Method for preparing 1, 4-cyclohexanedicarboxylic acid from waste PET plastic and preparing 1, 4-cyclohexanedimethanol through hydrogenolysis

Abstract

The invention discloses a method for preparing 1, 4-cyclohexanedicarboxylic acid (CHDA) from waste PET plastic and preparing 1, 4-cyclohexanedimethanol (CHDM) through hydrogenolysis, and belongs to the technical field of high-value conversion of waste plastic. According to the method, water is taken as a green reaction medium, and the waste PET plastic is subjected to two-step catalytic reaction to realize high-value conversion: step one, the waste PET is catalyzed by a specific catalyst in the water medium, a depolymerization hydrogenation reaction is completed at 180-210 DEG C to generate CHDA, the concentration of a PET substrate is controlled at 1.2%-15%, the hydrogen pressure is 1-3 MPa, and the reaction is performed for 3-13 h; and 2, carrying out hydrogenolysis reaction on the separated and purified CHDA at 200-230 DEG C under the action of a special catalyst to obtain CHDM, and reacting for 30-60 minutes under the hydrogen pressure of 2-5 MPa. Under the optimal reaction condition, the final molar yield of CHDM can reach 81%, and the separation purity reaches up to 99.5%; the highest molar yield of the intermediate product CHDA can reach 90%, and the intermediate product CHDA is a high-added-value polyester monomer and can be separated independently. According to the method, closed-loop high-valued circulation of the waste PET is achieved, white pollution is relieved, fossil resources are replaced to prepare high-end chemical raw materials, the catalyst can be regenerated and reused, environmental benefits, economic benefits and industrial application value are achieved, technological operation is flexible, and product diversity is high.

Description

A method for producing 1,4-cyclohexanedicarboxylic acid from waste PET plastic and then preparing 1,4-cyclohexanediethanol via hydrogenolysis. Technical Field

[0001] This application relates to the field of high-value conversion technology of waste plastics, and in particular to a method for producing CHDA from waste PET plastics and preparing CHDM by hydrogenolysis. Background Technology

[0002] Polyethylene terephthalate (PET) is currently the most widely used synthetic polyester material globally, with an annual production approaching 70 million tons. However, because waste PET is difficult to degrade in the natural environment, its long-term accumulation poses a serious threat to ecosystems and human health. At the same time, PET's molecular structure contains abundant carbon, hydrogen, and oxygen elements, making it a potential secondary carbon resource. However, currently only about 9% of waste PET plastics is recycled globally, with the vast majority remaining in the natural environment as waste, exacerbating environmental burdens and raw material waste. Therefore, whether for environmental protection or the practical needs of resource recycling, how to effectively recycle PET waste has become an urgent issue to be addressed.

[0003] Among various recycling strategies, compared to mechanical recycling, which is prone to material degradation and recycling, and incineration, which carries the risks of carbon emissions and toxic gas release, chemical recycling is considered one of the most promising directions for treating PET waste due to its high efficiency and sustainability. Currently, several chemical depolymerization processes have been developed and applied, covering hydrolysis, alcoholysis, methanolysis, and hydrogenolysis (related patents include CN113444284A, CN118561687A, CN114426483B, CN109705985A, etc.). These methods can break down PET polymer chains into smaller molecule compounds such as terephthalic acid (TPA), dimethyl terephthalate (DMT), and di(2-hydroxyethyl) terephthalate (BHET). These products can be directly used to regenerate PET or, after further processing, re-enter the polyester synthesis process. However, closed-loop recycling is not the only end point for resource utilization. To maximize the utilization value of waste resources, upgrading them into high-value-added chemicals is a more economically promising and strategically significant path.

[0004] CHDM is a key raw material for the production of high-end copolyester plastics and has high economic value. Considering the chemical structure of PET itself, its catalytic conversion to CHDM is a promising upgrade and recycling pathway. Therefore, this patent proposes a method for producing CHDA from waste PET plastic and then hydrogenating it to prepare CHDM. First, PET is converted to CHDA in an aqueous medium in a one-pot reaction, and then CHDA is further hydrogenated to obtain CHDM. The first step of this method uses water as the reaction medium, which not only conforms to the development concept of green chemistry, but the intermediate product CHDA itself is also an important polyester monomer that can be separated and extracted according to actual production needs. This increases the operational flexibility and product diversity of the process, providing a highly promising method for the high-value utilization of waste PET. Summary of the Invention

[0005] In view of this, the purpose of this application is to propose a method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis, so as to achieve the upgrading and recycling of waste PET plastic.

[0006] Based on the above objectives, this application provides a method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis. The method includes: Step 1, dispersing waste PET plastic in an aqueous medium, and reacting it at a temperature of 180~210°C under the action of a catalyst to obtain CHDA by depolymerization and hydrogenation.

[0007] Step 2: Separate the CHDA obtained in Step 1, and then react it at a temperature of 200~230℃ under the action of a catalyst to further hydrogenate the CHDA into CHDM.

[0008] Preferably, the catalyst in step one is selected from Pd / C, Ru / C, Pt / C, Ni / C, and Cu / C, with Pd / C being the most preferred.

[0009] Furthermore, the reaction temperature in step one is between 180-210°C, preferably 200°C.

[0010] Furthermore, the reaction time in step one is 3-13 hours, preferably 11 hours.

[0011] Furthermore, in step one, the hydrogen pressure is 1-3 MPa, preferably 2 MPa.

[0012] Furthermore, in step one, the concentration of the PET substrate is between 1.2% and 15%, preferably 10%.

[0013] Furthermore, the catalyst in step two is selected from CoO. x ZrCoO x ZnCoO x NiCoOx CeCoO x ZrCoO is preferred. x .

[0014] Furthermore, the reaction temperature in step two is 200-230℃, preferably 220℃.

[0015] Furthermore, the reaction time in step two is 30-60 min, preferably 45 min.

[0016] Furthermore, in step two, the hydrogen pressure is 2-5 MPa, preferably 4 MPa.

[0017] The catalytic conversion of waste PET plastic into CHDM first requires the conversion into the intermediate product CHDA, followed by the effective separation and purification of this intermediate. The catalytic system used in this process must possess two functions: the ability to hydrolyze and depolymerize the PET macromolecular chains, and the ability to hydrogenate and saturate the benzene rings, thereby efficiently converting waste PET into the high-value-added CHDA intermediate. In this invention, by employing a specific hydrogenation catalyst and reacting under mild conditions of 180–210°C in an aqueous medium, highly selective depolymerization and hydrogenation of waste PET plastic were successfully achieved to generate CHDA, which was then further separated and purified to obtain the intermediate product. Subsequently, the separated CHDA underwent selective hydrogenolysis at 200–230°C in the presence of a catalyst, ultimately converting it into the target product CHDM. The final molar yield of CHDM using this catalytic system can reach 81%, with a separation purity as high as 99.5%. CHDM, as a key raw material for synthesizing high-end copolyesters, has extremely high economic added value. Therefore, the process route proposed in this invention provides a solution with significant industrial application value for realizing the high-value recycling of waste PET.

[0018] Compared with the prior art, the present invention has the following significant advantages: it is green and environmentally friendly and conforms to the concept of sustainable development: in step one, water is used as the reaction medium to replace traditional organic solvents, thereby reducing process pollution and environmental burden.

[0019] Achieving high-value transformation of waste PET: Converting low-value-added waste PET into high-end chemical raw material CHDM (a key raw material for producing high-end copolyesters) and high-value-added intermediate CHDA, breaking through the limitations of traditional PET recycling in terms of downgrading and significantly improving the value of resource utilization.

[0020] The process is flexible and the products are highly diverse: the intermediate product CHDA can be separated and extracted separately, or it can be directly used for subsequent hydrogenolysis to prepare CHDM. The product structure can be adjusted according to market demand to adapt to different production scenarios.

[0021] High product yield and high purity: Under optimal conditions, the molar yield of CHDA reaches 90%, the molar yield of CHDM reaches 81%, and the purity of CHDM separation is ≥99.5%, meeting the quality requirements of high-end industrial raw materials.

[0022] The catalyst is regenerable and the process is economical: both the hydrogenation catalyst and the composite metal oxide catalyst used can be regenerated by calcination and reused, which greatly reduces the cost of the catalyst; both steps of the reaction are carried out in a batch high-pressure reactor, the process is simple and easy to scale up to industrial scale.

[0023] Alternative to fossil resources and promote carbon cycle: This method uses waste PET as a secondary carbon resource to prepare CHDM, which replaces the traditional fossil resource synthesis route, reduces fossil energy consumption, promotes the closed-loop recycling of carbon resources, and is in line with the "dual carbon" development goal. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is a schematic flowchart of a method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to an embodiment of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0027] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by a person skilled in the art to which this application pertains. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0028] Please refer to Figure 1. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis includes: Step 1, dispersing waste PET plastic in an aqueous medium, and reacting it at a temperature of 180~210℃ under the action of a catalyst to obtain CHDA by depolymerization and hydrogenation.

[0029] Step 2: Separate the CHDA obtained in Step 1, and then react it at a temperature of 200~230℃ under the action of a catalyst to further hydrogenate the CHDA into CHDM.

[0030] In step one, the concentration of waste PET substrate is 1.2%-15%, the reaction time is 3-13 h, and the hydrogen pressure is 1-3 MPa. In step two, the reaction time is 30-60 min, and the hydrogen pressure is 2-5 MPa.

[0031] In some embodiments, the resulting catalyst can be reused. This can be achieved by calcination, for example, calcining the catalyst at 500°C, which removes carbon deposits from the catalyst surface, allowing the catalyst to regenerate, extending its lifespan, reducing costs, and improving its efficiency.

[0032] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0033] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0034] Unless otherwise specified, all experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0035] Example 1 Test materials: waste PET plastic; mass of waste PET plastic: 60 mg; catalyst: Pd / C; mass ratio of catalyst to PET: 1:6; solvent: water; mass of solvent: 5 g.

[0036] Experimental conditions: Batch reactor; Hydrogen pressure: 3 MPa; Reaction temperature: 200℃; Reaction time: 11 h; Experimental method: 60 mg of waste PET plastic was dispersed in 5 g of water. The dispersion and 10 mg of Pd / C catalyst were then added to a 50 mL stainless steel high-pressure reactor, sealed, and purged with 3 MPa of hydrogen. The temperature was raised to the required 200℃ under rapid stirring, and the reaction was stopped after 11 hours. After cooling to room temperature, the water in the system was removed by vacuum distillation. Then, 1,4-dioxane was added to dissolve the reaction product. Subsequently, the reaction mixture was centrifuged to separate into solid and liquid phases. The solid phase contained the catalyst and undepolymerized PET, which was washed with ethanol, dried, and weighed to quantify the mass of undepolymerized PET. The liquid phase products were qualitatively analyzed using a GC-MS system (Agilent 7890A-5975C). Quantitative analysis of the liquid phase products was performed on a GC system (Agilent 7890B) equipped with an HP-5 column, using dodecane as an internal standard.

[0037] The only difference between Example 2 and Example 1 is that the catalyst is Ru / C.

[0038] The only difference between Example 3 and Example 1 is that the catalyst is Pt / C.

[0039] The only difference between Example 4 and Example 1 is that the catalyst is Ni / C.

[0040] The only difference between Example 5 and Example 1 is that the catalyst is Cu / C.

[0041] The only difference between Example 6 and Example 1 is that the reaction temperature is 180°C.

[0042] The only difference between Example 7 and Example 1 is that the reaction temperature is 190℃. The only difference between Example 8 and Example 1 is that the reaction temperature is 210℃. The only difference between Example 9 and Example 1 is that the reaction time is 3 h.

[0043] The only difference between Example 10 and Example 1 is that the reaction time is 5 hours.

[0044] The only difference between Example 11 and Example 1 is that the reaction time is 7 hours.

[0045] The only difference between Example 12 and Example 1 is that the reaction time is 9 hours.

[0046] The only difference between Example 13 and Example 1 is that the reaction time is 13 h.

[0047] The only difference between Example 14 and Example 1 is that the hydrogen pressure is 1 MPa.

[0048] The only difference between Example 15 and Example 1 is that the hydrogen pressure is 2 MPa.

[0049] The difference between Example 16 and Example 1 is that the hydrogen pressure is 2 MPa and the PET substrate concentration is 10%.

[0050] The difference between Example 17 and Example 1 is that the hydrogen pressure is 2 MPa and the PET substrate concentration is 15%.

[0051] The difference between Example 18 and Example 1 is that the hydrogen pressure is 2 MPa and the catalyst is Pd / C that has been used once.

[0052] The difference between Example 19 and Example 1 is that the hydrogen pressure is 2 MPa and the catalyst is Pd / C that has been used twice.

[0053] The difference between Example 20 and Example 1 is that the hydrogen pressure is 2 MPa and the catalyst is Pd / C that has been used three times.

[0054] The experimental results of Examples 1-20 are shown in Table 1. Table 1 shows the results of catalytic conversion of waste PET plastic to CHDA under different reaction conditions.

[0055]

[0056] As shown in the table above, in Examples 1-20, during the one-pot conversion of PET to the target product CHDA in step one, 4-(hydroxymethyl)cyclohexanoic acid and p-methylcyclohexanoic acid are generated. Both CHDA and 4-(hydroxymethyl)cyclohexanoic acid can be further converted to CHDM. In step one, the catalyst is selected from Pd / C, Ru / C, Pt / C, Ni / C, and Cu / C, with Pd / C being preferred. The molar yield of CHDA can reach 75%, and the total yield of CHDA and 4-(hydroxymethyl)cyclohexanoic acid reaches 85%. Furthermore, the reaction temperature in step one is 180-210℃, preferably 200℃. Lower reaction temperatures lead to incomplete depolymerization of PET, while higher reaction temperatures result in an increase in the byproduct p-methylcyclohexanoic acid. Furthermore, in step one, the reaction time is 3-13 h, and the hydrogen pressure is 1-3 MPa, preferably 11 h and 2 MPa H2 as the optimal reaction conditions. The molar yield of CHDA can reach 82%, while the total yield of CHDA and 4-(hydroxymethyl)cyclohexanoic acid reaches 90%. Further, in step one, the PET substrate concentration is 1.2%-15%, preferably 10%, and the molar yield of CHDA can reach 90%, while the total yield of CHDA and 4-(hydroxymethyl)cyclohexanoic acid reaches 94%. Finally, the cyclic stability of the catalyst was investigated. After three cycles, the yield of CHDA still reached 86%, and the total yield of CHDA and 4-(hydroxymethyl)cyclohexanoic acid reached 90%, indicating that the catalyst has excellent cyclic stability. Therefore, through the above examples, it can be seen that PET can be converted to CHDA and 4-(hydroxymethyl)cyclohexanoic acid in high yield in an aqueous medium, laying the groundwork for subsequent hydrogenolysis to prepare CHDM.

[0057] Example 21 Test materials: CHDA; CHDA mass: 100 mg; Catalyst: ZrCoO x Catalyst mass: 50 mg; Solvent: 1,4-dioxane; Solvent mass: 5 g.

[0058] Experimental conditions: A batch reactor was used; hydrogen pressure: 4 MPa; reaction temperature: 220℃; reaction time: 45 min; Experimental method: 100 mg CHDA was dispersed in 5 g of 1,4-dioxane, and then the dispersion and 50 mg catalyst were added to a 50 ml stainless steel high-pressure reactor. The reactor was sealed and charged with 4 MPa of hydrogen. The temperature was raised to the required temperature of 220℃ under rapid stirring. The reaction was stopped after 45 min and cooled to room temperature. An appropriate amount of dodecane internal standard was added to the reactor. The catalyst was separated by centrifugation. The supernatant was qualitatively and quantitatively analyzed by GC-MS (Agilent 7890A) and GC (Agileent 7890B).

[0059] The only difference between Example 22 and Example 21 is that the catalyst is CoO. x .

[0060] The only difference between Example 23 and Example 21 is that the catalyst is ZnCoO. x .

[0061] The only difference between Example 24 and Example 21 is that the catalyst is NiCoO. x .

[0062] The only difference between Example 25 and Example 21 is that the catalyst is CeCoO. x .

[0063] The only difference between Example 26 and Example 21 is that the reaction temperature is 200°C.

[0064] The only difference between Example 27 and Example 21 is that the reaction temperature is 210°C.

[0065] The only difference between Example 28 and Example 21 is that the reaction temperature is 230°C.

[0066] The only difference between Example 29 and Example 21 is that the reaction time is 30 min.

[0067] The only difference between Example 30 and Example 21 is that the reaction time is 60 min.

[0068] The only difference between Example 31 and Example 21 is that the hydrogen pressure is 2 MPa.

[0069] The only difference between Example 32 and Example 21 is that the hydrogen pressure is 3 MPa.

[0070] The only difference between Example 33 and Example 21 is that the hydrogen pressure is 5 MPa.

[0071] The only difference between Example 34 and Example 21 is that the catalyst is ZrCoO that has been used once. x .

[0072] The only difference between Example 35 and Example 21 is that the reaction raw materials are derived from the product of step one.

[0073] The experimental results of Examples 21-35 are shown in Table 2. Table 2 shows the results of the catalytic conversion of CHDA to CHDM under different reaction conditions.

[0074]

[0075] As shown in the table above, in Examples 18 to 31, the catalyst in step two is selected from CoO. x ZrCoO x ZnCoO x NiCoO x CeCoO x ZrCoO is preferred. x The molar yield of CHDM can reach 93%. Furthermore, the reaction temperature in step two is 200-230°C. Lower reaction temperatures cause some products to remain in the intermediate, while excessively high reaction temperatures lead to the appearance of byproducts. Preferably, 220°C is the optimal reaction temperature, where the molar yield of CHDM can reach 93%, and its selectivity reaches 95%.

[0076] Furthermore, in step two, the reaction time is 30-60 min, and the hydrogen pressure is 2-5 MPa, preferably 45 min. 4 MPa H2 is the optimal reaction condition, resulting in a CHDM molar yield of up to 93% and a selectivity of 95%. Finally, under the optimal reaction conditions, using the CHDA obtained in step one as the reaction feedstock, the CHDM yield is 91% and the selectivity is 95%, verifying the feasibility of a two-step method using CHDA as an intermediate to upgrade and recycle PET into CHDM.

[0077] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0078] Although this disclosure has been described in conjunction with specific embodiments thereof, many substitutions, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description.

[0079] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A method for producing 1,4-cyclohexanedicarboxylic acid from waste PET plastic and then preparing 1,4-cyclohexanediethanol via hydrogenolysis, characterized in that, The method includes: Step 1, dispersing waste PET plastic in an aqueous medium and reacting it at a temperature of 180~210℃ under the action of a catalyst to depolymerize and hydrogenate it to obtain CHDA; Step 2, separating the CHDA obtained in Step 1, and then reacting it at a temperature of 200~230℃ under the action of a catalyst to further hydrogenate the CHDA to CHDM.

2. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, The catalyst used in step one is selected from Pd / C, Ru / C, Pt / C, Ni / C, and Cu / C, with Pd / C being preferred.

3. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, The reaction temperature in step one is 180-210℃, preferably 200℃.

4. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, The reaction time in step one is 3-13 hours, preferably 11 hours.

5. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, In step one, the hydrogen pressure is 1-3 MPa, preferably 2 MPa.

6. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, In step one, the concentration of the PET substrate is between 1.2% and 15%, preferably 10%.

7. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, In step two, the catalyst is selected from CoO. x ZrCoO x ZnCoO x NiCoO x CeCoO x ZrCoO is preferred. x .

8. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, The reaction temperature in step two is 200-230℃, preferably 220℃.

9. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, The reaction time for step two is 30-60 minutes, preferably 45 minutes.

10. The method for producing CHDA from waste PET plastic and preparing CHDM by hydrogenolysis according to claim 1, characterized in that, In step two, the hydrogen pressure is 2-5 MPa, preferably 4 MPa.

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