Method for preparing nickel-based porous carbon catalyst from waste plastics and application of nickel-based porous carbon catalyst

Abstract

The invention relates to a method for preparing a nickel-based porous carbon catalyst by using waste plastics, which comprises the following steps: dissolving nickel salt and waste plastics in an alcohol solution, stirring at normal temperature, dipping, drying in a drying oven, and evaporating the alcohol solvent to obtain a nickel-containing plastic solid; and putting the obtained nickel-containing plastic solid into a tubular furnace, and heating to a corresponding plastic pyrolysis temperature under the protection of an inert atmosphere to finish the plastic pyrolysis, thereby obtaining the nickel-containing plastic. According to the preparation method for preparing the nickel-based porous carbon catalyst from the waste plastics, other auxiliaries, catalysts and high-pressure conditions are not needed, the preparation process is simple and environmentally friendly, raw materials are easy to obtain, universality is high, and batch preparation is easy to achieve. The prepared nickel-based porous carbon catalyst is applied to transfer hydrogenation of ethyl levulinate to prepare gamma-valerolactone, hydrogen does not need to be additionally added, and the yield of gamma-valerolactone exceeds 90% under proper reaction conditions.

Description

Technical Field

[0001] The present invention relates to a method for preparing a heterogeneous catalyst by recycling waste plastics, and in particular to a method for preparing a nickel-based porous carbon catalyst by recycling waste plastics, and application of the nickel-based porous carbon catalyst in preparing gamma-valerolactone. Background Art

[0002] Plastic pollution has become one of the major environmental problems worldwide. A large amount of waste plastic is disposed of by landfill or incineration, which not only occupies land, but also causes soil, water and air pollution, and releases toxic and harmful gases. In the context of circular economy, the use of advanced technology to recycle waste plastics is an important way to solve the problem of plastic pollution, which 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 are as high as 85.6%, 85.6%, and 92.2%, respectively.

[0005] High-temperature pyrolysis is a common method for recycling waste plastics to prepare carbon materials. Existing methods are often accompanied by a series of steps such as acid washing, water washing, activation, or require pyrolysis catalysts, high pressure conditions, etc.

[0006] CN108658055A discloses a method for preparing porous carbon by recycling waste polyvinyl chloride products, comprising the following steps: first, selecting impurities from waste polyvinyl chloride, crushing it into powder with a pulverizer, placing it in a mixer, heating it to softening, adding magnesium hydroxide, mixing, and sending it to a twin-screw extruder for extrusion granulation; then, placing the pellets in a tubular furnace for high-temperature carbonization, washing the carbonized product with hydrochloric acid after cooling it to room temperature, and then washing it with deionized water until the solution is neutral, and drying it; soaking the dried porous carbon material in 8-10 times the amount of nitric acid solution, ultrasonically oscillating it for 8-10 minutes, standing it at room temperature for 10-12 hours, filtering it, then washing it with deionized water until it is neutral, and finally placing it in a vacuum drying oven for drying and crushing it to obtain porous carbon. This method has a long process flow, and after two acid washings, water washings, and drying, a large amount of acidic wastewater is generated, which must be treated before it can be discharged, otherwise it will cause serious secondary pollution to the environment.

[0007] CN117049518A discloses a method for preparing hollow empty-wall carbon nanotubes using waste plastics, which comprises mixing waste plastics and halloysite nanotubes in a certain mass ratio to obtain a mixture of waste plastics and halloysite nanotubes; heating the obtained mixture to 500-900°C under a protective gas atmosphere and maintaining it for 10-90 minutes, and cooling to obtain a composite of hollow empty-wall carbon nanotubes and halloysite nanotubes; finally, removing the halloysite component in the composite using a hydrofluoric acid aqueous solution to obtain hollow empty-wall carbon nanotubes. The cost of the raw materials of the halloysite nanotubes used in this method is high, and a highly corrosive reagent such as hydrofluoric acid must be used to remove the template.

[0008] CN103183345A discloses a method for preparing nitrogen-doped activated carbon using chlorine-containing organic polymer waste plastics: mixing chlorine-containing organic polymer waste plastics with organic amines for dechlorination reaction, carbonizing the dechlorinated product under an inert atmosphere, mixing the carbonized product with phosphoric acid or potassium hydroxide activator, heating to activation temperature under an inert atmosphere for activation treatment; cooling to room temperature after activation, acid washing, water washing to neutrality, filtering, drying, and obtaining activated carbon. The method involves dechlorination, two pyrolysis, acid or alkali activation, washing and other steps, has a long process, produces acid and alkaline wastewater, and has high cost.

[0009] CN 118237580A discloses a method for preparing a waste plastic-derived carbon-coated metal nanoparticle catalyst. After grinding and mixing the waste plastic, nitrogen source and nickel-containing compound, the mixture is pyrolyzed at 700-1000°C for 1-3 hours, treated in a strong acid solution such as perchloric acid for several hours, washed with water and dried to obtain a carbon-coated metal nickel nanoparticle catalyst. The catalyst has good activity in the electrocatalytic reduction reaction of carbon dioxide, but the preparation method also has problems such as high energy consumption and generation of a large amount of acidic wastewater.

[0010] γ-Valerolactone is an important platform compound in the process of high-value conversion of biomass and upgrading of fine chemicals. It can be used as a raw material for the synthesis of green solvents, molecular fuels with extremely high energy density, food additives and other high-value-added chemicals. The preparation of γ-valerolactone by transfer hydrogenation of levulinic acid esters is a valuable biomass value-added reaction. So far, there has been no report on the conversion of ethyl levulinate into γ-valerolactone catalyzed by carbon material catalysts for the conversion of waste plastics.

[0011] From the above, it can be seen that the existing technology for preparing carbon materials using waste plastics as precursors has the following problems: the preparation process involves acid washing, alkali washing, water washing and template removal steps, which produces a large amount of waste acid and is not environmentally friendly; the preparation process is complex, the conditions are harsh, the cost is high, and it is not conducive to mass production, preparation, promotion and application. In addition, the prepared carbon materials have not been applied to the field of biomass catalytic conversion, especially the catalytic synthesis reaction 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 shortcomings of the prior art and provide a method for preparing a nickel-based porous carbon catalyst using waste plastics. The method has simple process, environmental protection, mild conditions and low 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 reaction of synthesizing γ-valerolactone by transfer hydrogenation of ethyl levulinate.

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

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

[0016] (2) dissolving a nickel salt in an alcohol solvent to obtain a nickel-containing alcohol solution; adding the waste plastic powder obtained in step (1) to the nickel-containing alcohol solution, stirring evenly at room temperature, impregnating, placing in an oven to dry, evaporating the alcohol solvent, and obtaining a nickel-containing plastic solid;

[0017] (3) placing the nickel-containing plastic solid obtained in step (2) in a tubular furnace, and heating it to the corresponding plastic pyrolysis temperature under the protection of an inert atmosphere, and the plastic pyrolysis is completed to obtain a nickel-based porous carbon catalyst.

[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; and 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 room temperature is 15-35°C, preferably 20-30°C; and the immersion time is 1-25h, preferably 12-24h.

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

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

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

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

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

[0027] The nickel-based porous carbon catalyst prepared by pyrolysis of waste plastics has an active component of Ni or / and NiO, and the mass of the active component in terms of nickel accounts for 5-50% of the total mass of the catalyst, preferably 20-40%.

[0028] The technical solution adopted by the present invention to further solve the technical problem is that the nickel-based porous carbon catalyst is used for preparing γ-valerolactone by transfer hydrogenation of ethyl levulinate, and the steps are: adding ethyl levulinate, the nickel-based porous carbon catalyst and isopropanol solvent into a reaction kettle, sealing the reaction kettle, using nitrogen as a protective gas, and carrying out a closed reaction at 150-200° C. and a stirring speed of 300-500 rpm for 5-11 hours under stirring conditions, and then cooling to room temperature to obtain γ-valerolactone.

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

[0030] The beneficial effects of the present invention are as follows: 1) The present invention utilizes nickel autocatalytic reduction pyrolysis, and does not require the additional addition of a pyrolysis catalyst and a pore-forming template agent, does not require the use of a reducing atmosphere, and can be pyrolyzed at normal pressure, with a short time (within 1 hour) and low energy consumption; the preparation process is simple, the operation is safe, the cost is low, the universality is good, and batch preparation is easy, providing an industrially promising resource utilization method for the treatment of a variety of waste plastics; 2) The nickel-based porous carbon catalyst prepared by the present invention has the characteristics of a large specific surface area and a dominant mesopore, which is beneficial to mass transfer and exposure of active sites during the reaction, and has good catalytic performance for preparing γ-valerolactone by transfer hydrogenation of ethyl levulinate; when used for preparing γ-valerolactone by transfer hydrogenation of ethyl levulinate, no external hydrogen is required, and under suitable reaction conditions, the yield of γ-valerolactone can reach more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The XRD patterns of Ni-based porous carbon catalysts (Ni / PETC-T, T is the pyrolysis temperature) prepared from polyethylene (PET) waste plastics as carbon sources at different pyrolysis temperatures in the present invention. Ni / PEC-T shows Ni at 44.51°(111), 51.85°(200) and 76.37°(220).0 Diffraction peaks (PDF#04-0850), NiO diffraction peaks (PDF#75-0197) are presented at 37.32°(111), 43.36°(200) and 62.99°(220).

[0032] Figure 2 FT-IR graphs of the Ni-based porous carbon catalyst (Ni / PETC-T, T is the pyrolysis temperature) prepared using polyethylene (PET) waste plastic as a carbon source at different pyrolysis temperatures of the present invention.

[0033] Figure 3 XPS graphs of the Ni-based porous carbon catalyst (Ni / PETC-T, T is the pyrolysis temperature) prepared using polyethylene (PET) waste plastic as a carbon source at different pyrolysis temperatures of the present invention.

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

[0035] Figure 5 N2 adsorption-desorption curves (a) and pore size distribution diagram (b) of Ni / PETC-500, Ni / PETC-600 and Ni / PETC-700 samples prepared in the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0037] Example 1

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

[0039] (1) crushing waste polyethylene plastic into powder to obtain waste polyethylene plastic powder;

[0040] (2) dissolving 0.4 g Ni(NO3)2·6H2O in 10 ml anhydrous ethanol to form a nickel nitrate ethanol solution; adding 1.0 g of the waste polyethylene plastic powder obtained in step (1) to the nickel nitrate ethanol solution, and then adding 10 ml anhydrous ethanol, and immersing for 24 h at 25° C. and a stirring speed of 500 rpm; then placing in a drying oven, drying at 120° C. for 1 h, evaporating the alcohol solvent, and obtaining a nickel-containing plastic solid;

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

[0042] The mass of active components in terms of 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 Figure 1 ; FT-IR diagram see Figure 2 ; XPS diagram see Figure 3 ; SEM images see Figure 4 .

[0044] Activity test of nickel-based catalyst Ni / PEC-500 for hydrogenation of ethyl levulinate to prepare γ-valerolactone:

[0045] Weigh 1mmol of ethyl levulinate, 0.05g of nickel-based catalyst Ni / PEC-500, and 10mL of isopropanol into a high-pressure reactor. React at 180°C for 11h. After the reaction, take the liquid for gas phase analysis. 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 difference between this embodiment and embodiment 1 is that the waste plastic used in embodiment 1 is replaced by polypropylene from polyethylene; the rest is the same as embodiment 1.

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

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is that the waste plastic in embodiment 1 is replaced by polyethylene terephthalate, and the rest is the same as embodiment 1.

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

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that the waste plastic in embodiment 1 is replaced by polyvinyl chloride from polyethylene, and the rest is the same as embodiment 1.

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

[0055] Example 5

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

[0057] The XRD pattern of the nickel-based catalyst Ni / PEC-600 obtained in this example is shown in Figure 1 ; FT-IR diagram see Figure 2 ; XPS diagram see Figure 3 .

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

[0059] Example 6

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

[0061] The XRD pattern of the nickel-based catalyst Ni / PEC-700 obtained in this example is shown in Figure 1 ; FT-IR diagram see Figure 2 ; XPS diagram see Figure 3 .

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

[0063] Example 7

[0064] The difference between this example and Example 1 is that the reaction temperature in the catalyst activity test method is adjusted to 170°C and the reaction time is adjusted to 5 hours. The rest is the same as 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 difference between this example and Example 1 is that the reaction temperature in the catalyst activity test method is adjusted to 170°C and the reaction time is adjusted to 9 hours. The rest is the same as 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 difference between this example and Example 1 is that the reaction time in the catalyst activity test method is adjusted to 11 hours. The rest is the same as 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 difference between this example and Example 1 is that the reaction time in the catalyst activity test method is adjusted to 5 hours. The rest is the same as 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 can be seen from 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 transfer of reactants and products.

[0075] The performance of the Ni-based porous carbon catalysts prepared in Examples 1-4 for catalyzing the preparation of γ-valerolactone from ethyl levulinate using different waste plastics, the performance of the Ni-based porous carbon catalysts Ni / PEC-600 and Ni / PEC-700 prepared in Examples 5-6 for catalyzing the preparation of γ-valerolactone from ethyl levulinate, and the performance of the Ni-based porous carbon catalyst Ni / PEC-500 in Examples 7-10 for catalyzing the preparation of γ-valerolactone from ethyl levulinate under different reaction conditions are summarized in Tables 2, 3, and 4, respectively.

[0076] Table 2 Performance of Ni-based porous carbon catalysts for preparing γ-valerolactone from ethyl levulinate using different waste plastics

[0077]

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

[0079]

[0080] Table 4 Catalytic performance of Ni / PEC-500 in preparing γ-valerolactone from ethyl levulinate under different reaction conditions

[0081]

[0082] The embodiments of the present invention are intended to facilitate those skilled in the art to understand and implement the present invention. Without departing from the core technical concept and spirit of the present invention, any modification of the technical solution in the embodiments, equivalent replacement, improvement, simplification, combination or adjustment of part or all of the technical features shall be deemed to be within the scope of protection of the patent of the present invention.

Claims

1. A method for preparing a nickel-based porous carbon catalyst using waste plastics, characterized in that: The following steps are involved: (1) crushing waste plastics into powder to obtain waste plastic powder; (2) dissolving the nickel salt in an alcohol solvent to obtain a nickel-containing alcohol solution; adding the waste plastic powder obtained in step (1) to the nickel-containing alcohol solution, stirring evenly at room temperature, impregnating, placing in an oven to dry, evaporating the alcohol solvent, and obtaining a nickel-containing plastic solid; (3) The nickel-containing plastic solid obtained in step (2) is placed in a tubular furnace and heated to the corresponding plastic pyrolysis temperature under the protection of an inert atmosphere. After the plastic pyrolysis is completed, a nickel-based porous carbon catalyst is obtained.

2. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in claim 1, characterized in that: In step (1), the waste plastics include polyethylene, polypropylene, polyethylene terephthalate or polyvinyl chloride waste plastics, or a mixture of two of the above.

3. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in claim 1 or 2, characterized in that: In step (2), the alcohol solvent includes anhydrous methanol and anhydrous ethanol; the amount of solvent used is 10-60 ml of the alcohol solvent required per gram of waste plastic.

4. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in any one of claims 1 to 3, characterized in that: 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.

5. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in any one of claims 1 to 4, characterized in that: In step (2), the room temperature is 15-35°C; the immersion time is 1-25 h, preferably 12-24 h.

6. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in any one of claims 1 to 5, characterized in that: In step (2), the drying temperature is 80-125°C, preferably 100-120°C; the drying time is 0.5-5 h, preferably 1-2 h.

7. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in any one of claims 1 to 6, characterized in that: In step (3), the inert gas is nitrogen or argon.

8. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in any one of claims 1 to 7, characterized in that: In step (3), the heating rate is 2-15°C / min, preferably 5-8°C / min.

9. A method for preparing a nickel-based porous carbon catalyst by pyrolysis of waste plastics as claimed in any one of claims 1 to 8, characterized in that: In step (3), the pyrolysis temperature is 400-800°C, preferably 500-700°C; the pyrolysis time is 5-60 min, preferably 25-50 min, more preferably 30-40 min.

10. Use of the nickel-based porous carbon catalyst prepared by the method according to any one of claims 1 to 9 in the preparation of γ-valerolactone by transfer hydrogenation of ethyl levulinate.

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