

[0055] Example 9: Preparation of Pt / ZrO2 catalyst

[0056] Weigh 2 g of ZrO2 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / ZrO2.

[0057] Example 10: Preparation of Pt / Fe2O3 catalyst

[0058] Weigh 2 g of Fe2O3 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / Fe2O3.

[0059] Example 11: Preparation of Pt / Co3O4 catalyst

[0060] Weigh 2 g of Co3O4 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / Co3O4.

[0061] Example 12: Preparation of Pt / Al2O3 catalyst

[0062] Weigh 2 g of Al2O3 and disperse it in 40 mL of aqueous solution. Add 53.3 g of chloroplatinic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pt / Al2O3.

[0063] Test Example 1

[0064] Weigh 0.2 g of the composite catalysts prepared in Examples 1 - 12 and 50 mL of 1 mol / L sodium hydroxide solution and add them to a 100 mL stainless steel autoclave. Add 2 g of PET plastic bottles, directly displace the air in the autoclave with high-purity oxygen three times, and fill it with oxygen to 1 Mpa. Seal the autoclave and react at a stirring speed of 500 rpm and a temperature of 140 °C for 3 h. After the reaction, analyze the solution composition by high-performance liquid chromatography and calculate the PET conversion rate and glycolic acid yield. The specific results are shown in Table 1.

[0065] Table 1

[0066] Example Catalyst PET Conversion Rate (%) Glycolic Acid Yield (%) Example 1 Pt / AC 99 91 Example 2 Pt / C 98 80 Example 3 Pt / G 96 77 Example 4 Pt / CN 94 75 Example 5 <![CDATA[Pt / C3N4]]> 95 70 Example 6 <![CDATA[Pt / TiO2]]> 95 82 Example 7 <![CDATA[Pt / SiO2]]> 94 75 Example 8 <![CDATA[Pt / CeO2]]> 96 78 Example 9 <![CDATA[Pt / ZrO2]]> 92 66 Example 10 <![CDATA[Pt / Fe2O3]]> 93 86 Example 11 <![CDATA[Pt / Co3O4]]> 95 70 Example 12 <![CDATA[Pt / Al2O3]]> 98 80

[0067] The reaction solution obtained from the depolymerization-oxidation cascade reaction using Pt / AC prepared in Example 1 as the catalyst was filtered, and the filtrate was collected. The first filtration could separate the catalyst and unreacted PET. Subsequently, hydrochloric acid was added to the filtrate for acidification, and the pH was adjusted to 2-3 to precipitate terephthalic acid. After filtering to remove the precipitated terephthalic acid, an aqueous solution containing sodium chloride, ethylene glycol, and glycolic acid was obtained. The filtrate was concentrated, and as the water evaporated, glycolic acid and sodium chloride gradually crystallized out. After concentrating to 10% of the original volume, filtering the concentrated solution could separate ethylene glycol (liquid at room temperature) and the solid product. Since glycolic acid has good solubility in acetone while sodium chloride is almost insoluble, glycolic acid and sodium chloride were separated by extraction. Finally, glycolic acid was collected in acetone and dried to obtain glycolic acid crystals.

[0068] Figure 2 and Figure 3 To characterize the glycolic acid crystals using nuclear magnetic resonance, the proton nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum indicated that the glycolic acid crystals were successfully prepared in this invention.

[0069] Example 13: Preparation of Au / AC Catalyst

[0070] Weigh 2 g of activated carbon support and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / AC.

[0071] Example 14: Preparation of Au / C Catalyst

[0072] Weigh 2 g of carbon black and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / C.

[0073] Example 15: Preparation of Au / G Catalyst

[0074] Weigh 2 g of graphene and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / G.

[0075] Example 16: Preparation of Au / CN catalyst

[0076] Weigh 2 g of carbon nanotubes and disperse them in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / CN.

[0077] Example 17: Preparation of Au / C3N4 catalyst

[0078] Weigh 2 g of C3N4 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / C3N4.

[0079] Example 18: Preparation of Au / TiO2 catalyst

[0080] Weigh 2 g of TiO2 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / TiO2.

[0081] Example 19: Preparation of Au / SiO2 catalyst

[0082] Weigh 2 g of SiO2 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / SiO2.

[0083] Example 20: Preparation of Au / CeO2 catalyst

[0084] Weigh 2 g of CeO2 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / CeO2.

[0085] Example 21: Preparation of Au / ZrO2 catalyst

[0086] Weigh 2 g of ZrO2 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / ZrO2.

[0087] Example 22: Preparation of Au / Fe2O3 catalyst

[0088] Weigh 2 g of Fe2O3 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / Fe2O3.

[0089] Example 23: Preparation of Au / Co3O4 catalyst

[0090] Weigh 2 g of Co3O4 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate, and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then reduce it in a hydrogen / argon atmosphere at a reduction temperature of 300 °C for 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / Co3O4.

[0091] Example 24: Preparation of Au / Al2O3 catalyst

[0092] Weigh 2 g of Al2O3 and disperse it in 40 mL of aqueous solution. Add 41.7 g of chloroauric acid hydrate, and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then reduce it in a hydrogen / argon atmosphere at a reduction temperature of 300 °C for 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Au / Al2O3.

[0093] Test Example 2

[0094] Weigh 0.2 g of the composite catalysts prepared in Examples 13 - 24 and 50 mL of 1 mol / L sodium hydroxide solution and add them to a 100 mL stainless steel autoclave. Add 2 g of PET plastic bottles, directly displace the air in the autoclave with high-purity oxygen three times, and fill it with oxygen to 1 Mpa. Seal the autoclave, react at a stirring speed of 500 rpm and a temperature of 140 °C for 3 h. After the reaction, analyze the solution composition by high-performance liquid chromatography, and calculate the PET conversion rate and glycolic acid yield. The specific results are shown in Table 2.

[0095] Table 2

[0096] Example Catalyst PET Conversion Rate (%) Glycolic Acid Yield (%) Example 13 Au / AC 98 89 Example 14 Au / C 90 83 Example 15 Au / G 99 85 Example 16 Au / CN 91 86 Example 17 <![CDATA[Au / C3N4]]> 98 82 Example 18 <![CDATA[Au / TiO2]]> 95 84 Example 19 <![CDATA[Au / SiO2]]> 97 75 Example 20 <![CDATA[Au / CeO2]]> 94 72 Example 21 <![CDATA[Au / ZrO2]]> 96 68 Example 22 <![CDATA[Au / Fe2O3]]> 95 77 Example 23 <![CDATA[Au / Co3O4]]> 96 73 Example 24 <![CDATA[Au / Al2O3]]> 95 78

[0097] Example 25: Preparation of Pd / AC catalyst

[0098] Weigh 2 g of activated carbon support and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate, and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then reduce it in a hydrogen / argon atmosphere at a reduction temperature of 300 °C for 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / AC.

[0099] Example 26: Preparation of Pd / C catalyst

[0100] Weigh 2 g of carbon black and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / C.

[0101] Example 27: Preparation of Pd / G catalyst

[0102] Weigh 2 g of graphene and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / G.

[0103] Example 28: Preparation of Pd / CN catalyst

[0104] Weigh 2 g of carbon nanotubes and disperse them in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / CN.

[0105] Example 29: Preparation of Pd / C3N4 catalyst

[0106] Weigh 2 g of C3N4 and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / C3N4.

[0107] Example 30: Preparation of Pd / TiO2 catalyst

[0108] Weigh 2 g of TiO2 and disperse it in 40 mL of aqueous solution. Add 33.7 g of palladium chloride hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / TiO2.

[0109] Example 31: Preparation of Pd / SiO2 catalyst

[0110] Weigh 2 g of SiO2 and disperse it in 40 mL of aqueous solution. Add 33.7 g of palladium chloride hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / SiO2.

[0111] Example 32: Preparation of Pd / CeO2 catalyst

[0112] Weigh 2 g of CeO2 and disperse it in 40 mL of aqueous solution. Add 33.7 g of palladium chloride hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / CeO2.

[0113] Example 33: Preparation of Pd / ZrO2 catalyst

[0114] Weigh 2 g of ZrO2 and disperse it in 40 mL of aqueous solution. Add 33.7 g of palladium chloride hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / ZrO2.

[0115] Example 34: Preparation of Pd / Fe2O3 catalyst

[0116] Weigh 2 g of Fe2O3 and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / Fe2O3.

[0117] Example 35: Preparation of Pd / Co3O4 catalyst

[0118] Weigh 2 g of Co3O4 and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / Co3O4.

[0119] Example 36: Preparation of Pd / Al2O3 catalyst

[0120] Weigh 2 g of Al2O3 and disperse it in 40 mL of aqueous solution. Add 33.7 g of chloropalladic acid hydrate and stir well at room temperature for 12 h to obtain a mixed solution A. Subsequently, heat the mixed solution A to 80 °C to evaporate the water until it is completely dried to obtain a solid powder. Calcinate the solid powder at 350 °C for 3 h, and then carry out reduction in a hydrogen / argon atmosphere. The reduction temperature is 300 °C and the reduction time is 3 h to obtain a composite catalyst with a platinum content of 1 wt%, denoted as Pd / Al2O3.

[0121] Test Example 3

[0122] Weigh 0.2 g of the composite catalysts prepared in Examples 25 - 36 and 50 mL of 1 mol / L sodium hydroxide solution and add them to a 100 mL stainless steel autoclave. Add 2 g of PET plastic bottles, directly displace the air in the autoclave with high-purity oxygen three times, and fill it with oxygen to 1 Mpa. Seal the autoclave and react at a stirring speed of 500 rpm and a temperature of 140 °C for 3 h. After the reaction, analyze the solution composition by high-performance liquid chromatography and calculate the PET conversion rate and glycolic acid yield. The specific results are shown in Table 3.

[0123] Table 3

[0124] Example Catalyst PET Conversion Rate (%) Glycolic Acid Yield (%) Example 25 Pd / AC 99 86 Example 26 Pd / C 98 84 Example 27 Pd / G 95 86 Example 28 Pd / CN 96 87 Example 29 <![CDATA[Pd / C3N4]]> 98 78 Example 30 <![CDATA[Pd / TiO2]]> 97 81 Example 31 <![CDATA[Pd / SiO2]]> 95 85 Example 32 <![CDATA[Pd / CeO2]]> 97 82 Example 33 <![CDATA[Pd / ZrO2]]> 95 71 Example 34 <![CDATA[Pd / Fe2O3]]> 98 79 Example 35 <![CDATA[Pd / Co3O4]]> 96 75 Example 36 <![CDATA[Pd / Al2O3]]> 95 78

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A process for preparing glycolic acid by catalytic conversion of waste plastic PET, characterized in that, It includes the following steps: Add the composite catalyst and the alkali solution into the reaction kettle, add waste plastic PET, replace with high-purity oxygen, then fill with oxygen to 0.5 - 2 MPa and seal the reaction kettle, and carry out the depolymerization-oxidation cascade reaction. After the reaction is completed, glycolic acid is obtained through separation and purification. Among them, the composite catalyst is a supported catalyst loaded with noble metal elements.

2. The process method according to claim 1, characterized in that, The noble metal elements are selected from one or more of Pt, Pd, and Au. The catalyst support is selected from one or more of activated carbon, carbon black, graphene, carbon nanotubes, carbon nitride, TiO2, SiO2, CeO2, ZrO2, Fe2O3, Co3O4, and Al2O3.

3. The process method according to claim 2, characterized in that, The composite catalyst is prepared according to the following steps: Disperse the catalyst support in an aqueous solution, add a soluble noble metal salt, and stir for 6 - 24 h to obtain a mixed solution A. Evaporate the water from the mixed solution A at 50 - 100 °C to obtain a solid. Grind the solid and then calcine it in a muffle furnace, and then reduce it in a hydrogen / argon atmosphere to obtain the product.

4. The process method according to claim 2, characterized in that, The mass ratio of the noble metal element to the catalyst support is 0.1 - 10 wt%.

5. The process method according to claim 3, characterized in that, The calcination temperature is 300 - 500 °C, and the calcination time is 1 - 10 h. The reduction temperature is 200 - 500 °C, and the reduction time is 1 - 5 h.

6. The process method according to claim 1, characterized in that, The mass ratio of the composite catalyst to the waste plastic PET is 0.1 - 1:1 - 5.

7. The process method according to claim 1, characterized in that, The alkali solution is selected from potassium hydroxide solution and / or sodium hydroxide solution, and its concentration is 0.5 - 2 mol / L.

8. The process method according to claim 1, characterized in that, The mass-volume ratio of the waste plastic PET to the alkali solution is 1 - 5 g:50 mL.

9. The process method according to claim 1, characterized in that, The reaction temperature of the depolymerization-oxidation cascade reaction is 80 - 160 °C, the reaction time is 1 - 12 h, and the stirring speed is 100 - 1000 rpm.

10. The process method according to claim 1, characterized in that, The separation and purification include the following steps: Filter the reaction solution obtained after the depolymerization-oxidation cascade reaction, adjust the pH value of the filtrate to 2 - 3, filter, concentrate the filtrate under reduced pressure. When the filtrate is concentrated to 1 / 8 - 1 / 15 of the original volume, filter, disperse the filter cake with ethanol and / or acetone, filter, obtain a filtrate rich in glycolic acid, and dry to obtain glycolic acid.

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