A catalyst for carbon dioxide hydrogenation to ethanol and in-situ alcoholysis of waste PET

Abstract

The application discloses a catalyst for preparing ethanol from CO2 hydrogenation and in-situ alcoholysis of waste polyethylene terephthalate (PET) and an application method thereof. The catalyst is prepared by first preparing ZIF-67, then loading Cu, and then sequentially performing heat treatment in N2 and NH3 atmospheres. The catalyst can be used for catalyzing CO2 hydrogenation to prepare ethanol and in-situ alcoholysis of waste PET to prepare p-xylene (PX) with a yield of 92%. The application can not only directly catalyze CO2 hydrogenation to prepare ethanol and realize resource utilization of CO2, but also efficiently degrade waste PET at a lower temperature to prepare high-value-added products, which is favorable for simultaneously solving the problems of waste plastic pollution and CO2 carbon emission, and has certain reference significance for resource utilization of CO2 and waste PET and environmental protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the degradation and recycling of polyethylene terephthalate (PET), and in particular to a catalyst for coupling CO2 hydrogenation with alcoholysis of waste PET and a method of use thereof. BACKGROUND

[0002] Plastics are widely used in everyday products (e.g. food packaging, disposable containers and textiles) and specialty products (e.g. electronics, hydrophobic coatings) due to their lightweight, durable and easy-to-process properties. However, 67% of plastics globally, including textiles (11%), packaging (40%) and consumer goods (12%), become waste within five years of use, and are often discarded into the natural environment without any treatment. Packaging materials and plastic bottles made of polyethylene terephthalate (PET) are mostly discarded after a single use, but due to the stability and durability of PET, it is difficult to degrade under natural conditions, and can easily cause white pollution. More threateningly, waste PET can be converted into microplastics in the environment, enter the food chain and harm human health. Therefore, developing green and efficient waste PET degradation and recycling technologies has become a current research hotspot.

[0003] The main methods for recycling waste PET reported so far are physical methods (cutting, crushing and melting, etc.), chemical methods (hydrolysis, alcoholysis, ammonolysis, etc.) and energy utilization (incineration). Among these methods, physical methods repeatedly use PET, which can reduce the strength of PET, increase brittleness and affect product quality. Incineration has low energy utilization rate and can easily emit toxic gases, causing secondary pollution. In contrast, chemical recycling involves depolymerization of waste PET into monomers or random chain scission into shorter fragments, which are converted into value-added chemicals. Therefore, chemical recycling is an environmentally friendly solution for waste PET.

[0004] Chemical recycling of waste PET includes hydrolysis, ammonolysis, and alcoholysis. Hydrolysis refers to the process of converting PET waste into ethylene glycol (EG) and terephthalic acid (TPA) under certain acid or base conditions. The reaction usually requires a temperature of 200-250 °C and a pressure of 1.4-2 MPa for 3-5 h. Ammonolysis usually uses a primary amine aqueous solution, but the process is complex and the product is difficult to separate and purify. Alcoholysis is a relatively easy process for degrading PET. It involves an ester exchange reaction between PET and an alcohol solvent under certain temperature and pressure conditions, resulting in the corresponding monomer and EG. Common solvents include methanol and ethanol. However, alcoholysis of waste PET faces two problems: first, the degradation rate of waste PET is limited by thermodynamics, requiring high temperatures and high energy consumption; second, the use of methanol or ethanol in the alcoholysis process is high, increasing costs. Many studies have shown that CO2 hydrogenation can produce high-value chemicals such as methanol or ethanol. Therefore, coupling CO2 hydrogenation with PET degradation is expected to provide methanol or ethanol for PET alcoholysis, while driving the CO2 hydrogenation and PET degradation reactions to improve efficiency. For example, Li et al. developed a Cu4Fe1Cr1 catalyst that can couple CO2 hydrogenation to produce methanol, methanol alcoholysis of PET, and dimethyl terephthalate (DMT) hydrogenation at 240 °C and 3 MPa (CO2:H2=1:1). This process can more efficiently convert PET into dimethyl cyclohexanedicarboxylate (DMCD) and p-xylene (PX) (Yinwen Li et al., Angew. Chem. Int. Ed., 2022, 134: e202117205). In addition, Rodrigues Fernandes et al. used a Co3O4 catalyst to react at 255 °C with a mass ratio of ethanol to PET of 10. By using a large amount of ethanol, the pressure reached 11.6 MPa at high temperature, which improved the degradation efficiency of PET (about 98%). The main product obtained was diethyl terephthalate (DET) with a selectivity of about 90% (Janalina Rodrigues Fernandes et al., The Journal of Supercritical Fluids, 2020, 158: e104715), which indicates that ethanol alcoholysis of waste PET may have potential advantages. However, the current ethanol alcoholysis of waste PET still has problems such as high consumption of ethanol, high energy consumption, and complex products.

[0005] In view of this, from the perspective of recycling of waste PET and CO2, the application provides a catalyst and process for preparing ethanol from CO2 hydrogenation and in-situ alcoholysis of waste PET. The catalyst can not only directly catalyze the preparation of ethanol from CO2 hydrogenation, realize the recycling of CO2, but also efficiently directly alcoholysis of waste PET at a lower temperature, realize the recycling of PET, reduce energy consumption and the use of ethanol, and is conducive to solving the problems of waste plastic pollution and CO2 carbon emission. SUMMARY

[0006] In view of the above problems, the purpose of the application is to provide a catalyst for preparing ethanol from CO2 hydrogenation and in-situ alcoholysis of waste PET and its application method. The catalyst can catalyze the preparation of ethanol from CO2 hydrogenation and in-situ alcoholysis of waste PET to prepare p-xylene (PX), and has a high yield, which provides a new method for simultaneously solving the problems of excessive CO2 emission and recycling of waste PET, and has important significance for alleviating energy crisis and protecting ecological environment.

[0007] To achieve the above purpose, the application adopts the following technical solutions:

[0008] A preparation method of a catalyst for preparing ethanol from CO2 hydrogenation and in-situ alcoholysis of waste PET, comprising the following steps:

[0009] (1) uniformly mix a methanol solution of cobalt nitrate with a methanol solution of 2-methylimidazole, age at room temperature, wash, and vacuum dry to obtain ZIF-67 as a precursor of Co;

[0010] (2) disperse the ZIF-67 obtained in step (1) in methanol, add a copper nitrate solution and mix, then age at room temperature, centrifuge, and vacuum dry to obtain a catalyst precursor;

[0011] (3) put the catalyst precursor obtained in step (2) into a tube furnace, and heat treat in N2 and NH3 atmospheres in sequence to obtain a catalyst CuCo@CN-NH3 for preparing ethanol from CO2 hydrogenation and in-situ alcoholysis of waste PET.

[0012] Further, in step (1), the molar ratio of 2-methylimidazole to cobalt nitrate is 1-8, the aging time at room temperature is 2-24 h, and the vacuum drying time is 6-60 h at a temperature of 20-60 DEG C.

[0013] Further, in step (2), the copper nitrate used is 0.1-10 % of the mass of ZIF-67, the aging time at room temperature is 1-48 h, and the vacuum drying time is 3-60 h at a temperature of 20-60 DEG C.

[0014] Further, the temperature of the heat treatment in step (3) is 300-800 DEG C, and the time is 1-5 hours.

[0015] The method for preparing the catalyst and using the catalyst to carry out CO2 hydrogenation to prepare ethanol and in-situ alcoholysis of waste PET is as follows: the catalyst and waste PET are placed in an autoclave, a solvent is added, then CO2 and H2 are filled, and the reaction is carried out by heating and stirring to simultaneously realize CO2 hydrogenation to prepare ethanol and alcoholysis of waste PET.

[0016] Further, the mass ratio of the catalyst to waste PET is 0.1-8.

[0017] Further, the solvent is 1,4-dioxane.

[0018] Further, the volume ratio of H2 to CO2 is 0.5-6, and the total gas pressure is 1-7 MPa.

[0019] Further, the stirring speed during the catalytic reaction is slow, and the stirring speed is 0-200 rpm.

[0020] Further, the temperature of the reaction is 150-280 DEG C, and the time is 3-24 hours.

[0021] From the above technical solution, the present application has the following beneficial effects:

[0022] (1) The catalyst provided by the present application can catalyze CO2 hydrogenation to prepare methanol and ethanol, and realize high-value utilization of CO2, which not only helps to reduce carbon emissions, but also can alleviate the energy crisis.

[0023] (2) The catalyst provided by the present application can simultaneously realize ethanol alcoholysis of waste PET, and the yield of PX is more than 90%, which not only can reduce the amount of ethanol, but also can produce products with high added value.

[0024] (3) The catalyst preparation method and catalytic process provided by the present application are simple and low in cost, which is conducive to industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The XRD spectrum of the catalyst prepared in Example 1 and Comparative Example 1.

[0026] Figure 2 The activity evaluation diagram of the catalyst prepared in Example 1 and Comparative Example 1.

[0027] Figure 3 The activity evaluation diagram of the catalytic reaction using different substrates in Comparative Example 2.

[0028] Figure 4The catalytic activity evaluation graph of the catalyst at different stirring speeds in Example 2.

[0029] Figure 5 The catalytic activity evaluation graph of the catalyst at different catalytic reaction temperatures in Example 3.

[0030] Figure 6 The catalytic activity evaluation graph of the catalyst at different gas ratios in Example 4.

[0031] Figure 7 The catalytic activity evaluation graph of the catalyst for degrading PET from different sources in Example 5. DETAILED DESCRIPTION

[0032] In order to make the content described in the present application more convenient to understand, the technical solutions described in the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0033] Example 1

[0034] 1. Preparation of the catalyst:

[0035] (1) 2.91 g of Co(NO3)2·6H2O was weighed and added to 10 mL of methanol, and stirred at room temperature for 15 min to obtain solution A; 3.28 g of 2-methylimidazole was weighed and added to 70 mL of methanol, and stirred at room temperature for 15 min to obtain solution B; solutions A and B were uniformly mixed and aged at room temperature for 8 h, and ZIF-67 (Co precursor) was collected by centrifugation, washed with methanol several times, and vacuum dried at room temperature for 12 h;

[0036] (2) 500 mg of the obtained ZIF-67 solid was weighed and added to 40 mL of methanol, and stirred at room temperature for 15 min to obtain solution C; 44 mg of Cu(NO3)2 was weighed and added to 10 mL of methanol, and stirred at room temperature for 15 min to obtain solution D; solutions C and D were uniformly mixed and aged at room temperature for 24 h, and vacuum dried at room temperature for 12 h after centrifugation to obtain a catalyst precursor;

[0037] (3) The catalyst precursor obtained in step (2) was placed in a small porcelain boat, N2 was filled in a tube furnace, and the temperature was raised from room temperature to 600 ℃ at a rate of 5 ℃ / min and kept constant for 2 h to obtain a sample, which was marked as CuCo@CN-N2; then CuCo@CN-N2 was placed in an NH3 atmosphere, and the temperature was raised from room temperature to 500 ℃ at a rate of 5 ℃ / min and kept constant for 4 h to obtain a CuCo@CN-NH3 catalyst.

[0038] 2. Activity evaluation of the catalyst:

[0039] Take 100 mg CuCo@CN-NH3 catalyst, 4 mL 1,4-dioxane, 50 mg PET into a 50 mL high-temperature and high-pressure reaction kettle, first replace 5 times with high-purity N2, then fill in 3 MPa H2 and 1 MPa CO2, then heat to 210℃, react for 12 h (the speed of magnetic stirring is 50 rpm), after the reaction is completed, cool to room temperature, and the obtained reaction mixture is detected by gas chromatography.

[0040] Comparative Example 1

[0041] CuCo@CN-N2 synthesized by the same method as Example 1 is used as a comparative catalyst, and the same catalyst activity evaluation method as Example 1 is used.

[0042] Figure 1 The XRD spectrum of the catalyst prepared in Example 1 and Comparative Example 1. From the figure, it can be seen that there is no obvious difference in the XRD diffraction peaks of CuCo@CN-NH3 and CuCo@CN-N2, which can be well matched with the Co standard card (PDF# No. 15-0806) and Cu standard card (PDF# No. 04-0836), indicating that the main components of the catalyst are C (carrier), Co and Cu, and there is no obvious change in the crystal phase before and after NH3 treatment.

[0043] Figure 2 The activity evaluation figure of the catalyst sample prepared in Example 1 and Comparative Example 1. From the figure, it can be seen that CuCo@CN-N2 and CuCo@CN-NH3 both have catalytic activity, and the products are: p-xylene (PX), toluene (PhMe), methane, methanol and ethanol, indicating that CO2 hydrogenation and PET degradation can be effectively coupled to prepare high-value-added chemicals. More importantly, through comparison, it can be found that the catalytic activity of CuCo@CN-NH3 treated by ammonia has been obviously improved, and the yield of PX has increased from 37% to 92%, which shows that ammonia treatment is beneficial to improve the catalytic activity of the catalyst for waste PET.

[0044] Comparative Example 2 (different substrates)

[0045] Using the catalyst prepared in Example 1, the substrate of the catalytic reaction is changed to explore the coupling mode of CO2 hydrogenation and PET degradation in the catalytic reaction. The specific experiment is as follows:

[0046] (1) Experiment A, no PET: no PET is put into the reaction kettle, and the rest remains unchanged, to investigate the products of CO2 hydrogenation;

[0047] (2) Experiment B, no CO2 and H2: replace CO2 and H2 with N2, and the rest remains unchanged, to investigate the ability of the catalyst to directly degrade PET;

[0048] (3) Experiment C, only H2: replace CO2 with N2 for reaction, and keep the rest unchanged, to investigate the role of CO2;

[0049] (4) Experiment D, only CO2: replace H2 with N2 for reaction, and keep the rest unchanged, to investigate the role of H2;

[0050] (5) Experiment E, adding methanol: on the basis of Experiment C, 1 mL of methanol is added to the reaction kettle, to investigate the role of methanol;

[0051] (6) Experiment F, adding ethanol: on the basis of Experiment C, 1 mL of ethanol is added to the reaction kettle, to investigate the role of ethanol.

[0052] Figure 3 The activity evaluation diagram of the CuCo@CN-NH3 catalyst in Comparative Example 2 for different substrates. As can be seen from the diagram, the CO2 hydrogenation products of the catalyst are: methane, methanol and ethanol (Experiment A), and the methanol or ethanol produced provides the possibility for in-situ alcoholysis of PET. By comparing Experiments B, C and D, it can be found that in the absence of both CO2 and H2 (Experiment B), PET does not occur degradation; in the presence of only H2 (Experiment C), PET occurs certain conversion, and the yield of dimethylbenzene is 43%, while in the presence of only CO2 (Experiment D), the reaction hardly proceeds, which shows that the coexistence of CO2, H2 and PET is conducive to the progress of the catalytic reaction, which may be due to the coupling between the CO2 hydrogenation reaction and the alcoholysis of PET, breaking the thermodynamic equilibrium. It is worth noting that CuCo@CN-NH3 contains both methanol and ethanol in the CO2 hydrogenation products, in order to further illustrate the problem, methanol (Experiment E) and ethanol (Experiment F) are respectively added to the catalytic reaction system, it is found that the PX yield is only 46% (Experiment E) when methanol is added to the reaction system, which is similar to the result of Experiment C, indicating that the key substance for alcoholysis is not methanol; while the PX yield is significantly improved (about 75%) when ethanol is added to the reaction system, indicating that ethanol plays an important role in the alcoholysis of PET. Therefore, the main reaction in this catalytic reaction process is the production of ethanol by CO2 hydrogenation and the in-situ alcoholysis of PET.

[0053] Example 2 (different stirring speeds)

[0054] The same catalyst activity evaluation method as in Example 1 is adopted, except that the stirring speed of the catalytic reaction in the evaluation process is 0, 50, 100 and 150 rpm, respectively.

[0055] Figure 4The catalytic activity evaluation diagram of the catalysts under different stirring speeds in Example 2 is shown in the figure. It can be seen from the figure that the stirring speed has a great influence on the catalyst activity. When the stirring speed is 0 rpm, the yield of PX is 82%, which increases to 92% when the stirring speed is 50 rpm. However, with the continuous increase of the stirring speed, the yield of PX decreases, and when the stirring speed is 100 rpm, the yield of PX decreases slightly to 80%, and when the stirring speed is further increased, the yield of PX decreases to 10%. This shows that the stirring speed has a great influence on the reaction, and the slower stirring speed is beneficial to the catalytic reaction.

[0056] Example 3 (different catalytic reaction temperatures)

[0057] The same catalyst activity evaluation method as in Example 1 is used, except that the catalytic reaction temperature in the evaluation process is 150, 180, 195, 210 and 240 °C, respectively.

[0058] Figure 5 The catalytic activity evaluation diagram of the catalysts under different catalytic reaction temperatures in Example 3 is shown in the figure. It can be seen from the figure that with the increase of the reaction temperature, the yield of the product PX also increases, and when the temperature is low, the yield of the product increases slowly, and when the temperature increases from 180 °C to 210 °C, the reaction activity suddenly begins to increase rapidly, and the yield of PX increases from 5% to 92%. Therefore, the best temperature for the reaction is 210 °C, at which the yield of PX is higher, and with the further increase of the reaction temperature, the yield of PX only increases by 2%, and the increase is small.

[0059] Example 4 (different ratios of CO2 and H2)

[0060] The same catalyst activity evaluation method as in Example 1 is used, except that the ratio of H2 to CO2 in the evaluation process is 1:1, 3:1 and 4:1, respectively.

[0061] Figure 6 The catalytic activity evaluation diagram of the catalysts under different ratios of H2 and CO2 in Example 4 is shown in the figure. It can be seen from the figure that under different ratios of H2 and CO2, the catalysts all have good catalytic activity, and the best gas ratio for the reaction is 3:1, which may be due to the fact that under this ratio, CO2 hydrogenation has better ethanol production activity.

[0062] Example 5 (different sources of PET)

[0063] The same catalyst activity evaluation method as in Example 1 is used, except that the sources of PET used in the evaluation process are purchased PET powder, PET mineral water bottle body, PET transparent box and PET film.

[0064] Figure 7The figure for evaluating the catalytic activity of the catalyst for degrading PET from different sources in Example 5 is shown. As can be seen from the figure, the catalyst has good catalytic activity for PET from different sources, which shows that the catalyst can adapt to the degradation of PET from different sources and can be widely applied to the degradation of waste PET plastics.

[0065] The above description is only the preferred embodiment of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be covered by the present application.

Claims

1. A method for preparing a catalyst for the hydrogenation of CO2 to ethanol and in situ glycolysis of waste PET, characterized in that, Comprise the following steps: (1) the methanol solution of cobalt nitrate and 2-methyl imidazole methanol solution is mixed uniformly, through room temperature aging, washing, vacuum drying, ZIF-67 is obtained; (2) after the ZIF-67 obtained in step (1) is dispersed in methanol, copper nitrate solution is added and mixed, then through room temperature aging, centrifugation, vacuum drying, catalyst precursor is obtained; (3) the catalyst precursor obtained in step (2) is placed into a tube furnace, and heat treatment is carried out in N2 and NH3 atmosphere respectively and in turn, to obtain a catalyst CuCo@CN-NH3 for CO2 hydrogenation to ethanol and in-situ alcoholysis of waste PET; The molar ratio of 2-methyl imidazole to cobalt nitrate used in step (1) is 1-8, the room temperature aging time is 2-24 h; The vacuum drying time is 6-60 h, and the temperature is 20-60 ℃; The copper nitrate used in step (2) is 0.1-10% of the mass of ZIF-67; The room temperature aging time is 1-48 h; The vacuum drying time is 3-60 h, and the temperature is 20-60 ℃; The heat treatment temperature in N2 and NH3 atmosphere in step (3) is 300-800 ℃, and the time is 1-5 h.

2. A method for the in situ glycolysis of waste PET by CO2 hydrogenation to ethanol using a catalyst prepared by the method of claim 1. The catalyst and waste PET are placed in an autoclave, a solvent is added, then CO2 and H2 are charged, heated and stirred to react, to simultaneously realize CO2 hydrogenation to ethanol and alcoholysis of waste PET; The mass ratio of the catalyst to waste PET used is 0.1-8; The stirring speed is 50-100 rpm; The reaction temperature is 210-280 ℃, and the time is 3-24 h.

3. The method of claim 2, wherein: The solvent is 1,4-dioxane.

4. The method of claim 2, wherein: The volume ratio of H2 and CO2 charged is 0.5-6; The total gas pressure is 1-7 MPa.

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