A catalyst for converting high concentration waste pet plastics to gasoline

Abstract

The application discloses a catalyst for converting high-concentration waste PET plastics into gasoline, which is mainly composed of transition metals, and is prepared by coprecipitation into a two-dimensional layered hydrotalcite (LDH) material, which is calculated as: wherein M 2+ is one or more of divalent transition metal cations such as Mg, Zn, Ni, Cu, Co, etc. 3+ is one or more of trivalent transition metal cations such as Fe, Al, Cr, etc., and A is an intercalated anion; then, the bulk hydrotalcite material is dispersed and exfoliated by a liquid-phase exfoliation technique to obtain a single-layer hydrotalcite m-LDH, which is subjected to subsequent heat treatment and applied to a hydrodeoxygenation (HDO) reaction in a PET depolymerization process. The catalyst can convert high-concentration waste PET into gasoline and antifreeze under mild conditions in a monohydric alcohol solvent, has high product selectivity, small catalyst consumption and strong stability. The conversion of high-concentration waste PET can greatly promote the recycling development of waste plastics and inject new impetus into the solution of the actual problem of island plastic pollution.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high-value utilization of waste plastics, in particular to a preparation method and application of a catalyst for converting high-concentration PET plastics into gasoline. BACKGROUND

[0002] PET (polyethylene terephthalate) is currently the largest polyester plastic in consumption, but due to the chemical properties of PET that are difficult to degrade naturally, a large amount of PET plastic after consumption flows to landfills and oceans, which causes great harm to the ecological environment. In this regard, a large number of researchers are committed to developing new chemical treatment methods to recycle waste PET plastics. Currently, PET chemical recycling mainly includes alcoholysis, glycolysis, hydrolysis, ammonolysis and the like, and corresponding depolymerization monomers are obtained. However, the chemical monomers obtained by treating waste PET through conventional chemical depolymerization methods have low economic value, and most of them are still in the laboratory stage due to low treatment concentration.

[0003] In addition to the monomers obtained by chemical depolymerization, researchers have also developed various new paths to realize the upgrading utilization of waste PET. Zhang et al. converted waste plastics into C7-C8 naphthenes and aromatic hydrocarbons as gasoline and aircraft fuel through multi-step reactions using waste PET as raw material; and Yan et al. also reported that Ru / Nb2O5 and Co / TiO2 were used as catalysts to convert waste PET into multi-component aromatic hydrocarbons, realizing the upgrading utilization of PET to liquid fuel. Compared with the production of multi-component mixed aromatic hydrocarbons and the use of noble metal catalysts and external hydrogen in the catalytic reaction, Chinese patent (CN 109705985A) reports a non-noble metal Cu-based catalyst that produces hydrogen to realize 100% conversion of waste PET to PX in one step, providing a feasible solution to the problem of island plastic pollution. Although the path of PET chemical recycling to liquid fuel has been widely reported, the low concentration conversion of waste plastics is a key factor limiting its industrialization and large-scale application. This is mainly due to the insufficient active sites of the catalyst in the reaction process and the insufficient treatment capacity of the waste PET. Therefore, developing new catalysts to improve the conversion concentration of waste plastics and promoting the degradation of plastics from laboratory exploration to the stage and industrialization are of great significance to realize the practical application value of waste PET.

[0004] Based on this, the application exposes the active sites of the catalyst in the reaction process to the maximum extent by regulating the components of hydrotalcite and then stripping the hydrotalcite bulk material through a subsequent liquid phase stripping method to obtain single-layer two-dimensional hydrotalcite nanosheets. Thus, the conversion of high-concentration waste PET to liquid fuel is facilitated. SUMMARY

[0005] The application provides a preparation method and application of a catalyst for converting high-concentration PET plastics into gasoline.

[0006] The technical solution adopted in this application is as follows:

[0007] Using massive hydrotalcite as a precursor, monolayer hydrotalcite was obtained through liquid-phase exfoliation technology, and then a catalyst was obtained through subsequent heat treatment for use in the conversion of high-concentration waste plastics. The catalyst preparation process is as follows: Figure 1 As shown.

[0008] The reaction process uses waste PET plastic as raw material in a one-pot reaction, comprising step 1: alcoholysis of PET in an alcohol solvent at high temperature to obtain ethylene glycol and aromatic esters, and step 2: hydrogenation and deoxygenation of the aromatic esters to obtain cycloalkanes, aromatic hydrocarbons, and alkanes within the gasoline range. The reaction route is as follows: Figure 2 As shown.

[0009] A catalyst for converting waste PET plastic into gasoline, characterized in that the catalyst is prepared by: obtaining a two-dimensional layered hydrotalcite (LDH) material through co-precipitation, as follows: Where M 2+ It is one or more of divalent transition metal cations such as Mg, Zn, Ni, Cu, and Co; M 3+ It is one or more trivalent transition metal cations such as Fe, Al, and Cr, where A is an intercalating anion: Subsequently, the bulk hydrotalcite material was dispersed and exfoliated using liquid-phase exfoliation technology, followed by centrifugal drying to obtain single-layer hydrotalcite, which was then subjected to further heat treatment for application in the hydrodeoxygenation (HDO) reaction during PET depolymerization. The specific reaction process involves adding cut waste PET plastic bottles, solvent, and catalyst into a high-pressure reactor. After sealing the reactor, nitrogen gas is introduced to replace the air inside. The reactor is then subjected to a hydrogen atmosphere for a period of time. After the reaction is complete, the catalyst and solvent are filtered and distilled to obtain the target product.

[0010] Furthermore, the catalyst is prepared by co-precipitation, and the precipitant is NaOH or Na2CO3.

[0011] Furthermore, the catalyst is prepared by a hydrothermal method, and the precipitant is CO(NH2)2 or NH4F.

[0012] Furthermore, the ratio of metal salt to precipitant during the co-precipitation method for preparing the catalyst is: OH... - :M x+ =2:1 M 3+ =3:1.

[0013] Furthermore, the ratio of metal salt to precipitant in the hydrothermal preparation process of the catalyst is: NH4F:M x+ =2:1-6:1, CO(NH2)2:Mx+ =3:1-6:1.

[0014] Furthermore, the hydrothermal synthesis conditions for the catalyst are a temperature of 80-150℃ and a time of 5-20h.

[0015] Furthermore, the volume ratio of PET plastic to solvent in the catalytic reaction process is 1:20-20:1.

[0016] Furthermore, the volume ratio of PET plastic to solvent is 1:20-20:1.

[0017] Furthermore, the solvent is one or a combination of methanol, ethanol, and isopropanol.

[0018] Furthermore, the catalytic reaction process is carried out at a temperature of 180-250℃.

[0019] Furthermore, the high-pressure hydrogen gas pressure is 0.5-8.0 MPa.

[0020] Compared with the prior art, the beneficial effects of this application are as follows:

[0021] This application utilizes monolayer LDH nanosheets obtained through liquid-phase exfoliation of bulk hydrotalcite material to promote the rapid adsorption and diffusion of reactants / products on the catalyst surface during plastic conversion, thereby improving the catalyst's ability to process reactants. The optimized design of the front-end catalyst effectively solves the key problem of low conversion concentration during waste plastic conversion. Simultaneously, the green alcoholysis method employed in this application rapidly and efficiently converts waste plastic into gasoline and ethylene glycol in a one-pot process, with the catalyst and alcohol solvent being recyclable. The entire process aligns with green and sustainable development. This application provides a catalyst preparation method and application for converting high-concentration PET plastic into gasoline, which can significantly advance the utilization of waste PET plastic on islands, addressing environmental pollution while achieving self-sufficiency in motor vehicle fuels. Attached Figure Description

[0022] Figure 1 A flowchart of the catalyst preparation process provided in the embodiments of the present invention;

[0023] Figure 2 A flowchart of the reaction process provided for an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Example 1

[0026] Preparation method of blocky CuFeAl-LDH (coprecipitation method): Dissolve 1.3g copper nitrate, 3.2g ferric nitrate, and 6.2g aluminum nitrate in 100mL of deionized water and stir for 30min, which is designated as solution A. Dissolve 2.3g sodium hydroxide and 3.6g sodium carbonate in 100mL of deionized water and stir for 30min, which is designated as solution B. Simultaneously, add solutions A and B dropwise to 100mL of deionized water, maintaining the pH of the solution at 10 during titration. After stirring at 1000rpm for 2h, transfer the solution to a hydrothermal reactor and age it at 90℃ for 10h. After cooling the hydrothermal reactor to room temperature, centrifuge and wash the reactants until the filtrate is neutral. Then, transfer the precipitate to an 80℃ oven and dry for 12h to obtain blocky CuFeAl-LDH.

[0027] Preparation method of monolayer CuFeAl-LDH: 0.5g of block CuFeAl-LDH was added to an aqueous solution containing 1M NaCl and 3.3mM HCl. After stirring at 1000rpm for 24h, the solution was centrifuged, washed, and dried to obtain a solution containing Cl. - Intercalated CuFeAl-LDH(CI) - Then take 0.3g CuFeAl-LDH(Cl) - Add to an aqueous solution containing 1M NaNO3, stir at 1000 rpm for 24 hours, then centrifuge, wash and dry to obtain the product containing... Intercalation Finally, The sample was added to 100 mL of formamide solution and stirred for 24 h. After centrifugation and drying, a monolayer CuFeAl-LDH was obtained. The dried sample was thoroughly ground and calcined in a muffle furnace at 600 °C for 6 h, followed by reduction in a hydrogen atmosphere for 8 h to obtain the CuFeAl catalyst. The preparation methods for monolayer CuNiAl, CuCoAl, CuZnFe, and CuZnCr catalysts are the same.

[0028] The catalyst prepared in Example 1 was used in a high-concentration waste PET conversion experiment.

[0029] Waste PET plastic, such as mineral water bottles, was cut into small pieces. 5.0 g of these pieces was placed in a high-pressure reactor, along with 30 mL of methanol and 0.1 g of CuFeAl catalyst. The reactor was sealed, and H2 was first introduced to displace the air in the reactor, repeating this process three times. Subsequently, H2 at 4 MPa was introduced into the reactor. The temperature of the reactor was programmed to reach 240 °C, and the reaction was allowed to proceed for 6 hours. After the reaction was complete, the reactor was cooled, H2 was released, and the reaction solution was obtained upon opening the high-pressure reactor. The catalyst could be separated by filtration, and the solvent and product could be separated by simple distillation.

[0030] The reaction results are as follows:

[0031]

[0032]

[0033] Example 2

[0034] Preparation method of bulk CuZnAl-LDH (hydrothermal method): Dissolve 0.8g copper nitrate, 1.2g zinc nitrate and 3.3g aluminum nitrate in 100mL deionized water. Stir for 30min until the reagents are completely dissolved. Then add 2.6g CO(NH2)2 and 3.8g NH4F, and continue stirring for 30min until the solution is clear. Transfer the solution to an 80mL hydrothermal reactor and react at 120℃ for 6h. Similarly, after cooling the hydrothermal reactor to room temperature, centrifuge and wash the reactants until the filtrate is neutral. Transfer the precipitate to an 80℃ oven and dry for 12h to obtain bulk CuZnAl-LDH.

[0035] The preparation method of monolayer CuZnAl-LDH is the same as in Example 1. The preparation methods of monolayer CuNiAl, CuCoAl, CuZnCr and other catalysts are the same as above.

[0036] The catalyst prepared in Example 2 was used in a high-concentration waste PET conversion experiment.

[0037] Waste PET plastic, such as mineral water bottles, was cut into small pieces. 5.0 g of these pieces was placed in a high-pressure reactor, along with 30 mL of a mixed solution of ethanol and methanol and 0.1 g of CuZnAl catalyst. The reactor was sealed, and H2 was first introduced to displace the air in the reactor, repeated three times. Then, 2 MPa of H2 was introduced into the reactor. The temperature of the reactor was programmed to reach 220 °C, and the reaction was allowed to proceed for 6 hours. After the reaction was complete, the reactor was cooled, H2 was released, and the reaction solution was obtained upon opening the high-pressure reactor. The catalyst could be separated by filtration, and the solvent and product could be separated by simple distillation.

[0038] The reaction results are as follows:

[0039]

[0040]

[0041] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for converting high-concentration waste PET plastic into gasoline using a catalyst, characterized in that, The catalyst was prepared by co-precipitation to obtain a two-dimensional layered hydrotalcite material, denoted as: Where M 2+ It is one or more of the divalent transition metal cations Mg, Zn, Ni, Cu, and Co; M 3+ It is one or more of the trivalent transition metal cations Fe, Al, and Cr, where A is an intercalating anion: Subsequently, the bulk hydrotalcite material was dispersed and peeled off using liquid phase exfoliation technology, and then a single layer of hydrotalcite was obtained by centrifugal drying. This single layer of hydrotalcite was then subjected to subsequent heat treatment and applied to the hydrodeoxygenation reaction in the PET depolymerization process. Preparation method of single-layer hydrotalcite: 0.5g of block hydrotalcite was added to an aqueous solution containing 1M NaCl and 3.3mM HCl. After stirring at 1000rpm for 24h, the solution was centrifuged, washed, and dried to obtain hydrotalcite containing Cl. - Intercalated hydrotalcite; then take 0.3g containing Cl - Intercalated hydrotalcite was added to an aqueous solution containing 1M NaNO3, stirred at 1000 rpm for 24 h, then centrifuged, washed, and dried to obtain a solution containing... Intercalated hydrotalcite; finally, containing Intercalated hydrotalcite was added to 100 mL of formamide solution and stirred for 24 h. After centrifugation and drying, monolayer hydrotalcite was obtained. The dried sample was thoroughly ground and calcined in a muffle furnace at 600 °C for 6 h, and then reduced in a hydrogen atmosphere for 8 h to obtain the catalyst. The catalyst was CuFeAl, CuNiAl, CuCoAl, CuZnFe, and CuZnCr. The specific reaction process involves adding cut waste PET plastic bottles, solvent, and catalyst into a high-pressure reactor. After sealing the reactor, nitrogen gas is introduced to replace the air in the reactor. Subsequently, the reactor is in a hydrogen atmosphere, and after a period of time, the target product is obtained by filtering the catalyst and distilling the solvent after the reaction is completed.

2. The method according to claim 1, characterized in that, The catalyst is prepared by co-precipitation, and the precipitant is NaOH and Na2CO3.

3. The method according to claim 1, characterized in that, The catalyst is prepared by a hydrothermal method, and the precipitants are CO(NH2)2 and NH4F.

4. The method according to claim 1, characterized in that, The volume ratio of PET plastic to solvent is 1:20-20:

1.

5. The method according to claim 1, characterized in that, The solvent is one or a combination of methanol, ethanol, and isopropanol.

6. The method according to claim 1, characterized in that, The reaction temperature is 180-250℃.

7. The method according to claim 1, characterized in that, High-pressure hydrogen has a pressure of 0.5-8.0 MPa.

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