A method for preparing nickel-based porous carbon catalysts from waste plastics and its application

Abstract

A method for preparing nickel-based porous carbon catalysts from waste plastics includes the following steps: dissolving nickel salts and waste plastics in an alcohol solution, stirring at room temperature, impregnating, drying in a drying oven, evaporating the alcohol solvent to obtain nickel-containing plastic solids; placing the obtained nickel-containing plastic solids in a tube furnace, heating to the corresponding plastic pyrolysis temperature under an inert atmosphere, and completing the plastic pyrolysis to obtain the catalyst. The method for preparing nickel-based porous carbon catalysts from waste plastics provided by this invention requires no other additives, catalysts, or high-pressure conditions. The preparation process is simple, environmentally friendly, uses readily available raw materials, has strong versatility, and is easy to implement in batches. This invention applies the obtained nickel-based porous carbon catalyst to the transfer hydrogenation of ethyl levulinate to prepare γ-valerolactone without the need for external hydrogen gas, and under suitable reaction conditions, the yield of γ-valerolactone exceeds 90%.

Description

Technical Field

[0001] This invention relates to a method for preparing heterogeneous catalysts using recycled waste plastics, specifically a method for preparing nickel-based porous carbon catalysts using waste plastics, and the application of the nickel-based porous carbon catalysts in the preparation of γ-valerol. Background Technology

[0002] Plastic pollution has become one of the major environmental problems worldwide. Large quantities of waste plastic are disposed of through landfills or incineration, not only occupying land but also causing soil, water, and air pollution, and releasing toxic and harmful gases. In the context of a circular economy, adopting advanced technologies to recycle waste plastic is an important way to solve the problem of plastic pollution and is of great significance to the sustainable development of human society.

[0003] Currently, the global recycling rate of waste plastics is low, with more than 90% not being effectively recycled.

[0004] Waste plastics all contain a large amount of carbon. For example, the carbon content of polyethylene, polypropylene, and polystyrene is as high as 85.6%, 85.6%, and 92.2%, respectively.

[0005] High-temperature pyrolysis is a common method for preparing carbon materials from recycled waste plastics. Existing methods often involve a series of steps such as acid washing, water washing, and activation, or require pyrolysis catalysts and high-pressure conditions.

[0006] CN108658055A discloses a method for preparing porous carbon from recycled waste polyvinyl chloride (PVC) products, comprising the following steps: First, impurities are removed from the waste PVC, which is then pulverized into powder using a pulverizer. The powder is placed in a mixer, heated until softened, and magnesium hydroxide is added. After mixing, the powder is extruded and granulated using a twin-screw extruder. Next, the granules are placed in a tubular furnace for high-temperature carbonization. After cooling to room temperature, the carbonized product is washed with hydrochloric acid, then washed with deionized water until the solution is neutral, and then dried. The dried porous carbon material is then immersed in 8-10 times its volume of nitric acid solution, ultrasonically vibrated for 8-10 minutes, allowed to stand at room temperature for 10-12 hours, filtered, washed with deionized water until neutral, and finally dried in a vacuum drying oven and pulverized to obtain porous carbon. This method has a long process flow, involving two acid washing, water washing, and drying steps, generating a large amount of acidic wastewater that must be treated before discharge; otherwise, it will cause serious secondary pollution to the environment.

[0007] CN117049518A discloses a method for preparing hollow-walled carbon nanotubes using waste plastics. The method involves mixing waste plastics and halloysite nanotubes at a certain mass ratio to obtain a mixture of waste plastics and halloysite nanotubes. This mixture is then heated to 500–900°C under a protective gas atmosphere and held for 10–90 minutes. After cooling, a composite of hollow-walled carbon nanotubes and halloysite nanotubes is obtained. Finally, the halloysite component in the composite is removed using an aqueous hydrofluoric acid solution to obtain the hollow-walled carbon nanotubes. This method uses expensive halloysite nanotubes as raw material and requires the use of highly corrosive reagents such as hydrofluoric acid to remove the template.

[0008] CN103183345A discloses a method for preparing nitrogen-doped activated carbon from chlorinated organic polymer waste plastics: The chlorinated organic polymer waste plastics are mixed with organic amines for dechlorination; the dechlorinated product is carbonized under an inert atmosphere; the carbonized product is mixed with phosphoric acid or potassium hydroxide activator and heated to the activation temperature under an inert atmosphere for activation; after activation, the mixture is cooled to room temperature, acid-washed, water-washed until neutral, filtered, and dried to obtain activated carbon. This method involves dechlorination, two pyrolysis processes, acid or alkali activation, and washing, resulting in a long process, the generation of acidic and alkaline wastewater, and high costs.

[0009] CN 118237580A discloses a method for preparing a carbon-coated metal nanoparticle catalyst derived from waste plastics. Waste plastics, a nitrogen source, and a nickel-containing compound are ground and mixed, then pyrolyzed at a constant temperature of 700–1000℃ for 1–3 hours. The mixture is then treated in a strong acid solution such as perchloric acid for several hours, washed with water, and dried to obtain the carbon-coated nickel nanoparticle catalyst. The catalyst exhibits good activity in the electrocatalytic reduction of carbon dioxide. However, this preparation method also suffers from high energy consumption and the generation of large amounts of acidic wastewater.

[0010] γ-Valactone is an important platform compound in the high-value conversion of biomass and the upgrading of fine chemicals. It can serve as a green solvent, a high-energy-density molecular fuel, a food additive, and a raw material for the synthesis of other high-value-added chemicals. The transfer hydrogenation of levulinates to prepare γ-valactone is a valuable biomass value-added reaction. Currently, there are no reports of using carbon materials from waste plastics conversion as catalysts to catalyze the conversion of ethyl levulinate to γ-valactone.

[0011] As can be seen from the above, existing technologies for preparing carbon materials using waste plastics as precursors have the following problems: the preparation process involves acid washing, alkali washing, water washing, and template removal, generating a large amount of waste acid, which is not environmentally friendly; the preparation process is complex, requires harsh conditions, and is costly, which is not conducive to mass production and widespread application. Furthermore, the prepared carbon materials have not been applied to the field of biomass catalytic conversion, especially the catalytic synthesis of γ-valerolactone. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to overcome the above-mentioned defects and deficiencies of the prior art and provide a method for preparing nickel-based porous carbon catalysts using waste plastics. This method is simple, environmentally friendly, has mild conditions, and is low in cost.

[0013] A further technical problem to be solved by the present invention is the application of the nickel-based porous carbon catalyst in the transfer hydrogenation of ethyl levulinate to synthesize γ-valerolactone.

[0014] The technical solution adopted by this invention to solve its technical problem is a method for preparing nickel-based porous carbon catalysts using waste plastics, comprising the following steps:

[0015] (1) Crush waste plastic into powder to obtain waste plastic powder;

[0016] (2) Dissolve the nickel salt in an alcohol solvent to obtain a nickel-containing alcohol solution; add the waste plastic powder obtained in step (1) to the nickel-containing alcohol solution, stir evenly at room temperature, impregnate, place in an oven to dry, evaporate the alcohol solvent, and obtain nickel-containing plastic solid;

[0017] (3) Place the nickel-containing plastic solid obtained in step (2) into a tube furnace and heat it to the corresponding plastic pyrolysis temperature under an inert atmosphere. After the plastic pyrolysis is completed, the nickel-based porous carbon catalyst is obtained.

[0018] Furthermore, in step (1), the waste plastics include, but are not limited to, polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride waste plastics, or a mixture of two or more of the waste plastics.

[0019] Furthermore, in step (2), the alcohol solvent includes anhydrous methanol and anhydrous ethanol; the amount of solvent used is 10-60 ml of alcohol solvent per gram of waste plastic.

[0020] Furthermore, in step (2), the nickel salt is nickel nitrate, nickel chloride, or nickel carbonate; the mass ratio of the nickel salt to the waste plastic is 0.05-0.5:1, preferably 0.2-0.4:1.

[0021] Furthermore, in step (2), the ambient temperature is 15-35℃, preferably 20-30℃; the soaking time is 1-25h, preferably 12-24h.

[0022] Furthermore, in step (2), the drying temperature is 80-125℃, preferably 100-120℃; the drying time is 0.5-5h, preferably 1-2h.

[0023] Furthermore, in step (3), the inert gas is nitrogen or argon.

[0024] Furthermore, in step (3), the heating rate is 2-15℃ / min, preferably 5-8℃ / min.

[0025] Furthermore, in step (3), the pyrolysis temperature is 400-800℃, preferably 500-700℃.

[0026] Furthermore, in step (3), the pyrolysis time is 5-60 min, preferably 25-50 min, and more preferably 30-40 min.

[0027] The present invention utilizes a nickel-based porous carbon catalyst prepared by the pyrolysis of waste plastics. The active component is Ni or / and NiO, and the active component accounts for 5-50% of the total mass of the catalyst, preferably 20-40%, based on nickel.

[0028] The technical solution adopted by the present invention to further solve its technical problem is that the nickel-based porous carbon catalyst is applied to the transfer hydrogenation of ethyl levulinate to prepare γ-valerol. The steps are as follows: ethyl levulinate, the nickel-based porous carbon catalyst and isopropanol solvent are added to a reaction vessel, the reaction vessel is sealed, nitrogen is used as a protective gas, and under stirring conditions, a closed reaction is carried out at 150-200℃ and a stirring speed of 300-500rpm for 5-11 hours, and then cooled to room temperature to obtain γ-valerol.

[0029] Furthermore, the reaction temperature is preferably 170-180℃, the reaction time is preferably 9-11h, and the stirring speed is 350rpm-450rpm.

[0030] The beneficial effects of this invention are as follows: 1) This invention utilizes nickel autocatalytic reduction pyrolysis, eliminating the need for additional pyrolysis catalysts and pore-forming templates, and requiring no reducing atmosphere. It involves atmospheric pressure pyrolysis, has a short reaction time (less than 1 hour), and low energy consumption. The preparation process is simple, safe, low-cost, widely applicable, and easy to prepare in batches, providing a promising industrial method for the resource utilization of various waste plastics. 2) The nickel-based porous carbon catalyst prepared by this invention has a large specific surface area and is predominantly mesoporous, which is beneficial for mass transfer and exposure of active sites during the reaction process. It exhibits excellent catalytic performance in the transfer hydrogenation of ethyl levulinate to prepare γ-valerolactone. When used for the transfer hydrogenation of ethyl levulinate to prepare γ-valerolactone, no external hydrogen is required, and under suitable reaction conditions, the yield of γ-valerolactone can reach over 90%. Attached Figure Description

[0031] Figure 1 The XRD patterns of the Ni-based porous carbon catalyst (Ni / PETC-T, where T is the pyrolysis temperature) prepared from waste polyethylene (PET) plastics at different pyrolysis temperatures according to this invention are shown. Ni / PETC-T exhibits Ni at 44.51° (111), 51.85° (200), and 76.37° (220).0 The diffraction peak (PDF#04-0850) shows NiO diffraction peaks at 37.32° (111), 43.36° (200) and 62.99° (220) (PDF#75-0197).

[0032] Figure 2 The image shows the FT-IR spectra of Ni-based porous carbon catalysts (Ni / PETC-T, where T is the pyrolysis temperature) prepared from polyethylene (PET) waste plastics at different pyrolysis temperatures according to the present invention.

[0033] Figure 3 XPS plots of Ni-based porous carbon catalysts (Ni / PETC-T, where T is the pyrolysis temperature) prepared from polyethylene (PET) waste plastics as a carbon source at different pyrolysis temperatures according to this invention.

[0034] Figure 4 This is a SEM image of the nickel-based catalyst Ni / PETC-500 prepared in this invention.

[0035] Figure 5 The N2 adsorption-desorption curves (a) and pore size distribution diagrams (b) of the Ni / PETC-500, Ni / PETC-600, and Ni / PETC-700 samples prepared for this invention are shown. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Example 1

[0038] Preparation of Ni / PEC-500 nickel-based catalyst:

[0039] (1) The waste polyethylene plastic is crushed into powder to obtain waste polyethylene plastic powder;

[0040] (2) Dissolve 0.4g Ni(NO3)2·6H2O in 10ml anhydrous ethanol to form a nickel nitrate ethanol solution; add 1.0g waste polyethylene plastic powder obtained in step (1) to the nickel nitrate ethanol solution, then add 10ml anhydrous ethanol, and impregnate for 24h at 25℃ and 500rpm; then place in a drying oven and dry at 120℃ for 1h to evaporate the alcohol solvent and obtain nickel-containing plastic solid;

[0041] (3) Place the dried nickel-containing plastic solid from step (2) into a pyrolysis furnace, and under the protection of an inert nitrogen atmosphere, heat it to 500°C at a heating rate of 8°C / min, and calcine and pyrolyze it for 30 min to obtain the nickel-based catalyst Ni / PEC-500.

[0042] The active component, calculated as nickel, accounts for 23.8% of the total mass of the catalyst.

[0043] The XRD pattern of the obtained nickel-based catalyst Ni / PEC-500 is shown in [reference]. Figure 1 ;See FT-IR plot Figure 2 See XPS graph Figure 3 See SEM image. Figure 4 .

[0044] Activity testing of the nickel-based catalyst Ni / PEC-500 for the hydrogenation of ethyl levulinate to γ-valerol:

[0045] Weigh 1 mmol of ethyl levulinate, 0.05 g of nickel-based catalyst Ni / PEC-500, and 10 mL of isopropanol into a high-pressure reactor. React at 180 °C for 11 h. After the reaction is complete, the liquid is analyzed by gas chromatography. The conversion rate of ethyl levulinate is 98.4%, the selectivity of γ-valerolactone is 98.9%, and the yield of γ-valerolactone is 97.3%.

[0046] Example 2

[0047] The only difference between this embodiment and Embodiment 1 is that the waste plastic used in Embodiment 1 is replaced with polypropylene instead of polyethylene; otherwise, it is the same as Embodiment 1.

[0048] The obtained nickel-based catalyst Ni / PEC-500 was used for the catalytic hydrogenation of ethyl levulinate to prepare γ-valerolactone. The conversion rate of ethyl levulinate was 99.4%, the selectivity of γ-valerolactone was 94.7%, and the yield of γ-valerolactone was 94.1%.

[0049] Example 3

[0050] The only difference between this embodiment and Embodiment 1 is that the waste plastic in Embodiment 1 is replaced with polyethylene terephthalate instead of polyethylene terephthalate; otherwise, they are the same as in Embodiment 1.

[0051] The obtained nickel-based catalyst Ni / PEC-500 was used for the catalytic hydrogenation of ethyl levulinate to prepare γ-valerolactone. The conversion rate of ethyl levulinate was 92.1%, the selectivity of γ-valerolactone was 91.6%, and the yield of γ-valerolactone was 84.4%.

[0052] Example 4

[0053] The only difference between this embodiment and Embodiment 1 is that the waste plastic in Embodiment 1 is replaced with polyvinyl chloride, otherwise the same as in Embodiment 1.

[0054] The obtained nickel-based catalyst Ni / PEC-500 was used for the catalytic hydrogenation of ethyl levulinate to prepare γ-valerolactone. The conversion rate of ethyl levulinate was 98.1%, the selectivity of γ-valerolactone was 91.1%, and the yield of γ-valerolactone was 89.4%.

[0055] Example 5

[0056] The only difference between this embodiment and Example 1 is that the calcination pyrolysis temperature in step (3) is adjusted to 600℃, and the reaction time in the activity testing method is adjusted to 9h.

[0057] The XRD pattern of the nickel-based catalyst Ni / PEC-600 obtained in this embodiment is shown in [reference needed]. Figure 1 ;See FT-IR plot Figure 2 See XPS graph Figure 3 .

[0058] The obtained nickel-based catalyst Ni / PEC-600 was used for the catalytic hydrogenation of ethyl levulinate to prepare γ-valerolactone. The conversion rate of ethyl levulinate was 96.1%, the selectivity of γ-valerolactone was 92.2%, and the yield of γ-valerolactone was 88.6%.

[0059] Example 6

[0060] The only difference between this embodiment and Example 1 is that the calcination pyrolysis temperature in step (3) is adjusted to 700℃ and the reaction time in the catalyst activity testing method is adjusted to 9h.

[0061] The XRD pattern of the nickel-based catalyst Ni / PEC-700 obtained in this embodiment is shown in [reference needed]. Figure 1 ;See FT-IR plot Figure 2 See XPS graph Figure 3 .

[0062] The obtained nickel-based catalyst Ni / PEC-700 was used for the catalytic hydrogenation of ethyl levulinate to prepare γ-valerolactone. The conversion rate of ethyl levulinate was 98.9%, the selectivity of γ-valerolactone was 94.1%, and the yield of γ-valerolactone was 93.1%.

[0063] Example 7

[0064] The only difference between this embodiment and Example 1 is that the reaction temperature in the catalyst activity testing method is adjusted to 170℃ and the reaction time is adjusted to 5 hours. Everything else is the same as in Example 1. The conversion rate of ethyl levulinate is 97.1%, the selectivity of γ-valerolactone is 63.8%, and the yield of γ-valerolactone is 61.9%.

[0065] Example 8

[0066] The only difference between this embodiment and Example 1 is that the reaction temperature in the catalyst activity testing method is adjusted to 170℃ and the reaction time is adjusted to 9 hours. Everything else is the same as in Example 1. The conversion rate of ethyl levulinate is 98.3%, the selectivity of γ-valerolactone is 81.3%, and the yield of γ-valerolactone is 79.9%.

[0067] Example 9

[0068] The only difference between this embodiment and Example 1 is that the reaction time in the catalyst activity testing method is adjusted to 11 hours. Everything else is the same as in Example 1. The conversion rate of ethyl levulinate is 97.2%, the selectivity of γ-valerolactone is 93.8%, and the yield of γ-valerolactone is 91.2%.

[0069] Example 10

[0070] The only difference between this embodiment and Example 1 is that the reaction time in the catalyst activity testing method is adjusted to 5 hours. Everything else is the same as in Example 1. The conversion rate of ethyl levulinate is 97.6%, the selectivity of γ-valerolactone is 79.5%, and the yield of γ-valerolactone is 77.6%.

[0071] Table 1 lists the specific surface area, pore volume, and pore size of Ni-carbon catalysts prepared at different carbonization temperatures.

[0072] Table 1. Specific surface area, pore volume, and pore size of nickel-based porous carbon catalysts prepared at different carbonization temperatures.

[0073]

[0074] As shown in Table 1, the nickel-based porous carbon catalysts Ni / PETC-500, Ni / PETC-600, and Ni / PETC-700 all have large specific surface areas and mesoporous structures, which are beneficial to the mass transport of reactant products.

[0075] The following table summarizes the performance of different waste plastic Ni-based porous carbon catalysts prepared in Examples 1-4 in catalyzing the preparation of γ-valerol from ethyl levulinum, the performance of Ni-based porous carbon catalysts Ni / PEC-600 and Ni / PEC-700 prepared in Examples 5-6 in catalyzing the preparation of γ-valerol from ethyl levulinum, and the performance of Ni-based porous carbon catalyst Ni / PEC-500 in Examples 7-10 in catalyzing the preparation of γ-valerol from ethyl levulinum under different reaction conditions, and lists them in Tables 2, 3, and 4 respectively.

[0076] Table 2 Performance of Ni-based porous carbon catalysts from different waste plastics in the preparation of γ-valerol from ethyl levulin.

[0077]

[0078] Table 3 Performance of Ni / PEC-600 and Ni / PEC-700 in catalyzing the preparation of γ-valerol from ethyl levulinate.

[0079]

[0080] Table 4. Performance of Ni / PEC-500 in catalyzing the preparation of γ-valerol from ethyl levulinate under different reaction conditions.

[0081]

[0082] The embodiments described herein are provided to facilitate understanding and implementation of the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, simplifications, combinations, or adjustments made to the technical solutions in the embodiments without departing from the core technical ideas and spirit of the invention should be considered within the scope of protection of this invention's patent.

Claims

1. The application of a nickel-based porous carbon catalyst prepared from waste plastics in the transfer hydrogenation of ethyl levulinate to prepare γ-valerolactone, characterized in that, The preparation method includes the following steps: (1) Crush waste plastic into powder to obtain waste plastic powder; (2) Dissolve the nickel salt in an alcohol solvent to obtain a nickel-containing alcohol solution; add the waste plastic powder obtained in step (1) to the nickel-containing alcohol solution, stir evenly at room temperature, impregnate, place in an oven to dry, evaporate the alcohol solvent, and obtain nickel-containing plastic solid; the nickel salt is nickel nitrate, nickel chloride or nickel carbonate; the mass ratio of nickel salt to waste plastic is 0.05-0.5:1; the alcohol solvent is anhydrous methanol or anhydrous ethanol; (3) Place the nickel-containing plastic solid obtained in step (2) in a tube furnace and heat it to the plastic pyrolysis temperature of 400-600℃ under the protection of an inert atmosphere. The pyrolysis time is 25-50 minutes. After the plastic pyrolysis is completed, the nickel-based porous carbon catalyst is obtained. In step (1), the waste plastic includes polyethylene.

2. The application as described in claim 1, characterized in that, In step (2), the amount of solvent used is 10-60 ml of alcohol solvent required per gram of waste plastic.

3. The application as described in claim 1, characterized in that, In step (2), the mass ratio of nickel salt to waste plastic is 0.2-0.4:

1.

4. The application as described in claim 1, characterized in that, In step (2), the ambient temperature is 15-35℃; the soaking time is 1-25 h.

5. The application as described in claim 4, characterized in that, In step (2), the soaking time is 12-24 h.

6. The application as described in claim 1, characterized in that, In step (2), the drying temperature is 80-125 ℃ and the drying time is 0.5-5 h.

7. The application as described in claim 6, characterized in that, In step (2), the drying temperature is 100-120 ℃; the drying time is 1-2 h.

8. The application as described in claim 1, characterized in that, In step (3), the inert atmosphere is nitrogen or argon.

9. The application as described in claim 1, characterized in that, In step (3), the heating rate is 2-15℃ / min.

10. The application as described in claim 9, characterized in that, In step (3), the heating rate is 5-8 ℃ / min.

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